Lesson Overview 12.2 The Structure of DNA.

Slides:



Advertisements
Similar presentations
Griffith and Transformation
Advertisements

1 Chapter 12 DNA & RNA DNA How do genes work? What are they made of? How do they determine characteristics of organisms? In the middle of the.
12.1 Identifying the Substance of Genes
End Show Slide 1 of 21 Copyright Pearson Prentice Hall 12-2 Chromosomes and DNA Replication 12–2 The Structure of DNA.
Chapter 12: DNA The Blueprint of Life.
Chapter 12.2 (Pg ): The Structure of DNA
The Structure of DNA Mendel Watson Chapter 12.2 Crick Franklin.
1953: The structure of the DNA molecule is first described.
12.1 Identifying the Substance of Genes. Lesson Overview Lesson Overview Identifying the Substance of Genes THINK ABOUT IT How do genes work? To answer.
Lesson Overview 12.2 The Structure of DNA.
Section 12-2: The structure of DNA
Lesson Overview 12.2 The Structure of DNA.
 MONDAY: Study the “old dead people” from this unit!  TUESDAY: QUIZ on DNA structure  WEDNESDAY:  THURSDAY:  FRIDAY: TEST—DNA.
Lesson Overview 12.2 The Structure of DNA. The Components of DNA What are the chemical components of DNA? DNA is a nucleic acid made up of nucleotides.
Objectives 12.2 The Structure of DNA
1 Review List the chemical components of DNA Relate Cause and Effect Why are hydrogen bonds so essential to the structure of DNA 2 Review Describe the.
DNA. Nucleic Acids Review – Nucleic acids store and transmit genetic information – Genetic information = instructions for making proteins – Monomers =
Warm Up Where is DNA located within a cell? Why is DNA important?
DNA How do genes work? What are they made of, and how do they determine the characteristics of organisms? In the middle 1900’s questions like these were.
Ch. 12 DNA and RNA What kind of DNA do clones have? Xeroxyribonucleic Acid What kind of DNA do joggers have? Reeboxyribonucleic Acid What do diarrhea and.
The Structure of DNA.
Objectives 12.2 The Structure of DNA -Identify the chemical components of DNA. -Discuss the experiments leading to the identification of DNA as the molecule.
End Show Slide 1 of 37 Copyright Pearson Prentice Hall Biology.
DNA & RNA Structure.
Biologist first had to discover the chemical nature of the genes.
Structure of DNA. Do Now Read and React 10 minutes to Read and React with 10 lines.
 Stores information needed for traits and cell processes  Copying information needed for new cells  Transferring information from generation to generation.
DNA STRUCTURE AND REPLICATION. DNA A NUCLEIC ACID MADE OF TWO STRANDS OF NUCLEOTIDES WOUND TOGETHER IN A SPIRAL CALLED A DOUBLE HELIX NUCLEOTIDE COMPOSED.
DNA DeoxyriboNucleic Acid. What can DNA do? Carries information from one generation to the next Determines the heritable characteristics of organisms.
The Structure of DNA Read the title aloud to students.
12.2 The Structure of DNA 1)What are the chemical components of DNA? 2)What clues helped scientists solve the structure of DNA? 3)What does the double-helix.
Chapter #12 – DNA, RNA, & Protein Synthesis. I. DNA – experiments & discoveries A. Griffith and Transformation Frederick Griffith – British scientist.
The Structure of DNA -Identify the components of DNA and how they pair up. -Discuss the scientists responsible for the identification of DNA’s structure.
Lesson Overview 12.2 The Structure of DNA.
DNA Structure and Replication Review!
Lesson Overview 12.2 The Structure of DNA.
DNA: History of discovery of its Structure & Function
Lesson Overview 12.2 The Structure of DNA.
Lesson Overview 12.2 The Structure of DNA.
12-1 and 12-2 DNA Structure and Replication
The Structure of dnA Big Q: What are the chemical components of DNA?
Copyright Pearson Prentice Hall
Lesson Overview 12.2 The Structure of DNA.
12.1 Identifying the Substance of Genes
Chapter 12-2 The Structure of DNA.
Solving the Structure of DNA
THINK ABOUT IT The DNA molecule must somehow specify how to assemble proteins, which are needed to regulate the various functions of each cell. What kind.
Lesson Overview 12.2 The Structure of DNA.
Copyright Pearson Prentice Hall
DNA.
The Structure of DNA Read the title aloud to students.
The Structure of DNA Read the title aloud to students.
Unit 7: DNA Structure and Function
Objectives: To understand how DNA was discovered
Copyright Pearson Prentice Hall
Lesson Overview 12.2 The Structure of DNA.
Lesson Overview 12.2 The Structure of DNA.
12.1 Identifying the Substance of Genes
Lesson Overview 12.2 The Structure of DNA.
Lesson Overview 12.2 The Structure of DNA.
Compare DNA and RNA in terms of structure, nucleotides and base pairs.
Lesson Overview 12.2 The Structure of DNA Objectives:
Solving the Structure of DNA
Lesson: Structure of DNA Key Questions:
The Structure of DNA (Ch 12.2)
DNA Structure.
Lesson Overview 12.2 The Structure of DNA.
DNA Chapter 12.
Copyright Pearson Prentice Hall
Presentation transcript:

