Biological Oxidation (Chapter 12)

Question 1

What is the need for Intermediary metabolism?

What is the advantages of this?

Answer 1

-If electrons were to be directly transferred to oxygen, most of the energy would be lost.

Advantages:

• Free energy change is harvested (because electron flow coupled to ATP synthesis).
• Process can be controlled
• Electrons can be used for other purposes (like antioxidant defence mechanism).

Question 2

• What is the Redox Potential?

- What conditions are used for Biological systems in terms of Redox Potential?

Answer 2

• Explains the free energy change of a REDOX reactions.

For biological systems, the Redox potential is described by pH 7, where E = -0.42V

Question 3

What are Oxidoreductase?

Types of these?

Answer 3

Enzymes involved in REDOX rxns.

Types:

1) Oxidases
2) Dehydrogenases
3) Hydroperoxidases
4) Oxygenases

Question 4

What do Oxidases do?

Notable examples?

Answer 4

They catalyse the removal of Hydrogen from a substrate.
Using oxygen as a Hydrogen Acceptor.

**removal of hydrogen = oxidation

Examples:

• Cytochrome Oxidase
• Flavoprotiens

Question 5

1) What is Cytochrome Oxidase’s other name?
2) What type of oxidoreducate enzyme is it?
3) What is it?

Answer 5

1) It is also known as Cytochrome aa3.
2) Oxidase (if you got this wrong… just close your computer.)
3) It’s the terminal part of the respiratory chain.
- It is a HEMOPROTEIN
- contains 2 molecules of Heme, each bound to one Fe atom which oscillates between Fe2+ and Fe3+

Question 6

1) What type of oxidoreducatse is Flavoproteins?

2) What prosthetic group do they have?

Answer 6

1) Oxidases

2) Has FAD, FMN is the prosthetic group they have.

Question 7

What is FAD/FMN formed from?

Answer 7

Formed from the vitamin Riboflavin.

Question 8

What do Dehydrogenases do?

Answer 8

They transfer hydrogen from one substrate to another via a redox reaction.
So they oxidate one substrate and reduce another substrate
They do not use oxygen as a hydrogen acceptor.

Question 9

Characteristics of Dehydrogenases?

Answer 9

1) specific to substrate
2) Often use co-enzymes
3) catalyse reversible reactions

Question 10

1) Which co-enzymes do Dehydrogenase use?

2) How are they produced

Answer 10

1) Use Nictinoamide coenzymes most often.

2) NAD/ NADP+ are produced by the vitamin - Niacin.

Question 11

1) What do NAD-Linked Dehydrogenases catalyse?

2) How does NAD become NADH?

Answer 11

1) Catalyse redox reactions involved in oxidative pathways.

2) Usually substrate is oxidised, losing 2 hydrogens and 2 electrons.
- One Hydrogen and two electrons accepted by NAD to form NADH

Question 12

1) What do NADP- Linked Dehydrogenases catalyse?

Answer 12

Involved in biosynthesis pathways where reductive reactions are needed.
eg//
1) extramitochondrial pathway of fatty acids
2)steroid synthesis
3)pentose phosphate pathway

Question 13

1) Types of Hydroperoxidases?

2) Purpose of Hydroperoxidases?

Answer 13

1) Peroxidases + Catalase

2) They protect against ROS (reactive oxygen species).

Question 14

How do ROS generate?

What can they cause if accumulate?

Answer 14

ROS generate during normal metabolism.
However if not removed, they accumulate which can cause:

• cancer (everything does nowadays anyway)
• Arteriosclerosis
• Aging

Question 15

1) What do peroxidase do?
2) Where is it found?
3) What is their prosthetic group?

Answer 15

1) They reduce peroxides using various electron acceptors.
2) They are found in Milk, Leuokocytes, Platlets
3) Their prosthetic group is called Protoheme.

Question 16

Electron acceptors for peroxides being catalysed by peroxidase?

