Section 12-1
Order! Order!
Genes are made of DNA, a large, complex molecule. DNA is
composed of individual units called nucleotides. Three of these
units form a code. The order, or sequence, of a code and the type
of code determine the meaning of the message.
1. On a sheet of paper, write the word cats. List the letters or units
that make up the word cats.
2. Try rearranging the units to form other words. Remember that
each new word can have only three units. Write each word on
your paper, and then add a definition for each word.
3. Did any of the codes you formed have the same meaning?
4. How do you think changing the order of the nucleotides in the
DNA codon changes the codon’s message?
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Section:
Section Outline
Section 12-1
12–1
DNA
A.Griffith and Transformation
1. Griffith’s Experiments
2. Transformation
B.Avery and DNA
C.The Hershey-Chase Experiment
1. Bacteriophages
2. Radioactive Markers
D.The Components and Structure of DNA
1. Chargaff’s Rules
2. X-Ray Evidence
3. The Double Helix
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Section:
Section 12-1
1928-British scientist, F. Griffith, was studying two strains
of bacteria that were associated with pneumonia
-one strain caused pneumonia (smooth)
-other strain was harmless (rough)
Initial experiment
a. inject mice with smooth strain-death
b. inject mice with rough strain-live
c. Inject mice with heat-killed smooth strain-live
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Section:
Section 12-1
Second experiment
mixed heat-killed, disease-causing bacteria with the
live harmless bacteria-death
- when he pulled fluids from the dead mice’s lungs
he found living smooth bacteria.
Griffith’s hypothesis:
transformation-process in which one strain of
bacteria is changed by a gene or genes from
another strain of bacteria
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Section:
Figure 12–2 Griffith’s Experiment
Section 12-1
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Disease-causing
bacteria (smooth
colonies)
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Dies of pneumonia
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Section:
Lives
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Figure 12–2 Griffith’s Experiment
Section 12-1
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Disease-causing
bacteria (smooth
colonies)
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Dies of pneumonia
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Section:
Lives
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Video 1
Video 1
Section 12-1
1944-O. Avery repeated Griffith’s work to determine which
molecule in the heat-killed bacteria was most
important for transformation
Initial experiment-destroyed the proteins,
lipids, carbohydrates, and RNA of the heat-killed
bacteria with enzymes-transformation still takes place
when added to harmless bacteria
Second experiment-used enzymes to break
down the molecule DNA and then added to this to the
harmless bacteria-no transformation
Conclusion: DNA stores and transmits genetic
information from generation to generation.
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Section:
Section 12-1
1952-Hershey and Chase designed an experiment to
verify that genes were made of DNA using
bacteriophages (viruses that attaches to bacteria,
injects its DNA into the bacteria, and causes the
bacteria to produce more viruses)
Grew virus cultures in radioactive isotopes that
would mark either the protein coat or DNA.
Hershey and Chase concluded that the genetic
material of the bacteriophage was DNA
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Section:
Figure 12–4 Hershey-Chase Experiment
Section 12-1
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Section:
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Figure 12–4 Hershey-Chase Experiment
Section 12-1
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Section:
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Figure 12–4 Hershey-Chase Experiment
Section 12-1
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Section:
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Section 12-1
Components and Structure of DNA
1. Long molecule made of units called nucleotides
2. Nucleotides composed of:
a. Deoxyribose-5-carbon sugar
b. Phosphate group
c. Nitrogenous base
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Section:
Figure 12–5 DNA Nucleotides
Section 12-1
Purines
Adenine
Guanine
Phosphate
group
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Section:
Pyrimidines
Cytosine
Thymine
Deoxyribose
Section 12-1
Chargaff’s Rules
States that the percentage of guanine and cytosine
present in DNA are equal and that adenine and
thymine are also equal.
A=T
C=G
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Section:
Percentage of Bases in Four Organisms
Section 12-1
Source of DNA
A
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8
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Section:
Section 12-1
1950’s-X-ray evidence gathered by Franklin was
used by Watson and Crick to further develop
the double helix model of DNA in which two
strands were wound around each other.
