carbohydrates

Question 1

Functions of carbohydrate (have 8)

Answer 1

1. Generating & storing biological energy
2. Molecular recognition, for immune systems
3. Cellular protection from physical damages (plant/bacterial cell wall)
4. Cell signaling
5. Cell adhesion
6. Biological lubricants
7. Controlling protein trafficking
8. Maintaining biological structures (cellulose)

Question 2

Name the 2 types of carbohydrates

Answer 2

Carbohydrates are polyhydroxy aldehydes (aldose) or polyhydroxy ketone (ketose)

*Based on the most highly oxidized functional group/ carbonyl group at/near the top.

Question 3

Name the 3 groups that carbohydrates can be classified into

Answer 3

1. Monosaccharides - simple sugars: glucose & fructose, cannot be hydrolyzed into smaller molecules under mild conditions
2. Oligosaccharides - more than 2, ~ 2-10 simple sugar residues: hydrolysis of oligosaccharides yields either all identical monosaccharides, or different monosaccharides
3. Polysaccharides - thousands covalently linked monosacs:
   - Homopolysaccharides: contains only 1 type of monosaccharide (starch, cellulose)
   - Heteropolysaccharides: contain more than 1 type of monosaccharides

Question 4

Draw the Fischer projection of an open-chained form of glucose

Answer 4

OHC-CHOH-CHOH-CHOH-CHOH-CH2OH

please look at google

Question 5

Why Fischer projection?

Answer 5

Fischer projection indicates chiral molecules by showing their 3D structure in 2D, without showing all the wedges & dashes on all the chiral centers (only lines in the drawing)

Question 6

What is the difference between L and D glucose?

Answer 6

Based on C5 of the glucose, L and D glucose rotate plane-polarized light in opposite directions, L = Left, D = Right

Question 7

How to determine direction of the glucose chiral molecule? Which is L and which is D?

Answer 7

Based on FOC, see all the atoms bonded to C5, and the 1st atom has the largest atomic mass, followed by the next,, until all 4 atoms are ranked, then the direction goes from 1-4

*my rabak explanation, can see foc notes

Question 8

What is Enantiomers and chiral vs achiral molecule?

Answer 8

Enantiomers are chiral molecules that are optical isomers that rotate plane-polarized light in opposite direction

Chiral (asymmetric centers) molecules: 4 nonidentical atoms surrounding the carbon atom, non-superimposable mirror image

Achiral molecule: superimposable mirror image

Question 9

What is a tautomer and an enediol intermediate?

Answer 9

Tautomer - structural isomers of chemical compounds that readily interconvert

The enediol intermediate has 2 hydroxyl groups, 1 each at the double bonded C1 and C2, which allows it to readily convert to an aldose or ketose. But the enediol is unstable and cannot be isolated

Question 10

What is the most common monosaccharide structure and which monosaccharide is the most abundant?

Answer 10

Most common monosaccharide structure is the hexoses, carbon hydrogen molecule with 6 carbon atom

D-glucose is the most abundant monosaccharides: stored as starch in plants and glycogen in animals

Question 11

D-ribose is a constituent of? Also, deoxyribose vs ribose?

Answer 11

1. Coenzyme A
2. ATP
3. Oxidizing and reducing agent coenzymes
4. Second messenger cyclic AMP

Deoxyribose is in DNA while ribose is in RNA

Question 12

How to determine number of possible stereoisomers in aldoses and ketoses with n number of chiral centers?

Answer 12

For aldoses: number of possible stereoisomer in molecule with n chiral center = 2^n, 2 to the power of n

For ketoses: 2 to the power of n BUT ketoses have 1 less chiral carbon than aldoses

e.g.
In 3 carbon chain, aldoses have 1 chiral carbon while ketoses have 0

In 4 carbon chain, aldoses: 2, ketoses: 1

Question 13

What are epimers?

Answer 13

Epimers are 2 sugars that differ only in the configuration around one carbon atom

e.g., for D-glucose and D-mannose, the -OH group is on the left for D-mannose and on the right for D glucose

Question 14

Interaction between an aldehyde or ketone with an alcohol yields a ___ or ___, creating a new chiral center at the ___ carbon.

