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Lesson 3
2.3 DNA
• DNA
• gene
• RNA
• mutation
Lesson 3
2.1 The Cell Cycle and Cell Division
What is DNA?
• Stands for deoxyribonucleic acid
• Genetic material in the nucleus of cells
• A chemical code that contains information
for an organism’s growth and function
• DNA helps determine nearly everything
your body is and does
Lesson 3
2.1 The Cell Cycle and Cell Division
Discovering DNA
• In 1952, Rosalind Franklin discovered that
DNA is two chains in a spiral form
• In 1953, James Watson and Francis
Crick made a model of a DNA molecule
Lesson 3
2.1 The Cell Cycle and Cell Division
DNA’s Structure
• A double helix or twisted ladder
• Sugar –phosphate backbone (sides of
ladder)
• Sugar is deoxyribose
• Four nitrogen bases make up the rungs
Adenine (A) always pairs with Thymine (T)
Cytosine (C) always pairs with Guanine (G)
Lesson 3
2.1 The Cell Cycle and Cell Division
Structure of DNA (cont.)
Lesson 3
Structure of DNA (cont.)
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animation online.
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Lesson 3
2.1 The Cell Cycle and Cell Division
Copying DNA
• Occurs during interphase before mitosis
• The two sides unwind and unzip
• New bases pair with bases on original DNA
Lesson 3
Copying DNA (cont.)
Lesson 3
Copying DNA (cont.)
Click here to see a short
animation online.
Click on this file
Lesson 3
Genes
• The instructions for making a specific
protein are found in a gene which is a
section of DNA on a chromosome
• Each chromosome
contains hundreds
of genes
Lesson 3
Making Proteins
• Genes are found in the nucleus, but
proteins are made on ribosomes in
cytoplasm
• The codes for making proteins are carried
to the ribosomes by RNA
Lesson 3
Ribonucleic Acid (RNA)
• RNA is made in the nucleus from DNA
• RNA is a single strand
• RNA has the nitrogen bases A, G, C, and
U (uracil)
• The sugar-phospate backbone contains
the sugar ribose
• There are three types of RNA
mRNA (messenger RNA)
rRNA (ribosomal RNA)
tRNA (transfer RNA)
Lesson 3
Ribonucleic Acid (RNA) (cont.)
Lesson 3
Controlling Genes
• Cells control genes by turning some genes
off and turning other genes on
• Each cell uses only some of the thousands
of genes that it has to make proteins
• For example, muscle proteins are made in
muscle cells, cells in the eye produce
proteins for eye color, cells in the stomach
produce proteins to digest food
• If the incorrect proteins are produced, the
organism cannot function properly
Lesson 3
Mutations
• Sometimes mistakes happen when DNA is
being copied
• These mistakes, called mutations, are any
permanent change in the DNA sequence
of a gene or chromosome
• Incorrect proteins are made
• Some mutations result in a missing or
extra chromosome
Lesson 3
Results of Mutations
• Mutations can occur in body cells (it may
or may not be life threatening) or in sex
cells (all the cells in the organism will be
affected)
• Mutations can be harmful, beneficial, or
have no effect on the organism
• Mutations add variety to a species when
the organism reproduces
Lesson 3
Section 3 DNA pages 110-115
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section on DNA.
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class. This file will open in PDF
format.
Lesson 3
2.1 The Cell Cycle and Cell Division
3 Review
1.
2.
3.
4.
A
B
C
D
1. Describe how DNA makes a copy of
itself.
2. Explain how the codes for proteins are
carried from the nucleus to the
ribosomes.
3. Apply: A strand of DNA has the bases
AGTAAC. Using letters, show a matching
DNA strand.
4. Use a Venn diagram, compare and
contrast DNA and RNA.
5. Construct a diagram of the structure of
DNA. Label the parts.
Lesson 3
2.1 The Cell Cycle and Cell Division
3 Summary
1.
2.
3.
4.
A
B
C
D
What is DNA?
•Each side of the DNA ladder is made
up of sugar-phosphate molecules, and
the rungs of the ladder are made up of
nitrogen bases.
•When DNA is copied, the new DNA
has bases that are identical to those of
the original DNA.
Lesson 3
2.1 The Cell Cycle and Cell Division
3 Summary
1.
2.
3.
4.
A
B
C
D
Genes
•The instructions for making a specific
protein are found in genes in the cell
nucleus. Proteins are made on
ribosomes in the cytoplasm.
•There are three main kinds of RNA –
mRNA, rRNA, and tRNA.
Lesson 3
2.1 The Cell Cycle and Cell Division
3 Summary
1.
2.
3.
4.
A
B
C
D
Mutations
•If DNA is not copied exactly, the
resulting mutations may cause proteins
to be made incorrectly.