Transcript Chapter 25: Molecular Basis of Inheritance

DNA Replication
What is it?
When is it done?
What is copied?
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Two New,
Identical
DNA
Strands
Result
from
Replication
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PROTEIN
SYNTHESIS
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Protein Synthesis
• After replication and cell division, each
new cell has its own DNA
• Now, how do those cells use that DNA to
make proteins?
• How do you go from DNA (nucleic acid)
to protein (amino acid)?
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Overview of Protein Synthesis
• Copy (mRNA) is
made of gene
• mRNA sent out
of nucleus
• Ribosomes use
mRNA as
instructions to
make a protein
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Protein Synthesis
 Two phases:
DNA
Transcription
mRNA
Translation
protein
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Transcription
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Transcription
 In nucleus
 DNA the template for mRNA
 RNA polymerase makes the
mRNA
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Only one DNA
strand is used
Just a portion
of the DNA is
copied (one
gene)
copy is called
mRNA
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RNA Differs from DNA
DNA
RNA
Deoxyribose sugar
Ribose sugar
Double stranded
Single stranded
T (thymine)
U (uracil)
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Question:
 What would be the
complementary RNA strand
for the following DNA
sequence?
DNA 5’-GCGTATG-3’
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Answer:
• DNA 5’-GCGTATG-3’
• RNA 3’-CGCAUAC-5’
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Translation
mRNA
protein
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Translation
mRNA
ribosome
Ribosome reads the mRNA
and makes protein
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• mRNA leaves nucleus
• ribosome attaches to mRNA
• ribosome reads the bases in groups
of 3 (codon)
AUG CUG
codon
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The ribosome uses the code
to make the protein
How?
How do you go from nucleic
acid to amino acid?
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tRNA
Amino acid
• Carries amino
acids to
ribosome
• Has anticodons
that are
complementary
to mRNA
codons
U A C
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AA
UAC
AUG
CUG
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Genetic Code
 DNA contains a triplet code
 Every three bases on DNA stands
for ONE amino acid
 Codon: Each group of 3 bases on
mRNA
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r
• http://www.wisconline.com/objects/index_tj.asp?objid=A
P1302
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Mutations
1. Gene Mutations
2. Chromosome Mutations
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What happens when there is a
mistake during replication?
• What could go wrong when the DNA is
being replicated?
• http://www.pbs.org/wgbh/nova/genome/
program.html
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Gene Mutations
1. Point Mutations
A. Substitution
2. Frame shift Mutations
A. Insertion
B. Deletion
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Point Mutations – substitution
One WRONG BASE is used
Original The fat cat ate the wee rat.
Mutation The fat hat ate the wee rat
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Examples of Point Mutations
• Sickle Cell Anemia
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Examples of Point Mutations
• Tay Sachs
Hemophilia B
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Frame Shift Mutations
A
• Insertion AAT AGG CAG GTT
• Deletion AAT AGG CAG GTT
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Frame Shift Mutations
A
• Insertion AAT AGG CAG GTT
becomes AAT AAG GCA GGT …
• Deletion AAT AGG CAG GTT
becomes AAA GGC AGG …
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Frame Shift
• Original
The fat cat ate the wee rat.
• Insertion
The fat caa tet hew eer at.
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Example of Frame Shift Mutation:
Huntington’s Disease
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Chromosome Mutations
1. Inversions
2. Duplications
3. Deletions
4. Translocations
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Incorrect Chromosome Number –
from nondisjunction during
meiosis
• Trisomy 21 causes Down’s Syndrome
• http://learn.genetics.utah.edu/units/disor
ders/whataregd/down/
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