U8L1 DNA Structure & Function

Unit 8 Lesson 1 DNA Structure and Function
Copyright © Houghton Mifflin Harcourt Publishing Company

Indiana Standards
• 8.3.4 Understand the relationship between
deoxyribonucleic acid (DNA), genes, and
chromosomes.

Cracking the Code
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.
• To understand how DNA functions, you first need
to learn about the structure of the DNA molecule.

How was DNA discovered?
• Many scientists from all over the world contributed
to our understanding of DNA.
• Some scientists discovered the chemicals that
make it up.
• Other scientists learned about how these
chemicals fit together.

Unraveling DNA
What does DNA look like?
• Experiments and imaging techniques have helped
scientists to infer the shape of DNA.
• The structure of DNA is called a double helix.

• The two sides of the ladder shape are made of
sugars and phosphate groups.
• The rungs of a DNA strand are made of pairs of
bases.

• The building block of DNA is called a nucleotide,
which is a base, a sugar, and a phosphate group.
• There are four different nucleotides in DNA.

• 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.

• Genes are segments of DNA that relate to a
certain trait.
• The code in the nucleotide order has information
about which proteins the cells should build.
• The types of proteins that your body makes help
determine your traits.

Replication and Mutation
How are copies of DNA made?
• The cell makes copies of DNA molecules through a
process known as replication.
• During replication, the DNA separates.
• The bases on each side are used as a pattern for a
new strand.

• As replication proceeds, complementary
nucleotides are added.
• When replication is complete, there are two
identical DNA molecules.

• Describe what is happening in the diagram.

When 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.

What 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.

What 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.

What are mutations?
• Which type of
mutation is shown
in each row?

What 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.

What are mutations?
• A genetic disorder results from mutations that
harm the normal function of the cell.
• Some harmful mutations are inherited, or passed
on from parent to offspring. Others can lead to
cancer.

Protein Factory
What is the role of DNA and RNA in
building proteins?
• To build 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.

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).
• There are three types of RNA. Each type has a
special role in making proteins.

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.

building proteins?
• In translation, the mRNA passes through a protein
assembly line within a ribosome.

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.

U8L1 DNA Structure & Function

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