dna, rna, & protein synthesis discovery of dna dna structure dna replication protein synthesis
TRANSCRIPT
DNA, RNA, & Protein Synthesis
Discovery of DNADNA Structure
DNA ReplicationProtein Synthesis
IntroductionMendel - concluded that hereditary factors
determine many of an organisms traitsBut he didn’t know what these hereditary factors
wereHow did they share info
Answers to these questions emerged during the pneumonia epidemic in London in the 1920s
Griffith’s ExperimentsGriffith was studying bacterium, Streptococcus
pneumoniaeCause lung disease pneumoniaTrying to develop a vaccine against a disease-
causing agent, or virulent strain of the bacteriumS strain & R strain
Nature of Hereditary Material
Experiments 1 & 2Injected either live R o live S cells into miceOnly S cells killed the mice
Experiment 3Injected heat killed S bacteria into miceMice survived
Experiment 4Injected mice w/ both heat-killed S cells and
live R cellsMice died
Conclusions from Griffiths Experemint
?
Heat-killed virulent bacterial cells release a hereditary factor that transfers the disease-causing ability to the live harmless cells
Transfer of genetic material from one cell to another cell or from one organism to another organism = Transformation
file:///Users/eastlmat/Documents/Biology%20'08-'09/Biology%20PPT/Ch10/60427.html
Avery’s Experiments1940s, Oswald Avery, wanted to test whether
the transforming agent in Griffith’s test was protein, RNA, or DNA
Used enzymes to separately destroy each of the 3 molecules in heat killed S cells
Protease Enzyme
Rnase
DNase
What Happened in Avery’s Exp?
They mixed the 3 experimental batches of heat-killed S cells w/ live R cells
What Happened?Cells missing RNA & Protein were able to
transform R cells into S cells = mice diedCells missing DNA did not transform R cells into S
cells = mice survived
DNA is transforming agent
Hershey-Chase Experiment
1952, Martha Chase & Alfred Hershey, tested whether DNA or protein was the hereditary material viruses transfer when viruses enter a bacterium
Viruses that infect a bacterium = bacteriophages
Steps of the Experiment1: radioactive isotopes to label protein & DNA
in the phageDNA labeled & protein labeled phages were
separately allowed to infect E. coli
2: removed the phage coats3: centrifuged to separate the phage from E.
coliFound all viral DNA & little protein entered
cellsDNA is the hereditary molecule in viruses file:///Users/eastlmat/Documents/Biology%20'08-'09/Biology%20PPT/Ch
10/61132.html
DNA StructureSection 2
DNA Double HelixWatson & Crick in
1953 created a model for the structure of DNA 2 chains that wrapped
around each other Double helix shape:
winding spiral staircase
Used X-ray diffraction and work of many scientists to determine structure
DNA NucleotidesDNA made of:
2 long chains of nucleotides, which are repeating subunits
Nucleotide consists of:5-carbon sugar = deoxyribosePhosphate group = P atom + 4 Oxygen Nitrogenous base = N atoms & C atoms, base
DNA Nucleotides
Bonds Hold DNA TogetherDNA Double Helix = Spiral Staircase
Alternating sugar & phosphate molecules = the side “handrails”
Nucleotides connected by covalent bondsNitrogenous bases face center & connect w/ bases
of opposite strand using H bondsEither 2 H bonds or 3 H bondsForm the “steps” of staircase
Visual Aid of DNA Bonds
Nitrogenous Bases
Adenine = A Guanine = G
Cytosine = C Thymine = T
4 Kinds:
Purines
Pyrimidines
Complementary Bases% of Adenine = % of Thymine
% of Cytosine = % of Guanine Helps understand structure
Base-pairing rules in DNA Cytosine–––Guanine Adenine–––Thymine
Complimentary Pairs C–G A–T Notice anything about the pairs?
Complimentary Bases
Base Sequence: AAAATTTGGC on one
strand, what is the opposite strand?