Answer 16

• Ascorbate (Vitamin C)
• Quinones
• Cytochrome C

Question 17

Equation for Peroxidase

Answer 17

H2O2 + AH2 –> 2(H20) + A

Question 18

Gluthione Peroxidase:

• where found?
• what is the prosthetic group?
• how does it destroy H2O2?

Answer 18

• found in erythocytes.
• the prosthetic group = selenium
• Destroys H2O2 via conversion of Gluthione to it’s oxidised form.

Question 19

1) What is Catalase?
2) Explain the two ways in which it catalyses peroxides?
3) Under normal conditions which way of catalysis is most preferred?

Answer 19

1) it is a hemoprotein, containing 4 heme groups.
2) Catalyse either exactly like how peroxidase does it.
H2O2 + AH2 –> 2(H2O) + A
Or catalyses via:
2(H2O2) –> 2(H2O) + O2
- in the way above, it uses one h2o2 as a reductant and other as oxidant.

3) the first way.

Question 20

Where is Catalase found?

Answer 20

• Blood
• Bone Marrow
• Mucous Membranes
• Kidneys
• Liver

(another pointless fact they will most likely base the whole exam upon).

Question 21

What do Peroxsomes posses?

Answer 21

They are rich in oxidases and catalase.

• Oxidase - take hydrogen from substrate and use oxygen as hydrogen acceptor.
• Catalase - type of hydroperoxidase. Catalyses breakdown of H2O2.

Perioxosomes found in liver.

Question 22

1) What do Oxygenases do?

2) Types of oxygenases?

Answer 22

1) they catalyse the transfer oxygen into the substrate.
2) - Monoxygenase
- Dioxygenase

Question 23

What do Dioxygenase do?

Write the equation.

Answer 23

Incorperate both atoms of oxygen into the substrate.

O2 + A -> AO2

Question 24

1) Function of Monoxygenase?
2) what is necessary for Monoxygenase to work?
3) Noteable Monoxygenase

Answer 24

1) Have a mixed function of:
- hydroxylases
- oxidases

One molecule of the O2 incorporated into the substrate, the other atom is reduced to form water.

2) They require a co-substrate.
3) Cytochrome P450, Superoxide Dismutase

Question 25

Write the reaction for Monoxygenase.

Answer 25

A-H + O2 + ZH2 –> A-OH + H2O + Z

Question 26

1) Where do we find Cytochrome p450?
2) What is it involved in?
3) What do we find it alongside?

Answer 26

1) In the intestines, mitochondria and ER of the liver.
2) Involved in:
- Steroid Hydroxylation
- Drug Metabolism + Detoxification
3) Found alongside Cytochrome B5 ( involved in fatty acid desaturase)

Question 27

Explain Class I and Class II system in regard to Cytochrome P450?

Answer 27

Class I contains:

• FAD containing Reductase
• P450 Heme Protein
• Fe-S Proteins

Class II:
- P450 reductase,
transfers electrons from FADH2 to FMN.

Question 28

1) What are superoxide free radicals?
2) How are they formed?
3) Effect on cytochrome?

Answer 28

1) They are oxygen atoms with addition of a electron.
2) They can be formed by the oxidation of reduced flavins.
3) They can reduce an Oxidised cytochrome C.

Question 29

1) What type of Enzyme is Superoxide Dismutase?

2) write the equation and explain how it works

Answer 29

1) it is a monoxygenase
2) O2- + O2- + 2H+ —> H2O2 + O2
In this reaction SOD uses one radical as a reductant and the other as an oxidant.

Question 30

What happens when you increase the O2% Atmosphere in regards to SOD?

Answer 30

Adaptive increase in SOD especially in the lungs.

Question 31

What also act as defence mechanisms to Superoxide Anions?

Answer 31

Antioxidants like Vitamin E (Alpha tocopherol) act as scavengers of these anions.