Chapter 5A: Carbohydrates and Lipids

Macromolecules 3: Sugar-based (Carbohydrates, Polysaccharides)

Functions

build/attach, construct bigger things: CELLULOSE holds structure in plants

Storage: STARCH (plants), GLYCOGEN (animals)

MONOSACCHARIDES (-ose denotes sugars), C:H:O ratio 1:2:1

things to know

Carbon chains: 6 carbon's = HEXOSES

Many HYDROXYL groups (polar, hydrophilic)

ex. glucose syrup is very soluble in water

when linear

C=O bond at end (ALDOSE)

C=O bond at position 2 (KETOSE)

monosaccharides to know: glucose, galactose, fructose Picture1

Monosaccharides in a pair are DISACCHARIDES

5-carbon example is a ribose (backbone of nucleotide)

In cells, monosaccharides are present as RINGS

glucose + fructose = sucrose

galactose + glucose = lactose

numbering starts at the position closest to the DOUBLE BOND

Hexoses can be linked end to end by GLYCOSIDIC BONDS

CONDENSATION REACTION: loss of a water molecule (take out a hydroxyl from one monosaccharide and H from the OH of another monosacharride)

forms a C-O-C bond

examples of polysaccharides

cellulose joins a bunch of glucose together (linen)

starch (glucose)

glycogen (glucose chains are branched)

pectin: mixture of monosaccharides

Macromolecules 4: Hydrophobic (hydrocarbon chains, lipids)

Important features

favor separation from water

compact (highly concentrated) storage of energy

Carbohydrates vs. hydrocarbons

carbohydrates are polar: have HYDROXYLS

hydrocarbons are nonpolar: made up of ONLY carbons and hydrogens

Water does not mix easily with hydrocarbons (lipids, hydrophobic amino acids)

in water, it's favorable to MINIMIZE the surface area of hydrophobic molecules by CLUMPING them together (example: oil clumps in water)

driving force for this clumping is water

Fatty acids are composed of repeated C2H4 elements (HYDROCARBON CHAIN) and carboxyl at the end

SATURATED: NO C=C double bonds

UNSATURATED: has C=C double bonds

C=C double bonds make chain STIFF

Lipids: 2-3 fatty acids linked through a glycerol

glycerol: 3-carbon molecule with OH attached to each carbon image

Triacylglycerol: 3 fatty acids w/ a glycerol

in triaglycerol, a CONDENSATION reaction occurs between each glycerol and carboxyl group

image

Phosphatidylcholine: choline head + phosphate group + glycerol backbone + 2 fatty acid tails

presence of double bonds influences FLUIDITY of fats, oils, and membranes

presence of cis double bonds in UNSATURATED FATTY ACIDS interferes with the tight packaging (LIQUID at room temperature)

SATURATED FATTY ACIDS packed very closely together into crystalline arrays, stabilized by hydrophobic interaction (SOLID at room temperature)

Van der waals forces help lipids COME TOGETHER TIGHTLY in water (non-covalent bonding)

SYNCHRONY of charge fluctuations can hold large molecules together

individual interactions are WEAK, but add them together to generate stronger interactions (larger molecules)

van der waals are strongest when molecules are VERY CLOSE (unsaturated fatty acids drive chains FURTHER apart making forces weak)

Why does the chain at the C=C double bond BEND?

cis fatty acids: when H's are on the same side, they REPEL each other (bend)

trans: when H's are on the opposite side, they DON'T BEND