Full transcript
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0:11description . Enjoy the lesson . Hey
0:18everyone , how's it going ? Welcome to
0:20another video lesson , and today we're
0:22going to talk about carbohydrates ,
0:25extremely important and interesting
0:27compounds to study . They are , of course
0:30, part of our biochemistry module . It's
0:32very important . If you haven't watched
0:34our introductory biochemistry lesson
0:36yet , just click on this card ; it's
0:38there . In the introductory lesson , we
0:40create that whole conceptual map to
0:42organize our studies . So , let's go ,
0:44everyone . Carbohydrates — we say
0:47carbohydrates , but other names can be
0:49associated with them , obviously having
0:51the same meaning , that is , they are
0:53synonyms for carbohydrates . These are
0:57sugars . So , if you say sugar , it's
1:00carbohydrate , glycides , saccharides ,
1:02hydrates of carbon , all of that is
1:05carbohydrate . Now look , carbohydrates ,
1:08hydrates of carbon , notice that it's
1:11almost the same name reversed . There's
1:14a logic to this , a reason that I'll
1:16explain later in class . Another
1:19important thing about carbohydrates is
1:21that they are organic compounds , just
1:23like lipids , vitamins , proteins , and
1:24nucleic acids . They are organic ,
1:27remember ? There are also inorganic
1:30compounds , water and mineral salts . All
1:32good . So , when we're studying
1:35biochemistry , an organic or inorganic
1:38compound , we have to know which atoms
1:40form these compounds . In the case of
1:45carbohydrates , carbon , hydrogen , and
1:48oxygen are present . Now , some of them
1:52may also contain nitrogen , phosphorus ,
1:55and sulfur . Not all of them . These here
1:58, you can write them down and highlight
2:00them . Some may contain these other
2:02three atoms . Okay ? Then comes the
2:04question : " Professor , what is the
2:08source of carbohydrates ? " There are
2:10many , folks . There are many . We find
2:12carbohydrates in many things , but
2:15thinking about our diet , we basically
2:19find carbohydrates in bread , pasta ,
2:22rice , potatoes , milk , and fruits . Each
2:28of these foods can have a type of sugar
2:30, because there are several types of
2:32sugar . But then comes a big question .
2:35Some people say : " Professor , but were
2:37you saying in class that milk has
2:39carbohydrates ? There's a type of
2:41carbohydrate in milk ? " Yes , I said that
2:43. But I was looking at the carton and
2:45said it has 3 % fat . Fat is lipid . Folks ,
2:50the interesting thing is that a food
2:52will have , for example , milk , it has
2:55sugar , but it also has fat , it also has
2:58proteins , it also has vitamins .
3:01Therefore , a food doesn't just provide
3:03one compound . It can have as its main
3:05component , for example , take meat , ah ,
3:08meat is protein , of course , but it also
3:10has fat . In other words , a food doesn't
3:12provide just one compound . This is
3:14really interesting to take to the exam
3:16because some exams have these tricky
3:18questions , okay ? Fruit , so fruit , fruit
3:21, quantity of fruit , and there's a very
3:23important sugar inside the fruit , in
3:25the fruits that I'm going to talk to
3:26you about . So , let's go to the function
3:29of carbohydrates . I told you that they
3:31are extremely important compounds . When
3:33we talk about carbohydrates , we're
3:35talking about food and energy-providing
3:37foods . Obviously , the main function of
3:40a carbohydrate that you have to keep in
3:42mind is its energy function . Our main
3:45source of energy is carbohydrates . Look
3:49, there is another source of energy . If
3:52you've already watched our lesson on
3:53lipids , if you haven't , watch it . Or
3:55also in the adipose tissue lesson , we
3:58talk about fats , folks . Lipids are also
4:01sources of energy . First , we use sugars
4:04, carbohydrates ; if they're lacking , we
4:06start burning fat . And in the third
4:10case , in cases of malnutrition , protein
4:12is broken down to obtain energy . In
4:16this case , the person is already
4:18extremely low on energy , extremely
4:20malnourished , so you can't burn protein
4:23or muscle for energy production . Now ,
4:26the immediate source of energy right
4:28now , what your body should be burning
4:30at this moment , is sugar . Once sugar
4:33starts to run low , then you start
4:34burning fat . And fat is very efficient
4:38because it's a lipid , not a
4:40carbohydrate , but you can store more
4:42energy in a smaller space , that is , in
4:45adipose tissue . You'd have to take a
4:48class on adipose tissue ethology to
4:50understand that . But when it comes to
4:52production , to immediate energy
4:54utilization , up to this point , it's
4:55carbohydrates . So it has the energetic
4:57function . If you're feeling a bit down ,
4:59a bit tired , sometimes you have a
5:01coffee , add some sugar , and that's how
5:02it starts , right ? And someone else is
5:05hungry , thinking , " Oh , I'm so tired
5:06today , " then they finish lunch , eat