Substitution of a second alcohol molecule (replaces the ___ group) produces an ___ or ___. If the second alcohol is part of another sugar molecule, the resulting bond is a ___ bond.

Answer 14

Interaction between an aldehyde or ketone with an alcohol yields a hemiacetal or hemiketal, creating a new chiral center at the carbonyl carbon.

Substitution of a second alcohol molecule (replaces the -OH group) produces an acetal or ketal. If the second alcohol is part of another sugar molecule, the resulting bond is a glycosidic bond.

Question 15

How is the cyclic structure of D-glucose formed?

Answer 15

Interactions between free hydroxyl group at C5 & aldehydic C1, producing α and β glucoses via intramolecular interaction

Question 16

α and β isomers are ___ & C1 is referred to as the ___ carbon atom

Mutarotation - ___ between α and β

Mutarotase - ___ which are ___ the process in vitro

Answer 16

α and β isomers are anomers & C1 is referred to as the anomeric carbon atom

Mutarotation - interconversion between α and β

Mutarotase - enzymes which are catalyzing the process in vitro

Question 17

In the nomenclature of cyclic monosaccharides, what does pyranose and furanose mean?

Answer 17

6-membered ring sugars are pyranose as it resembles a pyran structure, while 5-membered ring sugars are furanose as it resembles a furan structure.

Cyclic form of glucose: glucopyranose (α-D-Glucopyranose)
Cyclic form of fructose: fructofuranose (α-D-Fructofuranose)

Question 18

What does oxidation and reduction of monosaccharides produce?

Answer 18

Oxidation of monosaccharides produces a sugar acid (carboxylic acid functional group)
Reduction of monosaccharides produces a sugar alcohol (alcohol functional group)

Monosaccharides have an aldehyde functional group which can undergo oxidation by gaining oxygen or can undergo reduction by gaining hydrogen

Question 19

Monosaccharides are reducing agents, what happens when they are oxidized?

Answer 19

Mild oxidizing agents like Fe3+ (ferric ion) or Cu2+ (cupric ion) can oxidize monosaccharides, oxidizing the carbonyl carbon to a carboxyl group.
Only reducing sugars are capable of reducing ferric or cupric ion

Question 20

There’s reducing sugars, then what is a non-reducing sugar?

Answer 20

Non-reducing sugars have anomeric carbons involved in a glycosidic bond and cannot take the linear form and hence, cannot be oxidized

Question 21

List the derivatives of monosaccharides (have 7)

Answer 21

1. Oligosaccharides
2. Polysaccharides
   (non-polymerized compounds):
3. Sugar alcohol
4. Sugar acid
5. Amine group
6. Amino sugar
7. Deoxy sugars

Question 22

In derivatives of monosaccharides, ester with phosphoric acid forms the ___ ____, which are intermediates in metabolism of saccharides, and are constituents of ___

Answer 22

In derivatives of monosaccharides, ester with phosphoric acid forms the phosphate group, which are intermediates in metabolism of saccharides, and are constituents of nucleotides

Question 23

What are sugar alcohols?

Answer 23

Important components of lipid - glycerol & myo-inositol & ribitol (component of FMN & FAD, more in vitamins)

Question 24

What’s disaccharide and what are some commonly found disaccharides?

Answer 24

2 monosaccharides joined covalently by O-glycosidic bond formed between hydroxyl group of a sugar and an anomeric carbon of another
[N-glycosidic bond is formed between anomeric carbon and amine]

Commonly found:
1. Lactose (milk) - β-D-galactose + β-D-glucose
- Reducing disaccharide: anomeric carbon available for oxidation

2. Sucrose (nyamnyam sugar) - α-D-glucose + β-D-fructose
   - Non-reducing sugar: no free anomeric carbon. both involved in glycosidic bond
3. Trehalose - α-D-glucose + α-D-glucose
   - Non-reducing sugar, serves as energy-storage compound

Question 25

What causes lactose intolerance?

