1.3 Membrane structure

Question 1

Extrinsic protein

Answer 1

Extrinsic protein: embedded in membrane but does not penetrate

Question 2

Membrane in held by

Answer 2

Phospholipids in the membrane are held by hydrophobic interactions (weak)

Question 3

Role of cholesterol

Answer 3

CHOLESTEROL: reduces fluidity in high temp, does not let crystalize in cold temp, reduces permeability to hydrophilic ions, helps secure peripheral proteins inside the membrane

Question 4

Two models of plasma membrane

Answer 4

DAVSON-DANIELLI: sandwich model, phospholipds form a bilayer which is surrounded by two layers of proteins

SINGER-NICHOLSON: fluid mosaic model, phospholipids from a bilayer, proteins are free to move and of different size, function

Question 5

Evidence that lead to falsification of Davson-Danielli

Answer 5

1. Freeze dried cells and fractured them - proteins appeared globular, so were interpreted as transmembrane
2. Biochemical improvements allowed extract proteins from membranes and were found to be varied in size and globular, so would not form continuous layers, also found that some proteins were hydrophobic - could not be on the surface of membrane
3. Fluorescent antibody tagging proved fluidity of membrane, proteins are free to move - not fixed

Question 6

First membrane model

Answer 6

By Gorter and Grendel (1920s): extracted phospholipids from red blood cells - found out that they form a bilayer but did not explain where proteins were located

Question 7

Protein content in membranes meaning

Answer 7

The higher the protein conetnt is in cell membrane, the more active the membrane is - highest content in mitochondria and chloroplasts (75%)

Question 8

Contrast between integral and peripheral proteins

Answer 8

INTEGRAL: hydrophobic, embedded between phospholipd tails, many transmembrane

PERIPHERAL: hydrophilic, attached to the surface of membrane (or integral proteins), some have hydrocarbon chains that are inserted into the membrane (anchorage)

Question 9

Membrane protein functions

Answer 9

J - junctions

E - enzymes

T - trasnport

R - receptors

A - attachments

T - talk - cell singalling