DNA-APBio Ch 9

Chapter 9

DNA: Molecule DNA: Molecule of Heredityof Heredity

Chapter 9 2 Genes Are Made of DNAGenes Are Made of DNA

Known since the late 1800s:Known since the late 1800s:1.1. Heritable information is carried in Heritable information is carried in

discrete units called discrete units called genes genes 2.2. Genes are parts of structures called Genes are parts of structures called

chromosomeschromosomes3.3. Chromosomes are made of Chromosomes are made of

deoxyribonucleic acid (deoxyribonucleic acid (DNADNA) and ) and proteinprotein


Transformed bacteria revealed the link Transformed bacteria revealed the link between genes and DNAbetween genes and DNA

F. Griffith worked with two strains of F. Griffith worked with two strains of Streptococcus pneumoniaeStreptococcus pneumoniae bacteria bacteria

• S strain caused pneumonia when injected S strain caused pneumonia when injected into mice, killing theminto mice, killing them

• R strain did not cause pneumonia when R strain did not cause pneumonia when injectedinjected

Chapter 9 4

Mouse injected w/bacteriaMouse injected w/bacteria ResultsResults ConclusionsConclusions

R strain does R strain does notnot cause cause pneumoniapneumonia

S strain S strain doesdoes cause cause pneumoniapneumonia

Heat-killed S strain does Heat-killed S strain does notnot cause pneumonia cause pneumonia

Substance from heat-Substance from heat-killed S strain killed S strain cancan transform harmless R transform harmless R strain into deadly S strainstrain into deadly S strain

Transformed BacteriaTransformed Bacteria


Deductions from Griffith’s experiment Deductions from Griffith’s experiment (1920s)(1920s)

• Living safe bacteria (R strain) were Living safe bacteria (R strain) were changed by something in the dead (but changed by something in the dead (but normally disease-causing) S strainnormally disease-causing) S strain

• The living R strain bacteria were The living R strain bacteria were transformedtransformed by genetic material released by by genetic material released by the S strainthe S strain


Later findings by Avery, MacLeod, and Later findings by Avery, MacLeod, and McCarty (1940s)McCarty (1940s)

• The transforming molecule from the S The transforming molecule from the S strain was strain was DNADNA

Chapter 9 7

Chapter 9 8

Chapter 9 9

DNA Is Composed of Four NucleotidesDNA Is Composed of Four Nucleotides

DNA is made of chains of small subunits DNA is made of chains of small subunits called called nucleotidesnucleotides

Each nucleotide has three components:Each nucleotide has three components:1.1. Phosphate groupPhosphate group2.2. Deoxyribose sugarDeoxyribose sugar3.3. One of four One of four nitrogen-containing basesnitrogen-containing bases

ThymineThymine CytosineCytosineAdenineAdenine GuanineGuanine

Chapter 9 10


Types of Nitrogen Bases…Types of Nitrogen Bases…

PurinesPurines2 rings2 ringsA and GA and G

PyrimidinesPyrimidines1 ring1 ringT and CT and C

Chapter 9 11

DNA ThymineDNA Thymine DNA CytosineDNA Cytosine

DNA GuanineDNA GuanineDNA AdenineDNA Adenine

The Four NucleotidesThe Four Nucleotidesof DNAof DNA

Chapter 9 12


In 1940, biochemist E. Chargaff In 1940, biochemist E. Chargaff determined that:determined that:

• In a DNA molecule, amounts ofIn a DNA molecule, amounts of

A = T, G = CA = T, G = C• ““Chargaff’s Rule”Chargaff’s Rule”

Chapter 9 13 DNA Is a Double HelixDNA Is a Double Helix

Rosalind Franklin and Maurice Wilkins Rosalind Franklin and Maurice Wilkins studied DNA structure using X-ray studied DNA structure using X-ray scatteringscattering


From X-ray diffraction patterns they From X-ray diffraction patterns they deduced that DNA …deduced that DNA …

• Is long and thinIs long and thin• Has a uniform diameter of 2 nanometers Has a uniform diameter of 2 nanometers • Is helical, and is twisted like a corkscrewIs helical, and is twisted like a corkscrew• Consists of repeating subunitsConsists of repeating subunits


James Watson and Francis Crick James Watson and Francis Crick combined the X-ray data with bonding combined the X-ray data with bonding theory to deduce DNA structure:theory to deduce DNA structure:

• DNA is made of two strands of DNA is made of two strands of nucleotidesnucleotides

• The deoxyribose and phosphate The deoxyribose and phosphate portions make up the portions make up the sugar-phosphate sugar-phosphate backbonebackbone

Chapter 9 16

Chapter 9 17

Please don’t admire Dr Watson…Please don’t admire Dr Watson…

He is "inherently gloomy about the prospect He is "inherently gloomy about the prospect of Africa". –October 2007of Africa". –October 2007

To him, the real cause of Africa's woes is To him, the real cause of Africa's woes is that black people are inherently less that black people are inherently less intelligent than other races. "All our social intelligent than other races. "All our social policies are based on the fact that their policies are based on the fact that their intelligence is the same as ours — intelligence is the same as ours — whereas all the testing says not really," whereas all the testing says not really,"

He hoped that everyone was equal, he He hoped that everyone was equal, he continued, but "people who have to deal continued, but "people who have to deal with black employees find this not true". with black employees find this not true".