5:08some rice , something , and , oh , I feel a
5:09little better . Of course , there's the
5:12post-lunch sleepiness , which we discuss
5:14in physiology class , in the digestive
5:15system section , where we talk about why
5:17we get sleepy after lunch . But of
5:20course , this sugar that we eat is
5:22digested . I'll talk a little more about
5:25this digestion during the class . And
5:27glucose , a simple sugar , enters our
5:30cell and from this glucose , ATP is
5:33produced in cellular respiration . So
5:37look at the link . Why do we normally
5:39study this ? Ideally , we should study
5:42biochemistry before cellular metabolism
5:44, before cellular respiration , because
5:47you have to understand the molecule
5:49that enters cellular respiration . So ,
5:52when we eat , all this is digested , ah ,
5:54the digestive system digests , there's a
5:56single glucose molecule that enters
5:57your cell , goes there , and in the
5:59mitochondria it performs cellular
6:01respiration and produces energy . Here's
6:04the first function , the energy function
6:06. That's why , oh professor , but if I
6:08want to lose weight , then , well , you
6:10reduce carbohydrates , because when you
6:12reduce carbohydrates , your body , when
6:13it starts to have little carbohydrate ,
6:15it says : " Oops , let's start before the
6:17carbohydrates run out , let's start
6:18burning some fat too , create a
6:20counterbalance , and so on . " And then
6:21the person loses weight . Some people
6:24say : " But professor , then I'm going to
6:25lose weight , I'm going to cut
6:26carbohydrates out of our lives , out of
6:28my life . " That's wrong . You can't
6:30simply cut them out , you have to reduce
6:32them . I usually , and I never forget , my
6:35physiology classes in college had an
6:37extremely complicated formula , right ?
6:40For weight loss . There's a balance . To
6:44lose weight , you have to burn more
6:46calories or burn more energy than you
6:48consume . That's how you lose weight . Of
6:51course , hormonal function also comes
6:54into play , as well as various
6:56individual factors . But to lose weight ,
6:58it's not simply about cutting
7:00carbohydrates , it's about reducing them
7:01. And that's where other issues come in
7:03that we can discuss in another specific
7:05class . Now , look , carbohydrates also
7:07have a structural function . This is
7:13very important because the cell wall of
7:16plants , well , it's made of
7:18carbohydrates . It's a type of sugar . So
7:21, notice that the function of insects ,
7:23the exoskeleton of insects , it's not
7:25energy for the insect , it's a
7:27structural function for these organisms
7:30. So , it also has a structural function
7:32. It's worth remembering that some
7:34sugars , some carbohydrates in our body ,
7:36can , for example , associate with
7:38proteins and from there , or associate
7:40with fats and have other functions . You
7:42see that , in our joints , it has , it
7:45slides . This sliding , also in our
7:49stomach wall , so that the acid in our
7:51stomach , the gastro acid , doesn't
7:53corrode our stomach , there's a
7:56protection , a layer of sugar , called
7:58ulin , that also protects the cells .
8:02When you study cells , you'll see that
8:04there's a structure called
8:05glycoglycoglycolic acid . This
8:08glycocalyx is also sugar , it performs
8:10cell recognition . So , of course , these
8:12are the basic functions , but throughout
8:14your studies you will see that some
8:16sugars are associated with other
8:18molecules , generating various functions
8:20in our body as well . Now let's go . This
8:23, folks , is the most important thing .
8:25Of course , the exams will test you on
8:27the classification , but you have to
8:29understand all of this here , what the
8:31function is , why carbohydrates exist ,
8:33so that you can then understand their
8:35classification . So , look , now with
8:37great attention , now begins the
8:39somewhat tricky part because there are
8:41some names in biology , we can't avoid
8:43names , but regarding classification ,
8:45there are three main groups in the
8:47classification of carbohydrates . There
8:49are monosaccharides . There is only one
8:53simple sugar molecule . There is also
8:56oligosaccharide . Oligo means few sugars
9:01. Few sugar molecules . In this case ,
9:03there are two . That is , there was the
9:05union of two simple molecules , so there
9:07are already two , obviously . And
9:09consequently , they are oligosaccharides
9:12, which are the union of two up to 10
9:15monosaccharide molecules . Now , above 10
9:18molecules , we already have what we call
9:21poly . Poly means many , many saccharides
9:24. Polysaccharides are more than 10
9:26monosaccharide molecules linked
9:29together . So this is simple , it's just
9:31a classification . If your test is
9:33talking about polysaccharides , you know
9:35that it's not a simple sugar , nor with
9:36few molecules , it's with many ,
9:38sometimes millions , millions of sugar
9:39molecules , one linked to the other .
9:42I'll talk about this linkage too , OK ?
