The Carbohydrates

Carbohydrates What are they? Carbohydrates are polyhydroxy (they contain multiple hydroxyl groups) aldehydes or ketones, another name for it (saccharide) What are their functions? Functions: (Structural & Functional) Main Source of energy (the quickest especially in aerobic metabolism (and anaerobic as well). Structure (cellulose in plants and chitin which forms the outside (exoskeleton) structure of insect) Building blocks. : They are used to form larger molecules Cellular recognition, like immune cells which can recognize self-cells and antigens and non-self-cells by using the sugars on the surface of cells, which is important for signaling Carbohydrates are classified according to different criteria: Classification 1: They're classified by the number of units(monosaccharides) that constitute the sugar, to: Monosaccharides, Disaccharides, Oligosaccharides, Polysaccharides 1|Page 1) Monosaccharides: one single sugar molecule (ex: glucose, fructose and mannose). 2) Disaccharides: two monomers (monosaccharides) coming in together forming a two sugar molecule (ex: sucrose and lactose). 3) Oligosaccharides: "Oligo" means short, so they are chain made of 3-10 monosaccharides (ex: raffinose). 4) Polysaccharides: more than 10 monosaccharides (ex: glycogen and starch). Carbohydrates-natural forms Most carbohydrates are found naturally in bound form (complex molecules) rather than as simple sugars. Rarely, there are sugars in the body that are in the free form. So we are talking about sugars (molecules) that exist in a variety of shapes and forms in different molecules. Polysaccharides (starch, cellulose, inulin, gums, glycogen) Glycoproteins and proteoglycans (hormones, blood group substances, antibodies): Connect to protein (glycoproteins) or associated with peptides which are a small sequence of amino acids (proteoglycans). So they can decorate other molecules. Glycolipids: (cerebrosides, gangliosides) Glycosides: sugars modified by methyl, ethyl or amino acids groups Mucopolysaccharides (hyaluronic acid) (large structures like glycosaminoglycans) Nucleic acids (DNA, RNA), like ribose and deoxyribose Monosaccharides can be either integrated, conjugated or attached to other molecules like other monosaccharides, proteins (forming glycoproteins and proteoglycans), lipids (forming glycolipids), methyl groups (forming glycosides) and amino groups (forming GAGs). Carbohydrates are classified according to different criteria. 2|Page ~ The difference between glycoproteins and proteoglycans is the ratio between sugars and proteins. In the case of glycoproteins, the amount of proteins is greater than sugars, whereas in proteoglycans the amount of sugars is greater than proteins. Monosaccharides: They are highly soluble They are single unit sugar molecules, having a basic chemical formula of (CH2O)n, containing two or more hydroxyl groups. Monosaccharides may be aldose or ketose depending on the functional groups that they have. In aldoses, the aldehyde group (carbonyl functional group) is located at carbon no.1, while in ketoses, the ketone group (carbonyl functional group) is located at carbon no.2. ~ The name of every sugar ends with "ose". Mainly monosaccharides exist as aldoses The functional group (aldehyde group here) which includes the most oxidized carbon has to be ON TOP GROUPS THAT EXTEND SIDEWAYS ACTUALLY GO FORWARD . GROUPS THAT ARE VERTICAL GO BACKWARD This bond is extended in front of the molecule This bond 3|Page This bond is extended behind the molecule. Classification By the number of carbon atoms they contain Triose Tetrose The aldehyde group Pentose must be on the top Hexose Heptose Classification III By the functional group You should memorize the structure (The position and orientation of the hydroxyl groups on every single carbon atom) of these four squared sugars, in addition to the structure of Dglyceraldehyde 4|Page The ketone functional group is ALWAYS at carbon number 2 You should memorize the structure of fructose. Recognize how all molecules are structured (Drawn). Glucose: (main monosaccharide) Mild sweet flavor, known as blood sugar, essential energy source (metabolism usually start with glucose in terms of generation of energy), found in every disaccharide and polysaccharide (either in its form or as a modified sugar) Galactose: Hardly tastes sweet & rarely found naturally as a single sugar (associated with other molecules like proteins. Fructose Sweetest sugar, found in fruits and honey Added to soft drinks, cereals, desserts Found in manufactured drinks and food. 5|Page What is a chiral carbon? 