Chap 5 Cell Interaction and Signaling

Question 1

Why do cells communicate?

Answer 1

1. To carry out one or more specific functions
   - Coordinate behavior/activities
   - To accomplish biological processes
2. To enable body t function as a whole

Question 2

Explain the 3 stages of cell signaling.

Answer 2

1. Reception
   - Chemical signal binds to receptor,(cellular protein) typically at the cell surface. (can be in cell as well)
2. Transduction
   - Binding leads to change in the receptor that riggers a series of changes along a signal transduction pathway and the signal is amplified.
3. Response
   - The transduced signal triggers a specific cellular activity

Question 3

How does epinephrine trigger the breakdown of glycogen to glucose?

Answer 3

• The hormone epinephrine is released by the kidney’s adrenal glands and can bind to receptors on liver cells. Upon binding to liver cells, the receptor undergoes a conformational change which triggers G protein to trigger the formation of cAMP. cAMP activates a cascade of protein kinase which in turn activates lipase (phosphorolayse b) to break down glycogen into glucose.

R-Epinephrine binding to receptors on liver cell
T-Causes series of changes inside the cell including activation of enzymes
R-Leads to activation of enzyme (phosphorolayse b) that leads to the breakdown of glycogen.

Question 4

Where are 3 places receptors can be located? (Give examples if possible)

Answer 4

1. On the cell surface (e.g. plasma membrane, GPCRs)
2. In the nucleus
3. In the cytoplasm (thyroid and steroid hormone receptors)

Question 5

What mechanism do receptors use to bind to ligands?

Answer 5

Lock and Key mechanism

Question 6

Why are G proteins named as such?

Answer 6

They are name G proteins as they bind to guanine nucleotides GDP and GTP.

Question 7

Why are G proteins heterotrimers?

Answer 7

They are made of 3 different sub units alpha,beta,gamma.

Question 8

How do GPCRs link the receptor to the G protein?

Answer 8

A cytosolic loop links the 5th and 6th alpha helices of the receptor to the G protein.

Question 9

How does the receptor of NO act as an enzyme in smooth muscle cells? (Explain the process from NO formation to response)

Answer 9

A stimulus causes the production of NO by activating NO synthase. NO then diffuses out of the cell it was generated in and travels to its target cells (smooth muscle cells), and diffuses through the plasma membrane. NO binds to the receptor guanylyl cyclase an intracellular receptor which then acts an enzyme to produce produce cGMP from GTP. (cGMP is a secondary messenger). cGMP in turn causes release of neurotransmitters that cause smooth muscle relaxation, dilating blood vessels and increasing blood flow.

NO can either act within the cell it is produce in or penetrate the cell membrane to affect adjacent cells.

Question 10

What are 6 types of signaling molecules (ligands)?

Answer 10

1. Hormones
2. Amino Acids
3. Neurotransmitters
4. Proteins
5. Steroids
6. Nitrous Oxide

Question 11

Why are cell surface receptors required for some signaling molecules?

Answer 11

Some signaling molecules that are hydrophillic are unable to cross the cell membrane on their own and require receptors on the surface to receive the signal.

Question 12

How do hydrophobic molecules bind to intracellular receptors.

Answer 12

Hydrophobic molecules are able to diffuse through the membrane which allows them to bind with receptors either inside the cytoplasm or nucleus.

Question 13

Why do small hydrophobic molecules require the use of carrier proteins?

Answer 13

As small hydrophobic molecules are insoluble in aqueous solutions, they are transported through the blood stream or other extracellular fluids by binding to carrier proteins from which they disassociate from before entering the target cell.

Question 14

What is the difference between steroid hormones and non steroid hormones? (Give examples for steroid and non steroid hormones)

Answer 14

Steroid hormones being hydrophobic can pass through the plasma membrane while non steroid hormones being hydrophillic cannot pass through the membrane and thus bind to cell surface receptors.

(e. g. Cortisol,Testosterone,Estrogen,Progesterone) Steroid
(e. g. Epinephrine,Glucagon) Non-steroid

Question 15

What are some responses to a signal?

Answer 15

1. Regulation of intracellular enzyme activity
2. Changes in transcription (gene regulation,gene expression)
   - turning a gene on or off

Question 16

Define gene expression and gene regulation.

Answer 16

Gene regulation is the process of turning on or off a gene.

