Mitochondrial DNA Flashcards
What are the 37 genes encoded by mitochondrial DNA?
13 encodes for proteins (components of ETC)
accounts for 10% of mitochondrial proteins
2 rRNA’s
22 tRNASs
What is mitochondrial DNA?
DNA mitochondria inherited form our mothers
- circular and double stranded
- 37 encoding genes
How is mitochondria function affected?
anoxia, ischemia, cyanide, CO - inhibits electron flow and ATP synthesis
decreased oxidation of NADH and FADH2 - increased accumulation of lactate and triglycerides
genetic defects in mitochondrial DNA (or nuclear DNA) can affect electron transport chain
What happens when ETC and Oxphos are inhibited?
- decreased oxidation of NADH/FADH2
- ie accumulation of electron carriers and cant give up electrons
- change is redirected, and so there will be increase in lactate and synthesis of triglycerides
How low levels of O2 (hypoxia) affects ETC?
- can induce the expression of micro RNAs that can affect expression of protein encoding genes
- HIF-1 - transcription factor induced in response hypoxia
- HIG induces the production of iNOS - creates nitric oxide which inhibits complex 4
What type of genes do complex 2 has?
nuclear genes
What types of genes do complex 1, 3 and 4 have?
both mitochondiral and nuclear genes
Where does mitochondrial DNA come from
maternal inherittance
Homoplasmy versus heteroplasmy
Homoplasmy - all the (mitochondrial) DNA is normal or all the DNA has some type of mutation
Heteroplasmy - Combination of normal and mutant
Mitochondrial DNA Disease determined by
- type of mutation
- prevalence of abnormal mitochondrial DNA (Heteroplasmy - mixture or homoplasmy (the same)
- organ system that is affected
Why doesn’t mitochondrial DNA disease show symptoms early?
It might start off as few but then it replicates and becomes more and take over. So that will take time
What are the rules for mitochondrial inheritance?
- Both males an females can be affected
- The condition is transmitted though the female to her offspring
- if a male has the trait and his spouse doesnt, their offspring wont have the trait
Diseases of oxidative phosphorylation
- Pathology causes by gene mutations in either mitochondrial or nuclear DNA
- Disease usually becomes worse with age
- at some stage, ATP generating capacity falls below threshold so all the good ATP gets used up and the newly produced ATP with the mutations show up.
- symptoms appears in tissues with highest energy demands: nervous tissue, heart, skeletal muscle and kidney
What is mitochondrial uncoupling?
Electron transfer occurring during the ETC but no proton gradient there coupled with the electron transfer
What happens during mitochondrial uncoupling?
- increase in metabolism
- wo proton gradient, there is no ATP synthesis
- protons are being pumped across but at the same time, something is bringing them back to the matrix (and not through ATP synthase)
- the energy being generated by the electron transfer with no ATP gain is lost as heat
What are the types of uncouplers?
Chemical - eg DNP (used as a diet pill in the 1930s)
Physiological - uncoupling proteins used for heat generation
How do chemical uncouplers work?
- They grab the H+ being produced in the inner mitochondrial membrane
- They then diffuse through the IMM and release the H+ to the matrix
- In the absence of an electrochemical gradient, ATP synthesis stops, but electron transport increases
- the energy of electron transport is not conserved and heat is generated
What are the effects of chemical uncoupling?
- H+ is wasted as heat and increases the body temperature
- It accelerates flow of electron transport (bc ETC is thinking we need to keep pulling electrons faster to keep the proton gradient going, but its not happening so it keeps speeding up)
- metabolic rate is increased
- more fat is burned
How do biological uncouplers work?
- Uncoupling protein (UCP1) also known as thermogenin
- oxidation drives the proton pumping action in the complexes, and the complexes are working correctly to produce energy, but it just isn’t stored in the form of ATP.
- The energy of oxidation is not conserved in ATP synthesis and heat is generated
- High expressed in human infants, penguins, hibernating mammals, skunk cabbage
- occurs in brown adipose tissue
How do biological uncouplers work?
- the uncoupling protein is embedded in the membrane
- as electrons flow, gradient is being generated
- but it is the biological uncoupler that is taking the H and bring them to the matrix
- Therefore proton gradient is being dissipated and the ETC is thinking we need to move faster to get NADH and FADH2 to oxidize, but this isnt happening, just creating a lot of energy that will be lost as heat
How do the OXPHOX produce ROS?
- sometimes e- can leak out
- then they do, they react with surrounding O2 to form ROS
What are ROS?
Reactive oxygen species
- species with 1-2 unpaired electrons
- highly unstable
What are the types of ROS
- Superoxide
- H2O2
- Hydroxyl radical
What are sources of ROS?
