Lecture 15- Cell Signaling I

Question 1

differential gene expression theory

Answer 1

• genome is constant in all somatic cells
• only small proportion of genome in any cell type is expressed
• unused genes that are not transcribed are not mutated or destroyed, they retain potential to be expressed

Question 2

how many protein coding genes in humans are devoted to cell signaling?

Answer 2

over 7,000 out of 21,000

Question 3

general principles of signaling

Answer 3

• signaling cells send signaling molecule (ligand) that is detected by target cell
• receptors in target cells recognize and respond specifically to signal molecule (only cells that have a receptor for a signal can respond to that signal)
• triggers intracellular signaling pathway to effectors

Question 4

ligands can be…

Answer 4

proteins, peptides, amino acids, nucleotides, steroids, fatty acid derivatives, gases

Question 5

intracellular signaling pathway

Answer 5

relay, amplify, integrate, distribute

Question 6

effectors

Answer 6

may alter gene expression, metabolism, cell shape or movement, etc.

Question 7

signal transduction

Answer 7

process of translating an extracellular signal into intracellular effectors that alter cell behavior

Question 8

signals have act over long or short range

Answer 8

ex. insulin (produced by beta cells in pancreas and regulates glucose uptake in cells all over body)
ex. hormones secreted by endocrine cells

Question 9

neuron example of long/short range signals

Answer 9

• axon of neuron can be far away from neuronal cell body
• axon terminates at specialized junctions called synapses
• once activated, neuron sends electrical impulses along axon, leading to release of neurotransmitters (signals) at the nerve terminal

Question 10

lateral inhibition example

Answer 10

mediated by membrane-bound ligand (delta) and membrane-bound receptor (notch)

Question 11

information conveyed by signal depends on how target cells receives and interprets the signal (their developmental history and current state)

Question 12

signals can be of different types

Answer 12

small/large molecules, light, mechanosensation

Question 13

signals can act over long or short range

Answer 13

endocrine, paracrine (autocrine), synaptic, contact-dependent

Question 14

same signal can induce different responses

Answer 14

depending on history and status of target cell

Question 15

signals can act rapidly or slowly

Answer 15

changes of protein function or gene expression

Question 16

receptors can be intracellular or on cell surface

Answer 16

• intracellular receptors: can accept small hydrophobic signal molecules that have passed through cell membrane, often in cytosol or nucleus, regulate gene transcription or other functions
• cell surface: binds to large hydrophilic molecules on outside of cell and then generate 1+ intracellular signaling molecules inside cell

Question 17

steroid hormones regulate transcription

Answer 17

• each hormone binds a different receptor
• each receptor acts at different sites in DNA
• a given hormone usually regulates (activate or repress) different sets of genes in different cell types

Question 18

cell surface receptors relay extracellular signals via intracellular signaling pathways

Answer 18

extracellular signal molecule -> receptor protein -> intracellular signaling molecules -> effector proteins -> target cell responses

Question 19

intracellular signaling molecules

Answer 19

• adaptors, kinases, phosphatases, GTP binding proteins, proteases, other enzymes, lipids (PIP2)
• 2nd messengers: cGMP, cAMP, Ca++

Question 20

effector proteins and target cell responses

Answer 20

• metabolic enzyme -> altered metabolism
• cytoskeletal protein -> altered cell shape or movement
• transcription regulator -> altered gene expression

Question 21

functions of intracellular signaling pathways

Answer 21

primary transduction -> relay by adaptors -> transduce and amplify
-> integrate -> feedback (may integrate again) -> distribute -> target cell responses

Question 22

many key intracellular signaling proteins act as molecular switches

Answer 22

a) signaling by protein phosphorylation: kinases (serine/threonine kinases, tyrosine kinases)
b) signaling by GTP-binding proteins: small GTPases (Ras, Ran, Rab, etc)

Question 23

2nd messengers amplify and transduce the signal

Answer 23

• cGMP, cAMP, Ca++

- small intracellular messenger molecules

Question 24

feedback regulation within an intracellular signaling pathway can adjust the cell’s response to a signal

Answer 24

a) signaling pathway 1: positive feedback -> all or none response
b) signaling pathway 2: negative feedback -> response that oscillates on or off