LEC7-Protein targeting

Question 1

Transport through nuclear pores

mechanism 1

Answer 1

• proteins move between the cytosol and nucleus through nuclear pores
• proteins transported in their folded conformation
• nuclear pores=selective gates
• proteins destined for the nucleus have a ‘sorting signal’, the nuclear localisation signal
• this NLS binds to the cytosolic nuclear transport receptor

Question 2

What does the NLS of the folded protein bind to?

Answer 2

-the cytosolic nuclear transport receptor

Question 3

Protein transport: Translocation into mitochondria, chloroplasts and peroxisomes

Answer 3

proteins move from the cytosol into these organelles via protein translocators in the membrane
-TOM(Translocase in Outer Membrane)

Question 4

Proteins inserted into mitochondria

Answer 4

• Binding to import receptors (via signal sequence)
• Insertion into membrane by TOM complex
• Translocation into matrix
• cleavage by signal peptidase

Question 5

Secretory proteins destined for ER and onwards:

Mechanism 3

Answer 5

• carried via transport vesicles from compartments to others

- all secretory proteins enter the ER

Question 6

Two types of proteins transferred into the ER

Answer 6

1. Water-soluble proteins which pass into the lumen of the ER and are secreted
2. Prospective trans-membrane proteins

Question 7

Protein targetting:

Answer 7

• starts in the cytoplasm
• The stop sequence in a single pass membrane protein is hydrophobic and stays in the lipid bilayer
• Mechanisms of protein targeting are specific