- Coenzyme Q (CoQ)
- Oxidases, oygenases, peroxidases
- ionizing radiation
What are the effects of ROS on lipids?
Causes peroxidation of lipid molecules
This changes or damages the lipid bilayer structure therefore altering the bilayer arrangement
What are the effects of ROS on DNA?
Can cause DNA to break
Can lead to mutations in the DNA (approximately 20 types of oxidatively altered DNA molecules have been identified)
What are the effects of ROS on protein?
- They attack amino acids and change confirmation, aggregate enzymes
- Proline, histidine, arginine, cysteine and methionine are susceptible to hydroxyl radical attack and oxidative damage
How do we generate superoxide by CoQ?
- normally generated during complex 3 (the Q chcle)
- CoQ donates electrons to complex 3
if one of the e- gets in contact with O2, it produces a free radical - However, there are enzymes in place to ensure it doesnt stick around
What is reactive nitrogen oxygen species (RNOS)?
- NO is an oxygen-containing free radical that is both essential and toxic
- Generated from arginine
- NO combines with O2 or superoxide to form RNOS
- RNOS could be involved in neurodegenerative diseases such as Parkison disease and chronic inflammatory diseases such as rheumatoid arthritis
- NO can combine with Fe-containing proteins
Why is NO bad?
High levels can inhibit complex 4 in the ETC
What are some enzymatic cellular defense against oxygen toxicity?
- superoxide dismutase
- catalase
- glutathione peroxidase and reductase
What are some non-enzymatic (dietary) cellular defense against oxygen toxicity?
- Vitamin E
- ascorbic acid (vit C)
- carotenoids
- flavonoids
- endogenous antioxidants (uric acid, melatonin)
How does superoxide dismutase (SOD) work against oxygen toxicity??
Three forms of SOD in humans.
It converts superoxide to hydrogen peroxide
What happens if there are mutations in SOD
Mutations have been linked to ALS (amyotrophic lateral sclerosis)
How does catalase works against oxygen toxicity?
Found in peroxisomes and to a lesser extent in the cytosol
Converts hydrogen peroxide (from SODs) into water
How does glutathione peroxidase work against oxygen toxicity?
It takes two reduced glutathiones in the presence of hydrogen peroxide and produces two oxidized forms (glutathione disulfide )and water
In order for glutathione to be used again it has to be reduced by glutathione reductase
How do vitamin E and vitamin C work against oxygen toxicity?
It will inhibit lipid peroxidation in cellular membranes
- It donates an e- to the peroxidized lipid.
- an intermediate radical is formed
- this intermediate of Vit E will be regenerated by vit E
What is Cytochrome P450?
family of heme containing membrane protein
- it takes substrates that are endogenous and exogenous molecules
- powerful detoxification system
Importance of cytochrome P450 (CYP)
major enzymes involved in drug metabolism and drug-drug interactions
- metabolism of exogenous substrates ie anything considered foreign (alcohol medication)
- metabolism of therapeutic agents
- metabolism of carcinogenic agents
- lipid synthesis and steroid synthesis
- systems subject to induction (system can be either increased or decreased in levels0
Components of the cytochrome P450 system
- cytochrome P450
- flavoprotein cytochrome P450 reductase
- O2
Cytochrome P450 system and medication
- Some drugs are prodrugs (inactive)
- Cytochrome P450 can catalyze it to become active
- Depending on how the body metabolizes the drug, if not metabolized properly, there may not be enough of the active metabolites needed to treat condition = therapeutic failure
- If metabolized too much, then there is too much of the active drug and there will be side effects eg drug toxicity
Acetaminophen induced liver toxicity?
high doses of Tylenol can lead to toxicity
Drinking alcohol with tylenol can also increase liver toxicity
Alcohol metabolism
CytP450 system is involved in alcohol metabolism that results in ROS
The reactive oxygen species, superoxide anion, can be formed at which site on the mitochondrial electron transport chain?
A. Complex II
B. Coenzyme Q
C. Cytochrome oxidase
D. ATP synthase
B. Coenzyme Q
Complex III is a correct answer also
A 20 year old man exhibits a progressively worsening group pf symptoms that include rapid fatigue during physical exertion and droopy eyelids. Similar symptoms were observed in his mother, grandmother and sister but not his father. This is most consistent with:
A. A mutation in mitochondrial DNA
B. Chance of ingesting a toxin
C. Myocardial infarction
D. Age-related macular degeneration
A. A mutation in mitochondrial DNA.
Look at the wording: progressively worsening, its in his mother, sister, grandmother, but not father
