October 8, 2010
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Put strawberries on my desk for extra credit 
Warm – Up:
Yesterday we watched a video over DNA…
1. What is the universal genetic code stored in?
2. In DNA, how many bases are there?
3. What are the bases?
Griffith’s Experiments (1928)
(Trying to discover vaccine for pneumonia)
Used
different
strains of
bacteria
Transformation Principle
Gene from one cell is taken in by another cell
Genes can be transferred between cells
Avery and others (1944)
*Looked for molecule needed for
transformation
-Used bacteria
**Transformation did not occur
when enzymes added that break
down DNA
***First to conclude:
It is DNA that stores and transmits
genetic information!
Hershey and Chase (1952)
**Used bacteriophages
(Viruses that infect bacteria)
Used radioactive
phosphorous (found in DNA) and sulfur (found in protein coat)
to determine whether protein or DNA makes up genes….
***Finally concluded that DNA makes up genes, NOT protein!
Figure 12–4 HersheyChase Experiment
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Chargaff
Discovered percentage of
C (Cytosine) = G (Guanine)
and
T (Thymine) = A (Adenine)
Known as
Chargaff’s Rules – “Base
Pairing Rules”
A always pairs with T
C always pairs with G
Complete the following
using his base pairing rules:
A–
T–
C–
G–
Watson and Crick (1953)
Built a 3D model of DNA
Franklin’s X-Rays gave great clues that DNA was a double helix
structure
James Watson
Francis Crick
“Deoxyribonucleic Acid”
The molecule of heredity =
UNIVERSAL GENETIC CODE!
DNA Extraction Lab
Step One:
•
•
•
•
Place strawberry in the bag with 20mL of salt
water and seal.
Massage bag (squish strawberry) for 2
minutes.
Squeeze one drop of detergent into bag and
seal.
Massage bag CAREFULLY for an additional
2 minutes.
DNA Extraction Lab
Step Two:
1. Dampen cheesecloth
2. Cut a small hole in the corner of your ziploc bag
3. Press mixture onto cheesecloth into plastic cup.
Be sure to hold cheese cloth over cup!!!!!
4. If the mixture is too thick, add more salt water. Be
sure to hold the bag closed while pouring more salt
water!!!!!
DNA Extraction Lab
Step Three:
1. Tilt the cup and put 20 mL of ICE COLD
ethanol down the side of the cup
2. Use a stirring rod to gently spool (NOT
stir) the DNA onto the rod by turning it
continuously (DNA will be white and
stringy)
DNA Extraction Lab
Final Step:
Clean up!
1. Do NOT throw solids down the sink!
2. DO NOT poor left over salt water down the sink
– leave it on the table!
3. Clean out your plastic cup.
4. Throw everything away in the trash except for
the plastic cup, scissors, and wooden sticks.
Structure of DNA nucleotides:
1. Deoxyribose sugar
2. Phosphate group
3. Nitrogenous (nitrogencontaining) base
4 Possible Bases
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
DNA Nucleotides
Purines
Adenine
Guanine
Phosphate
group
Pyrimidines
Cytosine
Thymine
Deoxyribose
How do A & T fit and G & C fit together?
Due to hydrogen bonding
Sequence of bases can vary in countless ways…
Each gene has a unique order or base sequence.
DNA Shape
Double helix – twisted ladder
Backbone (sides) of sugar and phosphate
Rungs (steps) of bases A-T and G-C
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
If one side of the DNA molecule has this arrangement
of bases, what would the other side look like? Draw
it including the base pairs and sides of the ladder.
ACGAATCGGTTAGCCAT
October 23, 2009
Warm – Up:
• What are the 3 parts of a DNA molecule – the monomer?
• What are the 4 bases in a molecule of DNA?
• What type of bond holds two bases together?
• What bonds with A?
• What bonds with G?
• What is the shape of DNA?
– What is the backbone made up of?
– What are the rungs of the ladder made up of?
Replication of DNA
DNA is copied…
FYI – Each of your cells has 46
chromosomes which is over 6 billion
base pairs. If one letter symbols were
printed in normal type, it would fill
about 900 books as big as your biology
textbook. This amount of DNA is
copied in just a few hours with only a
few errors per billion nucleotides.