9:44Now , A , B , C. I'll talk about each of
9:47them here , starting with
9:49monosaccharides . Notice that all
9:52monosaccharides are a little more
9:54complicated . We're focusing on
9:55monosaccharides because we're going to
9:58understand the structure of a simple
10:00carbohydrate molecule . So , as I said ,
10:02it's a mono-carbohydrate molecule , just
10:05one . These are what we call simple
10:08sugars . Why ? Because it's just one
10:10molecule . So we call it a simple sugar .
10:12And how do we know that the basic
10:14structure of a carbohydrate is a
10:15monosaccharide ? It can't be broken down
10:18. Of course , it's broken down in
10:20cellular respiration and everything
10:22else , but it doesn't undergo hydrolysis
10:24; you can't break it down further
10:26unless it enters respiration , there
10:28will be the breakdown of glucose and so
10:31on , but they won't undergo hydrolysis .
10:33So it's the fundamental basic unit of a
10:36sugar . And that's the big question here
10:39. I'll even use a diagram to show that
10:42they have three , look , from three to
10:44seven , seven carbon atoms . Oh , it can't
10:48have two , it's 3 , 4 , 5 , 6 or seven .
10:52Each monosaccharide molecule has either
10:56three , or four , or five , or six , or
10:59seven carbon atoms . Look what I told
11:02you , it has carbon , OK ? Now , there's a
11:06very simple formula for classifying
11:09monosaccharides according to the number
11:11of carbon atoms they have . Don't worry ,
11:15I'll show you exactly how it works . So ,
11:18this is the basic formula for sugars ,
11:21for monosaccharides : C₆H₂NO . Notice
11:26that I told you , " I'm going to put that
11:28formula here . If I remove the N , what
11:30does it become ? " C₆H₂O . And I can
11:35put the N outside . That is , this N
11:37multiplies with O , becoming ON . This N
11:40multiplies with H₂ , becoming H₂N .
11:44And this N multiplies with N , becoming
11:47C₆H₂O , a carbohydrate . Hydrated
11:51water . Carbohydrate or carbohydrate .
11:56That's why the name . It's interesting
11:57for you to know this because , oh ,
11:58professor , what is it ? Why exactly ?
12:00What is the form of a carbohydrate ? A
12:02hydrated carbon . Add the water , put in
12:04parentheses , add the N , and it's done .
12:06Oh , on the test , if you forget , this
12:08will help you remember . So , look how
12:10the carbon is here , okay ? Since they
12:14can have from three to seven carbons ,
12:16this N here varies from three to seven .
12:19It's logical . If this N is 3 , you agree
12:23that it's C3H2N ? If I put the 3 here ,
12:30it's 2 x 3 , it will give H6O3 . This has
12:35three carbons and therefore it's a
12:38triose . So , if you say , look , here come
12:40the names , people , I know , I know , it's
12:42annoying . Oh , professor , please , I give
12:44up . No , don't give up . Okay , let's go ,
12:45let's do it together . Let's do it
12:46together . If you talk about triose , you
12:48know it's a monosaccharide with three
12:50carbons . Then you know the formula , you
12:52know how many hydrogens and how many
12:53oxygens it has to have in that formula .
12:56Then , professor , and if it has four
12:57carbons , it will be C4 . 2 x 4 gives 8.
13:03So , H8O4 , four carbons . Tetrose . Do I
13:09remember ? It's tetra . It's tetra . 1994.
13:13Yes , I was very young , but I watched
13:15that World Cup there , Roberto Bajo ,
13:16kicking the ball over the top , right ?
13:19Well , pentose pentose is five . Pentose ,
13:22so it has five carbons . If here it's 5 ,
13:262 x 5 will give 105. So that's the
13:31formula for a pentose , OK ? Exose , let's
13:36go . C6H12O6 and heptaeptose 7. Oops .
13:45C6H7 x 214O7 . These are the formulas . I
13:52highly advise you to do this . Take the
13:54formula and do it . You won't go wrong ,
13:57then you'll be ready for the test . Easy
13:59? Well , now something that's very
14:02important for you to know is that among
14:05the monosaccharides , some of them you
14:07have to know are the ones that are
14:09tested in the most in-depth biology
14:12exams in high school . Others I've never
14:14seen appear . There are , but the most
14:18important thing is for you to know
14:20three that are exoskeletons , that is ,
14:22three that have this formula here ,
14:24C6H12O6 , and you need to know two
14:26sugars , two monosaccharides that are
14:28pentoses and therefore have five
14:30carbons . Look , you already need to know
14:33this . See , if you put the formula here ,
14:36exoskeleton C6H1O6 , pentose C5H10O5 .
14:47You already need to know this . Ah ,
14:48professor , I'm fine . Because an
14:49exoskeleton is a pentose . Now , you need
14:51to know three exoskeletons . And you
14:54need to know two pentoses . Remember
14:56that this is a complete lesson for
14:57college entrance exams , for the ENEM (
14:58Brazilian National High School Exam ) .
