8.1 Metabolism

Question 1

What is metabolism?

Answer 1

It is the sum of all chemical reactions within an organism

Question 2

What is an anabolic reaction?

Answer 2

It uses energy to build complex organic molecules from simpler ones (typically by condensation). The reactions are endergonic and biosynthetic.

Question 3

Name an example of an anabolic reaction.

Answer 3

Photosynthesis

Question 4

What is an catabolic reaction?

Answer 4

It breaks down complex organic molecules to simpler ones with the release of energy (typically by hydrolysis). The reactions are exergonic and degradative.

Question 5

Name an example of a catabolic reaction.

Answer 5

Cellular respiration

Question 6

What is an endergonic reaction?

Answer 6

Products of a chemical reaction have more energy than the reactants or substrates of the reaction, tend to occur in biosynthetic reactions which are enzyme-catalyzed reactions where substrates are converted into more complex molecules.

Question 7

What is an exergonic reaction?

Answer 7

Products of a chemical reaction have less energy than the reactants or substrates of the reaction, tend to occur in degradative reactions which are enzyme-catalyzed reactions where substrates are converted into simpler molecules.

Question 8

What do metabolic pathways consist of?

Answer 8

Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions.

Question 9

Where do metabolic pathways occur?

Answer 9

In designated compartments of the cell where the enzymes are clustered and isolated.

Question 10

What is an enzyme?

Answer 10

Enzymes are globular proteins that, as a minimum have the tertiary level of organization.

Question 11

What allows enzymes to form the active site?

Answer 11

The higher levels of proteins structure allows enzymes to form the active site.

Question 12

What is the active site?

Answer 12

The active site is a region on the enzyme that binds to a substrate. The binding results in the reaction occuring much faster than would be expected without the enzyme.

Question 13

Define enzyme specificity.

Answer 13

Enzyme specificity is the ability of an enzyme to bind with substrates or catalyze a reactions and is made possible by enzyme structure.

Question 14

What is the model for enzyme actions called?

Answer 14

The induced-fit model

Question 15

What are the conformational changes and induced fit a result of?

Answer 15

The changes in the R-groups of the amino acids at the active site as the enzyme interacts with the substrate/s.

Question 16

What is activation energy (AE)?

Answer 16

It is the energy necessary to destabilize the existing chemical bonds in the substrate of an enzyme-substrate catalyzed reaction.

Question 17

How does enzymes affect the activation energy?

Answer 17

Enzymes lower the activation energy needed for the chemical reactions that they catalyze, which means that the enzymes cause chemical reactions to occur faster because they reduce the amount of energy needed to bring about the reaction.

Question 18

What is a competitive inhibition?

Answer 18

In competitive inhibition a molecule called a competitive inhibitior competes with the substrate directly for the active site. Because of this, the substrate will have fewer encounters with the active site and the reaction will be slower.

Question 19

Competitive inhibition may be ____ or ____

Answer 19

reversible, irreversible

Question 20

Give an example of competitive inhibition.

Answer 20

Relenza

• Viruses use the enzyme neuraminidase to release themselves from infected cells
• Relenza blocks the enzyme’s active site and thus prevents viral release and spread.

Question 21

What is a non-competitive inhibition?

Answer 21

Non-competitive inhibition involves an inhibitor that does not compete for active site. Instead, the inhibitor (allosteric inhibitor) binds to the allosteric site. The binding at the allosteric site causes the active site’s shape to change, making it non-functional which slows down the reaction.

Question 22

Non-competitive inhibition may be ____ or ____

Answer 22

reversible, irreversible

Question 23

Give an example of non-competitive inhibition.

Answer 23

Cyanide

• Cyanide is a poison which prevents ATP production via aerobic respiration, leading to eventual death
• It binds to an allosteric site on cytochrome oxidase – a carrier molecule that forms part of the electron transport chain
• By changing the shape of the active site, cytochrome oxidase can no longer pass electrons to the final acceptor (oxygen)
• Consequently, the electron transport chain cannot continue to function and ATP is not produced via aerobic respiration

Question 24

What is end-product inhibition?

Answer 24

End product inhibition is negative feedback used to regulate the production of a given molecule.

The initial substrate is a molecule that is altered in three steps by enzymes 1,2 and 3. The end product will combine with enzyme 1 to stop the reaction so there will not be an excess production of the end product.

Question 25

What are metabolic pathways controlled by?

Answer 25

End-product inhibition

Question 26

Give an example of end-product inhibition.

Answer 26

Isoleucine

• Threonine is converted into isoleucine by the enzyme threonine deaminase
• Isoleucine binds to an allosteric site on the enzyme and blocks it activity
• Thus, isoleucine synthesis inhibits further formation (end-product inhibition)

Question 27

Distinguish types of inhibition from graphs.

Answer 27

Highest to lowest:

• Uninhibited
• Competitive inhibition
• Non-competitive inhibition

Question 28

In competitive inhibition, how can the effects of a reversible inhibitor be overcome?

Answer 28

If it is a reversible inhibitor, then effects of the inhibitor can be overcome by increasing the substrate concentration, then the substrate can bind to the active site and the reaction can proceed more rapidly.

Question 29

Allosteric interactions can in some cases…

Answer 29

activate an enzyme instead of inhibiting it.