important concepts and details

Question 1

the reception of the signals depends on receptor proteins at the cell surface

Answer 1

the binding activates the receptor, which in turn activates one or more intracellular signaling pathways

Question 2

what does effectors do?

Answer 2

they can be transcription regulators, ion channels, components of metaboic pathways, or parts of cytoskeleton

Question 3

extracellular signals can act over short or long distances

Answer 3

many extracellular signals molecules remain bound to the surface of the signaling cell

Question 4

extracellular signal molecules bind to specific receptors

Answer 4

target cell responds by means of a receptor. the binding site of the receptor has a complex structure that is shaped to recognize the signal molecule with high specificity, helping to ensure that the receptor responds only to the appropriate signal

Question 5

in other cases, the receptor proteins are inside the target cell and the signal molecule has to enter the cell

Answer 5

this requires that the signal molecule by sufficiently small and hydrophobic to diffuse across the target cell’s plasma membrane

Question 6

most signal molecules are hydrophilic

Answer 6

they are unable to cross the target cell’s PM directly hence they bind to cell surface receptors

Question 7

some signal molecules are hydrophobic

Answer 7

they easily diffuse across the PM and bind to receptor proteins inside the target cell and are transported in the bloodstream

Question 7

some signal molecules are hydrophobic

Answer 7

they easily diffuse across the PM and bind to receptor proteins inside the target cell and are transported in the bloodstream

Question 8

each cell is programmed to respond to specific combinations of extracellular signals

Answer 8

many cells require a specific combination of extracellular survival factors to allow the cell to continue living, when deprived of these signals, the cell dies

Question 9

a signal molecule has diferent effects on different types of target cells

Answer 9

example:

neurotransmitter acetylcholine decreasess the rate of action potential firing in the heart pacemaker cells and stimulates th producrion of saliva by salivary gland cells.

in skeletal muscl, acetylcholine causes the cells to contract.

Question 10

cell-surface receptors relay signals via intracellular signaling molecules

Answer 10

these are called second messengers.

Question 11

many of the intracellular signaling molecules behave like molecular switches

Answer 11

when they receive a signal, they switch from an inactive to active state and vice versa.

Question 12

how does a signal remain strong, precise, and specific?

Answer 12

due to high affinity and specificity.

Question 13

the relationship between signal and response varies in differenct signaling pathways

Answer 13

each signal has evolved specialized behaviors

Question 14

there are slow and rapid responses to an extracellular signal

Answer 14

changes in gene expression occur slowly, changes in cell movement or metabolism need not involve changes in the gene expression and therefore occur quickly

Question 15

cells can adjust their sensitivity to a signal

Answer 15

cells and organisms are able to detect the same percentage of change in a signal over a wide range of stimulus strengths. these cells accomplish this through adaptaion or desensitization

Question 16

target cells use feedback loops to adjust the ways in which they respond to signals

Answer 16

positive feedback loop respond in an all or none fashion to a gradually increasing concentraion or even irreversible response.

negative feedback allows cells to adapt to a signal molecule

Question 17

the activation of PKA

Answer 17

the binding of camp to th regulatory subunits if the PKA induces a conformational change, causing these subunits to dissociate from the catalytic subunits, thereby activating the kinase activity

Question 18

some g proteins signal via phospholipds

Answer 18

many GPCRs exert their effects through G proteins that activate PLCb

Question 19

the fertilization of an egg by a sperm triggers a wave of cytosolic ca2+

Answer 19

the initial ncrease in ca2+ is thought to be caused by a sperm-specific form of PLC

Question 20

some g proteins directly regulate ion channels

Answer 20

g proteins directly activate or inactivate ion channels in the PM of the target cell, thereby altering the ion permeability. an example is the acetylcholine released by the vagus nerce reduces the heart rate.

other gproteins regulate the activity of ion channels less directly either by stimulating channel phosphorylation. this have a crucial role in olfaction and vision

Question 21

effect of nitric oxide on blood vessels is important for the mechanism of nitroglycerine used to treat patients with angina

Answer 21

the nitroglycerine is converted to NO. This reduces the worklod on the heart and reduces the oxygen requirement of the heart muscle

Question 22

GPRC desensitization depends on receptor phosphorylation

Answer 22

when target cells are exposed to high concentration of a ligand for a prolonged period, they become desensitized

Question 23

proteins with sh2 domains bind to phosphorylated tyrosines

Answer 23

not all proteins that bind to activated rtks via sh3 domains help to relay signal onward. some act to decrease the signaling process, provifing negative feedback.

Question 24

What happens when there is an excessive and nonstop cell signaling?

Answer 24

Could have mutation, leading to an enormous cell growth, which can be harmful

Question 25

role of autocrine signaling in cancer cells

Answer 25

Autocrine signaling is a process in which a cell produces signaling molecules which would then bind to signal receptors on the same cell. In other words, Autocrine signaling commonly induces cell division and regeneration, which could promote the growth of cancerous cells and tumor development.

Question 26

how positive feedback dictates cell growth

Answer 26

This is a form of positive feedback in which the cell would repeatedly auto stimulate itself to promote the expression of the signaling molecule from the signaling receptors.

Question 27

role of negative feedback in maintaining homeostasis

Answer 27

Negative feedback serves to reduce an excessive response and to keep a variable within the normal range

Question 28

how are second messengers turned off and on?

Answer 28

through phosphorylation and dephosphorylation of proteins. this is with the help of (1) protein kinase, where it phosphorolates proteins and dephosphorylates proteins due to protein phosphatases, and (2) gtp binding proteins.

Question 29

what happens when second messengers don’t turn off/on?

Answer 29

when messengers are not turned off, a prolonged on going cell response would happen, which can be detrimental to the cell. on the contrary, messengers that are not turned on will not initiate cell growth.

Question 30

role of notch protein in early onset of alzheimers

Answer 30

the protein complex of notch, called y-secretase, generates extracellular peptide fragments from a transmembrane neuronal protein; the fragments accumulate in excessive amounts and form aggregates of misfolded protein called amyloid plaques, which may injure nerve cells and contribute to their degeneration and loss.

Question 31

why is gpcr important for our sense of smell

Answer 31

an odorant signal binds to the an olfactory receptor, a gpcr, activating g protein, which turns on adenyl cyclase. this cyclase converts atp to camp which opens cation channels, allowing an influx of na2+ initiating a nerve impulse.

Question 32

discuss how NO and CGMP work together to muscle relaxation

Answer 32

NO activate guanyl cyclase to produce CGMP. This CGMP triggers a response that causes the muscles to relax.

Question 33

role of BAD proteins in cell survival and cell death

Answer 33

when BAD is phosphorylated by AKT, it releases proteins and blocks apoptosis. on the contrary, when BAD in unphosphorylated, it enables apoptosis-inhibitory proteins, causing cell death.

Question 34

why is b-catenin pathway important in carcinogenesis?

Answer 34

when b-catetin is activated, this means when its protein estruction complex is inhibited due to the binding of wnt, its level increases, creating cell proliferation. a nonstop increase in its levels can result to mutation, leading to deteroration of cancer cells.

Question 35

jak-stat pathway in inflammatory immune response

Answer 35

It acts as an activator for many cytokines which results in cell growth and death. for example, These activated cytokines cause inflammation in cells and are also responsible for cell death in the many regions of the brain.