How many membranes are there in the body?
Multiple different types of biological membranes with varying compositions and functions
Which part of the phospholipid is hydrophobic?
The tails - composed of the fatty acid chains
What significant structure do phospholipids form?
lipid Bi layers (membranes)
What causes the asymmetry of membranes?
The outside of the cell has a different composition to the inside
What are the different components of a lipid molecule?
- Polar head
- Choline, serine, ethanolamine, inositol
- Phosphate
- Glycerol
- Fatty acid chains
How can we describe the fluid nature of membranes?
Dynamic and flexible
Why does a slight temperature change not alter the membrane fluidity?
The composition of membranes are adapted to withstand a large range of temperatures
What is Spur Cell anemia?
When the plasma membranes of erythrocytes has up to 65% more cholesterol than normal
What are the two movement types in a membrane?
- Lateral
2. Transverse
What is apoptosis?
Programmed cell death
How does a highly saturated membrane affect fluidity?
Molecules pack closer together
Decrease fluidity
Increase rigidity
What facilitates the transverse movement of newly synthesised membrane?
ABC transport proteins (enzymes)
Where is the new membrane formed?
Formed from the ER to the golgi
What is transverse movement in the membrane?
Movement across the membrane (flipping to the other side)
What is the consequence of spur cell anemia on red blood cells?
RBC membrane is very rigid
so rbc can no longer morph to fit through small pores (e.g. capillaries)
Less able to function as successful rbc, due to increased cholesterol levels
What would a temperature decrease do to the fluidity of the membrane?
Energy associated with phospholipids decreases
Causes molecules to move closer together
Decreases membrane fluidity
What type of movement is required in newly synthesising membrane in order to make it structurally correct?
Transverse movement
List the common features of biological membranes
- Asymmetrical
- Fluid
- Bi layers
- Electrically polarised
- Specific protein functions
Why is lateral movement so rapid?
Due to diffusion being a passive process
Why are phospholipids described as being amphipathic?
They are both hydrophilic and hydrophobic
What are lipid anchored proteins?
Membrane proteins covalently linked to a lipid
e.g. glycerophosphatidylinositol
Why does the synthesis of new membrane cause the membrane shape to be deformed?
Membrane is synthesised on the the cytosilic membrane only
Causes a bowed shape - deformation
What is phosphotidylserine ?
A phospholipid involved in apoptosis
How much of the % cell weight is comprised of membrane carbohydrates?
membrane carbohydrates form 2% of cell weight
What factors affect the membrane fluidity?
Temperature
Degree of saturation
Fatty acid length
Cholesterol content
Where are new membrane synthesising enzymes found ?
Cytosilic surface of golgi apparatus
What is the purpose of apoptosis?
Allows body to turnover cells without inducing inflammatory response
Which membrane movement type is faster?
Lateral movement
Where are membrane carbohydrates found on the membrane?
Facing away from the cytosol
Where do the hydrophilic heads on the membrane face?
Extracellular surface
Where are peripheral membrane proteins found on the membrane?
Located on extracellular (cytosolic) side
What components can we expect in biological membranes?
- Phospholipids
- Cholesterol
- Glycolipids
(not all membranes contain all 3)
What facilitates movement in the membrane?
Enzymes
Describe what the structure of peripheral membrane proteins is like
- non covalent bonds
- loosely associated with membrane - easier to extract
- lipids and proteins can bind
How does an increase in temperature affect membrane fluidity?
Energy associated with phospholipids increases
Molecules able to move apart
Increases fluidity
Give examples of some membranes present in the body
Nuclear membrane
Plasma membrane
Mitochondrial membrane
Explain what is meant by lateral membrane movement
Along the plane of the membrane
How do the phospholipids arrange in bi layers?
They readily form bi molecular sheets in aqueous media
How is fluid is the membrane when unsaturated?
Molecules can’t pack as closely together due to C=C double bonds
so increases fluidity
less rigidity
What are 3 types of ABC enzyme proteins?
Floppase - Moves phospholipids from cytosilic to luminal side (inner -> outer surface), using ATP
Flippase - Moves phospholipids from outer to inner leaflet, using ATP
Synthase - Bidirectional movement of phospholipids, passive
What other molecules do membrane carbohydrates associate with?
Both lipids and proteins
Describe the structural features of integral membrane proteins
” ɒ helical transmembrane region
- strong non covalent bonds
- interlinked with membrane - difficult to extract
- Pass through membrane once or multiple times
- Hydrophobic side chains present on outer surface
What is the advantage of cholesterol at high temperatures in the membrane?
Cholesterol maintains membrane stability (decreases fluidity)
Outline how apoptosis occurs in cells
- Phosphatidylserine transversely transported to outer surface
- Causes cells to round up and form nodules
- Cells blister and burst
What is the role of membrane carbohydrates?
Allow cells to interact with each other and the extracellular membrane
What effect does cholesterol have on the membrane?
OH group forms H bonds between the phospholipid hydrophobic tails
Disrupting the interactions between the fatty acid chains
Prevents strong bonding in chains
Increases fluidity - esp. at low temp
What is the significance of ABC enzyme proteins?
They are crucial in establishing membrane asymmetry
Name the different proteins present in a membrane
Integral membrane proteins
Peripheral membrane proteins
Lipid anchored proteins
Why is the membrane described as fluid mosaic?
Fluid - components able to move around
Mosaic - composed of many different Proteins
How is apoptosis initiated?
The movement of phosphotidylserine from inner to outer surface signals to cells apoptosis will occur
What would an increase in fatty acid length do to membrane fluidity?
More interactions and bonds form between chains
Fluidity would decrease
Increase rigidity
Why is transverse movement slow?
Relatively significant amount of energy required to move a polar molecule through a hydrophobic region to opposite side of membrane