14:59And of course , students use this level
15:01of depth in college , they also use it
15:03in university , it does well on exams ,
15:05because we're talking about this in
15:07hardcore . Look , exoskeleton , glucose ,
15:10folks , the main source , bread . I mean ,
15:13bread , pasta , potatoes , we get glucose
15:16from these extremely energetic
15:18compounds . Remember that you'll see
15:22later when we talk about
15:23polysaccharides that this glucose is ,
15:26for example , in bread , but it's in
15:28another very large sugar called starch .
15:32Keep this information in mind because
15:33I'll come back to explain how we
15:34extract this glucose from this other
15:36sugar . But it's a simple sugar , it's
15:38this one , it's the glucose that enters
15:40our cells for cellular respiration .
15:42It's what will enter cellular
15:43respiration , you probably already know
15:44that . Fruit , look how easy . Fructose .
15:47Fructose is a sugar that we find in
15:49fruits . You can't go wrong , fructose .
15:52This sugar is extremely sweet . It's
15:55worth remembering . Oh , professor , is
15:57all sugar , all carbohydrates sweet ? No ,
15:59of course not . Fructose is sweet , OK ?
16:02It has this sweet quality , but not all
16:05sugar is sweet . Obviously . Galactose is
16:08the sugar found in milk . See how
16:10interesting . So , when we talked about
16:13milk here , the sugar that's here is
16:16galactose , OK ? Well , so far so good . Ah
16:20, now let's go here . Pentose , pay
16:22attention to its importance . A pentose ,
16:25folks , is C5H10O5 . You already know ,
16:28pentose . Two of them are important :
16:31deoxyribose and ribose . They are the
16:34sugars present in our RNA and DNA . This
16:38is very important for you to remember ,
16:39to know . When you look at the shape ,
16:42the structure of our DNA , there are
16:45these beautiful sugars there with five
16:47carbons . A house shape , professor . Yes ,
16:50because there are five . So , deoxyribose
16:53and ribose contain a sugar , OK ? In fact
16:57, they are sugars that are present in
16:59RNA and DNA . Therefore , it is RNA and
17:02DNA that contain the sugar . How many
17:04carbons does the sugar in RNA and DNA
17:06have ? It has five carbons because it's
17:09a monosaccharide called a pentose . Okay
17:11, folks ? This is the main part . It's
17:14the most theoretical part , the most
17:15formal , the most boring stuff . But
17:17what's going to happen now ? I'm going
17:18to erase this . Ah , I'm going to stay
17:20down . As I'm always there during the
17:22board change at the beginning of
17:23classes , you copy this down and we'll
17:25move on to the second part of the
17:27lesson shortly . Stay tuned . So , let's
17:31continue now talking about
17:33oligosaccharides . We've already studied
17:36monosaccharides , simple sugar molecules
17:38. Now we're going to start studying
17:41sugars that have two or more
17:43monosaccharide molecules . And then we
17:46call them oligosaccharides . Remember
17:47that oligosaccharides are few , few
17:50sugars , few saccharides . As you already
17:53know , they have two , that is , two
17:55monosaccharides , we already call them
17:58oligosaccharides . And this
18:00oligosaccharide is a union of up to 10
18:02sugar molecules , simple molecules ,
18:04obviously . So , look , I said that they
18:07link together , this is very important .
18:10This bond between two sugar molecules
18:13is called a glycosidic bond . Don't
18:17confuse it with the peptide bond of
18:19proteins . Here it's sugar , so it's a
18:22glycosidic bond . Notice that here we
18:24have one sugar molecule . Here I've
18:26represented another sugar molecule .
18:28They are separated . It doesn't matter
18:30which sugar this is or which one this
18:32is . They are separated here . Notice
18:34that the OH of one is facing the OH of
18:37the other . And I circled the H of one ,
18:41the hydrogen of one , and the OH of the
18:43other . An oxygen and a hydrogen of the
18:45other . If you counted , there are two
18:48hydrogens and one oxygen . Two hydrogens
18:51with oxygen form H2O . OK ? This means
18:56that to form , for these molecules to
18:58join and form a disaccharide , that is ,
19:01a sugar molecule with two atoms joined ,
19:03it has to lose water . Notice that an H
19:07leaves and an OH leaves , leaving only a
19:10small O here . This is the glycosidic
19:13bond . And notice , it's a synthesis ,
19:17that is , it forms a synthesis by
19:20dehydration . It dehydrates because it
19:23loses water . So , in this bond , there's
19:25a free sugar here , there's another free
19:27sugar . Let's join these sugars . Let's .
19:30The moment it joined , what happened ? A
19:33water molecule is released , and these
19:35sugars are now joined together . Now ,
19:37notice that the opposite has to happen .
19:39We're going to have to break this here ,
19:41break this glycosidic bond . If it has
19:43to break , we have to replace a hydrogen
19:45from one and an OH from the other .
