1.1 Biological Molecules

WJEC A-Level Biology

What is an atom?

smallest particle in an element that has the properties of the element

What is a molecule?

formed by the combination of two or more atoms

Magnesium

chlorophyll in leaves

Iron

haemoglobin in blood

Phosphate

required to make ATP/nucleic acids/cell membranes

Calcium

strong bones and teeth

What are carbohydrates made of?

• consist of carbon,hydrogen and oxygen

• Cx(H₂O)y

Main groups of carbohydrates

1. monosaccharides

2. disaccharides

3. polysaccharides

Monosaccharide examples

• triose (3 carbons)

• pentose (5 carbons) e.g. ribose

• hexose (6 carbons) e.g. glucose

α-glucose

OH on bottom of C 1

β-glucose

OH on top of C 1

Disaccharide examples

• maltose - 2 α-glucose

• sucrose - glucose+fructose

• lactose - glucose+galactose

Formation of dissacharide

• glycosidic bond formed

• condensation reaction

• opposite is hydrolysis

Polysaccharide

formed from many monosaccharides

Starch - polysaccharide

• polymer of α-glucose held by glycosidic bonds

• storage molecule in plants

• insoluble, compact, readily broken down

• made up of Amylase and Amylopectin

Amylase - polysaccharide

• linear (unbranched)

• condensation reactions between α-glucose molecules

• C1-C4 links

• coils into compact helix

Amylopectin - polysaccharide

• branches of C1-C6 links

• condensation reaction between α-glucose molecules

• C1-C4 links

• amylopectin molecule coils inside amylase

Glycogen - polysaccharide

• α-glucose molecules held together by glycosidic bonds

• storage molecule in animals

• insoluble, compact, readily broken down

• C1-C4 links

• branches of C1-C6 links

• liver cells and muscle fibers

Cellulose - polysaccharide

• long parallel chains connected by hydrogen bonds which prevent osmotic bursting

• β-glucose molecules rotated 180° everytime

• found in cell wall

• insoluble, tough, durable

• chains > microfibrils > microfibril > fiber

Chitin - polysaccharide

• glucosamine molecules held together

• long straight chains rotated 180° every molecule

• part of exoskeleton of insects

• light, strong, insoluble

What are lipids made of?

• Carbon, Hydrogen, and Oxygen

• glycerol + fatty acids

Are lipids insoluble?

Yes, in water as their non-polar

Lipids uses

• energy stores

• protect organs

• heat/electrical insulation

Glycerol - lipids

• 3 carbon atoms

• each have hydroxyl group

• hydrogen fills the rest

Saturated fatty acids - lipids

• no double bonds

• mostly animal fats

Unsaturated fatty acids - lipids

• double bonds

• mostly plant fats

Triglyceride - lipid

• common lipid

• condensation reaction forming an ester bond

Why are unsaturated fatty acids less dense than saturated fatty acids?

Their tails are not straight so molecules don’t pack close together, so bonds are harder to break and there is a lower melting point

Phospholipid

• one fatty acid is substituted for a phosphate group

• hydrophillic head

• hydrophobic tail

What are proteins made of?

• carbon, hydrogen, oxygen and nitrogen

• amino acids - 20 naturally occurring types

Protein uses

• amino acid order dictates the function

• haemoglobin

• antibodies

• enzymes

Dipeptide - proteins

• 2 proteins bonded with a peptide bond through a concentration reaction

Polypeptide

many amino acids

Collagen

• structural protein

• tough, insoluble, fibrous

• 3 polypeptide chains tightly bound by hydrogen bonds

Primary protein structure

• polypeptide

• peptide bonds

• all proteins

Secondary protein structure

• α-helix and β-sheet

• peptide + hydrogen bonds

Tertiary protein structure

• folded into compact, precise 3D structure

• disulphide bridges, hydrogen + ionic + peptide bonds

Quaternary protein structure

• multiple polypeptide chains

• disulphide bridges, hydrogen + ionic + peptide bonds

• e.g. Haemoglobin

Classifying protein

• fibrous - e.g. collagen

• globular - e.g. enzymes

Water

• polar molecule

• creates hydrogen bonds

Water - universal solvent

allows chemical reactions to take place

Water - high surface tension

cohesion is exploited by organisms like pond skaters

Water - high specific heat

prevents large fluctuations in temperature of water

Water - high latent heat

important in temperature control

Water - density

less dense in solid form

Water - transparent

plants can photosynthesise

Water - cohesive

many molecules stick together to be drawn up the xylem of plants