Unit 4: Cell Communication and Cell Cycle Study Guide AP BIOLOGY

Essential vocabulary and essential topic focuses, also be able to read and understand a pathway diagram

Positive Feedback

A process in which the effects of a small disturbance amplify through a system, leading to a greater change.

Negative Feedback

A process that counteracts changes in a system, helping to maintain stability and equilibrium.

Homeostasis

The ability of a system to maintain internal stability despite external changes.

Signal transduction

The process by which a cell converts one kind of signal or stimulus into another.

Feedback Loops

Interactions between positive and negative feedback processes that influence system behavior.

Ligand

A molecule that binds to a receptor, initiating a signal transduction pathway.

Receptor protein

A protein that receives and transmits signals from ligands.

Reception

The first step in cell signaling where a cell detects a signaling molecule.

Transduction

The second step in cell signaling that involves the relay of the signal from the receptor to target molecules.

Response

The final step in cell signaling; the actual change or activity within the cell due to signaling.

Juxtacrine

Cell signaling that involves direct contact between cells.

Paracrine

A type of signaling where molecules travel short distances to affect nearby cells.

Endocrine

Long-distance signaling involving hormones that originate from endocrine cells.

Autocrine

A type of signaling where a cell responds to substances it secretes itself.

Target cell

A cell that has the appropriate receptors to respond to a specific ligand.

Protein Modification

Changes to proteins that can affect their function, often by adding or removing chemical groups.

Phosphorylation cascade

A series of events where a protein kinase adds phosphate groups, amplifying the signal.

Kinase

An enzyme that transfers phosphate groups from high-energy donors to specific substrates.

Phosphatase

An enzyme that removes phosphate groups from proteins to regulate signaling pathways.

Cellular Response

The final outcome of a signaling pathway, leading to specific physiological effects.

Amplification

The process by which a small signal is increased significantly through biochemical reactions.

Second messenger

A molecule that relays signals from receptors to target molecules inside the cell.

Cyclic AMP (cAMP)

A second messenger involved in signaling pathways, playing a role in various physiological processes.

G-protein coupled receptor

A family of receptors that transmit signals from outside to inside the cell.

Tyrosine Kinase Receptors

These receptors activate downstream signaling cascades upon ligand binding.

Ion Channel Receptors

Receptors allowing the passage of ions across membranes in response to ligands.

Intracellular receptor

A receptor located within the cell that binds to ligands that penetrate the cell membrane.

Voltage gate

Channels that sustain action potentials by moving Na+ ions across the cell membrane.

Stimulus gate

Mechanism that opens or closes ion channels in response to specific stimuli.

Action potential

Electrical impulses carried along axons, consistent regardless of stimulus strength.

Threshold

The critical stimulus level required to trigger an action potential in a neuron.

Depolarization

A process where the inside of the membrane becomes less negative.

Repolarization

The process by which the membrane returns to its resting potential.

Hyperpolarization

A condition where the inside of the membrane becomes more negative than resting potential.

Sodium Potassium Pump

A mechanism that transports sodium out of and potassium into the cell to maintain resting potential.

Neurotransmitter

Chemicals used for communication between nerve cells.

Auxin

A class of plant hormones influencing plant growth and development.

Continuous Defenses

Ongoing protective mechanisms organisms use against threats.

Inducible Defenses

Protective mechanisms activated in response to specific threats.

Cell cycle

A series of events that cells undergo as they grow and divide.

Interphase

The phase of the cell cycle divided into G1, S, and G2 phases.

Mitosis (M phase)

The phase of the cell cycle that includes the division of the cell's nucleus.

Apoptosis

Programmed cell death that occurs in multicellular organisms.

(a) Describe the role of epinephrine in initiating the signal transduction pathway shown in the diagram.
(b) Explain how the activation of the G protein leads to the production of cyclic AMP (cAMP).
(c) Discuss how the phosphorylation cascade shown in the diagram amplifies the cellular response.

(a) Role of Epinephrine – Epinephrine binds to the receptor on the plasma membrane, initiating the signal transduction pathway. This is the first step in activating the "fight or flight" response. (1 point)

(b) G Protein Activation & cAMP Production – When epinephrine binds to the receptor, the receptor activates the G protein by exchanging GDP for GTP. The activated G protein then stimulates adenylyl cyclase, which converts ATP into cyclic AMP (cAMP), a second messenger. (1 point)

(c) Phosphorylation Cascade & Amplification – cAMP activates protein kinase A, which phosphorylates other kinases in a cascade. Each kinase in the cascade activates multiple downstream proteins, amplifying the response so that a small initial signal leads to a large-scale cellular effect. (1 point)

(a) Identify the second messenger in this pathway and explain its role in signal amplification. (1 point)
(b) Predict how a mutation that prevents the G protein from hydrolyzing GTP to GDP would affect the pathway. (1 point)
(c) Explain one potential mechanism by which this pathway could be downregulated after the fight-or-flight response is no longer needed. (1 point)
(d) Describe how this signaling pathway allows for the breakdown of glycogen into glucose. (1 point)
(e) Explain how this pathway contributes to homeostasis in response to a stressor. (1 point)

(a) Second Messenger & Amplification – The second messenger is cyclic AMP (cAMP). It amplifies the signal by activating multiple protein kinase A molecules, leading to a chain reaction that results in glucose release. (1 point)

(b) Effect of G Protein Mutation – If the G protein cannot hydrolyze GTP to GDP, it will remain active, continuously stimulating adenylyl cyclase. This would lead to excessive cAMP production, overactivation of the pathway, and uncontrolled glucose release. (1 point)

(c) Pathway Downregulation – The pathway can be turned off by breaking down cAMP with phosphodiesterase, deactivating protein kinases, or removing epinephrine from the receptor via receptor endocytosis. (1 point)

(d) Glycogen Breakdown – The phosphorylation cascade activates enzymes that catalyze the breakdown of glycogen into glucose, which can then be used for ATP production in cellular respiration. (1 point)

(e) Homeostasis & Stress Response – This pathway helps maintain homeostasis by ensuring energy is rapidly available during stressful situations. Once the stressor is gone, the body returns to normal energy storage. (1 point)

A researcher is studying the effects of different inhibitors on this signal transduction pathway. They apply an inhibitor that blocks the activity of adenylyl cyclase.
(a) Predict how this inhibitor would affect the production of cAMP and downstream signaling. (1 point)
(b) Describe an experimental setup to test the effect of this inhibitor on glucose production. (2 points)
(c) Identify an alternative step in the pathway where an inhibitor could be applied to achieve a similar effect and justify your choice. (2 points)
(d) Explain how a researcher could determine whether the inhibitor's effects are reversible. (1 point)

(a) Effect of Adenylyl Cyclase Inhibitor – Blocking adenylyl cyclase prevents ATP from being converted into cAMP, which stops activation of protein kinase A and prevents glycogen breakdown into glucose. (1 point)

(b) Experimental Setup –

• Treat one group of cells with epinephrine and another group with epinephrine + the inhibitor.

• Measure glucose concentration in both groups.

• If the inhibitor is effective, the glucose levels in the inhibitor-treated group should be lower than in the epinephrine-only group. (2 points)

(c) Alternative Inhibition & Justification – An inhibitor could also target protein kinase A. This would prevent the phosphorylation cascade from occurring, stopping glycogen breakdown. This is an effective target because it acts immediately downstream of cAMP. (2 points)

(d) Reversibility of Inhibition – To test reversibility, wash the inhibitor-treated cells and expose them to epinephrine again. If glucose production resumes, the inhibitor's effects were reversible. (1 point)