Answer 25

Deficiency in intestinal lactase leads to the inability to digest lactose The activity of lactase gradually diminishes over the years (most adult mammals have a low level of β-D-galactosidase/lactase) The inability to digest lactose leads to lactose being digested by bacteria in the intestinal tract, leading to production of carbon dioxide and other carbon metabolites which leads to bloating, diarrhea, and dehydration

Question 26

Function of polysaccharides: ___ - starch & glycogen ___ - chitin & cellulose ___/adhesion - cell surface polysaccharide ___/homoglycan: polysaccharide that contains ___ ___ type of monosaccharide ___/heteroglycan: polysaccharide made of ___ ___ of monosaccharides

Answer 26

Function of polysaccharides: Storage - starch & glycogen Structure - chitin & cellulose Recognition/adhesion - cell surface polysaccharide Homopolysaccharide/homoglycan: polysaccharide that contains only 1 type of monosaccharide Heteropolysaccharide/heteroglycan: polysaccharide made of different kind of monosaccharides

Question 27

Starch & glycogen are storage polysaccharides Starch - Present in ___ cells (___& ___) - Stored in ___ with range of diameter from 3-100µm (larger than ___ in liver/muscle cells) - Starch granules can resist ___ ___ - Cooking starch causes them to absorb water & ___ Glycogen - Main storage polysaccharide of ___ cells - ___ polymer of glucose residues (can contain up to 50000 glucose - Glycogen accounts for up to ___% of the mass of the ___ & ___% of the mass of the ___

Answer 27

Starch & glycogen are storage polysaccharides Starch - Present in plant cells (amylose & amylopectin) - Stored in granules with range of diameter from 3-100µm (larger than granules in liver/muscle cells) - Starch granules can resist enzymatic hydrolysis - Cooking starch causes them to absorb water & swell Glycogen - Main storage polysaccharide of animal cells - Branched polymer of glucose residues (can contain up to 50000 glucose - Glycogen accounts for up to 10% of the mass of the liver & 2% of the mass of the muscle

Question 28

What's the difference between amylose & amylopectin? (3 properties each)

Answer 28

Amylose: 1. Long, unbranched chains of D-glucose residues 2. α(1,4)glycosidic bond/linkages 3. Molecular weight vary from thousand to more than a million Amylopectin: 1. Branched version of amylose 2. α(1, 4)glycosidic bond between D-glucose residues in linear chain, α(1, 6)glycosidic bond between branches 3. Branching once every 25 residues, with side chains containing about 15 to 25 glucose residues

Question 29

What are the difference between amylose & cellulose?

Answer 29

1. Glucose residues in cellulose have β configuration while glucose residues in amylose have the α configuration 2. Cellulose with β(1, 4) linkages adopts a fully extended conformation, while amylose prefers a helical conformation due to its bent α(1, 4) linkages

Question 29

What's the difference between cellulose (have 5) & chitin (have 4)?

Answer 29

Cellulose (cell walls of plants): 1. Water insoluble 2. Linear, unbranched homopolysaccharide 3. Made of β-D-glucose monomers rotated 180° with respect to each other 4. Glucose are link by β(1, 4)glycosidic bonds 5. Chain can contain 10000-15000 D-glucose units Chitin (exoskeleton of insect): 1. Water insoluble 2. Linear homopolysaccharide of N-acetylglucosamine residues 3. Forms extended fibers similar to those of cellulose 4. Has β(1, 4)glycosidic bonds

Question 30

By removing acetyl group from chitin, it creates CHITOSAN! Shrimp shells are good source of chitosan Blood coagulation mechanism of chitosan: With chitosan cation (___), blood coagulation can be ___ by attracting ___-charged platelets to form a ___ ___. Coagulation molecules are ___ when platelets ___, accelerating the ___ of fibrin and red blood cells to form coherent blood clot in plugging the injured blood vessels

Answer 30

By removing acetyl group from chitin, it creates CHITOSAN! Shrimp shells are good source of chitosan Blood coagulation mechanism of chitosan: With chitosan cation (NH3+), blood coagulation can be accelerated by attracting negatively-charged platelets to form a loose clot. Coagulation molecules are activated when platelets aggregate, accelerating the aggregation of fibrin and red blood cells to form coherent blood clot in plugging the injured blood vessels

Question 31

What's the difference between Gram-positive & Gram-negative bacteria?

