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Intro. to Microbiology - Part 1 > Enzymes Part 3 > Flashcards

Enzymes Part 3 Flashcards

- importance of cofactors & prosthetic groups - enzyme activation - apoptosis - regulatory mechanisms of enzyme activity

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Biology 101 flashcards
1
Q

The catalytic activity of many enzymes depends on the presence of small molecules called:

A

cofactors or coenzymes

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2
Q

coenzymes

A
  • small non-protein molecules

- helpers

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3
Q

cofactors are subdivided into 2 groups

A
  1. metals

2. small organic molecules (coenzymes)

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4
Q

small organic molecules

A

coenzymes

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5
Q

cofactor

A

activate inactive form of enzymes to convert into active forms

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6
Q

apoenzyme

A

inactive form of enzyme

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7
Q

holoenzyme

A

active form of enzyme after being bound by coenzyme

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8
Q

prosthetic group

A

tightly bound coenzymes

- e.g. heme group

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9
Q

co-substrates

A

loosely associated coenzymes

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10
Q

coenzyme

A
  • small organic molecule
  • often derived from vitamins
  • can be tightly or loosely bound to an enzyme
  • tightly associated with enzyme’s active site + assists with catalytic function
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11
Q

Biotin

A
  • forms transient covalent bond to COO- group

- can’t be synthesized by humans; must be supplied by diet (vitamin)

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12
Q

zymogen

A
  • inactive precursor
  • aka proenzyme
  • biochemical change usually occurs in Golgi bodies
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13
Q

proteolytic activation

A
  • specific part of enzyme is cleaved in order to activate it
  • cleavage does not require energy (ATP)
  • occurs just once in the life of an enzyme molecule
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14
Q

proteolysis

A
  • digestive enzymes that hydrolyze proteins are synthesized as zymogens in stomach and pancreas
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15
Q

pancreas

A
  • secretes zymogens partly to present enzymes from digesting proteins in the cells in which they are synthesized
  • enzymes like pepsin and trypsin are created in the form of pepsinogen and trypsinogen (inactive zymogens)
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16
Q

pepsinogen

A
  • activated when chief cells release it into gastric acid -> hydrochloric acid partially activates it
  • another partially activated pepsinogen completes activation by removing peptide, turning pepsinogen into pepsin
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17
Q

accidental activation of zymogens

A
  • occur when secretion duct in pancreas in blocked by gallstone resulting in acute pancreatitis
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18
Q

protein hormones synthesized as inactive precursors

A
  • e.g. insulin is derived from proinsulin by proteolytic removal of a peptide
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19
Q

zymogen: pepsinogen

A
  • site of synthesis: stomach

- active enzyme: pepsin

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20
Q

zymogen: chymotrypsinogen

A
  • site of synthesis: pancreas

- active enzyme: chymotrypsin

21
Q

zymogen: trypsinogen

A
  • site of synthesis: pancreas

- active enzyme: trypsin

22
Q

secretion of zymogen granular by a cell of the pancreas

A
  • darker-staining cells form clusters -> acini
    • arranged in lobes separated by thin fibrous barrier
  • secretory cells of each acinus surround small intercalated duct
    • these cells have many small granules of zymogens
23
Q

coagulation (clotting)

A
  • blood changing from liquid to gel -> forming blood clot
  • leads to hemostasis
  • involves cellular (platelet) and protein (coagulation factor) component
24
Q

hemostasis

A

cessation of blood loss from damaged vessel

25
Q

mechanism of coagulation involves

A
  • activation
  • adhesion
  • aggregator of platelets
  • deposition and maturation of fibrin
26
Q

blood leaking through endothelium starts 2 processes

A
  1. changes in platelets

2. exposure of sub endothelial tissue factor to plasma Factor VII -> leads to fibrin formation

27
Q

primary hemostasis

A

platelets forming plug at injury site

28
Q

secondary hemostasis

A
  • occurs simultaneously
  • additional coagulation factors (clotting factors) beyond Factor VII respond in a complex cascade to form fibrin strands -> strengthen platelet plug
29
Q

coagulation factors

A
  • serine proteases (enzymes) which act by cleaving downstream proteins
  • circulate as inactive zymogens
30
Q

coagulation cascade divided into 3 pathways

A
  1. tissue factor pathway (extrinsic)
  2. contact activation pathway (intrinsic)
  3. final common pathway
31
Q

which pathways activate the final common pathway (factor x), thrombin and fibrin?

