Biological Membranes

Question 1

Function of plasma membranes

Answer 1

• Barrier between cell and environment, controlling what enters and leaves the cell. Partially permeable so are selective about what enters/leaves
• Recognation by other cells e.g. immune cells
• Cell communication e.g. cell signalling
• Conatin enzymes involved in metabolic pathways

Question 2

Function of membrane within the cell

Answer 2

• Separate contents of organelles from the cytoplasm
• Can form vesicles for transport
• Can control what substances entre and leave organelles e.g. RNA leaving through nuclear pore
• Membranes that are sites of chemical reactions e.g. cisternae in mitochondrion
• Thylakoid membranes that have chlorophylll in chloroplasts

Question 3

Fluid mosaic model

Answer 3

• Describes the strucutre of all membranes
• Composed of lipids, proteins and carbohydrates
• Phospholipid molecules make bilayer

Question 4

Molecules present in bilayer

Answer 4

• Phospholipids that make up the bilayer
• Cholesteral molecules
• Glycoproteins
• Glycolipids

Question 5

Glycoproteins

Answer 5

-Proteins with polysaccaride chain attached to it

Question 6

Glycolipids

Answer 6

-Lipids with polysaccaride chain attached

Question 7

Structure of the phospholipid bilayer

Answer 7

• Molecules arrange themselves with hydrophilic heads facing outwards and hydrophobic tails facing inwards
• The centre of the bilayer is hydrophobic so membrane doesn’t allow water soluable substances e.g. ions to pass
• Fat soluable substances can dissolve through the bilayer

Question 8

Function of cholesteral in the bilayer

Answer 8

• Fit between the phospholipids and bind the hydrophobic tails to make them packed more closely together
• Makes the membrane less fluid and more rigid
• Regulate membrane fluidity

Question 9

Function of proteins in bilayer

Answer 9

• Control what entres and leaves the cell
• Some form channels which only let small or charged particles through
• Carrier proteins which transport molecules and ions by active transport or facilitated diffusion
• Receptors for molecules in cell signalling

Question 10

Function of glycolipids or glycoprotiens

Answer 10

• Act as receptors for messenger molecules
• Stabalise the membrane by forming hydrogen bonds with surrounding water molecules
• Sites where drugs, horomones and antibodies bind
• Antigens

Question 11

How does cell signalling work

Answer 11

• One releases a messenger molecule e.g. hormone
• Molecule travels to another cell e.g. in the blood
• Messenger molecule is detected by the cell because it binds to a receptor on its cell membrane

Question 12

Why do cells signal

Answer 12

-Need to communicate with each other to control processes inside the body and to respond to environmental changes

Question 13

Glucogen

Answer 13

• A hormone that’s released when there isn’t enough glucose in the blood
• It binds to receptors on the liver cells, causing the liver cells to break down stores of glycogen to glucose

Question 14

How does the temp at 0 affect membrane permeablilty?

Answer 14

• Phospholipids don’t have as much energy so can’t move much
• Packed closely together and membrane is rigid
• Channel and carrier proteins deform making it more permeable

Question 15

Permeability at 0-45 degrees

Answer 15

• Phospholipids can move around and aren’t packed as tightly together = partially permeable
• As temp increases. move more because of more kinetic energy, so permeablilty increases

Question 16

What can affect the permeablitiy of a membrane?

Answer 16

-Temperature and solvent