In eukaryotes, enzymes (protein!) split and
unwind DNA by breaking the hydrogen bonds
between bases.
.
An enzyme add new
nucleotides along the
template strand of DNA
one at a time.
The same enzyme
proofreads each
nucleotide and corrects
errors so very few occur.
In humans, DNA is copied at about
50 base pairs per second. A cell’s DNA
is copied with less than one mistake in a
billion nucleotides. This is equal to a
person copying 100 large (1000 page)
dictionaries word for word with only one
error!
DNA Replication
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
Original
strand
Nitrogenous
bases
Protein Synthesis
After replication…
TRANSCRIPTION and
TRANSLATION
October 26, 2009
•
•
Write down your objectives and activities!
Take out your homework and leave it on your
desk!!
• Take out your notes from DNA Replication.
WARM – UP:
1. What are the three steps of DNA replication?
2. What is the end result of DNA replication?
3. Where does DNA replication occur?
Transcription
and
Translation
DNA  RNA
(Transcription)
RNA  Protein
(Translation)
RNA – The “Other”
Nucleic Acid
Differs from DNA :
1. RNA is a single strand of nucleotides
DNA is a double strand of nucleotides (helix)
2. Ribose is sugar
Deoxyribose is sugar in DNA
3. No Thymine, Uracil (U) replaces Thymine
Three Forms:
•Messenger RNA (mRNA)
•Ribosomal RNA (rRNA)
•Transfer RNA (tRNA)
Key Players:
mRNA – messenger RNA
Leaves nucleus with instructions!
tRNA – transfer RNA
Ribosome - rRNA
Transcription
**Occurs in the nucleus
1. Different enzyme binds to the start signal
on DNA
2. Unwinds and separates DNA
3. One side of DNA is used as the template
to make the copy of RNA
4. RNA Nucleotides bind with complementary bases
(U pairs with A)
5. Complete when enzyme reaches the stop code
T
T
A
T
G
C
A
T
C
G
What will be the complimentary RNA sequence?
New RNA dangles off the enzyme
DNA closes back to a double helix shape
Working copy of RNA is edited
Introns – Noncoding (intervening) sequences–
edited out
Exons – Code for amino acids – (exit nucleus)
spliced together
Example:
ACAAUGGACAGU
is the RNA code
If the code for the protein is
ACUGGU, what are the introns/exons?
Three Types of RNA Made in Transcription
mRNA – Blueprint for protein synthesis travels
from nucleus to ribosome
tRNA – Translates mRNA
code to amino acids
(monomers of protein!)
rRNA – Makes up
ribosomes
The Genetic Code
Instructions for building a protein
come from:
Codon – 3 base code on mRNA –
codes for amino acids or is a stop
signal
Genetic code is nearly universal for all
organisms!!
Codons
20 Different kinds of amino acids
Sequence of three bases gives enough different combinations
to code for all of them = CODONS!
64 possible codons –
61 code for amino acids
3 are stop signals
Each codon codes for one AA,
but there is more than one codon for most AA.
The Genetic Code
Remember the Key Players…
mRNA
tRNA
ribosome
Translation
*Occurs on ribosomes
*Strings Amino Acids together to form protein!
tRNA
RNA folded with three loops
One loop has three nucleotide
sequence (Anticodon)
which is complementary to
mRNA codon
For example, if codon is CAA
anticodon would be GUU…
“End” of tRNA carries
AA that corresponds
with the codon
(codon comes from
wheel/chart)
No anticodon for codons
UAG, UAA, OR UGA
(Stop Codons)
Translation
1. mRNA leaves nucleus & binds to ribosome
2. tRNA with anticodon UAC and AA
Methionine binds to start codon
3. Next tRNA
comes to ribosome
4. Enzyme joins
two AA
Ribosome
mRNA
tRNA
5. 1ST tRNA leaves
Amino Acid
Chain
6. 2ND tRNA slides over
bringing the mRNA and
AA chain along
tRNA
tRNA
anticodon
mRNA codon
7. Next codon in ribosome is ready for
new tRNA anticodon
(Process continues…)
8. Continues until stop codon
Finally, Step 9…. Ribosome complex falls
apart releasing new protein!!!
Concept Map
Section 12-3
RNA
can be
Messenger RNA
also called
Ribosomal RNA
which functions to
mRNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome