Free radicals

Question 1

We need O2 for…?

-give examples (3)

Answer 1

• ATP generation
• Detoxification
• Biosynthesis

Question 2

What can highly reactive oxygen radicals cause? (2)

Answer 2

• damage to cellular lipids, proteins and DNA

- cellular death and degeneration

Question 3

Free radical

-definition

Answer 3

• particles with an unpaired electron spinning around the nucleus
• tends to reach equilibrium, plucks an electrons from the nearest molecule

Question 4

Radical nature of O

Answer 4

• biradical

- two single electrons in different orbitals

Question 5

ROS (reactive oxygen species)

• free radicals - saskia harms paula and heiko (5)
• not free radicals (4)

Answer 5

• superoxide, hydroperoxyl, peroxyl, alkoxyl and hydroxyl radical
• hydrogen peroxide, ozone, singlet oxygen, hypochlorous acid

Question 6

Example of free radicals (3)

Answer 6

• Oxidative phosphorylation, when the electrons are transferred to oxygen by cytochrome C oxidase.
• Normally O2 accepts 4e- and becomes water
• Free radicals occur when it does not accept 4 but less than that, ex: superoxide, accepts only 1e-. hydroxyl radical accepts only 3e-

Question 7

Hydroxyl radical OH (2)

Answer 7

• most potent

- initiates chain reactions that froms lipid peroxides and organic radicals and adds directly to compounds

Question 8

Superoxide anion (3)

Answer 8

• highly reactive
• limited lipid solubility and cannot diffuse far
• can generate hydroxyl and hydroperoxyl radicals

Question 9

Hydrogen peroxide (3)

Answer 9

• not actually a radical, but it can generate the hydroxyl radical
• lipid soluble
• at localized Fe2+ or Cu+ sites (ex: mitochondria) is also the precursor of hypochlorous acid

Question 10

RNOS (reactive nitrogen oxygen species

• free radicals (2)
• not free radicals (5)

Answer 10

• nitrogen (II) oxide, nitrogen (IV) oxide

- nitrosyl, nitrous acid, nitrogen (III) oxide, peroxynitrite, alkylperoxinitrite

Question 11

ROS may be generated: (3)

Answer 11

• enzymatically
• non- enzmatically
• membranes enzymes and/ or coenzymes with flavine structures, enzymes containing Cu atom in an active site

Question 12

How can CoQ generates superoxide?

Answer 12

The one- electron reduced form of CoQ is free within the membrane and can accidentally transfer an electron to dissolved O2, forming superoxide

Question 13

Main sources of free radicals (2)

Answer 13

• oxidases, peroxidades, oxygenase in the cell bind O2 and transfer single electrons via a metal
• Cytochrome P450 enzymes are a major source of free radicals

Question 14

Ionizing radiation

-how does it cause damage to the body?

Answer 14

It has a high enough energy level that it can split water into the hydroxyl and hydrogen radicals, thus leading to radiation damage to the skin, mutation, cancer and cell death

Question 15

Radical chain reaction mechanism

Answer 15

1. Initiation: produce a chain carrying radical
2. Propagation: chain continues to grow
3. Degradation
4. Termination: if the chain carrying molecule combines with another radical, there are no other radicals to propagate the reaction

Question 16

Oxidative damage to lipids

• damage
• sequel

Answer 16

• unsaturated bonds loss

- changes in fluidity and permeability of membranes

Question 17

Oxidative damage to proteins

• damage
• sequel

Answer 17

• fragmentation and cleavage, functional group modification

- changes in: enzymes activity, ions transport, proteolysis

Question 18

Amino acids which are susceptible to hydroxyl radical attack and oxidative damage (5)

Answer 18

• proline
• histidine
• arginine
• cysteine
• methionine

Question 19

Oxidative damage to DNA

• damage
• sequel

Answer 19

• bases modification, chain breakage

- mutation, translational mistakes

Question 20

Respiratory burst (2)

Answer 20

• phagocytic cells of the immune system exhibit a rapid consumption of O2
• part of the antimicrobial defense system, it is intended to destroy invading microorganisms, tumor cells, etc.

