Organisaiton of eukaryotic genome

What is telomere

Telomeres are composed of telomeric DNA bound by telomeric specific binding proteins found at end of linear eukaryotic chromosomes

Telomeres have single stranded region of DNA at their 3’ ends known as 3’ overhang. The 3’ end of the telomeric DNA aided by telomeric specific binding proteins bend back on itself to form a physical loop to protect the ends of the chromosome.

(Telomeric DNA packaged into heterochromatin)

Function of telomere

1) Ensures genes are not lost or eroded due to end of replication problem, preventing loss of important genetic information

2) Protect and stabilise terminal ends of chromosomes (preventing fusion of ss end of one chromosome to ss end of another chromosome via cbp)

3) Cells with critically short telomeres may undergo apoptosis.

Role of telomerase

an enzyme that adds telomeric repeat sequence to 3’ ends of DNA strands.

is a ribonucleoprotein

Telomerase RNA provides a template for complementary base pairing of free DNA nucleotides, extending the parental DNA strand from its 3′ end. TERT catalyses phosphodiester bond formation between these nucleotides, elongating the DNA in the 5′ → 3′ direction by adding telomere repeat sequences.

Structure of Centromere

Structure: Constricted region on a chromosome. Spindle fibres attach to centromeres during nuclear division.

DNA in centromeric region consists if non coding DNA made up of a series of tandem repeats.

Centromere associated proteins bind to specific DNA sequences from centromere form kinetochore

Function of centromere

1) hold sister chromatids together

2) ensure proper alignment and segregation of homologous chromosomes (meiosis) / sister chromatids (mitosis) to opposite poles of cell where kinetochore assembles and spindle fibres from centrioles attach