Unit 4: Cell Communication and Signaling

Question 1

ligand

Answer 1

chemical signals that start off signal transduction; interact with target cells; may be hydrophilic or hydrophobic

Question 2

autocrine signaling

Answer 2

cell SECRETES a ligand; ligand binds to a receptor on the cell that secreted the ligand, triggering a response within the cell; REMEMBER: auto = self - cell signaling itself to generate a response; ex. cancer cell

Question 3

juxtacrine signaling

Answer 3

depends on DIRECT CONTACT between the cell sending the ligand and the cell receiving and responding to the ligand via a surface receptor; ex. plasmodesmata in plants (ligands move through channels connecting the plants) and antigen-presenting cells in the immune system (signal helper T cells through direct cell-to-cell contact)

Question 4

paracrine signaling

Answer 4

cell secretes a ligand that travels a SHORT DISTANCE, eliciting an effect on cells in the nearby area; these ligands are referred to as LOCAL REGULATORS as they only affect cells in the immediate vicinity of the cell sending the signals; ex. neurotransmitters that travel across a synapse

Question 5

endocrine signaling

Answer 5

some ligands travel a LONG DISTANCE between the sending and receiving cells; these are called HORMONES; ex. insulin is produced and released by the pancreas then travels through the circulatory system to trigger responses in cells throughout the body

Question 6

signal transduction

Answer 6

determines how a cell responds internally to a signal in its environment; important processes like gene expression, cell growth & division, and hormone release depend on this

Question 7

target cells

Answer 7

respond to the presence of a ligand after interacting with one

Question 8

hydrophilic ligands

Answer 8

cannot cross the phospholipid bilayer of the cell membrane and enter the cell; interact with cell membrane receptors to trigger a series of chemical reactions inside the cell

Question 9

hydrophobic ligands

Answer 9

enter the cell by sliding between the phospholipids of the cell membrane; bind to intracellular receptors in the cell’s cytosol; after binding, the ligand can then cross the nuclear membrane and bind to the DNA in the nucleus to change the expression of genes

Question 10

signal transduction’s three major steps

Answer 10

reception, transduction, response

Question 11

reception

Answer 11

ligand binds to specific receptor in/on target cell; receptors contain ligand-specific binding domains (if a cell doesn’t have the receptor for a specific ligand, the cell will not respond to that ligand); upon ligand’s binding to the receptor, the receptor undergoes a conformational shape change that triggers the next step in the cell’s processes

Question 12

G-protein coupled receptors

Answer 12

one of three major types of cell-surface transmembrane receptors; work with cytoplasmic G proteins; ligand binding activates the receptor, which activates a specific G protein, which activates another protein, propagating the signal

Question 13

receptor tyrosine kinases

Answer 13

one of three major types of cell-surface transmembrane receptors; react to the binding of signaling molecules by forming dimers, then adding phosphate groups to the tyrosines on the cytoplasmic part of the other monomer making up the dimer; relay proteins in the cell can then be activated by binding to different phosphorylated tyrosines, allowing this receptor to trigger several pathways at once

Question 14

ligand-gated ion channels

Answer 14

one of three major types of cell-surface transmembrane receptors; open or close in response to binding by specific signaling molecules, regulating the flow of specific ions across the membrane

Question 15

intracellular receptors

Answer 15

cytoplasmic or nuclear proteins; signaling molecules that are hydrophobic or small enough o cross the plasma membrane bind to these receptors inside the cell

Question 16

transduction

Answer 16

series of chemical reactions (triggered by the binding of the ligand to its receptor) that helps the cell choose the appropriate response; most complicated part of signal transduction; possible components include signaling cascades, kinases, phosphatases, and enzymes

Question 17

signaling cascades

Answer 17

a series of chemical reactions in which one molecule activates multiple molecules, amplifying the cell’s response to a signal (process known as signal amplification)

Question 18

phosphorylation cascade

Answer 18

when a series of protein kinases each add a phosphate group to the next one in line, activating it

Question 19

kinases

Answer 19

can transfer phosphate groups to other molecules, which activate those molecules (opposite of phosphatases)

Question 20

phosphatases

Answer 20

can remove phosphate groups from other molecules, which inactivates those molecules (opposite of kinases)

Question 21

enzymes (in cell communication)

Answer 21

produce secondary messengers; ex. adenylyl cyclase, which produces the secondary messenger cyclic AMP (cAMP) from ATP

Question 22

secondary messengers

Answer 22

diffuse throughout the cytosol to help signals broadcast quickly

Question 23

response

Answer 23

final step of signal transduction and ultimate result generated by the ligand; examples of cellular responses: activation of genes by steroid hormones, opening of ligand-gated ion channels, and the initiation of cell processes (like apoptosis); terminated by reversal of ligand bonding

Question 24

signal transduction pathways

Answer 24

series of chemical reactions that mediate the sensing and processing of stimuli

Question 25

long-distance signaling

Answer 25

includes hormones that are hydrophobic and can cross the membrane; once inside the cell, the hormone attaches to a protein, which brings it to the nucleus, where transcription can be stimulated

Question 26

disruptions to signal transduction pathways

Answer 26

(1) since receptors are specific to certain ligands, a mutation in a gene meant to code a receptor protein could result in changing the receptor’s shape to stop it from binding to its specific ligand; without a functional receptor for the ligand, the cell with the mutated receptor protein would not be able to respond to the ligand; (2) disruption can occur when molecules in the environment interfere with a ligand’s ability to bind to its receptor; (3) mutations in the gene for adenylyl cyclase can interfere with a cell’s ability to produce the secondary messenger cAMP, disrupting all steps in the signal transduction process that depend on that secondary messenger; (4) a disruption to any step in the signal transduction process will affect not only that step but will also affect any subsequent steps the process that are dependent on the products of the previous steps

Question 27

feedback mechanisms

Answer 27

help living organisms respond to changes in the environment while maintaining the internal environment of the cell; cell communication and signaling are crucial in feedback mechanisms

Question 28

negative feedback

Answer 28

returns a system to its original condition and helps maintain homeostasis; ex. (1) if the body temp is too high, cell signaling processes will trigger sweat release (2) control of blood glucose levels by insulin and glucagon: if blood sugar levels get too high, the pancreas releases insulin, which causes body cells to absorb glucose from the blood; the opposite happens with glucagon if the levels are too low

Question 29

positive feedback

Answer 29

magnifies cell processes; ex. oxytocin stimulates contractions of the uterine muscles in contractions during childbirth, and this contraction triggers the production of even more oxytocin, which in turn increases contractions of the uterine muscles (increases on both sides in a repeating cycle)

Question 30

scaffolding proteins

Answer 30

increase signaling efficiency