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Cell Signalling Flashcards

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Biology 101 flashcards
1
Q

What are the three cycles of cell signalling?

A
  1. Ligand-receptor interaction
  2. Signal transduction
  3. Cellular response
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2
Q

What is ligand-receptor interaction ?

A

A process by which a specific receptor protein on or in target cell detects the signal
This occurs during complementary binding of the ligand (signalling molecule) to the specific site on receptor

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3
Q

What is a ligand ?

A

Molecules that specifically bind to another molecule

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4
Q

What are the characteristics of ligands that bind to cell surface receptors ?

A

Water soluble
Generally too large to pass freely through plasma membrane

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5
Q

What are some examples of cell surface receptors ?

A

G-protein linked receptor
Receptor tyrosine kinase
Ion channel receptor

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6
Q

What are the two effects of ligand-receptor interaction ?

A
  1. Ligand binding generally causes receptor protein to undergo conformational change, which in many receptors would directly activates the receptor, enabling it to bind with other cellular molecules
  2. For other kinds of receptors, the immediate effect of ligand binding is to cause the aggregation of two or more receptor molecules, which leads to further molecular events inside the cell
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7
Q

What is signal transduction ?

A

A process by which extra cellular signals are converted into intracellular signals to generate specific cellular responses

Usually a multi step pathway, involving a series of interactions between relay molecules that operate in sequence

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8
Q

How is signal transduced ?

A
  1. Phosphorylation (and dephosphorylation) of relay proteins which changes conformation of these proteins and thus results in their activation (and deactivation)
  2. Production of small non-protein molecules and ions known as second messengers to relay the signal inside of the cell
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9
Q

What does upstream and downstream mean, relative to a particular molecule of interest ?

A

Upstream - molecules and events that come earlier in the relay chain
Downstream - molecules and events that come later

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10
Q

What is a kinase ?

A

An enzyme which catalyses the addition of phosphate groups from ATP to protein

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11
Q

What are phosphatases ?

A

Enzymes that can catalyse removal of phosphate groups from the proteins, making them inactive which ends signal transduction thus making proteins in the pathway available for reuse

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12
Q

What is a phosphorylation cascade ?

A

Where a series of different protein kinases arranged in a pathway are phosphorylated sequentially

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13
Q

What are second messengers ?

A

Small, non-protein, water-soluble molecules or ions
Able to spread throughout the cell by diffusion

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14
Q

What do second messengers do?

A

Molecules that relay signals received at receptors on the cell surface to target molecules in the cytoplasm and/or nucleus
They also serve to greatly amplify the strength of the signal

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15
Q

What are the widely used second messengers?

A

cAMP
Calcium ions

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16
Q

What is the significance of the multistep pathway in cell signalling ?

A

Amplification of signal

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17
Q

What is a phosphorylation cascade ?

A

An active kinase catalysing the phosphorylation of many kinases, thus activating them. Each of these active kinases go on to phosphorylate and activate many kinases in subsequent steps

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18
Q

At which point in the signal transduction pathway does the cell’s specific response occur ?

A

The end of the signal transduction pathway

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19
Q

What are the two types of cellular responses ?

A

Cytoplasmic responses
Nuclear responses

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20
Q

What is involved in cytoplasmic responses ?

A

Mainly changes in activity of enzyme and proteins in cytoplasm leading to changes in cell metabolism

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21
Q

What are nuclear responses ?

A

When specific genes coding for synthesis of enzymes or other proteins are switched on or off ( in nucleus )

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22
Q

Why can two cells respond differently to the same signal ?

A

Due to difference in one or more of the proteins that handle and respond to the signal

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23
Q

What does the response of a particular cell to a signal depend on ?

A

On the specific collection of signal receptor proteins, relays proteins and functional proteins need to carry out the response

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24
Q

What are scaffolding proteins ?

A

Large relay proteins to which several other relay proteins are simultaneously attached

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25
Q

What is the importance of scaffolding proteins ?

A

Physical arrangement facilitates signal transduction of these molecules by keeping them close together so that transduction pathway reaction can be organised closely together and in order, increasing speed of pathway

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26
Q

When do relay proteins participate in different signalling pathways ?

A

In different cell types
In the same cell at different times or conditions

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27
Q

What is the key to a cell being able to continuously being receptive to regulation by signals ?

A

The reversibility of the changes that the signal produce

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28
Q

What enzyme is involved in conversion of cAMP back into AMP ?

A

Enz phosphodiesterase

29
Q

What enzyme inactivates pkA ?

A

Enzyme phosphatases through removing the attached phosphates

30
Q

What is homeostasis ?

A

The mechanism by which the internal environment of an organism is kept constant

31
Q

What is the normal blood glucose level in humans ?

A

80-120 mg glucose / 100 cm3 of blood

32
Q

What is the blood glucose level after a meal ?

A

150 mg glucose/ 100cm3 of blood

33
Q

What is the blood glucose level after exercise ?

A

70 mg glucose / 100cm3 blood

34
Q

What are the two hormones that control blood glucose levels ?

