Karteikarten
Cell Membrane
Karten in diesem Stapel (51)
- 1What are the four functions of biological membranes?1. Delineation and compartmentalisation of the cell
2. Organisation and localisation within the cell
3. Transport into and out of the cell
4. Detection and transmission of signals from the external environment - 2What was Ernst Overton aware of in the 1890s?That cells were surrounded by a selectively permeable barrier. He studied the nature of this barrier by looking at which substances it let pass. Lipid-soluble substances crossed but water-soluble ones didn't, so he concluded lipids made up this barrier.
- 3What did Irwing Langmuir do in the 1930s?He invented the Langmuir trough which is a device that allows the measurement of lipids by separating lipids into a monolayer
- 4What did Gorter and Grendel do in `925?Studied the organisation of lipids in the membrane. Used erythrocytes and extracted an amount of lipids using benzene. Using a Langmuir trough, they measured the amount of lipids and could also work out the surface area of a RBC
- 5What were the issues with the idea of the membrane being made of only a lipid bilayer?Didn't explain surface tension, electrical resistance or solute permeability (why can glucose not galactose pass, why do some ions pass but some don't?)
- 6What did Davson and Danielli propose?In 1935, they proposed the 'Sandwich Model' which suggested the lipids were sandwiched between proteins. This came around from the emerging concept of enzyme-substrate specificity.
- 7Who proposed the fluid mosaic model and when?Singer and Necolson proposed it in 1973. It suggested that there were proteins AMONG the lipids in the membrane and that they could move fluidly.
- 8Assumptions of the fluid mosaic model?- Membranes contain lipids and proteins
-phospholipoids make bilayer due to being amphiphathic (hydrophobic/philic)
-phosopholipids move freely in membrane
-Some proteins can move around
-proteins are not uniform in the membrane
-membranes are asymmetrical
-membranes are selectively permeable - 9What did Urwin and Henderson contribute?They established the structure of certain membrane proteins, such as finding out they are in the form of alpha helixes.
- 10What is membrane topology?The membrane having two sides, the cytoplasmic side (the one that is in contact with the cytoplasm) and the exoplasmic side.
- 11What three kinds of phosophglycerides are there in the membrane?Phosphatidylcholine
Phosphatidylserine
Phosphatidylethanolamine - 12What is the sphingolipid in the membrane?Sphingomyelin
- 13Summarise structure of a typical membrane phospholipid?Phosphatidylcholine has a hydrophillic head made up of glycerol, phosphate and choline and a hydrophobic tail made up of a saturated hydrocarbon chain and an unsaturated hydrocarbon chain.
- 14Difference between saturated and unsaturated chains?Unsaturated have double bonds, saturated do not
- 15What are Van der Waals forces?At a very short distance, any two atoms show a weak bonding interaction due to their fluctuating electrical charge. However, if they get too close they will repel one another. They are individually weak interactions but can be quite strong when macromolecules contact one another
- 16How is phosphatidylcholine synthesised?Fatty acyl CoA and glyerol 3-phosphate are joined by acyl transferase, expelling CoA. This makes phosphatidic acid. Phosphatase turns this to diacylglycerol, expelling a phosphate. Lastly, choline phosphotransferase turns CDP-choline to CMP and attaches the choline to diacylglycerol, making phosphatidylcholine.
- 17Where are phospholipids placed when they are synthesised?They are only added to the cytosolic face of the bilayer
- 18How is this issue resolved?Phospholipid translocators called scramblases transfer phospholipids from one side of the bilayer to the other to ensure equal growth of the membrane. Scramblases are not specific for particular phospholipids.
- 19What is meant by the membrane being asymmetrical?There is an equal number of phospholipids on each side of the membrane but the phospholipids that make up the chain vary.
- 20What maintains membrane asymmetry?Flippases, which are specific phospholipid translocators that transfer phosphatidylserine and phosphatidyethanolamine from the exoplasmic to the cytosolic side of the bilayer. They operate continuously to counteract scramblases.
- 21Mitochondria don't synthesise their own phospholipids so how are phospholipids inserted into mitochondrial membranes?Phospholipid exchange proteins that transfer phospholipids between the membrane of the endoplasmic reticulum and the outter membrane of the mitochondrion
- 22What are glycolipids?They are lipids that contain sugar. They are found in all animal cell plasma membranes and some intracellular membranes. Constitute 2.5% of all membrane lipids .
- 23Why are glycolipids always found on the exoplasmic side of the bilayer?They are assembled in the lumen of the golgi and are not substrates for lipid translocators
- 24What does cholesterol consist of and what is its function in the membrane?It has a polar head group, rigid planar steroid ring structure and a non-polar hydrocarbon tail. It stabilises the phospholipid bilayer and regulates the membrane fluidity
- 25What are the three types of membrane proteins?1. Peripheral membrane proteins
2. Integral membrane proteins
3. Lipid anchored membrane proteins - 26What are integral membrane proteins?They go through the bilayer - they are either through both layers of just one of the photpholipid layers.
