Lipid membrane Flashcards
Example and location of integral proteins
Integral proteins are within the bilayer e.g. GPCRs
Polyprotic- both sides
Monoprotic- one side
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 denaturants
How and why can integral proteins be removed from the membrane?
Integral membrane proteins are very firmly associated with the lipid bilayer and are removable only by agents that interfere with hydrophobic interactions (cause a change in pH), such as detergents, chelating agents organic solvents, or denaturants
Hydrophobic domain become coated with the detergent
Where are amphiprotic proteins found? How are they attached?
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 are amphiprotic proteins detached from the membrane?
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 (amphitropic or integral protein) would be involved in cell signalling?
amphitropic as it can go into cytoplasm
Inner and outer layer are different/ the same
Different
Components that are involved in cell signaling such as PIP2, have a higher concentration on the inside/outside of the lipid bilayer
Inside
Phosphatidylserine is always maintained __ at __ concentration
Phosphatidylserine is always maintained inside at high concentration
What happens when Phosphatidylserine moves from inside to outside?
When is it moved to outer bilayer, the cells are targeted for apoptosis - marks the cell for phagocytosis by white blood cells
Also is involved in blood clotting
Which groups affect bilayer flexibility?
Acil
Ordered membrane state is more __ compared to disordered
Ordered membrane state is more solid compared to disordered
What are the factors affecting membrane flexibility?
Temperature (20-40C)
Saturation of FA chain
Uniformity of FA chains
Sterol content
How does saturation of FA chain affect order
Saturation of FA chain increases order
How does uniformity of FA chain affect order
Uniformity increases order
How does Sterol content affect order
Sterol content affects fluidity both ways- Think of them as of ball that can induce gaps (disordered-> more mobile and liquid) or fill them up (ordered-> more solid)
Cell mobility and division requires __ membrane mobility
Cell mobility and division requires higher membrane mobility
Structural cells such as muscle cells require __ membrane mobility
Structural cells such as muscle cells require lower membrane mobility
Describe Floppase
ABC transporter- moves phospholipids from inside out
Describe flippase
P-type ATPase
Moves PE and PS from outer to cytosolic (inner) leaflet
Membrane proteins are usually freeley mobile. Describe the cases when they aren’t
Proteins can be held in place when they are attached to other proteins
Integral proteins attached to cytoskeletal proteins are non-mobile
Lipid rafts contain clusters of __ and specific __. They are more __
Lipid rafts contain clusters of glycosphingolipids and specific doubly or triply acylated proteins They are more ordered
What kind of a domain is a lipid raft?
Microdomain
Which effect do lipid rafts have on surrounding area?
Whatever is within that region is less mobile, the structure as a whole though is fully mobile
Lipid rafts contain si__ that are attached to __ within that area
Lipid rafts contain signaling proteins that are attached to membrane within that area
What are lipid rafts enriched in?
In sphingolipids and cholesterol
What does fusion of 2 membrane require? (6)
Triggering signal Recognition of each other Close apposition Local disruption of bilayer before fusion Hemi- fusion Fusion proteins
What’s hemi fusion
The outer membrane of one component to inner membrane of other component if the two components are within each other
If the two components ae separate from each other ,the outer components fuse first
What are the situations when membrane fusion is required?
Budding of vesicles from Golgi complex Exocytosis Endocytosis Fusion of endosome and lysosome Viral infection Fusion of sperm and egg FUsion of small vacuoles Separation of two plasma membranes at cell division
What do fusion proteins do
the process is triggered at the appropriate time or in response to a specific signal. Integral proteins called fusion proteins mediate these events, bringing about specific recognition and a temporary local distortion of the bilayer structure that favors membrane fusion.
What are the 3 types of proteins involved in membrane fusion at synapse?
3 types of snare proteins: T-SNARE, V-SNARE, Q-SNARE
What does T-SNARE do? Where does it assemble
T-SNARE (target-snare) helps in recognition of the target membrane
Assembles on the target membrane
What does V-SNARE do? Where does it assemble
V-SNARE marks the vesicle that needs to be emptied out
Assembles on the vesicle membrane
In which process are SNARE proteins involved?
All neurons store their neurotransmitters in vesicles
Vesicle bilayer has to be integrated into neuronal cytoplasmic bilayer so that it opens up and empties vesicle’s contents
SNARE proteins are involved
Describe Q-SNARE. What does it do
Q-SNARE (e.g., SNAP-25) are
regulatory proteins that are
Ca2+ induced.
Help V and T SNARE to come together
What’s NSF?
NSF (N-ethylmaleimide sensitive
fusion factor) proteins disassemble the SNARE complex
Describe the process of vesicle emptying with SNARE proteins - neurotransmitter vesicle and neuron membrane
- Neurotransmitter-filled vesicle approaches plasma membrane.
- When a local increase in [Ca2+] signals release of neurotransmitter, the v-SNARE (on a vesicle), SNAP25 (on plasma membrane) , and t-SNARE (on plasma membrane )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.
What happens to SNARE proteins after the vesicle was emptied out
Snare proteins are degraded and recycled
Which compounds can be transported by simple diffusion?
Nonpolar compounds only
Describe secondary active transport
Against electrochemical gradient, driven by ion moving down its gradient
No ATP involved
Describe ionophores
Ionophores are lipid-soluble molecules that bind specific ions and carry them passively across membranes, dissipating the energy of electrochemical ion gradients.
