BIOL. 1406: CH11 Cell Communication

Question 1

Quorum Sensing

Answer 1

a process that allows bacteria to sense local population density through concentration of signaling molecules

Question 2

Example of Quorum Sensing

Answer 2

fromation of biofilm

Question 3

Biofilm

Answer 3

aggregation of bacterial cells adhered to a surface

Question 4

Local and Long-Distance Signaling

Answer 4

cells in a multicellular organism communicate via signaling molecules

Question 5

Local Signaling

Answer 5

paracrine signaling;
animal cells communicating by direct contact;

Question 5

Growth Factors

Answer 5

local regulators in animals that stimulate nearby target cells to grow and divide

Question 6

Synaptic Signaling

Answer 6

process that occurs in animal nervous system when a neurotransmitter is release in response to an electric signal

Question 7

Hormones

Answer 7

molecules released by plants and molecules in long-distance signaling

Question 8

Hormonal (Endocrine) Signaling

Answer 8

hormones travel to target cells via the circulatory system;
the ability of cell to respond to a signal depends on whether or not the cell has a receptor specific to that signal

Question 9

Three Steps of Cell Signaling

Answer 9

1) signal reception
2) signal transduction
3) cellular response

Question 10

Signal Reception

Answer 10

the target cell detects a signaling molecule that binds to a receptor protein on the cell surface

Question 11

Signal Transduction

Answer 11

binding of the signaling molecule altering the receptor and initiating a signal transduction pathway;
it often occurs in a series of steps

Question 12

Cellular Reception

Answer 12

transduced signal triggering a specific response in the target cell

Question 13

Signal Reception

Answer 13

the binding between a signal molecule (ligand) and receptor is highly specific;
a shape change of the receptor is usually the first step in the transduction of the signal;
most signal receptors are plasma membrane proteins, but other are located inside the cell

Question 14

3 Main Membranes of Plasma Membrane Receptors

Answer 14

1) G protein-coupled receptor
2) receptor tyrosine kinase
3) ion channel receptor

Question 15

Receptors in the Plasma Membrane

Answer 15

most water-soluble signal molecules bind to specific sites on receptor proteins that transmit information from the extracellular environment to the inside of cell;
G protein-coupled receptors are the largest group of plasma membrane receptors

Question 16

G protein-coupled receptor

Answer 16

is a cell-surface transmembrane receptor that works with the help of a G-protein;
G proteins bind the energy rich GTP;
G proteins are very similar in structure;
GPCRs are widespread and diverse in their functions

Question 17

Receptor Tyrosine Kinase (RTK)

Answer 17

a membrane receptor that catalyzes the transfer of phosphate groups from ATP to another protein;
this receptor can trigger multiple signal transduction pathways at once;
abnormal functioning of this receptor is associated with many types of cancers

Question 18

Ligand-Gated Ion Channel

Answer 18

receptor that acts as a gate that opens and closes when the receptor shape changes;
when a signal molecule binds as a ligand to the receptor, the gate allows specific ions to pass through

Question 19

Intracellular Receptor Protein

Answer 19

receptor that is found in cytoplasm or nucleus inside target cell;
small or hydrophobic molecules can cross the membrane t activate this type of receptor;
examples of hydrophobic messengers: steroid and thyroid hormones of animals;
an activated hormone-receptor may act as a transcription factor, turning on or off specific genes

Question 20

Signal Transduction

Answer 20

cell signaling is usually a multistep process;
multistep processing can greatly amplify a signal;
multistep pathways provide more opportunity for coordination and regulation of cellular response

Question 21

Signal Transduction Pathway

Answer 21

the binding of a ligand molecule to a receptor triggers the first step in a chain of molecular interactions;
the activated protein activates another, which in turn activates the next one until the the one producing the cellular response is activated;
at each step, the signal is is transduced into a different form (usually in the form of protein shape change)

Question 22

Phosphorylation and Dephosphorylation

Answer 22

Commonly used to regulate protein activity;
system that works as a molecular switch, turning activities on or off, up or down, as required

Question 23

Protein Kinase

Answer 23

transfer phosphates from ATP to a protein in a process of phosphorylation

Question 24

Phosphorylation Cascade

Answer 24

many relay molecules in signal pathways, which are protein kinases

Question 25

Protein Phosphatases

Answer 25

proteins that rapidly remove a phosphate group in a process of dephosphorylation

Question 26

Second Messengers

Answer 26

small, non-proteins, water soluble molecules or ions that spread throughout the cell by diffusion;
participate in pathways initiated by GPCRs and RTKs;
cAMPs and calcium ions serve as ones

