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DNA, RNA, and Protein Synthesis

Discovery of DNA, DNA structure, DNA Replication, Protein Synthesis

Sharon Blong

on 5 May 2013

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Transcript of DNA, RNA, and Protein Synthesis

Discovery of DNA Fredrick Griffith 1928 Experimented with bacterium called Streptococcus pneumoniae
which can cause lung disease in mammals
Griffith was trying to find vaccine for this bacteria S strain causes pneumonia, has smooth edge, has capsule
R strain- Harmless, rough edge, lacks capsule Conclusion:
Transformation: Heat killed S-strain transfers disease causing genetic material to R-strain 1940's Oswald Avery Was transforming agent in Griffith's experiment protein, RNA, or DNA? Cells missing RNA and protein- mice died.
Cells missing DNA- mice survived.
Result: DNA is responsible for transformation in bacteria.
DNA = hereditary factor that can transfer harmless R cells into harmful S cells 1952 Martha Chase and Alfred Hershey Are viruses the same as bacteria?
Do they also transfer DNA or do they transfer protein? Conclusion: DNA is also the hereditary molecule in viruses All viral DNA and little DNA had entered E. coli cells. 1953-1962 Rosalind Franklin and Maurice Wilkins X-ray diffraction photo of DNA James Watson and Francis Crick Used x-ray diffraction photo to build DNA model DNA Structure -DNA is a nucleic acid made of 2 long chains/strands of nucleotides
-Nucleotide has 3 parts:
1) 5 carbon sugar = deoxyribose
2) phosphate group= Phophorous bound to 4 Oxygen
3) Nitrogenous base = Nitrogen, Carbon. DNA is like a spiral staircase handrail= alternating sugar and phosphate Steps= nitrogenous bases Sugar and phosphate connected by covalent bonds

These are the same in all DNA nucleotides 1 full turn
10 nucleotide
pairs These are not the same in all DNA nucleotides
Nitrogenous base on one strand forms hydrogen bonds with nitrogenous base on other strand.
Uniform width between nitrogenous bases
Connected by hydrogen bonds-This holds the two DNA strands together! 4 possible nitrogenous bases in DNA
2 are purines: Adenine and Guanine
2 are pyrimidines: Cytosine and Thymine Complementary Base Pairs:
Adenine pairs with Thymine
Cytosine pairs with Guanine Base Sequence= Order of Nitrogenous bases on a chain of DNA One chain of DNA is complementary to the other chain A=T
C=G Sugar-phosphate backbone Complementary
base pairs DNA Replication DNA (deoxyribonucleic acid)-
Template that directs what traits
should be based off of parent's traits Process by which DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission. Review: In what phase of interphase
does DNA replication occur? At first scientists didn't know how DNA replicated.
What do you think? Step 1: Enzymes called helicase
separate DNA strand
It would be like splitting the steps down the middle so that half went with one railing and half went with the other railing. Replication Fork-
-Where DNA strands separate --Forms upside down "Y" Step 2:
DNA polymerase- Enzymes that
Add complementary nucleotides As new strand grows:
1) Covalent bonds are formed between deoxyribose sugar and phosphate
2) Hydrogen bonds between complementary nigrogenous bases. Step 3: DNA polymerase finishes replicating and falls off. Final Result = 2 separate and identical DNA molecules ready to go through cell division. Do you think these two strands are identical after replication? Based off of picture:Does DNA occur in 1 direction or 2 directions? DNA ligase- Fills gaps in new DNA strand (part of step 2) Rate of DNA Replication:
If the largest human chromosome were to use only 1 site of replication it would take 53 days.

How many days does it take to regenerate a skin cell? But replication begins at many points at the same time.Fruit flies- 3,500 sites at one time! In prokaryotic chromosomes (Bacteria)- only 1 site of replication There is a lot that the cell has to get right.
Sometimes errors in DNA replication can occur-
These are called Mutations
Sometimes mutations can be fixed, sometimes they can't
Some mutations cause cancer 1 in 10,000 errors occur
DNA polymerase repairs errors
Only @ 1 in 1,000,000 mutations don't get fixed Many mutations in somatic cells of your body don't affect you
When mutations are in germ cells (sex cells) genetic disorders get passed on. How does DNA communicate what your traits should be? . Transcription- RNA is synthesized from from DNA Translation- Proteins are synthesized from RNA. DNA contains deoxyribose---RNA contains ribose
DNA contains Thymine------RNA contains Uracil
This means that instead of A = T, A = U
DNA is double stranded------RNA is single stranded
DNA is longer than RNA 3 types of RNA
Messenger RNA
Ribosomal RNA
Transfer RNA Messenger RNA
Carries genetic message
(instructions) from DNA
to make protein Ribosomal RNA-
Part of structure of ribosomes tRNA- Transfers amino acids
to the ribosome to make protein RNA (ribonucleic acid)-
Transcribes (reads) DNA
and translates information to proteins Proteins- Express the information from RNA The difference between DNA and RNA 2 main parts of Protein synthesis Transcription Transcription:
When instructions are rewritten from DNA to RNA.
-Takes place in nucleus Step 1: Initiation
RNA polymerase binds to promoter (a specific nucelotide sequence of DNA)
-DNA begins to unwind. Step 2:
RNA polymerase adds free RNA nucleotides that are complementary to the DNA nucleotides.
ATCGAC would be ? Step 3: Termination:
- Stop codon marks the end of a gene.
- RNA polmerase releases DNA and RNA molecules. Genetic code- how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid. Codon: Each 3 nucleotide sequence in mRNA that encodes an amino acid or signfifies a start or stop signal. start codon: AUG
stop codon: UAA, UAG, or UGA.
See page 207 in your book for mRNA codons. Translation: The making of a protein
Polypeptide: Chains of amino acids linked by peptide bonds.
-20 different amino acids exist.
- Each protein has a specific arrangement of amino acids.
- This arrangement tells protein how to twist and fold.
-Protein shape = protein function. Steps of Translation
Step 1: Initiaion: mRNA and tRNA bind together.
Step 2: Elongation: rRNA carrying amino acid binds to codon.
Pepetide bond is formed between amino acids.
Ribosome moves the rRNA and mRNA
Step 3: Elongation (continued)
First tRNA detaches and leaves amino acid behind.
Polypeptide chain continues to grow.
Step 4: Termination:
Stop codon is reached
Step 5: Disassembly
Ribosome complex falls apart. Newly made polypeptide is released.
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