Chapter 4 Flashcards
1
Q
General functions of the plasma membrane
A
- Selectively permeable barrier
- Transporting solutes
- Responding to external signals
- Intracellular interaction
- Energy transduction
2
Q
The primary components of the membrane
A
- Phosphoglycerides
- Sphingolipids
- Cholesterol (Less amphipathic for structural stability)
3
Q
What is the significance of lipid bilayers in membranes?
A
- Flexible and can self-assemble.
- Maintain internal composition
- Liposomes (synthetic vesicles) are used in research and drug delivery.
4
Q
How does cholesterol contribute to membrane structure?
A
- Its carbon rings are flat and rigid, which helps stabilize the lipid bilayer by forming microdomains with sphingolipids (lipid rafts).
5
Q
What are lipid rafts and their functions?
A
- Cholesterol and sphingolipid-rich domains in the outer leaflet plasma membrane
- Organize proteins and receptors, help with cell signalling and membrane trafficking
6
Q
Three types of gated ion channels?
A
-
Voltage-gated: Open based on ionic charge differences
-Ligand-gated: Open when specific molecules bind
-Mechano-gated: Respond to mechanical forces
7
Q
How do RBC membrane proteins contribute to structure?
A
- Skeleton is made of spectrin attaches to ankyrin
- Essential for maintaining shape, flexibility and prevent clumping
8
Q
What is the difference between fully saturated, monounsaturated, and polyunsaturated fatty acids?
A
- Fully saturated: no double bonds between carbon atoms; all carbon atoms are fully saturated with hydrogen atoms.
- Monounsaturated: Have one double bond in the carbon chain.
Polyunsaturated: Contain two or more double bonds in the carbon chain.
9
Q
The role of flippases
A
- They flip specific phospholipids from one leaflet to the other on the bilayer to maintain asymmetry and fluidity
10
Q
How do carbohydrates contribute to cell function
A
- They are found as glycolipids and glycoproteins
- They help determine blood types, in cell recognition and interaction with the environment
11
Q
Which glycolipids determine the different blood types?
A
- Type A: Has N-acetylgalactosamine added to the glycolipid.
- Type B: Has galactose added to the glycolipid.
- Type AB: Has both modifications (A and B).
- Type O: Lacks the enzymes to add either sugar.
12
Q
Different types of membrane proteins
A
- Integral: Embedded within the lipid bilayer (channels, transporters or receptors)
- Peripheral: Associated with the membrane with weak interactions (enzymes/signalling factors)
13
Q
How do cells maintain membrane fluidity at different temperatures?
A
- Altering the composition of the phosopholipids
- Unsaturated fatty acids at lower temperatures (increase fluidity with double bonds)
- Saturated fatty acids at higher temperatures (reduce fluidity)
- Desaturation by desaturases to decrease the temperature
14
Q
What are the three major steps involved in neurotransmission across the synapse
A
- Nerve impulse is sent down the presynaptic neuron => depolarization (generating AP)
- Ca2+ channels open => synaptic vesicles fuse and neurotransmitters are released
- NTs bind to postsynaptic neuron’s ligand channel
- Na+ channels => (depolarization), Cl- channels open => (hyperpolarization)
15
Q
Difference between active transport and facilitated diffusion
A
- Active: moves substances against their concentration gradients and requires energy
- Facilitated diffusion: moves substances down their concentration gradients with transport proteins (no energy)
16
Q
What are the steps in an action potential in a neuron?
A
- Resting potential: K+ gradients maintained by Na+/K+ ATPase, inside PM has an excess (-), no net K+ movement
- Deporization: Na+ channels open, membrane potential decreases
- Repolarization: Na+ channels are inactivated (peptide), K+ channels open
17
Q
What are the effects of hyper, hypo and isotonic solutions on cells>
A
- Isotonic: No net water movement
- Hypertonic: There’s a higher [solute] outside the cell, causing the cell to shrink
- Hypotonic: There’s a higher [solute] inside the cell, causing the cell to swell
18
Q
Explain the steps to the conformational states of the Na+/K+ pump in primary active transport
A
-
Inside the cell: [Na+] is low & [K+] is high (vice versa on the outside
1. The pump is open to the inside of the cell (E1) binding 3 Na+
2. ATP binds and changes the conformation (closes to the inside of the cell)
3. ATP is hydrolyzed and the pump opens to the outside of the cell, 3Na+ =>, binds to 2 K+ (E2)
4. The pump is dephosphorylated, releases the two K+ and goes back to E1
19
Q
What are other primary active transport systems besides the Na⁺/K⁺ pump?
A
- Ca²⁺-ATPase: (P-type pump) Actively transports Ca2+ out of the cytosol => ER or out of the cell.
- H⁺/K⁺-ATPase: Found in the stomach lining, secretes H⁺ into the stomach to maintain acidity.
- V-type pumps: Actively transport protons (H⁺) across organelle membranes like lysosomes and vacuoles to maintain pH balance.
20
Q
How is Cystic fibrosis (CF) related to ion channels?
A
- CF is caused by a defect in the CFTR chloride channel
21
Q
Different types of active transport
A
- Primary: Directly uses ATP hydrolysis to move ions against their concentration gradient
-
Secondary (cotransport): Uses energy from an existing ion gradient from the primary AT
- Symport: 2 species moving in the same direction agiainst their concentration gradient
- Antiport: 2 species moving in opposite directions (Na+ in and H+ out)
22
Q
How does the facilitated diffusion of insulin work
A
- An increase in blood glucose stimulates insulin secretion
- Insulin binds to its receptors, this signal triggers GLUTs to move to the cell surface
- The GLUT proteins facilitate glucose into the cell from the bloodstream
23
Q
How does the acetylcholine receptor work, and what are its subunits?
A
- A ring-shaped ligand-gated channel with of 5 subunits: 2 α, 1 β, 1 γ, and 1 δ:
- 2ACh molecules bind to the two α subunits => conformational change, opening the ion channel.
- Na⁺ flow through the channel into the cell, causing depolarization.
- This triggers an action potential
24
Q
What are the three different states of a voltage-gated K⁺ channel?
A
- Closed: The channel is closed, and no ions flow through. Resting membrane potential.
- Open: Depolarization causes the channel to open, allowing K⁺ ions to flow out of the cell (repolarization)
- Inactivated: After being open, the channel becomes inactivated by an inactivation peptide, stopping the ion flow. Resets to the closed state.
25
How is membrane protein mobility controlled?
- Some proteins are **anchored to the cytoskeleton**, restricting their movement.
- Proteins can be restricted by **interacting with neighboring proteins** (limit their movement).
- Proteins embedded in **lipid rafts** (limited mobility—more ordered environment)
- Certain membrane regions have **tight junctions** that limit protein movement to specific areas.
26
How is an action potential propagated along a neuron?
- A neuron is stimulated, voltage-gated Na⁺ channels open, Na⁺ => into the cell, (**depolarization**)
- Na⁺ **influx** creates a current that depolarizes other sections of the membrane, more channels open.
- AP moves along the axon.
- Previous channels are **inactivated** (one direction movement)
- In myelinated axons, the AP jumps between the **nodes of Ranvier**, speeding up propagation
27
What are the building blocks of a phosphoglyceride?
- Glycerol backbone: (three-carbon molecule)
- 2 Fatty acid chains: Attached to the first and second carbons of glycerol; (hydrophobic)
- Phosphate group: Attached to the third carbon of glycerol; this (hydrophilic, polar head)
