Sensing the Conditions

Question 1

why do not all cells receive signals

Answer 1

signals secreted by one cell are detected by other cells that express the corresponding receptor
cells that do not express the receptor do not receive the signal

Question 2

where are receptors found

Answer 2

cells surface
inside cell

Question 3

name three transmembrane receptors in complex eukaryotes

Answer 3

protein kinases
ion channel receptors
g protein-linked receptors

Question 4

what do protein kinase receptors do

Answer 4

phosphorylate themselves and/or other proteins

Question 5

how do protein kinase receptors work

Answer 5

-phosphorylates itself and other insulin substrates
-initiates glucose transporters inserted into the plasma membrane

Question 6

what do ion channel receptors do

Answer 6

allow ions to enter or leave cell
Signals can be chemical ligands (hormones)
e.g. Acetylcholine receptor on muscle cells is a gated ion channel

Question 7

WHat does G protein-linked receptors initially do

Answer 7

Ligand binding changes shape of cytoplasmic region
this binds to a G protein

Question 8

What happens to the GTP-subunit after it separates form the G protein

Answer 8

moves through plasma membrane until it encounters an effector protein

Question 9

What occurs when the GTP-subunit binds to the effector protein

Answer 9

Effector activates changing function of cell

Question 10

What happens to GTP after the effector protein is activated

Answer 10

GTP hydrolysed to GDP

Question 11

WHat do G proteins do to effectors

Answer 11

activate or inhibit effector

Question 12

How do G proteins activate

Answer 12

-Epinephrine binds to G protein-linked receptor in heart muscle
-activates an enzyme to produce cyclic AMP (cAMP)

Question 13

how do g proteins inhibit

Answer 13

occurs with same hormone epinephrine in smooth muscle cells

Question 14

How does inhibition occur in smooth muscle cells

Answer 14

Epinephrine inhibits enzyme that produces cAMP
shows that the same signal molecule can have different effects in different cells due to differences in receptors

Question 15

how do cytoplasmic receptors work in steroid hormones

Answer 15

-steroid hormone (ligand) enters cell
-form complex with its receptor
-receptor dissociates from the chaperone
-enters nucleus
-acts as transcription factor

Question 16

What is direct transduction in cell signalling

Answer 16

when the receptor itself directly acts on effector proteins

Question 17

What is a common mechanism used in direct transduction

Answer 17

protein kinase cascade

Question 18

How is the cellular response affected during a protein kinase cascade

Answer 18

amplified

Question 19

how is information transmitted from the plasma membrane to the nucleus

Answer 19

through a series of steps in the signalling pathway

Question 20

what provides specificity and variation in direct transduction responses

Answer 20

different target proteins at each step of the cascade

Question 21

WHat does indirect transduction use

Answer 21

a second messenger
amplifies interaction between receptor and cellular reaction

Question 22

name some second messengers

Answer 22

cAMP
cGMP
Lipids
calcium ions (Ca++)
Nitric Oxide (NO)

Question 23

Where is the enzyme that catalyses the formation of cAMP from ATP and whats it called

Answer 23

Adenyl cyclase
cytoplasmic side of plasma membrane

Question 24

where does cAMP bind to mainly

Answer 24

1) ion channels in sensory cells =opens the channel
2) protein kinases in cytoplasm exposing active start = starting protein kinase cascade

Question 25

WHere are other second messengers derived from

Answer 25

phospholipids in plasma membrane

Question 26

what are phospholipids hydrlysed by

Answer 26

phospholipases

Question 27

Example of second messengers used for phospholipids

Answer 27

phosphatidyl inositolbiphosphate

Question 28

what is the hydrohphobic portion of PIP2 and where is it located

Answer 28

hydrophobic portion is diacylglycerol (DAG) in plasma membrane

Question 29

what is the hydrophilic portion of PIP2 and where does it project

Answer 29

Inositol triphosphate (IP3) projects into cytoplasm

Question 30

How do people get bipolar disorder

Answer 30

Overactive IP3/DAG signal transduction pathway in the brain

Question 31

WHy is there an overactive IP2/DAG signal

Answer 31

Lithium ions (li+) inhibit G protein activation of phospholipase C, and inhibits synthesis of IP3

Question 32

how are low Ca2+ concentrations maintained

Answer 32

Active transport proteins at plasma and ER membranes

Question 33

How do muscles relax involving acetylcholine step by step

Answer 33

1) Acetylcholine binds to endothelial cells receptors 2) activates IP3/DAG signal transduction pathway 3) influx of Ca2+ 4) leads to cGMP as a second messenger 5) relaxes muscles by dilating blood vessels

Question 34

How is nitric oxide produced and what is its role in smooth muscle relaxation

Answer 34

-In endothelial cells -Ca2+ activates NO synthase produces NO from arginine -NO diffuses into smooth muscle cells -cGMP synthesis leading to muscle relaxation

Question 35

What does epinephrine stimulate

Answer 35

protein kinase cascade in liver cells

Question 36

What two enzymes are phosphorylated in liver cells

Answer 36

Glycogen synthase phosphorylase kinase

Question 37

What does glycogen synthase do

Answer 37

inhibited prevents glucose being stores as glycogen

Question 38

what does phorphorylase do

Answer 38

activates glycogen phosphorylase that catalyses glycogen -> glucose

Question 39

Signal transduction pathway and amplification step by step for glucose

Answer 39

1) Epinephrine binds to specific epinephrine receptor on membrane 2) G protein activated 3) GTP-bound subunit activates adenyl cyclase 4) Adenyl cyclase converts ATP -> cAMP (second messenger) 5) cAMP activates protein kinase A releasing regulatory subunits 6) PKA phosphorylates glycogen synthase making it inactive 7) and actives phosphorylase kinase 8) Glycogen phosphorylase breaks down glycogen -> glucose 1-phosphate 9) Glucose 1 phosphate -> glucose and released into blood, increase blood glucose levels

Question 40

Summarise signal transduction pathway for glucose

Answer 40

1) 1 hormone -> many cAMP molecules 2) Many cAMP -> activate many PKA 3) Each PKA -> activates enzymes 4) Each enzyme -> affects many glycogen molecules 5) Massive blood glucose increase from single hormone binding

Question 41

Examples of fertilisation of egg

Answer 41

fertilisation of egg = triggers calcium ions that stimualte initiation of development

Question 42

Example of neurotransmitter response to serotonin

Answer 42

cAMP signalling pathway activates serotonin increase cAMP conc

Question 43

Sense of smell biological response example

Answer 43

G-protein-coupled receptors and cAMP-gated ion channels provide influx of Na+ and Ca2+ stimulates nerves to send signals to brain

Question 44

what is the basic biological circuit

Answer 44

Receptors -> Signal transduction -> biological response