Bio 256 Actual Exam Questions with Correct Answers
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Course
BIO 256
Institution
BIO 256
Bio 256 Actual Exam Questions with Correct Answers
Signal Transduction Mechanisms - Answer-• Cell-‐cell contact signaling - important in normal development and immunity
• Electrical signaling
- voltage-‐gated ion channels
in nerve and muscle tissue
- Channel opens in response to a ...
Bio 256 Actual Exam Questions with Correct Answers
Signaling between Cells - Answer-• Cell-to-cell -
cytoplasms connected via gap junctions
• Paracrine - signal diffuses to nearby target cell
• Autocrine - signal substance affects secretory cell
• Synaptic - neuron's axon terminal secretes neurotransmitter, diffuses to postsynaptic cell (through the synapse)
• Endocrine - endocrine gland secretes hormone into blood and reaches target cell through circulatory system
Chemical concentration
gradient - Answer-- Molecules move from area of high concentration to areas of lower concentration
- May have differing
concentrations across membrane due to permeability
Cell Membrane Potential - Answer-• Voltage across a membrane due to
differential concentration and charges
of ions inside/outside the cell
•Resting membrane potential, when
cell is not participating in signaling
- Ranges from -20 to -200 mV
- Neuron -‐70 mV, muscle - 95 mV
-Results from Na+, K+, and other charged molecule concentration
gradients across membrane
- Differential permeability of the plasma membrane to Na+ and K+
Resting Membrane Potential - Answer-• Resting membrane potential established by:
- passive, or leakage, channels - always open
(relatively
uncommon)
- ion pump action
• Especially
Sodium Potassium Pump: 3 Na+
out 2 K+ in,
one ATP used
- More + out than in → negativity, "electrogenic
pumping" • Also Ca++ is pumped out by Ca++ pumps working constantly in cell, ATP used
• Resting potential - membrane is
polarized - negative mV at rest
• Resting potential maintained by active transport of ions against concentration gradients
• If Na+ permeability increases then
the membrane
depolarizes (positive
change in mV)
→ activated cell
Signal Transduction Mechanisms - Answer-• Cell- ‐cell contact signaling - important in normal development and immunity
• Electrical signaling
- voltage-‐gated ion channels
in nerve and muscle tissue
- Channel opens in response to a change in the
membrane potential
• Voltage across a membrane due to differential
concentration and charges of ions inside/outside the cell
• Chemical signaling - ligand gated ion channels
detect a chemical such as a hormone
- Channel opens due to binding of correct chemical
Opera;on of a Voltage- ‐Gated Channel - Answer-Voltage- ‐gated channels - open and close in
response to a change in membrane potential
•When gated channels are open:
- Ions diffuse quickly across membrane down their
electrochemical gradients
- Electrical current created
- Voltage changes the membrane potential - ‐
depolarization
• Example: Na+ channel
• "Activation gate" closed
when intracellular
environment negative mV
- Na+ cannot enter cell
• Opens when
intracellular
environment positive mV
- Na+ can enter cell
Ligand
Gated Ion Channels - Answer-• Results in "graded potentials" or localized change in membrane potential
• Magnitude reflects the intensity of the stimulus
• Open when neurotransmitter is attached to receptor
Movement down
a concentration
gradient.
• Example: Na+‐K+ gated
channel
• Closed when
neurotransmitter not bound to extracellular
receptor
- Na+ cannot enter the cell and K+ cannot exit the cell
• Open when
neurotransmitter is attached to receptor - Na+ enters the cell and K+ exits the cell
Signal Propagation in Chemical Signaling - Answer-• Metabotropic receptors - act through a second messenger system and usually linked to a G protein
• G protein-linked receptors - extracellular ligand (primary
messenger), binds to a specific plasma membrane protein receptor → activates an intracellular G protein, causing a signaling cascade inside the cell:
- Closing/opening of ion channels
- Synthesis of a
diffusible second messenger, such as cyclic
AMP (cAMP)
Primary Signal Molecules and Second Messengers - Answer-• Nonpolar primary signal molecule (e.g. steroid hormone) - ‐ diffuses through membranes may effect gene expression directly
• Polar primary signal molecule - ‐ binds receptors on plasma membrane
• Second messengers relay signals from receptors on the cell surface to target molecules inside the cell
Common Second Messengers - Answer-• Inositol triphosphate (IP3) cleaved from cell
membrane and diffuses from into cytosol to
increase Ca2+ concentrations in cytoplasm
• cAMP made from ATP by the enzyme adenylyl cyclase, regulates many cellular processes
Signal Amplification - Answer-- Primary messenger
starts the cascade
- Second messenger
amplifies the signal
by activating further enzymes in a
pathway
- One primary
signaling molecule impacts the activity of millions of
proteins
Neurons - Answer-• Neurons - ‐ transmit nerve impulse as
ac.on
potentials
- Information travels from dendrite to cell body to axon
- Action potential flows down length of the axon
• Glial cells -‐ support neurons
- Schwann cells - ‐ produce myelin sheath
of PNS
-Oligodendrocytes -‐ form myelin sheath of CNS,
"white matter"
• Myelin sheath is electrically conductive
Membrane Potentials - Answer-• Integrate, send, and receive information
• Membrane potential changes produced by:
- Changes in membrane permeability to ions
- Alterations of ion concentrations across membrane
• Types of signals
- Graded potentials - small, localized changes in
membrane potential due to, and in proportion to, a
stimulus. Initiates an ac.on potential in a neuron.
- Action potentials ‐ neuron sends an impulse, an all-or ‐nothing phenomenon.
Graded Potentials - Answer-• Short- ‐lived, localized changes in membrane potential
typically due to opening of
ligand-‐gated channels
• Decrease in intensity with distance from site of stimulus
• Magnitude varies directly with strength of stimulus
- can be summed over time, "temporal summation"
- can be summed over multiple inputs of stimulus,
"spatial summation"
• Sufficiently strong depolarizing graded potentials can
initiate action potentials
• Voltage changes in
graded potentials die
out quickly due to leaky plasma membrane
• May be depolarizing or
hyperpolarizing
• If propagated due to
stimulus from another neuron = post- ‐synaptic
potential
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