19:47Therefore , water is necessary . In this
19:51case , we have what we call hydrolysis
19:53or breaking by water . For this breaking
19:57to occur , water must necessarily be
20:00present , because it is H , H2O , that
20:03will replace these lost atoms . So this
20:07can go either way . Okay ? Great ,
20:11professor ? I understand now . Look , now
20:13you put three dots here and three dots
20:16there . Why ? Because here I represented
20:19a bond between two simple sugars , but
20:21there could be 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10.
20:24Or it could even be a polysaccharide
20:26with millions of sugars , each one
20:28linked to the other by glycosidic bonds
20:31. Now , notice , we've already talked
20:33about monosaccharides and we're still
20:34on oligosaccharides . Within
20:36oligosaccharides there are some
20:38classifications . Oligosaccharides , I
20:41told you , are a few sugars . If it's a
20:44bond between two sugar molecules , we
20:47call them disaccharides . If it's
20:50between three simple sugar molecules ,
20:52of carbohydrates , we call them
20:54trisaccharides . If it's four , it's a
20:57tetraaccharide . If it's five , it's a
21:00pentasaccharide , hexasaccharide ,
21:02ethaccharide , octasaccharide ,
21:04nonsaccharide , and decasaccharide . I
21:07think that's it , right ? So , from 2 to
21:0910 , professor , and if there's an 11th ?
21:12Then it's no longer an oligo , then we
21:14consider it a polysaccharide . But then
21:16you must be scared , saying , professor ,
21:18with wide eyes , I'll have to know an
21:20example of each . No , don't worry . For
21:23the exam , for all college entrance
21:24exams , first and second phase , ENEM (
21:26Brazilian National High School Exam ) ,
21:27there are only a few examples of
21:29disaccharides that we have to take to
21:30the exam . You really have to know them ,
21:32okay ? So , notice that some people say :
21:34" Professor , but wouldn't a
21:36monosaccharide then be an oligo ? " No.
21:38Monosaccharides fall into another
21:40classification because they are simple
21:42sugars . Oligosaccharides , as I've
21:44already told you , are sugars with few
21:46monosaccharide molecules joined
21:48together . So there's only one molecule ,
21:50it's not an oligo , it's mono . When two
21:53monosaccharide molecules are joined , we
21:56classify them as oligosaccharides . But
21:59because there are two , it has another
22:01name which is disaccharides , two sugars
22:03, or three , or four , or five . Okay ?
22:06This is easy . Glycosidic bond . Now
22:08let's talk to you like this : What are
22:10these important oligosaccharides that I
22:12need to know ? As I told you , you need
22:15to know examples of disaccharides . And
22:18there are three . There's no escaping
22:20these three examples . You'll have to
22:22know them for your exam if you want to
22:23ace any college entrance exam or the
22:25ENEM . Look , the first one I'm going to
22:27tell you about is sucrose . Sucrose is a
22:29disaccharide , therefore it has to have
22:31two monosaccharides joined together .
22:34What are these monosaccharides ?
22:36Fructose , which I already told you
22:38about in the other section , and glucose
22:40. So , if fructose joins with glucose ,
22:42we have a disaccharide called sucrose .
22:46If galactose joins with glucose , we
22:49have lactose . Remember I told you , we
22:53find galactose in milk , but we find
22:55galactose in milk joined with glucose .
22:59Therefore , the sugar in milk is lactose
23:02. And finally , we have maltose . Maltose
23:06is glucose plus glucose . You'll see
23:09that I'll talk a little more about
23:11maltose when we're talking about starch
23:13here . Okay ? Now , going back here ,
23:16sucrose is the sugar we extract from
23:18sugar cane . It's the table sugar . And I
23:22also told you that fructose is very
23:24sweet . That's why sucrose is very sweet
23:27. And then we break down the sucrose ,
23:31of course , with sucrase , an enzyme from
23:33our digestive system , right ? An enzyme
23:36that breaks it down , and then we use
23:38the glucose . Oh , professor , and
23:40fructose ? I've never heard of fructose
23:41being involved in cellular respiration .
23:44That's because when we break down the
23:46sucrose , using sucrase , our enzyme , we
23:48break it down . So now it's no longer
23:52sucrose , it's fructose and glucose .
23:55This glucose is ready to enter the cell
23:57and perform cellular respiration . This
23:59fructose here cannot perform cellular
24:01respiration . It undergoes a small
24:03reaction , transforming into glucose ,
24:05and then it will also participate in
24:07cellular respiration . Okay , so here we
24:09have lactose . Lactose is very important
24:12to know about because it's from milk ,
24:14it's from mammals , it's the sugar of
24:16mammals . So , notice that it has
24:19galactose , which is a monosaccharide ,
24:21bonded to glucose . To break down
24:25lactose , we need an enzyme called
24:27lactase . All of this , folks , that I'm
24:30talking about here , we'll delve into in
24:31the digestive system class , okay ? The
24:33digestive part , I'm telling you , but
24:35you have to watch our digestive system
24:37class . Anyway , lactose , there are
24:39people who still drink milk today , put
24:41chocolate milk in it , drink their milk ,
24:43milk with coffee , everything is fine
24:46and it doesn't give me any problems .