Gene expression is the flow of information from gene to protein (effect of turning on/off a gene)

Question 17

Explain how a hydrophobic signaling molecule regulates the production of a protein. (intracellular receptor in cytoplasm) (give examples)

Answer 17

The signaling molecule being hydrophobic, diffuses through the plasma membrane into the cytoplasm where it binds to cytoplasmic receptor.Upon binding to the receptor, a conformational change causes DNA binding sites on the receptor to be exposed. The receptor ligand complex moves to the nucleus and binds to a specific regulatory region of the chromosomal DNA,promoting initiation of transcription either leading to a protein being produced or production to stop. (e.g. Steroid Hormones,Vitamin D,Thyroid Hormone)

Question 18

Explain how a hydrophillic signal molecule causes a protein to be produced. (Give example)

Answer 18

Hydrophilic signal molecule first binds to cell surface receptors on the target cell. This triggers the signal transduction pathway which in turn leads to the activation of transcription factors. This transcription factor enters the nucleus and binds to DNA, switching on the gene which later results in transcription on an mRNA eventually leading to translation and formation of a protein. (e.g. Beta islet cells in the pancreas that release insulin in response to high blood glucose levels after a meal)

Question 19

How does a signaling cascade amplify a signal?

Answer 19

At each step of the cascade, the signaling intermediate persists for long enough to stimulate the production of many molecules required for the next step in the cascade, thus multiplying the effect of a signal receptor ligand interaction.Thus small quantities of ligands are usually able to elicit a response from the target cells.

Question 20

Explain direct contact/direct intracellular signaling. (Draw diagram)

Answer 20

Cells in direct contact send signal molecules through gap junctions. (cells are connected)

Question 21

Explain contact dependent signaling. (Draw diagram)

Answer 21

Membrane bound signals and receptors on adjacent cells bind to trigger a response.

Question 22

Explain the nature of paracrine signaling. (Give example)

Answer 22

Signals released by a cell acts on neighboring cells that are not in contact. These signals are usually short lived as it gets destroyed quickly by extracellular enzymes after it is released thus giving it a short range. (e.g. Important in early development as it coordinates the activities of clusters of neighboring cells.)

Question 23

Explain autocrine signaling.

Answer 23

Cells release signaling molecules that affect itself and neighboring (nearby) target cells.

Question 24

Explain endocrine signaling.

Answer 24

Signaling molecules (hormones) are secreted by specialized endocrine cells and carried through the circulation to act on target cells at distant body sites.

Question 25

Explain synaptic signaling.

Answer 25

Neurotransmitters released by nerve cells cross the synapse to target cells.An action potential depolarizes the membrane of the synaptic terminal and triggers an influx of calcium ions. The influx of calcium ions causes the synaptic vesicles to fuse with the presynaptic neuron membrane. This causes exocytosis and neurotransmitters are released into the synaptic cleft. Neurotransmitters bind to receptors of the chemically gated ion channel in the postsynaptic membrane. This cause the ion channels to open after neurotransmitter molecules bind to receptors , this allows influx of sodium ions which depolarizes the postsynaptic membrane. This depolarization causes an action potential that runs through the postsynaptic neuron.

Question 26

Explain the glucagon signaling pathway.

Answer 26

When there is low blood sugar, pancreas releases the hormone glucagon.Glucagon triggers the liver to increase rates of gluconeogenesis and glycogenolysis in turn increasing blood glucose levels.

Question 27

Explain the effects of the insulin signaling pathway.

Answer 27

When there is high blood sugar, pancreas releases hormone insulin. Insulin decreases rates of glucose synthesis (glycogenolysis) and increases rate of glycogen synthesis (glycogenesis). Insulin also increases glucose metabolism, glucose uptake, and lipogenesis in fat while decreasing lipolysis. In muscle insulin increases glucose uptake,glucose metabolism and glycogen synthesis. (glycogenesis)

Question 28

Explain the TNF signaling pathway for apoptosis.

Answer 28

TNF binds to TNF-R1 receptor with an intracellular death domain. the binding causes a conformational change casuing formation of TRADD and which leads to formation of FADD producing Pro Caspase 8 which activates and cause cell apoptosis.

Question 29

Explain the FAS signaling pathway for apoptosis.

Answer 29

Fas receptor binds to Fas L ligand causing a conformational change and triggering formation of FADD and the Pro Caspase 8 which then activates casuing cell apoptosis.

Question 30

Why is 2 pathways for apoptosis needed?

Answer 30

This is to ensure that the cell still dies in the event that one of the pathways fails to function