B2.1 Cell membrane
What is the role of an aquaporin?
A Channel protein for water
B Movement of ions against their concentration gradient
C Movement of glucose down a concentration gradient
D Moving water out, not into, a cell
A Channel protein for water
What is the name given to the molecule that binds to the particular three-dimensional structure of a receptor site?
A Ligand
B Scaffold protein
C Ion channel
D G protein
A Ligand
List the 6 transport mechanisms that we covered when a neuron cell goes through depolarization, repolarization leading to the release of a neurotransmiter. Also state their location!
Ligand-gated channel at dendrites,
Na vgc at axon
K vgc at axon
na/k pump at axon
Ca vgc at axon terminal
Exocytosis of neurotransmitter at terminal end
Which features of phospholipids give them theri amphipathic properties?
A Acidic phosphate groups and basic lipids
B Basic phosphate groups and acidic lipids
C Hydrophobic phosphate groups and hydrophilic fatty acids
D Hydrophilic phosphate groups and hydrophobic fatty acids
D
Hydrophilic phosphate groups and hydrophobic
fatty acids
Which one of the following is the best description of cell signalling in multicellular organisms?
A Intracellular
B Intercellular
C Both intercellular and intracellular
D Neither intercellular or intracellular
C Both intercellular and intracellular
What occurs during the transmission of an impulse at a synapse?
I. Acetylcholine is released into the synaptic cleft by exocytosis when calcium ions enter the presynaptic neuron.
II. Acetylcholine diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane.
III. Acetylcholine is broken down by cholinesterase and resorbed into the presynaptic neuron once an impulse has been initiated on the postsynaptic membrane.
What occurs during the transmission of an impulse at a synapse?
I. Acetylcholine is released into the synaptic cleft by exocytosis when calcium ions enter the presynaptic neuron.
II. Acetylcholine diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane.
III. Acetylcholine is broken down by cholinesterase and resorbed into the presynaptic neuron once an impulse has been initiated on the postsynaptic membrane.
Nicotinic acetylcholine receptors are an example of:
A Voltage-gated potassium channels
B Voltage-gated sodium channels
C Ligand–receptor interaction
D Neurotransmitter-gated ion channels
D Neurotransmitter-gated ion channels
Which substance can act as a second messenger?
A A kinase
B ADP
C Cyclic AMP
D A peptide hormone
C Cyclic AMP
Why causes the difference between na voltage gated channels opening and k voltage gated channels opening?
They both are stimulated to open based on cell charge change of -55mV. But, it takes the k+ vgc longer to open than the na vgc
Cholesterol is found in the cell membrane. An experiment was carried out to investigate the effects of temperature on the fluidity of the membrane.
Explain the effects of cholesterol on membrane fluidity at different temperatures. (5 marks)
Cholesterol affects membrane fluidity by forming strong interactions with phospholipids; cholesterol in the bilayer orientates itself with its polar head group facing the aqueous external cell environment and its non-polar region facing the interior of the membrane; one of cholesterol’s functions is to reduce the fluidity of the membrane by forming strong interactions with phospholipids using its rigid steroid ring structure; cholesterol lowers membrane fluidity at high temperatures; cholesterol increases membrane fluidity at low temperatures; at high temperatures, these interactions harden the membrane and interfere with phospholipid mobility; at low temperatures, the flexible, nonpolar tail of cholesterol interferes with the tight packing of adjacent phospholipid chains maintaining membrane fluidity.
Why do many signal transduction pathways use second messengers?
A To amplify the message by directly phosphorylating proteins
B To induce a signal from the outside to the inside of the cell
C To relay the message from the inside of the membrane throughout the cytoplasm
D To transport a signal through the lipid bilayer portion of the plasma membrane
C To relay the message from the inside of the membrane throughout the cytoplasm
How do exogenous chemicals affect synaptic transmission?
A Causing vesicles to fuse to the presynaptic membrane
B Increasing the concentration of cholinesterase
C Causing a reduction in the diameter of the synaptic cleft
D Blocking reuptake of the neurotransmitter
D Blocking reuptake of the neurotransmitter
Describe four types of membrane transport, including their use of energy. (6 marks)
Simple diffusion is passive movement of molecules/ions along a concentration gradient; facilitated diffusion is passive movement of molecules/ions along a concentration gradient/down a concentration gradient through a protein channel (without use of energy); osmosis is the passage of water through a membrane from lower solute concentration to higher; water can move though the phospholipid bilayer or through aquaporins; active transport is movement of molecules/ions against the concentration gradient (through membrane pumps) with the use of ATP/energy; sodium–potassium pumps use active transport to move sodium and potassium ions against their concentration gradient.
HL only: endocytosis is the infolding of membrane/formation of vesicles to bring molecules into a cell
with the use of energy OR exocytosis is when vesicles fuse with the membrane to release molecules from
the cell with use of energy; chemiosmosis occurs when protons diffuse through ATP synthase (in the
membrane) to produce ATP.
Explain the signal transduction pathway of a muscle cell when insulin binds to it. (5 marks)
Insulin secreted by the beta cells of the pancreas will travel to muscle/liver cells and will bind to the Receptor Tyrosine Kinase (RTK), as a response this causes a cascade of phosphorylations leading to the activation of vesicles containing GLUT-4 (glucose recetors) to fuse with the cell membrane, and embed GLUT 4 so that the cell can now accept glucose
Explain neuron communication starting with presynaptic neuron releasing the neurotransmitter acetylcholine. (8 marks)
Neurotransmitter attaches to receptor site, initiating transmission; nerve impulses are action potentials propagated along the axons of neurons; resting potential is more negative inside/−70 mV/more positive outside the membrane OR a resting potential has greater concentration of Na+ ions outside than K+ ions inside the axon; (voltage-gated) channels open and Na+ ions diffuse in; causes depolarization of the membrane/−70 mV to +40 mV; local currents affect adjacent channels/cause action potential; depolarization is followed by repolarization of the neuron; (voltage-gated) channels open and K+ionsdiffuse out/repolarize the membrane; Na+ /K+ pumps restore Na+ /K+ balance/resting potential; myelin around the neuron insulates the axon OR speeds the transmission; myelin permits saltatory conduction OR permits jumping from node to node.