2.1.2 Biological Molecules (Lipids and Proteins)

Structure of Lipids (Macromolecules)

Triglyceride

Phospholipid

Synthesis and Breakdown of Triglycerides

Esterification

Hydrolysis

formation of ester (-COO-) bonds between fatty acids and glycerol

breakage of ester bonds between fatty acids and glycerol

Properties of Lipids, and Function

Phospholipids

Triglycerides

Cholesterol

steroid alcohol made of four carbon based rings (isoprene units)

polar, hydrophilic phosphate head

Synthesis and Breakdown of Polypeptides

Sammer Sheikh

Condensation

formation of peptide bonds (-CN-)

Hydrolysis

breakdown of peptide bonds (-CN-)

Levels of Protein Structure

Primary

Secondary

Tertiary

Quaternary

Globular Proteins

Haemoglobin (conjugated protein)

Insulin

Pepsin (enzyme)

Fibrous Proteins

Collagen

Keratin

Elastin

Organic Ions

Cations:

Ca2+

Na+

K+

H+

NH4+

Anions

NO3-

HCO3-

Cl-

PO43-

OH-

Lipid: a group of substances that are soluble in alcohol rather than water; non-polar; not polymers

macromolecule: a very large organic molecule

glycerol: 3-carbon molecule with 3 alcohol groups

three fatty acid chains; 2-20 carbon chain with carboxyl group on one end; can be saturated (no double C=C bonds), or unsaturated (contain C=C bonds)

having one (monounsaturated) or more than one (polyunsaturated) gives the carbon change a kink; decreases melting point and makes lipid more fluid

same structure as triglyceride but one of the fatty acid chains are replaced by a phosphate group

fatty acid chains normally have even number of carbons (usually 16 or 18); commonly one saturated, and one unstaurated

-COOH group of fatty acid chain reacts with -OH group of glycerol to form a covalent ester bond

water molecule is lost, per ester bond formed (when triglycerides are formed, three water molecules are lost in total)

covalent ester bond is broken, and a water molecule is lost

energy source; broken down in respiration to release energy

energy store: are insoluble in water so can be stored without affecting water potential of the cell; releases more energy than glucose

insulation e.g. blubber in whales

buoyancy: less dense than water, so help animals float e.g. aquatic animals

protection of delicate organs: shock absorber

non-polar hydrophobic fatty acid tails

ampipathic

forma plasma membrane; phospholipid bilayer; individual phospholipids are free to move around but tails will not be exposed to water; stable membrane e.g. most plant and animal cells

membrane is selectively permeable; only small, non-polar molecules can pass through the bilayer; plasma membrane controls what goes in and out of the cell

small and hydrophobic molecule; can sit in middle of hydrophobic part of bilayer; regulates fluidity of membrane

made in liver in animals

steroid hormones e.g. testosterone, oestrogen are made from cholesterol so can pass though plasma membrane as they are small and non-polar

sequence of amino acids in a chain; determines function of end protein, and secondary, tertiary, quaternary structure

amino acid general structure: amine group (-NH2) on one end, and carboxyl group (-COOH) on other end of central C atom, and an R group

linked together by covalent peptide bonds

folding of primary structure

α-helix

β-pleated sheet

bonds:

Hydrogen bonds: between -NH of one amino acid, and -CO of another

3D folding of the secondary structure

bonds:

hydrogen bonding

disulphide bridges: bonds between S in R group of amino acid (cystine); strong covalent bonds

ionic bonds: bonds between carboxyl groups and amino groups; ionise into NH3+ and COO-

hydrophobic and hydrophilic interactions: hydrophobic R groups in the centre of the peptide chains to avoid water, and hydrophilic R groups found at the edge of the structure, close to water; case twisting of amino acid chain; stable structure

two or more polypeptide chains joined together

bonds:

hydrogen bonds

ionic bonds

disulfide bridges

hydrophobic and hydrophilic interactions

two amino acids join together to form a dipeptide molecule

water molecule is lost

dipeptide molecule is broken down into two amino acids, and a water molecule is lost

relatively long, thin structure; insoluble in water; metabolically inactive; usually have a structural role in organism

provide mechanical strenght

e.g. in artery wall; withstand high blood pressure and prevent the artery all from bursting

e.g. tendons; connect muscle and bone

e.g. bones, cartilage, and connective tissue; are strong

rich in cystine; many disulphide bridges are formed

e.g. hair, nails, hooves, horns, feathers

mechanical protection

impermeable barrier to pathogens

waterproof

cross-linking and coiling

e.g. skin; stretch around bones and muscles

e.g. in lungs; lungs can expand and recoil without bursting

e.g. in blood vessels; prevent bursting

molecules of relatively spherical shape; soluble in water; often have metabolic roles in organism

quaternary structure; four polypeptide chains (2 α and 2 β)

prosthetic haem group: a non-protein component that forms a permanent part of the functioning protein; contains and iron ion

function: carry oxygen form lungs to tissue; oxygen binds to iron

made of two polypeptide chains; first chain starts of α helix and second chain ends β pleated sheet; fold into tertiary structure

soluble, due to hydrophilic R groups on outside of molecule

function: increase rate of uptake of glucose from blood into muscle and fat cells

function: digest protein in the stomach

made up of single polypeptide chain folded into symmetrical tertiary structure; contains many more acidic R groups than basic R groups, so is stable in acidic stomach, as there are less OH- to accept H+ ions and change structure of enzyme

held together by hydrogen bonds and disulphide bridges

component of amino acids; nucleic acids; regulates pH; in nitrogen cycle

control of water level in body fluid; maintain pH; assist active transport across plasma membrane; healthy leaves and flowers; muscle contraction; vacuoles retain turgidity

strong bones; clotting blood; muscle contraction; cell wall development in plants; regulate permeability of plasma membrane

control water levels; ; maintain pH; muscle contraction; vacuoles maintain turgidity

photosynthesis; respiration; transport of oxygen and carbon dioxide in the blood; regulate blood pH

component of amino acids; nucleic acids; nitrogen cycle

regulate blood pH

transport CO2 into and out of the blood