Ch. 10 DNA, RNA and Protein Synthesisfalconsbiology.weebly.com/uploads/2/0/8/1/20811508/ch... ·...
Transcript of Ch. 10 DNA, RNA and Protein Synthesisfalconsbiology.weebly.com/uploads/2/0/8/1/20811508/ch... ·...
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Ch. 10
DNA, RNA and Protein Synthesis
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10.1 DNA Structure
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Discovery of DNA
Frederick Griffith: 1928
Discovered that harmless bacteria could change & become virulent
Griffith called this process transformation
Avery & McCarty: 1944 □ DNA is the transforming factor.
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Hershey & Chase: 1952
Studied bacteriophages
Proved conclusively: DNA carries genetic code.
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DNA Structure
polymer of nucleotides
nucleotide has 3 parts:
- deoxyribose (5-C sugar)
- phosphate group
- a nitrogenous base
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Nitrogenous Bases
DNA contains 4 nitrogenous bases:
Purines (double ring)
1. adenine (A)
2. guanine (G)
Pyrimidines (single ring)
3. cytosine (C)
4. thymine (T)
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nucleotides link together - form long chains
backbone of DNA: sugars and phosphates bond covalently
bases stick out from chain:
DNA is double stranded P
S B
P
S B
P
S B
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X-ray Evidence
Franklin & Wilkins (1950)
took x-ray of DNA molecule
Indicates DNA molecule is twisted
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Watson & Crick (1950’s)
built 3-D model of DNA
Franklin’s x-ray helped w/ structure
Watson & Crick twisted model like a spiral:
“double helix”
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Chargraff
• research showed:
% adenine = % thymine
% cytosine = % guanine
• So…
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adenine pairs w/ thymine
(A - T)
guanine pairs w/ cytosine
(G - C)
Base Pairing (A-T & C-G):
hydrogen bonds holds 2
strands of DNA together
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1962 Watson, Crick & Wilkins receive Nobel Prize
for discovery of DNA structure
**Franklin did not receive prize because she had died (prize not awarded post-humously)
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10.2 DNA & RNA
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DNA Replication
Each strand is a pattern for a new strand.
Before a cell can divide:
DNA must replicate so each new cell has a complete copy of DNA
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Watson & Crick hypothesized that DNA UNZIPS:
- Enzyme (DNA helicase) breaks bonds between base pairs
- New base pairs match up w/ freed bases (DNA polymerase catalyzes reaction)
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T
A
G
C
C
T
A
G
C
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The DNA Code
DNA has set of instructions coded in sequence of nucleotides.
To decode message: part of the DNA sequence is copied into RNA.
RNA: nucleic acid that is a messenger between DNA and ribosomes.
RNA carries out protein synthesis
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Structure of RNA
Long polymer of nucleotides
Differences from DNA:
RNA sugar is ribose (DNA is deoxyribose)
RNA is single stranded (DNA is double)
RNA has Uracil instead of Thymine
U bonds with A
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3 Forms of RNA
Each form has a different job:
1. messenger RNA (mRNA)- carries DNA code to ribosome
2. transfer RNA (tRNA)- brings amino acids to ribosome
3. ribosomal RNA (rRNA)- forms structure of ribosome
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RNA Transcription
DNA’s code is copied into RNA
Transcription transfers info from DNA to RNA
RNA polymerase (enzyme) attaches to DNA
It separates stands, & builds complimentary strand of RNA
ex:
DNA: A C T A T A C A T G
RNA: U G A U A U G U A C
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10.3 Protein Synthesis
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Protein Synthesis
Nucleotides arranged in groups of 3 bases called a Codon
Each codon codes for 1 amino acid
Remember: proteins are polymers of amino acids
All proteins are made of different combinations of 20 amino acids
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One codon (AUG) is the start codon
Codes for the a.a. methionine (met)
3 codons are STOP codons: UAA, UAG, UGA.
Do not code for an a.a.
Stops protein synthesis
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Translation
Translation is the decoding of mRNA message into protein.
mRNA does not work alone:
tRNA brings a.a. to ribosomes
rRNA forms ribosome (site of protein synthesis)
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Anticodon - 3 bases on tRNA molecule
Anticodon base pairs w/ codon on mRNA
matching tRNA anticodon to mRNA codon, puts correct a.a. place
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Steps in protein synthesis
1.Ribosome binds to molecule of mRNA
2.START codon (AUG) binds to 1st tRNA anticodon
3.2nd tRNA anticodon binds to 2nd mRNA codon
4. Peptide bond forms between 2 a.a.
5. protein grows until ribosome reaches STOP codon
6. no anticodon matches STOP codon: protein synthesis stops
7. ribosome releases new protein