Section 1 the structure of dna
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Preview Bellringer Key Ideas DNA: The Genetic Material Searching for the Genetic Material The Shape of DNA The Information in DNA Discovering DNA’s Structure Summary. Section 1: The Structure of DNA. Read each question, and answer based upon what you learn in the section.

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Section 1: The Structure of DNA

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Section 1 the structure of dna

Preview

  • Bellringer

  • Key Ideas

  • DNA: The Genetic Material

  • Searching for the Genetic Material

  • The Shape of DNA

  • The Information in DNA

  • Discovering DNA’s Structure

  • Summary

Section 1: The Structure of DNA


Dr 13 1 section the structure of dna

Read 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, complementary

21.Wilkins and Franklin, DNA structure

a. a five-carbon sugar

b. type of weak bond between base pairs that holds the double helix together

c. four kinds and they form specific pairs

d. subunits that make up DNA

e. one of two pyrimidines used as a nitrogenous base in nucleotides

f. one of two purines used as a nitrogenous base in nucleotides

g. discovered that the amount of adenine always equaled the amount of cytosine and that guanine always equaled cytosine

h. two strands of nucleotides twisted around each other

DR 13.1. Section: The Structure of DNA


Section 1 the structure of dna

  • This 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?

  • How does the information contained therein get accessed?

DNA


Section 1 the structure of dna

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.


Properties of life linking to current content

  • What are the 7 properties all living things have on common?

  • Heredity is one of them.

  • What is this?

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

Properties of Life:Linking to Current Content


Dna the genetic 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.

DNA: The Genetic Material


Objectives 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.

Objectives: DNA Structure


Vocabulary

  • Gene

  • DNA

  • Nucleotide

  • Purine

  • Pyrimidine

Vocabulary


Part i dna history

Part I: DNA History


Dna the genetic material1

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

  • Traits are contained 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.

DNA, the Genetic Material


From cell to gene

From Cell to Gene


Searching for the genetic material

Searching for the Genetic Material

  • Three major experiments led to the conclusion that DNA is the genetic material in cells.

  • These experiments were performed by:


Searching for the genetic material1

  • 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.

Searching for the Genetic Material


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…

Griffith’s Discovery of Transformation

Conclusion… Whatever made the deadly bacteria deadly was being transferred into the harmless bacteria. This process of exchanging information between organisms is called TRANSFORMATION…


Section 1 the structure of dna

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


Searching for the genetic material2

  • Griffith 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.

Searching for the Genetic Material


Section 1 the structure of dna

  • 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 material3

  • Hershey 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.

Searching for the Genetic Material


Section 1 the structure of dna

  • So first genetic material was known to exist and it can be transferred. – Griffith

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

  • Next a discovery lead to the realization that DNA, not anything else, was responsible for containing the genetic information that is passed between organisms. – Hershey & Chase

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


Discovering dna s structure

Discovering DNA’s Structure

  • The search for DNA’s structure was headed by several scientists that each contributed a little at a time:


Discovering dna s structure1

  • The discovery of the structure of DNA was credited to Watson & Crickbut 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 continued

  • 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.

Discovering DNA’s Structure, continued


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.

Concept Check:


Part ii dna structure

Part II: DNA Structure


The shape of dna

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

The Shape of DNA


The shape of dna1

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

The Shape of DNA


The structure of dna

  • A 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 Structure of DNA


The shape of dna2

  • The two strands are antiparallel.

  • The backbones are equidistant but going in opposite directions.

The Shape of DNA


Section 1 the structure of dna

The Structure 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’ direction

  • The other goes in the 5”  3’ direction

  • The 3’ or 5’ refers the carbons in the ribose sugar.


Anti 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.

C#5

C#4

C#1

Ribose

C#3

C#2

Anti-Parallel


The shape of dna3

  • The two strands are complimentary.

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

The Shape of DNA

Compliments… not mirror images


The shape of dna4

  • The blue ribbon area is known as the BACKBONE

    • These are always the same.

    • PhosphateRibosePhosphateRibosePhosphate…

The Shape of DNA


Dna backbone

Phosphate

Deoxyribose

Phosphate

DNA Backbone


Dna hydrogen bonding

  • 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.

Hydrogen Bonds

Hydrogen Bonds

Hydrogen Bonds

Hydrogen Bonds

DNA: Hydrogen Bonding


Visual concept dna overview

Visual Concept: DNA Overview


The 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

The Bases

Hydrogen Bond

Hydrogen Bond


Base 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.

Base-Pairing


Complimentary 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.

Complimentary Bases


How the bases fit into larger molecules

How The Bases Fit Into Larger Molecules


Visual concept complementary base pairing

Visual Concept: Complementary Base Pairing


What to know at this point

  • The 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.

What to Know at This Point


Section 1 the structure of dna

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

To solve:

Look at the number of rings then the number of bonds…


Section 1 the structure of dna

Ribose

Nitrogenous base

Tyrosine

Phosphate

Phosphate

Nitrogenous base

Adenine

Ribose

Ribose

Nitrogenous base

Guanine

Phosphate

Phosphate

Nitrogenous base

Cytosine

Ribose


Day 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.

Day 2


The 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.

  • Different arrangements, called “spellings”, give different genes.

    • AATGCTAGC would be part of one gene

    • TGCATACCG would be part of another

    • It’s the same stuff, just a different arrangement

  • & The strict base-pairing structure allows the information to be stored and copied.

The Information in DNA


The information in dna continued

  • Paired bases are said to be complementary because they fit together like puzzle pieces.

    • Think about Dr. Watson explaining the bonds in the video.

  • 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….

  • GACTT this is the complimentary strand

  • What is the complimentary strand for.

    • CCGTATACCGATTG?

    • GGCATATGGCTAAC

The Information in DNA, continued


Homework

  • Pick up an assignment sheet from the back.

  • This is HOMEWORK and is due by tomorrow.

  • Scissors and tape are up front.

Homework


Summary

  • 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.

Summary


Nitrogenous bases categories pairing

Nitrogenous Bases: Categories, pairing


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