Chapter (11) - Cell Communication/Signal Transduction

Question 1

Can cells take multiple signaling molecules at once? What happens with different signaling molecules?

Answer 1

Of course they can!

Different combinations of signaling molecules lead to different outcomes (survival, differentiation, division)

Lack of signals usually leads to apoptosis

Question 2

Can unicellular organisms communicate? Is it important for them? Give an example of unicellular organisms communicating and explain what happens.

Answer 2

Unicellular organisms communicate all the time!

Yeast cells can mate by exchanging mating factors

1) yeast cells a and alpha exchange their signaling molecules, which bind to the other cell

2) yeast cell a and alpha fuse and mate

3) now a new a/alpha cell is made

Question 3

What is quorum sensing? (example of unicellular organisms communicating)

Answer 3

Quorum sensing is a concentration of signaling molecules that allows bacteria to sense local population density.

ROD CELLS can clump up together and form a spore-forming structure and release fruiting bodies.

This is favorable for their survival.

Question 4

What is local signaling (direct)? How is it achieved? (2 ways)

Answer 4

local signaling is between adjacent cells

Achieved by
1) cell junctions (gap junctions in animal cells and plasmodesmata between plant cells)

cytoplasm has continuity between the cells. so things can move quickly between

2) cell-cell recognition by receptors

Question 5

local signaling (with no direct contact). (what is it called? how is it achieved)

Answer 5

cells can secrete signals to other cells nearby
this is called paracrine signaling

Question 6

local signaling in the brain

Answer 6

1) axon extends from the cell body
2) neurotransmitters travel across the synapse cleft (cleft refers to the gap between the cells) to the target cell

Question 7

what is it called when the cell secretes a signal and the signal modulates the cell itself

Answer 7

Autocrine signaling! can lead to behavioral modification

Question 8

whta is longer distance signaling?

Answer 8

endocrine signaling!

1) endocrine cells secrete signals that travel thru blood stream
2) signaling molecules contact the target cell

Question 9

non polar signaling molecules (can they go thru membrane? where do they bind)

Answer 9

non polar signals can diffuse through the membrane and bind to cytoplasmic receptors

Question 10

polar signaling molecules (can they go thru membrane? where do they bind)

Answer 10

they cant go thru so they need a membrane bound receptor!!!!!!!

Question 11

3 types of signaling molecules

Answer 11

1) polypeptides (large polar). Need a receptor on surface

2) smaller polar (need receptor)

3) steriods (NON POLAR CAN GO THRU MEMBRANEES BC LIPID SOLUBLE)

Question 12

4 types of receptors (where are they found)

Answer 12

1) intracellular (nucleus or cytoplasm)
2) ion channel receptor (ligand gated, changes conformation to allow ions to pass or it can close)
3) GPCR
4) Protein Kinase (enzyme-linked) receptors

Question 13

intracellular receptors (1/4 receptor types)

Answer 13

1) lipid soluble signaling molecule passes thru the membrane
2) binds to receptor and allows the receptor to migrate into nucleus
3) transcription factor!

Question 14

3 parts of signal transduction

Answer 14

1) binding
2) transduction (relay proteins)
3) response

Question 15

3 responses that can occur from signal transduction

Answer 15

1) altered metabolism
2) altered gene expression
3) altered cell shape or movement

Question 16

GPCR cycle with adenylyl cyclase along with inactivation

Answer 16

1) ligand binds to the GPCR and GPCR undergoes conformational change
2) G-protein:GDP swaps GDP for GTP and becomes activated
3) G-protein:GTP binds to inactive adenylyl cyclase
4) adenylyl cylcase takes ATPand uses the 3’ hydroxyl group as a nucleophile to kick out inorganic pyrophosphate (drives rxn forward)

INACTIVATION

5) ligand dissociates
6) G protein hydrolyses GTP and diffuses away from adenylyl cylcase (GTP IS A TIMER)

Question 17

calcium dependent pathway (GPCR)

Answer 17

1) GPCR shit happens
2) G protein activates phospholipase C
3) phospholipase C cleaves pip2 ligand into DAG and ip3
4) ip3 goes to the ip3 gated ca2+ ion channel which releases ca2+ into cytoplasm

Question 18

RTK

Answer 18

1) either two ligands bind to each monomer or big ass ligand binds to both
2) RTKs form a dimer
3) autophosphorylation
4) cellular proteins pull up and bind to the activated receptors

Question 19

different pathways

Answer 19

A) ligand –> relay proteins –> response

B) branching

C) cross talk

D) different receptor completely

Question 20

can the same molecule bring about different effects?

Answer 20

yes! what matters is the receptor gang

Question 21

ced-9 apoptosis

Answer 21

1) death signaling molecule binds
2) ced-9 becomes inactive and no longer inactivates ced 4
3) ced4 without inhibitory ced9 is now active! and activated ced3
4) ced 3 activates nucleases and other proteases
5) cell death