Cell-Cell Interactions

Question 1

How are adjacent cells held together?

Answer 1

1. tight junctions
2. desmosomes
3. gap junctions
4. plasmodesmata (plants only)

Question 2

Tight junctions are ___________ formed between adjacent cells

Answer 2

water-tight seals

Question 3

Tight junctions prevent what?

Answer 3

passage of molecules between cells

Question 4

Tight junctions are found between _________ cells

Answer 4

epithelial (intestines, lungs, etc)

Question 5

Desmosomes are __________ that anchor the _________

Answer 5

strong adhesions; cytoskeleton

Question 6

Desmosomes provide __________________ between cells

Answer 6

continuous structural support

Question 7

Where are desmosomes found?

Answer 7

tissues that experience intense mechanical support (cardiac muscle, bladder, epithelia)

Question 8

Gap junctions are _________ between adjacent cells

Answer 8

protein channels

Question 9

Gap junctions allow __________ between cells

Answer 9

direct communication (animal and plant)

Question 10

What are plasmodesmatas?

Answer 10

gaps in cell walls

Question 11

Describe plasmodesmata?

Answer 11

no proteins involved and continuous plasma membrane and cytoplasm

Question 12

What is involved in cell-cell signaling and distant communication?

Answer 12

hormones

Question 13

What are hormones?

Answer 13

small molecules secreted to act on distant target cells

Question 14

What are some examples of hormones?

Answer 14

steroids, peptides, gas, amino acid derivatives

Question 15

What are the steps of cell-cell signaling?

Answer 15

1. signal reception
2. signal processing (transduction)
3. signal response
4. signal deactivation

Question 16

What is signal reception?

Answer 16

different for lipid-soluble (hydrophylic) and lipid insoluble (hydrophobic) hormones

Question 17

What is signal processing?

Answer 17

second messengers or phosphorylation cascade

Question 18

What is a signal receptor?

Answer 18

protein that changes shape and activity after binding to a signal molecule

Question 19

receptors are _______ and the number of receptors can ________ over time

Answer 19

dynamic; change

Question 20

What does the dynamic characteristic of receptors cause?

Answer 20

increased/decreased sensitivity

Question 21

How can receptors be blocked?

Answer 21

drugs (beta blockers- block adrenaline binding to lower blood pressure)

Question 22

Describe signal reception with lipid soluble molecules

Answer 22

• diffuse across cell membranes
• bind to receptors in cytosol
• can skip signal processing
• typically transported to nucleus to affect transcription of DNA

Question 23

For signal reception w/ insoluble molecules, receptors are ___________

Answer 23

transmembrane proteins (signal binding initiates signaling pathway)

Question 24

Instead of direct response, lipid insoluble receptors trigger ________.

Answer 24

signal transduction

Question 25

What is signal transduction?

Answer 25

conversion of an extracellular signal to an intracellular signal

Question 26

What are examples of signal transduction?

Answer 26

second messengers and phosphorylation cascade

Question 27

What are the steps for signal reception with a lipid-insoluble molecules?

Answer 27

1. signal molecule binds 2. receptor undergoes conformational change 3. receptor activates signal transduction inside the cell

Question 28

Receptor examples for lipid-insoluble

Answer 28

gated ion channels; GPCRs and RTKs

Question 29

What are second messengers in signal transduction?

Answer 29

small molecules that relay intracellular signals (ex cAMP derivative of ATP - activates kinases; and ions)

Question 30

What are phosphorylation cascades?

Answer 30

each kinase phosphorylates a different kinase until a response is triggered

Question 31

What are the typical responses of signal response?

Answer 31

1. change in gene expression 2. change in the activity of proteins

Question 32

Describe the characteristics of signal deactivation.

Answer 32

1. responses and deactivation can occur very rapidly 2. deactivation is different for different signal types

Question 33

When are G proteins deactivated?

Answer 33

- after GTP hydrolysis

Question 34

Describe the deactivation of phosphorylation cascades.

Answer 34

Phosphatases remove phosphate groups from components

Question 35

Describe deactivation with second messengers.

Answer 35

- Ca2+ - membrane pumps to return storage - cAMP, etc - enzymes break down

Question 36

What are the steps of cell signaling for lipid-soluble molecules?

Answer 36

lipid soluble --> directly to signal response --> signal deactivation

Question 37

What are the steps of cell signaling for lipid-INsoluble molecules?

Answer 37

lipid insoluble (GPCRs or RTKs) --> signal transduction (phosphorylation cascade OR second messengers) --> signal response --> signal deactivation

Question 38

What do unicellular organisms use for signaling?

Answer 38

quorum sensing

Question 39

What is quorum sensing?

Answer 39

organisms secrete signaling molecules into the surrounding environment, sensed by others of the same type