Lipids membrane Flashcards
Where are integral proteins located? + give an example
Integral proteins are within the bilayer e.g. GPCRs
Can be only on one side, but they are still integrated
Can integral proteins be removed?
Integral membrane proteins are very firmly associated with the lipid bilayer and are removable only by agents that interfere with hydrophobic interactions, such as detergents, organic solvents, or denaturant
Where are amphitropic proteins located? How are they bound?
Amphitropic proteins are found both in the cytosol and in association with membranes.
Their affinity for membranes results in some cases from the protein’s noncovalent interaction with a membrane protein or lipid, and in other cases from the presence of one or more lipids covalently attached to the amphitropic protein
How can amphitropic proteins be removed?
Can be cleaved off membrane and go to cytoplasm Need enzymes (phospholipase C) or post-translational covalent modifications (phosphorylation) to be cleaved off and taken away from the membrane
Which type of membrane protein re the once that would be involved in signaling or structurally involved?
Amphitropic proteins
Phosphatidylserine is always maintained inside at __ concentration
Phosphatidylserine is always maintained inside at high concentration
Where is Phosphatidylserine normally found? What happens when it changes it’s location?
Normally maintained inside
When is it moved to outer bilayer, the cells are targeted for apoptosis - marks the cell for phagocytosis by white blood cells. Also results in blood clotting
What determines the membrane state?
Arrangement of Acyl determines the states of membrane
What are the factors affecting membrane flexibility? (4)
- Temperature
- Saturation of FA
- Uniformity of length
- Sterol content
What’s the temperature range for cell membranes?
20-40C
How does saturation of FA affect order?
Saturation increases order
Solid state is more ordered/disordred
ordered
How does temp affect orderly state of lipids?
Heat imparts thermal motion in acyl groups so the state becomes more disordered
Increase in temperature results in the membrane becoming more fluid
How does uniformity of length of FA affect order?
uniformity of length of FA increases order
Combination of short and long-> more gaps-> more disordered-> more mobility
Sterol content of FA affects order __
Sterol content of FA affects order in both ways
Which situations require more mobile membranes? Less mobile?
Cell mobility and division requires higher membrane mobility
Structural cells such as muscle cells require more stiff membranes
How are proteins in cell membrane made less mobile?
Proteins can be held in place when they are attached to other proteins
Integral proteins attached to cytoskeletal proteins are non-mobile
Give an example of microdomain
Lipid rafts
What are lipid rafts? What’s their effect?
Lipid rafts are small regions within cell membrane that contain sphingolipids
Sphingolipids offer orderly, less flexible state to the lipid bilayer
As these are small areas within lipid bilayer which are more rigid
Whatever is within that region is less mobile
The structure as a whole is fully mobile
Play a role in signal localization and integration
What do lipid rafts contain?
Lipid rafts contain signaling proteins
They also contain specific double or triply acylated proteins (have fatty acids attached to them)
What does fusion of 2 membrane require? (6)
v Triggering signal v Recognize each other v Close apposition v Local disruption of bilayer v Hemi-fusion v Fusion proteins
What gets hemi fused if two components are within each other? If the two components are separate from each other ?
The outer membrane of one component to inner membrane of other component if the two components are within each other
If the two components are separate from each other ,the outer components fuse first
What type of protein are fusion proteins? What do they do?
Integral proteins called fusion proteins mediate these events, bringing about specific recognition and a transient (временное) local distortion of the bilayer structure that favors membrane fusion.
What are the 3 types of SNARE proteins? What does each of them do?
T-SNARE (target-snare) helps in recognition of the target membrane
V-SNARE (vesicle snare) marks the vesicle that needs to be emptied out. Assembles on that vesicle
Q-SNARE (e.g. SNAP25) helps V and T SNARE to come together
What is the role of NSF?
NSF (N-ethylmaleimide sensitive fusion factor) proteins disassemble the SNARE complex
Explain membrane fusion steps at synapse
- Neurotransmitter-filled vesicle approaches plasma membrane.
