Download Great Ideas in Science: Lecture 3

Great Ideas in Science:
Lecture 12
Great Idea: All living things share the
same genetic code.
Professor Robert Hazen
UNIV 301
Key Idea
All living things share the same genetic code
1. DNA carries the genetic message
2. Messenger RNA copies the DNA
3. Transfer RNA holds an amino acid
4. Ribosomal RNA assembles a protein
Classical Genetics
Gregor Mendel used pea
plants to discover three
laws of inheritance
1. Genes exist
2. Each parent
contributes half
3. Some traits are
dominant and some
are recessive traits
Cellular Genetics
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Chromosomes
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Mitosis (one cell becomes two)
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Humans have 23 pairs
2 daughter cells same as parent
Most cellular division in your body
Meiosis (one becomes 4 gametes)
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Crossing-Over (reshuffle = end of
meiosis)
Recombination makes every gamete
unique.
Mitosis
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Simple cell division
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Observe chromosomes
Not for sexual reproduction
Process
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Copy chromosomes
Separate into two cells
Meiosis
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Sexual reproduction
Begins like mitosis
Chromosome crossover
1 cell forms 4 gametes
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Gametes are genetically
unique
½ normal chromosomes
Nucleotides: The Building
Blocks of Nucleic Acids
Nucleotides are made
from three molecules:
1. Sugar
DNA: deoxyribose
RNA: ribose
2. Phosphate ion
3. Base
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
DNA’s Double Helix
DNA Base Pairing
Adenine:Thymine
Cytosine:Guanine
The Replication of DNA

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DNA replication occurs
before mitosis & meiosis
Process
 DNA double helix splits
 New bases bond to
exposed bases
 Results in two identical
DNA strands
How Does DNA Make Protein?
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Chromosomes (DNA)
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Messenger RNA
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Copies the genetic message
Transfer RNA
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Carry the genetic message
Holds an amino acid
Ribosomal RNA

Assembles a protein
RNA Structure
1. Single strand of
nucleotides
2. The sugar is ribose
3. Thymine is
replaced by uracil
(U), which bonds
with adenine
Synthesis of Proteins
Step 1: Transcription of DNA
Messenger RNA (mRNA)
Synthesis of Proteins
Step 2: Match tRNA to mRNA
Transfer RNA (tRNA)
The Ribosome
The Genetic
Code
Protein Synthesis Summary
4. Fold the amino acid chain into a protein.
DNA & RNA Vocabulary
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Nucleotide = one genetic letter –
phosphate-sugar-base (A, T, C or G)
Codon = one 3-letter genetic word that
defines an amino acid
Gene = the recipe for one protein,
typically with >100 genetic words
Chromosome = a genetic cookbook
with thousands of protein recipes
Genome = all of the genetic material of
an organism (23 volumes for humans)
From DNA to Protein
Step 1: DNA  mRNA
From DNA to Protein
mRNA  tRNA  Amino Acid
From DNA to Protein
Step 2: mRNA locks
onto the ribosome
From DNA to Protein
Step 2: mRNA locks
onto the ribosome
From DNA to Protein
Step 3: tRNA matches mRNA
From DNA to Protein
Step 4: Amino acids link up
From DNA to Protein
Step 4: Amino acids link up
From DNA to Protein
Recharge the tRNA with AA
Genetics – Key Concepts
1.
2.
3.
4.
5.
6.
7.
Human genome project
Viruses
DNA Fingerprinting (PCR)
Behavioral Genetics
Genetic Engineering
Microbes
Plants
Animals
Gene Therapy
Cancer
1. Human Genome Project
(Our DNA)
23 pairs of chromosomes
~ 25,000 genes; each codes for a protein
~ 3,000,000,000 base pairs (rungs of the
DNA ladder)
1. Human Genome Project
Mapping
Mapping = locating the genes
1. Human Genome Project
Sequencing
Sequencing = exact sequence of A,T,C, & G
1. Human Genome Project
Other Organisms
Mouse, Rat, Rabbit, Cat, Dog
Chimpanzee, Elephant, Whale, Zebrafish
Frog, Fly, Flatworm
Several plants
Yeast
Hundreds of microbes (pathogens)
Thousands of viruses
Mammoth!!!
Unanswered Question:
Why Are Genes Expressed?
All your cells contain the same genes.
But not all cells have same the function.
Therefore, some process must turn
genes on and off.
How and why are certain genes
activated?
2. Viruses
2. Viruses
What is a Virus?

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A virus is a loop of genetic material
(DNA or RNA) wrapped in proteins
It “infects” a cell by using the
universal genetic code
Viruses
Viruses versus cells:
Not alive, no metabolism
Cannot reproduce on own
Structure
Short DNA or RNA
Protein coating
How it works
Taken into cell
Takes over cell
Produces more copies
Kills cell
Viral Epidemics
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Treatment of Viruses
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Cannot use medication
Use vaccination
Viruses evolve rapidly
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HIV
Influenza
SARS
Bird flu
H1N1
3. DNA Fingerprinting (PCR)
DNA Fingerprinting
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DNA fingerprinting
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Analysis of DNA in
human tissue
Uses
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identify criminals
identify victims
paternity disputes
Process
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Analyze DNA sections
for repeats
Compare to individual
of interest
3. DNA Fingerprinting (PCR)
Step 4: Repeat with 2 strands of DNA.
4. Behavioral Genetics
4. Behavioral Genetics
Is your personality defined by your
genetic makeup?
Study by knocking out genes.
Three Assumptions:
1. You can quantify behavioral functions.
Extroversion, Neuroticism, Conscientiousness,
Agreeableness, & Openness
2. You can identify environmental factors.
3. You can do genetic tests to tell you
about the person.
5. Genetic Engineering
Genetic Engineering
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Genetic engineering
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Technique
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Foreign genes inserted
Existing genes altered
Restriction enzymes cut
DNA
Another DNA strand binds
New gene is expressed
Examples
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Insulin
Agriculture
“knockout” mice
Bioterrorism
Stem Cells, Cloning, and
Regenerative Medicine
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First cells can be anything
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Later cells differentiate
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Gene Control
 Genes may turn on or off
 Some genes are blocked
Stem Cell Line
 Reproduce without differentiation
6. Gene Therapy
6. Gene Therapy
Gene therapy
Replace defective gene with
healthy gene
In vivo
In vitro
Problems
Genes are inserted randomly
Often no proteins are made
Therapeutic viruses
6. Gene Therapy
7. Cancer
Cancer-A Different Kind of
Genetic Disease
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Normal cell division is controlled
Cancer cells reproduce without restraint
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Genetic defects
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Due to genetic defect
Usually 5-6 damaged genes
Collection of diseases
Increase cancer probability
Lifetime risk >80%
Cure
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Surgery, radiation, chemotherapy
Gene therapy
7. Cancer
P53 gene
(and process)
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Defective gene
Gene therapy
Ethics in Genetics
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Who should have access to
your genetic profile?
Under what circumstances
should genetic discrimination
be allowed?
If you could alter the genetic
makeup of your child, where
would you draw the line?
What limits should society
place on genetically engineered
organisms?