Molecular biology

The study of many biological processes can be approached by looking

at the chemical structure of the molecules involved and how they

interact with each other

 The molecular structures are diverse, and the interactions are complex

 The structures of the most important biological molecules are

dominated by a handful of key elements:

 Carbon, oxygen, hydrogen, nitrogen, phosphorous

 There are numerous other elements that also play key roles in

biological processes:

 Sodium, potassium, calcium, magnesium, iron etc

Carbon is a component of a range of important

biological molecules

 Carbon atoms readily form stable covalent

bonds with other atoms

 A covalent bond is where two atoms share a pair of

electrons

 They are the strongest type of bond and help

produce stable molecules

 Each carbon atom can form up to four covalent

bonds, enabling complex structures

Side Chains

 A side chain is a

chemical group that

is attached to a core

part of the molecule,

usually referred to

as the main chain or

backbone

 Some common

examples are shown

in the table to the

right

Name Full Structure Simplified

Notation

Hydroxyl -OH

Amine -NH2

Carboxyl -COOH

Methyl -CH3

Isomers are molecules with the same chemical formula but different

arrangement of their atoms

 This means they can have different properties

Monomers and Polymers

 Organic compounds are

typically composed of

recurring subunits referred

to as monomers

 Monomers can be covalently

joined to form polymers

 This process is called

polymerization

Condensation and Hydrolysis

 A condensation reaction is the process by which monomers join together to produce

polymers

 This involves the removal of water (H2O), to form a covalent bond to link two monomers

 Polymers can be broken down by hydrolysis reactions

 This involves the addition of a water molecule two break the covalent bond between two

monomers

Overview of Biomolecules

 There are four main groups of

biomolecules that contribute to

the structure and function of a

cell:

 Carbohydrates

 Lipids

 Proteins

 Nucleic Acids

Carbohydrates

 Molecules consisting of carbon, hydrogen and oxygen, typically in a

consistent ratio of (CH2O)n

 Monomer – typically closed ringed molecules referred to as monosaccharides

 Polymer – disaccharides and polysaccharides

 Mainly used as an energy source but can also be used for structure and

to form part of other complex molecules such as DNA/RNA and ATP

 Examples – glucose, lactose, cellulose

 Can also be classified based on the number of carbons

 Pentose (five carbons), hexose (six carbons) etc

Carbohydrates

 Example – Glucose

 Formula – C6H1206

 Hexose molecule, five carbons in a

ring and one in a side chain

 The positions of the carbons and

the hydroxyl groups (-OH) (either

up or down) is relevant

 Primary form of energy used in

cellular respiration

Lipids

 Non-polar/hydrophobic molecules consisting of carbon, hydrogen and

oxygen

 Typically consist of either unbranched chains (fatty acids) or ringed

structures (steroids)

 Monomer – no true monomers, but there are multiple different fatty acids

 Polymer – no true polymers but triglycerides are three fatty acids and a glycerol

 Diverse functions (cell membranes, energy, hormones, water-proofing etc)

 Examples – linolenic acid (omega-3), phospholipids, testosterone

 Can also be classified based on saturation

 Saturated (single bonds in chain only), unsaturated (double/triple bonds in chain)

Lipids

 Example – Butyric Acid

 Formula – C4H8O2 or

CH3CH2CH2COOH

 Short chain fatty acid

 Saturated

 Found in some animal fats and

plant oils, produced by our gut

bacteria when they break down

dietary fibre

Proteins

 Molecules consisting of carbon, hydrogen, oxygen, and nitrogen (some

can contain sulphur)

 Monomer – amino acids

 Polymer – polypeptides/proteins

 Diverse functions (structure, enzymes, hormones, transport etc)

 Examples – insulin, collagen, spider silk

 Structures are also diverse

 Some proteins can have non-amino acid groups attached which contribute to the

overall function of the molecule

 Proteins comprise over 50% of the dry weight of the cell

Proteins

 Example – Generalised Amino

Acid

 Comprised of a central carbon

bonded to:

 A single hydrogen

 An amine group

 A carboxyl group

 An R group

 There are twenty unique amino

acids used by all life to build

proteins, differentiated by their

R groups

Nucleic Acids

 Molecules consisting of carbon, hydrogen,

oxygen, nitrogen, and phosphorous

 Monomer – nucleotides

 Polymer – nucleic acids (DNA and RNA)

 Genetic material that determines the

inherited features of an organism