Bioenergentics & Metabolism BS MicroBiology 1st Sem

1. Bioenergentics & Metabolism
Mitochondria
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2. Mitochondria Structure & Function
Generation of metabolic energy is a major activity of all cells
Two cytoplasmic organelles are specifically devoted to energy metabolism and production of ATP
•Mitochondria
Generates useful energy derived from breakdown of lipids & carbohydrates
•Chloroplast
Use energy captured from sunlight to generate ATP and the reducing power needed to synthesize carbohydrates from CO2 and H2O
Mitochondria Structure & Function
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3. Mitochondria
Mitochondria are
◦Responsible for most of the useful energy derived from breakdown of carbohydrates and fattyacids
Converted to ATP by oxidative phosphorylation
Mitochondria are unique among cytosolic organelles in that
They contain their own DNA which encodes
tRNA, rRNA, and some other mitochondrial proteins
Assembly of mitochondria contain
•Proteins encoded by their own genome
•Proteins encoded by nuclear genome and imported from cytosol
Mitochondria Structure & Function
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4. Structure of Mitochondria
Mitochondria are surrounded by a double membrane system
•Consist of inner and outer membrane separated by intermembrane space
•Innermembrane form numerous folds (cristae) which extends into matrix
•Large surface area
•Matrix contains mitochondrial genetic system & enzymes responsible for oxidative metabolism
•Houses the machinery for aerobic respiration
Mitochondria Structure & Function
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5. Mitochondria consist of two aqueous compartments
Interior – the matrix
Between the inner and outer membranes – intermembrane space
Inner Membrane
High percentage of proteins(> 70%)
Involved in oxidative phosphorylation
•Transport of metabolites (pyruvate, fatty acids)
Impermeable to most ions and small molecules
 a property critical to determining proton gradient that drives oxidative phosphorylation
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Mitochondria Structure & Function

6. Outer Membrane
Porins – integral proteins
Large internal channel
 Allows free diffusion of molecules smaller than about 1000 daltons
Composition of intermembrane is therefore similar to cytosol with respect to ions and small molecules
Mitochondria Structure & Function
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7. Mitochondria are positioned near to locations of high energy use i-e synapses in nerve cells, muscle cells
Continuously fusing and dividing , remodel the network of mitochondria in cell, and affect function and morphology
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Mitochondria Structure & Function

8. Endosymbiotic Origin
Mitochondria contain their own genetic system
Mitochondria are thought to have evolved from bacteria that developed a symbiotic relationship in which they lived within larger cells (Endosymbiosis)
Genomes of living organisms that are similar to mitochondria are that of
α-proteobacterium Rickettsia prowazeki
It is able to reproduce only in eukaryotic cells
But unlike mitochondria it transcribes most of its own genes
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Mitochondria Structure & Function

9. Mitochondrial Genome
Mitochondrial genome are usually circular DNA molecules, like bacteria
Present in multiple copies per organelle
Vary considerably in size between different species
Genomes of human and most other animal mitochondria are only about 16kb
Larger mitochondrial genome are found in yeast (approx 80kb) and plants (more than 200kb)
e.g
Mitochondrial DNA in Arabidopsis is 367 kb, encodes only 31 proteins
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Mitochondria Structure & Function

10. Contd…
Smallest mitochondrial genome
◦Protist: plasmodium falciparum 6kb, codes for only 3 proteins
Largest mitochondrial genome
◦Protozoan Reclinomonas americana
◦69 kb and contain 67 genes
Most present day mitochondrial genome encode
◦ Small number of proteins
Mammalian mitochondria (1000 to 5000 different proteins) representing approx 5% of proteins encoded by mammalian genome
◦tRNA, rRNA
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Mitochondria Structure & Function

11. Human mitochondrial 16 Kb genome encodes
◦Circular DNA molecule
◦Maternal inheritance
Map
Origin of replication and transcriptional promoter sequences (D loop)
16sRNA, 12sRNA, 22tRNA
13 proteins (essential for oxidative phosphorylation)
Electron transfer chain complexes, including I, III, IV and V
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Mitochondria Structure & Function
The Human Mitochondrial Genome

12. Mitochondrial Genetics
Mitochondria use a slightly different genetic code than in prokaryotic and eukaryotic cells
 Human mitochondria encode only 22 tRNAs ,approx 30 different tRNAs are required to translate the universal code according to wobble rule
Translational of mitochondrial mRNA is accomplished by extreme form of wobble
U in anticodon of tRNA can pair with any of four bases in third codon position of mRNA
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Mitochondria Structure & Function

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14. Differences between the universal and Mitochondrial Genetic codes
Codon
Universal Code
Human Mitochondrial code
UGA
Stop
Trp
AGA
Arg
Stop
AGG
Arg
Stop
AUA
IIe
Met
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Mitochondria Structure & Function

15. Mutations in mtDNA
Mitochondrial DNA can be altered by mutations
Germ-line mutations in mitochondrial DNA are transmitted from mother
•Mutation in tRNA gene
Metabolic syndrome; obesity, diabetes
•Mutation in gene that encode components of electron transport chain
Leber’s hereditary optic neuropathy; blindness
•Progressive Mutations in mitochondrial DNA
Aging
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16. Mitochondrial proteins
Contain 1000 to 5000 different proteins but nearly half of them remain unidentified (~5% of mammalian encoded proteins)
Mitochondria from different tissues contains different proteins (tissue specific functions)
Genes for mitochondrial proteins are in nucleus(95% of mt proteins)
Some of these genes were transferred to mitochondria by original prokaryotic ancestor
Cytosoloic protein synthesis mt transport
All kerb cycle enzymes/ rep/trans/translation
Complex because of mt double membrane
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Mitochondria Structure & Function

17. Transport & assembly of matrix proteins
Pre-sequence, N-terminal 20- 35 a.a target proteins to matrix
Partially unfolded by Hsp70 chaperon
◦Prevent aggregation as emerge from free ribosomes
Bind to receptors on Tom protein complex(translocase of outer membrane)
Bind Tim complex(Translocase of inner membrane)
The presequence is cleaved by a matrix protease
a mitochondrial Hsp70 binds the polypeptide chain as it crosses the inner membrane, driving further protein translocation.
A mitochondrial Hsp60 then facilitates folding of the imported polypeptide within the matrix
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Mitochondria Structure & Function