week 10 - kreb cycle, ETC, ROS

structure of the mitochondria

outer membrane: permeable for fatty acids and pyruvate

inner membrane: impermeable

pyruvate dehydrogenase complex (PDC)

converts pyruvate into acetyl-CoA

links glycolysis with kreb cycle

acetyl-CoA

all leads to acetyl-CoA

acetyl-coa = kreb cycle = mitochondria = atp

kreb cycle: initial step

acetyl-coa (2-carbon) combines with oxaloacetate (4-carbon) to make citrate (6-carbon)

kreb cycle: further steps

chunks are then removed from previous step

some notable products: GTP, NADH & FADH2, succinate

ETC: complex I

transfers electrons from NADH to Q

oxidizes NADH to alleviate 2 electrons and it gets passed through a series of reactions until it reaches Q

ETC: complex II

transfers electrons from succinate to Q via FADH2

also alleviates 2 electrons

ETC: complex III

transfers electrons from Q to cytochrome. c

ETC: complex IV

contains oxygen so it pulls the process forward

transfers electrons from cytochrome.c ti oxygen also forming water

complex V

using H+ gradient created by the previous complexes to convert ADP→ ATP

NOT part of ETC

oxidation fuels phosphorylation

2 types of electron carriers inside

ubiquinone (Q):

• able to move throughout the layer due to hydrophobic tail

cytochrome. c (CytC)

• bound to the outer surface

• moves electrons from III → IV

ATP synthase

majority of ATP is made through this mechanism

rotates to produce ATP

it uses the energy of the protons flowing down the gradient towards it due to the pull of the oxygen to move and create ATP

cellular treason

consuming ATP to make ADP

how much ATP does each NADH and FADH2 make

NADH: 2.5 ATP

FADH2: 1.5 ATP

theoretical max/glucose = 30-32

reactive oxygen species (ROS)

highly reactive molecules that contain oxygen

oxygen is very electronegative so its constantly trying to steal electrons

radicals and free radicals

radicals: an unpaired electron and this makes them very reactive and unstable

free radicals: free roaming electrons that move around and cause trouble

examples of ROS

superoxide (O2- or O2*)

hydroxyl radical (OH*)

hydrogen peroxide (H2O2)

good usage of ROS

macrophages use ROS normally to attack pathogens

fenton reaction

iron reacts with hydrogen peroxide to produce hydroxyl radical

VERY DANGEROUS, damages DNA

haber-weiss reaction

superoxide reacts with hydrogen peroxide to create hydroxyl radical

converts iron to repeat fenton reaction

which complexes cause electrons to escape

complexes I, III are the main ones

source of ROS: radiation

radiation adds a lot of energy to a molecule which puts stress on the chemical bond → can cause weird reactions to occur that don’t normally happen

ROS increases when energy increases

source of ROS: drug metabolism

cytochrome P450s

Cytochrome P450 enzymes metabolize drugs using oxygen, but incomplete reactions can leak electrons and generate ROS like superoxide and hydrogen peroxide.

sources of ROS: inflammation

During inflammation, immune cells generate ROS via a respiratory burst to kill pathogens, but excess ROS can also damage the body’s own tissues.

respiratory burst

consumes oxygen but only lasts 30-60 min

reactive nitrogen species (RNS)

like ROS but nitrogen instead

can also be form through dietary exposure and air pollution

can form nitric oxide and peroxynitrite (ONOO)

high levels of ROS and RNS

VERY BAD, they amplify each other

triggers chain reactions that produce even more free radicals and cause more damage

lipid peroxidation

free radical chain reaction

initiation: starts when a hydroxyl radical takes an electron and creating a lipid radical

propagation: lipid radical reacts with O2 and forms lipid peroxyl radical (LOO)

termination: radicals are neutralized by an antioxidant such as vit E that removes the extra electron

DNA damage: 8-hydroxyguanine

ROS attacks DNA and modifies guanine

body mistakes it and pairs with adenine

can cause point mutation

cellular defense mechanisms

antioxidant enzymes:

• neutralize radicals (SOD, CAT)

antioxidant molecules

• donate to electrons to radicals but don’t become free radicals themselves (vit C, Vit E)

antioxidant enzymes

superoxide dismutase (SOD)

• detoxifies superoxide

catalase (CAT)

• detoxifies hydrogen peroxide

glutathione peroxidase (GPX)

• maintains

antioxidant molecules

vitamin E

• protects other molecules from damage by donating electron

vitamin C

• protects DNA and proteins by donating electron

• can also regenerate vit E

oxidative stress

NOT a reaction

damage or loss of function by excess ROS/RNS

• when the rate of ROS/RNS overwhelms rate of detoxification