Question 21

Production of ROS during the respiratory burst

-steps (6)

Answer 21

1. Activation of NADPH oxidase initiates it with the generation of superoxide
2. Superoxide (enzymatically or spontaneously) generates H2O2
3. Myeloperoxidase generates HOCL
4. H2O2 can generate hydroxyl radical from the Fenton reaction
5. Inducible nitric oxide synthase may be activated and generate NO
6. Nitric oxide + superoxide forms peroxynitrite, it may generate addtional RNOS

Question 22

Antioxidant defense system

Answer 22

Can eliminate free radicals by donating electrons
3 levels:
1. Inhibition of production of ROS
2. Capture of radicals (scavengers, trappers)
3. Correction mechanism of destroyed biomolecules

Question 23

Endogenous antioxidants

• enzymes
• non- enzymatic

Answer 23

Enzymes: cytochrome c, catalase

Non- enzymatic: fixed in membranes (a- tocopherol, B- caroten), out of membranes (ascorbate, transferrin)

Question 24

Exogenous antioxidants (3)

Answer 24

• FR scavengers
• Trace elements
• Drugs and compounds influence to FR metabolism

Question 25

Enzymatic defense against ROS includes: (3)

Answer 25

- Superoxide dismutase - Catalase - Glutathione peroxidase

Question 26

Superoxide dismutase

Answer 26

- present in all oxygen- metabolizing cells - inducible in case of superoxide overproduction 3 isoenzymes forms: Cu+ - Zn2+ present in the cytosol Mn2+ present in mitochondria Cu+ - Zn2+ found extracellulary

Question 27

Catalase (3)

Answer 27

- capable of reducing hydrogen peroxide to water and oxygen - high affinity to H2O2- cytoplasm of erythrocytes - tetramer with Fe, need NADPH

Question 28

Glutathion (3)

Answer 28

- principal means of protecting against oxidative damage - tripeptide - glutamate, cysteine, glycine

Question 29

Glutathion peroxidases (4)

Answer 29

- family of selenium enzymes - in the cytosol and mitochondria - major means of removing H2O2 produced outside of peroxisomes - it also oxidizes 2 GSH, turning it into GSSG

Question 30

Glutathione Reductase (3)

Answer 30

- catalyzes transfer of electrons from NADPH - major source is pentose phosphate pathway - turn oxidized glutathione back into its normal form (2 GSH)

Question 31

Non- enzymatic antioxidants = free radical scavengers

Answer 31

They convert free radicals to a non-radical nontoxic form in non- enzymatic reactions

Question 32

Antioxidants | -definitions

Answer 32

Compounds that neutralize free radicals by donating a hydrogen atom (with its one electron) to the radical

Question 33

Sources of antioxidants

Answer 33

Dietary - vitamin E, vitamin C, carotenoids Endogenously produced - urate and melatonin

Question 34

Vitamin E (3)

Answer 34

- a- tocopherol - lipid- soluble antioxidant vitamin - protect against lipid peroxidation in membranes

Question 35

Vitamin C (5) MEMORIZE THIS!!!!!!!!!!!

Answer 35

- ascorbic acid - it is an oxidation- reduction coenzyme - plays a role in free radical defense - reduced ascorbate can regenerate the reduced form of vitamin E through donating electrons in a redox cycle - it is water- soluble and circulates unbound in blood and extracellular fluid, where it has access to the lipid- soluble vitamin

Question 36

Oxidative stress

Answer 36

Equilibrium failure between creation and elimination of RNOS leads to oxidative stress (imbalance between free radicals and antioxidants in your body)

Question 37

Oxidative stree markers: 1. Lipoperoxidation markers 2. Oxidative damage to protein markers 3. Oxidative damage to DNA

Answer 37

1. conjudated diens, isoprostanes 2. protein hydroperoxides 3. modified nucleosides

Question 38

Diseases associated with free radical injury

Answer 38

Diabetes Acute renal failure Alcohol induce liver disease Aging