Genetics 7

Question 0

Translocation is directed by interaction of _____ with the signal sequence on the ____ end of the protein

Answer 0

signal related peptide (SRP) on N terminal end

Question 1

Signal Hypothesis

Answer 1

Certain sequences direct the ribosome to a translocator in the membrane of the ER, which forms a pore for translocation

• protein is processed by signal peptidases to cleave off signal sequence
• primary sequence dictates if protein is soluble or membrane

Question 2

SRP targets ribosome to

Answer 2

Translocator

Question 3

SRP binds to ______ to stop transation

Answer 3

Large ribosomal subunit

Question 4

Translocator

Answer 4

• functions like a pore with a plug
• can open so protein can access membrane
• allows hydrophilic sequences to make their way to ER lumen, hydrophobic sequences can sequester themselves in the membrane.

Question 5

Hydropathy plots

Answer 5

• free energy driven
• used to determine the free energy of a reaction where a section of protein leaves the membrane to enter an aqueous environment.
• hydrophobic= high + free energy
• hydrophilic= - free energy

Question 6

Key characteristics of a signal peptide/leader sequence

Answer 6

1) 12-36 AA in length
2) Significant amount of basic AA
3) Includes initiator methionine and at least one positively charged AA
4) Cleavage site preceded by residues with small R groups at 1 and 3 position.

Question 7

Constitutive secretory pathway

Answer 7

• Unregulated

- How many secretory proteins access pm

Question 8

Regulated secretory pathway

Answer 8

• tightly coupled to signaling cascades/secretory vesicles
• Vesicles can be modified for association with membrane’s architecture to allow for fusion and exocytosis.
• Ex: GLUT2

Question 9

Where does cleavage take place in the pre-pro-protein?

Answer 9

Each side of the peptide has pairs of basic AA. This is where cleavage happens.

Question 10

What signals amidation in amidated peptides?

Answer 10

Glycine residue.

Question 11

When is a protein considered a pro-protein?

Answer 11

After the signal peptide is cleaved and the protein enters the ER.

Question 12

Proprotein convertase (PC)

Answer 12

Endopeptidase. Cuts on C terminal of basic AA

Question 13

Caboxypeptidase H

Answer 13

Chews off C terminal AA until it reaches glycine

Question 14

PAM

Answer 14

cuts glycine in half, leaves amide from peptide bond.

• uses O2 and vitamin C
• releases glyoxylate molecule, dehydroascorbate, water, and amidated peptide
• has a transmembrane domain, is found in vesicle membrane.

Question 15

PERK

Answer 15

Pancreatic endoplasmic reticulum-resident kinase.

• dimerizes and phosphorylates eIF2, inhibiting protein synthesis
• allows ER to catch up with protein folding
• somehow changes ability to eIF2 to scan for initiator codon during translation–> selects for transcripts that encode proteins that help with folding in ER.