mitochondria Flashcards
(11 cards)
functions of mitochondria:
cell signalling
cell differentiation
cell death
control of the cell cycle and cell growth.
mitochondrial proteins:
mitochondrial proteins vary depending on the tissues and species.
humans have 615 distinct types of mitochondrial proteins identified from cardiac mitochondria. mice have 940 mitochondrial proteins encoded by distinct genes.
the mitochondrial proteome is thought to be dynamically regulated.
outer membrane:
encloses the entire organelle.
has protein-to-phospholipid ratio similar to the plasma membrane.
contains large numbers of integral proteins called porins- channels that allow molecules <5000 Da to freely diffuse across the membrane.
larger proteins can enter if they have a signalling sequence to utilise an active transport protein called a translocase.
disruption of the outer membrane permits protein in the intermembrane space to leak into the cytosol which leads to cell death.
intermembrane space:
space between the outer membrane and the inner membrane.
same concentrations of small molecules (ions and sugars) as cytosol as outer membrane is freely permeable.
protein composition differs to that of the cytosol. as active transport is needed.
1 protein that is localised to the intermembrane space is cytochrome c- part of the electron transport chain.
inner membrane (proteins):
contains proteins with 4 types of functions: 1. those that perform the redox reactions of oxidative phosphorylation. 2. ATP synthase, which generates ATP in the matrix. 3. protein import machinery.
contains more than 100 different polypeptides.
home to around 20% of the total protein in a mitochondrion.
does not contain porins and is highly impermeable to all molecules.
ATP synthase:
an enzyme that synthesises ATP and inorganic phosphate (pi).
ATP synthesis uses energy. protons (H+) moving down an electrochemical gradient from the inter membrane space into the matrix.
inner membrane (phospholipids):
has a very high protein to phospholipid ratio. is rich in an unusual phospholipid called cardiolipin. cardiolipin contains 4 fatty acids rather than 2 and may help to make the inner membrane impermeable.
almost all ions and molecules require special membrane transporters to enter or exit the matrix.
cristae:
invaginations of inner membrane.
expand the surface area of the inner mitochondrial membrane. in typical liver mitochondria, the surface area (including cristae) is about 5x that of the outer membrane.
enhance its ability to produce ATP.
muscle cell mitochondria contain more cristae than typical liver mitochondria as greater demand for ATP.
matrix:
space enclosed by the inner membrane. contains about 2/3 of the total protein in a mitochondrion, highly concentrated mixture of hundreds of enzymes, special mitochondrial ribosomes, tRNA, several copies of the mitochondrial DNS genome. important in the production of ATP with the aid of the ATP synthase contained in the inner membrane.
major functions of the enzymes include oxidation of pyruvate and fatty acids and citric acid (krebs) cycle.
mitochondrial DNA:
cell has 100s of mitochondria each with 2-10 copies of mtDNA. heterogeneous within tissues.
codes for some but not all of its own proteins. 37 genes. 13 protein encoding regions for respiratory complexes. 2 for r RNAs, 22 for tRNAs.
mitochondrial diseases:
genetic defects of muscle or nerve tissue. high consumers of ATP.
severe- infant death, blindness, deafness, seizures, stroke like episodes.
milder- muscle weakness, intolerance of exercise, muscle deterioration, infertility.
may play a role in the ageing process.
most defects in genes encoding mitochondrial tRNA. particularly those for leucine and isoleucine. see translation lecture for more on tRNA.
arise when most of mitochondria in a tissue have a certain mutant gene.
maternal inheritance from mitochondria from egg not sperm.
