Classical and Modern Genetics Chapter 23 Great Idea: All living things use the same genetic code to guide the chemical reactions in every cell.
Classical and Modern Genetics
Chapter 23
Great Idea:All living things use the same genetic code to guide the chemical reactions in
every cell.
Chapter Outline
• Classical Genetics• DNA and the Birth of Molecular Genetics
• The Genetic Code
Classical Genetics
Classical Genetics
• Gregor Mendel– Basic laws of inheritance– Classic pea plant experiments
•Purebred•Hybrid
Classical Genetics – cont.
• Results– Parent generation– First generation– Second generation
• Gene– Dominant– Recessive
Typical Mendel Genetic Cross
Pea Plants
Hybrid Cross
9:3:3:1 Distribution
Rules of Classical Genetics
• Traits (genes) are passed from parent to offspring – Mechanism unknown
• Two genes for each trait– One from each parent
• There are dominant and recessive genes– Dominant expressed
Qualitative versus Quantitative Genetics
• Qualitative– Observational
• Quantitative– Predictive model
– Used to trace genetic disease
Qualitative Aspects
Science in the Making
• Mendel lost and found– 8 years and 28,000 experiments
• Karl Correns, Erich von Tschermak, and Hugo de Vries– Independently deduced Mendel’s laws
DNA and the Birth of Molecular Genetics
Nucleotides: The Building Blocks of Nucleic Acids
• Nucleotide– Three molecules
•Sugar– DNA: deoxyribose– RNA: ribose
•Phosphate ion•Base
– Adenine (A)– Guanine (G)– Cytosine (C)– Thymine (T); uracil (U) in RNA
Ribose and Deoxyribose
Nucleotide
DNA Structure
• Join nucleotides– Alternating phosphate and sugar
• DNA– 2 strands of nucleotides– Joined by base pairs
• Bonding pattern– Adenine:Thymine– Cytosine:Guanine
DNA Structure
RNA Structure
• Differences– One string of nucleotides– Sugar is ribose– Thymine replaced by uracil
•Uracil (U) bonds with adenine
The Replication of DNA
• DNA replication– Occurs before mitosis and meiosis
• Process– DNA double helix splits– New bases bond to exposed bases– Result
•Two double-stranded DNA molecules, each identical to the original molecule
DNA Replication
Electron Micrograph of DNA
The Genetic Code
Transcription of DNA
• Transcription– Information transport– Uses RNA
• Process– Unzip DNA– RNA binds to exposed bases– RNA moves out of nucleus (mRNA)
Transcription of DNA
tRNA
• tRNA– Reads message– Structure
•Amino acid•3 bases
The Synthesis of Proteins
• Process– mRNA moves to ribosome– rRNA aligns mRNA and tRNA– tRNA matches codon on mRNA– Amino acid chain forms
•Basis for protein
Computer-Generated Model of tRNA
The Interaction of mRNA and tRNA
The Formation of a Protein
The Genetic Code
Protein Synthesis - cont.
• One gene codes for one protein• Protein drives chemical process in cell
• DNA– Introns– Exons
• All living things on Earth use the same genetic code
Protein Production from DNA
Mutations and DNA Repair
• Mutations– Change in DNA of parent– Causes
•Nuclear radiation•X-rays•UV light
• DNA repair– 10,000 ‘hits’ per day– Cells repair damage
Why Are Genes Expressed?
• Gene control– Turning genes on and off– Each cell contains same genes– Not all cells have same function– Certain genes activated
•Scientists currently studying how
Viruses
• Virus– Not alive– No metabolism– Cannot reproduce on own
• Structure– Short DNA or RNA– Protein coating
Viruses – cont.
• How it works– Taken into cell– Takes over cell– Produces more copies– Kills cell
Bacterial Virus
Herpes Virus
HIV
• Human Immunodeficiency Virus (HIV)– Contains RNA– Codes back to DNA– DNA incorporated into cell– Makes new viruses– Cell dies
• Complex– Two protein coats
•Outer coat fits T cell receptors•Inner coat encloses RNA
HIV
Viral Epidemics
• Viruses– Cannot use medication– Use vaccination
• Viruses evolve rapidly– HIV– Influenza – SARS– Bird flu
Role of Phagocytes
The Human Genome
• Human Genome Project– DNA sequencing– 3 billion bases
Wooly Mammoth
DNA, Genes, Chromosomes, and Genomes
Science in the Making
• Connecting genes and DNA– Thomas Hunt Morgan– Alfred Sturtevant
Technology
• New ways to sequence– J. Craig Venter
•Faster sequencing
Thinking More about Genetics
• The ethics of genes– What should we do with genetic information?