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DNA Structure and Function Basis of Heredity. Chemical Basis of Life.

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Presentation on theme: "DNA Structure and Function Basis of Heredity. Chemical Basis of Life."— Presentation transcript:

1 DNA Structure and Function Basis of Heredity

2 Chemical Basis of Life

3 The Central Dogma replication transcriptionprocessing 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

4 Nucleotides DNAvsRNA 2' oxygen thymine (T)uracil (U) double stranded single stranded DNA = deoxyribonucleic acid RNA = ribonucleic acid 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)

5 nucleic acids are polymers of nucleotides nucleotides linked through phosphate bonds strand has polarity5'-PO 4 and 3'-OH ends order of the nucleotides defines a sequence 4 letter alphabet Nucleic Acid Structure

6 specific base pairing A and T G and C hydrogen bonds anti-parallel (5'-3') complementary strands template for synthesis Double Strands

7 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

8 DNA Polymerase Activity 'replication fork' moves along DNA leading strand lagging strand numerous replication forks act simultaneously

9 Chromosomes genomic DNA is very long humans, 6 x 10 9 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)

10 Chromosome Replication unfolding of chromosomes, DNA replication, and refolding chromosomal duplication sister chromatids joined at centromeres

11 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

12 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)


14 Recombination independent chromosome assortment 2 n possible variants 'crossing-over' recombination between homologous chromosomes at least once per chromosome pair positions ~ random

15 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

16 Types of Inheritance dominant- recessive dominant allele 'masks' recessive allele incomplete dominance phenotype between dominant and recessive traits co-dominanceshared expression of traits (eg, AB blood type) polygenicseveral genes influence trait (often continuous variation) pleiotrophysingle gene affecting several traits

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