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Section:
Figure 12–7 Structure of DNA
Section 12-1
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
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Section:
Section 12-2
A Perfect Copy
When a cell divides, each daughter cell receives
a complete set of chromosomes. This means
that each new cell has a complete set of the
DNA code. Before a cell can divide, the DNA
must be copied so that there are two sets ready
to be distributed to the new cells.
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Section:
Section 12-2
1. On a sheet of paper, draw a curving or zig-zagging line
that divides the paper into two halves. Vary the bends in
the line as you draw it. Without tracing, copy the line on a
second sheet of paper.
2. Hold the papers side by side, and compare the lines. Do
they look the same?
3. Now, stack the papers, one on top of the other, and hold
the papers up to the light. Are the lines the same?
4. How could you use the original paper to draw exact copies
of the line without tracing it?
5. Why is it important that the copies of DNA that are given
to new daughter cells be exact copies of the original?
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Section:
Section Outline
Section 12-2
12–2 Chromosomes and DNA
Replication
A.DNA and Chromosomes
1. DNA Length
2. Chromosome Structure
B.DNA Replication
1. Duplicating DNA
2. How Replication Occurs
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Section:
Section 12-2
PROKARYOTES
Prokaryotic cells lack nuclei and membrane-bound
organelles. Their DNA is located in the cytoplasm
usually as a single circular DNA molecule that
contains nearly all of the cell’s genetic information.
This is the prokaryotic cell’s chromosome.
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Section:
Prokaryotic Chromosome Structure
Section 12-2
Chromosome
E. coli bacterium
Bases on the chromosome
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Section:
Section 12-2
EUKARYOTES
Eukaryotic cells can have up to 1000 times more DNA
DNA is generally found in nucleus in the form of a number
of chromosomes
ex. Diploid human cells=46 chromosomes
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Section:
Section 12-2
DNA Length
The relative length of DNA is very long. The chromosome
of bacteria, E. coli, is 1.6 mm. This is 1000 times
longer than the bacteria itself.
Chromosome Structure
The DNA in a Eukaryotic cell is packed even tighter. The
nucleus of a human cell contains more than a meter
of DNA!
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Section:
Figure 12-10 Chromosome Structure
of Eukaryotes
Section 12-2
DNA is tightly coiled around a protein called histones to form
a substance called chromatin. Each histone molecule along
with the DNA that is coiled around it is called a nucleosome.
Nucleosomes enable cells to fold enormous lengths of DNA
into the cell’s nucleus.
Nucleosome
Chromosome
DNA
double
Coils
helix
Supercoils
Histones
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Section:
Section 12-2
DNA Replication
Before a cell divides it duplicates its DNA in a copying
process called replication. The DNA molecule
separates into two strands, and then forms two new
complementary strands following the base pair rules
Replication forks are the separation of the two strands of
DNA that allow replication. These forks are created
by an enzyme that “unzips” the DNA molecule.
Another enzyme called DNA polymerase joins
individual nucleotides to the two strands producing
two identical DNA molecules.
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Section:
Figure 12–11 DNA Replication
Section 12-2
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
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Section:
Original
strand
Nitrogenous
bases
Video 2
Video 2
Section 12-3
Information, Please
DNA contains the information that a cell needs to carry out all of its
functions. In a way, DNA is like the cell’s encyclopedia. Suppose that
you go to the library to do research for a science project. You find the
information in an encyclopedia. You go to the desk to sign out the
book, but the librarian informs you that this book is for reference only
and may not be taken out.
1. Why do you think the library holds some books for reference
only?
2. If you can’t borrow a book, how can you take home the
information in it?
3. All of the parts of a cell are controlled by the information in DNA,
yet DNA does not leave the nucleus. How do you think the
information in DNA might get from the nucleus to the rest of the
cell?
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Section:
Section Outline
Section 12-3
12–3 RNA and Protein Synthesis
A. The Structure of RNA
B. Types of RNA
C. Transcription
D. RNA Editing
E. The Genetic Code
F. Translation
G.The Roles of RNA and DNA
H. Genes and Proteins
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Section:
Section 12-3
RNA and Protein Synthesis
Genes-sequence of DNA that codes for production of a
protein thus determines a trait
This segment of DNA is copied into RNA and transferred
outside of the nucleus to the site of protein synthesis.
