Cell Communication (College Board AP® Biology): Flashcards

Hormone is a ligand that can travel a long distance from its source to bind specific receptors on target cells (endocrine signaling).

Hormones travel a long distance from their source by moving in the blood to reach their target cells.

Insulin is released by the pancreas in response to increased blood glucose. It travels in the blood to the liver, where it binds to receptors on liver cells to increase their uptake of glucose.

False.

They are hormones, which travel long distances in the blood to their target cells (endocrine signaling), not local regulators.

A signal transduction pathway is the sequence of events that links the receipt of a cell signal with a cellular response.

A ligand is a chemical signaling molecule that binds to a specific receptor on or in a target cell.

• Protein modification, e.g. the binding of cAMP can activate enzymes

• Phosphorylation cascades, where adding a phosphate group activates an enzyme and sets off a cascade of reactions

1. Reception of a signal

1. Transduction

1. A cellular response

Cells receive a signal when a ligand binds to the ligand-binding domain of a receptor protein.

True.

A receptor recognizes only its specific ligand; if a cell lacks the specific receptor for a ligand, that ligand will have no effect on the cell.

On the cell surface membrane, or within the cytosol of the target cell.

G protein-coupled receptors are an example of a receptor protein in eukaryotes.

Ligand binding causes a conformational change in the receptor (in its intracellular domain for extracellular receptors), which triggers transduction.

Transduction is the series of chemical changes that occurs inside a cell following signal reception, resulting in an eventual cellular response.

• Kinase enzymes transfer phosphate groups to other molecules to activate them

• Phosphatase enzymes remove phosphate groups from other molecules to deactivate them

A second messenger is a molecule that relays and amplifies the intracellular signal after an extracellular ligand binds, e.g. cyclic AMP (cAMP), produced by adenylyl cyclase.

True.

Each step in a cascade triggers the next, so relaying and amplifying the signal allows a small initial signal to bring about a significant cellular response.

Any of:

• Regulation of gene expression

• Changes in metabolic activity

• Secretion of molecules, e.g. enzymes or hormones

• Cell growth or cell death

Signal transduction is the process by which a signal received at a cell's surface is converted into a specific cellular response inside the cell.

• changes in gene expression

• changes in cell function

• programmed cell death (apoptosis)

Apoptosis is programmed cell death, which can be one outcome of a signal transduction pathway.

Quorum sensing is the process by which bacteria detect the level of released chemical signals as a measure of population density and adjust their cellular processes accordingly.

• Bacteria constantly release chemical signals into their environment

• Individual bacteria detect the level of these chemicals as a measure of population density

• They adjust their cellular processes accordingly, e.g. increasing expression of chemicals that make them better competitors at high density

Epinephrine binds to receptors on liver cells and activates the enzyme adenylyl cyclase, which converts ATP to cAMP.

• Epinephrine binds to specific receptors on the liver cell membrane

• This activates the enzyme adenylyl cyclase, which converts ATP to the secondary messenger cyclic AMP (cAMP)

• cAMP activates protein kinase A, triggering an enzyme cascade

• This ends with glycogen phosphorylase catalyzing the breakdown of glycogen to glucose

True.

cAMP relays the signal inside the cell, activating protein kinase A after epinephrine binds to the cell-surface receptor.

Mutations in any domain of a receptor protein, or in any other component of the pathway, can alter downstream steps, e.g.

• a mutation in the ligand-binding domain may produce a receptor that ligands can no longer bind to

• a mutation in the gene for adenylyl cyclase may prevent formation of cAMP

True.

Such a mutation can change the receptor's shape so that the ligand can no longer bind, blocking the signal from being transduced.

It binds to G-protein-coupled receptors and disrupts the signaling cascade that regulates chloride ion channels, resulting in severe diarrhea.

Cytokines are proteins important in cell signaling that regulate gene expression to allow cell replication and division, e.g. during coordination of the immune response.

In yeast, mating pheromones bind to G protein-coupled receptors, triggering a cascade that leads to transcription of mating-specific genes.

Hox genes code for proteins that regulate transcription during embryonic development, controlling genes involved in cell division, differentiation and apoptosis so that body parts form in the correct place.

Homeostasis is the maintenance of constant internal conditions within suitable limits, in response to internal and external changes.

Feedback mechanism is a process by which an organism detects and responds to change, by receiving information about the environment and initiating an internal response.

Negative feedback, which acts to reverse the effects of change, and positive feedback, which acts to amplify the effects of change.

Negative feedback is a mechanism that maintains a constant internal environment by reducing the initial stimulus, returning a system back to its target set point.

True.

If a variable deviates from normal levels, negative feedback activates processes that bring it back toward the set point, e.g. lowering body temperature when it rises.

Negative feedback processes operate at the molecular, cellular and whole organism level.

Insulin is released by the pancreas and binds to target cells, which:

• increases uptake of glucose from the blood

• converts glucose into glycogen

• increases glucose metabolism

Glucagon is released by the pancreas and binds to target cells, which:

• converts glycogen into glucose

• converts other biological molecules into glucose

Positive feedback is a mechanism that amplifies change, moving a variable further away from its set point and intensifying the stimulus.

False.

Positive feedback amplifies change, moving the variable further away from the set point; it is negative feedback that returns a system to its set point.

Ethylene gas produced by a ripening fruit diffuses to neighboring fruits, triggering further release of ethylene, so the ripening of one fruit encourages the ripening of others.

Oxytocin stimulates uterine contractions; stretch receptors in the cervix detect these and signal the pituitary gland to release more oxytocin, causing further contractions until childbirth.

In lactation, suckling stimulates production of the hormone prolactin, which leads to milk production and increased suckling.