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Chapter 6
Genes and DNA
Table of Contents
Section 1 What Does DNA Look Like?
Section 2 How DNA Works
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Chapter 6
Section 1 What Does DNA Look Like?
Bellringer
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.
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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
Bellringer
Unscramble the following words:
tpsoneir
neesg
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.
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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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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
Genes and DNA
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Genes and DNA
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Chapter 6
Standardized Test Preparation
Reading
Read each of the passages. Then, answer the
questions that follow each passage.
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Passage 1 The tension in the courtroom was so
thick that you could cut it with a knife. The
prosecuting attorney presented this evidence: “DNA
analysis indicates that blood found on the
defendant’s shoes matches the blood of the victim.
The odds of this match happening by chance are 1 in
20 million.” The jury members were stunned by these
figures. Can there be any doubt that the defendant is
guilty?
Continued on the next slide
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Passage 1, continued
DNA is increasingly used as evidence in court
cases. Traditional fingerprinting has been used for
more than 100 years, and it has been an extremely
important identification tool. Recently, DNA
fingerprinting, also called DNA profiling, has started
to replace traditional techniques. DNA profiling has
been used to clear thousands of wrongly accused or
convicted individuals. However, there is some
controversy over whether DNA evidence should be
used to prove a suspect’s guilt.
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1. What does the first sentence in this passage
describe?
A the air pollution in a particular place
B the feeling that a person might experience during
an event
C the motion of an object
D the reason that a person was probably guilty of a
crime
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1. What does the first sentence in this passage
describe?
A the air pollution in a particular place
B the feeling that a person might experience during
an event
C the motion of an object
D the reason that a person was probably guilty of a
crime
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Chapter 6
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2. Which of the following best describes the main
idea of the second paragraph of this passage?
F A defendant was proven guilty by DNA analysis.
G Court battles involving DNA fingerprinting are very
exciting.
H The technique of DNA profiling is increasingly used
in court cases.
I The technique of DNA profiling is controversial.
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2. Which of the following best describes the main
idea of the second paragraph of this passage?
F A defendant was proven guilty by DNA analysis.
G Court battles involving DNA fingerprinting are very
exciting.
H The technique of DNA profiling is increasingly used
in court cases.
I The technique of DNA profiling is controversial.
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Chapter 6
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Passage 2 Most of the biochemicals found in living
things are proteins. In fact, other than water, proteins
are the most abundant molecules in your cells.
Proteins have many functions, including regulating
chemical activities, transporting and storing materials,
and providing structural support.
Every protein is composed of small “building
blocks” called amino acids. Amino acids are
molecules that are composed of carbon, hydrogen,
oxygen, and nitrogen atoms.
Continued on the next slide
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Passage 2, continued Some amino acids also
include sulfur atoms. Amino acids chemically bond to
form proteins of many shapes and sizes.
The function of a protein depends on the shape of
the bonded amino acids. If even a single amino acid
is missing or out of place, the protein may not
function correctly or may not function. Foods such as
meat, fish, cheese, and beans contain proteins,
which are broken down into amino acids as the foods
are digested. Your body can then use these amino
acids to make new proteins.
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1. In the passage, what does biochemical mean?
A a chemical found in nonliving things
B a chemical found in living things
C a pair of chemicals
D a protein
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1. In the passage, what does biochemical mean?
A a chemical found in nonliving things
B a chemical found in living things
C a pair of chemicals
D a protein
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2. According to the passage, which of the following
statements is true?
F Amino acids contain carbon dioxide.
G Amino acids contain proteins.
H Proteins are made of living things.
I Proteins are made of amino acids.
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2. According to the passage, which of the following
statements is true?
F Amino acids contain carbon dioxide.
G Amino acids contain proteins.
H Proteins are made of living things.
I Proteins are made of amino acids.
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Interpreting Graphics
The diagram below shows an original sequence of DNA
and three possible mutations. Use the diagram to
answer the questions that follow.
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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.
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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.
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2. In which mutation was a
new base pair added?
F Mutation A
G Mutation B
H Mutation C
I There is not enough
information to determine the
answer.
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2. In which mutation was a
new base pair added?
F Mutation A
G Mutation B
H Mutation C
I There is not enough
information to determine the
answer.
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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.
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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.
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Chapter 6
Standardized Test Preparation
Math
Read each question, and choose the best answer.
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1. Mary was making a design on top of her desk with
marbles. She put 3 marbles in the first row, 7 marbles
in the second row, 15 marbles in the third row, and 31
marbles in the fourth row. If Mary continues this
pattern, how many marbles will she put in the
seventh row?
A 46
B 63
C 127
D 25500
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1. Mary was making a design on top of her desk with
marbles. She put 3 marbles in the first row, 7 marbles
in the second row, 15 marbles in the third row, and 31
marbles in the fourth row. If Mary continues this
pattern, how many marbles will she put in the
seventh row?
A 46
B 63
C 127
D 25500
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2. Bobby walked 3 1/2 km on Saturday, 2 1/3 km on
Sunday, and 1 km on Monday. How many kilometers
did Bobby walk on those 3 days?
F 5 1/6
G 5 5/6
H 6 1/6
I 6 5/6
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2. Bobby walked 3 1/2 km on Saturday, 2 1/3 km on
Sunday, and 1 km on Monday. How many kilometers
did Bobby walk on those 3 days?
F 5 1/6
G 5 5/6
H 6 1/6
I 6 5/6
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3. Marie bought a new aquarium for her goldfish. The
aquarium is 60 cm long, 20 cm wide, and 30 cm high.
Which equation could be used to find the volume of
water needed to fill the aquarium to 25 cm deep?
A V  30  60  20
B V  25  60  20
C V  30  60  20 – 5
D V  30  60  25
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3. Marie bought a new aquarium for her goldfish. The
aquarium is 60 cm long, 20 cm wide, and 30 cm high.
Which equation could be used to find the volume of
water needed to fill the aquarium to 25 cm deep?
A V  30  60  20
B V  25  60  20
C V  30  60  20 – 5
D V  30  60  25
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4. How is the product of 6  6  6  4  4  4
expressed in scientific notation?
F 64  36
G 63  43
H 36  34
I 246
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4. How is the product of 6  6  6  4  4  4
expressed in scientific notation?
F 64  36
G 63  43
H 36  34
I 246
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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
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