Midterm 2 (Lec 6) Flashcards
Fruits and veggies!
-Well accepted that consumption decreases rates of cancer and heart disease
- often attributed to antioxidants
- should we go beyond “eat lots of fruits and veggies?
Micronutrient essential antioxidant defense System
- Vitamin E
-Vitamin C - selenium, riboflavin, niacin
- zinc, copper, manganese
-Iron - beta carotene
Why do we need antioxidants
- All about balance between Pro oxidants and anti oxidants
-Oppose toxic effects of oxygen - 95% of oxygen is used for energy production (good)
- 1-3.%. Results in production of reactive oxygen species ( can be bad)
Oxidative stress
serious imbalance between ROS generation and antioxidant supply
- increased ROS production (many ways)
- decreased antioxidant intake
Cells can sometimes ADAPT: “things remain unbalanced but cells make due ex - insufficiency”
Severe oxidative stress can cause CELL DAMAGE (“accommodation instead of adaptation - something has to change ex- deficiency the accommodation is the symptoms)
Cell damage- cellular mutations, tissue breakdown, immune compromise etc
Free radicals
Formed during oxidative metabolism
Contribute to oxidative stress
Molecules with one or more UNPAIRED electrons - VERY unstable and highly reactive
Need to steal an electron from another molecule to stabilize - can set off a chain reaction
Atoms bind together by sharing electrons - two electrons can exist in one bind
- unpaired state (ROS) is unstable and reactive
Types of free radicals
- ROS: reactive oxygen species
- RNA: reactive nitrogen species
- R: other reactive radicals
Free radicals are a bi product of normal cellular reactions
They do have useful biological function
- key is to control their quantity
Types of ROS
Free radicals
- superoxide radical (O2)
- hydroxy radical (OH)
- fatty acid peroxide radical (ROO)
- nitric oxide (NO)
Unstable molecules
- hydrogen peroxide (H2O2)
- ozone (O3)
Not inclusive list
Reasons for ROS generation
- Useful production (intended; to deal with sickness)
- important defence mechanism
- produced by activated phagocytes
- mechanism to kill bacteria/fungi and inactivate viruses
- can be inappropriately activated (inflammatory diseases)
- Accidental production
- instability in the presence of oxygen
- many molecules spontaneously react with oxygen
- electron transport chain
- some electrons escape and react with oxygen : free radicals are formed
Problem with free radicals
They’re unstable and need to steal an electron from a non radical to become stable
When they react with non radicals, CHAIN REACTIONS start
Hard to control quantity - products build up and cause cell damage
Best example is lipid peroxidation
Lipid peroxidation
- Generation of free radical (can be controlled at this point)
RH -> R. + H where R. = free radical
- Propagation/chain reaction (what makes free radical uncontrollable)
Free radical is regenerated in the presence of oxygen
R. + O2 -> ROO.
ROO. + RH -> R. + ROOH (fatty acid hydroperoxide- BUILD UP PRODUCT)
and the cycle continues
Fatty acid hydroperoxide (ROOH)
Can build up and cause oxidative stress
- disruption of cell membranes, cell damage
Can also combine with IRON:
ROOH + FE2+ -> FE3+ + OH. + RO-
Produced hydroxy radical (most potent free radical)
Iron can also react with H2O2
Hydroxy radical (OH.)
Bad bad news - no positive role in the body
Reacts instantaneously with anything - leads to many problems
- initiates free radical chain reaction
- mutates DNA
- possibly cancer initiation
- protein damage; function disrupted
Superoxide (O2.) and hydrogen peroxide (H2O2)
Reactive oxygen species’
- superoxide is a free radical
- hydrogen peroxide is an unstable form of oxygen
Much less reactive than OH.
BUT can react with EACHOTHER to form OH. ( worst)
- called the Haber-Weiss reaction; iron is involved
O2.- + H2O2 -> OH. + OH- + O2
Dealing with ROS
Need to keep them at a manageable level
Need to prevent oxidative damage - aka need radical scavengers
- answer is ANTIOXIDANTS!
Want antioxidants to react with free radicals before they react with something else (like DNA)
Micronutrient antioxidant defence system
Vitamins and minerals from diet plus enzymes that need vitamins and minerals
Allow balance between PROoxidant and ANTIoxidant systems
Goal is to avoid oxidative stress
Beside micronutrients, there are other compounds we can obtain from our diet such as phytochemicals
Micronutrient antioxidant defence system list
Vitamin E
Vitamin C
Selenium (glutathione peroxidase) riboflavin niacin (glutathione reductase)
Zinc copper manganese (SOD superoxide dismutase)
Iron (catalase)
Beta carotene
Vitamin E: chain breaking
Able to terminate chain reactions
Key structural features
- OH group; reacts with oxygen (ROO.)
- ring structure; makes it a non reactive free radical “and chain makes it fat soluble to stick into cell membrane”
QUENCHES the free radical - acts as an antioxidant
SLIDE 23 AND 24 STRUCTURE