Mitochondria and Peroxisomes Flashcards
What are the features of the double membranes of a mitochondria?
Outer membrane: lipid bilayer is permeable to small molecules and contains proteins called porins that form channels which allow for free diffusion of small molecules.
Inner membrane: lipid bilayer not permeable to small molecules. It forms cristae which extend into the matrix.
What are the spaces found in a mitochondria?
- Intermembrane space between outer and inner membrane
- Innermost space is the matrix
What occurs in the matrix?
Most reactions take place at the matrix
What are cristae and why are there so many?
Cristae are numerous folds that are formed by the inner membrane.
Cristae are extremely dense and convoluted.
There are so many because the membranes are packed with proteins which are used for the electron transport chain.
Why do mitochondria look elongated in images produced by dimension electron tomograms?
Mitochondria can change shape dramatically (known as mitochondrial plasticity) and not alway a micrometer especially because they move along microtubules.
Mitochondrial morphology changes during what processes?
- Apoptosis
- Ca2+ transfer
- Cell cycle
- Nutrient starvation
What is nutrient starvation?
When cells are starved of nutrients and this causes mitochondria to spread out and fuse to become longer, but they are able to split up again.
*it is thought that elongation and fusion stops mitochondria from being broken down by autophagy as they are too long to be engulfed by macrophages.
How many proteins does a mitochondria have?
1500-3000 different proteins.
What is the pathway for most mitochondrial proteins?
- most of which are encoded by genes are found in nuclear DNA
- DNA will be transcribed forming RNA
- RNA will be translated into protein in cytosol
- Proteins often in precursor form having specific signal sequences will be imported into mitochondria
How are mitochondria able to encode,translate and transcribe their own proteins?
Mitochondria contain their own DNA and ribosomes so they are able to do this. Their DNA is called mtDNA and is found in the matrix.
What are the features of human mtDNA?
Human mtDNA contains a small number (16,569) of base pairs that encode 2 rRNAs, 22 tRNAs and 50 proteins (some used in the electron transport chain.
Mitochondrial chromosomes are circular.
How are mitochondrial diseases passed through?
They are passed through the mother as sperm only contain little amount of mitochondria.
Mitochondrial genes are inherited cytoplasmically (transmissions of genes occurs outside the nucleus)
This is extracellular inheritance and refers to any genes that are passed on from structures that are not in the nucleus (mitochondria are found outside the nucleus and is passed through the mother).
How does the mitochondrial genetic code differ from the standard nuclear code?
Different codons code for different amino acids e.g. UGA is recognised as a stop codon in the nucleus, but in mitochondria it codes for tryptophan.
What is the endosymbiosis theory for the origin of mitochondria?
Mitochondria were evolved from the phagocytosis of a bacterium that evolved 1-2 billion years ago:
-Ancestral anaerobic eukaryote (can’t use molecular oxygen to produce ATP) had engulfed an anaerobic bacterium
-The bacterium carries out efficient metabolism and has bacterial genome unlike the eukaryote and started to increase the number of communities
-The engulfed bacterium has evolved to become mitochondria and forms either a non-photosynthetic eukaryote or photosynthetic eukaryote.
-The photosynthetic eukaryote must also have had to engulf a chloroplast also.
This all leads to the formation of multicellular organisms.
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What are the different functions of mitochondria?
- Breaks down fatty acids into acetyl CoA (to get energy from fatty acids).
- Decarboxylation of pyruvate to acetyl CoA, used in krebs cycle
- Citric acid cycle, an important metabolic pathway generating equivalents for ATP generation and metabolic intermediates for anabolic pathways (which lead to the production of more complicated molecules), uses energy.
- Oxidative phosphorylation, the formation of ATP, reducing equivalents derived from the breakdown of acetyl CoA and electrons combine to with O2 to form water.
- Thermogenesis
- Apoptosis