6|Page What does constitutional isomer mean?! When two molecules have the same number of carbon, hydrogen, oxygen and nitrogen atoms, but they are connected differently (different chemical structure) Isomers of glucose How do you know how many isomers a molecule would have? Have 4 chiral carbon so 24=2*2*2*2=16 isomers One of these 16 molecules is glucose, these are all isomers having the same number of carbons, hydrogens and oxygen, but they're connected differently in space. Some of the stereoisomers can be enantiomers. What does enantiomer mean? Two stereoisomers that are mirror images of each other and they are non-superimposable. Not identical so they cannot be put on same. Superimposable means that they overlap, they can be put on top of each other and they would be exactly the same. 7|Page Sugar enantiomers (D- vs. L-) How would I know if a specific molecule has a mirror image molecule? If it contains a chiral carbon, then it would have a mirror image. If the hydroxyl group is oriented to the right, then it is known as a D glyceraldehyde. (D for Dextro) If it is oriented to the Left, then it is known as L-glyceraldehyde. (L for Levo). Every molecule has one enantiomer but it can have different isomers like in glucose. How about molecules that have more than one chiral carbon How do we know if it is an L or D sugar? (because we can have different orientations) The roles: it depends on the chiral carbon that is the farthest from the functional group So it depends on the orientation of the hydroxyl group connected to the chiral carbon that is farthest from the oxidized group (if the hydroxyl group is on the left then i s an L sugar and if it is oriented to the right then it is a D sugar The oxidized group if the two stereoisomers arent enantiomers have diastereomers 8|Page mirror images of each other >we Stereoisomers, but non-mirror images and non-superimposable, then diastereomers Enantiomer Diastereomer Enantiomer The two diastereomers differ only in the orientation of one OH group of one chiral carbon then we call them epimers at carbon no.2, meaning that they are diastereomers and they differ in the orientation of the hydroxyl group at carbon no.2 or we said Epimers at carbon no.4, 3, etc. So we have to specify the orientation or the carbon number in which the orientation of the OH group differs . Diastereomers that differ in the orientation of one chiral carbon...epimers 9|Page Each one of the following sugars contain four chiral carbons. D-mannose and D-glucose are epimers at carbon no.2 (OH group is directed to the left in Ddirected to the right in D-glucose), D-galactose and D-glucose are epimers at carbon no.4. Is L-glucose an epimer with D-mannose and D-galactose? NO What is the relationship between D-mannose and DGalactose? Diastereomers (not epimers) Why is D-mannose a D sugar and why is D-galactose a Dsugar? (Remember the rules) Acetal/ketal vs. hemiacetal/hemiketal Hemiacetal and hemiketal: ether and alcohol on the same carbon Acetal and ketal: two ethers on the same carbon Hemiacetal: alcohol group + ether group + hydrogen Acetal: two ether groups at the same carbon + Hydrogen. Hemiketal: differs from hemiacetal only in hydrogen. It bonds to OH group, ether, and two R groups. Ketal: two ether groups and two R groups on the same carbon. (Focus on the photo to understand the difference better) Formation of a ring structure: Why did we talk about hemiacetal and hemiketal? Because we can have a sugar in a chain structure converted to a hemiacetal group. 10 | P a g e For example: Glucose: A reaction between the aldehyde group on carbon #1 and the hydroxyl group on carbon #4 or carbon #5 produces a hemiacetal. Aldehyde ROH hemiacetal Remember that: we always start numbering the carbons from the one that has the aldehyde -functional group, and then continue clockwise. If a reaction between carbons #1 & #5 or #1 & #4 takes place, a ring structure of the sugar will be formed. NOTE: Glucose is found in the ring structure 99% of the time, and 1% in the chain structure, why? Because it is more stable in the ring structure. There are two ring structures that glucose can form: 1) A Pyranose: as result of the reaction between carbon #1 and carbon #5. 2) A Furanose: as result of the reaction between carbon #1 and carbon #4. 11 | P a g e It is called a hemiacetal, because carbon #1 is connected to an ether group and a hydroxyl/alcohol group. It applies to both Pyranose and Furanose. Q: Which ring structure is more stable (Pyranose or Furanose)? A: It is more stable in the Pyranose structure. Q: Where did the names of the two structures come from? A: depending on the form of the ring: A A 6 membered ring is known as pyran -- ose: sugar ** SUGARS (monosaccharides) can be drawn in a Fischer projection (chain form), and can also be drawn using the Haworth representation. Haworth representation: is a way to draw and represent sugars in a cyclic or a ring form, where the structure looks almost 3-dimensional, as if someone is looking at it from an angle from below. It can be seen as a 3-dimensional structure, because the OH groups from carbons # (2&4) are going downward, and the rest are looking upward (above the ring). 