TTTTAAACCGImportant for 2 reasons:
H bonds hold togetherExplains replication of DNA
DNA ReplicationSection 3
How DNA Replication Occurs
DNA Replication = process by which DNA is copied in a cell before mitosis, meiosis, or binary fission
2 Nucleotide strands separate along the bases
Complimentary strands serve as templates for new strands
Steps of DNA Replication 1: helicase enzyme
separate DNA strands by breaking the H bonds Y-shaped region that
results from the separation is a replication fork
Steps of DNA Replication 2: DNA polymerases add
complimentary nucleotides to each strand Covalent bonds form b/w
adjacent nucleotides, deoxyribose sugar and P groups
Steps of DNA Replication 3: DNA polymerases
finish & fall off Results in 2 new DNA
strands that are identical Semi-conservative
replication: replication in which each new DNA molecule has kept one of the 2 original strands
Steps of DNA Replication
Action at the Replication Fork
DNA synthesis: Occurs in different
directions on each strands
Synthesis of one strand follows the movement of the replication fork
Replication occurs from 5’ to 3’
http://www.youtube.com/watch?v=nIwu5MevZyg&feature=related
Prokaryotic & Eukaryotic Replication
Prokaryotic 1 circular chromos. Repl. begins at one place 2 repl. forks moving in
opposite directions at the origin
Repl. continues until entire molecule is copied
Eukaryotic Long chromos. DNA polymerase adds
nucleotides at 50/sec, if there were only one DNA polym. it would take 53 days to finish
Multiple points of origin for replication
2 repl forks moving in opposite directions at each origin
Fruit fly has 3500 origin sites
DNA Errors in Replication Usually has great
accuracy 1:1,000,000,000 error
chances in paired nucleotides added
Proofreading functions in DNA polymerases
When a mistake does happen a mutation occurs
Mutation = a change in the nucleotide sequence of a DNA molecule Can have serious effects
on fxns of genes
Chemicals & UV light damage DNA & lead to Cancer
DNA Replication & Cancer
DNA replication is an amazing process that passes genetic info from cell to cell
It also explains how mutations arise & lead to altered cells May allow for better survival and repro, & these variations
increase in populations over time May cause diseases, like cancer
Protein SynthesisSection 4
Flow of Genetic Information
Gene: Hair Color
Directs making of protein, called Melanin, in the hair follicle, through an intermediateRibonucleic acid: RNA
Flow of Genetic Information
Transcription: In Nucleus, DNA is template for RNA
Translation: In Cytoplasm, RNA directs assembly of proteins
Protein Synthesis: Forming proteins based on information in DNA &
carried out by RNA
RNA Structure & Function
Contains sugar ribose
Contains nitrogenous base, uracil, instead of thymine
Usually, single stranded
Usually, much shorter than DNA
Types of RNAmessenger RNA: mRNA
Single-strandedCarries instructions from gene to make protein
Types of RNAribosomal RNA: rRNA
Part of a ribosomeWhere protein synthesis occurs
Types of RNA
transfer RNA: tRNATransfers amino acids to the ribosome to make the
protein
TranscriptionGenetic instructions in a specific gene are
transcribed or “rewritten” into an RNA molecule
Takes place in Nucleus in eukaryotesCytoplasm in prokaryotes
Steps of Transcription1: RNA polymerase binds to a promoter
RNA polymerase = enzyme that catalyzes the formation of RNA on DNA template
Promoter = specific nucleotide sequence of DNA where RNA polymerase binds and initiates transcriptions
Steps of Transcription2: RNA polymerase adds free RNA nucleotides
that are complementary to the nucleotides on one of the DNA strandsResults in an RNA moleculeDNA strand = ATCGACRNA strand = UAGCUG
Only uses a gene, not the whole DNA strand
Steps of Transcription3: RNA polymerase reaches a termination signal,
or stop signal Termination signal = specific sequence of
nucleotides that marks the end of a gene
Newly formed RNA can now perform its job in the cell
The Genetic CodeDef: rules that relate how a sequence of
nitrogenous bases in nucleotides corresponds to a particular amino acid
3 adjacent nucleotides in mRNA specify an amino acid in a polypeptide
Codon: 3-nucleotide sequence in mRNA that encodes an amino acid, or signifies a start or stop signal
TranslationProtein Structure
Made of one or more polypeptides, chains of amino acids linked by peptide bonds
20 different amino acids in living thingsEach polypeptide chain may consist of
hundreds or thousands of the 20 a.a., arranged in a specific sequence
Sequence determines how the polypeptides will twist and fold into the 3-D structure of the protein.
Shape is critical to its function
Steps of TranslationStep 1: Initiation
2 Ribosomal subunits, mRNA, and the tRNA carrying methionine bind togetherOne end of tRNA contains a specific a.a.Other end contains anticodon = 3 nucleotides on the
RNA that are complementary to the sequence of a codon in mRNA
Steps of Translation
Step 2: ElongationtRNA carrying the appropriate a.a., pairs its
anticodon with the second codon in the mRNARibosome detaches methionine from the first tRNAPeptide bond forms b/w methionine & 2nd a.a.Ribosome moves a distance of 1 codon along mRNA
Steps of TranslationStep 3: Elongation, cont’d
1st tRNA detaches and leaves it’s a.a. behindPolypeptide chain continues to grow one a.a. at a
time
Steps of TranslationStep 4: Termination
Ribosome reaches the stop codon, tRNA has no complementary anticodon
Newly made polypeptide falls off
Steps of TranslationStep 5: Disassembly
Ribosome complex falls apartNewly made polypeptide is releasedhttp://www.youtube.com/watch?v=WsofH466lqk&f
eature=related
http://www.youtube.com/watch?v=5bLEDd-PSTQ
The Human GenomeDef: entire gene sequence of the complete
genetic content of humans
Now known: 3.2 billion base pairs/10 yrs.
Learn what info the DNA sequences encode
Info is important b/c help diagnose, treat, and prevent genetic disorders, cancer, and infectious diseases