DNA and the DNA and the Language of LifeLanguage of LifeChapter 12Chapter 12

How did scientists How did scientists learned that DNA is learned that DNA is the genetic material?the genetic material?

Genes are Made of DNAGenes are Made of DNA

Griffin’s experiment (1928)Griffin’s experiment (1928) Avery’s experiment (1944)Avery’s experiment (1944) Hershey and Chase experiment (1952)Hershey and Chase experiment (1952)

Griffith’s experiment - Griffith’s experiment - 19281928

Griffith showed that although a deadly Griffith showed that although a deadly strain of bacteria could be made strain of bacteria could be made harmless by heating it, some factor in harmless by heating it, some factor in that strain is still able to change other that strain is still able to change other harmless bacteria into deadly ones. He harmless bacteria into deadly ones. He called this the "transforming factor."called this the "transforming factor."

Avery’s experiment - Avery’s experiment - 19441944

Transforming factor - Protein or DNA?Transforming factor - Protein or DNA?

Avery and colleagues treated a mixture of Avery and colleagues treated a mixture of heat- treated deadly strain and harmless heat- treated deadly strain and harmless strain of bacteria with:strain of bacteria with:

Protein-destroying enzymeProtein-destroying enzyme DNA-destroying enzymeDNA-destroying enzyme

Hershey and Chase Hershey and Chase experiment -1952experiment -1952

The basic unit of the DNA molecule is The basic unit of the DNA molecule is called:called:

NUCLEOTIDENUCLEOTIDE

A NUCLEOTIDE in DNA has three parts:A NUCLEOTIDE in DNA has three parts: A ring-shaped sugar called A ring-shaped sugar called deoxyribosedeoxyribose A A phosphate groupphosphate group A A nitrogenous basenitrogenous base (single or double ring of (single or double ring of

carbon and nitrogen atoms) carbon and nitrogen atoms)

Nucleotide monomers join together by covalent bonds between the sugar of one nucleotide and the phosphate of the next, forming a sugar-phosphate backbone.

Nitrogenous BasesNitrogenous Bases

The bases pair up (The bases pair up (A-TA-T & & G-CG-C) forming the ) forming the DOUBLE HELIX DOUBLE HELIX first first described by Watson described by Watson and Crickand Crick

Watson, Crick and Watson, Crick and FranklinFranklin

Various ways to model DNA Various ways to model DNA structurestructure

•http://www.umass.edu/molvis/tutorials/dna/dnapairs.htm manipulate DNA

Why does DNA need to Why does DNA need to be replicated?be replicated?

Growth – new cells - reproductionGrowth – new cells - reproduction

How does this process How does this process happens?happens?

REPLICATION IN 3 STEPSREPLICATION IN 3 STEPS DNA replication DNA replication

results in two results in two new strands, new strands, each each containing one containing one new strand new strand ((yellowyellow) and ) and one original one original strand (strand (blueblue))

Weak bonds Weak bonds Hydrogen bondsHydrogen bonds Comes apart Comes apart

easilyeasily Comes together Comes together

easilyeasily

Overview of DNA Overview of DNA replicationreplication

DNA separatesDNA separates Complementary Complementary

nucleotides are nucleotides are linked along linked along separated strandsseparated strands

initiateinitiate

Initiator protein Initiator protein guides guides unzipper unzipper protein protein (helicase) to (helicase) to correct position correct position on DNAon DNA

untwisteruntwister

Untwister Untwister (topoisomerase) (topoisomerase) unwinds the unwinds the DNA double DNA double helix in advance helix in advance of the unzipperof the unzipper

• Unzipper separates DNA strands, breaking weak bonds between the nucleotides

unzipunzip

assembleassemble

• Builders (polymerases) assemble new DNA strand by joining nucleotides to their matching complements on the exposed strands

straightnersstraightners

Straighteners Straighteners (single-strand (single-strand DNA binding DNA binding proteins) proteins) keep single keep single strand of strand of DNA from DNA from tanglingtangling

Phosphate provides Phosphate provides energyenergy

• Phosphate bond energy from the new nucleotides is used to make the new bonds

Leading vs. Lagging Leading vs. Lagging strandstrand

Leading (top) Leading (top) strand is built strand is built continuously as continuously as the builder the builder follows behind follows behind the unzipper, the unzipper, but the Lagging but the Lagging (lower) strand (lower) strand builds in the builds in the opposite opposite directiondirection

Lagging strandLagging strand

Lagging Lagging (lower) (lower) builder builder makes a makes a loop with the loop with the DNA strand DNA strand and builds in and builds in opposite opposite directiondirection

Lagging strandLagging strand

Built in small Built in small sections sections

Sections Sections linked by linked by enzyme ligase enzyme ligase

Repairs of DNARepairs of DNA

Erasers (Repair Erasers (Repair Nuclease): find Nuclease): find poorly matched poorly matched or damaged or damaged nucleotides and nucleotides and cut them outcut them out

Repairs of DNARepairs of DNA

Builders Builders (Polymerase): (Polymerase): fill gaps using fill gaps using other DNA other DNA strand as a strand as a guideguide

Repairs of DNARepairs of DNA

Stitchers Stitchers (Ligase): uses (Ligase): uses ATP to restore ATP to restore continuity of continuity of backbone of backbone of repaired strandrepaired strand

Big picture of DNA Big picture of DNA replicationreplication

Replication reviewReplication review

REPLICATION IN 3 STEPSREPLICATION IN 3 STEPS DNA DNA

replication replication results in results in two DNA two DNA molecules, molecules, each with each with one new one new strand strand ((yellowyellow) and ) and one old one old strand strand ((blueblue))

DNA replication DNA replication animationsanimations

http://www.youtube.com/watch?http://www.youtube.com/watch?v=4jtmOZaIvS0v=4jtmOZaIvS0

http://www.youtube.com/watch?http://www.youtube.com/watch?v=gW3qZF9cLIAv=gW3qZF9cLIA

http://www.youtube.com/watch?http://www.youtube.com/watch?v=oNW_ykH3AvAv=oNW_ykH3AvA

http://www.youtube.com/watch?http://www.youtube.com/watch?v=hC_8y8fNkCwv=hC_8y8fNkCw

TED talk – DNA replication – TED talk – DNA replication – Chromosomes- malariaChromosomes- malariahttp://www.youtube.com/watch?http://www.youtube.com/watch?v=dMPXu6GF18Mv=dMPXu6GF18M