Biological Membranes Flashcards
Outline the phospholipid bilayer
1- hydrophobic fatty acid tails ( face Inwards )
2- hydrophilic heads ( on the outside )
What’s the difference between saturated and unsaturated fatty acid tails ?
(4)
Saturated fatty acids are straight chained
-no double bonds
- unsaturated fatty acid tails have kinks in them preventing them form packing closely together
- at least one C=C
What’s a phospholipid ?
- hydrophilic (head)
- hydrophobic ( tail )
- glycerol -2 fatty acid chains and a phosphate group ( hydrophilic )
Why is the fluid mosaic model used to describe the cell membrane ?
(2)
- Bilayer = fluid ( constantly moving
- protein molecule scattered through the molecule like tiles in a Mosaic .
What can diffuse through the bilayer ?
Lipid soluble small molecules
What is the function of plasma membrane ?
4
- barrier between cell and outside
- partially permeable allows it to let some molecules in and other out
- recognition by other cells
- cell communication
What is the function of membranes within cells ?
5
- divide the organelle and cytoplasm
- form vesicles
- control what enters and leaves the organelle
- membranes within organelle =barrier between membrane and rest of the organelle ( thylakoids membranes )
- site of chemical reactions
What is cholesterol ?
- cholesterol is a lipid
What is the function of cholesterol and where does is fit ?
3
Function : maintain fluidity
(Buffer for temperature )
- cholesterol fits between the phospholipid, causing them to pack more closely = less fluid and more rigid
What is the function of glycolipids , Glycoproteins ?
4
- stabilise the membrane by forming hydrogen bonds with surrounding water molecules
- sites where drugs , hormones , antibodies bind
- receptors (cell signalling )
- antigens- involved in immune response .
How do Neurones have specialised membranes ?
2
- protein channels ( move ions so electrical impulses are conducted )
- Myelin sheath
How to White blood cells have specialised membranes ?
1
- special protein receptors to recognise antigens / foreign cells
How are root hairs cells specialised ( membrane wise) ?
1
- many carrier proteins ( active transport of nitrate ions )
What can pass via simple diffusion ?
3
- O2
- CO2
- lipid soluble molecules (steroids )
How do water molecules pass through the membrane ?
2
- some diffuse through the bilayer
- Specific water channels- Aquaporins
How is the concentration maintained ?
1
- many of the molecules are used up in metabolic reactions to keep molecules moving
What factors make diffusion faster ?
5
1- high temp 2-large SA 3-Small size of diffusing molecules 4-concentration gradient = steep 5-small diffusion distance
Where does water move in Osmosis ?
1
- high water potential to low water potential
What is it called when a plant cell is completely filled with water? How does this effect osmosis?
(2)
- Turgid
Cell wall high pressure ( less water can come in now )
What happens when an animal cell bursts?
1
- Cytolysed
What is it called when the plant cell shrinks ?
- plasmolysed
What happens when animal cells shrink ?
1
- no water leads to the cell being Crenated
What’s active transport ?
1
- movement of substances against concentration gradient
What kind of transport is endo/exocytosis ?
What does It require ?
(2)
- bulk active transport
- requires ATP
How does the sodium potassium pump work ?
5
1-3 Na+ bind to cytoplasmic side of protein
2-ATP=ADP+P
Phosphorus binds to protein
3-phosphorylation of the protein = conformational change so Na+ is released on to the outside
4-2 K+ binds to sure in the outside
5- Phosphorus is released = shape change and k+ is released into the cell
What’s endocytosis ?
1
Bulk transport into cell via vesicles
What’s the process of exocytosis ?
3
- vesicles moves to membrane
- membrane fuses with the vesicles walls
- fused sites opens and contents are released to the outside
What happens to the Phospholipid bilayer when temp decrease ?
(3)
1- saturated fatty acids = compressed
2- unsaturated fatty acids maintain fluidity ( kink in tails)
3-cholesterol = buffet prevents the tails from getting to close and hence prevents the membrane form being too rigid
What happens when you increase the temp ( bilayer ) ?
2
- phospholipids gain KE
- Permeability increase
What happens to proteins in higher temperature ?
4
- large molecule vibrate
- H bonds break
- ionic bonds break
- Unfold to give primary structure = denatured
What do proteins do in the membrane ?
- pores / channels
- carrier
- extrinsic and intrinsic proteins
- facilitated diffusion
- diffusion
How does cell signalling work ?
5
1- release signal via exocytosis 2-Glycoproteins / lipids = receptors 3-shape receptor (signal is specific ) 4-conformational change of glycoproteins or glycolipid 5-molecule enters cell
How do vesicles work ?
3
1-microtubules provide pathway
2-vesicles move across this pathway
3-ATP used
Where does the sodium potassium pump work ? Cell ?
1
- Neurones
How does water move into the plant ?
1
Osmosis
How do you make experiment more reliable ?
1
- repeat and find average
How do you make experiment more accurate ? (1)
Smaller gap between measurements of independent variable ( ie : smaller gap between concentrations )
