MT and CP Flashcards Preview

CDB > MT and CP > Flashcards

Flashcards in MT and CP Deck (19)
Loading flashcards...
1
Q

mt genome

A

Circular, linear, fragmented
Trypanosomes maxi- and minicircles

Direct repeats - recombination, fragmentation - recombination.

Large variation in size, gene order due to intergenic regions

3-60 genes

Occurs in a complex with TFAM

2
Q

mitochondrial transcription

A

Phage-like polymerase, encoded in nucleus. Specificity factor provides specificity for promoters
Transcripts initiate at a conserved ‘a’ residue within recognition sequence

3
Q

mt post-transcriptional procecssing in yeast

A

tRNA in between mRNA or tRNA cistrons in unprocessed transcript

RNase P cleaves 5' of tRNA
RNase Z cleaves 3' of tRNA
CCA added onto 3' of tRNA
Cleavage at U-rich region on 3' of mRNA
Splicing
4
Q

Mt RNA processing in other organisms

A

Plants: Splicing, C–>U editing
ANimals: polyadenylation for stop codon
Trypanosomes: RNA editing by adding/removing UMP from mRNAs, from poly(U) tail of guide RNAs derived from minicircles

5
Q

Splicing in mitochondrial RNA

A

Yeast and plants, but not animals.

Type I intron: GTP and Mg, circular intron
Type II intron, Mg2+, lariat - adapted to spliceosomal machinery for nuclear genes

RNA maturases encoded within introns of Cyt b, that mediate splicing of Cyt B itself.

6
Q

Animal mt genome and transcription

A

Animal mitochondria have 3 promoters in the ‘D-loop’ - two transcripts from heavy-strand promoter, one from light-strand promoter

RNA Pol similar to yeast, with specificity factor

No splicing, but poly(A) to add stop codon.

7
Q

Translation in mitochondria

A

mt ribosomes and tRNA use vary across species

Sensitive to chloramphenicol but not cycloheximide

Yeast tRNA - wobble since only 25tRNAs encoded

Genetic code varies between species

8
Q

Transcription in chloroplasts

A

PEP - a2BB’B’’, with sigma factor encoded by nucleus - same mechanism of transcription as bacterial RNA Pol

NEP - Phage-like polymerase

9
Q

RNA Processing in chloroplasts

A

Cleavage at 5’-side to stability proteins by RNase J

Cleavage at 3’-side to secondary structure by PNPase

Cis-splicing to remove introns - type I and type II

trans-splicing to join ORFs that are separate on the genome (rbs12)

RNA editing C–>U

Polyadenylation promotes degradation

10
Q

Regulation of psbA translation

A

Light –> Reducing –> Breaks S-S bridge of cPABP –> cPABP binds to stem-loop on 5’-UTR –> promotes translation

11
Q

OM proteins

A

No N-terminal presequence
Single-pass a-helices can insert into OM directly via MIM complex

Porins are bound by hsp70, recruited to TOM70, pass through TOM40 into IMS, binds to SAM complex via B signal, inserts laterally into OM via SAM complex

12
Q

IMS proteins

A

No N-terminal presequence.

Translocate via TOM40, and folds in the IMS, preventing further translocation.

Mia complex facilitates S-S formation

Cyt c haem lyase inserts co-factor into Cyt C

(Cytb2 uses conservative sorting mechanism, cleaved by MPP in the matrix, IMP in the IMS)

13
Q

Metabolite carriers sorting

A

No n-terminal presequence

Hsp70, TOM70 –> Tom40 –> Tim9/10 chaperones in the IMS

TIM22 (voltage-dependent) –> IM carrier protein

14
Q

IM proteins with N-terminal preseq or matrix proteins

A

N-terminal presequence
Recognised by TOM20, translocates to TOM40, recognised by TIM50, translocates via TIM23.

Stop-transfer pathway for single-pass helical proteins

Conservative pathway for multi-pass helical proteins (and cyt b2, cleaved by MPP then IMP)

Matrix protein imported into matrix

All have N-term signal seq cleaved by MPP

15
Q

Important components of TIM23

A

PAM is the import motor - drives ATP hydrolysis via mtHsp70

TIM50 recognises presequence

Tim21 interacts with Tom22 - forming a substrate channel between the two.

Tim21 also interacts with Complex III and IV - ensures imported proteins are within vicinity of ETC

16
Q

Protein sorting in chloroplast

A

OM proteins - no presequence, inserts directly

IM proteins - presequence, TOC, TIC cleaved off in the stroma by MPP, stop-transfer or conservative

Stromal proteins - TOC, TIC, preseq cleaved off by SPP

Thylakoid membrane proteins - thylakoid-targeting internal sequence, remains in mature protein

Thylakoid lumenal proteins - bipartite sequence, one cleaved off in stroma by SPP, one cleaved off in thylakoid by TPP. Uses both Sec and Tat pathway for import into thylakoid.

17
Q

Yeast mitochondrial biogenesis

A

Haem is the O2 sensor

O2 –> haem biosynthesis –> HAP1 –> activates Cyt C transcription in the nucleus

HAP1 also activates expression of HAP2/3/4/5, which induces expression of small subunits of COX.

18
Q

Chloroplast biogenesis

A

Etioplasts convert into chloroplasts by:

Reduction in haem synthesis, which promotes chlorophyll synthesis from protoporphyrin IX.

LHC expression in the nucleus due to phytochrome activation, which degrades PIF repressors

19
Q

PRR proteins

A

RNA-binding proteins
Each repeat forms a double a-helix that binds a single RNA nucleotide, and facilitates correct processing of the RNA transcript