Down electrochemical gradient
Are GLUT transporters active or passive?
passive
What is GLUT4 is sensitive to ?
GLUT4 is sensitive to insulin signaling
What is the purpose of passive transporters?
Transporter enhances the rate of the transport
GLUT1
Tissue where expressed
Role
Expressed in Erythrocytes and most tissues at a low level
Role: Basal glucose uptake
GLUT2
Tissue where expressed
Role
Expressed: Liver, pancreatic islets, intestine, kidney
Role: In liver and kidney,
GLUT4
Tissue where expressed
Role
Expressed: Muscle, fat, heart
Role: Activity increased by insulin
Steps of insulin control of GLUT4
- Glucose transporters “stored” within cell in membrane vesicles.
- When insulin interacts with RTK, 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 is the the consequence of lack of signal transduction by insulin signaling
Diabetes mellitus
Describe CO2 transport by RBC
CO2 concentration is high outside RBC
CO2 easily enters erythrocyte, where it is converted to bicarbonate (HCO3- ) by the enzyme carbonic anhydrase.
Now there’s a high concentration of HCO3- in RBC which is excreted into blood plasma and then travels to the lungs. There, HCO3- concentration is high and it reenters the erythrocyte. When Bicarbonate concentration in the RBC is high, an enzyme converts it to CO2 which can be excreted into the lung space and exhaled.
What does carbonic anhydrase do
Converts CO2 to bicarbonate (HCO3- ) in RBC
How is the movement of HCO2- across the erythrocyte
membrane is made more effective?
The chloride-bicarbonate exchanger, also called the anion exchange (AE) protein, increases the rate of HCO3- transport across the erythrocyte membrane.
It’s an antiporter- moves HCO3- and Cl- with no net transfer of charge; the exchange is electroneutral.
What is a chloride-bicarbonate exchanger
The chloride-bicarbonate exchanger, also
called the anion exchange (AE) protein is an integral protein and aintipoter that mediates the simultaneous movement of HCO3- and Cl-
What happens when Cl- is absent?
In the absence of chloride, bicarbonate transport stops.
What’s primary active transport?
solute is transported to the transporter and is moved against the gradient by using ATP
solute accumulation is coupled directly to an exergonic chemical reaction, such as conversion of ATP to ADP
What’s secondary active transport?
a gradient of ion X (S1) (often Na) has been established by primary active transport. Movement of X (S1) down its electrochemical gradient now provides the energy to drive cotransport of a second solute (S2) against its electrochemical gradient
active transport occurs when endergonic (uphill) transport of one solute is coupled to the exergonic (downhill) flow of a different solute that was originally pumped uphill by primary active transport
Describe a symport system that is important in digestion
Secondary or primary?
Na+:Glucose and Na+:amino acid in intestinal epithelium- occurs when food is eaten
Secondary
Describe an antiport system that is important in water balance
Secondary or primary?
Na+:K+-ATPase; Na+:H+ pumps in kidney
Secondary
Describe transport through F-type ATPase
Found in mitochondria
Can do both ATP synthesis and hydrolysis
What can serves as solutes for ABC transporters?
amino acids, peptides, proteins, metal ions, lipids, bile salts and drugs
Cassette is another name for __
Cassette is another name for domain
Explain ABC transporters
When ATP is bound to the cassette, the transporter is opened outward, when ADP- inward, when the molecule comes there is a change in conformation, because of ATP\ADP
Difference between RBC and stem cells
Stems cells proliferate-
RBCs don’t
Stems cells have nuclei, mitochondria; RBCs don’t
Mitochondria are needed for ATP production
RBCs use glycolysis to make ATP-> can’t survive without glucose
Energy sources of cardiac myocytes, RBC and neurones
Neurons and RBC depend more on glucose
Cardiac myocytes depend more on fatty acids
What do you need for any regulatory mechanism to take place? WHat does it generally lead to?
You need a signal which will result in a response
This signal generally lead to a change in gene expression
How are TF generally regulated?
by phosphorylation or dephosphorylation; by TF interactions
What are the methods of regulation enzymatic levels (6)
- Extracellular signal
- Transcriptional regulation –
a. TF phosphorylation/ dephosphorylation
b. TF interactions - mRNA stability
- mRNA translation
- Protein stability (half-life)
e. g. Cyclins - Enzyme localization e.g. Mitorchondrial enzymes
How mRNA stability can affect enzymatic levels?
the length of time mRNA is maintained inside the cells (the longer mRNA is maintained inside the cell ,the more protein is produced)
Cyclins as an example of cell degradation
Cyclins - enzymes involved in cell division- degraded immediately after completion of division - targeted through ubiquitination
Pathways in opposite directions are favored/ not favored simultaneously
not favored
Common regulatory mechanisms at organism level (5)
ü Pathways in opposite directions are not favored simultaneously
ü Maximizes product utilization (e.g Glycolysis and Gluconeogenesis)
ü Ability to partition metabolites between alternate pathway- e.g. Glycolysis or pentose-phosphate pathway
ü Draw on fuel best suited for the need
ü Slow down synthetic pathways when products accumulate
What is GPI?
Glycosylphosphatidyllinositol
An example of GPI linked protein
Phosphatases
