Mitochondria and Peroxisomes Flashcards
Describe the structure of mitochondria
· Between the inner and outer is the inter-membrane space. Located in the inner membrane is the matrix where metabolic process occurs
· Small circular genome, double membrane
· The outer membrane contains many channels formed by the protein porin and acts like a sieve and filters out molecules that are too big.
The inner membrane is highly folded so structures called cristae form which increase the surface area for respiratory enzymes to work on.
They range between 1-10um in length, mitochondria change shape rapidly and appear to be moving around the cell
Present in all eukaryotic organism.
What happens to cells that dont have mitochondria?
Retain a similar organelle
Why do mature RBCs not have mitochondria?
They are destroyed during maturation
What is organisation of mitochondria dependent on?
Type of cell
Describe the difference between mitochondria in fibroblast cell and cardiac cells
· In fibroblast mitochondria they are interconnected forming networks which is hardly dynamic.
· In cardiac cells they are highly abundant and found in distinct zones- mitochondria may perform zonal functions
Explain the endosymbiotic theory
· All of mitochondria ever existed can be trace back to one mitochondrion.
· Primitive form of eukaryotic cell forms a symbiotic relationship with a prokaryote.
The larger organism providing the smaller one with nutrients and the mitochondria providing ATP.
Prokaryote divided inside the host and producing daughter cells so when host divided, it would contain the mitochondria”
What evidence is there for mitochondria being a prehistoric mitochondria?
·Evidence comes from phylogenetics
· If the mitochondrial genome is sequenced they all share similarity to the typhus bacteria, which exist today and these bacteria are symbionts of eukaryotes.
· The proteins made in the mitochondria are made by its own ribosomes, some proteins are encoded for in the nucleus and are imported into the mitochondria.
Describe mitochondria transportation
· Facilitated by microtubules- requiring moto proteins eg Dynein and Kinesin to which mitochondria binds by the adaptor proteins (Milton and miro) located on surface of mitochondria
Milton and miro bind to Kinesin
· Important in cells such as neurons- delivered to synapses where they are required for neural signalling
Describe the cycle life of mitochondria(4)
· Like bacterial mitochondria can divide and fuse together.
· New mitochondrion is not made from scratch- making new ones involve growing the mass of existing ones which undergo fission.
· Macromolecules inside the mitochondria become damaged because of oxidative insult.
· Damaged mitochondria are destroyed via mitophagy, a form of autophagy.
What are the functions of mitochondria? (9)
· Produce ATP in process of oxidative phosphorylation
· Central hubs of metabolism
· Anabolic synthesis of nucleotide required for DNA replication
· Calcium homeostasis- critical for muscle contraction
· Production of amino acids such as glutamates- function as neurotransmitters.
· Important in apoptosis- cell death-release of proteins from the space between themitochondrialinner and outer membrane that, once in the cytosol, activate caspase proteases that dismantle cells
· Immune response- protein receptors that detect invading viral RNA molecules. Protein receptors are located on the outer membrane- activate innate immune response
· Energy conversion: generation of ATP by phosphorylation (OXPHOS)
· Nutrients in food are oxidized to produce acetyl co enzyme A- processed in the Kreb’s cycle
Describe the oxidation of NADH and FADH
NADH and FADH serve as electron donors in the electron transport chain. They are oxidized and leads to production of ATP
Where is Acetyl-CoA derived from?
Acetyl-CoA is derived from carbohydrates in the cytoplasm and fatty acids metabolized by beta oxidation inside the mitochondria
Explain the importance of citric acid
Produce reduced electron donors used for production of ATP in oxidative phosphorylation
Provide biosynthetic precursors for the synthesis of fatty acids and amino acids.
Where does citric acid take place?
In the matrix
where is succinate dehydrogenase found?
It is found in the inner membrane unlike other citric acid cycle enzymes which are soluble inside the membrane
It is involved in oxidative phosphorylation
What process are NADH and FADH2 involved in?
ETC to produce ATP
Describe the oxidative phosphorylation process(5)
Electrons derived from NADH and FADH 2 generated in the citric acid cycle flow through respiratory chain complexes.
2, Flow of electrons leads to protons being pumped out of the matrix into inter membrane space.
- Build-up of protons generate a proton motive force consisting of a transmembrane potential and a pH gradient
- Protons are transported back into the matrix by protein complex called ATP synthase in a process known as chemiosmosis.
- Flow of protons through ATPase drive the process of ATP Involve 5 protein complexes embedded in the inner mitochondrial membrane
Describe each of the five complexes involved in oxidative phosphorylation
Complexes 1-4 are involved in transfer of electrons and generation of proton motive force.
Part of electron transport chain- respiratory chain complexes. There are two electron carries- ubiquinone and cytochrome C
Complex 2 does not pump proton so does not contribute to proton motive force.
The 5th complex is not respiratory chain complex.
High membrane potential Protons flow back into the membrane through complex 5 which harness energy to generate ATP
Describe the structure of peroxisomes
· Single bilayer
Two main functions
· Approximately 0.1-1 μm in diameter
· Contains no DNA or ribosomes
What are the functions of peroxisomes?
· Metabolic roles: Some fatty acids are broken down inside peroxisomes in beta oxidation.
· Beta oxidation takes place in mitochondria, but mitochondria is unable to break down long chain fatty acids by peroxisome can
· Detoxification of hydrogen peroxide by enzyme catalase - highly reactive that can react and damage- contribute to aging process.
· Catalase is abundant in peroxisome but not elsewhere
· Metabolism of bile acids- important for synthesis of cholesterol
Peroxisome proteins contain a Peroxisomal targeting signal (PTS), which binds to a receptor molecule that take the protein into the Peroxisome
How do mitochondria replicate?
Replicate by fission
Requires a set of proteins- some of these proteins are involve in fission of both mitochondria and peroxisome eg. DNM1L, and FIS1
What are some shared features between mitochondria and peroxisomes?
Important in cell metabolism eg fatty acids Able to divide and the protein machinery are locate don the outside of these organelles
Antiviral signaling- mitochondrial antiviral signalling complex is found don the mitochondria and peroxisomes”
What is peroxisomes biogenesis?
Peroxisome biogenesis disorders in the Zellweger spectrum (PBD-ZSD) is anautosomal recessive disordercaused by mutations in genes that encode peroxins, proteins required for the normal assembly of peroxisomes.
Recall in order the intermediates in the TCA cycle
- Citrate
- cis- aconitase
isocitrate - alpha-ketoglutarate(5C)
- succinyl- CoA(4C)
- succinate
- fumerate
- malate
- oxaloacetate(4C)
Recall the products of the the TCA cycle
3x NADH
2x CO2
1x FADH2
1xGTP
