Unit 1, AOS1, Chapter 3A: Introduction to the Plasma Membrane

Define the Plasma Membrane

The selectively permeable phospholipid bilayer and embedded proteins that separate the intracellular environment from the extracellular environment

Identify the primary function of the Plasma Membrane

To control the the substances that enter or exit the cell

Define a Phospholipid

A lipid molecule with a head containing a phosphate group and two fatty acid tails

Describe the charge/s of a phospholipid

Phospholipids are amphipathic, meaning they are molecules with both polar/hydrophilic (the phosphate head) parts and non-polar/hydrophobic (the fatty acid tails) parts

Describe how the amphipathic nature of phospholipids results in a bilayer

The hydrophilic phosphate heads are attracted to, and orient towards, the aqueous intra- and extracellular environments while the hydrophobic fatty acid tails orient themselves away from water to form the interior of the bilayer

Identify the 2 main concepts of the Fluid Mosaic Model

1. Molecules that make up the membrane are not held static in one place (fluid)

2. many different types of molecules are embedded in the plasma membrane (mosaic)

List the 3 ways that phospholipids can move

1. Rotationally

2. Laterally (side to side)

3. Transversely ('flip flop')

Describe usaturated fatty acid tails

Saturated fatty acid tails have a kink from double C=C bonds and allow the membrane to remain fluid, even at low temperatures, by maintaining space between phospholipids

Describe saturated fatty acid tails

Unsaturated fatty acid tails form straight chains and can pack together tightly

List the 3 types of proteins found in a plasma membrane

Integral, transmembrane and peripheral

Define Peripheral Proteins

Proteins that are temporarily attached to the plasma membrane

Define Integral Proteins

Proteins that are permanently embedded in the membrane

Define Transmembrane Proteins

Integral proteins that span the entire phospholipid bilayer

List 6 roles of proteins in the plasma membrane

(hint: TRACIE)

1. Transport (of substances across the bilayer)

2. Reception (recieve signals)

3. Anchorage (attach to another cell/substance)

4. Cell Identity (identify whether the cell belongs)

5. Intercellular Joining (joining cells)

6. Enzymatic Activity (catalyse reactions)

Identify the 2 types of carbohydrates that extend from the membrane

1. Glycoproteins

2. Glycolipids

Identify 4 roles of carbohydrates on the plasma membrane

1. Cell identity

2. Signalling

3. Cell-cell communication

4. Adhesion

Define cholesterol within a plasma mebrane

A lipid steroid that embeds itself between the fatty acid tails of

the phospholipid bilayer in animal cells

Describe the role of cholesterol in the plasma membrane

Cholesterol regulates the fluidity of the membrane by binding phospholipids together in high temperatures and keeping them separate at lower temperatures