Cell Communication SEM1

Question 1

What are gap junctions

Answer 1

Cell-cell junctions between apposed plasma membranes - direct connect for small soluble signals (not large molecules)

Question 2

What signals are moved across membranes through vesicle fusion (exocytosis)

Answer 2

-proteins
-peptides
-amino acids
-nucleotides

Question 3

What signals are released through channels and transporters

Answer 3

Ions

Question 4

What does it mean for a signal to be released constitutively

Answer 4

Passive flow down concentration gradient

Question 5

What does it mean for a signal to be evoked when released

Answer 5

Channels can be gated

Question 6

What signals are released through free diffusion

Answer 6

Steroids
Gasses
(Both are hydrophobic)

Question 7

What are the three main forms of signaling of secreted molecules

Answer 7

-paracrine
-synaptic
-endocrine

Question 8

What is the action of signals released through paracrine signaling

Answer 8

Released signals only affect cells in the immediate cellular environment

Question 9

How do signals terminate in paracrine signalling

Answer 9

-uptake into neighboring cells
-destruction by extracellualr enzymes
-sequestration by extracellular matrix

Question 10

What is the action of signals released through autocrine signalling

Answer 10

The signal is released onto the same cell type

Question 11

What can a group of identical cells in autocrine signaling result in

Answer 11

Group of identical cells produces a higher concentration secreted signal than a single cell can - 1 cell releases signal, binds to receptors on neighboring cells => amplify signal

Question 12

What does the activation of the dendrite trigger in synaptic signaling

Answer 12

-activation at dendrite triggers electrical impulses (action potentials) along neuronal axon

Question 13

What happens when an impulse reaches the nerve terminal in synaptic signalling

Answer 13

It stimulates secretion of chemical neurotransmitters

Question 14

What is the role of endocrine cells

Answer 14

Secrete signals - hormones - into the blood

Question 15

How is specificity of signalling maintained in endocrine signalling

Answer 15

Only certain cells have appropriate receptors to recognise specific hormone

Question 16

How can specificity of signalling be achieved by synaptic signalling

Answer 16

Arises from the physical location of the signalling site and the receptor

Question 17

How can specificity of signalling be achieved by endocrine signalling

Answer 17

Arises from combination of different signalling molecules being recognised by equally array of receptors (wide range of signals and receptors)

Question 18

What is the difference in distance travelled by endocrine and synaptic signalling

Answer 18

-endocrine targets anywhere in body - long distance
-synaptic targets 100nm away from signal -short distance

Question 19

What is the difference in speed between endocrine and synaptic receptors

Answer 19

-endocrine realised on diffusion and blood flow to reach target - slow
-synaptic signals take <1 sec to reach target - fast

Question 20

What is the difference between the affinity of target between endocrine and synaptic signalling

Answer 20

—endocrine signals diluted in bloodstream - receptors high affinity
-synaptic signals highly concentrated at synapse - receptors low affinity

Question 21

Which cells do not require receptors

Answer 21

Cells that use signalling via gap junctions or gasses

Question 22

What does binding of the signal (ligand) cause

Answer 22

Receptor activation

Question 23

What does receptor activation stimulate production of

Answer 23

Stimulates production of intracellular signals

Question 24

Where are receptors located in relation to steroid signalling

Answer 24

Receptors located within the cell

Question 25

What are the 4 major types of receptors

Answer 25

-ionotropic
-metabotropic
-kinase
-steroid

Question 26

Function of ionotropic receptors

Answer 26

Allow flow of ions across membranes

Question 27

Function of metabotropic receptors

Answer 27

Generate new signals inside cell (2nd messengers)

Question 28

Function of kinase receptors

Answer 28

Modify existing molecules to generate new signals

Question 29

Function of steroid receptors

Answer 29

Change expression of genes

Question 30

What effect can ionotropic receptors induce

Answer 30

Changing the membrane potential

Question 31

What are the two types of ionotropic receptors

Answer 31

Excitatory - influx of positive charged ions e.g Na+ or Ca2+
Inhibitory - influx of negative charged ions e.g Cl-

Question 32

How do metabotropic or G-protein-linked receptors act to regulate the activity of a plasma-membrane-bound target protein

Answer 32

The receptors act indirectly to a target which is either an enzyme or an ion channel

Question 33

What is the intermediate between the receptor and target in metabotropic processes

Answer 33

A trimeric G-protein

Question 34

What are the 3 subunits of G-proteins

Answer 34

Alpha (a), beta (B) and gamma (y) subunits

Question 35

What do the subunits of g-proteins bind to

Answer 35

Bind to metabotropic receptors which have 7 transmembrane domain structures (Metabotropic and G protein linked receptors have same structures)

Question 36

How is the G-protein attached to the receptor and membrane

Answer 36

Attached to receptor by its alpha (a)- subunit
Attached to membrane by its alpha(a) and gamma(y)-subunits

Question 37

What does the ligand binding cause the alpha(a subunit to release

Answer 37

Releases GDP for GTP (gtp replaces gdp and binds to alpha subunit of protein)

Question 38

What does ligand biding and the a-subunit release of GDP and GTP cause

Answer 38

1)activation of the alpha(a) subunit and
2)release of the beta(B)/gamma(y) subunits

Question 39

What does the activation of the alpha-subunit allow for

Answer 39

To alter enzyme activities therefor change concentration of intracellular signals inside cell

Question 40

How is signalling from metabotropic receptors terminated

Answer 40

Terminated by hydrolysis of GTP to GDP by the alpha-subunit

Question 41

What are kinase receptors

Answer 41

Either enzymes themselves or associated with enzymes

Question 42

What is the structure of a kinase receptor

Answer 42

One transmembrane domain with a ligand binding site outside the cell and enzyme activity inside cell