Chapter 9 18

Please don’t admire Dr Watson…Please don’t admire Dr Watson…

(Amount of melanin in the skin) was why (Amount of melanin in the skin) was why black people and Latinos had reputations black people and Latinos had reputations as lovers — something, he said, of which as lovers — something, he said, of which the English could not be accused. -2000the English could not be accused. -2000

"Whenever you interview fat people, you "Whenever you interview fat people, you feel bad because you know you're not feel bad because you know you're not going to hire them," -2000going to hire them," -2000

In 1997, he even said a woman should be In 1997, he even said a woman should be allowed to abort a fetus if tests had shown allowed to abort a fetus if tests had shown it would be a homosexual and the mother it would be a homosexual and the mother deemed this undesirable. deemed this undesirable.

Chapter 9 19

James Watson is AMERICAN. Not British. James Watson is AMERICAN. Not British. He was born in Chicago. Studied and He was born in Chicago. Studied and researched in London but spent less that 5 researched in London but spent less that 5 years there. years there.

He currently resides at Cold Spring Harbor He currently resides at Cold Spring Harbor Lab in Huntington, Long Island NY. He is Lab in Huntington, Long Island NY. He is currently suspended from the lab he currently suspended from the lab he founded due to his remarks. (Update founded due to his remarks. (Update 10/25/07…he just “retired”)10/25/07…he just “retired”)

More quotes…More quotes…

Chapter 9 20

Watson has repeatedly supported genetic Watson has repeatedly supported genetic screening and genetic engineering in screening and genetic engineering in public lectures and interviews, arguing public lectures and interviews, arguing that stupidity is a disease and the "really that stupidity is a disease and the "really stupid" bottom 10% of people should be stupid" bottom 10% of people should be curedcured

He has also suggested that beauty could be He has also suggested that beauty could be genetically engineered, saying "People say genetically engineered, saying "People say it would be terrible if we made all girls it would be terrible if we made all girls pretty. I think it would be great .”pretty. I think it would be great .”

Chapter 9 21

Hydrogen bonds form between complementary bases

Complementary base Complementary base pairs hold the two DNA pairs hold the two DNA strands togetherstrands together

DNA is a double helix DNA is a double helix of two nucleotide of two nucleotide strandsstrands

The Watson-CrickThe Watson-CrickModel of DNA StructureModel of DNA Structure

Chapter 9 22 Hydrogen BondsHydrogen Bonds

Nitrogen-containing bases protrude Nitrogen-containing bases protrude inward from sugar-phosphate backboneinward from sugar-phosphate backbone

Hydrogen bonds hold certain nitrogenous Hydrogen bonds hold certain nitrogenous base pairs togetherbase pairs together

• A bonds with T, G bonds with CA bonds with T, G bonds with C• Bonding bases called Bonding bases called complementary base complementary base

pairspairs• A and T bond with TWO Hydrogen bondsA and T bond with TWO Hydrogen bonds• G and C bond with THREE Hydro. bondsG and C bond with THREE Hydro. bonds

Chapter 9 23

How Does DNA Encode Information?How Does DNA Encode Information?

How can a molecule with only 4 simple How can a molecule with only 4 simple parts be the carrier of genetic parts be the carrier of genetic information?information?

The key lies in the The key lies in the sequencesequence, not , not numbernumber, of , of subunitssubunits

Within a DNA strand, the four types of Within a DNA strand, the four types of bases can be arranged in any linear bases can be arranged in any linear order, and this sequence is what order, and this sequence is what encodes genetic informationencodes genetic information

Chapter 9 24


The genetic code is analogous to The genetic code is analogous to languages, where small sets of letters languages, where small sets of letters combine in various ways to make up combine in various ways to make up many different wordsmany different words

• English has 26 lettersEnglish has 26 letters• Hawaiian has 12 lettersHawaiian has 12 letters• The binary language of computers uses The binary language of computers uses

only 2 “letters” (0 and 1, or “on” and “off”)only 2 “letters” (0 and 1, or “on” and “off”)

Chapter 9 25


The sequence of only four nucleotides can The sequence of only four nucleotides can produce many different combinationsproduce many different combinations

• A 10 nucleotide sequence can code for A 10 nucleotide sequence can code for greater than 1 million different greater than 1 million different combinationscombinations

