Mitochondria and Chloroplast Flashcards
What are the mitochondrial protein complexes?
- NADH dehydrogenase (Complex I;NDH)
- succinate dehydrogenase (Complex II)
- bc1 or cytochrome complex (Complex III)
- cytochrome oxidase (Complex IV; COX)
- ATP synthase
- cytochrome c
- lipid soluble ubiquinone
What topologies can mt genomes take?
- circular
- linear
- maxicircles
- minicircles
How does yeast mt splicing occur?
- Type I splicing requires GTP and Mg and creates circular intron
- Type II requires a hairpin and Mg and produces a lariat
How does animal mt transcription work?
- Similar RNA polymerase to yeast but transcription intitated at one site
- Translation stop codon not encoded but added via polyadenylation
- The mt likely use altered codons which differ between species
How to higher plants use RNA editing to alter codon usage?
- predominantly modify C to U
- Typansomes make more extensive use of RNA editing
What’s different with mt mRNA transcription?
- Don’t have all tRNA genes, import from nucleus
- Make use of wobble to recognise some codons
- Sensitive to antibiotics
- No evidence for mRNA import
What are plastids
- Chloroplasts are plastids and are interconvertible. Originate from protoplastid
- Chromoplasts, in flowers and fruits, red, yellow orange
- Leucoplats, in mature plant cells(roots) drive synthesis of fatty acids, amino acids and cofactors
- Amyloplasts in roots, seeds, storage, contain starch
What are the structures in chloroplast membranes?
- Photosystem II, oxygen evolving complex
- b6f cytochrome complex
- Photosystem I
- ATP synthase
- plastocyanin (PC)
- ferredoxin (Fd)
- ferredoxin-NADP reductase (FNR)
- ## Plastoquinone, lipid soluable
Do mt and chloroplast genomes vary in size?
- mt vary significantly
- chloroplast not as much
What evidence indicates strong homology between chloroplast and Ecoli genomes?
- Chloroplast genes can be expressed in ecoli
What polymerases does chloroplast have?
- plastid encoded polymerase (PEP), similar to ecoli
- nucleaur encoded polymerase (NEP), similar to bacteriophage/mt
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Do most genes in mt and chloroplast originate from nucleus or organelle?
- Nucleus due to limited coding capacity
What ribosomes translate mt and cp proteins?
- Free ribosomes
What signals do mt/cp directed proteins have?
- presequence or transit peptide which guide it through membrane transport
- no signal seq as they don’t arise in ER
- no sequence similarity between species but tend to have; rich hydroxyl amino acids, positive charge, few acidic
Is the presequence necessary and sufficient for mt/cp protein import?
- Yes, mature proteins not imported
What are the TOM complexes made of?
- tom20, receptor for presequence
- tom22 organizer of TOM
- tom40 outer membrane channel
- tom70 receptor for hydrophobic carriers, transfers to Mitochondrial Import Complex( MIM)
- MIM inserts alpha helical proteins into outer membrane
What are the TIM complexes made of?
- tim15 receptor for presequence
- tim21 connects tim to tom
- tim23 channel for precursor protein from TOM,
- tim22 inserts proteins into inner membrane, carrier translocase
- OXA inserts mt or imported proteins into membrane
What is the mt inter membrane space?
- Contains chaperons
- Eukaryote specific
- Mitochondrial intermembrane assembly (MIA) helps for disulphide bridges, no homolog
How are nuclear proteins processed in mt matrix?
- Mitochondrial Processing Peptide cleaves presequence
- Hsp60 helps fold in mt
- Hsp70 attached to tim23 as a heat shock protein which helps pull protein across membrane
What is the SAM complex in mt import?
- inserts beta barrel proteins into outer membrane
How does plastid to cp biogenisis occur in higher plants(not genes)?
- Chloroplasts genisis requires light, absence forms etioplast plastids
- Regulation posttranslational, so transcripts present in dark
How do chloroplast transcripts regulate nucleus transcription (retrograde signalling)?
- tagetoxin and lincomycin nd chloramphenicol prevent nuclear expression of early seedling development
- An example is etioplast exposure to light releasing haem and phytochromoilin which upregulate LHC gene in nucleus which causes chloroplast transiiton
How can nuclear mt incompatibilities affect resistance to disease?
- different peoples will have different resistances to different diseases and conditions
