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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.
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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.
• Nucleotides: The
Subunits of DNA DNA is
made of subunits called
nucleotides. A nucleotide
consists of a sugar, a
phosphate, and a base.
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Chapter 6
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.
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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.
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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.
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Chapter 6
Section 1 What Does DNA Look Like?
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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.
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Chapter 6
Section 1 What Does DNA Look Like?
Making Copies of DNA, continued
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Chapter 6
Section 1 What Does DNA Look Like?
DNA Replication
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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.
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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.
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Chapter 6
Section 2 How DNA Works
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Chapter 6
Section 2 How DNA Works
Genes and Proteins
• 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.
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Chapter 6
Section 2 How DNA Works
Genes and Proteins, continued
• 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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Chapter 6
Section 2 How DNA Works
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Chapter 6
Section 2 How DNA Works
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Chapter 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.
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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.
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Chapter 6
Section 2 How DNA Works
Carcinogens and Mutagens
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Chapter 6
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.
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Chapter 6
Section 2 How DNA Works
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Chapter 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.
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Chapter 6
Genes and DNA
Concept Map
Use the terms below to complete the concept map on
the next slide.
mutation
amino acid
nucleotide
DNA
adenine
genes
guanine
proteins
chromosomes
cytosine
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Chapter 6
Concept Map
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Chapter 6
Concept Map
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End of Chapter 6 Show
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Chapter 6
Section 1 What Does DNA Look Like?
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Chapter 6
Section 1 What Does DNA Look Like?
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Chapter 6
Section 2 How DNA Works
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Chapter 6
Standardized Test Preparation
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Chapter 6
Standardized Test Preparation
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