Chapter 6 - Cellular Communication and Signal Transduction

Question 1

Methods of cell to cell communication

Answer 1

•gap junctions: direct cytoplasmic transfer between adjacent cells
•contact-dependent signals: surface to surface contact between membranes
•cells release messengers to the ECF
1) long distance communication: hormones, neurohormones and neurotransmitters
2) local communication:paracrine and autocrine

Question 2

Cellular messengers (long distance)

Answer 2

• hormones: released from tissue and travels to target cell through blood
• neurotransmitter: released from the neuron to adjacent effector
• neurohormone: released from a neuron and travels to target cell through blood

Question 3

Cellular messengers (short distance)

Answer 3

• paracrine agent: released from interstitial fluid and affects neighboring target cell
• autocrine agent: released into interstitial fluid sand affects the cell that released it

Question 4

Receptor (def and characteristics)

Answer 4

Protein associated with the membrane or cellular interior which will bind a chemical messenger and exert an effect
• highly specific
• high affinity for specific messenger
• can be saturated or blocked
• can undergo down-regulation
• can undergo up-regulation

Question 5

Down-regulation (def)

Answer 5

Decrease in receptor numbers in responses to chronic elevated levels of messenger (type II diabetes)

Question 6

Up-regulation (def)

Answer 6

Increase in receptor number in response to chronic low levels of messenger (cargo load)

Question 7

Routes of messenger action

Answer 7

1) lipophilic messengers diffuse directly through the membrane to an internal receptor, commonly response in nucleus (steroids)
• relatively slow process, hours or days for messengers
to produce response
• hydrophobic, difficult time getting to the cells, must be
transported by a transport protein (typically
amphipathic)
2) lipophobic messengers must enter the cell through transport or bind to a surface receptor (adrenaline, insulin)
• hydrophilic, rapid cellular response

Question 8

Lipid messengers act on four types of membrane receptors

Answer 8

1) ligand-gated receptor channels: receptor proteins that act as an ion channel (nicotinic)
2) receptor enzymes: receptor acts as enzyme and messenger binding initiates enzymatic activity resulting in cellular response (insulin)
3) GTP-binding protein: messenger activates G protein which opens an ion channel or activates an enzyme (beta 2 adrenergic)
4) integrin receptor: messengers binding caused a change in the cytoskeleton

Question 9

Signal transduction benefits the cell through

Answer 9

Signal amplification and multi-tasking

Question 10

Mechanisms of signal transduction

Answer 10

1) messenger binds to ligand gated channel
2) receptor enzymes
3) GTP-binding proteins

Question 11

Draw messenger binding to ligand gated channel

Answer 11

P. 21

Question 12

Receptor enzymes (def, characteristics, draw)

Answer 12

• when activated, receptor enzymes act as enzymes to alter cytoplasmic proteins
» kinase receptors: include many families of growth factors including epidermal GF, platelet-derived GF, fibroblasts, and insulin receptors
• p. 22

Question 13

GTP-binding proteins (characteristics and types)

Answer 13

• second messenger systems or G-protein coupled receptors (GPCR)
• In a second messenger system, the intracellular messenger (or first messenger) binds non-covalently to a surface protein and activates a G-protein that initiates an internal chemical (or second messenger) that initiates the cell’s response
1) cyclic AMP system
2) phospholipase-C pathway

Question 14

Draw cyclic AMP system

Answer 14

P. 24 and 26

Question 15

Draw phospholipase-C pathway

Answer 15

P. 27

Question 16

Agonist (def)

Answer 16

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

Question 17

Antagonist (def)

Answer 17

Molecule that competes with another for a receptor and binds to the receptor, but does not trigger a cellular response

Question 18

Signal termination

Answer 18

•After the cell’s response has been initiated, the first messenger must be stopped. Messengers can be:

 - degraded by extracellular enzymes
 - endocytosis of receptor ligand complex 

•After the cell’s response has been initiated, second messenger must also be removed by

 - degradation of the second messenger
 - pumping of ions out of the cytoplasm

Question 19

Transducer (def)

Answer 19

Convert extracellular signals into intracellular messages to create a response