24:48There are some people who have what we
24:50call lactose intolerance . Lactose
24:53intolerance , why ? Because they no
24:55longer produce lactase , which is the
24:57enzyme that can break down this sugar .
25:00If it can't break it down , your
25:02intestine starts to get , oops , these
25:04molecules are too big . They won't be
25:05able to absorb it , man . It's too big ,
25:07it's not producing . So what's going to
25:09happen ? Your intestine starts to get
25:11like this and starts making stronger
25:12movements and producing , and even stops
25:14absorbing liquids and says : " Let's go ,
25:16this is going to make us sick . " The
25:18person has that terrible diarrhea ,
25:20right ? Temporarily because they
25:22couldn't break down that enzyme .
25:24Normally in mammals , we are the only
25:26mammals , I'm observing nature , that
25:28continue drinking milk after old age .
25:32All the others drink it , while they are
25:34dependent on their mother and so on ,
25:36then they stop . So , naturally it's
25:39normal to stop producing lactase , which
25:41is the enzyme that breaks down lactose ,
25:43but over time we have started to
25:45continue producing it . It's very good
25:48for us , OK ? But it's worth remembering
25:50that this exists , right ? If you are
25:51lactose intolerant , put here your
25:53stories of the adventures you must have
25:55already experienced in this life , right
25:57? Well , and maltose , as I told you ,
26:00it's a double sugar , right ? In other
26:02words , it's a disaccharide : glucose
26:04with glucose . Look , glucose is in all
26:06of them , it's hard to memorize , but ,
26:08you know . Ah , sucrose , lactose , and
26:10maltose all have glucose . What differs
26:13here is this : sucrose , which is very
26:14sweet , has to have fructose . Lactose ,
26:16which is from milk , has to have
26:18galactose . And maltose is just glucose .
26:20Okay . Ah , professor , you have to
26:22memorize this . This , you know , uh , that
26:24thing , right ? Biology has names .
26:26Unfortunately , some names we end up
26:28having to memorize . And if you want to
26:30be the hardcore expert on the medical
26:32exam , the second phase , any entrance
26:34exam , then you'll have to know a little
26:36more than the competition . Okay , so now
26:38that we've finished with
26:40oligosaccharides , we're moving on to
26:41polysaccharides . Starting with 11
26:44monosaccharides linked together , we
26:46consider it a polysaccharide , but
26:48normally there are more than 20 ,
26:49hundreds , thousands , or even millions
26:51of monosaccharides linked to each other
26:53. And here we have , you know , right ?
26:56They're linked by what , professor ?
26:58They're linked by glycosidic bonds . The
26:59bond is the same , but now there are
27:01several . And there are four examples
27:03you need to know for your exam . You
27:05don't need to know more than these four
27:06for a college entrance exam . " Oh ,
27:08professor , but I'm in college , I need
27:09to know more . " Well , if your
27:10biochemistry professor at college gave
27:12other examples , sure , but these are the
27:14most important fundamental ones you
27:15need to know for the ENEM exam , for the
27:17college entrance exam , for all the
27:18second phases of all the federal
27:19universities in Brazil , for the biology
27:21exam . So , look , starch is the first one
27:23we're going to talk about . Starch is
27:25the union of glucose ... So , there's
27:26glucose , glucose , glucose , glucose ,
27:28glucose , glucose , millions of glucose
27:30molecules . That's starch . But starch ,
27:33notice where , why do we need to
27:34accumulate so much glucose ? Tell me ,
27:36professor , didn't you say that glucose
27:38is for cellular respiration ? Why do I
27:39need to accumulate this glucose ?
27:41Because plants and algae need to have
27:45an energy reserve . Oh , that's right ,
27:47professor . I've never seen a plant with
27:49a belly full of fat . No. How do these
27:52plants and algae store the energy they
27:55need , and how can they not produce , or
27:57something like that , and still need , a
28:00plant , ah , professor , that plant
28:02produced , lost all its leaves in the
28:04winter , how did it not die without
28:06photosynthesizing ? It has an energy
28:09reserve . This energy reserve of plants
28:12and algae is in the form of starch .
