Enzymes Part 3

Question 1

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

Answer 1

cofactors or coenzymes

Question 2

coenzymes

Answer 2

• small non-protein molecules

- helpers

Question 3

cofactors are subdivided into 2 groups

Answer 3

1. metals

2. small organic molecules (coenzymes)

Question 4

small organic molecules

Answer 4

coenzymes

Question 5

cofactor

Answer 5

activate inactive form of enzymes to convert into active forms

Question 6

apoenzyme

Answer 6

inactive form of enzyme

Question 7

holoenzyme

Answer 7

active form of enzyme after being bound by coenzyme

Question 8

prosthetic group

Answer 8

tightly bound coenzymes

- e.g. heme group

Question 9

co-substrates

Answer 9

loosely associated coenzymes

Question 10

coenzyme

Answer 10

• 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

Question 11

Biotin

Answer 11

• forms transient covalent bond to COO- group

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

Question 12

zymogen

Answer 12

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

Question 13

proteolytic activation

Answer 13

• 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

Question 14

proteolysis

Answer 14

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

Question 15

pancreas

Answer 15

• 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)

Question 16

pepsinogen

Answer 16

• 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

Question 17

accidental activation of zymogens

Answer 17

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

Question 18

protein hormones synthesized as inactive precursors

Answer 18

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

Question 19

zymogen: pepsinogen

Answer 19

• site of synthesis: stomach

- active enzyme: pepsin

Question 20

zymogen: chymotrypsinogen

Answer 20

• site of synthesis: pancreas

- active enzyme: chymotrypsin

Question 21

zymogen: trypsinogen

Answer 21

• site of synthesis: pancreas

- active enzyme: trypsin

Question 22

secretion of zymogen granular by a cell of the pancreas

Answer 22

• 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

Question 23

coagulation (clotting)

Answer 23

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

Question 24

hemostasis

Answer 24

cessation of blood loss from damaged vessel

Question 25

mechanism of coagulation involves

Answer 25

- activation - adhesion - aggregator of platelets - deposition and maturation of fibrin

Question 26

blood leaking through endothelium starts 2 processes

Answer 26

1. changes in platelets | 2. exposure of sub endothelial tissue factor to plasma Factor VII -> leads to fibrin formation

Question 27

primary hemostasis

Answer 27

platelets forming plug at injury site

Question 28

secondary hemostasis

Answer 28

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

Question 29

coagulation factors

Answer 29

- serine proteases (enzymes) which act by cleaving downstream proteins - circulate as inactive zymogens

Question 30

coagulation cascade divided into 3 pathways

Answer 30

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

Question 31

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

Answer 31

tissue factor and contact activation pathway

Question 32

cofactors necessary for proper functioning of coagulation cascade

Answer 32

- calcium and phospholipid | - Vitamin K

Question 33

procoagulant

Answer 33

?

Question 34

anticoagulant

Answer 34

??

Question 35

coagulation cascade

Answer 35

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

Question 36

collagen

Answer 36

- fibrous protein - major constituent of skin and bone - derived from procollagen (soluble precursor)

Question 37

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

Answer 37

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

Question 38

apoptosis

Answer 38

- 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)

Question 39

capsases

Answer 39

- proteolytic enzymes that mediate apoptosis - synthesized in precursor form as procaspases - when activated, function to cause cell death

Question 40

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

Answer 40

- regulation of allosteric enzymes - regulation of enzymes by covalent modification - induction and repression of enzyme synthesis

Question 41

allosteric enzymes

Answer 41

- 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

Question 42

positive effector/negative effector

Answer 42

- effectors can influence affinity of enzyme for its substrate K0.5 - modify maximal catalytic velocity Vmax - or both

Question 43

homotropic effectors

Answer 43

- 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

Question 44

hemoglobin

Answer 44

- 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)

Question 45

other allosteric effects found in hemoglobin

Answer 45

- 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

Question 46

2,3-bisphosphate

Answer 46

- 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

Question 47

heterotropic effectors

Answer 47

- effector different from substrate | - ex: feedback inhibition of a metabolic pathway

Question 48

covalent modifications

Answer 48

- 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