Biochem Carbohydrates and Glycoproteins

Characteristics of Carbohydrates

At least one asymmetric center, capacity to form polymeric structures through glycosidic bonds, potential to form multiple hydrogen bonds with water or other molecules, ability to be linear or ring

Oligosaccharides

2- 10 monosaccharides bound by glycosidic bond

Polysaccharides

11+ monosaccharides, polymers of simple sugars

How are carbs named?

“ose” ending, tri/tetr/pent/hex prefix, aldo or keto forms

How do you tell if a carb is alpha in a haworth projection?

If the hydroxyl group is down on the anomeric carbon

How do you tell if a monosaccharide is beta in a haworth projection?

If the hydroxyl is up on the anomeric carbon

What carbs can have chiral centers?

Aldoses with at least 3 carbons, and ketoses with at least 4 carbons

What are enantiomers and how are they signified?

Stereoisomers that are non super-imposable mirror images. Marked as D or L

Diastereomers

Stereoisomers that are not mirror images of each other

Epimers

Diastereomers differing at only one chiral center in a linear structure

What are Anomers and how are the signified?

Epimers differing at the anomeric atom. Marked as alpha or beta. Only in cyclic structure

Tautomers

keto vs aldo, monosaccharide isomers that differ only at C1/C2 functional groups

What are aldoses?

Monosaccharides that have a terminal aldehyde denoting carbon 1 (anomeric C). Can have up to 4 chiral carbons

What are ketoses?

Monosaccharides with a ketone on carbon 2 (anomeric C). Can have up to 3 chiral centers

What enantiomer of monosaccharides predominates in nature?

D

How to tell if enantiomer is D or L in Fischer projection?

Highest priority on the right is D, highest priority on the left is L

How are hemiacetals formed?

Reaction of alcohol with aldehydes to form hemiacetals

What happens when monosaccharides form a cyclic structure?

An additional asymmetric center is created

How are cyclic hemiacetals formed?

Intramolecular reactions of glucose (and other aldohexoses)

How are hemiketals formed?

Reactions of ketones with alcohol

How are cyclic hemiketals formed?

Intramolecular reaction of a ketose sugar like fructose

When hemiacetals and hemiketals form, what happens to the carbon that had the carbonyl group?

It becomes the anomeric carbon (asymmetric carbon)

What are Haworth projections?

represent the cycliccc structure of monosaccharides in a 3D format

What are the defining features of Haworth projections?

Oxygen atom at the top, carbons numbered clockwise starting with anomeric carbon, hydroxyl groups pointing upward are drawn above plane of ring (axial), hydroxyl groups pointing down are drawn below ring plane (equatorial)

How to determine alpha or beta in Haworth?

D sugars- alpha has OH down, beta has it up

L sugars- Alpha has OH up, beta has it down

What can simple sugars cyclize into?

Pyranose or furanose structures

What sugars are good at reducing?

Sugars with free anomeric carbon atoms

What are sugar acids?

Carboxylic acid derivative of monosaccharides

How are sugar alcohols formed and what are there characteristics?

By the reduction of an aldose or ketoses. They prefer an open chain

What are deoxy sugars?

Monosaccharides with one or more hydroxyl groups replaced by H

What are sugar phosphate esters?

Replacement of OH with O-PO3²-

What are amino sugars?

Sugars with an amino group at C2

What are muramic and neuraminic acid?

Glycosamines in the polysaccharides of cell membranes and bacterial cell walls. They play crucial structural and functional roles

Difference between muramic and neuraminic acid?

MA= ether linkage between lactic acid moiety and C3 of glucosamine

NA= connects N-acetylmannosamine to pyruvic acid through a C1 bond

What are glycosides?

Sugar and another functional group bound through glycosidic (ether) bond)

How are glycosides formed?

The reaction of pyranose and furanose with alcohols in dehydration synthesis

Where do glycosides retain the alpha and beta conformation?

The C1 Carbon

What is a residue?

Each unit in an oligosaccharide

What links residues?

Glycosidic bonds

What are the functions of polysaccharides?

Storage, structure, and recognition

Homopolysaccharide definition?

Polysaccharides containing only one kind of monosaccharide

Heteropolysaccharides definition?

Polysaccharides made of several kinds of monosaccharides

What kind of linkage results in a branch?

alpha 1-6

What cleaves glucose residues from amylose?

Starch phosphorylase reactions

What allows amylopectin to have an easy mechanism for releasing glucose units?

Its branches

What are the characteristics of cellulose?

cellulose (structural) has Beta 1-4 linkages and can be fully extended in conformation. Its strands are parallel

Characteristics of chitin?

Beta 1-4 bonds, C2s are N-acetyl, strands can be parallel or antiparallel

What are glycosaminoglycans?

Linear chains of repeating disaccharides where one unit is an amino sugar and one or both is negatively charged

What are proteoglycans made of?

glycosaminoglycans

What are peptidoglycans made of?

Sugars and amino acids in a network

What is a gram positive bacterial cell wall?

A thick peptidoglycan outer shell surrounding the cell membrane, with a pentaglycine bridge connecting tetrapeptides. The peptidoglycan layer outside the cell membrane is what reacts with the gram stain

What is a gram negative bacterial cell wall?

Thin peptidoglycan shell between outer membrane and inner cell membrane, direct amide bond between tetrapeptides

What is the structure of lipopolysaccharides?

Lipid portion is embedded in outer membrane and is linked to a complex polysaccharide

What do glycoproteins and proteoglycans do in animal cells and where are they located?

They are located on animal cell surfaces, and they regulate cell-cell recognition and interaction

How are N- linked glycoproteins attached?

Through the amide nitrogens of asparagine residues

How are O-linked glycoproteins attached?

They are attached to hydroxyl groups of serine or threonine residues

What do glycoproteins do?

They send and act as receptors for cellular signals

What do glycoproteins look like?

Their extended conformations resemble bristles, and these strucctures can extend functional domains above the glycocalyx

What does N-linked glycosylation in Eukaryotic proteins do?

Use glycan-mediated sorting signals to direct proteins to specific membrane compartments, alter solubility, mass, and electrical charge, stabilize conformations and shield against proteolysis, facilitate polypeptide folding thru chaperone interactions, and influence immune function, hormone activity, and protein lifespan

What are proteoglycans?

Glycoproteins whose carbohydrates are mostly glycosaminoglycans

What do proteoglycans do?

Compose the cell membrane and the glycoalyx (sugar shell around the cell)

What are proteoglycans usually made of?

Typically, they are proteins with one or more types of glycosaminoglycans, with the carbohydrate groups typically consisting of Glycosaminoglycans are o-linked to serine residues

What do proteoglycans do?

They modulate cell growth processes and provide joint cushioning

How do proteoglycans modulate cell growth processes?

They bind growth factor proteins in the glycocalyx, providing a reservoir of growth factors at the cell surface

How do proteoglycans provide joint cushioning?

Proteoglycans in the cartilage matrix absorb lots of water. When joints move, cartilage is compressed and the water is expelled