Flashcards in Cell Biology Deck (247)
What are the general properties of biological membranes?
- Self repairing
- Selectively permeable
What are the role of lipids in biological membranes?
- Phospholipids - fatty acid tails are hydrophobic and consist of saturated or unsaturated - creates kinks in tail
- Cholesterol - poor head group, non polar hydrocarbon tail
What are the role of proteins in biological membranes?
- Peripheral membrane protein - bound to lipids which insert into the membrane
- Integral membrane proteins - protein its self is in phospholipid bilayer
What are the role of carbohydrates in biological membranes?
What is the role of phospholipids in membrane structure?
- Provide the structure and permeability barrier of membranes
- Have important roles in cell signalling and membrane interactions
What are integral membrane proteins?
- Proteins that directly insert in the membrane by a hydrophobic domain
- The transmembrane domain of proteins usually form alpha helix because there is a high conc. of hydrophobic acid
- Can also from beta barrels
What are peripheral membrane proteins?
- Covalently bound lipids which insert into the membrane and associate with integral membrane proteins or directly bind lipids
- Attach to membrane via covalently bound fatty acid or phenyl group
What are the advantages of peripheral membrane proteins?
Mobility at the cell surface
Rapid release into the extra cellular space
What is the role of peripheral proteins in red blood cells?
Cell shape determination - cytoskeleton
What peripheral proteins are present in red blood cells?
- Spectrin - forms dimers - mutation can cause certain types of haemolytic anaemia
- Actin - junctional complex with tropomyosin - Ankyrin
What integral proteins are present in red blood cells?
- Band 3
- They are restrained by the cytoskeleton of red blood cells
Where can phospholipids move?
Can rotate or exchange on the lateral plane but move slowly between leaflets
Do saturated or non saturated phospholipids make the membrane more fluid?
Saturated as it means that the membrane is less densely packed
Cold blooded animals have more saturated phospholipids so that the membranes are fluid at lower temperatures
What is the role of cholesterol in biological membranes?
- Lowers permeability - makes it less fluid in the area it is present but doesn't affect the whole membrane
- Stops crystallisation
Why are membranes asymmetric?
- Enzymes and transport proteins take up substances from one side to the other
- Receptors are orientated so they can bind to extracellular ligands
- Maintains electrochemical gradient as inner surface is negatively charged
- Can lead to different fluidity in the leaflets
- Some proteins involved in cell signalling need to interact with inner leaflets
How is asymmetry of the membrane maintained?
- New phospholipids move into the membrane creating gaps which are filled by scramblase which ensures equal growth on both halves
- Flipase ensure asymmetry is maintained
What is the function of carrier proteins?
- Carrier proteins undergo conformational changes to transport solute
- Carrier mediated diffusion has higher rate of transport than simple diffusion
What are the three types of carrier mediated transport?
- Uniport - 1 molecule transported
- Symport - coupled transport - transport molecule and co -transported ion pass through
- Antiport - coupled transport - transport molecule and co -transported ion pass in opposite direction
How is the blood group of an individual is determined?
By the structure of the oligosaccharides attached to sphingomyelin and proteins in the red blood cell membrane
What sugars do the different blood groups have on the oligosaccharide chains?
O - no extra sugar
A - Has GALNAC
B - Galactose
AB - both
What are the electrical properties of membranes?
- Voltage difference across cell because excess positive ions on one side and negative on the other
- Combination of membrane potential and concentration gradient gives an electrochemical gradients
- Inner surface of plasma membrane os neg and outer is pos
- Created by carriers and pumps
How do ion channels allow transport across membranes?
- Form narrow hydrophobic pores through the membrane
- Specific to different ions
- Allow rapid movement of ions down conc gradient
- Regulated by binding of ions
- Often target for many toxins and medicines
How does active transport allow transport across membranes?
- Coupled carriers
- ATP and light driven pumps
- Driven by Na+ gradients in mammals and by H+ gradients in bacteria
What are the uses of liposomes?
- Drug delivery
- Delivery of DNA and RNA into cells
- Cosmetic industry
How is the cytoskeleton of RBC's purified?
- Solubise in detergent
- proteins analysed by Gel electrophoresis
Why is important for phospholipids to be asymmetric?
- Scotts disease - lack of scramblase - stops the efficient movement of phosphatidylserine causing the inhibition of coagulation
Cell recognition and apoptosis
- Receptors on plasma membrane of macrophages recognise those on old red blood cells
- Signals phagocytosis
Give the structure of the nuclear envelope
- Formed from two membranes
- Membranes enclose perinuclear space
- Outer membrane is continuous with the endoplasmic reticulum
- Perinuclear space can fill with newly synthesised proteins
Give the structure and function of the nucleoplasm
- Layers of filaments lying close to inner membrane of the nuclear envelope
- Polymerisation and dephospho rylation makes the lamina stronger
- Involved in regulation of genetic activity
Also contains ions, enzymes and nucleotides
What disease can mutations in the lamina cause?
Hutchinson - Gilford progeria syndrome which prevents cleavage and can cause premature ageing