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Where a protein goes

Where a protein goes

1.[2p]

Put these compartments in the order Palade's radioactive leucine passed through them.

  1. Zymogen granules

  2. Golgi

  3. Rough endoplasmic reticulum

  4. Condensing vacuoles

Show the answer

a, b, c, d

2.[3p]

Translating a secretory protein's mRNA without membranes gave a product slightly longer than the mature protein. What did that show?

Correct
The answer is: There is an extra amino-terminal sequence that is removed during transport into the endoplasmic reticulum
The answer is: There is an extra amino-terminal sequence that is removed during transport into the endoplasmic reticulum
The answer is: There is an extra amino-terminal sequence that is removed during transport into the endoplasmic reticulum

3.[2p]

Adding microsomal membranes after translation is complete allows the protein to enter them just as well as adding them beforehand.

The answer is: False
Correct

4.[3p]

Match each targeting signal to its destination.

  • A short run of basic residues, not cleaved

  • A positively charged amphipathic helix, cleaved on arrival

  • Serine, lysine and leucine at the far end

  • A hydrophobic sequence at the amino end, clipped off

  • No signal at all

  • the secretory pathway

  • the mitochondrial matrix

  • the cytosol

  • the nucleus

  • a peroxisome

Show the answer

A short run of basic residues, not cleaved: the nucleus A positively charged amphipathic helix, cleaved on arrival: the mitochondrial matrix Serine, lysine and leucine at the far end: a peroxisome A hydrophobic sequence at the amino end, clipped off: the secretory pathway No signal at all: the cytosol

5.[3p]

Why is Anfinsen's conclusion, that sequence determines structure, incomplete as a description of folding in a cell?

Correct
The answer is: Folding cannot be an exhaustive search, and at 200 g per litre a partly folded chain is likely to aggregate before it finishes
The answer is: Folding cannot be an exhaustive search, and at 200 g per litre a partly folded chain is likely to aggregate before it finishes
The answer is: Folding cannot be an exhaustive search, and at 200 g per litre a partly folded chain is likely to aggregate before it finishes

6.[3p]

What is the commonest cystic fibrosis mutation actually doing?

Correct
The answer is: Producing a channel that would largely work, but which fails quality control and is destroyed before reaching the surface
The answer is: Producing a channel that would largely work, but which fails quality control and is destroyed before reaching the surface
The answer is: Producing a channel that would largely work, but which fails quality control and is destroyed before reaching the surface

7.[3p]

Which observations support the endosymbiotic origin of mitochondria?

Select all that apply

Correct
Correct
Correct
Correct

8.[2p]

How many proteins does the human mitochondrial genome encode?

CorrectNot quite: 13

9.[3p]

Why does chloramphenicol, an inhibitor of bacterial ribosomes, suppress human bone marrow?

Correct
The answer is: Mitochondrial ribosomes are bacterial in type, so respiratory subunits made inside mitochondria are lost, and marrow is among the most demanding tissues
The answer is: Mitochondrial ribosomes are bacterial in type, so respiratory subunits made inside mitochondria are lost, and marrow is among the most demanding tissues
The answer is: Mitochondrial ribosomes are bacterial in type, so respiratory subunits made inside mitochondria are lost, and marrow is among the most demanding tissues