- When a local increase in [Ca2+] signals release of neurotransmitter, the v-SNARE, SNAP25, and t-SNARE interact, forming a coiled bundle of four helices, pulling the two membranes together and disrupting the bilayer locally.
v-SNARE and t-SNARE bind to each other, zipping up from the amino termini and drawing the two membranes together.
Zipping causes curvature and lateral tension on bilayers, favoring hemi-fusion between outer leaflets. - Hemi-fusion: outer leaflets of both membranes come into contact.
- Complete fusion creates a fusion pore.
- Pore widens; vesicle contents are released outside cell.
Snare proteins are degraded and recycled
- When a local increase in [Ca2+] signals release of neurotransmitter, the v-SNARE, SNAP25, and t-SNARE interact, forming a coiled bundle of four helices, pulling the two membranes together and disrupting the bilayer locally.
Describe secondary active transport
Happens against electrochemical gradient, driven by ion moving down its gradient
Describe the direction of movement in ionophore mediated ion transport
Down electrochemical gradient
What are the 3 cotransport systems?
Symport
Antiport
GLUTs are __ transporters / __ transporters
Are they active or passive?
GLUTs are glucose transporters / solute transporters
Passive
What is GLUT4 sensitive to?
Insulin signaling
GLUT1
Tissues where it is expressed
Role
Tissues where it is expressed: Erythrocytes and most tissues at a low level Role: Basal glucose uptake;
GLUT2
Tissues where it is expressed
Role
Tissues where it is expressed: Liver, pancreatic islets, intestine, kidney
Role: In liver and kidney,
GLUT4
Tissues where it is expressed
Role
Tissues where it is expressed: Muscle, fat, heart Role: Activity increased by insulin
What is the purpose of the insulin signaling pathway?
This cycle regulates the availability of the transporter at the cell membrane by regulating where the transporters are- inside the cytoplasm or at the cytoplasmic membrane
By regulating the amount of the transporter present at the cell membrane, it regulates how much of glucose transporters are available for glucose transport
The more transporters- the more glucose comes in as on the inside there’s low concentration of glucose
Outline insulin signaling pathway
- Glucose transporters “stored” within cell in membrane vesicles.
- When insulin interacts with its receptor, vesicles move to surface and fuse with the plasma membrane, increasing the number of glucose transporters in the plasma membrane.
- When insulin level drops, glucose transporters are removed from the plasma membrane by endocytosis, forming small vesicles.
- The smaller vesicles fuse with larger endosome.
- Patches of the endosome enriched with glucose transporters bud of to become small vesicles, ready to return to the surface when insulin levels rise again
What does lack of insulin signal transduction signify?
Diabetes
Describe the steps of getting rid of CO2 in the blood
Outside of RBC there’s a high concentration of CO2 which is excreted by cells into blood
CO2 easily enters an erythrocyte, where it is converted to bicarbonate (HCO3- ) by the enzyme carbonic anhydrase.
Now there’s a high concentration of HCO3- which is excreted from RBC into blood plasma and then travels to the lungs
In the lungs, HCO3- reenters the erythrocyte and is converted to CO2, which is eventually released into the lung space
and exhaled. To be effective, this shuttle requires very rapid movement of HCO3- across the erythrocyte membrane.
What does carbonic anhydrase do?
Converts CO2 to HCO3-
How is the process of getting rid of CO2 in RBC made more effective?
The chloride-bicarbonate exchanger, also called the anion exchange (AE) protein, increases the rate of HCO3- transport across the erythrocyte membrane.
This protein mediates the simultaneous movement of two anions: for each HCO3- ion that moves in one direction, one Cl- ion moves in the opposite direction, with no net transfer of charge; the exchange is electroneutral.
This cotransport system allows the entry and exit of HCO3 without changing the membrane potential
What happens if there’s no HCl available in RBC?
The coupling of Cl and HCO3- movements is obligatory; in the absence of chloride, bicarbonate transport stops
