Unit 4: Cell Communication

Question 1

Parts involved in cell communication

Answer 1

Secreting cell

Ligand

Target cell (has receptor for specific ligand)

Question 2

Define

Autocrine signaling

Answer 2

Cell that secretes a ligand also has receptors and is also the target cell

Question 3

Importance / Relevance of

Autocrine signaling

Answer 3

1. Developing cells reinforce cell type
2. Cancers increase their own growth

Question 4

Define

Paracrine signaling

Answer 4

Ligand can diffuse from secreting cell to target cell

Question 5

Importance / Relevance of

Paracrine signaling

Answer 5

Developing tissues will specialize based on what types of cells are around it

Question 6

Example of

Paracrine signaling

Answer 6

Developing tissues

Nervous system

Question 7

Parts of

Nerve cell signaling

Answer 7

• Presynaptic neuron releases neurotransmitter
• Neurotransmitter diffuses across small gap (synapse)
• Postsynaptic neuron responds to neuron

Question 8

Define

Cell-to-cell signaling

Answer 8

Direct contact between two cells;

Proteins on the surface of one cell acts as a ligand to bind to the receptor of a target cell

Question 9

Importance / Relevance of

Cell-to-cell signaling

Answer 9

Immune cells “activate” each other by direct contact

Question 10

What type of signaling involves the sharing of cytoplasm between cells?

Answer 10

In animals: Gap junctions

In plants: Plasmodesmata

Question 11

Define

Endocrine signaling

Answer 11

Target cell is a far distance from the secreting cell

Question 12

Parts of endocrine signaling pathways in vertebrates

Answer 12

Glands secrete the ligand (called hormones)

Hormones travel in circulatory system

Question 13

List

Endocrine organs

Answer 13

Hypothalamus, adrenal glands, sex organs (ovaries or testes), others

Question 14

Steps of

Signal transduction

Answer 14

1. Reception: Signal hits target cell
2. Transduction: Cell relays message within cytoplasm
3. Response

Question 15

Description of

Reception

(in signal transduction)

Answer 15

Signal (chemical, electrical, touch, etc) reaches receptor on target cell;

Cytoplasmic portion of receptor changes due to the signal;

Receptor changes to initiate transduction cascade

Question 16

Examples of

Cell surface receptors

Answer 16

G-Protein coupled receptors

Receptor tyrosine kinases

Receptor mediated ion channels

Question 17

Describe

G-protein coupled receptors

Answer 17

GPCR with no ligand: Internal portion of GPCR is bound to G protein/GDP (guanosine di-phosphate)

When ligand binds, G protein separates from GDP and binds to GTP

G protein/GTP is “active” and separates from GPCR; can then affect other molecules in the cell

Question 18

Define

Second messenger

Answer 18

Small, soluble molecules that move within the cytoplasm during transduction (ex: cAMP, Ca²⁺)

Question 19

Define

Kinase

Answer 19

An enzyme that phosphorylates a protein (often another kinase or enzyme)

Question 20

Define

Phosphatase

Answer 20

An enzyme that removes the phosphate group from a protein; often “inactivates” the other protein

Question 21

Describe

Phosphorylation cascades

Answer 21

A series of kinases phosphorylate each other and other molecules, allowing for a signal to be amplified in the cytoplasm

Question 22

Define

Amplification

Answer 22

A single ligand can lead to exponentially greater changes within the cell because each step in a transduction cascade can activate multiple of the next step

Question 23

Explain why different cell types respond to different signals or respond differently to the same signal

Answer 23

Each cell type has unique sets of receptors and transduction proteins.

• Only those with the right receptor can respond
• How the receptor interacts with cytoplasmic molecules will differ between cell types

Question 24

List examples of

Responses

(in signal transduction)

Answer 24

• Increase/decrease transcription
  
  • Change amounts/types of enzymes
  • Lead to or prevent cell growth/division
  • Change what membrane proteins are present (pumps, fac. diffusion, and other receptors)
• Endocytosis or exocytosis
• Apoptosis

Question 25

Relate cell signaling to tumors / cancers

Answer 25

Unregulated cell growth due to:

• Up/down-regulation of production of cyclins
• Cancerous cells often:
  
  • fail to respond to signals to stop growth
  • over-respond to signals to grow
  • constitutively say active even without the signal present

Question 26

Define

Homeostasis

Answer 26

Maintaining an internal environment that differs from external environment

Question 27

Relate cell signaling to negative feedback

Answer 27

• Change in conditions is sensed by a sensor cell, which will have signal transduction pathway that leads to a response
• Response of the sensor is often the release of ligand to communicate with other cells
• Eventually, effector cells will receive signal and respond by negating the original stimulus

Question 28

Define

Negative feedback

Answer 28

Responding to a change in conditions by negating that change

Question 29

Define

Positive feedback

Answer 29

Responding to a change in conditions by amplifying that change

Question 30

Examples of

Negative feedback

Answer 30

Temperature regulation

Glucose regulation

Oxygen/CO2/pH regulation

Solute regulation (osmotic balance)

Blood pressure regulation

Question 31

Describe

Thermoregulation

Answer 31

Increased body temp → Sensed by brain → Signals sent to effectors include (1) sweat glands, which produce sweat; (2) blood vessels, which dilate

Decreased body temp → Sensed by brain → Signals sent to effectors include (1) Blood vessels, which constrict; (2) Muscles, which shiver

Question 32

Describe

Glucose regulation

Answer 32

• High glucose
  
  • Sensor: Pancreas
  • Response by pancreas: Secrete insulin
  • Insulin target: Liver and muscle cells
  • Response of liver/muscle cells: Increase glucose uptake and conversion to glycogen
  • Result: Blood glucose levels drop and glucose is stored as glycogen
• Low glucose
  
  • Sensor: Pancrase
  • Response by pancreas: Secrete glucagon
  • Glucagon target: Liver cells
  • Response of liver cells: Increase hydrolysis of glycogen and release into blood
  • Result: Blood glucose increases