Organisation Of The Genome Mutataions Notes

Organisation of the genome

• There are two genomes in an eukaryote

Nuclear Genome

-linear chromosomes which are inherited from the mother and father

-23 number of different DNA molecules (XX cells), 24 DNA in (XY cell). In diploid cells there are a total of 46 DNA molecules

-associated with histone and non histone proteins

-21 OOO protein encoding genes, more than 6000 RNA genes- some RNA

-Large amount of repeats- satellite DNA- repeat units of 170 nucleotides, mini-satellite (repeat units of 10-50 nucleotides, microsatellite (1,2,4 nucleotides

-1% of DNA codes for a protein, the rest codes for regulatory elements and intron

Mitachondrial Genome

-has circular chromosomes and is inherited from the mother

-one circular DNA molecule. There are a thousand copies

-It encodes for 37 genes, 24 genes code for non coding RNA (22 tRNAs and 2 rRNAs) and only 13 polypeptides.

-no assoaciated histones

-genes are tightly clustered and don’t contain introns

-66% of the DNA encodes for a protein

-majority of the mitochondrial proteome is encoded in the nucleus and peptides are imported into the mitochondria.

Functions of non coding RNA

- tRNA –

- rRNA –

-snRNA -

-miRNA-

DNA sequences

-Single copy DNA- represents half of the genome- small fraction codes for protein, rest are introns and regulatory sequences

-multiple copy genes- Histones and Rrna

-highly repeated non coding sequences are found in the Telomere and in the centromere

Gene expression

-Gene- inherited unit of information- shown by mendel in his experiments with the garden pea

-at a gross level: genes determine the phenotype, morphological characteristics such as eye/hair colour

-molecular level genes are a stretch of nucleotides that code for a polypeptide, determines the amino acid sequence and the function of a protein. Each amino is coded by a three base pair sequence (codon). There are 22 homologous chromosomes, so most genes are present twice, alleles- homozygous: both alleles are the same for the gene, heterozygous both alleles are different for a gene

MUTATIONS

-can spontaneously occur

-due to the chemical properties of the nucleic acids

a) deaminations- spontaneous deamination is the hydrolysis reaction of cytosine into uracil releasing ammonia in the process. When a strand with the deaminated cytosine is replicated it results in the 2^nd strand with the complentary base of A instead of G

b) depurination- spontaneous hydrolysis of the base-sugar link results in the loss of adenine or guanine bases. After depurination, sugar phosphate remains whilst guanine is lost. Consequence of this mutation leads to the loss of the base pair- base pair deletion.

-problems during...

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