Structure of RNA
RNA consists of a long chain of nucleotides, similar to DNA;
however there are 3 main differences:
1. Ribose instead of Deoxyribose
2. RNA is generally single stranded
3. Uracil instead of Thymine
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Section:
Section 12-3
Types of RNA
The main function of RNA is to control the assembly
of amino acids into proteins- protein synthesis
3 Types of RNA:
1. messenger RNA(mRNA)-carries instructions
from the DNA to the rest of the cell
2. ribosomal RNA(rRNA)-helps make up
ribosomes along with several proteins
3. transfer RNA(tRNA)- transfers each amino acid
to the ribosome as coded by mRNA
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Section:
Section 12-3
Transcription
This is when an RNA molecule is produced by
copying part of the DNA strand into a
complementary sequence of RNA. It is
accomplished by an enzyme (RNA polymerase)
binding to and separating the DNA strands. RNA
polymerase then uses one strand of DNA as
template to assemble the sequence of RNA.
promoters-site on DNA in which the enzymes will
bind
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Section:
Figure 12–14 Transcription
Section 12-3
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
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Section:
Video 3
Video 3
Section 12-3
RNA EditingRNA molecules require editing before they leave the
nucleus and are used to assemble proteins.
introns-sequences of nucleotides not involved in
coding for proteins
exons-sequences that are expressed in protein
synthesis
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Section:
Section 12-3
The Genetic Code
Proteins are made up of long chains of amino acids
called polypeptides. The order in which these
amino acids are assembled is determined by the
order of the nucleotides on the strand of mRNA.
During translation , the code is read three
nucleotides at a time. This is known as a codon.
Example UCGCACGGU
UCG-CAC-GGU
serine-histidine-glycine
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Section:
Figure 12–17 The Genetic Code
Section 12-3
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Section:
Section 12-3
Translation
The decoding of an mRNA molecule
into a polypeptide chain and ultimately
a protein.
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Section:
Figure 12–18 Translation
Section 12-3
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Section:
Figure 12–18 Translation (continued)
Section 12-3
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Section:
Video 4
Video 4
Concept Map
Section 12-3
RNA
can be
Messenger RNA
also called
Ribosomal RNA
which functions to
mRNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
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Section:
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome
Section 12-4
Determining the Sequence of a Gene
DNA contains the code of instructions for cells.
Sometimes, an error occurs when the code is
copied. Such errors are called mutations.
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Section:
Section 12-4
1. Copy the following information about Protein X: Methionine—
Phenylalanine—Tryptophan—Asparagine—Isoleucine—STOP.
2. Use Figure 12–17 on page 303 in your textbook to determine one
possible sequence of RNA to code for this information. Write this code
below the description of Protein X. Below this, write the DNA code that
would produce this RNA sequence.
3. Now, cause a mutation in the gene sequence that you just determined
by deleting the fourth base in the DNA sequence. Write this new
sequence.
4. Write the new RNA sequence that would be produced. Below that,
write the amino acid sequence that would result from this mutation in
your gene. Call this Protein Y.
5. Did this single deletion cause much change in your protein? Explain
your answer.
Go to
Section:
Figure 12–17 The Genetic Code
Section 12-3
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Section:
Section Outline
Section 12-4
12–4 Mutations
A.Kinds of Mutations
1. Gene Mutations
2. Chromosomal Mutations
B.Significance of Mutations
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Section:
Section 12-4
Mutations are changes in the genetic material.
Point mutations -gene mutations involving changes in
one or a few nucleotides. These include:
a. Substitutions
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Section:
Section 12-4
Frameshift mutations -gene mutations in which
one nucleotide change can alter the assembly
of every amino acid that follows the point of
the mutation.
a. Insertions
b. Deletions
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Section:
Gene Mutations: Substitution, Insertion,
and Deletion
Section 12-4
Deletion
Substitution
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Section:
Insertion
Video 5
Section 12-4
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Section:
Section 12-4
Chromosomal mutations - mutations that involve
changes in the number or structure of
chromosomes.