Chapter 9 26 DNA ReplicationDNA Replication

All cells come from pre-existing cellsAll cells come from pre-existing cellsCells reproduce by dividing in halfCells reproduce by dividing in halfEach of two daughter cells gets an exact Each of two daughter cells gets an exact

copy of parent cell’s genetic copy of parent cell’s genetic informationinformation

Duplication of the parent cell DNA is Duplication of the parent cell DNA is called called replicationreplication

Chapter 9 27

Parental DNA double helix

New double helix with 1 old &1 new strand

DNA DNA ReplicationReplication

DNA replication DNA replication begins when begins when DNA DNA helicaseshelicases separate separate the two strandsthe two strands

• Hydrogen bonds Hydrogen bonds between bases between bases are brokenare broken

FreeNucleotides

Chapter 9 28

Parental DNA double helix

New double helix with 1 old &1 new strand

DNA DNA ReplicationReplicationA second strand of A second strand of

new DNA is new DNA is synthesized along synthesized along each separated each separated strand by strand by DNA DNA polymerases, polymerases, which which positionposition free free nucleotidesnucleotides across across from from complementary complementary nucleotidesnucleotides

FreeNucleotides

Chapter 9 29 DNA ReplicationDNA Replication

The two resulting DNA molecules have The two resulting DNA molecules have one old parental strand and one new one old parental strand and one new strand (strand (semiconservative replicationsemiconservative replication))

Chapter 9 30

The SemiconservativeThe SemiconservativeReplication ModelReplication Model

One DNAOne DNAdouble helixdouble helix

Dup

licat

edD

uplic

ated

Chr

omos

ome

Chr

omos

ome

Chr

omos

ome

Chr

omos

ome

Daughter Daughter chromosomes chromosomes

half half oldold, half , half newnew

Both strands Both strands of original of original DNA serve DNA serve

as templatesas templates

SisterSisterChromatidsChromatids

Chapter 9 31

Replication forksmove in opposite directions

ParentalDaughter

Replication Forks

DNA replication begins

ReplicationBubble

DNA replication progresses

DNA replication completed

ReplicationReplicationBubbleBubble

Chapter 9 32

Replication Details (1)Replication Details (1)One strand replicated as continuous segmentOne strand replicated as continuous segmentOther replicated in short segmentsOther replicated in short segments

(to be joined later by ligase)(to be joined later by ligase)

ReplicationReplicationForkFork

PPPP PP

PPSS

SSSS SS

C o n t i n u o u sC o n t i n u o u s

S e g m e n t e dS e g m e n t e d

UnzippingUnzipping

Chapter 9 33

Replication Details (2)Replication Details (2)

Chapter 9 34

Replication Details (3)Replication Details (3)

Helicase unzips DNAHelicase unzips DNA

DNA polymerases add loose nucleotides to DNA polymerases add loose nucleotides to growing strandsgrowing strands

DNA ligase connects short strands togetherDNA ligase connects short strands together

Chapter 9 35 Replication And ProofreadingReplication And Proofreading

During replication, DNA polymerase During replication, DNA polymerase mismatches nucleotides once every mismatches nucleotides once every 10,000 base pairs10,000 base pairs

DNA repair enzymes “proofread” each DNA repair enzymes “proofread” each new daughter strand, replacing new daughter strand, replacing mismatched nucleotidesmismatched nucleotides

However…However…

Chapter 9 36 Mistakes Do HappenMistakes Do Happen

DNA is damaged in a number of waysDNA is damaged in a number of waysSpontaneous chemical breakdown at body Spontaneous chemical breakdown at body

temperaturetemperatureCertain chemicals (some components of Certain chemicals (some components of

cigarette smoke)cigarette smoke)UV light from the sun causes DNA damageUV light from the sun causes DNA damage

• DNA damage leads to uncontrollable DNA damage leads to uncontrollable cell division and skin cancercell division and skin cancer

Chapter 9 37 Types of MutationsTypes of Mutations

Point mutation Point mutation - individual nucleotide in - individual nucleotide in the DNA sequence is changed the DNA sequence is changed

Insertion mutationInsertion mutation - one or more - one or more nucleotide pairs are inserted into the nucleotide pairs are inserted into the DNA double helix DNA double helix

Deletion mutationDeletion mutation - one or more - one or more nucleotide pairs are removed from nucleotide pairs are removed from the double helix the double helix

Chapter 9 38

Chapter 9 39

Chapter 9 40

Chapter 9 41 Types of MutationsTypes of Mutations

InversionInversion - piece of DNA is cut out of a - piece of DNA is cut out of a chromosome, turned around, and re-chromosome, turned around, and re-inserted into the gap inserted into the gap

TranslocationTranslocation - chunk of DNA (often very - chunk of DNA (often very large) is removed from one large) is removed from one chromosome and attached to chromosome and attached to anotheranother

Chapter 9 42

Chapter 9 43

Chapter 9

The endThe end

Technology

DNA-APBio Ch 9