Biochem Exam 2

Carbohydrates are characterized by

• one + chiral center

• can form rings or linear structures

• can form polymeric structures via glycosidic bonds

• can from h-bonds

What type of bonds do carbohydrates form polymeric structures with

glycosidic

Carbohydrates are hydrated of

carbon

monosaccharaides

• simple sugar

• cannot be broken down into simpler structures

oligosaccharides have how many monosaccharides

2-10

Polysaccharides have how many monosaccharides

11

T or F: Cellulose is soluble

F

Suffix of carbohydrates

-ose

Prefixes of carbohydrates

tri-, tetra-, penta-, hex-

Carbohydrates with an aldehyde have the prefix

aldo-

carbohydrates with a ketone have the prefix

keto-

How many carbons do aldoeses and ketosis have respectively to have chiral centers

3, 4

How is D or L assigned when naming carbohydrates

based on the configuration at the 2nd to last c in the chain (chiral carbon furthest from the carbonyl)

Enantiomers

non-superimposable mirror images that’s configurations differ at each chiral center

Tautomers

structural isomers that can convert between other forms by rapid migration of a hydrogen atom and a shift in a double bond

in aldose form the carbonyl is

at C1

in ketose form the carbon is

at c2

Aldoses can have up to - chiral carbons from c- to c-

4, 2, 5

Ketoses can have up to - chiral carbons from c- to c-

3, 3, 5

D and L monosaccharides are

enantiomers

Are D or L sugars predominant in nature

D

L monosaccharide means the OH group is on which side?

Left

Diastereoisomers

differ at more than one chiral center

Epimers

differ at only one chiral center

Epimers examples

mannose, glucose

How can monosaccharides form cyclic structures

with the formation of an additional asymmetric center

What can alcohols react with to form hemiacetals

aldehydes

glucose is an

aldose

Glucose and other aldohexoses can react with themselves (intramolecularly) to form

a cyclic hemiacetal

OH pointing up in hemiacetal is

beta

OH pointing down in hemiacetal is

alpha

T or F: cyclization is reversable

T

What is the most stable structure of glucose

ring

ketones react with alcohol to form

hemiketals

When a ketose sugar like fructose reacts with itself (intramolecularly) it yields a

hemiketal

T or F: Cyclic structure is favorable in all polysaccharides

T

anomeric carbon is the carbon that was the - before the sugar became a ring

carbonyl carbon

Anomeric carbon in aldoses

C-1

Anomeric carbon in ketoses

C-2

Anomers

isomers of monosaccharides that differ only at the anomeric carbon

In Haworth projections where is the oxygen atom

at the top

Haworth projections represent the

cyclic structure of monosaccharides in 3D format

In Haworth projections how are c atoms numbered?

clockwise from the anomeric carbon

Where on the plane are hydroxyl groups pointing upward drawn?

Above the plane

Where on the plane are hydroxyl groups pointing downwards drawn

below the ring plane

For D-sugars in the alpha confirmation the anomeric OH points

down

For L-sugars in the alpha confirmation the anomeric OH points

up

Why does glucose prefer the chair confirmation

because bulky OH groups are equatorial

T or F: multiple cyclizations are possible in monosaccharides

T

5-membraned ring

furanose

6-membraned ring

pyranose

Mutarotation is the fact that a and b anomers

spontaneously interconvert through the open-chain form

At equilibrium glucose is -% a and -% b with trace % in open chain form

36, 64

Why do both anomers always coexist in solution

because the free anomeric carbon is in equilibrium between a, b, and open chain

The open chain form of anomers is responsible for the

reducing properties

Sugars with free anomeric carbons can act as

reducing agents

T or F: Monosaccharides cannot be converted into derivative forms

F

Deoxy sugars

monosaccharides with 1+ hydroxyl groups replaced by H

2-deoxy-D-ribose is found in

DNA

Why is ribose more easily degraded than DNA?

because of ribose’s two side hydroxy (OH) groups

hydroxyl group

-OH

Sugar phosphate esters have their hydroxyl group replaced with

O-PO3^2-

Metabolic intermediates

phosphate esters of glucose, fructose, and other monosaccharides

Where are the ribose residues of nucleotides such as ATP and GTP phosphorylated?

at the 5’ position

Amino sugars have an amino group at c-

2

Where are amino sugars found in

many oligosaccharides and polysaccharides

Where are muramic acid and neuraminic acid present

in polysaccharides of cell membranes and bacterial cell walls

What roles do muramic acid and neuraminic acid play

structural and functional

Muramic acid has what linkage and where?

ether linkage between a lactic acid portion and c-3 of glucosamine

Where does Neuraminic acid connect N-acetyl-mannosamine to pyruvic acid

at c-1

Sialic acids are derivatives of

neuraminic acid

Sialic acids are found in

bacteria and animal systems

Where do glycosidic bonds form

between the anomeric C of one sugar and an OH (or NH) group, with the loss of water

How are glycosidic bonds named?

by the carbons they link and the anomeric confirmations

• read from carbon 1 on the left

What are the simplest oligosaccharides?

Disaccharides

Each individual sugar unit in an oligosaccharide is termed

a residue

beta

alpha

Main functions of polysaccharides

storage, structure, recognition

Starch and glycogen are - molecules

storage

Chitin and cellulose are - molecules

structural

cell surface polysaccharides are - molecules

recognition

Homopolysaccharide

a polysaccharide that contains only one kind of monosaccharide

Heteropolysaccharide

a polysaccharide made of several monosaccharides

What is the storage polysaccharide of plants?

starch

Starch is made of - which is linear and - which is branched

amylose, amylopectin

What % of starch is amylose

10-30

What % of starch is amylopectin

70-90

How often do branches in amylopectin occur? At what linkage?

every 12-30 residues , alpha(1-6) glycosidic bonds

What kind of linkage for amylopectin and amylose have?

a(1-4)

Do amylopectin and amylose have a reducing end?

yes

Is it amylose or amylopectin that is not very soluble in water and forms micellar helical suspensions?

amylose

Phosphorylase reaction purpose

releases glucose units for metabolic energy

How do the starch phosphorylase reactions work

they cleave glucose residues from amylose to produce a-D-glucose-1-phosphate, an energy source for the organism.

What is the purpose of branches in amylopectin?

to provide a mechanism for quickly releasing glucose units for energy metabolism

What is the storage polysaccharide of animals?

glycogen

What % of liver mass and muscle mass does glycogen constitute?

10, 1-2

How is glycogen different from amylopectin?

it is even more highly branched

glycogen has an a(1-6) linkage every - residues

8-12

T or F: The composition of structural polysaccharides is similar to storage polysaccharides

T