table of contents section 1 what does dna look like? section 2 how dna works chapter 6 genes and dna
TRANSCRIPT
Table of Contents
Section 1 What Does DNA Look Like?
Section 2 How DNA Works
Chapter 6 Genes and DNA
Section 1 What Does DNA Look Like?
Journal Entry
Can you explain the difference between traits and characteristics? Which is more closely associated with DNA and genes? Do you know where DNA and genes are found in the body? In specific cells?
Write your answers in your science journal.
Chapter 6
Section 1 What Does DNA Look Like?
Objectives
• List three important events that led to understanding the structure of DNA.
• Describe the basic structure of a DNA molecule.
• Explain how DNA molecules can be copied.
Chapter 6
Section 1 What Does DNA Look Like?
The Pieces of the Puzzle
• DNA stands for deoxyribonucleic acid. DNA is the genetic material that determines inherited characteristics.
Chapter 6
• Nucleotides: The Subunits of DNA DNA is made of subunits called nucleotides. A nucleotide consists of a sugar, a phosphate, and a base.
Section 1 What Does DNA Look Like?
The Pieces of the Puzzle, continued
• Chargaff’s Rule Erwin Chargaff found that the amount of adenine in DNA always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine.
• Franklin’s Discovery Chemist Rosalind Franklin was able to make images of DNA molecules by using X-ray diffraction.
Chapter 6
Section 1 What Does DNA Look Like?
The Pieces of the Puzzle, continued
• Watson and Crick’s Model James Watson and Francis Crick used Chargaff’s and Franklin’s research to build a model of DNA.
• The model, which looked like a long, twisted ladder, eventually helped explain how DNA is copied and how it functions in the cell.
Chapter 6
Section 1 What Does DNA Look Like?
DNA’s Double Structure
• The Double Helix The shape of DNA is known as a double helix.
• The two sides of the ladder are made of alternating sugar parts and phosphate parts.
• The rungs of the ladder are made of a pair of bases.
Chapter 6
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Section 1 What Does DNA Look Like?Chapter 6
Section 1 What Does DNA Look Like?
Making Copies of DNA
• How Copies Are Made During replication, a DNA molecule is split down the middle, where the bases meet. The bases on each side of the molecule are used as a pattern for a new strand.
• When Copies Are Made DNA is copied every time a cell divides. Each new cell gets a complete copy of all the DNA.
Chapter 6
Section 1 What Does DNA Look Like?
Making Copies of DNA, continued
Chapter 6
Section 1 What Does DNA Look Like?
DNA Replication
Chapter 6
Click below to watch the Visual Concept.
You may stop the video at any time by pressing the Esc key.
Visual Concept
Section 2 How DNA Works
Journal Entry
Unscramble the following words:tpsoneirneesg
Now think of three words you associate with each of the above words and use them all in a paragraph that highlights what you know about DNA.
Write your paragraph in your science journal.
Chapter 6
Section 2 How DNA Works
Objectives
• Explain the relationship between DNA, genes, and proteins.
• Outline the basic steps in making a protein.
• Describe three types of mutations, and provide an example of a gene mutation.
• Describe two examples of uses of genetic knowledge.
Chapter 6
Section 2 How DNA Works
Unraveling DNA
• DNA is often wound around proteins, coiled into strands, and then bundled up even more. In a cell that has a nucleus, the strands of DNA and proteins are bundled into chromosomes.
• A gene consists of a string of nucleotides that give the cell information about how to make a specific trait.
Chapter 6
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Section 2 How DNA WorksChapter 6
Section 2 How DNA Works
Genes and Proteins
Chapter 6
• Proteins and Traits Proteins act as chemical triggers for many of the processes within cells. Proteins help determine traits.
• Help from RNA Another type of molecule that helps make proteins is called RNA, or ribonucleic acid. RNA is so similar to DNA that RNA can serve as a temporary copy of a DNA sequence.
Section 2 How DNA Works
Genes and Proteins, continued
Chapter 6
• The Making of a Protein The first step in making a protein is to copy one side of the segment of DNA containing a gene. This copy is called messenger RNA (mRNA).
• A ribosome is a cell organelle composed of RNA and protein. A ribosome uses mRNA, transfer RNA (tRNA), and amino acids to make proteins.
• You can see the steps of protein production on the following two slides.
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Section 2 How DNA WorksChapter 6
Copyright © by Holt, Rinehart and Winston. All rights reserved.
ResourcesChapter menu
Section 2 How DNA WorksChapter 6
Section 2 How DNA Works
Changes in Genes
• Mutations Changes in the number, type, or order of bases on a piece of DNA are known as mutations.
Chapter 6
Section 2 How DNA Works
Changes in Genes, continued
• Do Mutations Matter? There are three possible consequences to changes in DNA: an improved trait, no change, or a harmful trait.
• How Do Mutations Happen? Mutations happen regularly because of random errors when DNA is copied. Any physical or chemical agent that can cause a mutation in DNA is called a mutagen.
Chapter 6
Section 2 How DNA Works
Carcinogens and Mutagens
Chapter 6
Click below to watch the Visual Concept.
You may stop the video at any time by pressing the Esc key.
Visual Concept
Section 2 How DNA Works
An Example of Substitution
• A mutation, such as a substitution, can be harmful because it may cause a gene to produce the wrong protein.
• A simple change in an amino acid can cause a disease such as sickle cell anemia, as shown on the next slide.
Chapter 6
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Section 2 How DNA WorksChapter 6
Section 2 How DNA Works
Uses of Genetic Knowledge
• Genetic Engineering Scientists can manipulate individual genes within organisms. This kind of manipulation is called genetic engineering.
• Genetic Identification Your DNA is unique, so it can be used like a fingerprint to identify you. DNA fingerprinting identifies the unique patterns in an individual’s DNA.
Chapter 6
Genes and DNA
Concept Map
Use the terms below to complete the concept map on the next slide.
Chapter 6
mutation amino acidnucleotideDNAadenine
genesguanineproteinschromosomescytosine
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ResourcesChapter menu
Chapter 6 Genes and DNA
Copyright © by Holt, Rinehart and Winston. All rights reserved.
ResourcesChapter menu
Chapter 6 Genes and DNA
1. In which mutation was an original base pair replaced?
A Mutation A
B Mutation B
C Mutation C
D There is not enough information to determine the answer.
Chapter 6 Standardized Test Preparation
2. In which mutation was anew base pair added?
F Mutation A
G Mutation B
H Mutation C
I There is not enough information to determine the answer.
Chapter 6 Standardized Test Preparation
2. In which mutation was anew base pair added?
F Mutation A
G Mutation B
H Mutation C
I There is not enough information to determine the answer.
Chapter 6 Standardized Test Preparation
3. In which mutation was an original base pair removed?
A Mutation A
B Mutation B
C Mutation C
D There is not enough information to determine the answer.
Chapter 6 Standardized Test Preparation
3. In which mutation was an original base pair removed?
A Mutation A
B Mutation B
C Mutation C
D There is not enough information to determine the answer.
Chapter 6 Standardized Test Preparation
Section 1 What Does DNA Look Like?Chapter 6
Section 1 What Does DNA Look Like?Chapter 6
Section 2 How DNA WorksChapter 6
Chapter 6 Standardized Test Preparation