Creating Transmembrane Proteins

Question 1

Topology

Answer 1

Proteins can be oriented in several ways relative to the ER Membrane
- proteins have a slightly different way of entering the ER during synthesis

Question 2

Single-Pass Transmembrane Protein integrated into the ER Membrane within the Lumenal N-Terminus

Answer 2

1. N-Terminus signal sequence initiates transfer into the ER lumen and another hydrophobic sequence (within the same polypeptide) is a stop sequence
2. when the stop sequence enters the translocator, the channel discharged the protein laterally into the ER
3. Signal Peptidase cleaves the signal sequence
   RESULT: N-Terminus is in the ER Lumen, and C-Terminus is cytosolic. The transmembrane domain is embedded into the membrane

Question 3

Double Pass Transmembrane Protein- with an Internal Start-Transfer Sequence

Answer 3

1.The Internal Start-Transfer Signal Sequence initiates the transfer and it is never removed from the protein
2. Hydrophobic Signal sequences work in pairs (start and Stop sequences)
-Start translocator is stuck in the translocator then
the polypeptide chain will thread through the
translocator until it reaches the stop hydrophobic
patch
3. Two hydrophobic sequences are released into the bilayer and do not get cleaved

Question 4

Many Proteins are Glycosylated in the ER to become….

Answer 4

Glycoproteins
- some proteins will become glycoproteins as a sugar group is covalently bonded to an amino acid (Asparagine) of a polypeptide

Question 5

Glycosolation

Answer 5

in the ER, N-Linked glycosylation happens on the lumenal side. sugar is attached to the amino acid asparagine side chain.

Question 6

what does glycosylation do?

Answer 6

Helps the protein fold properly and increases its stability and will help facilitate cell-to-cell interactions

Question 7

what is the name of the sugar that is involved with Glycosylation?

Answer 7

Dolichol: it is able to associate with the ER membrane and contains 2 phosphate groups and 14 sugar blocks

Question 8

Where can glycoproteins be further modified?

Answer 8

The Golgi Apparatus

Question 9

Disulfide Bonds

Answer 9

Forms between 2 cysteine amino acids
- covalent bonds that are very strong and protect the tertiary structure of a protein
-for these bonds to form the amino must be in an oxidizing environment

Question 10

What do disulfide bonds help with>

Answer 10

proteins with a lot of disulfide bonds are more protected and and can survive in harsh environments