Ch 6: Communication

Question 1

Methods of cell-to-cell communication

Answer 1

1. Gap junctions
2. Contact-dependent signals
3. Cells release messengers to the ECF

Question 2

Gap junctions

Answer 2

Direct cytoplasmic transfer b/t adjacent cells
*aka communicating junction
- short distance
- transfer both chemical and electrical signals

Question 3

Contact-dependent signals

Answer 3

Surface to surface contact b/t membranes
- proteins embedded in membrane
- short distance

Question 4

Cells release messengers to the ECF

Answer 4

1. Long-distance communication
   —hormones, neurohormones, & neurotransmitters
2. Local communication
   —paracrine & autocrine
   *can go long distances

Question 5

Cellular messengers

Answer 5

• Hormones
• Neurotransmitters
• Neurohormones
• Paracrine agent
• Autocrine agent

Question 6

Hormones

Answer 6

Released from tissue and travels to target cell thru blood

Question 7

Neurotransmitters

Answer 7

Released from neurons to adjacent effector
- only from synapse to adjacent cell

Question 8

Neurohormones

Answer 8

Released from neuron & travels to target cell thru blood

Question 9

Paracrine agent

Answer 9

Released into interstitial fluid & affects neighboring target cell

Question 10

Autocrine agent

Answer 10

Released into interstitial fluid & affects the cell that released it

Question 11

Communication b/t cells also accomplished by?

Answer 11

SIGNAL MOLECULES (intracellular chemical messenger) & RECEPTOR

Question 12

Receptors

Answer 12

Protein associated w/ the membrane or cellular interior which will bind a chemical messenger & exert an effect
*protein binding to a ligand
- highly specific
- high affinity for specific messenger
- can be saturated or blocked

Question 13

Receptors can undergo…

Answer 13

• Down-regulation
• Up-regulation

Question 14

Down-regulation

Answer 14

Decrease in receptor # in response to chronic elevated levels of messenger
- ex: Type II diabetes

Question 15

Up-regulation

Answer 15

Increase in receptor # in response to chronic low levels of messengers

Question 16

Routes of messenger action

Answer 16

1. Lipophilic messengers
2. Lipophobic messengers

Question 17

Lipophilic messengers

Answer 17

Diffuse directly thru the membrane to an internal receptor
- lipophilic generally hydrophobic
- contains binding protein (amphipathic)
- relatively slow response, but persist in body
—ex: steroid (modifies transcription)

Question 18

Lipophobic messengers

Answer 18

Must enter cell thru transport or bind to a surface receptor
- signal transduction
- fast responses (internal), but degrades quickly
- generally hydrophilic
- must bind noncovalently, causing protein to flex

Question 19

Signal transduction

Answer 19

Message is conveyed from outside of cell to a new signal inside of the cell which then creates a cellular response
- converts one form of signal into a different form

Question 19

Signal transduction benefits the cell thru?

Answer 19

1. Signal amplification (start small get big)
2. Mutli-tasking (more than one effect)

Question 19

Transducers

Answer 19

Convert extracellular signals into intracellular messages which create a response

Question 20

Lipophobic messengers act on 4 types of membrane receptors

Answer 20

1. Ligand-gated receptor channels
2. Receptor enzymes
3. GTP-binding proteins
4. Integrin receptors

Question 21

Ligand-gated receptor channels

Answer 21

Receptor proteins that can act as an ion channel

Question 22

Receptor enzymes

Answer 22

Receptor acts as an enzyme & messenger binding initiates enzymatic activity resulting in cellular response

Question 23

GTP-binding proteins

Answer 23

Messenger activates a G-protein which opens an ion channel or activates an enzyme

Question 24

Integrin receptors

Answer 24

Messenger binding causes a change in the cytoskeleton

Question 25

Mechanisms of signal transduction (non-covalent binding)

Answer 25

1. Messenger binds to ligand-gated channel 2. Receptor enzymes ---Kinase receptors 3. GTP-binding proteins

Question 26

Messenger binds to ligand-gated channel

Answer 26

Now permeable to ion flux - nicotinic, GABA, glycine - depolarize, hyperpolarize, repolarize

Question 27

Receptor enzymes

Answer 27

When activated, receptor enzymes act as enzymes to alter cytoplasmic proteins - allosteric activation

Question 28

Receptor enzymes: kinase receptors

Answer 28

Kinase receptors include many families of growth factors including: epidermal GF, platelet-derived GF, fibroblasts & insulin - covalent modulation = phosphorylation of protein

Question 29

GTP-binding proteins (2nd messenger systems/ G protein coupled receptors [GPCR])

Answer 29

In a second messenger system, the intracellular messenger (or 1st messenger) binds non-covalently to a surface protein & activates a G-protein that initiates an internal chemical (or 2nd messenger) that initiates the cell's response - may open a channel or activate an enzyme - "extra steps"

Question 30

2nd messengers

Answer 30

- Cyclic AMP (cAMP) - Phospholipase C (GPCR)

Question 31

CAMs

Answer 31

Transfer signals in both directions

Question 32

Beta 2-Adrenergic Receptor

Answer 32

Transmembrane protein that noncovalently binds to epinephrine (adrenaline) *signal transduction

Question 33

Steroid hormone influences?

Answer 33

Transcription - slower responses related to changes in gene activity

Question 34

cAMP system (detail)

Answer 34

1. Signal molecule binds to G protein-linked receptor, which activates the G protein 2. G protein turns on adenylyl cyclase, an amplifier enzyme 3. Adenylyl cyclase converts ATP to cyclic AMP 4. cAMP (2nd messenger) activates protein kinase A 5. Protein kinase A phosphorylates other proteins, leading ultimately to a cellular response

Question 35

ATP to cAMP to AMP

Answer 35

Phosphate group originally on C5, now on C3 - cAMP is an intermediate

Question 36

Cells prefer ATP

Answer 36

Energy is from phosphate to phosphate bond - not influenced by bases

Question 37

GPCR: The Phospholipase C system

Answer 37

*Doesn't attack phospholipids at random, only attacks one type 1 Signal molecule activates receptor and associated G protein 2. G protein activates phospholipase C (PL-C), an amplifier enzyme 3. PL-C converts membrane phospholipids into diacylglycerol (DAG), which remains in the membrane, and IP3, which diffuses into the cytoplasm 4. DAG activates protein kinase C (PK-C), which phosphorylates proteins (allosteric mod) 5. IP3 causes release of Ca+2 from organelles, creating a Ca+2 signal

Question 38

Agonist

Answer 38

Chemical messenger that binds to a receptor and triggers a cell's response

Question 39

Antagonist

Answer 39

Molecule that competes w/ another for a receptor and binds to the receptor but does not trigger a cellular response aka: anti-histamine?

Question 40

Epinephrine can bind to different isoforms of the adrenergic receptor...

Answer 40

Target response depends on the target receptor - diff receptor = diff results

Question 41

Signal termination

Answer 41

- After the cell's response has been initiated, the 1st messenger must be stopped. - After the cell's response has been initiated the 2nd messenger must also be removed.

Question 42

Many diseases & drugs have their effects at the?

Answer 42

Receptor or signal transduction step

Question 43

Signal termination: 1st messengers can be...

Answer 43

- Degraded by extracellular enzymes (outside cell) -----ex: ACHE, MAO - Endocytosis of receptor-ligand complex (inside cell)

Question 44

Signal termination: 2nd messengers can be...

Answer 44

- Degradation of the 2nd messenger - Pumping of ions out of the cytoplasm (put it back into its rightful organelle)