Section 1: The Structure of DNASection 1: The Structure of DNA

PreviewBellringerKey IdeasDNA: The Genetic MaterialSearching for the Genetic MaterialThe Shape of DNAThe Information in DNADiscovering DNA’s StructureSummary

DR 13.1. Section: The Structure of DNADR 13.1. Section: The Structure of DNARead each question, and answer based upon what you learn in the section.1. With what kinds of bacteria did Griffith inject mice?2. What was different about the S bacteria and the R bacteria?3. Why were the heat-killed S bacteria harmless?4. Why was the mixture of heat-killed S bacteria and R bacteria virulent?5. What did Griffith discover as a result of his experiments?6. How did Avery discover that the material responsible for transformation in bacteria

was DNA?7. Viruses that infect bacteria are called [bacteriophages / rough].8. A virus is made of DNA and [proteins / cell walls].9. Radioactive sulfur was used to label the [DNA / protein] in the viruses.10. Radioactive phosphorus was used to label the [DNA / protein] in the viruses.11. Hershey and Chase discovered that after the 32P-labeled phages infected the

bacteria, most of the radioactive phosphorus was found in the layer containing [bacteria / phage].

Match the letter of the phrase with the appropriate term_____ 12. double helix_____ 13. nucleotides_____ 14. deoxyribose_____ 15. hydrogen bond_____ 16. nitrogenous bases_____ 17. adenine_____ 18. cytosine_____ 19. Chargaff

Explain how the terms in each pair are related to each other.20. base-pairing rules, complementary21.Wilkins and Franklin, DNA structure

a. a five-carbon sugarb. type of weak bond between base pairs that holds the double helix togetherc. four kinds and they form specific pairsd. subunits that make up DNAe. one of two pyrimidines used as a nitrogenous base in nucleotidesf. one of two purines used as a nitrogenous base in nucleotidesg. discovered that the amount of adenine always equaled the amount of cytosine and that guanine always equaled cytosineh. two strands of nucleotides twisted around each other

DNADNAThis is DNA.What do you

know about it? What is its job & why

is it important?How was it discovered?

What is its structure?How does it get

created/duplicated?How does the

information contained therein get accessed?

Properties of Life:Properties of Life:Linking to Current ContentLinking to Current Content

Heredity is one of the 7 properties of life.

What is this?

How is the passing of traits from parents to offspring achieved?

DNA: The DNA: The Genetic MaterialGenetic Material

In the 1800’s, Austrian monk Gregor Mendel discovered how traits (the physical things you can see on the outside of an organism) are passed on from parent to offspring.

The information Mendel lacked was what these traits were transported in or on.◦ Physically, how did the trait exist in an organism?

We now know that traits are transferred from parents to offspring through the transfer and sharing of genes contained in DNA.

But it took 50 years of research in studies performed by important scientists.

Objectives: DNA StructureObjectives: DNA Structure

Today you are going to learn all about the basic structure of the molecule that holds our heredity… DNA.

By the end of this lesson you will be able to…◦ Identify the substance that makes up genetic material.◦ Name the experiments that identified the role of DNA as

the genetic material.◦ Name the studies that led to the discovery of DNA’s

structure. ◦ Relate the structure of DNA to the function of DNA as a

carrier of information.◦ Build a model of a DNA molecule.

VocabularyVocabulary

GeneDNA NucleotidePurine Pyrimidine

Part I: DNA HistoryPart I: DNA History

DNA, the Genetic MaterialDNA, the Genetic Material

So, Mendel knew what happens with traits but not how they were stored and transferred.

Traits are contained as directions in DNA (deoxyribonucleic acid): the primary genetic material that contains genes.◦ It causes recognizable, inheritable characteristics in

related groups of organisms. Traits are “written” into specific areas, called

genes, within the large, continuous DNA molecules called chromosomes.

A gene is the most basic physical unit of heredity◦ A gene contains the instructions for to make a trait, just

like a recipe contains the instructions for a meal.

Searching for the Genetic MaterialSearching for the Genetic Material Three major experiments led to the

conclusion that DNA is the genetic material in cells.

These experiments were performed by:

Discovering DNA as the genetic material

Scientist (s) Contribution

Griffith

Avery

Hershey and Chase

Searching for the Genetic MaterialSearching for the Genetic Material Griffith worked with two related strains of bacteria which cause

pneumonia in mice.◦ One strain was deadly… it made the mice sick and killed them.◦ The other strain did little to nothing to the mice.

Griffith discovered that when harmless live bacteria were mixed with heat-killed disease-causing bacteria and then injected into mice, the mice died.

These results led Griffith to discover transformation. Transformation is a change in genotype that is caused when cells take up foreign genetic material.

Griffith’s experiments led to the conclusion that genetic material could be transferred between cells.

Griffith’s Discovery of Transformation Griffith’s Discovery of Transformation

Harmless bacteria

Deadly bacteria

Deadly bacteria that was made harmless because

it was boiled to death.

