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DNA Structure and Function Basis of Heredity Chemical Basis of Life Molecule Building Block DNA Nucleotides RNA Nucleotides Protein Amino Acids Lipid Fatty Acids Carbohydrate Sugars Major Function Hereditary Material Protein Synthesis Cell Structure and Function Membrane Component Energy Production The Central Dogma replication transcription processing translation • cells can make exact copies of DNA • DNA encodes all of the information necessary for cellular functions • RNA is made from a DNA template and functions in protein synthesis • proteins are translated from messenger RNA and carry out cellular functions Nucleotides • nucleotides are the building blocks of nucleic acids • ribose + base + 5' phosphate • 5 different bases • • • • • adenine (A) guanine (G) cytosine (C) thymine (T) uracil (U) DNA = deoxyribonucleic acid RNA = ribonucleic acid DNA vs RNA 2' oxygen thymine (T) double stranded uracil (U) single stranded Nucleic Acid Structure • nucleic acids are polymers of nucleotides • nucleotides linked through phosphate bonds • strand has polarity—5'-PO4 and 3'-OH ends • order of the nucleotides defines a sequence • 4 letter alphabet Double Strands • specific base pairing • A and T • G and C • hydrogen bonds • anti-parallel (5'-3') • complementary strands • template for synthesis DNA Replication • the DNA strands are separated • each strand serves as template • complementary strands are synthesized (5'3') • yields 2 identical DNA molecules • semi-conservative replication • carried out by cellular proteins (= enzymes) • complex process involving many proteins • DNA polymerase DNA Polymerase Activity • 'replication fork' moves along DNA • leading strand • lagging strand • numerous replication forks act simultaneously Chromosomes • genomic DNA is very long • humans, 6 x 109 bp • ~1.8 meters total length • total length reduced via associates with proteins • individual DNA molecules condensed into chromosomes • humans have 22 pairs + X/X or X/Y (ie, diploid) Chromosome Replication • unfolding of chromosomes, DNA replication, and refolding • chromosomal duplication • sister chromatids • joined at centromeres Mitosis • • • • DNA synthesis chromosomal duplication separation of sister chromatids cell division (cytokinesis) results in 2 identical daughter cells • somatic cell reproduction • asexual process • sexual reproduction involves germ line cells • oogenesis (egg formation) • spermatogenesis (sperm formation Meiosis • two consecutive rounds of cell division • meiosis I • DNA replication (2n4n) • separation of chromosome pairs (4n2n) • meiosis II • no DNA replication • separation of chromatids (2n1n) • fertilization (1n2n) Recombination • independent chromosome assortment • 2n possible variants • 'crossing-over' • recombination between homologous chromosomes • at least once per chromosome pair • positions ~ random Genes and Alleles • gene = unit of information (~protein) • locus = physical location on a chromosome • allele = different molecular forms (ie, sequence) of a gene • homozygous = same allele on both chromosomes • heterozygous = different alleles on chromosome pairs genotype = genetic makeup (ie, total genes) phenotype = observable traits Types of Inheritance dominantrecessive dominant allele 'masks' recessive allele incomplete dominance phenotype between dominant and recessive traits co-dominance shared expression of traits (eg, AB blood type) polygenic several genes influence trait (often continuous variation) pleiotrophy single gene affecting several traits
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