Proteins and their Functions

Question 1

Why is the genetic code said to be redundant / degenerate?

Answer 1

One amino acid can be coded for by multiple codons.

Question 2

Describe the primary structure of a protein.

Answer 2

• Amino acid sequence
• Covalent peptide bonds
• Projecting side chains

Question 3

Describe the secondary structure of a protein.

Answer 3

• Alpha helices and beta plated sheets
• Local structural conformation
• non-covalent bonds:

•Mainly hydrogen bonds

also:

• Hydrophobic interactions
• Van der Waals interactions
• Ionic interactions

Question 4

Give an example of the role of non-covalent interactions in secondary protein structure.

Answer 4

Hydrogen bonds stabilise the alpha helix.

Question 5

Describe the tertiary structure of a protein. Name 5 bonds that contribute to it.

Answer 5

• Three-dimensional conformation
• Proteins fold into lowest energy structure.
• Formed by stabilising forces due to side-chain interactions:
• Hydrogen bonds
• Hydrophobic interactions
• Ionic interactions
• Disulfide bridges.
• Salt bridges

Question 6

Describe the quarternary structure of a protein.

Answer 6

A complex of more than one polypeptide chain.

Question 7

What are the two main classes of protein tertiary structure?

Answer 7

Fibrous and globular.

Question 8

What are the 4 main functions of proteins?

Answer 8

• Binding (e.g. ligands and receptors)
• Catalysis (e.g. enzymes)
• Switching (e.g. signalling pathways)
• Structural (e.g. the cytoskeleton)

Question 9

Which four processes are involved in the regulation of protein function?

Answer 9

• Synthesis
• Localisation (where)
• Modification (active/inactive?)
• Degradation

Question 10

What does a centrosome consist of? What is its function?

Answer 10

• Two centrioles.

- Organises microtubules for cell structure and pulling apart chromatids during cell division.

Question 11

What is a sorting signal?

Answer 11

Amino acid sequences in proteins that direct the proteins to the correct site in the cell.

Question 12

Where are most proteins modified?

Answer 12

• In the endoplasmic reticulum.

- Further modifications in the golgi apparatus.

Question 13

What modifications are usually made to proteins?

Answer 13

• Glycosylation
• Disulfide bonds
• Phosphorylation

Question 14

What is phosphorylation?

Answer 14

The addition of a covalently attached phosphate group to amino acid side chains.

Question 15

Which protein catalyses phosphorylation reactions?

Answer 15

Kinases

Question 16

Which protein catalyses dephosphorylation reactions?

Answer 16

Phosphatases

Question 17

Which two reactions of the tyrosine chains of a tyrosine-kinase receptor follow membrane receptor activation?

Answer 17

Dimerisation and phosphorylation.

Question 18

Which adaptor protein binds to the phosphorylated tyrosine-kinase receptor in growth factor signalling?

Answer 18

Ras (G-Protein)

Question 19

What is the unfolded protein response?

Answer 19

• A stress response related to ER stress that is activated in response to accumulation of unfolded proteins in the ER.
• Halts protein translation
• Degrades misfolded proteins
• Increases production of proteins that assist in molecular folding.
• Can lead to cell death.

Question 20

What does the UPR help prevent?

Answer 20

Protein conformational diseases linked to aggregation.

Question 21

What is ERAD?

Answer 21

A pathway which targets misfolded proteins of the ER for degradation.

Question 22

What is cystic fibrosis caused by?

Answer 22

• A mutated CFTR membrane protein.
• Mutated protein incorrectly folded, degraded in ER
• Receptor does not reach the membrane.