Populations of some species are prone to extinction for two reasons

1. The landscapes they live in are patchy (making dispersal between populations difficult).

2. Environmental conditions often change in a rapid and unpredictable manner.

TLS Online TPP Program

#Id: 6695

#Unit 3. Fundamental Processes

Deamination of the human apolipoprotein B mRNA takes place by an enzyme called APOBEC1

TLS Online TPP Program

#Id: 6696

#Unit 3. Fundamental Processes

APOBEC3G (A3G)—is a potent inhibitor of infection by a range of retroviruses, including HIV. deaminates Cs to produce Us in that DNA strand, leading to hypermutation at levels the virus cannot accommodate, or even to destruction of the damaged strand by DNA glycosylase and apurinic apyrimidinic endonuclease

TLS Online TPP Program

#Id: 6697

#Unit 3. Fundamental Processes

Wild-type HIV produces a protein called Vif (viral infectivity factor) that directs proteosomal degradation of the A3G enzyme

TLS Online TPP Program

#Id: 6698

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6699

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6700

#Unit 3. Fundamental Processes

The introns in pre-tRNA vary in length from 14 to 60 bases and only single intron is found in each pre-tRNA transcript A pre-tRNA intron is excised in one step  Finally, hydrolysis of GTP and ATP is required to join the two tRNA halves generated by cleavage on either side of the intron.