05 Biomolecules 2 AJH

8/13/2019 05 Biomolecules 2 AJH

http://slidepdf.com/reader/full/05-biomolecules-2-ajh 1/28

Macromolecules of Life

Understanding the Basis of

Cellular Form and Function



Carbohydrates

The Basics

• Structure: CHO

• Categories:• Monosaccharides

• Disaccharides

• Polysaccharides



Carbohydrates

• Functions:

– precursors

– energy storage (short-term)

– cell structure

– cell-to-cell recognition

• Structure:

– composed of monosaccharides

– C:H:O ratio 1:2:1

Glyceraldehyde

C3H6O3

Glucose

C6H12O6



Group Question: Carbohydrates

• What functional groups

do you see?

• Are carbohydrates polar

or non-polar? Hydrophilic

or hydrophobic?

Glucose



Monosaccharides (simple sugars)

• Carbon backbone

– Trioses – 3 carbon sugars

– Pentoses – 5 carbon sugars

– Hexoses – 6 carbon sugars

• Numerous hydroxyl groups

• Position of carbonyl group

Glyceraldehyde

t r iose

Glucose

hexose




• Carbon backbone


– Optical isomers – samechemical formula, but

different structure

• Position of carbonyl group Galactose

Glucose

Position of

hydroxyl

groups differ




• Carbon backbone


• Position of carbonyl group

– Aldose – carbonyl at end

– Ketose – carbonyl in middleGylceraldehyde

(aldose)

Dihydroxyacetone

(ketose)

Position of

carbonyl groupdiffers





Polymerization of Monosaccharides



Disaccharides

• Maltose = glucose + glucose

• Used in fermentation of beer

•

Lactose = glucose + galactose – Milk sugar

– Crucial energy source for infant mammals

•

Sucrose = glucose + fructose – Transported form of sugar in plants

– Less readily metabolized than glucose




to Make Polysaccharides

Glycogen

α-1,6-glycosidic linkage

α-1,4-glycosidic linkage



Carbohydrate Functions

Energy Storage

Structure

Cell Identity

Precursors



Polysaccharides:Short-Term Energy Storage Molecules

Carbohydrate (energy)

storage and release

http://static.howstuffworks.com/gif/diabetes-glucose-regulation.gif

ATP







to Make Polysaccharides

• Glycogen

– Energy storage molecule in animal cells

– Large number of glucose monomers

(2,000–

600,000)

– Highly-branched – Why?




Why are carbohydrates well-suited for energy storage?

Large number of C-H and C-C bonds!




When the atoms in a bond have

little/no difference in

electronegativity …

Electrons are shared equally

between atoms

Electrons are far from an atom

and have more free energy

(more potential/chemical energy

stored in the bond!)




Why are carbohydrates well-suited for energy storage?

Large number of C-H and C-C bonds

There is a lot of energy stored in these bonds!




http://static.howstuffworks.com/gif/diabetes-glucose-regulation.gif

ATP

Carbohydrate (energy)

storage and release



Cellulose in plant cellwall

Chitin in insectexoskeleton

Peptidoglycan in bacterial cellwall

Polysaccharides:Structural Molecules




• Cellulose

– Structural molecule in plant cell walls; fiber, roughage

– Polymer of -glucose monomers

•

-1,4 linkages• Hydrogen bonds form between adjacent parallel strands



Polysaccharides

• Cellulose – long chains of β-glucose

– β -1,4 (chain) linkages

What makes

this a strong

structural

molecule?



Cellulose chains form

sheets held together byH bonds…

…sheets stack due tovan der Waals forces...

…and theseare “glued”into a hardmatrix.




• Peptidoglycan

– Structural molecule in bacteria (cell walls)

– Polymer of N-acetylglucosamine and N-acetylmuramic acid

(monosaccharide) monomers

• Covalent peptide linkages form between adjacent parallel

strands



Peptidoglycan and Antibiotics

• Penicillin and Cephalosporin inhibit formation of

cross-links between peptidoglycan strands

– Inhibits bacterial cell wall production

– Weakens bacterial cell wall



Polysaccharides

•

Animals do not have enzymes that can hydrolyze the -linkages found in structural polysaccharides (cellulose)

– Some bacteria posses these enzymes

– Found in digestive systems of animals that eat grasses

(ruminants); termites

Why aren’t structural polysaccharides used as a source of energy?



• Glycoproteins – proteins covalently bonded to a

carbohydrate (oligosaccharide)

– Cell-cell recognition; cell “fingerprints”/PIN number

– Cell-cell signaling

Polysaccharides:Cell Identification Molecules

Outside

of cell

Inside

of cell

Glycoprotein

Lot of d ivers i ty in

ol igosacchar ides

Therefore… many

unique “fingerprints”



Group Questions: Carbohydrates

#2 - Branches in glycogen are the result of

A. α-1,4 glycosidic linkages

B. β-1,4 glycosidic linkages

C. α-1,6 glycosidic linkages

#3 - Which is not a function of carbohydrates?

A. Energy storage

B. Cell identificationC. Cell wall structure

D. Crosslinks between NAG and NAM chains in peptidoglycan

Documents

05 Biomolecules 2 AJH