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Mitochondrion & Chloroplasts (Mitochondrial functions (Heme…
Mitochondrion & Chloroplasts
Mitochondria form branched tubular network through the cell.
Mitochondrial Membranes
Outer membrane is about 50% protein
Inner membrane more that 75% protein
Outer membrane contains large pore-forming proteins called porin
Inner membrane contains cardiolipin (stop proteins crossing membrane) but not cholesterol
Inner membrane is impermeable to even small molecules
Outer membrane is permeable to large molecules - even some proteins
Mitochondrial Matrix
Contains DNA, ribosomes and enzymes
RNA and proteins synthesised in the matrix
For functional mitochondria we use proteins coded by nucleus and DNA of mitochondrion
Mitochondrial DNA code for 13 proteins subunits and ribosomal and transfer RNA in mammals
Main role of mitochondria is to make ATP
Uses the Kreb cycle and ETC
Uses oxygen as final electron acceptor
Make about 32 molecules of ATP per molecule of glucose
ATP formed by substrate level phosphorylation in glycolysis
Oxidative phosphorylation in mitochondria
Accounts for >160kg ATP in our bodies per day
Human body contains approx 250g ATP
Hibernating animals have special mitochondria in their brown fat
Contain specialised channel protein
Allows protons to return through membrane and not make ATP
Energy associated with this is lost as heat instead
Mitochondrial functions
Heme biosynthesis
Steroid synthesis
Metabolism of fatty acids
Regulation of the cellular redox state
Calcium homeostasis
Amino acid and protein metabolism
Carbohydrate metabolism
Involved in programmed cell death
Unicellular eukaryotes (protists lack ETC
Synthesis ATP from pyruvate breakdown
Simple fermentations involve the production of molecular hydrogen as major metabolic end product.
These mitochondria are called hydrogenosomes
This allows the cell to gain about 4 mol of ATP per glucose
Rickettsia is an obligate intracellular bacterium that seems to be most closely related to the mitochondria
By-products of oxygen metabolism (radical) cause damage to molecules in the mitochondria.
Speculated that accumlations of mutations in mtDNA is major cause of aging
Chloroplasts
Double membrane
Outer contains porins and is permeable to large molecules
Inner membrane contains light-absorbing pigment, electron carries and ATP-synthesising enzymes
Inner membrane of chloroplast is folded into flatten sacs (thylakoids) arranged into grana
Self replicating organelles with their own DNA
Carbon dioxide fixation is the stroma
Photosynthesis
Oxidises water to oxygen and respiration is opposite
Respiration removes high energy electrons from reduced organic substrate to for ATP and NADH
Photosynthesis uses low energy electrons to form ATP and NADPH, which are then used to reduce co2 to carbohydrate