Chapter 3A - intro to the plasma membrane

Question 1

What type of cells have a plasma membrane and what is it?

Answer 1

ALL cells have a plasma membrane. It is a thin boundary made up of lipids (fats) that separates the intracellular and extracellular environments.
It is selectively permeable - meaning that only particular molecules can enter & exit the cell.

Question 2

What is the plasma membrane made up of?

Answer 2

A phospholipid bilayer (phospholipids arranged in 2 layers) embedded with proteins, carbohydrates & cholesterol.

Question 3

Phospholipids…

Answer 3

Have a phosphate head - which is made up of glycerol and a phosphate group. It is negatively charged, making it hydrophilic and polar.
They also have 2 fatty acid chains - which are made of long chains of carbon and hydrogen. They are uncharged, hydrophobic and non-polar.

Question 4

Define:
- Hydrophilic
- Hydrophobic
- Polar
- Nonpolar

Answer 4

Hydrophilic - having a tendency to be attracted to and dissolve into water
Hydrophobic - having a tendency to repel from and be insoluble in water
Polar - describes a molecule with both a positive end and a negative end. These tend to be hydrophilic
Nonpolar - describes a molecule without a clearly positive or negative end. These tend to be hydrophobic.

Question 5

What type of molecule are phospholipids?

Answer 5

They are an amphipathic molecule. This makes the plasma membrane stable: the fatty acid tails are repelled from the water whilst the phosphate heads are attracted to water, so a stable bilayer naturally forms

Question 6

Carbohydrates…

Answer 6

are usually in chains that extend outside the cell, rooted in the membrane to lipids (glycolipids) or proteins (glycoproteins).

FUNCTION(S):
Aids with cell-communication, signalling, recognition of self or non-self molecules, and adhesion.

Question 7

Cholesterol…

Answer 7

is a lipid steroid that embeds itself between the fatty acid tails of the phospholipid bilayer in animal cells.

FUNCTION(S):
Regulates the fluidity of the membrane. At higher temperatures, the cholesterol keeps phospholipids bound together. At lower temperatures, cholesterol disrupts the fatty acids, stopping phospholipids from becoming a solid boundary.

Question 8

There are three types of proteins…

Answer 8

Integral proteins - are a permanent part of the membrane.

Transmembrane proteins - span the entire bilayer

Peripheral proteins - are temporarily attached to the plasma membrane.

FUNCTION(S):
Transport - channels or pumps that control what enters and exits the cell, making the plasma membrane selectively permeable.
Catalysis - speeding up chemical reactions with the help of a protein group called enzymes.
Communication - receive signals or recognise cells and molecules. Often attached to the cytoskeleton to transmit signals into the cell.
Adhesion - stick to other cells, the extracellular matrix, or the cytoskeleton.

Question 9

The fluid mosaic model explains that:

Answer 9

• molecules that make up the membrane are not held static in one place.
• many different types of molecules are embedded in the plasma membrane.

The plasma membrane is ‘fluid’ because phospholipids continually move laterally (side to side) in the membrane.