Chromosome Abnormalities

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Chromosome Abnormalities

• Non-disjunction during meiosis can cause a gamete
  to have an extra chromosome
• Trisomy three copies of the same chromosome.
• Most are lethal before birth, but three of
  chromosome 21 causes Down syndrome.

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Trisomy of Chromosome 21
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Chapter 10 DNA Replication and Expression
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DNA (Deoxyribose Nucleic Acid)

• Polymer made of subunits called nucleotides
• Nucleotides have three parts
• Phosphate
• Sugar (deoxyribose)
• Nitrogen bases

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Four Nitrogen bases of DNA (9.1)

• Adenine
• Guanine
• Cytosine
• Thymine

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DNA structure (Fig. 10-2)

• Double helix
• James Watson and Francis Crick (Nobel Prize)
• Two strands held together by hydrogen bonds
• Bases are paired up
• Adenine to Thymine
• Cytosine to Guanine
• DNA is twisted (helix)

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X Ray Crystallography of DNA (10.3)
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DNA inside a Eukaryote

• DNA wraps around proteins (histones) to form
  chromatin.
• Chromatin coils up into chromosomes.

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DNA is Replicated

• Parent DNA strands act as templates for new DNA
• Strands separate and new bases are added to each
  side

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DNA replication (10.6)
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DNA replication requires three enzymes (10.7)

• Helicase
• DNA polymerase
• Ligase

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DNA Expression
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Central Dogma of Molecular Biology DNA ? RNA ?
Protein
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Flow of Genetic Information (10.8)
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What is RNA?

• Ribose Nucleic Acid
• Nucleic acid similar to DNA
• Three important differences
• Single strand
• Sugar is Ribose
• Uracil instead of Thymine

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DNA contains information used to make proteins

• 95 of DNA sequence is meaningless or junk
• 5 that has information is contained in genes
• Gene is a sequence of DNA that codes for a protein

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DNA to Protein (10.10)
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How a gene produces a protein

• Genes are TRANSCRIBED into messenger RNA
• mRNA goes to ribosomes for protein synthesis
• Transfer RNA carries Amino Acids to be assembled
  at the ribosomes
• mRNA is TRANSLATED into proteins.

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Transcription 10.13
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Transfer RNA
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So how do we know what the amino acid order will
be?
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A gene sequence is divide into groups of three
(codons)
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Codons on mRNA are recognized by tRNA
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Each codon codes for an amino acid
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How are codons read? (10.10)
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Viral genetics
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What about viruses?

• Viruses are nucleic acids surrounded by a protein
  capsule.
• Viruses invade host cells by injecting their DNA
• Viral DNA incorporates into the host cells
  genome ( Lysogenic Phase)
• Viruses use their DNA to force host cells to
  produce more viruses ( Lytic Phase)
• Viruses do not fit into the cell theory.

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Phage Virus Cycles (10.26)
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Mutations

• Mistakes in copying of DNA
• Three types
• Insertion
• Deletion
• Substitution

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Consequences of mutations

• Most mutations are neutral no noticeable effect
  on the protein
• Some mutations are deleterious
• Genetic disorders
• Cancer
• Some mutations may produce a good trait
• In both cases a change in the bases changes
  sequence of amino acids

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