Chromosome Evolution

Fissions and fusion is the most common way for the number of chromosomes to change.

Humans have 23 pairs of chromosomes, but all of the other great apes have 24 pairs. At some point since our lineage split from that of chimpanzees, two chromosomes fused

TLS Online TPP Program

#Id: 6762

#Unit 3. Fundamental Processes

The exposed cap is then removed by a decapping enzyme (DCP1/DCP2), unprotected mRNA susceptible to degradation by XRN1, a 5′→3′ exoribonuclease. Removal of the poly(A) tail also makes mRNAs susceptible to degradation by cytoplasmic exosomes containing 3′→5′ exonucleases.

TLS Online TPP Program

#Id: 6763

#Unit 3. Fundamental Processes

The 5′→3′ exonuclease pathway predominates in yeast, and the 3′→5′ exosome pathway predominates in mammalian cells.  The decapping enzymes and 5′→3′ exonuclease are concentrated in P bodies

TLS Online TPP Program

#Id: 6764

#Unit 3. Fundamental Processes

The rate of mRNA deadenylation varies inversely with the frequency of translation initiation for an mRNA:  the higher the frequency of initiation, the slower the rate of deadenylation.

TLS Online TPP Program

#Id: 6765

#Unit 3. Fundamental Processes

P bodies are dense cytoplasmic domains many times the size of a ribosome. They are sites of translational repression that contain no ribosomes or translation factors. They are also major sites of mRNA degradation in the cytoplasm. Exon-junction complexes upf complex functions in nonsense-mediated decay and induces degradation of the mRNA by P body–associated 5′→3′ exoribonuclease XRN1 

TLS Online TPP Program

#Id: 6766

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6767

#Unit 3. Fundamental Processes

The most well studied type of DE is the AU-rich element (ARE) AUUUA, found in the 3’ UTR of up to 8% of mammalian mRNAs