4 types:
a. Deletion
b. Duplication
c. Inversion
d. Translocation
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Section:
Figure 12–20 Chromosomal Mutations
Section 12-4
Deletion
Duplication
Inversion
Translocation
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Section:
Video 6
Video 7
Video 7
Video 6
Interest Grabber Answers
1. On a sheet of paper, write the word cats. List the letters or units that make
up the word cats.
The units that make up cats are c, a, t, and s.
2. Try rearranging the units to form other words. Remember that each
new word can have only three units. Write each word on your paper, and
then add a definition for each word.
Student codes may include: Act; Sat; Cat
3. Did any of the codes you formed have the same meaning?
No
4. How do you think changing the order of the nucleotides in the DNA codon
changes the codon’s message?
Changing the order of the nucleotides changes the meaning of the codon.
Interest Grabber Answers
1. On a sheet of paper, draw a curving or zig-zagging line that divides the paper
into two halves. Vary the bends in the line as you draw it. Without tracing,
copy the line on a second sheet of paper.
2. Hold the papers side by side, and compare the lines. Do they look the same?
Lines will likely look similar.
3. Now, stack the papers, one on top of the other, and hold the papers up to the
light. Are the lines the same?
Overlaying the papers will show variations in the lines.
4. How could you use the original paper to draw exact copies of the line without
tracing it?
Possible answer: Cut along the line and use it as a template to draw the line
on another sheet of paper.
5. Why is it important that the copies of DNA that are given to new daughter
cells be exact copies of the original?
Each cell must have the correct DNA, or the cell will not
have the correct characteristics.
Interest Grabber Answers
1. Why do you think the library holds some books for reference only?
Possible answers: The books are too valuable to risk loss or damage to
them. The library wants to make sure the information is always available
and not tied up by one person.
2. If you can’t borrow a book, how can you take home the information in it?
Students may suggest making a photocopy or taking notes.
3. All of the parts of a cell are controlled by the information in DNA, yet DNA
does not leave the nucleus. How do you think the information in DNA might
get from the nucleus to the rest of the cell?
Students will likely say that the cell has some way to copy the information
without damaging the DNA.
Interest Grabber Answers
1. Copy the following information about Protein X: Methionine—Phenylalanine—
Tryptophan—Asparagine—Isoleucine—STOP.
2. Use Figure 12–17 on page 303 in your textbook to determine one possible sequence of
RNA to code for this information. Write this code below the description of Protein X.
Below this, write the DNA code that would produce this RNA sequence.
Sequences may vary. One example follows: Protein X: mRNA: AUG-UUU-UGG-AAUAUU-UGA; DNA: TAC-AAA-ACC-TTA-TAA-ACT
3. Now, cause a mutation in the gene sequence that you just determined by deleting the
fourth base in the DNA sequence. Write this new sequence.
(with deletion of 4th base U) DNA: TAC-AAA-CCT-TAT-AAA-CT
4. Write the new RNA sequence that would be produced. Below that, write the amino acid
sequence that would result from this mutation in your gene. Call this Protein Y.
mRNA: AUG-UUU-GGA-AUA-UUU-GA Codes for amino acid sequence: Methionine—
Phenylalaine—Glycine—Isoleucine—Phenylalanine—?
5. Did this single deletion cause much change in your protein? Explain your answer.
Yes, Protein Y was entirely different from Protein X.
Interest Grabber Answers
1. Do you think that cells produce all the proteins for which the DNA (genes)
code? Why or why not? How do the proteins made affect the type and
function of cells?
Cells do not make all of the proteins for which they have genes (DNA).
The structure and function of each cell are determined by the types of
proteins present.
2. Consider what you now know about genes and protein synthesis. What
might be some ways that a cell has control over the proteins it produces?
There must be certain types of compounds that are involved in determining
what types of mRNA transcripts are made and when this mRNA translates
at the ribosome.
3. What type(s) of organic compounds are most likely the ones that help to
regulate protein synthesis? Justify your answer.
The type of compound responsible is probably a protein, specifically
enzymes, because these catalyze the chemical reactions
that take place.