Mitochondria and peroxisomes Flashcards
Describe the structure of mitochondrion.
- The mitochonrion has 2 membranes and is usually rod-shaped.
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What does the number of mitochondria in the cell depend on?
It depends on the metabolic requirements of the cell.
Why is the mitochondria different from most organelles?
The mitochondria has its own circular DNA similar to prokaryotic DNA.
What is the use of microtubules network in the mitochondria?
- The microtubules determines the orientation and distribution of mitochondria in different cell types.
- E.g. So that they don’t all cluster in one of th e daughter cell during cell division.
What are the 4 times mitochondria are able to change their structure (called mitochondrial morphology)?
Mitochondria can change its shape during :-
- Apoptosis
- Ca2+ transfer
- Cell cycle
- Nutrient starvation
Give information on mitochondrial DNA (mtDNA) and mitochondrial proteins.
- Mitochondrial chromosomes are circular, as in bacteria.
- Mitochondrial genes are inherited cytoplasmically from the mother.
- The mitochondrial DNA (‘mtDNA’) is located in the matrix.
- The mitochondrial genetic code differes from the standard nuclear code. [For example UGA is a stop codon in the nucleus but codes for tryptophan in mitochondria; conversely AGA and AGG usually code for arginine but are stop codons in the mitochondrial translation system].
- Mitochondria also contain their own ribosomes and make some of their own proteins.
- Other mitochondrial proteins ar encoded in the nucleus, translated in the cytoplasm and imported into the mitochondria.
What is the endosymbiosis theory?
The endosymbiosis theory states that:-
- The mitochondria of eukaryotes evolved from an aerobic bacterium living within an archaeal host cell.
- The chloroplasts of photosynthetic eukaryote (plants and algae) evolved from an endosymbiotic cyanobacterium living within a mitochondria-containing eukaryotic host cell.
Cyanobacteria:- they are a phylum of bacteria that obtain their energy through photosynthesis, and are the only photosynthetic prokaryotes able to produce oxygen.
What is the evidence for endosymbiosis theory?
- Both mitochondria and chloroplasts can arise only from pre-existing mitochondria and chloroplasts. They cannot be formed in a cell that lacks them because nuclear genes encode only some of the proteins which they are made of.
- Both mitochondria and chloroplasts have their own genome, and it resembles that of bacteria not that of the nuclear genome.
- Both genomes consist of a single circular molecule of DNA.
- There are no histones associated with the DNA.
- Both mitochondria and chloroplasts have their own protein-synthesizing machinery, and it more closely resembles that of bacteria than that found in the cytoplasm of eukaryotes.
- E.g. The first amino acid of their transcripts is always fMet as it is in bacteria (not methionine [Met] that is the first amino acid in eukaryotic proteins).
What are some functions of the mitochondria?
Mitochondria is responsible for :-
- The breakdown of fatty acids to acetyl CoA in the matrix.
- Decarboxylation of pyruvate to acetyl CoA. (Pyruvate is formed in cytoplasm as an end product of glycolysis.)
- Citric acid cycle/ kerbs cycle is a pivotal metabolic pathway generating reducing equivalents for ATP generation and metabolic intermediates for anabolic pathways.
- Oxidative phosphorylation is a process that leads to the formation of ATP and water by combining ADP, Pi, reducing equivalents and oxygen.
- Thermogenesis (generation of heat).
- Mitochondria play an important role during apoptosis (programmed cell death).
What is Beriberi? What is it caused due to?
Beriberi is a neurologic and cardiovascular disorder, is caused by a dietary deficiency of thiamine (also called vitamin B1).
- Thiamine pyrophosphate is a prothetic group for two mitochondrial enzymes, pyruvate dehydrogenase and α-ketoglutarate dehydrogenase.
- Patients suffering from beriberi have higher than normal serum levels of these enzymes’ substrates (pyruvate and α-ketoglutarate)
What are some symptoms of Beriberi?
- Damage to the peripheral nervous system as not enough ATP is made.
- Pain in the limbs.
- Weakness of the musculature.
- Distorted skin sensation.
- The heart may be enlarged and the cardiac output inadequate.
What are peroxisomes?
Peroxisomes are a small organelle present in the cytoplasm of many cells, which contains the reducing enzyme catalase and usually some oxidases.
Describe the structure of peroxisomes.
- Peroxisomes are ~ 0.2 to 1 µm in diameter.
- They’re surrounded by a single lipid bilayer membrane.
- They contain no DNA or ribosomes (meaning that they do not make the proteins that they contain, instead the acquire them).
- Most peroxisomal proteins are encoded in the nucleus, translated in the cytoplasm and then imported.
- At least some peroxisomal membrane proteins originate in the ER.
Describe the function of peroxisomes.
- All peroxisomes contain enzymes that use molecular oxygen to oxidize various substrates.
- Reactions produce hydrogen peroxide (H2O2), which is broken down to water by the enzyme catalase.
- Peroxisomes are important for the metabolism of long-chain fatty acids.
- Peroxisomes perform critical steps in the synthesis of certain lipids, e.g. cholesterol, plasmalogens, bile acids.
- Breakdown of excess purines (AMP, GMP) to uric acid.
How many base pairs does mtDNA have?
It has 16,569 base pairs.
