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DNA, RNA, & PROTEIN SYNTHESIS
DNA DISCOVERY
DNA DISCOVERY
Frederick Griffith-British• Studied the cause of pneumonia and
possible vaccines.• Discovered two strains, S and R.• S-strain is live and causes disease. Named
for smooth sugar-coat colonies.• R-strain does not cause disease and has
rough colonies without a sugar-coat.
Griffith’s Experiment
Observation: Organisms are able to pass on their traits to their offspring according to the Laws of Genetics as developed by Gregor Mendel.
Question: What, within cells, serves as the genetic code material?
Griffith’s Experiment
Hypothesis: – By manipulating exposure to
different strains of bacteria, the specific chemical within cells that serves as the genetic material will be isolated.
Griffith’s Experiment
Procedure: • Griffith injected
some of the R-strain bacteria into mice. – What do you think
happened?
Griffith’s Experiment• Griffith injected
some of the S-strain bacteria into mice. – What do you
think happened?
Griffith’s Experiment• Griffith knew that
polysaccharides are not affected by heat, so he used heat to kill some of the S-strain bacteria and then injected them into mice.
• What do you think happened?
Griffith’s Experiment• Keep in mind that neither
dead S-strain nor live R-strain bacteria killed the mice.
• Griffith then mixed some of the heat-killed S-strain and some of the live R-strain bacteria and then injected them into mice.
• What do you think happened?
Griffith’s Experiment
Conclusion:• The polysaccharide coating is not the
genetic material. • When mixed, the R-strain bacteria
were able, somehow, to absorb genetic material from the dead S-strain and turn into S-strain bacteria.
• This ability was subsequently named transformation.
Griffith’s Experiment
Theory: A specific chemical controlled the transformation of cells.
DNA DISCOVERYOswald Avery-American• Expanded on Griffith’s experiments.Observation:
A specific chemical controls transformation.
Question: What chemicals are present in cells that can control transformation?
Hypothesis: Either protein, RNA, or DNA control cell transformation.
AVERY’S EXPERIMENT
Procedure• Using live S cells, Avery separately
destroyed the proteins, RNA, and then DNA.
• These separate batches were mixed with R cells again and injected into the mice.
AVERY’S EXPERIMENT
• R-cell with no-protein S cells= dead mice.
• R-cell with no-RNA S cells = dead mice.
• R-cell with no-DNA S cells= normal mice.
AVERY’S EXPERIMENT
Conclusion: Without DNA, the S cells could not transform the R cells. DNA must be the transforming agent.
DNA DISCOVERY
Hershey-Chase Experiment- Americans• Set out to determine if DNA or
proteins were hereditary material in viruses.
Observation: Previewed Griffith/Avery experiment results.
HERSHEY-CHASE EXPERIMENT
Question: What chemical allows a virus to infect a bacterium?
Hypothesis: If DNA and proteins are chemically labeled, then the hereditary chemical will show up in the reproduced cells.
HERSHEY-CHASE EXPERIMENT
Experiment:• Labeled virus proteins with radioactive
sulfur.• Labeled virus DNA with radioactive
phosphorus.• Allowed each sample to separately infect
E. coli.• Once viruses are removed from the
bacterium, the bacterial cells could be tested for each radioactive sample.
HERSHEY-CHASE EXPERIMENT
Conclusion: The DNA had completely transferred, while
trace amounts of protein were present in the new cells.
DNA…. -is the hereditary material in viruses.-Controls and determines the traits of an organism-Maintains control by producing proteins
Proteins control all body processes.
Discovery of DNA1. What makes the S strain bacteria
virulent?2. Why was Griffith’s Fourth experiment
so important?3. What did the Hershey-Chase
experiment prove?4. According to Avery, what is the role of
DNA during Griffith’s experiments?5. List the steps of the Scientific Method.
DNA STRUCTURE
DNA STRUCTURE
• Consists of repeating subunits called nucleotides
• Nucleotide parts are all held together with covalent bonds
• Nucleotides have 3 parts:– SUGAR– NITROGENOUS BASE– PHOSPHATE GROUP
DNA Nucleotide
DNA STRUCTURE• Sugar: Deoxyribose, a 5
carbon sugar• Phosphate Group: One
phosphorus atom with four oxygen atoms. – The phosphate attaches to
the deoxyribose at the methyl group.
