Revision questions - week 7

Question 1

Free radicals

Answer 1

• Any molecule species existing with an unpaired valency electron
• to be stable must have a paired electron
• will create a chain reaction

has exogenous and endogenous sources

Question 2

Oxidative stress

Answer 2

• an imbalance of reactive oxygen species (free radicals) and antioxidant defense, favouring the free radicals

Question 3

Oxidative damage

Answer 3

• prolonged oxidative stress
• an imbalance between the production of free radicals and the ability of the body to counteract or detoxify their harmful effects through neutralization by antioxidants

Question 4

redox homeostasis

Answer 4

when free radicals are present in amounts (equilibrium of pro and antioxidants) that facilitate growth

Question 5

antioxidant capacity

Answer 5

• Defines the synergistic work between the endogenous and the exogenous, enzymatic and non-enzymatic antioxidant systems in keeping free radicals in equilibrium

the synergy of endogenous and exogenous compounds that are to keep free radicals in equilibrium

Question 6

Free-radical theory of ageing

Answer 6

• Postulates that ageing changes are caused by an accumulation of free radical at a cellular level

solution
- Vitamins supplementation (with exogenous antioxidants) is thought to play a role in chronic and ageing disease prevention, and in healthspan, via the therapeutic antioxidant theory of fighting free radicals 
.

Question 7

Enzymatic antioxidant system -endogenous

Answer 7

antioxidant enzymes
- Catalase: converts hydrogen perioxide to water and oxygen
- Glutathione enzyme system: reductase, peroxidase (GPX – Se dependant) and S transferases
- GPX: 4 different isoenzymes
– catalyses breakdown of hydrogen peroxides and hydro-peroxides

or from slides
Gene products:
Catalases, superoxide dismutase (SOD), glutathione peroxidase (GPX), hemoxygenase etc…
- Deactivate free radicals in a number of processes. E.g.: conversion to water and oxygen
- Require co-factors for function:
zinc, copper, iron, manganese, selenium

Question 8

non-enzymatic antioxidant system - exogenous (CHECK)

Answer 8

Vitamins (V)
- V: E & C electrons donors
Phytochemicals: carotenoids,
flavonoids, epicatechins, resveratrol etc.
• Mild electron donors
• Signals for gene transcription of enzymatic system

more specifically

• vit E -removes free radicals intermediates and prevents propagation reaction to continue, produces oxidized alpha tocopheryl radicals that can be recycled by other antioxidants in active form
• ascorbic acid – maintained in reduced form by reaction with glutathione, reduces and neutralises ROS

Question 9

Main principles of antioxidant activity

Answer 9

1- Chain breaking mechanisms by donating electrons to the free radicals.
2- Removal of ROS/reactive nitrogen species by quenching the chain initiating catalyst.

Question 10

How can one improve their antioxidant defense (CHECK)

Answer 10

Dietary source of antioxidant and activators of
Nrf2
– Substrate for glutathione production
– Exercise to raise ROS acutely
– Dietary sources of minerals to provide all cofactors

Question 11

differences in fat soluble and water soluble as groups of vitamins

Answer 11

fat soluble
absorption - required bile and pancreatic lipase (40-60% absorbed when recommended intake)
storage - adipose tissue and liver
transport - in lymphatic system via chylomicrons, in blood via protein carrier
toxicyt - doeses of 5-10* NRVs

water soluble
straight into blood
no storage or toxicity

Question 12

Calcitriol

Answer 12

active form of vit D

Question 13

How is calcitriol made

Answer 13

frotified foods

Question 14

calcitriol endogenously made

Answer 14

cholesterol -(UVB)-> Vit D3-(hydroxylation in liver) -> 25(OH)D3 -(hydroxylation in kidney) ->calcitriol (1,25(OH)D3)

Question 15

Vit D found in diet and supplementation

Answer 15

Fish, fish oil in the diet (D3); Supplement or fortified food
(usually D2)

Question 16

deficiency of VIt D

Answer 16

osteomalecia

Question 17

How is vitamin D measured in blood

Answer 17

The biomarker is the concentration of 25,hydroxyvitamin D3

Question 18

toxicity of vit d

Answer 18

hypercalcemia, calcium
deposit in kidney, joints, arterial wall, and eventually also
bone demineralisation (through promotion of resorption)

Question 19

How vit d involved in bone health

Answer 19

Increased calcium absorption in the GIT by upregulating the
expression of calcium receptors and transporters in the
enterocyte. Increase phosphorous absorption

Question 20

1IU of VIt D =

Answer 20

0.025µg vitamin D3; 0.005µg 25-hydroxycholecalciferol

Question 21

phytochemicals in non-enzymatic system

Answer 21

sulforaphane, carotenoids, resveratrol etc

Question 22

Nrf2 is involved in the redox homeostasis by

Answer 22

being a transcription factor promoting the expression of antioxidant enzymes. It can be activated by elevated ROS or by phytochemicals like sulphorafane

Question 23

non-enzymatic antioxidant system - Endogenous

Answer 23

plasma constituents - bilirubin,
uric acid, melatonin, albumin, glutathione
more specifically

• glutathione – maintains redox status in cells, formed from cellular cysteine (thiol group in cysteine is reducing agent), kept in reduced form,
• melatonin crosses cell membranes and BBB – once oxidized cannot be recuded to former state because as formed endproducts with free radicals
• uric acid – 50% of antioxidant ability of plasma

Question 24

enzymatic antioxidant system - exogenous

Answer 24

minerals - cofactor to antioxidant enzymes
 - SOD 1 – Cu and Zn dependent
 - SOD 2 – Mn dependent
 - SOD 3 - Fe dependent
GPX - selenium

Question 25

The non-enzymatic anti-oxidant system contributes to redox homeostasis mainly by

Answer 25

electron donation to free radical

Question 26

The enzymatic anti-oxidant system contributes to redox homeostasis mainly by

Answer 26

converting ROS (free-radicals) to non-reactive products (e.g. oxygen and water)

Question 27

Endogenous free radicals are produced by

Answer 27

oxygen metabolism in mitochondria, for example when excess energy is consumed;

Question 28

Oxidative damage to nucleic acid results in

Answer 28

expression of dysfunctional protein expression and the start of disease

Question 29

SOD (Mn, Cu, Zn, Fe) , GPx (Se), Catalase (Fe), Glutathione enzyme system act as inhibiting ROS

Answer 29

by conversion to non-reactive compounds.

Question 30

exogenous free radicals come from

Answer 30

pollution, smoking, radiation etc.