28:15Starch , the image is a big ball like
28:16this , I'm speaking very roughly , but
28:18it's inside the cell , right ? But it's a
28:20big ball of glucose all joined together
28:22. That's starch , folks . When you eat a
28:25piece of bread , it's starch . This
28:27starch , in your mouth , in your saliva ,
28:29produces an enzyme called salivary
28:31amylase , part of the digestive system ,
28:33to complete this process . Then you
28:36break down the starch into smaller
28:38molecules called maltose . Notice , I
28:41told you that starch is glucose ,
28:42glucose , glucose , glucose , glucose ,
28:44glucose . Our saliva , which has amylase ,
28:48breaks down the starch and transforms
28:50this polysaccharide into many
28:52disaccharides called maltose . Then
28:56comes maltase , which is another enzyme ,
28:58breaks this last bond , and the glucose
29:00is ready for us to dissolve . So all
29:03this , folks , uh , of course , I'm making
29:05this link because biology is a spider
29:06web with everything connected . It's so
29:08you know that everything is
29:09interconnected , but you would have to
29:11watch this other lesson to delve deeper
29:13. If your focus at this moment is
29:15really biochemistry , this alone is
29:17enough , okay ? Great ? Then we also have
29:19to learn about glycogen . Glycogen is
29:21very important for us , I'll explain why
29:23, for us and for fungi as well . First ,
29:26glycogen is also a combination of
29:28glucose , glucose , glucose , glucose ,
29:30glucose , glucose . But why , professor ,
29:32do you say that glycogen is important
29:34for us ? Consider this : if I were to eat
29:36a sweet , a lot of ice cream , a lot of
29:38things , what would happen to the
29:40glucose in my blood ? It would be very
29:42high , it would start to rise . But our
29:44body thinks , no , it's starting to rise ,
29:46there's too much sugar here , we're not
29:48going to use this now . So , what does
29:50our body do immediately with this
29:52rising glucose ? Does it eat it ? It
29:54assembles it , it gathers the glucose
29:56molecules and starts to combine them ,
29:58it gathers them and sends it to the
30:00liver to be temporarily stored . In
30:03other words , our body takes the glucose
30:05that is in our blood in large
30:07quantities , combines it into glycogen
30:09and sends it to our liver , to the cells
30:12of our liver . Now , notice that for this
30:15to happen , we need insulin . It's
30:18insulin , the famous hormone insulin ,
30:20that causes the formation of glycogen
30:23and lowers the sugar , the glucose , in
30:25our blood . This is very important .
30:29People who don't produce insulin have
30:31diabetes , which we call diabetes . They
30:34have to artificially inject insulin
30:36into the muscle and everything else so
30:38that this happens and doesn't cause
30:40very high sugar levels , because too
30:42much sugar in the blood can cause small
30:44... clogs in small capillaries and then
30:46have difficulty circulating . This is
30:48very important . Then the opposite
30:50happens . So , you ate a lot of sweets at
30:52lunch , you're like this , full of sweets
30:53. Let's suppose you don't have diabetes
30:56, everything's normal , everything's
30:58fine . You get there , you didn't feel
31:00sick , but you ate a lot of sugar .
31:02What's going to happen ? You go a while
31:04without eating . A while without eating .
31:06After a while , what will your body say ?
31:08" Oops , we have very little sugar now .
31:10We were full , but now there's little
31:12sugar . " What does your body do ? It
31:14produces another hormone called
31:16glucagon . This hormone goes to your
31:19liver and starts breaking down glycogen
31:22to send glucose into our bloodstream .
31:26In other words , insulin and glucagon
31:28are two hormones that maintain ideal
31:30blood sugar levels . Because if your
31:33blood sugar level drops below 50 ,
31:35you're in really bad shape . Oh , if your
31:37blood sugar level is 200 , you have too
31:39much sugar in your blood . There has to
31:40be an ideal level . These are the
31:41hormones involved . Of course , we have
31:44the endocrine system class talking
31:45about all these hormones and how they
31:46work ; you would have to delve deeper
31:48into that , but it's important for you
31:49to know this relationship . Then there's
31:52cellulose . Cellulose is also a
31:54polysaccharide , which is the most
31:57abundant sugar on Earth for a very
31:59simple reason . It's part of the cell
32:03wall of plants , the cell wall of ... So
32:05you might say , " Wow , professor , there
32:07really are a lot of plants in the world
32:09. " Yes . Imagine that each of the cells
32:13in that leaf or plant structure , each
32:17of those cells is surrounded by a cell
32:20wall . So it's very simple to understand
32:23why cellulose is the most abundant
32:24sugar on Earth . Wherever you look
32:26there's a plant , and the plant has to
32:27have cells . If there are cells , there's
32:29a wall surrounding them , which is the
32:31cell wall of plants . So cellulose is
32:33very important . It's worth remembering
32:35that we don't digest cellulose , like
32:36corn . When you eat corn , corn is cell
32:38walls , it has many cells . That little
32:40yellow thing that appeared there . If
32:42you swallow the whole corn kernel , the
32:44inside part , we often eliminate starch
32:46through grinding and everything else ,
32:47you use that . But you don't digest the
32:50yellow husk . Do this experiment : eat a
32:53lot of corn . Then when you go to the
32:56bathroom , take a quick look , you'll see
32:57that there will be little corn kernels
32:59there , because we didn't digest that
33:00corn . Now , ruminants have it , because
33:02they have associations with protozoa
33:04that do this digestion . Okay , that's
33:06another topic for the ecology section
33:08that we also study . So , cellulose is
33:11very important . Then there's chitin .
