Chapter 8Energy Generation in
Mitochondria and Chloroplasts
(1) Mitochondria: in all eukaryotic cellsThe relationship between the structure and function of mit.
(2) Chloroplasts: in plant cellsThe relationship between the structure and function of chl.
Mit: Oxidative phosphorylation→ATP
1. Mitochondria and oxidative phosphorylation
A. Mitochondrial structure and function
The size and number of mitochondria reflect the energyrequirements of the cell.
Inner and outer mitochondrial membranes enclose twospaces:
the matrix and intermembrane space.
(1) Outer membrane:Contains channel-forming protein, called Porin.Permeable to all molecules of 5000 daltons or less.
(2) Inner membrane(Impermeability):Contains proteins with three types of functions:(1) Electron-transport chain: Carry out oxidation reactions; (2)ATP synthase: Makes ATP in the matrix; (3)Transport proteins: Allow the passage of metabolites
(3) Intermembrane space:Contains several enzymes use ATP to phosphorylate othernucleotides.
(4) Matrix:Enzymes; Mit DNA, Ribosomes, etc.
B. Specific functions localized within the Mit by disruption of the organelle and fractionation
Localization of metabolic functions within the mitochondrion
(1) Outer membrane:Phospholipid synthesis; Fatty acid desaturation;Fatty acid elongation;
(2) Intermembrane space: Nucleotide phosphorylation;
(3) Inner membrane:Electron transport;Oxidative phosphorylation;Metabolite transport;
(4) Matrix:Pyruvate oxidation;TCA cycle;? oxidation of fats;DNA replication;RNA transcription;Protein translation;
2. Molecular basis of oxidative phosphorylation
A. Molecular basis of oxidation: Electron-transport chain
B. Molecular basis of phosphorylation:ATP synthase
The structure of the ATP synthase
F1particle is the catalytic subunit;The F0particle attaches to F1and is embedded in the inner membrane.
F1: 5 subunits in the ratio 3a:3b:1g:1d:1e
F1 particles have ATP synthase activity
Proton translocation through F0drives ATP synthesis by F1:
Binding Change Model and rotational catalysis
Boyer proposed in 1979, and was greatly stimulated by thepublication in 1994 of the structure for F1 complex (X-ray) frombovine heart mitochondria
Direct experimental evidence supporting therotational catalysis.
Japan researcher, Nature 386: 300, 1997.
The ATP synthase is a reversible coupling device
Other roles for the proton-motive force inaddition to ATP synthase
C.Mithchell'sChemiosmotic theory (1961)
The pH and electrical gradient resulting from transport ofprotons links oxidation to phosphorylation.
When electrons are passed to carriers only able to acceptelectrons, the H+is translocated across the inner membrane.
More than 2*10^26molecules (>160kg) of ATP per day in our bodies.
(1) Electrons pass from NADH or FADH2to O2, the terminal electronacceptor, through a chain of carriers in the inner membrane(FMN, Fe-S center, Heme group Fe, CoQ);
(2) As electrons move through the electron-transport chain, H+arepumped out across the inner membrane, and formProton motiveforce;
(3) Electrons move through the inner membrane via a series of carriers of decreasing redox potential
A testable prediction followedfrom Mitchell's hypothesis
If not all the detergent is removed, what will happen?
Summary of the major activities during aerobic respiration in a mitochondrion
NADH->O2: 3ATP/2e; FADH2->O2: 2ATP/2e
3. Chloroplast and photosynthesis
A. The structure of Chloroplasts
C. The antenna complex and photochemical reactioncenter in a photosystem
Light-dependent reaction: Electron transport in the thylakoid membrane and noncyclic photophosphorylation
Fig. Simplified scheme for cyclic photophosphorylation. Absorption of light by PSI excites an electron, which is transferred to ferredoxin (step 1) and on to cytochrome b6f (step 2), plastocyanin (step 3), and back to P700+ (step 4). In the process, protons are translocated by cytochrome b6f to form a gradient utilized for ATP synthesis (step 5)
Changes in redox potential during photosynthesis.
v Carbon dioxide fixation and the synthesis of carbohydrate in C3 plants (Calvin cycle)
The structure and function in C4 plants
4. Organelle DNA and protein importing
A. Organelle DNA
The size range of organelle DNA is similar to that of viral DNAs.
(1) Mit DNA: from <6000bp (plasmodium falciparum) ～ >300000bp (some land plants ). DNA of Mit genome(in mammals ) ≈ 16500bp( <0.001% of nuclear genome ) ; Chl genomes are about 10 times larger and contain about 120 genes.
(2) Chl DNA: from 70000 to 200000bp (genome ofland plants );
Genes in mtDNA encode rRNAs, tRNAs, and some mitochondrial proteins
Human mt DNA: 16,569bp 2 rRNAs, 22 tRNAs,
13 polypeptides: NADH reductase. 7 sub;
Cty b-c1 complex 1 cytb;
Cyt oxidase 3 subunits;
ATP synthase: 2 F0 sub ;
The organization of the liverwort ( 地钱 ) Chl genome
B. Mit and Chl have their own genetic systems
Mit and Chl are organelles semiautocephaly.
The synthesis of mt proteins is coordinated
C. The transport protein into Mit. And Chl.
Tree proteins translocators in Mit membranes:
(1) T OM, TIM,and OXA complex are multimeric membrane protein, that catalyze protein transport across Mit membrane, TOM, TIM stand for translocase of the outer and inner Mit membranes respectively.
(2) TOM functions across the outer membrane; TIM(TIM23 and TIM22) function across the inner membrane.
(3) OXA mediates the insertion of inner membrane proteins that are synthesized within the Mit. OXA also helps TOM and TIM to insert some proteins into the matrix.
Translocation of precursors to the matrix occurs at the sites where the outer and inner membranes are close together;
Fig. Proteins transiently span both the inner and outer mitochondrial membranes during their translocation into the matrix. When isolated mitochondria are incubated with a precursor protein at 5°C, the precursor is only partially translocated. The amino-terminal signal peptide (red) is cleaved off in the matrix; most of the polypeptide chain remains outside the mitochondria, where it is accessible to proteolytic enzymes. Upon warming to 25°C, the translocation is completed. Once inside the mitochondrion, the polypeptide chain is protected from externally added proteolytic enzymes unless detergents are added to disrupt the mitochondrial membranes, w hich allows the imported proteins to be digested.
The protein import by Mit:
N-terminal signal sequence is recognized by receptors of TOM;
The protein is translocated across both Mit membranes at or near special contact sites.
Only unfolded proteins can be imported into Mit;
Mit precursor proteins remain unfolded through interactions with hsp70 chaperone proteins in the cytosol after they are synthesized.
ATP hydrolysis and H+ gradient are used to dtive protein import into Mit
Protein transport into the inner Mit membrane and the intermembrane space requires two signal sequences
Two signal sequences are required to direct proteins to the Thylakoid membrane in Chl.
Translocation into thylakoid space or thylakoid M can occur by any one of at least four routes.
5. The proliferation and origin of Mit and Chl.
A. Organelle growth and division determine the number of Mitochondria and Plastids in a cell
(1) Mit fission and fusion (a dividing Mit in a liver cell); Dividing or Budding of Mit.
(2) Chloroplasts: dividing and formation of chloroplasts from proplastids begins by the light-induced budding of the inner membrane.
B. Origin: The endosymbiont theory
Compare the ribosomal RNA with the base sequence of various bacterial rRNAs: Purple bactria-Mitochondria Cyanobacteria-Chloroplasts
Suggested evolutionary pathway for the origin of Mit.