1. Oxidative Stress

Question 1

How is alcohol oxidised?

Answer 1

By alcohol dehydrogenase to acetaldehyde and then to acetate by aldehyde dehydrogenase
Small amounts can be oxidised by cytochrome P450 2E1 enzyme, or by catalase in brain

Question 2

What is the rate of metabolism of alcohol?

Answer 2

One unit of alcohol = 8g

Eliminated at rate of around 7g per hour

Question 3

What causes hangover?

Answer 3

Accumulation of toxic metabolite acetaldehyde

Question 4

What can excess NADH and Acetyl-CoA lead to?

Answer 4

Changes in liver metabolism

Question 5

What is disulfiram used for and how does it work?

Answer 5

Used as an adjunct in the treatment of chronic alcohol dependence
It is an inhibitor of aldehyde dehydrogenase
If patient drink alcohol, acetaldehyde will accumulate causing symptoms of a hangover

Question 6

What are ROS?

Answer 6

Reactive oxygen species

Question 7

What are RNS?

Answer 7

Reactive nitrogen species

Question 8

What do ROS and RNS do to cells?

Answer 8

Damage nucleic acids, proteins and lipids

Question 9

What are free radicals?

Answer 9

An atom or molecule that contains one or more unpaired electrons and is capable of independent existence

Question 10

How can ROS cause damage to DNA?

Answer 10

Reacts with base:
Modified base can lead to mispairing and mutation

Reacts with sugar:
Can cause strand break and mutation on repair

Can lead to cancer

Question 11

How does ROS damage protein side chains?

Answer 11

Can add/modify carbonyls, hydroxylated adducts, ring opened species, dimers, disulphide bond (Cys)
Causes change in protein structure
Leading to protein degradation, loss of function or gain of function

Question 12

What is the role of disulphide bonds in proteins?

Answer 12

Important role in folding and stability of some proteins

Formed between thiol groups of cysteine residues

Question 13

When does inappropriate disulphide bond formation occur?

Answer 13

If ROS takes electrons from cysteines causing misfolding, crosslinking and disruption of function

Question 14

How do ROS damages lipids?

Answer 14

Free radical extracts hydrogen atom from a polyunsaturated fatty acid in membrane lipid - damaged membrane
Lipid radical formed which can react with oxygen to form a lipid pyroxylin radical
Chain reaction formed as lipid pyroxylin radical extracts hydrogen form nearby fatty acid

Question 15

What are endogenous sources of biological oxidants?

Answer 15

Electron transport chain
Nitric oxide synthases
NADPH oxidases

Question 16

What are exogenous sources of biological oxidants?

Answer 16

Radiation
Pollutants
Dugs
Toxins

Question 17

What is the electron transport chain a source of?

Answer 17

ROS

Question 18

What happens to electrons that escape the electron transport chain?

Answer 18

React with dissolved O2 to form superoxide

Question 19

What is iNOS?

Answer 19

Inducible nitric oxide synthase

Produces high NO concentrations in phagocytes for direct toxic effect

Question 20

What is eNOS?

Answer 20

Endothelial nitric oxide synthase

Signalling

Question 21

What is nNOS?

Answer 21

Neuronal nitric oxide synthase

Signalling

Question 22

What reaction does nitric oxide synthase catalyse?

Answer 22

Arginine to citrulline + NO radical

Question 23

What is nitric oxide radical used for?

Answer 23

Signalling molecule:
Vasodilation
Neurotransmission
S-Nitrosylation

Question 24

What is respiratory burst?

Answer 24

Rapid release of superoxide and H2O2 from phagocytic cells (neutrophils and monocytes)
ROS and peroxynitrite destroy invading bacteria
Part of antimicrobial defence system

Question 25

What is chronic granulomatous disease?

Answer 25

Genetic defect in NADPH oxidase complex causes enhanced susceptibility to bacterial infections
E.g. atypical infections, pneumonia, abscesses, impetigo, cellulitis

Question 26

What is the role of superoxide dismutase (SOD)?

Answer 26

Converts superoxide to H2O2 and oxygen

Primary defence because superoxide is strong initiator of chain reactions

Question 27

What is the role of catalase?

Answer 27

Converts H2O2 to water and oxygen

Widespread enzyme, important in immune cells to protect against oxidative burst

Question 28

What is the reduced form of glutathione?

Answer 28

GSH
Glycine-cysteine-glutamate
I
SH

Question 29

What is the oxidised form of glutathione?

Answer 29

GSSG
Thiol group of Cys donates e- to ROS
GSH then reacts with another GSH to form disulphide

Question 30

What enzyme is used to catalyse GSH to GSSG?

Answer 30

Glutathione peroxidase which requires Selenium

Question 31

What enzyme is used to catalyse GSSG to GSH?

Answer 31

Glutathione reductase, catalyse transfer of electrons from NADPH to disulphide bond

Question 32

What is NADPH used for in cellular defences?

Answer 32

NADPH from pentose phosphate pathway is essential for protection against free radical damage

Question 33

What is NADPH required for?

Answer 33

Reducing power for biosynthesis
Maintenance of GSH levels
Detoxification reactions

Question 34

What is the rate limiting enzyme of the pentose phosphate pathway?

Answer 34

Glucose 6-phosphate dehydrogenase

Question 35

What is the role of vitamin E in cellular defences?

Answer 35

Lipid soluble antioxidant
Donates electrons
Important for protection against lipid peroxidation

Question 36

What is the role of vitamin C in cellular defences?

Answer 36

Water soluble antioxidant

Important role in regenerating reduced form of vitamin E

Question 37

What are vitamin C and E in terms of cellular defences?

Answer 37

Free radical scavengers - reduce free radical damage by donating hydrogen atom to free radicals in a nonenzymatic reaction

Question 38

What are Heinz bodies?

Answer 38

Dark staining within RBC resulting from precipitated haemoglobin
Bind to cell membrane altering rigidity
Spleen removes bound Heinz bodies resulting in blister cells
Clinical sign of G6PDH deficiency