A

Insulin
Glucagon

35
Q

How are changes in blood glucose levels detected ?

A

Blood flows to pancreas and the alpha and beta cells of the islets of langerhans detect the changes

36
Q

What detects high blood glucose above norma levels ?

A

ß cells of the islets of langerhans

37
Q

What detects Low blood glucose below normal levels ?

A

Alpha cells of the islets of langerhans

38
Q

When blood glucose concentration is higher than normal, which hormones is secreted ?

A

Insulin

39
Q

When blood glucose concentration is lower than normal, what hormone is secreted?

A

Glucagon

40
Q

Which organs are part of response to insulin ?

A

Liver and muscle

41
Q

Which organs are part of response to glucagon ?

A

Liver

42
Q

When does type I diabetes occur ? How to overcome ?

A

When the pancreas does not produce enough insulin, patients must take insulin shots

43
Q

What is type II diabetes ? How to overcome ?

A

When body is resistant to insulin in the blood
Regulated through increased exercise, controlled diet and other medications

44
Q

What is the receptor for insulin ?

A

Receptor tyrosine kinase

45
Q

What are RTKs?

A

Transmembrane receptors which span across the entire plasma membrane

46
Q

What does the part of the RTK which extend into the cytoplasm function as ?

A

Tyrosine kinase - catalyses transfer of phosphate group from ATP specifically to AA tyrosine on substrate protein

47
Q

What is special about the insulin receptor RTK compared to other RTKs ?

A

Insulin receptor RTK exists in inactive covalent disulfide-linked dimer in the absence of a ligand (already in dimerised formed before activation) while for most RTKs, each receptor exists as individual polypeptide in its inactive state

48
Q

What happens when insulin binds to RTK ?

A

Ligand binding causes conformation change to receptor, activating it

49
Q

Where does insulin bind to on RTK ?

A

Extracellular ligand binding site

50
Q

What happens after insulin activates RTK ?

A

The tyrosine kinase region at the intracellular region of each polypeptide is activated
Cross phosphorylation occurs

51
Q

What is cross phosphorylation in RTK ?

A

When each tyrosine kinase of each polypeptide of the RTK phosphorylated tyrosine residues on the tail of the other polypeptide

52
Q

What does activation of RTK result in (signalling pathway) ?

A

Specific relay proteins recognise the activated RTK, bind to specific phosphorylated tyrosine reside and undergoes conformational change that activates the relay proteins

53
Q

What are the four effects of insulin on target cells ?

A
  1. Facilitates transport of glucose into cells by increasing the number of glucose carriers on cell membranes
  2. Activation of glucokinase
  3. Stimulate glycogenesis
  4. Inhibits glycogenolysis
54
Q

How does insulin result in increase in number of glucose carriers on cell membrane ?

A

Signal transduction pathway causes vesicles in the cytoplasm that contain glucose carriers to move and fuse to the cell membrane

55
Q

What does glucokinase do ?

A

Attach phosphate group to glucose molecule

56
Q

Why does insulin signal for activation of glucokinase ?

A

Liver cells are impermeable to phosphorylated glucose, thus by phosphorylating glucose it becomes trapped within cell and steep concentration gradient is maintained to continually take in glucose by facilitated diffusion

57
Q

What is glycogenesis ?

A

Glycogen synthesis from glucose

58
Q

Which enzyme is involved in glycogenesis ?

A

Glycogen synthetase - polymerises phosphorylated glucose into glycogen in liver cells

59
Q

What is glycogenolysis ?

A

Breakdown of glycogen to glucose

60
Q

Which enzyme is involved in inhibition of glycogenolysis (insulin) ?

A

Glycogen phosphorylase is inhibited - enz which catalyses breakdown of glycogen to glucose

61
Q

What are G-protein linked receptors ?

A

Membrane receptors which consists of seven a-helixes spanning the membrane
Specific loops between the helices form specific binding sites for attachment of extracellular ligand binding and intracellular G-protein

62
Q

What happens after G-protein coupled receptor is activated ? (Signal transduction)

A

Cytoplasmic side of the receptor binds to inactive G-protein causing GTP to displace GDP resulting in G-protein activation

63
Q

What does the G-protein do after activation ?

A

It dissociates from the receptor, moves along the membrane and binds to and activates an enzyme on the cytoplasmic side of the membrane

64
Q

What enzyme does activated G-protein activate ?

A

Adenylyl cyclase

65
Q

What does activated adenylyl cyclase do ?

A

Catalyses conversion of many ATP into many cAMP molecules

66
Q

What do cAMP do as part of signal pathway for glucagon ?

A

Serve as second messengers which bind to and activate protein kinase A

67
Q

What are the three effects of glucagon on target cells ?

A
  1. Results in glycogenolysis
  2. Prevent formation of glycogen from glucose
  3. Stimulate gluconeogenesis
68
Q

Which enzyme is involved in glycogenolysis ?

A

Glycogen phosphorylase - catalyse breakdown of glycogen

69
Q

What is gluconeogenesis ?

A

Generation of glucose from non-carbohydrate carbon substrates in the liver

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