Metabolism

Question 1

What is metabolism, anabolism and catabolism?

Answer 1

• Metabolism: all chemical reactions that take place within an organisms body, which includes the breakdown and build up of molecules. Enzymes control these.
• Anabolism: synthesis of complex molecules from smaller molecules through condensation reactions (water removal). Process requires energy.
• Catabolism: breakdown of complex molecules into smaller molecules through hydrolysis (water addition). Process releases energy.

Question 2

What is a metabolic pathway?

Answer 2

• Chains or cycles of reactions that are catalyzed by enzymes.
• The different pathways may be interconnected which is called link reaction
• These reaction only occur with the help of enzymes as they lower the activation energy and hence speed up the reactions

Question 3

What is a linear metabolic pathway and give an example?

Answer 3

• The substrate is converted into an end product in a few steps
  e. g. glycolysis

Question 4

What is a cyclic metabolic pathway?

Answer 4

• A pathway that is complex with many intermediate products before the end product is produced
• e.g. Krebs cycle

Question 5

What do enzymes do to speed up reactions? What is activation energy?

Answer 5

• Enzymes lower the activation energy
• Activation energy: the minimum energy that reacting particles require in order for a reaction to take place
  Be able to draw the graph

Question 6

What are enzyme inhibitors and what types exist?

Answer 6

• A poisonous substance that stops the RNA polymerase II enzyme from transcribing DNA and therefore inhibits a reaction from happening
• Competitive and non-competitive enzyme inhibitors

Question 7

What do competitive and non-competitive inhibitors do?

Answer 7

• They compete with the substrate for the same active site. They ‘race’ the substrate in order to inhibit the reaction from happening (diagram in book)
• They attach to the enzyme at a point away from the active site which changes the shape of the enzyme and hence the shape of the active site (diagram in book)

Question 8

Give an example of a competitive inhibitor.

Answer 8

• Enzyme: acetaldehyde dehydrogenase
• Substrate: acetaldehyde
• Product: acetic acid
• Inhibitor: disulfiram

Question 9

Give an example of a non-competitive inhibitor.

Answer 9

• Enzyme: Pyruvate kinase
• Substrate: Phosphoenol pyruvate
• Product: Pyruvate
• Inhibitor: Alanine

Question 10

How do you distinguish between the two types of inhibition on a graph?

Answer 10

• The maximum rate of reaction (V max) of a competitive inhibitor is the same as without inhibitor
• When the substrate concentration increases, the chance of substrates binding to enzymes increases and hence an increased rate of reaction, effect of inhibitor is reduced
• The rate of reaction (V) with non-competitive inhibitions is lower than without inhibitors because enzymes to which an inhibitor is attached are blocked from reacting with any substrate due to the modification of the active site
• The less non-competitive inhibitors there are, the higher the rate of reaction
  Be able to draw the graph (diagram in book)

Question 11

What does end-product inhibition do?

Answer 11

• When the ‘end-product’ of a pathway is no longer needed and the reaction is stopped to reduce the waste of resources
• When the cycle repeats and the first step of the metabolic pathway is initiated, the enzymes are inhibited by non-competitive inhibition to stop the reaction
• The resources can then be used for other reactions

Question 12

How are the enzymes in end-product inhibition inhibited?

Answer 12

• The first reaction of the pathway is allosterically inhibited which is a type of non-competitive inhibitor
• The product of the last reaction of an enzyme binds to the allosteric site (binding site which is not the active site) and the non-competitive enzyme blocks the activity of the enzyme

Question 13

What is an example of end-product inhibition?

Answer 13

• The synthesis of isoleucine from threonine.
• Isoleucine is an amino acid that is consumed from food, in order to be used a bacteria synthesised isoleucine from threonine
• When isoleucine (end-product) binds with the first enzyme (threonine deaminase), the conformation of the active site is changed. The substrate cannot bind to the enzyme anymore. The reaction is stopped.

Question 14

How do you use databases to find new anti-malarial drugs?

Answer 14

• Malaria is caused by the parasite Plasmodium flaciparum
• A chemical and an enzyme of a metabolic pathway may change the infectivity of a pathogen, hence the interactions are studied to find cures
• Databases with the genome of the parasite and protein sequence information were used to screen chemicals for possible interactions before starting lab research
• 35 chemicals showed treatment for malaria. The parasite may become resistant to most antimalarial drugs, hence new ones have to be found

Question 15

How do you calculate and plot rates of reactions on a graph?

Answer 15

• Enzyme catalysed reactions measure: time taken for substrate to be used up, time taken for a specific product to be made, volume/mass of substrate used up over time or volume/mass of product made over time

Question 15

How do you calculate and plot rates of reactions on a graph?

Answer 15

• Enzyme catalysed reactions measure: time taken for substrate to be used up, time taken for a specific product to be made, volume/mass of substrate used up over time or volume/mass of product made over time
• Rate: change % / time (s)
• To plot this on a graph, the independent variable (x axis) and rate of reaction (y axis)
• Makes sure to lable and used appropriate units