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DNA and The Language of Life
Objectives…
• Chapter
– Structure of DNA
– How proteins are made
– Mutations
• Today:
– Early experiments that led to
discovery of DNA
Guided Question
• What do the experiments of Mendel,
Morgan, Griffith, Avery, Hershey &
Chase show us about science?
Most Significant Biological Discovery of the
20th Century
• DNA
– “Life’s Blue Prints”
– Mystery of
what makes us humans
Our “design” is
95-98% similar to
chimpanzees
85% similar to mice
How did we Discover DNA
Go to the DNA Discovery Center Of COURSE!
First Steps Towards DNA
• Remember
– Mendel – Inheritance (chromosomes)
– Morgan – Sex Linked Genes
• But what is the hereditary information?
– Griffith
– Avery
– Hershey & Chase
Frederick Griffith
&
The “Transforming Factor”
• 1920s, studying two
strains of bacteria
– One fatal pneumonia,
the other none fatal
Rough: none
(mice live)
Smooth: capsule
(mice die b/c immune system
cant break it)
What this showed…
• Some “substance” in the deadly strain remained
active despite the heat treatment
– Caused the heritable change in the other strain
• What we know today
• bacteria can salvage genes from their environment from
bacteria that have died.
The DNA from the heated smooth “jumped” into the
rough bacteria…
Overwhelmed immune system and killed mice
But WHAT IS the “transformed” substance?
• Focused on either protein or DNA
– (from other experiments like Mendel & Morgan)
• Oswald Avery tested Griffith’s heat-treated
deadly strain with…
– Protein destroying enzymes
• Bacteria killed
– DNA destroying enzymes
• Bacteria didn’t kill
So it’s settled then?
• DNA too simple!!???
– Only 4 nucleotide bases??
– ….protein has 20 AA!??
• Hershey & Chase
– Used Avery’s idea applied to viruses!!
• Protein coat & DNA (not made of cells!)
• Bacteriophage (bacteria-infecting virus)
Hershey & Chase’s Bacteriophage
• Trial 1
– Tested protein coat
– Radioactive isotope of
sulfur on protein coat
– CONCLUSION
• No radioactivity
• Trial 2
– Tested DNA
– Radioactive isotope of
phosphorus in DNA
– CONCLUSION
• Radioactive!
FINALLY
• DNA is the “transforming factor” that
carries hereditary information
Making Connections
• Make a “web” connecting the experiments
and conclusions of the following scientists
•
•
•
•
•
Mendel
Morgan
Griffith
Avery
Hershey & Chase
How are they connected?
Example
Surviving mice had resistance passed down
Mendel
Morgan
Avery
Hershey & Chase
Patterns of Inheritance
with Pea Plants
• Guided Question…
– What does this show us about science?
DNA Check List
• Pre-View Checklist
1.
2.
3.
4.
etc
• Post-View Checklist
Building Blocks of DNA
• Know DNA is the genetic material passed
from parent to offspring
– How is it arranged?
– Does it matter?
– How is it able to store genetic information,
copy it and pass it to offspring?
Structure & Function!!
Building Blocks of DNA
• Genetic heredity stored in
DNA
– Deoxyribonucleic Acid
(nucleic acid)
• Molecule built from
nucleotides (monomers)
• 4 types of nucleotides made
DNA
– 4 types of nitrogen bases made
nucleotides
Nitrogen Bases
• 4 Nitrogen Bases
Pyrimidines (single rings)
– Thymine (T)
– Cytosine (C)
Purines (double rings)
– Adenine (A)
– Guanine (G)
DNA Structure
• Nucleotides covalently bonded
– Sugar of one – phosphate of next
• Forms sugar-phosphate “backbone”
• Nitrogen bases attach to backbone
– Nucleotides can bond in any order
• GACCTCATATACATGACTACAGAGG
DNA Structure
• Rosalind Franklin & Maurice Wilkins
– Photographed DNA (helix)
• James Watson & Francis Crick
– Double helical shape
• Sugar phosphate backbone on outside
• Nitrogen bases on the inside
Base Pairs
• DNA sequence
GATCATTACATTAAAAG
• “other side of helix” is the complement
• A-T
• C-G
“Down the Slide” = sequence (any order)
“Across the Bridge”= complement
11.3 DNA Replication
What we are looking at today
1.
How DNA replicates
2.
Relationship between genes and proteins
3. How proteins are made
DNA Replication
• How does a cell copy its
genetic material?
– Replication
• Double helix separate
• Copy instructions (DNA) with a
DNA template that produces a new,
complementary strand for each of
the old template strands
• (DNA copied before or after cell
division?)
DNA Replication
• DNA replication starts at “origins of
replication”
– Outwards in both direction (bubble)
– Eukaryotic DNA = many origins (efficient)
• Many enzymes catalyze replication
– DNA polymerase
• Covalent bonds b/w nucleotides of new DNA & old
• Very few errors
Leading and Lagging Strands…what?
• When the two parent strands of DNA are separated to
begin replication, one strand is oriented in the 5' to 3'
direction while the other strand is oriented in the 3' to 5'
direction.
• DNA replication is inflexible…
– DNA polymerase (enzyme), only functions in the 5' to 3' direction.
– This means that the daughter strands are synthesize
through different methods,
• one adding nucleotides one by one in the direction of the
replication fork
• the other able to add nucleotides only in chunks (backwards)
– The first strand, which replicates nucleotides one by one is called
the leading strand; the other strand, which replicates in chunks, is
called the lagging strand.
DNA Replication
1. Original parent strand of DNA
5’  3’
and 3’  5’
2. DNA helicase (bonds?)
3. DNA polymerase
Direction, Okazaki, Leading, Lagging..
4. Replication Fork, origins of replication
5. Eukaryotic Vs Prokaryotic?
Using the information above, draw me an
illustrated picture of DNA replication
2
2
1
3
3
5
4
4
5
1
11.4 Making Proteins
• Genotype & Phenotype
– Sequence of nucleotide bases in DNA (genes)
– Proteins and their functions (traits)
• Relationship between genes and proteins?
– Tatum & Beadle
• Genes dictate production of polypeptide (effect
larger molecules like enzymes of proteins
Pause!!
• Ready 11.4 and complete 5 Post it
responses!
DNARNAProtein
• Language of genes are in
sequence
– Connection b/w gene and
polypeptides? (enzymes
/proteins?)
• RNA (ribonucleic acid)= SINGLE
ribose
– Uracil, U-A … no THYMINE
G-C still
DNA is converted into RNA
during transcription..
Transcription
• DNA nucleotide sequence converted into
single stranded mRNA (transcribed)
• RNA leaves nucleus and directs protein
synthesis in the cytoplasm
– Transcribe a speech
• Same language, but changes form (spoken to
written)
In translation, we convert nucleic acid
language into AA language
Introns and Exons
• During Transcription
Translation
• Converting nucleic acid AA through use
of codons
– Three base “word” that codes for one AA
– Several codons form a sentence that forms the
polypeptide (protein)
The Triplet Code
• Codons = protein
forming codes
• DNA sequence
RNA sequence
AUGUCUUAUAGUUGA
START SER TYR SER STOP
The Genetic Code
Transcription
 mRNA

