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Introductory Biochemistry > Secondary Messengers > Flashcards

Secondary Messengers Flashcards

1
Q

What type of protein activates the enzyme adenylyl cyclase?

A

G proteins

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2
Q

Adenylyl cyclase cleaves two phosphate groups from ATP. What does it convert ATP into?

A

Cyclic adenosine monophosphate (cAMP)

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3
Q

Cyclic adenosine monophosphate (cAMP) is a secondary messenger. What is it degraded into to stop it acting as a signalling molecule?

A

cAMP -> AMP

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4
Q

cAMP is generated from ATP by what enzyme?

A

Adenylyl cyclase

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5
Q

In signalling pathways initiated by receptor tyrosine kinases, how does cAMP function?

A

It does not function

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6
Q

What type of receptor is adenylyl cyclase?

A

It is a membrane-bound enzyme (transmembrane protein)

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7
Q

Adenylyl cyclase has catalytic domains so that it can bind to ATP. What does it break ATP down into?

A

cAMP and inorganic phosphate

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8
Q

What are the fast-acting targets of cAMP?

A

Kinases, and cAMP-dependant protein kinases

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9
Q

What is the longer-lasting target of cAMP?

A

CREB

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10
Q

What is protein kinase A (PKA) a regulator of?

A

Most cAMP dependant physiological processes in cells

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11
Q

Inactive PKA is a tetramer. What does this mean?

A

It has four subunits in its protein complex

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12
Q

What are the four subunits of inactive PKA?

A
  1. Two regulatory subunits/empty cAMP sites
  2. Two catalytic subunits which are substrate-binding sites blocked by domains of the regulatory subunits
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13
Q

How many subunits does active PKA have?

A

Two catalytic subunits which are open substrate-binding sites

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14
Q

Transcription is regulated by cAMP kinase. However, only genes that have what sequence are activated by those receptors?

A

CRE sequences

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15
Q

How is CREB activated?

A

By serine phosphorylation

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16
Q

cAMP is involved in odorant receptors. When it acts on a calcium ion channel, does it open or close it?

A

Opens it

17
Q

How is cAMP binding to odorant receptors inhibited in the odorant pathway?

A

By the calcium influx

18
Q

What are the two forms that guanylyl cyclase can take on?

A
  1. Soluble (acts as an enzyme)
  2. Transmembrane receptor
19
Q

How is the soluble form of guanylyl cyclase induced?

A

By NO

20
Q

How is the transmembrane receptor form of guanylyl cyclase induced?

A

By peptide hormones

21
Q

cGMP signalling regulates the activity of cGMP-activated-protein kinases. It directly binds to and regulates what in the rods and cones of the retina?

A

The ion channels

22
Q

Between the rod and cone cells, which is more sensitive?

A

The rod cells

23
Q

Between the rod and cone cells, which can distinguish between different wavelengths of light?

A

The cone cells

24
Q

Between the rod and cone cells, which is more suited for daytime vision?

A

The cone cells

25
Q

When there is no light stimulus, do the sodium channels in the retina remain open or closed?

A

The channels stay open

26
Q

In the dark, photoreceptors have a constant influx of sodium ions. Why is this?

A

Because there are lots of cGMP proteins which keep the sodium channels open

27
Q

What does rhodopsin do to cGMP via a cascade G protein signal?

A

Switches it off

28
Q

Nitric oxide signalling is produced by what molecule?

A

Nitric oxide synthase (NOS)

29
Q

Nitric oxide synthase converts L-arginine and O2 to what?

A

Citrulline and NO

30
Q

What are the two forms of nitric oxide synthase?

A
  1. Inducible
  2. Constitutive
31
Q

Where is the inducible form of nitric oxide synthase found?

A

In macrophages stimulated by bacterial toxins

32
Q

Where is the constitutive form of nitric oxide synthase found?

A

In epithelial and neuronal tissues

33
Q

Nitric oxide can kill microorganisms directly. What else does it target and activate

A

It targets and activates guanylyl cyclase and cGMP production

34
Q

What effect does guanylyl cyclase have on smooth muscles and as a result, blood flow?

A

It relaxes smooth muscles and increases blood flow to remove toxins

35
Q

Sildenafil citrate (Viagra) inhibits cGMP-specific phosphodiesterase type 5. What effect does this have on signalling and blood flow?

A

It prolongs signalling beyond the normal level and increases blood flow around the body

36
Q

What does altered gene expression controlled by the cAMP response element require?

A

Activation of protein kinase A and CREB phosphorylation

37
Q

How is visual stimuli communicated in terms of cGMP levels?

A

A reduction in cGMP levels

38
Q

Following photon activation, which protein maintains rhodopsin in an inactive form?

A

Arrestin

39
Q

Which amino acid acts as a precursor in nitric oxide biosynthesis?

A

Arginine

Introductory Biochemistry (16 decks)

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