33:13Some people say chitin , " Oh , chitin is
33:15from hair . " No , no , you can't confuse
33:18chitin with keratin . Keratin is a
33:20protein , forget about that for protein
33:22class . Here , chitin is a sugar that is
33:26part of , first , structurally speaking ,
33:28the exoskeleton of arthropods . What are
33:32arthropods ? Take the little shrimp you
33:34eat , that little sound of the shell
33:36being bitten . That's an exoskeleton
33:38made of a sugar called chitin . Insects ,
33:41folks , why are insects so resistant ?
33:43Take a beetle , it has a carapace , a
33:47very resistant exoskeleton . It's very
33:50resistant indeed . Of course . Oh ,
33:51professor , but if I step on it , it
33:52crushes . No , man , it's a giant , right ?
33:54But imagine in a fight , that creature
33:57manages to pierce through that
34:00same-sized exoskeleton of beetles ,
34:03right ? Of catfish . No. So chitin is
34:06part of it , remembering that our
34:08internal skeleton has nothing to do
34:10with the exoskeleton of arthropods , the
34:12external skeleton of all arthropods .
34:14And chitin is also part of the cell
34:17wall in fungi . Ah , fungi have a cell
34:20wall here . If there's a cell wall there
34:22, it means it's made of chitin . Notice
34:25that these two here , these two here ,
34:27they are structural , they don't have an
34:29energy function . These two here have an
34:32energy function . Remembering that we
34:35talked about it at the beginning of the
34:37class , carbohydrates can have an energy
34:38function and they can also have a
34:39structural function . And so we're
34:42getting to the end . Of course , folks ,
34:45another very important tip I'll give
34:47you here is this : the biological aspect
34:50of carbohydrates . There's a part , a
34:54branch within chemistry called organic
34:56chemistry , where we study , you go back
34:59to studying carbohydrates and their
35:01classification : mat , eth , prot ,
35:03pentexons and dextrose , that whole
35:06thing about classifying carbons ,
35:08whether it's a umase , a ketose , and so
35:10on . You study that in organic chemistry
35:14. So , of course , now you're ready to
35:17ace the carbohydrate section of a
35:19biology exam . Now , ideally , you should
35:24study carbohydrates now with a chemical
35:27perspective , so you can really excel
35:30anywhere . Okay ? Listen , I want to give
35:33you a piece of advice . If your dream is
35:35the entrance exam , if your dream is
35:37college , and you're tired . We're very
35:38tired . Just today , before recording
35:40this class , I was having one of those
35:41days ... you know ? Today , here I am in
35:44Curitiba , it's a rainy day , one of
35:45those days when you just want to play
35:47video games , watch series , eat popcorn ,
35:49Nutella , and all that . But I thought ,
35:53no , I have a goal , I have a dream ,
35:55which is to improve my YouTube lessons ,
35:58to share my knowledge and help some
36:00people . That's my goal , my professional
36:05goal in life . So I overcame all that
36:08laziness , that stress I was feeling ,
36:11and I came here to record . I set
36:14everything up in my studio , man , I'm
36:16going to get out of my comfort zone .
36:17And that's what we have to do every day
36:19. You're tired , if you're tired , that's
36:23very normal . The difference between
36:26someone who manages to reach their goal
36:28and someone who doesn't is that even
36:30when tired , they keep going , even when
36:33destroyed , they keep going . Obviously ,
36:36there are days when we have to stop . "
36:38Wow , professor , there are days when
36:40we're really sad , there are days when
36:42something really bad happens , you have
36:43to stop , it's part of it , it's
36:45fundamental . But laziness , if laziness
36:48starts to win , you don't have any
36:49family problems , you don't have
36:51anything , but you're lazy , you're tired
36:53. Ah , then if you let that laziness
36:56speak louder than your will , then you
36:59won't get there . That's the cruel
37:01reality . You have to stay motivated .
37:04And one of the hardest things , you know
37:06, so that we can stay motivated , we
37:09have to have a boost of energy every
37:11day . And the advice I give to students
37:14who are going to take the college
37:15entrance exam , who are going to take
37:17the ENEM , what can motivate you the
37:19most is to imagine , to dream , to close
37:20your eyes , you realizing your dream ,
37:22passing the course of your dreams ,
37:23raising your diploma , you know ? "
37:27Hugging , I don't know , your parents up
37:29there on stage at your graduation and
37:31saying : " Wow , all this stress and
37:33suffering was worth it . " Because
37:36studying is tiring , we know , it
37:38requires thinking , and thinking
37:39consumes energy . But I want you all to
37:42know that I , Professor Samuel Cunha ,
37:44wish you all success , all of you who
37:46follow my hard work here , and that we
37:47always try to improve . Here's to
37:50everyone , my big kiss , my big hug , and
37:51see you later . Ciao . Ciao .