2.1.5 - Plasma Membranes

Question 1

Plasma membrane

Answer 1

The cell surface membrane that separates the cell from its external environment

Question 2

Phospholipids

Answer 2

• Glycerol molecule
• Two hydrophobic fatty acid tails
• One hydrophilic phosphate head

Question 3

How does a bilayer form

Answer 3

• The phosphate head is charged, it attracts water, so it is hydrophilic
• The fatty acid tail is non-polar, it repels water, it is hydrophobic
• Phosphate heads form both the inner and outer surface of a membrane
• Fatty acid tails are sandwiched inside the membrane

Question 4

Fluid mosaic model

Answer 4

Model of the structure of a cell membrane in which phospholipids within the phospholipid bilayer are free to move and proteins of various shapes and sizes are embedded in various positions.

Question 5

Roles of the plasma membrane

Answer 5

1. Act as a barrier between the organelle and cytoplasm
2. Sites of chemical reactions
3. Control the substances that enter/exit the organelle
4. Cell communication

Question 6

Compartmentalisation

Answer 6

• Membranes form cells and separate areas within cells
• Membranes isolate each area from its environment
• Different organelles can have different conditions making reactions efficient

Question 7

Sites of chemical reactions

Answer 7

• Highly folded
• Increase SA
• More enzymes

Question 8

Cell communication

Answer 8

• Receptors on membranes detect messenger molecules
• Some intrinsic proteins are receptors
• They bind specifically with their hormone or neurotransmitter

Question 9

Intrinsic proteins

Answer 9

• Embedded through both layers of a membrane
• They have amino acids with hydrophobic R-groups on their external surface which interacts with the hydrophobic core
• Channel proteins and carrier proteins

Question 10

Channel proteins

Answer 10

• Hydrophilic channel allows the passive movement of polar molecules and ions

Question 11

Carrier proteins

Answer 11

• Can change shape to reveal hydrophilic interiors

- Can move substances by passive and active transport

Question 12

Extrinsic proteins

Answer 12

• Present in one side of the bilayer
• Have hydrophilic R-groups on outer surfaces
• Interact with polar heads of the phospholipids or with intrinsic proteins

Question 13

Glycoproteins

Answer 13

• Intrinsic protein
• Protein molecule with a carbohydrates chain.
• Cell adhesion : Bind cells together in tissues
• Cell signalling : Receptors for neurotransmitters, receptors for peptide hormones

Question 14

Glycolipids

Answer 14

• Lipids with carbohydrate chain attached

- Cell recognition : Cell markers or antigens and can be recognised by cells of immune system as self or non-self

Question 15

Cholesterol

Answer 15

• Lipid with hydrophobic and hydrophilic end
• Positioned between phospholipids in bilayer
• Hydrophilic end attracts the phosphate heads
• Hydrophobic end attracts the tails
• This pulls them together
• Adds stability to the membrane

Question 16

Membrane - bound receptors

Answer 16

• Receptor proteins have a specific shape
• Only messenger molecules with a complementary shape can bind to them
• Many drugs work by binding to receptors - They trigger a response of block the receptor