Question 27

Adenylyl Cyclase

Answer 27

an enzyme in the plasma membrane that converts ATP to cAMP in response to an extracellular signal;
regulation of cell metabolism is provided by G protein systems that inhibit its activity

Question 28

Cyclic AMP (cAMP)

Answer 28

a molecule produced from ATP; it is one of the most widely used second messengers;
many small molecules trigger its formation;
components of its pathways are GPCR, GP, and protein kinases;
it activates protein kinase A that phosphorylates a protein

Question 29

Cholera Bacterium

Answer 29

vibrio cholerae;
it produces a toxin that modifies G protein, so it is stuck in its active form;
the protein continually makes cAMP, causing the intestinal walls to secrete salt;
water follows by diffusion;
if untreated a person can die from loss of salt and water

Question 30

Calcium Ions and Inositol Triphosphate (IP3)

Answer 30

Ca+ ions are used widely as second messengers (even more than cAMPs);
its concentration is much lower in cytosol;
diffusion results in great change of concentration;
a signal relayed by signal transduction pathway may trigger the release of Ca+ into the cytosol;
pathways leading to the release of Ca+ ions involve inositol triphosphate (IP3) and diacyglycerol (DAG) as additional second messengers;
IP3 and DAG are produced by cleavage of certain kind of phospholipid in the plasma membrane

Question 31

Cellular Response

Answer 31

cell signaling leads to regulation of transcription or cytoplasmic activities

Question 32

Output Response

Answer 32

a cell’s response to an extracellular signal

Question 33

Nuclear and Cytoplasmic Responses

Answer 33

a cell transduction leads to regulation of one or more cellular activities;
signal molecules, relay molecules, second messengers participate in a variety of pathways that lead to the following responses

Question 34

Nuclear Responses

Answer 34

many signaling pathways regulate the synthesis of enzymes or other proteins by turning genes on or off inside the nucleus;
the final activated molecule in a signaling pathway acts as a transcription factor

Question 35

Regulation of the Response

Answer 35

a response to a signal may not be simply on or off;
there are four aspects of its regulation:
1) amplification of the response
2) specificity of the response
3) overall efficiency of response (enhanced by scaffolding proteins)
4) termination of the signal

Question 36

Signal Amplification

Answer 36

enzyme cascades amplify the cell’s response to a signal;
at each step, the products are much greater than in the preceding one

Question 37

Specificity of Cell Signaling and Coordination of the Response

Answer 37

different kinds of cells have different kinds of proteins;
these different proteins allow cells to detect and respond to different signals;
the same signal can have different effects in cells with different proteins and pathways;
pathway branching and cross-talk help cell further coordinate incoming signals

Question 38

Signaling Efficiency

Answer 38

Scaffolding Proteins and Signaling Complexes

Question 39

Scaffolding Proteins

Answer 39

large relay proteins to which other proteins are attached;
increase signal transduction efficiency by grouping together different proteins involved in the same pathway;
in some cases, may also help activate some relay proteins

Question 40

Termination of the Signal

Answer 40

inactivation mechanisms are essential part of cell signaling;
if the concentration of extracellular signaling falls fewer receptors are activated;
unbound receptors revert to an inactive state

Question 41

Apoptosis

Answer 41

cells that are infected, damaged, or at the end of the functional lives often undergo “programmed cell death”;
components of cells are chopped up and packaged into vesicles that are digested by scavenger cells;
it prevents enzymes from backing out of dying cells and damaging neighboring cells

Question 42

Apoptosis in Soil Worm Caenorhabditis Elegans

Answer 42

is triggered by signals that activate a cascade of suicide proteins in cells destined to die;
a protein Ced-9 in the outer mitochondrial membrane serves as a master regulator of this process;
when death signal is activated Ced-9 (apoptosis-inhibiting protein) is inactivated;
a pathway activates proteases and nucleases that cut up proteins and DNA of cell;
main proteases are caspases (the chief caspase is Ced-9)

Question 43

Apoptotic Pathways and the Signals that Trigger Them

Answer 43

in humans and other mammals, several different pathways, involving about 15 caspases, can carry out apoptosis;
apoptosis may be triggered by external or internal signals;
internal signals result from excessive protein misfolding or irreparable DNA damage;
apoptosis is essential in animal evolution and is essential in development and maintenance;
ex: formation of hands and feet;
apoptosis may be involved in some diseases (Parkinson’s, Alzheimer’s, etc)

Question 44

Relay Molecules

Answer 44

Simply pass signal onto the next member in the chain