2.5 - Cell Metabolism

Question 1

What are Metabolic Pathways?

Answer 1

• Biological reaction usually occur as a series of small regulated steps called a metabolic pathway.
  - eg. Aerobic Respiration

Question 2

Why are small regulated steps important in metabolic pathways?

Answer 2

• It provides a controlled release of small packets of energy that can be conveniently trapped to form ATP.
• With such a controlled release of energy, cells can operate under normal temperatures for living systems (large steps produce unfavourable conditions eg. High temperature and acidity)
• The cells end up with greater control over the rate of the reaction (as each step is catalysed by a different enzyme) so the reaction can be sped up or slowed down.
• Small steps create intermediate compounds that are essential biological molecules required by cells.

Question 3

What is Metabolism?

Answer 3

• Describes all chemical reactions occurring inside a cell.

Question 4

What is Anabolism?

Answer 4

• Synthetic reactions, small molecules are used to build bigger molecules. (eg. photosynthesis)

Question 5

What is Catabolism?

Answer 5

• Large molecules are broken down to form smaller molecules, releasing free energy to form ATP. (eg. aerobic respiration)

Question 6

How do these reactions occur? (metabolism, anabolism and catabolism)

Answer 6

• All of these reaction occur in a series ie. the product of one reaction becomes the substrate for the next and so on and each requires a different enzyme.

Question 7

What is Phenylketonuria (PKU)?

Answer 7

• Phenylketonuria (PKU) is a common example of metabolic pathways that can have faulty pathways resulting in health problems.

Question 8

How is Free Energy released during metabolic pathways?

Answer 8

• Free energy is released as heat by each step of a chain reaction or metabolic pathway whereby intermediate compounds are being produced.
  - This heat energy is not particularly useful but it can aid the maintenance of a stable body temperature in blooded animals (endothermic) and increases activity in variable temperature (endothermic) animals eg. snakes.

Question 9

Explain how Aerobic Respiration is a metabolic pathway:

Answer 9

-Aerobic respiration is an example of one reaction that is a multistep process (metabolic pathways)
○ Many different enzymes are therefore present at different steps to regulate the process.
○ Glycolysis occurs in cytoplasm, whilst the remainder of the process occurs in the mitochondria.

Question 10

What are the two types of metabolic pathways?

Answer 10

• Mitochondrion Structure

- Photosynthesis

Question 11

What is the Metabolic Pathway in the Mitochondrion?

Answer 11

• Metabolic enzymes are present in the cristae membrane.
• Infolding of the cristae increases the surface area and therefore increasing the amount of enzymes.
• The breakdown of the molecules inside the cristae causes Hydrogen ions to be pumped out into the intermembrane space ——-> The hydrogen ions the flow back though ATP synthase causing ATP to be produced.

Question 12

What is the Metabolic Pathway for Photosynthesis?

Answer 12

• Photosynthesis is another example of an important metabolic pathway.
• This reaction is broken down into two separate (also multistep) reactions:
  
  • The light-dependent reaction – which occurs in the thylakoids containing chlorophyll where light energy is trapped and results in oxygen, ATP and other energy storing molecules being produced.
    
    • The light-independent reaction (also called the Calvin cycle) – which occurs in the stroma and is where carbon dioxide, ATP and other energy storing molecules from above are turned into glucose and water.

Question 13

Explain the how the metabolic pathway for photosynthesis occurs:

Answer 13

• Similar to aerobic respiration, Hydrogen ions are pumped out of the thylakoid lumen and into the stoma ——-> The Hydrogen ions then flow back through ATP synthase causing ATP to be produced.
  - As enzymes catalyse all of these reactions (below), metabolic activity (rate of reaction) is influenced by environmental factors also.

Question 14

What chemicals can interfere with metabolism?

Answer 14

• Many chemicals in the environment interact with metabolic pathways in all organisms, where some benefit humans, whilst others are harmful.
  - Cyanide
  - Herbicides
  - Anti-Depressants

Question 15

How does binding with any other these inhibitors cause them to become reversible or irreversible?

Answer 15

• Binding of these inhibitors can be reversible or irreversible.
  ○ Irreversible inhibitors often react with an enzyme and chemically change the amino acid structure of a protein.
  - This therefore causes changes to the shape of the enzymes and therefore their activity.
  Many drugs are chemical inhibitors of enzymes

Question 16

How does Cyanide interfere with metabolism?

Answer 16

• Potassium cyanide is an irreversible inhibitor of cytochrome c oxidase, which is an enzyme involved in a vital part of aerobic respiration, as discussed earlier
  - It binds to the active site of the enzyme, preventing oxygen from binding, and significantly impacting on ATP production resulting in death

Question 17

How do Herbicides interfere with metabolism?

Answer 17

• These are chemicals that are used to kill weeds/plants.
• Glyphosate (Roundup) acts as a competitive inhibitor of an important metabolic pathway in plants, which produces substances needed for plants to grow.
• As a result, sprayed plants die within a couple of weeks.

Question 18

How do Anti-Depressants interfere with metabolism?

Answer 18

• Norepinephrine and serotonin are normally destroyed by the enzyme monoamine oxidase (MAO).
• MAO inhibitors block this enzyme, inhibiting the destruction of norepinephrine and serotonin, allowing neurotransmitters to remain active longer.