Answer 31

All bacterial cell walls have strong, protective peptide-polysaccharide layer: peptidoglycan Gram-positive bacteria have thick cell wall of ~25nm, with multiple layers of peptidoglycan Gram-negative bacteria have thin cell wall of 2-3nm, with a single layer of peptidoglycan sandwiched between the inner & outer lipid bilayer membranes

Question 32

Describe the structure of bacterial cell wall

Answer 32

Bacterial cell wall: heteropolymer of alternating N-acetylglucosamine (GlcNAc) & N-acetylmuramic acid (Mur2Ac) residues linked by β(1, 4)glycosidic bond Linear polymers are cross-linked by short peptides depending on the bacterial species. Enzyme lysozyme kills bacteria by hydrolyzing the β(1, 4) glycosidic bond

Question 33

What do the peptide cross-links in bacterial cell wall do?

Answer 33

The cross-links creates a strong sheath that envelops the entire cell & prevent cellular swelling & lysis due to the osmotic entry of water.

Question 34

Structure of peptidoglycan

Answer 34

The backbone is made of alternating NAG & NAM acid units linked by β(1, 4)glycosidic bond The structure is joined to a tetra peptide (4 peptides linked), usually L-Ala & D-Glu & L-Lys & D-Ala, in which the L-lysine is linked to the γ-COOH of D-glutamate The peptide is linked to the NAM units via its D-lactate moiety and the ε-amino group of lysine in this peptide is linked to the -COOH of D-alanine of an adjacent tetra peptide

Question 35

Difference in peptidoglycan of Gram-positive & Gram-negative

Answer 35

Gram-positive cell walls have a pentaglycine chain (5 glycine residue) bridging the lysine (of the ε-amino group) & the D-Ala carboxyl group Gram-negative cell walls have the lysine (of the ε-amino group) form a direct amide bond with the D-alanine carboxyl (from neighboring peptidoglycan chain)

Question 36

What are glycosaminoglycans?

Answer 36

Glycosaminoglycans are involved in a variety of extracellular functions They are fundamentally constituents of proteoglycans, represented by linear chains of repeating disaccharides where one of the monosaccharide units is an amino sugar & one (or both) of the monosaccharide units contain at least 1 negatively charged sulfate or carboxylate group/carboxylate group

Question 37

What are some glycoconjugates?

Answer 37

Oligosaccharides covalently links to lipids &/or proteins forms glycoconjugates Saccharides attached to the cell surfaces are responsible for cell-cell recognition Different kinds of glycoconjugates include: proteoglycans, glycoproteins, glycolipids

Question 38

Distinct structures of proteoglycans

Answer 38

A macromolecule with one or more glycosaminoglycan chains are joined covalently to a membrane protein or a secreted protein (extracellular matrix) Trisaccharide linker connects a glycosaminoglycan to a Ser residue in the core protein of proteoglycans The xylose residue at the reducing end of the linker is joined at its anomeric carbon to the hydroxyl of the Ser residue

Question 39

What are glycoproteins?

Answer 39

Carbohydrate-protein conjugates Carbohydrate moieties are smaller & more structurally diverse than the glycosaminoglycan Glycosidic link between carbohydrates & protein: - O-glycosidic bonds: anomeric carbon interacts with -OH group of Ser/Thr - N-glycosidic bond: anomeric carbon interacts with amide nitrogen of an Asn residue (less complex than proteoglycan)

Question 40

Function of glycolipids & lipopolysaccharides

Answer 40

Glycolipid have outer membrane lipids in which the hydrophilic head groups are oligosaccharides Glycolipids act as specific sites for recognition by carbohydrate binding proteins The 4 types of human RBC have different oligosaccharides in cell membranes (antigens) and blood group depends on the gangliosides int he surface of the RBC