BIOL 300 Discussion 5: Genome Evolution and DNA Packaging

Introns Early Hypothesis

Genes were always interrupted

Introns Late Hypothesis

Genes started as uninterrupted

Exon Shuffling

Results in many different proteins, caused by Unequal Crossing Over and Transposons

Recombination Exon Shuffling

Mismatching portions of homologous chromosomes align during meiosis.

Transposons Exon Shuffling

AKA "Jumping Genes" is a chromosomal segment that can undergo transposition (Change position in the genome)

Result of Exon Shuffling

This shuffling can result in the evolution of a new protein.

Protein Domain

Distinct functional unit of a protein that can exist independently with a specific function

Nucleosome

a section of DNA that is wrapped around a core of proteins

Structure of Chromatin

An octamer of histones wrapped with DNA

The 4 Histone Proteins

H2A, H2B, H3, H4

Major Enzyme used in Transcription

RNA Polymerase

Major Enzyme used in Replication

DNA Polymerase

Do you need more histones to be synthesized during transcription?

No, because the number of DNA strands is the same

Do you need more histones to be synthesized during replication?

Yes, because the number of DNA strands is doubled

Histone repositioning on DNA after transcription

Simply re-form the nucleosome

How do the histones reposition

themselves on DNA after replication?

New Octamer is bound to new strand and old octamer is bound back to old strand .

FACT

dismantles nucleosomes ahead of transcribing polymerases

Histone Positioning

Histones inhibit reading of DNA and must be moved for it to be read.

Histone Phased

Histones are placed in specific location to prevent or allow the reading of certain regions.

Hypersensitive Regions Histone Positioning

Regions that are more actively being expressed, they are more easily digested by DNAses

Telomere

A region of repetitive nucleotide sequences at each end of a chromosome

Telomerase

An enzyme that adds DNA sequence repeats to the 3' end of the DNA strand in the telomere regions

Telomere Importance

Telomeres protect eukaryotes from gene loss or mutation during replication

T Loop

Something that acts like a knot at the end of the chromosome to stabilize it

D Loop

A region of the animal mitochondrial DNA molecule that is variable in size and sequence and contains the origin of replication.

Shelterin Complex

Makes DNA inaccessible in the d-loop.