Mol.Bio.PartIII - Molecular Biology Part III What carries...

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Molecular Biology Part III
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What carries information between DNA to Proteins
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Genes and gene expression A gene is a a segment of DNA molecule which codes for a single protein. It is also the functional unit of inheritance. The biological information contained in a gene acts as a set of instructions that produces a single protein via a set of intermediate processes. The entire process is called gene expression . gene expression Double Stranded DNA Gene A Gene B Gene C Protein B Protein C Protein A
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DNA layout Genes are DNA segments. The sections of the genome that contain biological information are called exons which are separated by vast regions of apparently useless intergenic DNA called introns which occupies apprximately 70% of human genome. Furthermore, the actual information is carried by only one strand of the double helix called the template strand ( sometimes also called coding strand). This information is always read in the 3’ - 5’ direction and could reside on any one of the strand. A gene 3’ 5’ 5’ 3’ 5’ 3’ 5’ 3’ 3’ 5’ 3’ 5’ The template or coding strand A gene A gene A gene
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Gene Organization In higher organisms, genes are located in a small number of chromosomes. A chromosomes contains a long chain of a single DNA molecule or sequence (in duplicate) compactly packed around proteins. A large number of genes are Located in this one DNA strand. Organism Number of Approx. no. Avg.no.genes per Chromosomes of genes chromosomes ___________________________________________________________ E.coli 1 2800 2800 Yeast 16 8750 550 Human 23 50 000 2200 http://www.ncbi.nlm.nih.gov/genome/seq/
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Definition of a Gene Regulatory regions: up to 50 kb upstream of +1 site Exons: protein coding and untranslated regions (UTR) 1 to 178 exons per gene (mean 8.8) 8 bp to 17 kb per exon (mean 145 bp) Introns: splice acceptor and donor sites, junk DNA average 1 kb 50 kb per intron Gene size: Largest 2.4 Mb (Dystrophin). Mean 27 kb.
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Human genome sequence
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There are two types of gene clusters: (a) Operon : occurs in bacteria. This is a cluster of genes that encodes a group of enzymes (proteins) that work collaboratively in a chemical pathway (viz. conversion of lactose absorbed by a cell Into glucose and galactose). (b) Multigene family : Sometimes a single gene will occur many times in the chromosome. This is because it enhances the rate of production of a particular protein expressing the same gene in parallel. There may also be a number of similar genes that produce component structures that combine to produce a complex protein. There are also examples of gene family that are scattered over a chromosome or over more than one chromosomes. 3’
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Mol.Bio.PartIII - Molecular Biology Part III What carries...

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