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History of DNA• Oswald Avery (1944) repeated Griffith’s work
and discovered that nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next
He’s such a dork.
Alfred and Martha
Hmm..she’s cute!
•Alfred Hershey and Martha Chase and the Hershey-Chase Experiment (1952):
-Studied viruses that infect bacteria = bacteriophage-Bacteriophages = “bacteria eaters” inject their own DNA into cell and use the cell to produce many copies of themselves, killing the bacteria because it splits open, releasing hundreds of new viruses! Eeek! -What Hershey and Chase found:
-Used “markers” or radioactive isotopes-Discovered that the genetic material of bacteriophage was DNA, not protein
Rosalind Franklin• Rosalind Franklin (1950’s) studied DNA
structure by using X-ray diffraction• Discovered that the bases, A G C and T,
were near the center of the X, or the double helix
Story #1:Maurice Wilkens, Franklin’s colleague, showed her photos to James Watson, without her knowledge or consent. For Watson, seeing Franklin’s work was like fitting the missing piece in the puzzle of DNA’s structure. "My jaw fell open and my pulse began to race," Watson said. He went back to his lab and along with Francis Crick, assembled the double helix structure of DNA.
THE CONTROVERSY
Rosalind died of ovarian cancer in 1958.
Story #2:Rosalind was in love with Watson, and she showed him her work because of her love and trust. Once Watson saw her photos, he used the data to piece together the information he needed to assemble the structure of DNA. He and Crick became famous, while hardly knows about Rosalind.
Who has DNA? All living things do!• Prokaryotes (bacteria) don’t have a nucleus,
and their DNA is found floating in the cytoplasm; usually they have a single strand of DNA, or chromosome
• Of course, Eukaryotes are more complicated!– Eukaryote = YOU! And, any organism with
their DNA inside the nucleus. Eukaryotes generally have 1000X more DNA than bacteria
– Eukaryote DNA is organized into Chromosomes
Having MORE chromosomes doesn’t mean an organism is bigger or smarter!Cows are smarter than humans?NO!Chickens are bigger and smarter than dogs? Hmm…..
DNA Replication• Watson and Crick realized that by the rules of
Base Pairing, each strand of DNA has the information needed to reconstruct the opposite strand.
• Because each strand can reconstruct its opposite strand, the strands are said to be Complementary
DNA strand: A G C T C C G T C A A T T G
Opposite strand:T T TC C CG G G GA A A A
Complementary DNA strands
You look very nice
today!
Why, thank you! You look rather lovely yourself.
Complementary Strand of DNA
Complementary Strand of DNA
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Replication = the process where DNA makes a copy of itself, base by base, producing 2 new complementary strands , and each strand serves as a template for the new strand.
RNA Structure• RNA is like DNA, but with 3 main differences:
– 1. Sugar in RNA is ribose instead of deoxyribose– 2. RNA is generally single-stranded, not double
stranded– 3. RNA contains Uracil instead of Thymine
Think of RNA this way: Would you give your friend your original CD, or would you give
them a copy of it?
You’d give them a copy, of course! If you keep the original safe, then you can make thousands of copies of it as needed, as often as you want. DNA and RNA replication functions in the same way.
How It’s Done4 different bases (AGCT) = 64 possible 3-base codons
4 x 4 x 4 = 64
stop
stop1
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Some amino acids, like Valine, Serine, Alanine, Arginine, etc. can be specified by more than one codon.
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Some codons, like AUG, specify only 1 amino acid. Ex. AUG can either be a “start” codon, or a Methionine.
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There are 3 “stop” codons that don’t code for any amino acid. Stop codons act like the period at the end of a sentence- they signal the end of the polypeptide sequence.
1. Messenger RNA is transcribed in the Nucleus then it enters the cytoplasm and attaches to a ribosome.
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2. As each codon of the mRNA moves through the ribosome, the proper amino acid is brought to the ribosome by tRNA (transfer RNA).
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3. Each tRNA carries only 1 amino acid, and has 3 unpaired bases on the end, where it attaches to the mRNA.Because these bases are the opposite of the mRNA, they are called the Anticodon.
4. The ribosome forms a Peptide bond between the 1st and 2nd amino acids, and releases the tRNA. It then moves on to the next codon, where another tRNA brings it the amino acid that codon specifies.
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5. The polypeptide chain continues to grow until the ribosome reaches a “stop” codon on the mRNA. It then releases the newly formed polypeptide chain and the mRNA, completing translation.
Roles of RNA and DNA• DNA is the “Master Plan” for a building
(your body), and builders never take the master plan to a job site- it’s too important.
• Instead, they make inexpensive copies called Blueprints
• DNA is safely stored in the nucleus, and the copies of DNA, or the RNA, go out into the cytoplasm where the proteins are built.
• What else can we compare this process to?
A painting by Renoir- the original is safe in a museum, but anyone can buy a print of it.A designer dress- copies are made and sold, but the original is kept with the designer.
Your favorite CD- you make copies of it and keep the original safe at home.
4 Types of Chromosomal Mutations:1. Deletions = lose part of a chromosome (many genes!)
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2. Duplications = gain extra parts of a chromosome, or an extra whole chromosome3. Inversions = reverse the direction of parts of a chromosome- mixes it up!4. Translocations = part of a chromosome breaks off and attaches to another chromosome
Gene Regulation• Not all genes are expressed all the time• Expressed genes = a gene that is transcribed
into mRNA, which leads to creating a protein• Humans have ~30-40,000 genes and our
bodies can’t be making all those proteins all at once!
• In the jumble of DNA, there are patterns, and biologists have identified patterns that represent how gene expression is controlled
Section 12-5
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–3 Examples are:–Promotors = binding sites for RNA polymerase–Start and Stop signals = starts and stops transcription–Operons = group of genes that operate together
Eukaryote Gene Regulation• Prokaryote = organisms without a nucleus,
most are bacteria• Eukaryotes = (YOU!) organisms with their
DNA contained in a nucleus (humans, plants, animals, fungi, etc.)
• Eukaryote genes are mostly controlled individually and have complex regulatory sequences
1. TATAA = the “TATA” box, a sequence that occurs before the start codon, a place where RNA polymerase binds2. Promotors = sequences that are signals for RNA polymerase found just before the TATA box
Development and Differentiation• Differentiation = when cells become specialized
in structure and functionEarly development, in the beginning, all of an embryo’s cells have the ability to become anything- heart, eye, leg, toe, wing, etc. Later development, cells specialize and become the toe, heart, leg or wing cell, and once they have specialized, they lose the ability to be anything else
Normal fruit fly Legs instead of antennae!Caused by Human Hox-13 mutation
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Hox genes = series of genes that control the differentiation of cells and tissues in the embryo, the BODY PLAN. A mutation in the Hox Genes can completely change the organs that develop in specific parts of the body.