Enzymes

Question 1

examples of molecules that assist enzymes

Answer 1

○ Prosthetic groups: non-amino acid groups bounds to enzymes
○ Inorganic cofactors: ions permanently bound to an enzyme
○ Coenzymes: small carbon-containing molecules; not permanently bound

Question 2

Ph graphs compared to temperature graph

Answer 2

pH graphs are usually symmetrical and look like a bell curve

Temperature usually steeper for higher then optimal and gradually decline for lower then optimal

Question 3

what are coenzymes

Answer 3

• Complex non-protein organic molecules
• Transfer chemicals from the active site or one enzyme to the active site of another enzyme
• Some coenzymes are permanently bound to the enzyme molecule, this is known as a prosthetic group

Question 4

What are prosthetic groups

Answer 4

• Prosthetic groups are non-protein organic molecules, which are attached to the enzyme molecule, and act like built-in coenzymes
• An example of a prosthetic group is pyridoxal phosphate for the enzymes AST and ALT
• They transfer atomic or chemical groups from the active site of the enzyme to some other substance
• Prosthetic groups do not usually have to be added to the reaction mixture, an exception being where there was previous treatment of the enzyme (because they are permanently attached you usually don’t need to add them unless you have fucked with the enzyme and removed them, or synthesised it without it in the first place)
• Vitamin b6 is a prosthetic group for AST and ALT- used in important metabolic processes

Question 5

competitive or non competitive inhibitors

Answer 5

• Competitive inhibitors bind to the active site of an enzyme, competing with the substrate
• Non-competitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape, making the active site less effective
  You cannot reverse non-competitive inhibitors unless you remove them, however, you can reverse competitive inhibitors

Question 6

Irrevesible inhibitors

Answer 6

• Irreversible inhibition: inhibitors covalently bond to side chains in the active site and permanently inactivates the enzyme
• Aspirin binds to cyclooxygenase (COX) and transfers an acetyl group which binds to the active site
• Prostaglandin is no longer produced and its stimulation of inflammation and pain are blocked
• This sounds nice :)
• These are often toxic substances in nature or the reason substances are toxic
• However, in medicine we use this to prevent inflammation and other things

Question 7

Allosteric regulation

Answer 7

• Allosteric regulation: a non-substrate molecule binds to enzymes at a site different from the active site, which changes enzyme shape
  ○ Active form- proper shape to bind to the substrate
  ○ Inactive form- cannot bind to substrate
• Most allosteric enzymes are proteins with quaternary structure
• The active site is on the catalytic subunit
• Inhibitors and activators bind to other polypeptides called regulatory subunits, at regulatory sites (allosteric sites)
• Very sensitive to low conc. Of inhibitors and substrate concentrations- therefore they’re important for regulation of processes

Question 8

Cooperativity

Answer 8

• Where the binding of one substrate molecule to the active site of one subunit locks all subunits in active conformation
• Therefore once you get the one binded thing, you can now bind to everything

Question 9

Allosteric activators

Answer 9

• Holds in stabilised form and it can now bond to substrates
• The active and inactive form oscillate between each other trying to reach equilibrium (difficult to do in the body because it isn’t a closed system and its constantly changing)
• In the bottom panel, there is an inhibitor
• When an inhibitor is attached, it changed the tertiary conformation of the enzyme and changes the enzyme into the inactive form and it cannot bond to the substrates anymore

Question 10

Metabolism regulation as an allosteric process with negative feedback- for ATP

Answer 10

• Allosteric enzymes at certain points in the respiratory pathway respond to inhibitors and activators that help set the pace of glycolysis and the citric acid cycle
• Phosphofructokinase, which catalyses an early step in glycolysis, is one such enzyme
• It is stimulated by AMP (derived from ADP), but is inhibited by ATP and by citrate
• This feedback regulation adjusts the rate of respiration as the cell’s catabolic and anabolic demands change
• ATP can be inhibitor, and ADP can be an activator of enzymes
• It makes sense because if there isnt enough ATP, then there will be a build up of ADP, and if there is too much ATP it will built up and prevent the production of more ATP
• The allosteric inhibition of an enzyme in an ATP-generating pathway by ATP itself is a common mode of metabolic control, called feedback inhibition
• Control points- points where a process can be activated or regulated/inhibited