L8

Question 1

What are all proteins encoded by?

Answer 1

Genes

Question 2

Name 6 functions proteins perform (receptors, hormones etc)

Answer 2

Structural proteins = Actin, Micro-tubules, intermediate filaments

Secereted proteins = Hormones

Membrane bound proteins = Receptors

Molecular motors = DNa helicase

Secreted structural proteins = cartialage

Intracellular proteins = cytosolic signalling molecules

Question 3

How many genes encode proteins?

Answer 3

20,000

Question 4

What are the difference between essential and non-essential amino acids?

Answer 4

Non-essential are made by the body from the essential AA or by breakdown of proteins.

Essential AA come from food in our diet..

Question 5

What bonds are AA held together by and how are they formed?

Answer 5

AA held by peptide bonds, formed by condensation reaction to form a covalent bond.

Question 6

How many AA do proteins contain?

Answer 6

Usually from 50-2000

Can be 30-10,000

Question 7

Name 4 secondary structures of protein

Answer 7

a-helices
b-pleated sheets
Loops and turns
Random coils

Question 8

What is the structure of an a-helix

Answer 8

Polypeptide backbone foldied into a spiral formed as H bonds form between carbonyl group and amine group 4aa along the chain
3.6 aa per turn
side chains face outwards

Question 9

Where are a-helices abundant and why

Answer 9

Abundant in membrane proteins
Hydrophobic side chains interact w hydrophobic H-C tails of phospholipids
Hydrophilic backbone shielded from lipid environment and form H bonds

Question 10

What is the b-sheet structure?

Answer 10

Flat structure(sheet)
Laterally packed strands
Each strand w 5-8AA
Shape due to H bonds between carbonyl group and amine group of neighbouring chain
Side chains extend above and below b-sheet

Question 11

Describe the secondary structure “loops and turns”

Answer 11

3-5 AA long, form sharp bend redirecting polypeptide backbone
Hydrophilic residues found on surface of proteins

Question 12

Describe the secondary structure “random coils”

Answer 12

Polypeptide chains w random configuration

Question 13

How are tertiary structures formed? Name 3 tertiary structures

Answer 13

Secondary structure spontaneously fold into 3D conformations
Myoglobin
Tumour necrosis factor alpha
Barrels - 1st/last strand form H bonds forming a barrel

Question 14

What is a coiled coil?

2 examples

Answer 14

2/3 a-helices wound around each other. Hydrophobic AA line up where helices meet.
Keratin
Collagen

Question 15

What is a post translational modification (PTM)?

Answer 15

Covalent processing event from proteolytic cleavage(breaking of peptide bonds between AA) or addition of a modifying group
They modulate function of most eukaryote proteins by altering activity state, localization, turnover and interactions w other proteins.

Question 16

When is protein denaturation permanent and when is it reversible?

Answer 16

Solvent denature proteins disrupting non-covalent interaction losing secondary and tertiary structures. But when solvent is removed the protein will renature

Heat can denature protein but it is irreversible denatured e.g. cooking an egg

Question 17

What is assisted folding?

What are the two classes that assist in folding?

Answer 17

Molecular chaperones bind to partially folded polypeptide chains and assist in folding

Two classes are: Heat shock proteins
Chaperonins

Question 18

What is protein charge dependent on>?

Answer 18

The AA side chains for example, carboxylic group :glutamic acid and aspartic acid will be negative
Whereas, N group: lysine, arginine, histidine will be positive

Question 19

What is a protein domain?

Answer 19

Part of the protein tertiary structure that can exist independently of the rest of the protein chain. The domains can independently fold and be stable.

Question 20

What is the signal sequence?

What happens if a protein does not have 1?

Answer 20

Protein leaves ribosome, part of AA sequence will contain the signal sequence to provide info of correct location of protein.

Proteins with none remain in the cytosol

Question 21

What causes cystic fibrosis?

Answer 21

DNA mutation that alters protein shape.

The deletion causes mutant CTFR protein to become stuck in ER and abnormal chloride conductance occurs.

Question 22

What causes Creutzfeldt-Jakob disease (CJD)?

Answer 22

Misfolding proteins.
Normal protein adopt misfolded prion
This binds to normal protein inducing conversion to abnormal conformation
Abnormal prions form tightly pakced b-sheets that are very stable
Misfolded prions build up in the brain forming amyloid plaques cause progressive slow death of nerves in the brain