L8 Protein Structure & Function

Question 1

Examples of secreted structural proteins

Answer 1

Keratin - nails and hair

Collagen - cartilage

Question 2

Examples of molecular motors

Answer 2

Muscle contraction - actin & myosin

DNA helicase - unwinds DNA

Question 3

What do proteins regulate?

Answer 3

growth, metabolism, maturation, digestion, inflammation, movement and reproduction

Question 4

What holds AA together?

Answer 4

Amino acids held together by peptide bonds, which are formed by a condensation reaction to form a covalent bond. Amino acids are joined in a genetically determined sequence.

Question 5

Secondary structure - what is it? [5]

Answer 5

Polypeptide backbone folded into a spiral (5-20aa in length)

Shape forms due to hydrogen bonds forming between carbonyl groups and an amine group 4aa along the chain

3.6 amino acids per turn

Side chains face outwards

Alpha helices are abundant in membrane proteins like receptors.

Question 6

Backbone in secondary structure is protected by…?

Answer 6

The hydrophilic backbone is shielded from the lipid environment of the membrane.

Question 7

Beta-sheet - what are they?

Answer 7

Flat structure 
Laterally packed 
5-8 AA long 
Hydrogen bind between carbonyl and amine groups 
side chains above and below

Question 8

Turns

Answer 8

3-4 AA long
Glycine and proline are common
Sharp bend - redirect polypeptide backbone

Question 9

Quaternary structure - what is it?

Answer 9

some proteins associate with each other by hydrophobic interaction to generate higher order structures - subunits

Question 10

How is the tertiary structure stabilised?

Answer 10

With covalent cross linkages. The most common is a disulfide bond between cysteines that are next to each other in the folded structure. They give strength but do not alter the shape

Question 11

Post translational modifications

Answer 11

A covalent processing event resulting from a proteolytic cleavage or the addition of a modifying group.

Over 200 PTMs have been characterized.

PTMs modulate the function of most eukaryote proteins by altering their activity state, localization, turnover, and interactions with other proteins.

Question 12

Examples of PTM

Answer 12

Phosphorylation: A biochemical process that involves the addition of phosphate to specific amino acids

Glycosylation: Addition of carbohydrates to specific sites on the protein

Question 13

What do chaperones do? [3]

Answer 13

do not change the 3D structure;

help to speed up the folding process; prevent protein aggregation;

prevent non productive intermediates

Question 14

Negatively charged AA side chains

Answer 14

Glutamic acid
Aspartic acid

Carboxylic group

Question 15

Positively charged AA side chains

Answer 15

Lysine
Arginine
histidine

N group

Question 16

What is a signal sequence?

Answer 16

15-60 aa in length

After the protein leaves the ribosome, part of the aa sequence will contain what is called the signal sequence or sorting sequence

Question 17

CF

Answer 17

Over 800 mutations detected
70% of patients share mutation at aa508

Phenylalanine

Pulmonary obstruction due to thickened mucus in the small airways causing recurrent bacterial infections

Question 18

Creutzfeldt–Jakob disease (CJD )

Answer 18

The disease is transmitted by misfolded prions. They promote refolding of other prions into a disease conformation upon contact

The misfolded protein forms tightly packed β-sheets that are very stable

Misfolded prions build up in the brain forming amyloid plaques that cause a progressive slow death of the nerves in the brain