Lecture 9 Study Guide

Question 1

Define selectively permeable.

Answer 1

The plasma membrane of a cell allows some substances in (such as non polar molecules) while others are unable to enter the membrane without a channel

Question 2

Identify three main biomolecules found in cellular membrane

Answer 2

1. lipids
2. proteins
3. carbohydrates

Question 3

Compare and contrast the permeability of the lipid bilayer to non-polar molecules, ions, and polar molecules. List three molecules that freely diffuse across the bilayer.

Answer 3

The lipid bilayer allows non polar molecules to freely diffuse across the membrane. However, ions and polar molecules require a channel to pass through.

1. sugars
2. amino acids
3. other nutrients

Question 4

Describe how the hydrophobic interactions in the membrane contribute to the fluidity of membrane.

Answer 4

The phospholipids move sideway rapidly within the membrane. The phospholipids settle into a closely packed arrangement and the membrane solidifies as temperature increases but remains fluid. Unsaturated hydrocarbon tails contribute to fluidity.

Question 5

Outline two reasons for the importance of proper membrane fluidity.

Answer 5

1. affects permeability

2. allows proteins to move where their function is needed

Question 6

Describe the effect cooling has on the fluidity of the membrane.

Answer 6

as temperature decreases, fluidity decreases

Question 7

Outline the correlation between the temperature at which a membrane solidifies and the degree of saturation of the hydrocarbon chains.

Answer 7

as temperatures decrease, the degree of saturation increases and the membrane solidifies

Question 8

Why is cholesterol considered a ‘fluidity buffer’? Describe the conditions when it increases or decreases membrane fluidity.

Answer 8

it allows the membrane to stay fluid in the saturated areas

Question 9

Describe six functions of the plasma membrane proteins.

Answer 9

1. transport
2. enzymatic stability
3. signal transduction
4. cell-cell recognition
5. intercellular joining
6. attachment to the cytoskeleton and extracellular matrix

Question 10

Compare and contrast these broad types of membrane proteins: 
Integral proteins:
Transmembrane:
Peripheral proteins:
Glycoproteins:
Transport proteins:
Aquaporins:
Carrier proteins:

Answer 10

Integral proteins: partially or wholly embedded in the bilayer
Transmembrane: extends all the way through the membrane
peripheral proteins: not embedded in the bilayer
glycoproteins: short oligosaccharides covalently bonded to proteins
transport proteins: specific for the substance it channels through the bilayer
aquaporins: channel protein for water
carrier proteins: holds on to substance and transports it through membrane