3. Structure and regulation of biochemical pathways Part 1

Question 1

What is cellular metabolism?

Answer 1

All the chemical reactions that occur in each living cell (the sum total of all the biochemical pathways and systems)

Question 2

List the 2 types of cellular metabolism reactions:

Answer 2

• Anabolic

- Catabolic

Question 3

When do anabolic reactions occur and how is energy involved? Give an example:

Answer 3

When simple molecules, such as atoms, are joined together to create complex ones, where energy is required to form new chemical bonds (endergonic reactions).
-Eg. Photosynthesis where solar energy is used

Question 4

When do catabolic reactions occur and how is energy involved? Give an example:

Answer 4

When complex molecules are broken down into simpler ones, where the energy stored in chemical bonds is released (exogernic reactions).
-Eg. Cellular respiration, where glucose is broken down

Question 5

What are metabolites?

Answer 5

The reactants, products, and intermediates of an enzymatic reaction, which are modified by a sequence of chemical reactions catalysed by enzymes.

Question 6

Describe the process of biochemical pathways:

Answer 6

• The products or outputs of the first step become the reactants or inputs in the next step until the final products are reached.
• Each step is regulated by a specific enzyme
• If one of the steps in the pathway can’t occur (Eg. If an enzyme in the pathway doesn’t work), metabolic diseases can occur.

Question 7

What is adenosine triphosphate (ATP) and when is it available to be used in endergonic reactions?

Answer 7

The universal primary source of free energy for all living organisms, which contains adenosine attached to a ribose sugar which is bound to 3 phosphate groups.
-When the high-energy bonds attaching the last phosphate group are broken.

Question 8

What is adenosine diphosphate (ADP)?

Answer 8

Is the resulting molecule with 2 phosphate groups of an endergonic reaction.

Question 9

How can ADP be converted back to ATP?

Answer 9

Free energy from an exergonic reaction can be used to add a phosphate group to ADP converting it to ATP.
-The addition of a phosphate group is called phosphorylation.

Question 10

What are enzymes, how do they speed up reactions, how are they generally specific, and why can’t they be reused?

Answer 10

Are biological catalysts made of protein, which speed up chemical reactions by lowering the activation energy (Eg. the energy required to make the reaction proceed). Enzymes do this by weakening critical bonds within the substrate molecule/s, when they (Eg. their active site) contact the substrate. This weakening of bonds lowers the activation energy because it makes the bonds much easier to break.

• Enzymes modify their shape slightly, after binding, to maximise contact with the substrate.
• Are generally specific, where one enzyme initiates one reaction.
• Enzymes can be reused since they are not destroyed or changed.

Question 11

What is an active site?

Answer 11

The area of an enzyme’s surface, which has a specific shape due to the folding of the polypeptide chain, where the substrate binds to and undergoes a reaction.

Question 12

List the 2 models of how enzymes work:

Answer 12

• Lock and key model

- Induced fit model

Question 13

Describe the lock and key model:

Answer 13

The substrate fits into the active site like a key fits into a lock (precise fit).

Question 14

Describe the induced fit model:

Answer 14

Where the interaction between the substrate and the enzyme changes the shape of the active site.

Question 15

What is a cofactor? Give an example:

Answer 15

A small molecule that binds to the active site of an enzyme and in doing so increases the affinity of the enzyme for the substrate (helps the enzyme work on the substrate).
Eg. Small metal irons

Question 16

What are coenzymes? Give an example:

Answer 16

Are small organic molecules which are reversibly loaded and unloaded with the groups of atoms they carry.
-Are a type of cofactor
Eg. ATP

Question 17

What must some enzymes do before they can act as catalysts?

Answer 17

They have to bind to other molecules or ions that change the shape and charge of the enzyme’s active site.

Question 18

List 4 factors which affect enzyme activity:

Answer 18

• Temperature
• pH
• Enzyme concentration
• Substrate concentration

Question 19

Describe how temperature affects enzyme activity:

Answer 19

• Molecules move slower at cool temperatures, and faster at warm temperatures
• Enzyme function relies on enzymes and substrate bumping into each other due to their molecular motion
• As the temperature increases, the rate of reaction also increases as they collide more frequently
• Above the critical temperature, denaturation may occur

Question 20

What happens to an enzyme when it denatures?

Answer 20

The bonds determining the 3D shape break and the protein/enzyme loses its functional structure, causing the substrate to no longer be able to fit into the active site.
-Is usually irreversible

Question 21

Why does the optimum temperature, as well as the temperature that causes the enzyme to denature depend on the type of species of an organism?

Answer 21

Not all organisms live in the same environment or have the same body temperature.

Question 22

Describe how pH affects enzyme activity:

Answer 22

As the pH departs from the optimal pH, the rate of reaction will slow, as the shape of the enzyme will change, and even denature the enzyme.

Question 23

List the 2 types of reversible inhibition:

Answer 23

• Competitive inhibition

- Non-competitive inhibition

Question 24

What are competitive inhibitors?

Answer 24

Competitive inhibitors bind to the active site of an enzyme, preventing the substrate from binding.

Question 25

What are non-competitive inhibitors?

Answer 25

Non-competitive inhibitors prevent the substrate from binding to the active site of an enzyme by attaching themselves to another part of the enzyme, and in doing so, change the shape of the enzyme so that the active site no longer fits the binding site of the substrate.
-Non-competitive inhibitors cannot be removed by increasing the concentration of substrate.

Question 26

What is a binding site?

Answer 26

The part of the substrate that binds to the active site of an enzyme.

Question 27

How does the enzyme concentration affect enzyme activity?

Answer 27

As the concentration of enzyme increases, the rate of reaction will increase.

Question 28

How does the substrate concentration affect enzyme activity?

Answer 28

As the concentration of substrate increases, the rate of reaction will increase up to a point, where the enzyme is saturated with substrate.
-Adding more substrate after this point will not increase the rate of reaction any further since the concentration of substrate is already so high that all the active sites of the enzyme are occupied at any given time.