Amino acids and proteins

Question 1

Describe the nature of amino acids

Answer 1

Amino acids consist of a central alpha carbon atom, bonded to a hydrogen atom, an amine group, a carboxyl group and a variable R group.

Question 2

What are the 9 essential amino acids to humans (those we cannot produce)?

Answer 2

Histidine, lysine, threonine, valine, leucine, isoleucine, methionine, phenylalanine and tryptophan.

Question 3

Name the 2 polar acidic side chained-amino acids

Answer 3

Aspartic acid and glutamic acid

Question 4

Name the 3 polar basic side chained-amino acids

Answer 4

Arginine, histidine and lysine

Question 5

Name the 7 polar neutral side chained-amino acids

Answer 5

Asparagine, glutamine, serine, threonine, tyrosine, cysteine and glycine

Question 6

Name the 8 non-polar side chained-amino acids

Answer 6

Alanine, valine, leucine, isoleucine, methionine, proline, phenylalanine and tryptophan

Question 7

What is the primary structure of a protein?

Answer 7

The sequence of amino acids in the polypeptide

Question 8

What is the secondary structure of a polypeptide?

Answer 8

The folding of the polypeptide due to hydrogen bonds between amino acids, to form alpha helices or beta pleated sheets

Question 9

What is the tertiary structure of a polypeptide?

Answer 9

The way in which the helices and sheets are folded up into more densely packed globular structures and held in these conformations by weak chemical bonds, such as H bonds and ionic bonds between side chains. The structures may be stabilised by covalent disulphide bonds between cysteine molecules

Question 10

What is quaternary structure of polypeptides?

Answer 10

In proteins made of multiple polypeptide chains, the quaternary structure is how the chains are arranged in relation to each other to form the mature protein

Question 11

Name 3 fibrous proteins

Answer 11

Collagen, myosin and keratin

Question 12

Name 2 properties of collagen protein

Answer 12

Collagen has a triple helix, not an alpha helix.

Collagen molecules may assemble into long fibres.

Question 13

Water soluble proteins are often ________ in shape

Answer 13

globular

Question 14

In water soluble proteins, hydrophilic residues are mostly found where?

Answer 14

The external surface

Question 15

What causes sickle-cell anaemia?

Answer 15

A mutation in a single amino acid in the beta chain of haemoglobin

Question 16

What is the amino acid substitution involved in sickle-cell anaemia?

Answer 16

Glutamic acid is replaced by valine at position 6 due to mutation.

Question 17

What is the cellular target in bacteria of the antibiotics streptomycin and tetracyclines?

Answer 17

Streptomycin and tetracyclines target the small subunit of ribosomes to prevent protein synthesis

Question 18

What is the cellular target in bacteria of the antibiotics chloramphenicol and erythromycin?

Answer 18

Chloramphenicol and erythromycin target the large subunit of ribosomes in bacteria

Question 19

Name 3 limitations of antibiotics acting on protein synthesis

Answer 19

They can’t act on viruses.
There can be antibiotic resistance, via alteration of target sites or destruction of the antibiotic.
They may inhibit protein synthesis in mammalian mitochondria.

Question 20

How do penicillins work?

Answer 20

Penicillins are antibiotics that inhibit cell wall synthesis by inhibiting the enzymes that make pentapeptide links

Question 21

How does aspirin work?

Answer 21

Aspirin is an anti-inflammatory drug which blocks prostaglandin

Question 22

How does methotrexate work?

Answer 22

Methotrexate is an anticancer drug and a folate analogue- it interferes with DNA precursor synthesis

Question 23

In what 3 ways is the rough ER involved in protein synthesis/ processing?

Answer 23

• Synthesis of proteins for subsequent packaging and secretion from the cell or for insertion into intracellular structures such as other membranes.
• Involved in the initial steps of glycosylation
• Site of disulphide bond formation

Question 24

In what way is the smooth ER involved in protein synthesis/ processing?

Answer 24

Modification of newly synthesised proteins via addition of carbohydrates/ phosphates/ lipid groups