10 Lecture Energy Conversion: Mitochondria and Chloroplasts
Chemiosmotic coupling:
the common pathway used by mito, chloroplasts and procaryotes ATP (chemi) membrane transport (osmotic)
electrochemical proton gradient
Large amount of internal membrane in mitochondria and chloroplasts
Chemiosmotic coupling
Electron transport processes
High-energy
Low-energy
chlorophyll
Electron transport chain; the entire set of proteins in the membrane and the small molecules involved in the orderly sequence of electron transfers
Photosystems: drive electrons in opposite directions
photosynthesis: from H2O eventually to CO2
mitochondria: from carbohydrate to O2 and make H2O
Mitochondrial plasticity
not stiff elongated cylinders
Mitochondria move along MT
there are many of them!
some move a lot
MT wind along axoneme in development and then disappears and mito fuse others are fixed in position
Biochemical fractionation of purified mito Study different proteins in each compartment Process large numbers of mito at the same time
Low osmotic strength Cristae of the inner membrane unfold Outer membrane (no folds) break
four compartments: outer and inner membrane, intermembrane and matrix
Oxidative phosphorylation
ATP synthase Respiratory enzyme complexes
F0F1 ATPase, 500 kd multisubunit
Proton causes rotation and rubbing of two sets of proteins against each other: rotating stalk proteins and head proteins
F1
Lollipop head
>100 ATPs Per minute
ATP synthase can also function in reverse to hydrolyze ATP and pump H+
Reversible coupling device
if proton gradient is flat and ATP is abundant
Plastids
A proplastid from a root tip cell of a bean plant Three amyloplasts (leucoplasts) or starchstoring plastids in a root tip cell of soybean
Purine and pyrimidine synthesis, aa synthesis FA synthesis All take place in plastids!
Intermediary metabolism
proplastids development into chloroplasts when exposed to light in leaf cells
starch and granules lipid droplets: biosynthesis
Inner membrane is not folded Electron transport chains, photosystems, ATP synthase are present in thylakoid membrane
ATP synthase protrudes into the matrix from the inner mitochondrial membrane
ATP synthase protrudes into the stroma from the thylakoid membrane
Photosynthesis
Photosynthestic electron transfer reactions (light reactions): Chlorophyll energizes an electron using Light energy Electron comes from H2O and O2 is a by-product ATP synthesis and NADPH
Carbon fixation reactions (dark reactions): Ribulose bisphosphate carboxylase
The antenna complex and photochemical reaction center form a photosystem
Funnel
A dividing mito
many copies of genome
Various sizes of mitochondrial genomes
Nucleoids: similar to bacterial DNA, no histones circular 6000-300,000 nt
Suggested evolutionary pathway for the origin of mitochondria
Human mitochondria genome: 16,569 nt. Sequenced in 1981. 1. Dense gene packing--not much regulatory sequences 2. Relaxed codon usage--only 22 tRNA (30 in cytosol), many tRNAs recognize any one of the four Nt in the third (wobble) position 3. Variant genetic code-- 4 of the 64 codons have different meanings
More than 20 chloroplast genomes have been sequenced Similarity to bacteria is striking
In higher animals, the progeny contain only maternal mito. In 2/3 higher plants, chloroplasts are also maternally inherited
In other plants, pollen chloroplasts enter the zygote-biparental-variegation
white: defective chloroplasts
Mitochondria import lipids Chloroplasts make their own
Mito converts imported lipids to cardiolipin (inner membrane)
Summary 1. 2. 3. 4. 5. 6. 7. Chemiosmotic coupling and electron transport Mitochondria are plastic and can be motile Oxidative phosphorylation and ATP synthase Plastids and chloroplasts Photosynthesis, antenna and reaction center Mitochondrial and chloroplast genomes Inheritance of organelle genomes and biosynthesis