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chapter+7 - Chapter 7 Genomes and Chromosomes Genetics...

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Chapter 7- Genomes and Chromosomes Genetics Molecule of heredity Deoxyribonucleic acid (DNA) Gene info in DNA that codes for a single polypeptide Sequence of nucleotides corresponds to sequence of amino acids RNA serves as an intermediate The three key processes of macromolecular synthesis are: (1) DNA replication – making a copy of DNA (2) Transcription – synthesis of translation – synthesis of RNA from a DNA template (3) Translation 0 synthesis of proteins using messenger RNA as a template Basic processes are the same in prokaryotes & eukaryotes, but the organization of genetic information is more complex in eukaryotes. Two major differences: 1. Eukaryotes contain non-coding regions called introns 2. Single prokaryotic mRNA often contains more than one coding region DNA is a double-stranded helix (twisted ladder) The two strands in the double helix are anti-parallel (run in opposite directions) The 2 DNA polynucleotide strands have base sequences that are complementary Adenine always pairs with thymine (A=T) Guanine always pairs with cytosine (G=C) Hydrogen bonds hold the two strands together 1
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DNA is made of deoxyribonucleotides linked by phosphodiester bonds Deoxyribonucleotide = sugar deoxyribose + nitrogenous base + phosphate Nitrogen Bases : purine (adenine and guanine) and pyrimidines (cytosine and thymine) Size of DNA Expressed as number of thousands of nucleotide bases or base pairs per molecule 1000 bases = 1 kb (kilobase) or 1kbp (kilobase pairs) Escherichia coli 4640 kbp humans > 3.2 million kbp Nucleoid of E. coli- circle of dsDNA 1500x the size of the cell Prokaryotic circular DNA can be packaged into the cell because it is supercoiled DNA gyrase/topoisomerases assist in supercoiling
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