Protein Targeting and Sorting

Question 1

Where does translation start for all proteins?

Answer 1

In the cytoplasm, although mitochondria and chloroplasts make some of their own

Question 2

What 3 things are required for protein targeting and sorting?

Answer 2

1. A signal sequence
2. Transport proteins
3. Energy source

Question 3

What are signal sequences?

Answer 3

Stretches of amino acids that tell where a protein is supposed to go

Question 4

Is the signal sequence the same for every protein going to the same location?

Answer 4

No, although they will have similar chemical characteristics

Question 5

Where can the signal sequence be on the polypeptide chain?

Answer 5

Anywhere

Question 6

How do proteins get across membranes?

Answer 6

They have to get unfolded to get in through the channel and are refolded on the other side

Question 7

What are the two major pathways of protein sorting?

Answer 7

1. Cytoplasm or intracellular organelle

2. Secretory pathway

Question 8

What locations can be the final destination for proteins in the cytoplasm/intracellular organelle pathway?

Answer 8

Cytoplasm, nucleus, mitochondria, chloroplast, peroxisome

Question 9

What locations can be the final destination for proteins in the secretory pathway?

Answer 9

ER, Golgi, lysosomes, plasma membrane, leaving the cell

Question 10

What is the difference between necessity and sufficiency in terms of targeting sequences?

Answer 10

If a sequence is necessary, the protein will not be able to get to the location without it. If a sequence is sufficient, that sequence is enough to get any protein to the location

Question 11

How do we test if a sequence is necessary for targeting?

Answer 11

Remove it from the protein. If the protein no longer goes to the location, the sequence is necessary

Question 12

How do we test if a sequence is sufficient for targeting?

Answer 12

Transfer the sequence to another protein. If that protein goes to the nucleus, the sequence is sufficient