Biological Molecules - Proteins

Question 1

Monomer, dimer and polypeptide of protein

Answer 1

Amino acid
Dipeptide
Polypeptide

Question 2

Basic functions of proteins

Answer 2

Transport molecules across membranes
Enzymes
Antibodies
Glycoproteins in membranes
Haemoglobin, carry oxygen
Blood clotting
Muscle contraction
Structure
Hormones
Histones in chromosomes

Question 3

Essential amino acids

Answer 3

Cannot be synthesised by humans

Question 4

Non-essential amino acids

Answer 4

Body already synthesises them (11/20)

Question 5

Elements in proteins

Answer 5

Carbon, hydrogen, oxygen and nitrogen (and sulfur)

Question 6

First class proteins

Answer 6

Food containing all essential amino acids eg. Steak

Question 7

Properties and structure of globular proteins

Answer 7

Round, compact, soluble in water, usually metabolically reactive, hydrophilic R groups found in the outside.

Question 8

Structure and properties of fibrous proteins

Answer 8

Long, tough, role shaped, insoluble in water, structural, usually metabolically un reactive, strong, high proportion of hydrophobic R groups

Question 9

Primary structure explanation

Answer 9

The order of amino acids that occur in the chain

Determined by DNA, and made by ribosomes

Question 10

Secondary structure explanation

Answer 10

Automatic folding or coiling of chain when hydrogen bonds form BETWEEN AMINE AND CO GROUPS of non adjacent amino acids.
Common shapes: alpha helix and beta pleated sheet
For stability
No R groups involved so non-specific to the amino acid

Question 11

Tertiary structure explanation

Answer 11

Further folding caused by bonds and interactions between R groups to make the most stable shape. 
Potentially: disulfide bridge
Ionic bonds
Hydrogen bonds
Hydrophobic interactions

Occur in most but not all proteins

Question 12

Quaternary structure explanation

Answer 12

Association of more than one polypeptide to form a protein.

Not all have this sort of complexity

Question 13

Haemoglobin

Answer 13

Oxygen carrying pigment in red blood cells
Quarternary as made of two alpha and two beta subunits
Each subunit has prosthetic group (haem group) from which iron II ions can react reversibly with oxygen molecule

Question 14

Catalase

Answer 14

Enzyme which helps break down hydrogen peroxide
Quarternary structure, as globular with four haem groups
Hydrogen peroxide is a bi-product of metabolism but needs to be broken down or will damage cells.

Question 15

Insulin

Answer 15

Globular protein

Involved in blood glucose concentration regulation

Question 16

Keratin

Answer 16

Group of fibrous proteins
Large proportion of cysteine (contains sulfur) hence many disulfide bridges
Strong, inflexible and insoluble
Present in hair, skin and nails

Question 17

Elastin

Answer 17

Fibrous protein in elastic fibres

Structure which need flexibility require this, eg. Blood vessels and alveoli

Question 18

Collagen

Answer 18

Fibrous protein
Found in connective tissue, skin, tendons, ligaments and nervous system
Made of these polypeptides in strong flexible rope structure
Every third amino acid = small glycine so packs tight and forms hydrogen bonds

Question 19

Conjugated protein

Answer 19

A protein joined to a non protein group called a prosthetic group, eg, haemoglobin

Question 20

Ways in which a protein can be denatured

Answer 20

Heat or radiation - breaking hydrogen and ionic bonds
Strong acids and alkalis - pH alters charges on R groups and so interrupts ionic bonds
Heavy metal ions - as form bonds with negatively charged R groups disrupting bonds and overall charge so solubility.
Organic solvents and detergents, as hydrocarbon R groups will be moved to the outside of the molecule

Question 21

Renaturation

Answer 21

After limited denaturation, protein may be able to regain its shape and therefore it’s function.