– This forms the backbone of DNA.
DNA STRUCTURE
• Nitrogen Bases: – Adenine, Thymine, Guanine, and Cytosine
• Nitrogen bases are carbon rings with random nitrogen atoms– Purines= double-ringed bases, Adenine and
Guanine– Pyrimidines= single-ringed bases, Thymine
and Cytosine
DNA STRUCTURE
DNA STRUCTURE
DNA STRUCTURE• Nitrogen bases stick out to the inside,
toward each other. • Adenine always pairs with Thymine, and
Cytosine always pairs with Guanine.• The base pairs are held together with
weak hydrogen bonds.• The percentage of Adenine always equals
the percent of Thymine; Guanine percentage always equals Cytosine percentage.
Base PairingStars represent hydrogen bonds
DNA STRUCTURE
Two single strands of DNA are bound together, forming a double-helix
The strands are complementary to each other, not identical.
Watson and Crick first proposed this theory of a double helix.
DNA Structure1. Compare a purine to a pyrimidine.2. Why does Adenine bond with Thymine and
not with Cytosine?3. Weak hydrogen bonds hold the DNA helix
together. What is the importance of using weak bonds?
4. If 15% of the nucleotides in DNA are cytosine, what percentage of the nucleotides are adenine? Why?
5. What types of bonds exist in DNA and where do they work?
DNA Replication
DNA Replication
Chromosomes are long strands of DNA that must be duplicated before cell division.
Complementary strands of the double helix must separate before replication occurs.
Leading Strand
Lagging Strands
DNA Replication
These strands divide by breaking the weak hydrogen bonds between the nucleotides.
DNA Helicase is the enzyme that breaks the hydrogen bonds between the nitrogen bases.-The area where the helix splits is called the replication fork.
DNA Replication
DNA Replication
Free-floating nucleotides bind to the newly uncovered nucleotide sequences.
DNA Polymerase is an enzyme that adds the new nucleotides.
DNA Polymerase works in opposite directions on the separated DNA strand.
DNA Replication
The double helix unzips entirely and forms two identical double helix.
These two helices are each made of one original strand and one new strand. (Semi-Conservative Replication)
Replication1. What makes DNA replication semi-
conservative?2. Compare DNA Helicase to DNA
Polymerase.3. How do the DNA polymerases
travel on the DNA strands?4. How is eukaryotic DNA replicated
so quickly?5. Compare the Leading and Lagging
Strands.
1 2
3
4
Protein Synthesis
Protein Synthesis
Directions of DNADNA follows a specific path to produce
proteins.
RNA is used as an intermediate to proteins.
DNA > Transcription > RNA > Translation > Protein
Protein SynthesisRNA vs. DNA
RNA has one strand… DNA has two strands
RNA uses Ribose sugar….DNA uses Deoxyribose.
Uracil replaces Thymine in RNARNA strands are very short, and DNA strands are very long.
RNA with Guanine
RNA with Adenine
RNA with Cytosine
RNA with Uracil
Protein Synthesis
Types of RNAmRNA- Messenger RNA takes the directions of DNA to the rRNA.
rRNA- Ribosomal RNA uses the DNA code to produce proteins.
tRNA- Transfer RNA brings amino acids together to produce proteins.
Types of RNA
TRANSCRIPTIONJohn Kyrk Transcription Transcription Animation
Simple Animation
TRANSCRIPTION
RNA Polymerase binds to a DNA promoter region, which is a specific DNA sequence.
– This causes DNA strands to relax and unwind in one section.
TRANSCRIPTIONRNA Polymerase adds free RNA nucleotides
to begin producing an RNA strand.
– This RNA strand is COMPLEMENTARY to the DNA strand.
– Once the RNA Polymerase has finished, the DNA retwists.
TRANSCRIPTIONA Termination Signal stops the RNA
Polymerase. – This signal is another specific DNA
sequence.– Both DNA and RNA strands are released.– The new RNA strand can be rRNA, mRNA, or
tRNA.– RNA strands are then manipulated in
Translation to make proteins.
