University:
The University Of Western Ontario
Course:
Biology 2290F | Scientific Method in Biology
Academic year:

2022
Views:

306

Pages:

3
Author:

Kyuwon J.

Telomerase ● End replication problem ○ When blue primer is removed form end (each lagging strand ○ The gaps cannot be filled in completely ○ No 3’ OH ■ For polymerase to extend ■ Chromosome should get shorter as the replication continues ● Theres no problem like this in prokaryotes ○ It has circular continuous DNA ○ Only one replication bubble Telomeres can resolve this issues in eukaryotes ● Problem occurs on the 5’ end of synthesized strand ● 3’ end in the template ● Telomeres are repetitive sequences at the ends of our chromosomes that protect our genes from being shortened ● ● ● ● ○ They are shortened instead ○ Restores shortened telomeres with RNA template ■ Extending DNA template available ■ Primase then can add RNA primer that DNA polymerase is able to extend ■ Ligase will seal in tight ● Seals nick ■ Telomerase is not present in somatic cells ● Stemcell, cancer cells, germline cell have telomerase ○ Once limit is reached, cell will undergo senescence Telomere repetitive sequence (TTAGGG) ○ repeat thousands of times ○ act as a buffer why telomere shortening occurs. ○ have a fixed number of repetitive sequences mechanism of telomerase action to solve the problem of replication of ends of chromosomes ○ restores length of telomeres (doesn't prevent telomere shortening) ○ provides more template strand for dna pool ○ telomerase also need a template → it has its own ■ RNA primer complementary to repetitive sequence ○ does this multiple times cell senescence and Hayflick limit definitions and why cells reach these stages ○ when telomere repetitive sequences run out → reach Hayflick limit ■ number of times a cell divides before cell division stops, about 60-70 ○ cell senescence: irreversible cell cycle arrest ● Most of our DNA is in junk material ● Only 10% is actual coding DNA ○ Only 2% codes for protein ● relative distribution of various components of genome sequence ("junk" vs. essential DNA) ○ essential 10%, junk 90% (introns, transposons, viruses, unknown) ● proportion of human genome coding for protein