12 | P a g e *** When sugars exist in the cyclic form and have the OH group attached to carbon #1, the OH will be either face upward or downward: If the (OH) is facing upward: beta-D-glucose If the (OH) is facing downward: alpha-D-glucose A way to remember this: 1 - The alpha sign looks like a fish that swims under water alpha-D-glucose (OH - downward). 2 - The beta sign has a similar pronunciation to above the ground that is found beta-D-glucose, (OH - upward). Important notes: 1) Glucose in the cycle form is more stable than the chain form. 2) Glucose mainly exists in nature in the _D_ form, and this applies to all sugars in general. 3) _L_ sugars are found in bacteria, and not very common inside our body. Q: How to know if the sugar is _D_ or _L_ in the cycle form? A: : If the CH2OH group is above the ring >>> _D_ sugar If the CH2OH group is below the ring >>> _L_ sugar 13 | P a g e SHORT QUIZ 1)Which of the following isn't a function of carbohydrates A) storage B) structure C) cell recognition D) catalytic function 2) which monosaccharide is best describes as being : An aldose ... a hexose ....and blood sugar ? A) fructose B) glucose C) mannose D) galactose 3) what is the main difference between hemi acetals and Hemi ketals A) they are aldoses and ketoses that reacted with different Chemical group B)hemi acetal is bound to only one R group while hemi ketals Are bound to two C) hemi acetal are produced from ketoses while hemi ketals Come from aldoses 4) what is the relationship between each of the following ? A) D - Glucose and D - Galactose B) D - Glucose and D - Fructose C) D) D - Glucose and D - Altrose ↳ ( very fun) 5) which of the following statements is acuurate about : 1) D - Mannose. 2) D - Glucose. 3) D - Galactose A) 1 and 2 are epimers while 2 and 3 are diastereomers B) 2 and 3 are epimers and 1 and 3 are epimers C) 1 and 3 are diastereomers while 1 and 2 are epimers D) 1 and 2 are diastereomers and 2 and 3 are diastereomers 6) the most stable ring structure for Glucose is ....... Which forms between the .... and ..... carbons : A) pyranose / 1 / 5 B) furanose / 1 / 4 C) furanose / 1 / 5 D) pyranose / 1 / 4 ( not so fun ) 7) here's a last little question...... It is said that in order to aquire a sugar diastereomer you have to change the orientation of 2 atoms ( switch them up ) at at least one chiral carbon up to ( all of them except one) but not all of them ...... why is that ? ¥ ANSWERS Q1 D Q4). Q2 Q3 Q5 Q6 B B C A A) epimers. B) constitutional isomers. C)epimers. D) Diastereomers Q7) if we flip all the chiral carbon we will turn the molecule into its enantiomer Extra isomers Questions below EXTRA QUESTIONS A. The following structure is D-sorbose. 1) Which describes the relationship between D-sorbose and D-fructose? a) They are diastereomers that are also epimers. b) They are diastereomers but not epimers. c) They are epimers but not diastereomers. d) They are neither epimers nor diastereomers. D-sarbose 2) The enantiomer of D-sorbose: a) is a D-sugar that has opposite configuration around one carbon. b) is a D-sugar that has opposite configuration around three carbons. c) is an L-sugar that has opposite configuration around one carbon. d) is an L-sugar that has opposite configuration around three carbons. 3) When comparing D-sorbose with D-glucose a) they have the same number of equatorial substituents. b) they have the same number of epimers. c) they have the same chemical formula. d) they have the same osazone. 4) Which characteristic is different when comparing the openchain forms of D-sorbose and D-ribose? a) the number of primary alcohol groups. b) the number of secondary alcohol groups. c) the number of stereogenic centers. d) the number of carbonyl groups. B. The following structure is D-talose. 5) When comparing D-talose to D-fructose a) D-gulose has the same number of aldehyde groups as D-fructose. b) D-gulose has the same number of carbon atoms as D-fructose. c) D-gulose has the same number of primary alcohol groups as D-fructose. d) D-gulose has the same number of secondary alcohol groups as D-fructose. 6) When comparing D-talose to D-ribose a) D-ribose has more anomers than D-gulose. b) D-ribose has more epimers than D-gulose. c) D-gulose has more diastereomers than D-ribose. d) D-gulose has more enantiomers than D-ribose. D-talose 7) What is the relationship between D-talose and D-galactose? a) They are C-2 epimers. b) They are C-3 epimers. c) They are C-4 epimers. d) They are diastereomers but not epimers J j ANSWERS TH Q1 Q2 Q3 Q4 Q5 B C A D B Q6 Q7 C A