Pre-mRNA Editing1. 5’ Cap-
2. 3’ Tail-
3. Introns vs Exons
Transcription Practice
• DNA: AATCGA• RNA:
• DNA: ATACGGACA• RNA:
• DNA: TACGATCGCCGA• RNA:
The Genetic Code
A set of rules that govern how nucleotide sequence correlates to a specific amino acid.
Following Transcription, the mRNA strand is “read” in units of three adjacent nucleotides called a Codon.
The Genetic Code
CODONS are 3-nucleotide sequences on mRNA that code for specific amino acids or a start/stop signal.
Several codons may code for the same amino acid, but each codon codes for only one amino acid.
The Genetic Code
AUG is the universal START codon, while UGA, UAA, and UAG are all STOP codons.
Translation starts with start codons and ends with stop codons.
TRANSLATION
A ribosome attaches to a strand of mRNA, allowing a tRNA anti-codon molecule to attach to the correct mRNA codon.
The ribosome moves down the mRNA from 5’ to 3’.
TRANSLATION
While the first tRNA molecule is attached to the mRNA, the ribosome moves down the sequence of nucleotides.
When the ribosome moves, it allows the next tRNA molecule to attach to the next codon.
TRANSLATION
When two consecutive tRNA molecules are attached to the mRNA, peptide bonds form between the carried amino acids.
Both remain attached to the second tRNA molecule.
TRANSLATION
These steps continue producing a long strand of amino acids until the ribosome reaches a stop codon. This releases the new polypeptide.
Translation components break apart and the newly created protein is sent to its final destination.
Protein Synthesis1. Contrast Codons and Anti-codons.
2. Compare Translation to Transcription.
3. What does the Genetic Code do?
4. What are the roles of each type of RNA?
5. How does a tRNA anti-codon sequence compare to the original DNA sequence?
LINKS TO ANIMATIONS • http://www.bioteach.ubc.ca/TeachingResources/MolecularBiology/DNAReplication.sw
f
• http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf
• http://www.johnkyrk.com/DNAreplication.html
• http://learn.genetics.utah.edu/content/begin/dna/transcribe/
• http://www.johnkyrk.com/DNAtranscription.html
• http://www.biostudio.com/demo_freeman_protein_synthesis.htm
• http://www.johnkyrk.com/DNAtranslation.html
CREDITS• Outline information adapted from http://biology.clc.uc.edu/courses/bio104/dna.htm• http://porpax.bio.miami.edu/~cmallery/150/gene/sf11x1a.jpg• http://www.offresonance.com/wp-content/uploads/2008/05/450px-griffith_experimentsvg.png• https://filebox.vt.edu/users/mahogan2/Filebox%20Portfolio/Webquest%20for%20DNA_files/image004.jpg• https://www.msu.edu/course/isb/202/ebertmay/drivers/nucleotide.jpg• http://coris.noaa.gov/glossary/nucleotide_186.jpg• http://www.dnahandbook.com/s/10009/Images/purines.gif• http://www.brooksdesign-cg.com/Images/cg/SCdna6.gif• http://www.mariemontschools.org/halsall/images/dna_molecule.gif• http://porpax.bio.miami.edu/~cmallery/150/gene/c7.16.14.fork.jpg• http://www.elmhurst.edu/~chm/vchembook/images/582dnarepline.gif• http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-2/ch10_DNA-rep.jpg• http://www.biologycorner.com/resources/replication.gif• http://library.thinkquest.org/18617/media/replication-simple.gif• http://upload.wikimedia.org/wikipedia/commons/2/2c/RNA_chemical_structure.GIF• http://porpax.bio.miami.edu/~cmallery/150/gene/c7.17.7b.transcription.jpg• http://stardec.ascc.neu.edu/~bba/CBIO3580/DOGMA/Fig13_18.JPG• https://www.msu.edu/course/lbs/333/fall/images/geneticcode.gif• http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Translation.gif• http://www.biologycorner.com/resources/translation_lettered.jpg