T4 Flashcards Preview

MolBi > T4 > Flashcards

Flashcards in T4 Deck (92)
Loading flashcards...

Describe the translocation of mitochondrial protein from the cytosol to the matrix.

1. Binding of N-terminal signal sequence to TOM complex receptor
2. Stripping of cytosolic Hsp70 from protein
3. Binding of signal sequence to TIM23
4. Translocation of protein by mitochondrial Hsp70 and electrophoresis
5. Cleavage of signal sequence


How is a translocated polypeptide released from TIM23 complex?

Through action of ATPase.


How are mitochondrial proteins integrated into the outer/inner mitochondrial membrane?

In the outer by the SAM complex (aids in insertion and folding). OXA complex aids in mitochondria native protein insertion in inner membrane.


How is peptide folding inhibited in the intramembranous space?

By chaperones.


Outline the four mechanisms of translocated protein recognition/sig.seq. release inside mitochondria by integral protein complexes.

1. Recognition by inner membrane integral protein complex of N-terminal signal sequence and then hydrophobic sequence (stops translocation in intermembraneous space).
2. Recognition by TIM23 complex of signal sequence and then cleavage sequence/second signal sequence. Recognition of 2nd sig.seq. by OXA complex (also mitochondria native peptides) and translocation to intermembranous space.
3. Binding to inner membrane complex and release by 2nd signal peptidase.
4. Internal sig.seq. recognised by TOM complex (running through of peptide), binding of chaperones and transport to TIM22 (yes, 22).


What structures allow proteins to traverse inner resp. outer mitochondrial membrane?

Porins in outer membrane, metabolite-specific transporters in inner.


Does the mitochondria export protein into the cytosol at any point?

Normally no, protein transport is unidirectional, from cytosol to mitochondrion. However, during apoptosis protein transport may take place in the opposite direction.


awhre is the mitochondrial gneome located?

In the matrix.


How does mitochondrial protein synthesis resemble that of bacteria?

1. Both start with N-formyl methionine
2. Also mitochondrial ribosomes are sensitive to antibacterial antibiotics


How is mitochondrion number and shape in a cell controlled?

Through fission and fusion, mediated by GTPase dependent enzymes.


When does mitochondrion genome replication take place?

Throughout the cell cycle.


What determines what mitochondrial DNA molecules are to be replicated?

Random selection. However regulated during constant conditions to ensure "constant amount of organelle DNA".


Is the majority of mitochondrial protein coded by mitoDNA or by nuclear DNA?



Ehat does the human mitoDN encode for?

"2 ribosomal RNAs, 22 tRNAs and 13 different polypeptide chains"


What are nucleoids?

Multiple structures containing mitoDNA, attached to the inner membrane. A simple circle.


What is the endosymbiont hypothesis and how is it supported?

The theory of an anaerobic cell engulfing an aerobic one in order to cope with the oxygen rich environment, and the subsequent gene transfer from the aerobic organism (mitoc.) to the anaerobic host (nucleus). Similar gene transfers have been observed in modern time.


What features distinguish mitochondrial genome?

1. Dense gene packing (very few non-coding nucleotides)
2. Relaxed codon usage (many tRNAs recognize any of four nucleotides in position 3)
3. Variant genetic coding (4/64 codons code different proteins than the nuclear genome)


In what form is the mitochondrial genome?

Circular, non histone-bound.


How is the mitochondrial genome transcribed?

Symmetric transcription of both strands, starting from the same promotor region and progressing in opposite direction produces 2 giant RNAs.


How are the mitoRNA transcripts processed?

1: extensive nucleade cleavage produces 2 rRNAs, most tRNAs and ca 10 poly-A RNAs
2: 8 tRNAs and 1 small poly-A RNA


What is the function of the non-coding part of the genome of the mitochondria?

Complimentary sequences to coding parts on opposite strand.


What defines mitochondrial substitue for mRNA?

poly-A-containing RNA (and lack of 5'cap).


Are human mitochondrial mRNAs spliced?



What is mitotic segregation in mitocDNA inheritance?

Mitochondrial genome in haploid cell isn't inherited 50/50 from each parent cell but is instead enriched over time (inheritance of more of one type/mitotic enriching), to produce individual cells with predominantly one type of mitochondrial genome vs. the other.


What does cytoplasmic inheritance entail?

All daughter cells (of diploid cell) contain the same mitochondrial genome.


Through what mechanism is the mitochondrial genome inherited in humans?

Through maternal inheritance.


What is the basis for maternal inheritance?

The greater contribution of cytoplasm to the zygote from the egg cell (vs. the sperm cell).


Are all the copies of mitchondrial genome inherited from the mother (in humans)?

No. One or two may be from the father/sperm cell.


Why are muscles and nerves most susceptible to mitochondrial disease?

Due to their greater need of ATP.


What might be the mechanism for eruption of mitochondrial disease (ex. MERRF)?

Mutation in one tRNA gene and inheritance of a threshhold amount to a cell and later, tissue.