Intro to Genomes

Chromosome structure

2 sister chromatids joined at a centromere

telomeres

cap at the ends of eukaryotic chromosomes that function in maintaining chromosome structure

Euchromatin

less tightly bound and dispersed throughout the nucleus. DNA is more easily accessed by transcription factors and polymerases

Heterochromatin

tightly packed chromatin that is very unlikely to be expressed

constitutive heterochromatin

chromatin that is always condensed and inactive; largely repetitive DNA found by centromeres

faculative heterochromatin

chromatin that exists in either genetically active or inactive from

human chromosomes

46 chromosomes, 23 pairs of chromosomes, each made up of a linear double stranded DNA molecule with histones and other proteins, 22 autosomes + one sex chromosome pair

Human Genome project key findings

there are about 20500 protein coding genes in human beings

the human genome has significantly more segmental duplications than other mammalian genomes

coding DNA

DNA containing protein coding sequences, ultimately leads to the production of all human proteins; coding DNA unevenly distributed across the chromosome (high on 19 and 17)

non-coding DNA

all of the DNA sequences within a genome that are not found within protein coding exons and so are never expressed within an amino acid sequence (introns, ncRNA, pseudogenes)

introns + untranslated RNA

a type of ncDNA, includes introns that are spliced out of mRNA and 5’ and 3’ untranslated regions

pseudogenes

a type of ncDNA containing inactive copies of protein-coding genes, often generated by duplication that later becomes non functional, ~13000 in human genome

non coding RNA

comes from ncDNA and plays essential role in cells, especially in protein synthesis and RNA processing, human genome codes for 100,000s; tRNA, rRNA, microRNA, long non-coding RNA

extragenic DNA

DNA that is not related to genes (regulatory DNA, repetitive DNA, mobile genetic elements)

Regulatory DNA

a type of extragenic DNA, crucial to controlling gene expression, estimated to be 20-40% of the genome, includes promotors, polyA sequences, 5’ regulatory sequences, 3’ regulatory sequences

Repetitive DNA

about 8% of the human genome, tandem arrays and repeats, highly variable, minisatellites and microsatellites, includes telomeres, trinucleotide repeats are important

minisatellites

repeated sequence of DNA that is more than 10 nucleotides

microsatellites

repeated sequence of DNA that is less than 10 nucleotides

trinucleotide repeats

important repetitive DNA, if it occurs in a coding region it can lead to genetic disorders like Huntington’s (more than 40 repeats of CAG on huntingtin gene leads to the disorder)

Transposable Elements

sequences that can change position within the genome by replicating and inserting copies into other parts of the genome; can be class one or class two; accounts for about 45% of human genome

Class one transposable elements

long terminal repeats, short interspersed nucleotide elements, long interspersed nucleotide elements

class two transposable elements

DNA transposons

Mitochondrial Genome

about 93% of the genome is a coding sequence, lacks introns, tightly packed genes with most overlapping, all 13 proteins encoded in mtDNA are subunits in enzymes of ATP production; can account for up to 0.5% Of DNA in a cell because of how many mitochondria there are; maternally inherited; little to no recombination occurs; fast mutation rate

DNA methylation

tags DNA to activate or repress genes

histone modification

increases or decreases the extent to which the DNA is wrapped up