Proteins, Intracellular Transport and Membrane Transport

Question 1

What happens to the protein following translation?

Answer 1

Long polypeptide chain is formed
Must undergo folding and modification to produce the final functioning protein

Question 2

Protein Structures

Answer 2

Primary:
- linear sequence of amino acids
Secondary:
- alpha helix or beta pleated sheets
- stabilised with hydrogen bonds
Tertiary:
- folding of secondary structures to form a 3D structure
Quaternary:
- formation of protein complex comprising of 2 or more polypeptide chains

Question 3

Intracellular Transport

Answer 3

Routes can be uni or bi-directional
Proteins entering the ER enter the secretory pathway
Protein destination dependent on the location of the ribosome during translation
During translation the ribosome can either be free in the cytosol or bound the RER

Question 4

If ribosomes are free in the cytosol, where would the synthesised proteins end up?

Answer 4

Cytosol
Mitochondria
Nucleus
Peroxisome

Question 5

How do ribosomes get to the ER?

Answer 5

Translation begins in the cytosol
SRP binds to the ribosome via the signal sequence
Translation in the cytosol is paused
SRP bound ribosome binds to the SRP receptor
SRP recycled and translation proceeds into ER lumen

Question 6

What happens after arrival at the ER?

Answer 6

Vesicles transport proteins to the golgi
Proteins are sorted for their final destination
Vesicles form to pack proteins off to other organelles
All proteins contain a bit of Information to signal to Golgi where they need to go

Question 7

Exocytosis

Answer 7

Movement of proteins out of a cell

Question 8

Endocytosis

Answer 8

Movement of proteins into a cell

Question 9

How do proteins on the surface of organelles help with vesicular transport?

Answer 9

1) Clathrin
- protein on plasma membrane which helps form vesicles to allow transport into the cell
- also helps vesicles move towards the Golgi
2) COPI
- protein which helps the formation of vesicles at Golgi to allow transport away from Golgi
3) COPII
- protein helps things move from the ER to the Golgi

Question 10

Cystic Fibrosis

Answer 10

CFTR protein misfolds in the ER
CFTR is not released by chaperones
CFTR are rapidly delivered to the cytosol and degraded by the proteasome
CFTR doesn’t reach cell membrane

Question 11

How do things get through the membrane?

Answer 11

Directly through lipid bilayer
Via integral membrane proteins
- Facilitated diffusion
- Secondary active transport
- Primary active transport

Question 12

Facilitated Diffusion

Answer 12

Through pores, channels and carriers

Question 13

Secondary Active Transport

Answer 13

Uses the kinetic energy provided by electrochemical gradients
There are two types:
1) Co-transporters
- allowing transport of 2 or more molecules in the same direction
2) Counter-transporters
- allowing transport of 2 or more molecules in the opposite direction

Question 14

Primary Active Transport

Answer 14

Uses energy from hydrolysis of ATP to transport a solute from a low concentration to a high concentration

Question 15

Intracellular Fluid

Answer 15

Fluid inside cells - 25L
High concentrations of K+ and Mg2+

Question 16

Extracellular Fluid

Answer 16

Fluid outside cells - 15L
High concentrations of Na+, Cl- and HCO3-