Lesson Overview 12.2 The Structure of DNA

THINK ABOUT IT The DNA molecule must somehow specify how to assemble proteins, which are needed to regulate the various functions of each cell. What kind of structure could serve this purpose without varying from cell to cell? Understanding the structure of DNA has been the key to understanding how genes work.

The Components of DNA What are the chemical components of DNA?

The Components of DNA What are the chemical components of DNA? DNA is a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds.

Nucleic Acids and Nucleotides Nucleic acids are long, slightly acidic molecules originally identified in cell nuclei. Nucleic acids are made up of nucleotides, linked together to form long chains. The nucleotides that make up DNA are shown.

Nucleic Acids and Nucleotides DNA’s nucleotides are made up of three basic components: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base.

Nitrogenous Bases and Covalent Bonds The nucleotides in a strand of DNA are joined by covalent bonds formed between their sugar and phosphate groups.

Nitrogenous Bases and Covalent Bonds DNA has four kinds of nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The nitrogenous bases stick out sideways from the nucleotide chain.

Nitrogenous Bases and Covalent Bonds The nucleotides can be joined together in any order, meaning that any sequence of bases is possible.

Solving the Structure of DNA What clues helped scientists solve the structure of DNA?

Solving the Structure of DNA What clues helped scientists solve the structure of DNA? The clues in Franklin’s X-ray pattern enabled Watson and Crick to build a model that explained the specific structure and properties of DNA.

Chargaff’s Rules Erwin Chargaff discovered that the percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA. The same thing is true for the other two nucleotides, guanine [G] and cytosine [C]. The observation that [A] = [T] and [G] = [C] became known as one of “Chargaff’s rules.”

Franklin’s X-Rays In the 1950s, British scientist Rosalind Franklin used a technique called X-ray diffraction to get information about the structure of the DNA molecule.

Franklin’s X-Rays X-ray diffraction revealed an X-shaped pattern showing that the strands in DNA are twisted around each other like the coils of a spring. The angle of the X-shaped pattern suggested that there are two strands in the structure. Other clues suggest that the nitrogenous bases are near the center of the DNA molecule.

The Work of Watson and Crick At the same time, James Watson, an American biologist, and Francis Crick, a British physicist, were also trying to understand the structure of DNA. They built three-dimensional models of the molecule.

The Work of Watson and Crick Early in 1953, Watson was shown a copy of Franklin’s X-ray pattern. The clues in Franklin’s X-ray pattern enabled Watson and Crick to build a model that explained the specific structure and properties of DNA.

The Work of Watson and Crick Watson and Crick’s breakthrough model of DNA was a double helix, in which two strands were wound around each other.

The Double-Helix Model What does the double-helix model tell us about DNA?

The Double-Helix Model What does the double-helix model tell us about DNA? The double-helix model explains Chargaff’s rule of base pairing and how the two strands of DNA are held together.

The Double-Helix Model A double helix looks like a twisted ladder. In the double-helix model of DNA, the two strands twist around each other like spiral staircases. The double helix accounted for Franklin’s X-ray pattern and explains Chargaff’s rule of base pairing and how the two strands of DNA are held together.

Antiparallel Strands In the double-helix model, the two strands of DNA are “antiparallel”—they run in opposite directions. This arrangement enables the nitrogenous bases on both strands to come into contact at the center of the molecule. It also allows each strand of the double helix to carry a sequence of nucleotides, arranged almost like letters in a four-letter alphabet.

Hydrogen Bonding Watson and Crick discovered that hydrogen bonds could form between certain nitrogenous bases, providing just enough force to hold the two DNA strands together. Hydrogen bonds are relatively weak chemical forces that allow the two strands of the helix to separate. The ability of the two strands to separate is critical to DNA’s functions.

Base Pairing Watson and Crick’s model showed that hydrogen bonds could create a nearly perfect fit between nitrogenous bases along the center of the molecule. These bonds would form only between certain base pairs—adenine with thymine, and guanine with cytosine. This nearly perfect fit between A–T and G–C nucleotides is known as base pairing, and is illustrated in the figure.

Base Pairing Watson and Crick realized that base pairing explained Chargaff’s rule. It gave a reason why [A] = [T] and [G] = [C]. For every adenine in a double-stranded DNA molecule, there had to be exactly one thymine. For each cytosine, there was one guanine.