Topic 1

Question 1

what affects the mode of mechanism used for cell communication?

Answer 1

distance between the signaling and responding cells

Question 2

what are the four basic mechanisms cells use for communication

Answer 2

direct contact, paracrine signaling, endocrine signaling and synaptic signaling

Question 3

describe direct contact

Answer 3

• cell surface molecules (proteins, lipids and carbohydrates) of one cell recognised by the receptor on the plasma membrane of adjacent cells
• adjacent cells can communicate through gap junctions

-surface of an eukaryotic cell is richly populated with proteins, carbohydrates and lipids attached to and extending outward from plasma membrane

-when cells are very close to one another some molecules on the plasma membrane of the cell can be recognised by the receptors on the plasma membrane of adjacent cell

Question 4

describe paracrine signaling

Answer 4

• signals with short lived, local effects

-affects cells of immediate vicinity

• signal molecules released by cell can diffuse into the extracellular fluid into the cell
• if those molecules are …
  + taken up by neighboring cells
  + destroyed by extracellular enzymes
  + or quickly removed from the extracellular fluid in some other way

…their influence is restricted within the immediate vicinity of the releasing cell

• instances of which paracrine signaling is used: signaling between immune cells in vertebrates

Question 5

describe endocrine signaling

Answer 5

• longer lived signal molecules
• signal molecules may enter the circulatory system and travel widely throughout the body

-affect cells very distant from releasing cell

• example of such signal molecule: hormones

Question 6

describe synaptic signaling

Answer 6

• mediated by neurotransmitters in chemical synapse

-example: between neuron and its target cells

• in animals, the cells of nervous system provide rapid communication with distant cells
• their signal molecules, neurotransmitters do not travel to distant cells through circulatory system like hormones
• instead, the long, fiber-like extensions of nerve cells release neurotransmitters from their tips very close to the target cells
• the association of a neuron and its target cell is called chemical synapse
• and this type of intercellular communication is called synaptic signaling

Question 7

what are the two things required for communication between cells?

Answer 7

ligand - signaling molecule

receptor protein - molecule to which the ligand binds

Question 8

what happens when the ligand and receptor protein interact?

Answer 8

the interaction between the two components initiates the process of signal transduction (refers to events within the cell that occur in response to a signal) which converts the information in the external signal into a cellular response.

Question 9

the cells of multicellular organisms use a variety of molecules as signals, including but not limited to…

Answer 9

• peptides
• large proteins
• individual amino acids

-nucleotides

• steroids and other lipids
• even dissolved gases such as nitrogen oxide used as signals

Question 10

what are the two locations that receptor proteins can be found at?

Answer 10

• intracellular
• plasma membrane (cell surface)

Question 11

usage of intracellular receptor?

Answer 11

for hydrophobic ligands which can pass through the membrane

Question 12

usage of cell surface receptor?

Answer 12

for hydrophilic ligands that cannot pass through the membrane

Question 13

overview of cell signaling?

Answer 13

cell signaling involves a signal molecule called ligand, a receptor protein and a signal transduction pathway that produces a cellular response

Question 14

major type of ligands?

Answer 14

hydrophobic ligands- can easily pass through cell membrane

hydrophilic ligands cannot easily cross the cell membrane

Question 15

major type of receptors?

Answer 15

differentiated based on location and chemical nature of their ligands

1. membrane receptor
   - channel linked receptors
   - enzymatic receptors
   - g protein coupled receptors
2. intracellular receptor
   - steroid hormone receptor
   - nitric oxide receptor

Question 16

what is phosphorylation?

Answer 16

• addition of phosphate group to a molecule
• a cell’s response to a signal often involves activation or deactivating proteins
• phosphorylation is a common way to change activity of protein

Question 17

what is phosphatase?

Answer 17

an enzyme that removes phosphate from a protein

Question 17

what is protein kinase?

Answer 17

enzyme that adds phosphate to protein

Question 18

what does the phosphorylation and dephosphorylation of protein do?

Answer 18

many proteins are controlled by their phosphorylation state: that is, they are activated by phosphorylation and deactivated by phosphorylation , or the reverse

Question 19

what reverses the action of kinases?

Answer 19

protein phosphatase enzymes

Question 20

what are the two types of kinases?

Answer 20

• serine threonine kinases
• tyrosine kinases

Question 21

what are serine threonine kinases?

Answer 21

kinases enzymes that add a phosphate group to the serine or threonine amino acid residue

Question 22

what are tyrosine kinases?

Answer 22

kinase enzymes that adds a phosphate group to the tyrosine amino acid residue

Question 23

what are channel linked receptors

Answer 23

• chemically gated ion channels that allow passage of ions
• the channel only opens when the chemical (ligand) bind to it
• there are gated channels for sodium, potassium, calcium and chloride ions
• for example: acetylcholine receptor on muscle cell membrane is a channel linked receptor for sodium ion

when the receptor binds to acetylcholine, the channel opens, allowing Na+ to flow into muscle cell.

this is a critical step linking signal from a motor neuron to muscle cell contraction

Question 24

what are enzymatic receptors?

Answer 24

• receptors that also act as enzymes
• enzymes activity of receptor
  is activated when bounded by the ligand

-most of them are protein kinases e.g. receptor tyrosine kinases

Question 25

what are receptor tyrosine kinases (RTK)?

Answer 25

• a large class of membrane receptors that recognise hydrophilic ligands (hormones or growth factors that cannot pass through the plasma membrane)

-a kind of transmembrane enzyme receptor (receptor itself is an enzyme)

-enzyme that add a phosphate group to tyrosine amino acid residue of a protein

-mainly influence cell cycle, cell migration, cell metabolism and cell proliferation

• made up of three domains
  + extracellular ligand binding domain
  + single transmembrane domain
  + intracellular kinase domain

Question 26

activation of RTK

Answer 26

• ligands binds to receptors
• two of these receptor-ligand complexes associate together (dimerise)
• they phosphorylate each other too in a process called autophosphorylation
• the autophosphorylation event transmits the extra cellular signal across the membrane
• the propagation of the signal in cytoplasm can take place in a variety of forms:+ binding of response proteins to phosphotyrosine on receptor (role as docking protein)+ phosphorylation of response proteins by the activated kinase domain

Question 27

why do two different cells with same receptor still have a different response?

Answer 27

as it depends on the response protein present in the cytoplasm

Question 28

what is insulin?

Answer 28

the hormone, insulin, is important in maintaining a constant level of blood glucose.

it acts to lower blood glucose by signaling through an RTK

Question 29

what is an insulin receptor?

Answer 29

a type of receptor tyrosine kinase

Question 30

activation of insulin receptor

Answer 30

• binding of insulin on the insulin receptor to the extra cellular domain of alpha subunit of insulin receptor lead
  to auto-phosphorylation of the receptor
• the beta subunit of one insulin receptor phosphorylates the other
• the insulin response protein binds to phosphorylation receptor and passes the signal on to another response protein that activates glycogen synthase, which converts glucose to glycogen

Question 31

what would the other insulin response proteins do?

Answer 31

• inhibit the production of enzymes involved in making glucose
• increase the number of glucose transporter proteins in plasma membrane, such that more glucose will be transported into cell from blood stream(together, these responses act to lower blood glucose levels)