Biological Oxidation (Chapter 12) Flashcards
What is the need for Intermediary metabolism?
What is the advantages of this?
-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).
- What is the Redox Potential?
- What conditions are used for Biological systems in terms of Redox Potential?
- Explains the free energy change of a REDOX reactions.
For biological systems, the Redox potential is described by pH 7, where E = -0.42V
What are Oxidoreductase?
Types of these?
Enzymes involved in REDOX rxns.
Types:
1) Oxidases
2) Dehydrogenases
3) Hydroperoxidases
4) Oxygenases
What do Oxidases do?
Notable examples?
They catalyse the removal of Hydrogen from a substrate.
Using oxygen as a Hydrogen Acceptor.
**removal of hydrogen = oxidation
Examples:
- Cytochrome Oxidase
- Flavoprotiens
1) What is Cytochrome Oxidase’s other name?
2) What type of oxidoreducate enzyme is it?
3) What is it?
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+
1) What type of oxidoreducatse is Flavoproteins?
2) What prosthetic group do they have?
1) Oxidases
2) Has FAD, FMN is the prosthetic group they have.
What is FAD/FMN formed from?
Formed from the vitamin Riboflavin.
What do Dehydrogenases do?
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.
Characteristics of Dehydrogenases?
1) specific to substrate
2) Often use co-enzymes
3) catalyse reversible reactions
1) Which co-enzymes do Dehydrogenase use?
2) How are they produced
1) Use Nictinoamide coenzymes most often.
2) NAD/ NADP+ are produced by the vitamin - Niacin.
1) What do NAD-Linked Dehydrogenases catalyse?
2) How does NAD become NADH?
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
1) What do NADP- Linked Dehydrogenases catalyse?
Involved in biosynthesis pathways where reductive reactions are needed.
eg//
1) extramitochondrial pathway of fatty acids
2)steroid synthesis
3)pentose phosphate pathway
1) Types of Hydroperoxidases?
2) Purpose of Hydroperoxidases?
1) Peroxidases + Catalase
2) They protect against ROS (reactive oxygen species).
How do ROS generate?
What can they cause if accumulate?
ROS generate during normal metabolism.
However if not removed, they accumulate which can cause:
- cancer (everything does nowadays anyway)
- Arteriosclerosis
- Aging
1) What do peroxidase do?
2) Where is it found?
3) What is their prosthetic group?
1) They reduce peroxides using various electron acceptors.
2) They are found in Milk, Leuokocytes, Platlets
3) Their prosthetic group is called Protoheme.
Electron acceptors for peroxides being catalysed by peroxidase?
- Ascorbate (Vitamin C)
- Quinones
- Cytochrome C
Equation for Peroxidase
H2O2 + AH2 –> 2(H20) + A
Gluthione Peroxidase:
- where found?
- what is the prosthetic group?
- how does it destroy H2O2?
- found in erythocytes.
- the prosthetic group = selenium
- Destroys H2O2 via conversion of Gluthione to it’s oxidised form.
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?
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.
Where is Catalase found?
- Blood
- Bone Marrow
- Mucous Membranes
- Kidneys
- Liver
(another pointless fact they will most likely base the whole exam upon).
What do Peroxsomes posses?
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.
1) What do Oxygenases do?
2) Types of oxygenases?
1) they catalyse the transfer oxygen into the substrate.
2) - Monoxygenase
- Dioxygenase
What do Dioxygenase do?
Write the equation.
Incorperate both atoms of oxygen into the substrate.
O2 + A -> AO2
1) Function of Monoxygenase?
2) what is necessary for Monoxygenase to work?
3) Noteable Monoxygenase
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
Write the reaction for Monoxygenase.
A-H + O2 + ZH2 –> A-OH + H2O + Z
1) Where do we find Cytochrome p450?
2) What is it involved in?
3) What do we find it alongside?
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)
Explain Class I and Class II system in regard to Cytochrome P450?
Class I contains:
- FAD containing Reductase
- P450 Heme Protein
- Fe-S Proteins
Class II:
- P450 reductase,
transfers electrons from FADH2 to FMN.
1) What are superoxide free radicals?
2) How are they formed?
3) Effect on cytochrome?
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.
1) What type of Enzyme is Superoxide Dismutase?
2) write the equation and explain how it works
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.
What happens when you increase the O2% Atmosphere in regards to SOD?
Adaptive increase in SOD especially in the lungs.
What also act as defence mechanisms to Superoxide Anions?
Antioxidants like Vitamin E (Alpha tocopherol) act as scavengers of these anions.
