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