Harmless bacteria mixed with killed deadly bacteria…

Conclusion… Whatever made the deadly bacteria deadly was being transferred into the harmless bacteria. This process of exchanging information

between organisms is called TRANSFORMATION…

So first, genetic material is known to exist and it can be transferred in a process called transformation.

Searching for the Genetic MaterialSearching for the Genetic MaterialGriffith proved hereditary information can

be transferred but what was it?Avery wanted to determine whether the

transforming agent in Griffith’s experiments was protein, RNA, or DNA.

Avery used enzymes to destroy each of these molecules in heat-killed bacteria.

Avery’s experiments led to the conclusion that DNA is responsible for transformation in bacteria.

So first genetic material is known to exist and it can be transferred in a process called transformation.

Then we knew that DNA was the genetic material being passed on…but was it the only genetic material?

Searching for the Genetic MaterialSearching for the Genetic MaterialHershey and Chase studied

bacteriophages.

Bacteriophages are viruses that infects bacteria.

By using radioactive isotopes (chemical that emit light when charged with UV radiation) painted in the virus’s DNA and proteins, Hershey and Chase showed that DNA, not protein, is the genetic material in viruses.

– Griffith So first genetic material was known to exist

and it can be transferred. – Avery Then we knew that DNA was the genetic

material being passed on…but was it the only genetic material?

– Hershey & ChaseNext a discovery lead to the realization that

DNA, not anything else, was responsible for containing the genetic information that is passed between organisms.

The next question…What is the structure?...

Discovering DNA’s StructureDiscovering DNA’s StructureThe search for DNA’s structure was

headed by several scientists that each contributed a little at a time:

Discovering DNA Structure

Scientist (s) Contribution

Watson & Crick

Chargaff

Franklin & Wilkins

Discovering DNA’s StructureDiscovering DNA’s Structure

The discovery of the structure of DNA was credited to Watson & Crick

but they borrowed information from several other scientists.

Chargaff:◦ Showed that the amount of adenine always equaled the

amount of thymine◦ & the amount of guanine always equaled the amount of

cytosine.

Franklin and Wilkins:◦ Developed X-ray diffraction images of strands of DNA

that suggested the DNA molecule resembled a tightly coiled helix.

Discovering DNA’s Structure, Discovering DNA’s Structure, continuedcontinued

Watson and Crick used both Chargaff’s data and the X-ray diffraction studies to create a complete three-dimensional model of DNA.

Their model showed a “spiral staircase” in which two strands of nucleotides twisted around a central axis.

These pictures are looking straight down the staircase.

Concept Check:Concept Check:

What were the three experiments that lead to the discovering what the genetic material in humans was?

What is the name of the molecule that contains genetic information?

Who is credited for discovering the structure of DNA?

Name two other contributing scientists and what they discovered.

Part II: DNA StructurePart II: DNA Structure

How is the structure of DNA similar to that of a ladder or spiral staircase?

How is it different from that of a ladder or spiral staircase?

DNA is often compared to a ladder or a spiral staircase. Look at picture to the right and answer the following questions.

The Shape of DNAThe Shape of DNA

The spiral shape of DNA is known as a double helix.

Double = two strandsHelix = spiraled around itself.

DNA is made up of individual nucleotides bonded to each other.

The Structure of The Structure of DNADNA

The Structure of DNAThe Structure of DNAA nucleotide is a DNA subunit made up of three

parts: a phosphate group, a 5-carbon sugar group, and a nitrogen-containing base.

The five-carbon sugar in DNA is called deoxyribose, from which DNA gets its full name, deoxyribonucleic acid.◦ “de” means removed =

it lacks one hydroxide group present in RNA

The Shape of The Shape of DNADNAThe blue ribbon area is known as

the BACKBONE◦ These are always the same.◦ PhosphateRibosePhosphateRibose

Phosphate…

PR

PR

PR

PR

DNA BackboneDNA Backbone

Phosphate

Deoxyribose

Phosphate

The two strands are antiparallel.The backbones are equidistant but

going in opposite directions.

The Shape of DNAThe Shape of DNA

The term “anti-parallel” refers to the fact that whereas DNA backbones are equidistant from each other, they go in opposite directions.

One strand goes in the 3’5’ directionThe other goes in the 5” 3’ directionThe 3’ or 5’ refers the carbons in the ribose sugar.

The Structure of DNAThe Structure of DNA

Anti-ParallelAnti-Parallel

Ribose is a 5-carbon sugar.

5’ refers to the end of the nucleotide closest to the #5 carbon.

3’ refers to the end of the nucleotide closest to the #3 carbon.

Carbon#1

C#2C#3

C#4

C#5

Ribose

The Shape of The Shape of DNADNA

The two strands are complimentary.

One strand contains bases that are complimentary to the other strand’s bases.

