chromosome abnormalities non-disjunction during meiosis can cause a gamete to have an extra...
TRANSCRIPT
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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 wraps around proteins (histones) to form chromatin.
• Chromatin coils up into chromosomes.
DNA inside a Eukaryote
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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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• Helicase• DNA polymerase• Ligase
DNA replication requires three enzymes (10.7)
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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 cell’s 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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