- 27What are peripheral membrane proteins?They are anchored into the membrane somewhere but the protein itself is on the outside of the bilayer
- 28What are the four types of linkages between proteins and the lipid bilayer?Amide, thioether, myristyl, fernesyl
- 29Why is it important for membranes to be fluid?Allows membranes to fuse with other membranes which is important in processes like endocytosis. It also helps cell migration and ensures membranes are equally shared between daughter cells following cell division.
- 30What is phase transition?The transition in phospholipids between the ordered gel phase and a disordered liquid-crystalline phase caused by transition over a narrow temperature range.
- 31What happens to membrane fluidity in prokaryotes as the temperature decreases?Fatty acid chain length decreases resulting in decreasing Van der Waals forces between jeighbouring phospholipids and a degree of unsaturation increases which results in increased spacing between fatty acid chains, hence decreased van der waals.
- 32How does cholesterol regulate membrane fluidity in eukaryotes?At 37 degrees it tends to make the membrane less fluid as it stabilises interactions between neighbouring phospholipids. At lower temps, it prevents phase transition as cholesterol prevents the fatty acyl chains from interacting with each other.
- 33proof of lateral movement of proteins in cells?Take two cells, label the proteins of one with fluorescein and the other cells proteins with rhodamine. Fuse them. There will be a clear barrier between where the fluroscein labelled and rhodamine labelled proteins are but after 40 minutes they will have completely merged in the fused cell.
- 34What prevents lateral movement of proteins in many cells?'Tight junctions' between cells. They prevent the movement of membrane proteins from going all around the cell perimeter if undesired.
- 35Two types of passive transport?Simple diffusion (no membrane proteins involved and is driven by concentration gradients) and facilitated diffusion (membrane proteins involved and driven by concentration gradients). No energy input required for either.
- 36Summarise what can pass the lipid bilayer?All hydrophobic molecules like O2, CO2, N2, benzene. Some small uncharged polar molecules like H2O, urea and glycerol. Very few large uncharged polar molecules, only glucose and sucrose can. No ions can pass.
- 37What are the two types of membrane proteins that help with facilitated diffusion?Channels (membrane proteins that form hydrophilic pores through the membrane) and carriers.
- 38How do channels work?They are usually non-directional ion channels. They show some selectivity and are driven by concentration gradients (electrochemical gradients). They are fast.
- 39Different kinds of proteins?voltage gated, ligand-gated (extracellular or intracellular ligand) or mechanically gated
- 40What are carrier proteins?They are required for the transport of almost all small organic molecules. They are highly selective and relatively slow. They can be with or against the concentration gradient.
- 41Example of a membrane protein that carries out facilitated diffusion?Glut1. Glucose binds to the binding site open to outside the cell. Transport protein shifts to alternative conformation. Glucose is released to the inside and protein returns to its original conformation.
- 42How is Glu1 concentration gradient maintained?When the glucose enters the cell it goes through the glycolysis pathway and is concerted to glucose-6-phosphate by hexokinase which makes it no longer able to bind to Glut1
- 43What is active transport?It moves solutes against their electrochemical gradient. Electrochemical gradient is the way they are supposed to move due to membrane potential
- 44Three main ways of carrying out active transport?1. coupled transporters (couple the transport of one solute with the gradient with another solute against its gradient)
2. ATP driven pumps (couple transport of solute against gradient to the hydrolysis of ATP)
3. Light-driven pumps (transport against gradient coupled with input of energy from light) - 45Difference between direct and indirect active transport?Direct is when the one solute is passed alone (like ATP driving hydrogen pumping) and indirect is when active transport relies on another molecule moving with its gradient to get through the channel
- 46Why is active transport needed?To maintain electrochemical gradients. Approximately 70% of all energy expenditure is used to maintain these gradients. We need these gradients as electrical forces inside and outside the cell must be balanced.
- 47What is the sodium potassium ATPase (pump)It is found in all animal cells. Uses energy derived from ATP hydrolysis to transport sodium out the cell and potassium in against their eletrochemical gradients. Coupled transport. Inhibited by ouabain and digoxin.
- 48How does the sodium potassium pump work?3 sodium are taken from the inside. ATP phosphorylates alpha subunits of the pump. Conformational change following phosphorylation expels sodium. Two potassium from outside enter. Dephosphorylation triggers conformational change. Potassium enters.
- 49Which ion can glucose pass through a carrier protein with?Sodium
- 50Difference between symport and antiport transport?Symport is when both things being transported enter the same way (eg, Na+ and glucose). Antiport is when both transported molecules go in opposite directions (eg, the Na+/Ca2+ transporter)
- 51What are Ouabain and Digoxin?They are drugs commonly used to treat heart failure. They inhibit the Na+/K+ ATPase resulting in an increase in intracellular Na+. Intracellular Ca+ rises leading to stronger cardiac muscle contraction.
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- Cell Biology and Physiology Karteikarten am Cell Membrane, erstellt von Emma Lloyd am 07/05/2018.
- Erstellt von
- Emma Lloyd
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