Compliments… not mirror images

DNA: Hydrogen BondingDNA: Hydrogen Bonding

Hydrogen Bonds Hydrogen BondsHydrogen Bonds

Hydrogen Bonds

• DNA is held together by hydrogen bonds.• They are represented by dashed lines.• Notice the # of H-bonds. They change depending

on the bases involved.

The BasesThe Bases

The four kinds of bases are adenine (A), guanine (G), thymine (T), and cytosine (C).

Bases A and G have a double-ring structure and are classified as purines.

Bases T and C have a single-ring structure and are classified as pyrimidines.

A purine on one strand of a DNA molecule is always paired with a pyrimidine on the other strand.

Specifically, adenine always pairs with thymine, and guanine always pairs with cytosine.

Hydrogen Bond

Hydrogen Bond

Hydrogen Bond

Hydrogen Bond

Hydrogen Bond

Base-PairingBase-Pairing

Base-pairing rules (as given to us by Chargaff) are dictated by the chemical structure of the bases.

It has to do with the category (purine/pyrimidine) as well as their hydrogen bonding characteristics.◦A double bonds with T◦G triple bonds with C◦The bonds are HYDROGEN BONDS

Whereas hydrogen bonds are weak individually, the billions of bonds between bases keep the two long strands of DNA together.

Complimentary BasesComplimentary Bases

The “puzzle piece” refers to the hydrogen bonding between the paired bases.

Guanine and cytosine have 3 hydrogen bonds

whereas thymine and adenine have 2 hydrogen bonds.

How The Bases Fit Into Larger How The Bases Fit Into Larger MoleculesMolecules

What to Know at This PointWhat to Know at This PointThe three experiments that lead to the discovery of

DNA as the genetic material.Who contributed to the discovery of the structure

of DNA?The structure of DNA

◦What a nucleotide is composed of.◦How the nucleotides are arranged to create strands of

DNA.◦What holds the bases together…Hydrogen Bonds (H-

bonds)◦The base-paring rules

A – T, C – G, pyrimidine, purine. How many hydrogen bonds between the bases

HW: Complete the half-sheet. Fill in all shapes with abbreviations for the part that goes there. Label the hydrogen bonds too.

Summary: Complete the Illustration in Summary: Complete the Illustration in your notes.your notes.Using the rules of complementary bases and h-bonding, Using the rules of complementary bases and h-bonding, determine what each shape is.determine what each shape is.

To solve:Look at the number of rings then the number of bonds…

Phosphate

Phosphate

Phosphate

Phosphate

Ribose

Ribose

Ribose

Ribose

Nitrogenous base

Adenine

Nitrogenous baseCytosine

Nitr

ogen

ous

base

Tyr

osin

e

Nitrog

enou

s ba

se

Gua

nine

Day 2Day 2

Take out your homework◦The half sheet you had from yesterday.

We’ll discuss in 5 minutes.Make sure you check with neighbors and

get clarification on anything you couldn’t get.

The Information in DNAThe Information in DNA

The information in DNA is contained in the order of the bases.

The order of how the bases are arranged determines the trait that will result.

This order is called the “sequence”Different sequences, called “spellings”,

give different genes.◦AATGCTAGC would be spelling of one the

sequence in one gene ◦TGCATACCG would be part of another◦It’s the same stuff, just a different arrangement

The Information in DNAThe Information in DNA

Paired bases on opposite sides of a double helix are said to be complementary because they fit together like puzzle pieces.

Because of base-pairing rules, if the sequence (the order) of bases is known for one strand of DNA, then the sequence of bases for the complementary strand (the other) can be quickly identified or predicted.

Ex. CTGAA BONDS WITH…. This is the TEMPLATE strand GACTT This is the COMPLEMENTARY strand What is the complementary strand for.

◦ CCGTATACCGATTG?◦ GGCATATGGCTAAC

(Template Strand)(Complimentary Strand)

HomeworkHomework

Pick up an assignment sheet from the back.

This is HOMEWORK and is due by tomorrow.

Scissors and tape are up front.

Check in when complete.It’s due tomorrow if not.

SummarySummary

DNA is the primary material that causes inheritable characteristics in related groups of organisms.

Three major experiments led to the conclusion that DNA is the genetic material in cells. These experiments were performed by Griffith, Avery, and Hershey and Chase.

A DNA molecule is shaped like a spiral staircase and is composed of two parallel strands of linked subunits.

The information in DNA is contained in the order of the bases, while the base-pairing structure allows the information to be copied.

Watson and Crick used information from experiments by Chargaff, Wilkins, and Franklin to determine the three-dimensional structure of DNA.

Nitrogenous Bases: Categories, Nitrogenous Bases: Categories, pairingpairing

Base Number of rings

Makes it a Hydrogen bonds with

Structure

Adenine 2 Purine Thymine

Guanine 2 Purine Cytosine

Thymine 1 Pyrimidine Adenine

Cytosine 1 Pyrimidine Guanine