Chapter 9 - cell communication

Question 1

cell communication

Answer 1

• the process of cells detecting and responding to signals in the extracellular environment

Question 2

how do receptors translate the signal from outside to inside the cell?

Answer 2

• when the signal attaches, the receptor changes conformation

Question 3

ligand

Answer 3

• signaling molecule binds to a protein, such as an enzyme, a receptor, or a channel
• signaling molecule

Question 4

what happens to a receptor when a ligand binds to it?

Answer 4

• it changes conformation

Question 5

Cell surface receptors

Answer 5

• receptors found in the plasma membrane that enables a cell to respond to different kinds of extracellular signaling molecules

Question 6

enzyme- linked receptors

Answer 6

• found in all living species
• extracellular domain binds to signal
• intracellular domain becomes functional catalyst
• most are protein kinases

Question 7

why is cell signaling important?

Answer 7

• allows the cell to respond to a changing environment

Question 8

explain yeast cell response to glucose

Answer 8

• glucose attaches to glucose receptors
• receptors cause response inside cell to produce glucose transporters and enzymes to metabolize glucose
• without the presence of glucose, these genes stop being expressed

Question 9

phototrophism

Answer 9

• cellular response to allow the plant to bend towards the sun
• triggered by auxin

Question 10

auxin

Answer 10

• signaling molecule for phototropism
• inhibited by light
• transmitted from cell to cell

Question 11

direct intercellular signaling

Answer 11

• cell junctions allow signaling molecules to pass from one cell to another
• pass directly from the cytosol of one cell to the next

Question 12

contact-dependent signaling

Answer 12

• molecules bound to the surface of cells serve as signals to cells coming in contact with them

Question 13

autocrine signaling

Answer 13

• cells secrete signaling molecules that bind to their own cell surface or similar neighboring cells

Question 14

paracrine signaling

Answer 14

• signal does not affect originating cell but does influence nearby cells

Question 15

endocrine signaling

Answer 15

• signals called hormones travel long distances and are usually longer lasting in effect

Question 16

three stages of cell signaling

Answer 16

1. receptor activation
   - signaling molecule binds to receptor
2. signal transduction
   - activated receptor stimulates a sequence of changes
   - done via signal transduction pathway
3. cellular response
   - different responses possible
   
   • change enzyme activity
   • change function of structural proteins
   • change gene expression

Question 17

describe the binding between a receptor and a ligand

Answer 17

• highly specific
• non covalent
• rapid bond and release
• causes conformational change, which causes the ligand to detach

Question 18

three types of cell surface receptors

Answer 18

1. enzyme-linked receptors
2. G-protein coupled receptors (GPCR)
3. ligand gated ion channels

Question 19

Enzyme linked receptors

Answer 19

• found in all living species
• extracellular domain binds to signal
• intracellular domain becomes functional catalyst
• most are protein kinases (phosphorylates things)

Question 20

G-protein coupled receptors (GPCR)

Answer 20

• found in all eukaryotic cells
• has 7 transmembrane segments
• when activated by a signaling molecule, binds to G proteins to replace GDP with GTP
• alpha and beta/y subunits separate and can promote cellular responses

Question 21

kinase

Answer 21

• enzyme that phosphorylates things
• takes a phosphate and attaches it to something else

Question 22

Ligand-gated ion channels

Answer 22

• found in plant and animal cells
• ligand binding causes the channel to open and ions flow through
• used in synaptic signals between neurons and muscles or between two neurons
• allows the body to create current/action potentials

Question 23

intracellular receptors

Answer 23

• some receptors such as estrogen are inside the cell
• hormone passes through the membrane and into the nucleus where it binds to the estrogen receptor

Question 24

what is phosphotase

Answer 24

removes phosphates

Question 25

Signal transduction pathways (what causes them and what they do)

Answer 25

- signaling molecule binds to the cell surface receptor, causing conformation change on the inside of the cell - some lead to kinase cascade - some cause generation of second messengers (relay signal to proteins)

Question 26

Receptor tyrosine kinase (RTK)

Answer 26

- category of enzyme-linked receptors found in animals - can target certain amino acid called tyrosine to phosphorylate it - ex: growth factor

Question 27

Epidermal growth factor (EGF) pathway

Answer 27

- growth factor stimulates cell growth or division - mostly stimulates epidermal cells to divide but has other functions - binding of EGF signal to receptor triggers protein kinase cascade all to way to nucleus, where cellular response occurs

Question 28

what does RAS do?

Answer 28

- GDP is replaced with GTP to activate RAS - actives a protein kinase cascade - has auto GTPase activity to prevent cell from uncontrollable dividing - mutations in raw are associated with most cancers because it inhibits the GTPase activity

Question 29

cAMP

Answer 29

- epinephrine binds to signaling molecule - alpa subunit of G protein binds to adenylyl cyclase, which stimulates cAMP from ATP - cAMP binds to regulatory subunits of PKA, releasing the catalytic subunit - catalytic subunits of PKA can phosphorylate other proteins, which causes cellular response

Question 30

second messengers

Answer 30

- small molecules or ions that relay signals inside the cells - produced quickly and duration is short - ex: cAMP

Question 31

synthesis and breakdown of cAMP

Answer 31

- synthesis is triggered by an alpha subunit of a G protein binding to adenylyl cyclase - adenylyl cyclase makes cAMP out of ATP - cAMP is inactivated by phosphodiesterase - converts cAMP back to AMP

Question 32

adenylyl cyclase

Answer 32

- synthetic enzyme responsible for the synthesis of cAMP

Question 33

phosphodiesterase

Answer 33

- breaks down cAMP

Question 34

advantages of cAMP

Answer 34

- signal can be easily amplified - activates lots of PKA, which leads to more phosphorylation of proteins - fast - substantial amount of cAMP can be made within 20 so the signal

Question 35

How does hormone signaling work in multicellular organisms

Answer 35

- hormones are spread to lots of cells via endocrine signaling - response to the signal depends on which cell is responding - variation in response is determined by the proteome - ex: epinepherine

Question 36

differential gene expression

Answer 36

- all cells contain the same genome but only express particular genes effects cellular response by: 1. receptor may not be expressed 2. different receptors for the same signal 3. different affinities for signal 4. signal transduction pathways different

Question 37

apoptosis (general)

Answer 37

- programmed cell death - nucleus and cytoskeleton destroyed, causing cell to shrink - plasma membrane forms blebs that break away - macrophages take blebs away

Question 38

caspase

Answer 38

- drives apoptotic cascade - inactive version is procaspases - cleaves cellular protein, causing cell to shrink and form blebs

Question 39

Apoptosis through signal transduction

Answer 39