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October 8, 2010• 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)
Transformation PrincipleGene from one cell is taken in by another cell
Genes can be transferred between cells
Used different strains of bacteria
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!
Bacteriophage with phosphorus-32 in DNA
Phage infectsbacterium
Radioactivity inside bacterium
Bacteriophage with sulfur-35 in protein coat
Phage infectsbacterium
No radioactivity inside bacterium
Figure 12–4 Hershey-Chase Experiment
ChargaffDiscovered 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 –
Francis CrickJames Watson
Watson and Crick (1953)
Built a 3D model of DNA
Franklin’s X-Rays gave great clues that DNA was a double helix structure
“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 (nitrogen-containing) base
4 Possible Bases
Adenine (A)Guanine (G)Cytosine (C)Thymine (T)
Purines Pyrimidines
Adenine Guanine Cytosine Thymine
Phosphate group Deoxyribose
DNA Nucleotides
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.
Hydrogen bonds
Nucleotide
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
DNA Shape
Double helix – twisted ladderBackbone (sides) of sugar and phosphate
Rungs (steps) of bases A-T and G-C
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
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.
DNA is copied…
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
DNAis copied with less than one mistake
in abillion nucleotides. This is equal to a
person copying 100 large (1000 page)
dictionaries word for word with only one
error!
DNA Replication
Growth
Growth
Replication fork
DNA polymerase
New strand
Original strand DNA
polymerase
Nitrogenous bases
Replication fork
Original strand
New strand
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?
Transcriptionand
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 sugarDeoxyribose is sugar in DNA
3. No Thymine, Uracil (U) replaces Thymine
•Messenger RNA (mRNA)
•Ribosomal RNA (rRNA)
•Transfer RNA (tRNA)
Three Forms:
Key Players:
Ribosome - rRNAtRNA – transfer RNA
mRNA – messenger RNALeaves nucleus with instructions!
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 templateto make the copy of RNA
4. RNA Nucleotides bind with complementary bases
(U pairs with A)
5. Complete when enzyme reaches the stop code
TTATGCATCG
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?
mRNA – Blueprint for protein synthesis travels from nucleus to ribosome
Three Types of RNA Made in Transcription
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!!
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.
Codons
The Genetic Code
Remember the Key Players…
ribosometRNA
mRNA
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 CAAanticodon would be GUU…
“End” of tRNA carries AA that corresponds
with the codon (codon comes from
wheel/chart)
No anticodon for codonsUAG, UAA, OR UGA
(Stop Codons)
1. mRNA leaves nucleus & binds to ribosome
2. tRNA with anticodon UAC and AA Methionine binds to start codon
Translation
3. Next tRNA comes to ribosome
4. Enzyme joins two AA
Ribosome
mRNA tRNA
5. 1ST tRNA leaves
6. 2ND tRNA slides over bringing the mRNA and AA chain along tRNA
mRNA codon
tRNAanticodon
Amino AcidChain
7. Next codon in ribosome is ready for new tRNA anticodon (Process continues…)
Finally, Step 9…. Ribosome complex falls apart releasing new protein!!!
8. Continues until stop codon
from to to make up
Concept MapSection 12-3
also called which functions to also called also called which functions towhich functions to
can be
RNA
Messenger RNA Ribosomal RNA Transfer RNA
mRNA Carry instructions rRNACombine
with proteins tRNABring
amino acids toribosome
DNA Ribosome Ribosomes