DNA Structure and Function Basis of Heredity

Chemical Basis of Life

The Central Dogma cells can make exact copies of DNA 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 vs RNA 2' oxygen thymine (T) uracil (U) double stranded single stranded DNA = deoxyribonucleic acid RNA = ribonucleic acid

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 (2n4n) separation of chromosome pairs (4n2n) meiosis II no DNA replication separation of chromatids (2n1n) fertilization (1n2n)

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 dominant-recessive 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