A

tissue factor and contact activation pathway

32
Q

cofactors necessary for proper functioning of coagulation cascade

A
  • calcium and phospholipid

- Vitamin K

33
Q

procoagulant

A

?

34
Q

anticoagulant

A

??

35
Q

coagulation cascade

A

blood clotting mediated by cascade of proteolytic activations that ensure a rapid and amplified response to trauma

36
Q

collagen

A
  • fibrous protein
  • major constituent of skin and bone
  • derived from procollagen (soluble precursor)
37
Q

many developmental processes are controlled by activation of zymogens. T/F?

A

True

  • e.g. large amounts of collagen resorbed from tail of tadpole -> metamorphosis into frog
  • e.g. conversion of procollagenase into collagenase (active protease)
38
Q

apoptosis

A
  • programmed cell death
  • mediated by proteolytic enzymes -> capsases
  • produces special cell fragments -> phagocytic cells
  • can’t stop once it starts
  • initiated through 1 of 2 pathways: intrinsic and extrinsic pathway
    • both pathways use caspases (proteases)
39
Q

capsases

A
  • proteolytic enzymes that mediate apoptosis
  • synthesized in precursor form as procaspases
  • when activated, function to cause cell death
40
Q

some enzymes with specialized regulatory functions can be regulated when physiologic conditions change, by:

A
  • regulation of allosteric enzymes
  • regulation of enzymes by covalent modification
  • induction and repression of enzyme synthesis
41
Q

allosteric enzymes

A
  • consist of multiple subunits
  • regulated by effectors (modifiers) that bind noncovalently at a site other than the active site altering the affinity of the enzyme for its substrate or modifying the maximal catalytic activity of the enzyme
    • can increase of decrease affinity for substrate
42
Q

positive effector/negative effector

A
  • effectors can influence affinity of enzyme for its substrate K0.5
  • modify maximal catalytic velocity Vmax
  • or both
43
Q

homotropic effectors

A
  • when substrate itself serves as an effector
  • most allosteric enzymes serve as positive homotropic effectors:
    • presence of substrate molecule at one site of the enzyme enhances the catalytic properties of the other substrate-binding sites
    • ex: hemoglobin is a homotropic allosteric protein
44
Q

hemoglobin

A
  • sigmoidal shape -> subunits cooperate in binding oxygen
  • binding of oxygen molecule increases the oxygen affinity of the remaining heme groups in the same hemoglobin molecule (homotropic effector)
45
Q

other allosteric effects found in hemoglobin

A
  • caused by pH, pCO2 and the cocentration of 2,3-bisphosphoglycerate
    • at high pO2, and high pH (such as in lungs): Hb has a very high affinity to oxygen
    • at low pO2 and low pH (such as in tissues): Hb has a low affinity to oxygen, and releases oxygen to myoglobin and to tissue cells
46
Q

2,3-bisphosphate

A
  • generated from an intermediate of the glycolysis
  • important regulator of binding of O2 to hemoglobin
    • > allosteric effector
  • binds to deoxyhemoglobin and decreases O2 affinity of hemoglobin
47
Q

heterotropic effectors

A
  • effector different from substrate

- ex: feedback inhibition of a metabolic pathway

48
Q

covalent modifications

A
  • addition or removal of phosphate groups from specific amino acids of the enzyme (Ser, Tyr, Thr)
    • phosphorylation reactions are catalyzed by kinases using ATP as a phosphate donor

Intro. to Microbiology - Part 1 (11 decks)

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