Ch. 16 DNA DNA: the Central Dogma, history, structure Replication

Ch. 16Ch. 16DNADNA

DNA: the Central Dogma, DNA: the Central Dogma, history, structurehistory, structure

ReplicationReplication

History: timeline, people and History: timeline, people and their accomplishmentstheir accomplishments

• Mendel (heredity)• Thomas Hunt Morgan (flies, linkage)• Griffith (1928) transformation and mice

• Avery and colleagues (1944): – proposed DNA as the transforming agent

• Chargaff (late 40’s-early 50’s) – base pairing (AT CG)

• Hershey-Chase (1952) DNA IS hereditary material

• Watson and Crick (1953) (Franklin) chemical structure of DNA

• Meselson-Stahl mid 1950’s – DNA Replication details

Griffith:Griffith: Transformation

Hershey / Chase Hershey / Chase (the hereditary material is not a protein)

Radio-active P and S

Whose rule? A-T C-GWhose rule? A-T C-G

Purine? Pyrimidine?You have 6 billion pair

in every cell!

How’s it all fit?How’s it all fit?

• DNA coiling – Let’s see it!DNA coiling – Let’s see it!

Chargaff’s Rule

• Purines (A, G, double rings) always pair with Pyrimidines (T, C, single rings)

• A-T, C-G (& in RNA? ____)• Old AP test question: if in a cell the

DNA bases are 17% A’s then what are the %’s of the other bases?

• CUT your PY or Pure Silver (Ag)

DNA Replication:

SEMICONSERVATIVE MODEL

How did they (Meselson-Stahl) prove this? FIG 16.10

KNOW: Steps of ReplicationEnzymesLeading and Lagging strands Okazaki FragmentsAnti-parallel

Video

This process is fueled by…nucleoside nucleoside triphosphatestriphosphates

Semi-conservative

“Bubbles”

Replication forks,

simultaneous replication**Eukaryotes - multiple origins of replication

**Prokaryotes have one

DNA is made from DNA is made from 5’ to 3’5’ to 3’ and it is and it is read from 3’-5’.read from 3’-5’.

The 3’ end is the end which elongates (grows)

Why is this direction important to consider in Replication?

What do the terms 5’ and 3’ mean?What do the terms 5’ and 3’ mean?

Leading & Lagging strands, made 5’-3’

Okazaki Okazaki fragmentsfragments

(are of the (are of the lagging lagging strand)strand)

ENZYMES: helicase, DNA Polymerase, ligase

Enzymes :Enzymes :

•Helicase•Single strand binding proteins•Primase (RNA Primer)•DNA Polymerase•Ligase

•Nuclease and DNA Polymerase (both are repair enzymes)

Let’s see this in ActionLet’s see this in Action

• Leading StrandLeading Strand (Nobelprize.org)(Nobelprize.org)

• Lagging StrandLagging Strand(Nobelprize.org)(Nobelprize.org)

• Overall Overall (wiley)(wiley)

• Overall 3D viewOverall 3D view(wehi.edu.au or dnai.org)(wehi.edu.au or dnai.org)(Youtube has a music version)(Youtube has a music version)

Telomeres Telomeres (Ch.16)(Ch.16)Unfilled gap left at the ends of the DNA strands due to the use of RNA primers

Eventual shortening of DNA over time

Dolly, cancer, HeLa cells (telomerase fig16.19)

Enzyme: Telomerase extends the (3’) long strand so the 5’ strand can finish.

WOW! ? ? ?

Where is telomerase naturally found?

DNA from a single skin cell, if straightened out, would be about six feet long but invisible. Half a gram of DNA,

uncoiled, would stretch to the sun. Again, you couldn't see it.

http://www.pixar.com/featurefilms/nemo/images/index_lwide.jpg

Story Time!! (Due Tuesday Nov. 6)

Select a figure, process, topic, or high level vocabulary word from chapter 16 or 17.

Your job is to make a poster of your selected topic.

-The poster should be kid-friendly as to say an intelligent 8-10 year old would be able to understand it yet make sure that all information communicated is true to the text.

- Finally, you may not use English, do the best you can, ask friends, relatives, teachers, etc for help if necessary. Potential topics include but are not limited to the following…..Experiments that identified DNA as the “genetic material”, DNA Structure, DNA Replication, Telomers and telomerase, Transcription, Modification of RNA, Translation, Mutations.

Ch.17 One gene/One Ch.17 One gene/One polypeptidepolypeptide

Define transcription and translationCompare Prokaryotic and Eukaryotic cellsvideo

• (21 different (21 different AA’s)AA’s)

• mRNA codemRNA code• Ave. protein is Ave. protein is

400AA long400AA long• Titin is Titin is

30,000AA 30,000AA long! long! (this is _____ (this is _____ nucleotides?)nucleotides?)

• DNA=DNA=tripletstriplets

• RNA=RNA=codonscodons

• 5’ to 3’5’ to 3’• Pre-Pre-

mRNA mRNA (primary (primary transcritranscript)pt)

• Promoter: Promoter: TATA BoxTATA Box

• Transcription Transcription factorsfactors

• RNA poly-RNA poly-merasemerase

• Transcription Transcription initiation initiation complexcomplex

• MovieMovie

Finishing the pre-Finishing the pre-mRNAmRNA

Introns:Introns: (intruding) spliced out (intruding) spliced out

ExonsExons: kept, will be Expressed in : kept, will be Expressed in the cell the cell

• snRNP’s snRNP’s identify identify intronsintrons

• Introns are cut Introns are cut out at a out at a SpliceosomeSpliceosome

• Final mRNA has Final mRNA has only genes that only genes that will be tran-will be tran-scribed in cellscribed in cellno “junk genes”no “junk genes”

• videovideo

• TranslationTranslation• The production The production

of polypeptidesof polypeptides• On a RibosomeOn a Ribosome• tRNA, transfer tRNA, transfer

RNA carries in RNA carries in the amino acids the amino acids to the ribosome to the ribosome ( (transferstransfers the the

A.A A.A))

Read 5’ to 3’Read 5’ to 3’

• A P E:A P E:• AAminoacyl-minoacyl-

tRNA tRNA synthetasesynthetase

• PPeptidyl tRNA eptidyl tRNA binding sitebinding site

• EExitxit

• VideoVideo• MovieMovie

Termination of the Termination of the translationtranslation

Translation of many Translation of many polypeptide chains at oncepolypeptide chains at once

The signal mechanism: signal peptides

Free or bound ribosomes?

• Coupled Coupled transcriptitranscripti

on and on and translatiotranslatio

nn

One base difference out of One base difference out of 574 Amino acids 574 Amino acids (1722 (1722 bases)bases)

Nothing formed

The wrong protein

•Happy Happy Homecoming Homecoming (again!)(again!)

•Have fun, be safeHave fun, be safe

Repairing mistakes