Amino acid and proteins

Question 1

What are the functions of proteins?

Answer 1

Structural support, enzymes (amylase and digestive enzymes), transcription factors, translation factors, hormones (e.g. insulin) and Intracellular signalling

Question 2

GDNF used to cure Parkinson’s disease.

Answer 2

used to produce dopaminergic neuron from embryonic

& inducible stem cells for cell therapy (experimental)

Question 3

What is the isoelectric point?

Answer 3

It is the pH at which the amino acid has no net charge. It does not migrate in an electric field, and it exists predominantly as zwitterions.

It is the midpoint concentration between the 2 pKa values of the amino acid.

Question 4

What gives rise to the different protein structures?

Answer 4

alternative splicing & post-translational modifications.

Question 5

Which amino acid stereoisomer exists predominantly in cells?

Answer 5

L-amino acid

Question 6

What is condensation?

Answer 6

A process whereby two molecules/groups (e.g. COOH and NH2 groups of two amino acids) forms a covalent bond, resulting in the elimination of one water molecule.

Question 7

Why are non-polar amino acids still able to dissolve in water?

Answer 7

It may have R groups that are able to be ionised

Question 8

How are amino acids classified?

Answer 8

Non-polar (aliphatic and aromatic) and polar (acidic, basic and uncharged)

Question 9

Examples of non-polar amino acids

Answer 9

Leucine, Proline, Alanine, Valine, Methionine, Phenylalanine, Isoleucine, Tryptophan

Only Tryptophan and Phenylalanine are aromatic

Question 10

Examples of acidic amino acids

Answer 10

Aspartic acid, Glutamic acid

Question 11

Examples of basic amino acids.

Answer 11

Histidine, Lysine and Arginine

Question 12

Examples of polar uncharged amino acids

Answer 12

Glycine, Serine, Asparagine, Glutamine, Tyrosine, Cysteine, Threonine

Question 13

Which amino acid can act as a neurotransmitter?

Answer 13

Glycine

Question 14

What is Hydroxyproline and what is the function?

Answer 14

• Hydroxylated form of proline
• It provides stability to collagen fibres
• Insufficient hydroxylation will lead to scurvy - lack of vitamin c resulting in bleeding gums - due to weak collagen

Question 15

How do cells convey signals from external to internal?

Answer 15

by exploiting reversible changes in some amino acids (e.g. phosphorylation)

-cell signalling involves the relay of information from protein to protein

Question 16

What is one unit of amino acid called?

Answer 16

Residue

Question 17

Different types/groups of proteins

Answer 17

Fibrous/Globular/Membrane

Question 18

What are integral proteins?

Answer 18

Receptors and transporters

Question 19

What are lipid anchored proteins?

Answer 19

Proteins linked via lipids to the membrane

Question 20

What are peripheral proteins?

Answer 20

Proteins associated with the membrane

Question 21

Properties of globular protein

Answer 21

• Soluble in aqueous medium
• Diffuse readily
• tightly folded into a compact globular shape with hydrophobic parts on the inside and hydrophilic parts on the outside
• e.g. enzymes, transport proteins and antibodies

Question 22

Properties of fibrous protein

Answer 22

• Insoluble in aqueous medium. Hydrophobic parts on the exterior
• Structural or protective role
• e.g. Collagen and a-keratin

Question 23

Non-covalent forces that stabilise protein structure

Answer 23

• Hydrogen bonds
• Hydrophobic interactions (clathrate)
• Electrostatic interactions (ionic)
• Van der Waal’s forces

Question 24

Secondary structure of proteins

Answer 24

alpha-helix and beta-pleated sheets

Commonly found in globular proteins

Beta-pleated sheets

• intermolecular H bonds
• Favour amino acids with compact R groups

Question 25

Why is proline only found at the start/end of helices but not usually found in the middle?

Answer 25

It disrupts a-helix formation because of its backward twist which destabilise the kink

Question 26

What is a domain?

Answer 26

Discreet and independently folded globular units which consists about 100-200 amino acid residues. Each module has a specific function

Question 27

Quaternary structure of a protein

Answer 27

Stabilised by non-covalent interactions between subunits

Question 28

Advantages of quaternary structure

Answer 28

Lower error of synthesised when smaller subunits are held together by non-covalent interactions rather than synthesising a long/large protein chain

Question 29

What is denaturation of protein

Answer 29

Loss of biological activity due to altered conformations/structure as a result of heat/pH/organic solvents/urea. It destroys the secondary,tertiary and quaternary structures of the protein but the primary structure remains intact.

Question 30

Intracellular control of protein folding

Answer 30

Break down the protein or exported to the lysosome to help it to fold
When cell is stressful – nucleus will receive a signal to produce more chaperones to help the protein to fold correctly
Cell dies if protein is unable to fold correctly

Question 31

Diseases associated with protein misfolding

Answer 31

Alzheimer’s disease, Parkinson’s disease

Question 32

How does urea/Organic solvents/pH/Temp alter the shape of protein?

Answer 32

Urea: planar uncharged and highly soluble in water. Bonds to polarised areas of charge, which destroys the secondary and tertiary structure. Urea can bind to the surface of the protein and disrupts its structure.

pH: change the conformation of the protein, disrupts the hydrogen bond and other IMF. Disrupts the secondary and tertiary and quaternary structure of the protein.

High temperature disrupts the interactions between h bond and other IMF. Disrupts secondary and tertiary structure of proteins.

Detergents: Have hydrophilic and hydrophobic ends, same as detergent. The detergents also have hydrophilic and hydrophobic ends. The detergent is attracted to these ends, forcing the protein apart.