Cell communication and signaling

Question 1

What must cells be able to do in order to function/survive?

Answer 1

• Sense their environment
• Respond to their environment
• Coordinate with other cells for overall survival (especially in multicellular organisms)

Question 2

Types of cellular communication

Answer 2

1.) Gap junctions
2.) Plasmodesmata
3.) Juxtacrine
4.) Neuronal
5.) Paracrine
6.) Endocrine

Question 3

Gap Junctions (animals)/Plasmodesmata (plants)

Answer 3

Direct contact (fast!)
- local cell-to-cell communication
~ Transfer both chemical and electrical signals

Question 4

Juxtacrine

Answer 4

Transmembrane protein signaling between two neighboring cells in physical contact
(ex. developmental; delta = signal, notch = receptor)
(ex. apoptosis; death ligand, death receptor Fas)

Question 5

Neuronal

Answer 5

Short range neurotransmitters released into synapse (gap) between cells in nervous system
- Through synaptic clefts
- Neurotransmitters

Question 6

What is one important neurotransmitter?

Answer 6

Acetylcholine

Question 7

What is the issue with neuronal?

Answer 7

Small fraction of cells are innervated
- Nervous system commands are very specific and short lived but many life processes are not short lived (ex. growth and reproduction)

Question 8

Paracrine

Answer 8

Short range proteins released by neighboring cells
(ex. EGF=Epidermal Growth Factor)
(ex. Histamine and inflammation response)

Question 9

Endocrine

Answer 9

Long range peptide or steroid hormones delivered through circulatory system
(ex. estrogen-steroid hormone)
(ex. insulin-peptide hormone)

Question 10

Signal and response

Answer 10

Same signal can lead to diverse responses depending on the target cell

Question 11

What are 3 common signal responses?

Answer 11

1.) Heart muscle decreased rate and force of contraction
2.) Salivary gland secretion
3.) Skeletal muscle cell contraction

Question 12

Combinatorial signaling

Answer 12

Functional consequences: different combinations equal different outcomes
1.) survive
2.) grow and divide
3.) differentiate
4.) die (apoptotic cell)

Question 13

How do cells communicate?

Answer 13

Signaling molecule and target cells

Question 14

Signaling molecule

Answer 14

Chemical messenger secreted from another cell

Question 15

Target cells

Answer 15

Specific cells that possess receptors
- Receptors needed to bind and “read” the signaling molecule

Question 16

3 steps of cell signaling

Answer 16

1.) Reception
2.) Transduction
3.) Response

Question 17

Reception

Answer 17

Signal is bound to receptor
- Signal relayed into cytoplasm

Question 18

Transduction

Answer 18

Signal transduction pathway relays signal into cell

Question 19

Response

Answer 19

Cellular responses are activated in both cytoplasm and nucleus to respond to signal

Question 20

What happens during Reception?

Answer 20

receptors span the plasma membrane and relay signal to signal transduction pathways in cell
- Signaling molecules released by another cell bind here

Question 21

What is the Signal Transduction Pathway

Answer 21

a series of steps by which a signal on a cell’s surface is converted into a specific cellular response
(involves both phosphorylation cascade & enzyme activation to make a second messenger)

Question 22

What is the phosphorylation cascade of Transduction?

Answer 22

sequential activation of a series of kinases (amplifies signal at each step)
- Kinases are subsequently turned off again by phosphatases

Question 23

What happens during the activation of reusable molecular switches of Transduction?

Answer 23

A.) Signaling by protein-phosphorylation
B.) Signaling by GTP-Binding Protein

Question 24

What happens during Response?

Answer 24

Signal transduction pathways relay outside signals to affect intracellular responses via cytoplasmic signaling and nuclear signaling

Question 25

Cytoplasmic signaling

Answer 25

• Changes activity of existing proteins
• Fast (and easily changed)

Question 26

Nuclear signaling

Answer 26

• Changes gene expression to reinforce signal
• Slow (but longer lasting)

Question 27

Three general types of cell surface receptors

Answer 27

1.) Ion-channel-linked receptor
2.) G-protein-linked receptors
3.) Enzyme-linked receptors

Question 28

What does a G-protein coupled receptor (GPCRs) contain?

Answer 28

7-transmembrane receptors and Trimeric G protein

Question 29

What makes up a Trimeric G protein?

Answer 29

Alpha subunit, beta subunit, and Y subunit (beta Y complex)

Question 30

G protein coupled receptors (GPCRs) steps

Answer 30

Unstimulated –> stimulated –> GTP activation alpha subunit and beta Y complex both activated –> Activated alpha subunit and beta Y complex find target protein –> target protein activation –> GTP hydrolysis/target protein inactivation –> G protein inactive

Question 31

G-proteins can activate membrane bound enzymes

Answer 31

ex. adenylyl cyclase
(2nd messenger, example is cAMP, amplify the signal)

Question 32

Adrenaline (GPCRs)

Answer 32

epinephrine; signals through GPCR to break down glycogen

Question 33

Cytoplasm

Answer 33

• Adrenaline activates adenylyl cyclase and makes cAMP
• Activates protein kinase A (PKA)
• Activates glycogen phosphorylase= glycogen breakdown

Question 34

Nucleus

Answer 34

Signaling makes more PKA and glycogen phosphorylase

Question 35

Receptor Tyrosine Kinases (RTKs)

Answer 35

phosphorylation cascades lead to gene activation
- Ex. EGF (Epidermal Growth Factor)
- Ligand binding causes dimerization and activation of the RTK receptor
~ Receptors phosphorylate each other (trans-phosphorylation)
~ Signaling proteins bind and are activated

Question 36

What do RTKs often activate?

Answer 36

Ras

Question 37

What does Ras activate?

Answer 37

a signal transduction phosphorylation cascade
- Ras activated by nucleotide exchange: GDP swapped for GTP
- Signal relayed into cell by MAP kinase cascade, which results in changing protein activity and changes in gene expression