 Carries
protein making instructions to site of
translation
 “message” is translated from language of
RNA to language of amino acids by using
“codons”
A
G
U
A
C
U
U
U
A
C
G
G
Start
Methionine
U
A
Stop
Threonine
Leucine
Arginine
A
Codon-Amino Acid Table
A
U
G
A
C
U
U
U
A
C
G
RNA sequence
G
Start
Methionine
U
A
Stop
Threonine
Leucine
Arginine
A
Topic 2: Translation

Second Step of Protein Synthesis (in cytoplasm)
 (mRNA has left nucleus)
 Another
type of RNA (tRNA) carry
complement bases & amino acids to mRNA

Anti-codon complement base “codon” that
matches to mRNA strand
Trp
Serine (AA)
U
C
A
A
G
U
A
C
U
U
U
A
C
G
G
U
A
A
mRNA
Topic 3: Translation Steps
1.
2.
mRNA moves into cytoplasm as a
ribosome attached onto mRNA at the
“START” location (AUG) on the “P” site
of the ribosome (has 1 amino acid)
Next tRNA comes in and attaches its
complementary anticodon to the mRNA
codon…also attaches its amino acid
Translation Animation!
Serine (AA)
U
C
A
Methionine (AA)
Start
U
A
C
A
U
G
A Site
A
G
P Site
U
U
U
A
C
G
G
U
A
A
Translation Animation!
Asparagine (AA)
Methionine (AA)
Serine (AA)
Start
A
A
A Site
U
G
U
C
A
A
G
U
P Site
U
U
A
C
G
G
A
U
U
A
A
codon
Anti-codon
Mutations

Mutagen- cause of mutation
 Base

Substitution (not such a big problem)


substitution & base deletion/insertion
GAA and GAG code for the same amino acid
Deletion/Insertion (PROBLEM)

Changes the following sequence
QUIZ FRIDAY!!

11.3-11.6
Tuesday- Review
 Wednesday- TEST

Complete 11.6 Concept Checks (by end of
period!)