Copyright Houghton Mifflin Harcourt Publishing Company Cracking the Code Copyright Houghton Mifflin Harcourt Publishing Company What is DNA The genetic material in cells is contained in a molecule called deoxyribonucleic acid or ID: 784655
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Slide1
DNA Structure and Function
Copyright © Houghton Mifflin Harcourt Publishing Company
Slide2Cracking the Code
Copyright © Houghton Mifflin Harcourt Publishing Company
What is DNA?
The genetic material in cells is contained in a molecule called deoxyribonucleic acid, or
DNA
.
Scientists describe DNA as containing a code. A
code
is a set of rules and symbols used to carry information.
Slide3How was DNA discovered?
Some
scientists discovered the chemicals that make up DNA, and others learned how these chemicals fit together.
Still others determined the three-dimensional structure of the DNA molecule.
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Slide4Unraveling DNA
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What does DNA look like?
Experiments and
improving imaging
techniques have helped scientists to infer the shape of DNA.
The structure of DNA is a twisted ladder shape called a
double helix
.
Slide5What does DNA look like?
The two sides of the ladder are made of sugars and phosphate groups.
The rungs of the ladder are made of pairs of bases.
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Slide6What does DNA look like?
A base, a sugar, and a phosphate group make a building block of DNA called a
nucleotide
.
There are four different
nucleotides in DNA.
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Slide7What does DNA look like?
The bases in nucleotides are paired, or
complementary
.
Adenine always pairs with thymine (A-T).
Cytosine always pairs with guanine (C-G).
The order of the nucleotides in DNA is a code that carries information.
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Slide8What does DNA look like?
Genes
are segments of DNA that relate to a certain trait.
The
specific nucleotide sequence provides the “code” for
which proteins the cells should build.
The types of proteins that your body makes help determine your traits.
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Slide9Replication and Mutation
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How are copies of DNA made?
The cell makes copies of DNA molecules through a process known as
replication
.
During replication, the two strands of DNA separate.
The bases on each side of the molecule are used as a
template
for a new strand.
Slide10How are copies of DNA made?
As bases on the original molecule are exposed, complementary nucleotides are added.
When replication is complete, there are two identical DNA molecules.
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Slide11When are copies of DNA made?
Before a cell divides, it copies its DNA.
Our cells can replicate DNA in just a few hours, because replication begins in many places along a DNA strand.
Many groups of proteins are working to replicate your DNA at the same time.
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Unit 2
Lesson 6
DNA Structure and Function
Slide12Describe what is happening in the diagram.
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Slide13What are mutations?
Mutations
are changes in the number, type, or order of bases on a piece of DNA.
There are three main kinds of mutations: deletions, insertions, and substitutions.
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Unit 2
Lesson 6
DNA Structure and Function
Slide14What are mutations?
In a
deletion
mutation, a base is left out.
In an
insertion
mutation, an extra base is added.
The most common mutation,
substitution
, happens when one base replaces another.
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Unit 2
Lesson 6
DNA Structure and Function
Slide15What are mutations?
Which type of mutation is shown in each row? (The first row is the original sequence.)
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2
Lesson 6
DNA Structure and Function
Slide16What are mutations?
Mutations can happen by random error, and also by damage to the DNA molecule by physical or chemical agents called
mutagens
.
Cells make proteins that can fix errors in DNA, but sometimes the mistake is not corrected.
The mistake then becomes part of the genetic code.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2
Lesson 6
DNA Structure and Function
Slide17What are mutations?
A
genetic disorder
results from mutations that harm the normal function of the cell.
Some genetic disorders are
inherited
, or passed on from parent to offspring.
Other disorders result from mutations during a person’s lifetime. Most cancers fall in this category.
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Unit 2
Lesson 6
DNA Structure and Function
Slide18Protein Factory
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What is the role of DNA and RNA in building proteins?
Some of the information in the DNA is copied to a separate molecule called
RNA
, or ribonucleic acid.
RNA is used to build proteins.
Unit 2
Lesson 6
DNA Structure and Function
Slide19What is the role of DNA and RNA in building proteins?
Like DNA, RNA has a sugar-phosphate backbone and the bases adenine (A), guanine (G), and cytosine (C).
Instead of thymine (T), RNA contains uracil (U).
Three types of RNA have special roles in making proteins.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2
Lesson 6
DNA Structure and Function
Slide20What is the role of DNA and RNA in building proteins?
When a cell needs to make a protein, it makes an RNA copy of a section of the DNA. This is called
transcription
.
In
transcription, DNA is used as a template to make a complementary strand of messenger RNA (mRNA).
The information in the mRNA is then used to build proteins. This is called
translation
.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2
Lesson 6
DNA Structure and Function
Slide21What is the role of DNA and RNA in building proteins?
In translation, the mRNA passes through a protein assembly line within a ribosome.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2
Lesson 6
DNA Structure and Function
Slide22What is the role of DNA and RNA in building proteins?
A
ribosome
is a cell organelle made of ribosomal RNA (rRNA) and protein.
As mRNA passes through, transfer RNA (tRNA) delivers amino acids to the ribosomes.
The order of the bases codes for which amino acid is attached.
The amino acids are joined together to form a protein.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 2
Lesson 6
DNA Structure and Function