Lecture 4- Macromolecules: Polysaccharides and Lipids

Polysaccharides

- long chain polymers of sugar and their derivatives

- repeating units of mono and disaccharides

Function of Polysaccharides

- serve primarily in energy storage

- cellular structures rather than carrying information

- store energy as starch and glycogen

Cell Structure of Polysaccharides

- cell wall

- exoskeletons of arthropods

Monosaccharides

- monomers

- glucose, fructose, galactose

Most Common Monosaccharide

D-glucose (C6H12O6)

Formula for Sugars

CnH2nOn

- n= the number of carbons

Carbons in Monosaccharides

- all carbons hydrated

- most sugars have between 3 and 7 carbon atoms

Common Pentoses

1. ribose

2. deoxyribose

Aldosugars

have a terminal carbonyl group

Ketosugars

have a terminal carbonyl group at carbon 2

Structure of D-glucose

- dynamic equilibrium between linear configuration figure and the ring

- based on spatial orientation of hydroxyl group on C1

Structure of D-glucose: Ring Forms

1. alpha

- hydroxyl group points down

2. beta

- hydroxyl group points up

Disaccharides

- formed by monomers

- uses glycosidic bonds (covalent bonds)

- maltose, lactose, sucrose

Alpha Glycosidic Bond

involves carbon atom 1 with hydroxyl group in the alpha configuration

- ex; maltose

Beta Glycosidic Bond

hydroxyl group on carbon atom 1 of the galactose is in the beta configuration

- ex; lactose

Polymers

- storage and structural polysaccharides

- both are alpha-d-glucose polymers with alpha glycosidic bonds

- glycogen/starch is brokendown to release glucose

Storage Polysaccharides

starch in plant cells and glycogen in animal cells

Polysaccharides

- can be linear or branched

- glycogen is highly branched

- protein and nucleic acid are linear polymers

- branches allow more glucose to be released quickly

Starch

- amylopectin branched structure

- fewer branches

- longer side chains

Amylose

unbranched starch found commonly in plants

Glycogen

- branched structure

- more branches

- shorter side chains

Polysaccharide identity and function comes from:

1. sugar monomers used

2. type of glycosidic bond

3. amount of branching vs linearity

These factors determine structure:

1. amount of hydrogen bonding

2. chain length, number of monosaccharide units

1. Amount of hydrogen bonding

- inter intra molecular bonding

- affect the rigidity and solubility

Lipids

- not formed by linear polymerization that gives rise to others

- high molecular weight

- present in important cell structures

Main feature of lipids

- hydrophobic nature

- some are amphipathic

Amphipathic

having both a hydrophilic region and a hydrophobic region

Main roles of lipids

- energy storage

- membrane structure

- specific biological functions

Lipid Classes

1. fatty acids

2. triaglycerols

3. phospholipids

4. glycolipids

5. steroids

6. terpenes

Fatty Acids

- building units of some lipids

- long unbranched hydrocarbon chain with carboxyl group at end

- amphipathic

- 12 to 20 carbon atoms

Fatty Acids Structure; Saturated

- without double bonds

- long straight chains

- packed well together

Fatty Acid Structure; Unsaturated

- with double bonds

- bend or kink in the chain

- not packed well

Triacylglycerols (triglycerides)

- storage lipids

- glycerol molecule + 3 fatty acids

- 3 carbon alcohol with hydroxyl group on each carbon

- linked to fatty acids via ester bonds

Ester bonds

bond between fatty acids and glycerol formed between a carboxyl and hydroxyl group by the removal of water

Phospholipids

- membrane structure

- 2 fatty acids + phosphate modified with polar alcohol

- phosphoglycerides or sphingolipids

Phosphoglycerides

the predominant phospholipids present in most membranes

Sphingolipids

important in membrane structure and cell signalling

Glycolipids

carbohydrates instead of phosphate

Steroids

- lipids with variety of functions

- derivatives of a 4 ringed hydrocarbon

- nonpolar

Sterols

steroids with alcohol groups

Cholesterol

most common animal steroid

Steroid Hormones

used in cell communication