Download Section 12-1

Interest Grabber
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 Structure of DNA
1. Chargaff’s Rules
2. X-Ray Evidence
3. The Double Helix
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Section:
Objectives
1. Be able to define transformation, bacteriophage, nucleotide, and base
pairing.
2. Be able to describe the Griffith, Avery, and Hershey-Chase
experiments.
3. Be able to explain what scientists discovered about the relationship
between genes and DNA.
4. Be able to explain the overall structure of the DNA molecule.
Vocabulary Words
Transformation – process in which one strain of bacteria is changed by a
gene or genes from another strain of bacteria
Bacteriophage – a kind of virus that infects and kills bacteria
Nucleotide – monomer of nucleic acids made up of a 5-carbon sugar, a
phosphate group, and a nitrogenous base
Base pairing – principle that bonds in DNA can form only between adenine
and thymine and between guanine and cytosine
Griffith and Transformation
Griffith (mice injected with bacteria) – genetic
information could be transformed from one
bacterium to another
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
Go to
Section:
Lives
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Avery and DNA
Avery (“juice” from heat-killed bacteria and
enzymes) – DNA is the nucleic acid that stores
and transmits the genetic information from one
generation of an organism to the next
Alfred Hershey- Martha Chase
Hershey-Chase – genetic material of the
bacteriophage is DNA, not protein
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
Figure 12–5 DNA Nucleotides
Section 12-1
Purines
Adenine
Guanine
Phosphate
group
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Section:
Pyrimidines
Cytosine
Thymine
Deoxyribose
Percentage of Bases in Four
Organisms
Section 12-1
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Section:
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
Sugar-Phosphate Backbone and Chargaff’s Rule
Chargaff’s Rules: If there
are a certain number of
cytosines, there will be
about the same number
of guanines. Same with
A’s and T’s.
Rosalind Franklin 1950
Diffraction
Clues from the X-Ray
– Coiled (forming Helix)
– Double-stranded
– Nitrogeneous bases are
in the center
X-Ray
Watson & Crick
Francis Crick – British physicist
James Watson – American Biologist
– Building a 3D model of DNA
– Franklin’s X-Ray opened their eyes to the Double Helix
Watson and Crick’s model of DNA was a double helix, in which two
strands were wound around each other.
Double Helix
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:
Questions
List the conclusions and explain how each of these
scientists derived the conclusions:
– Griffith
– Avery
– Hershey and Chase
Why did Hershey and Chase grow viruses in cultures that
contained both radioactive phosphorus and
radioactive sulfur? What might have happened if they
only used one?
How did Watson and Crick’s model explain why there are
equal amounts of thymine and adenine in DNA?
Interest Grabber
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:
Interest Grabber continued
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?
Go to
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:
Prokaryotic Chromosome Structure
Section 12-2
•No Nucleus
Chromosome
E. coli bacterium
Bases on the chromosome
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Section:
Prokaryote DNA
Most have one circular chromosome located in the cytoplasm
with some plasmids (circular DNA molecule found in bacteria) as
well
– E.Coli (1.6μm diameter)
– 4,639,221 base pairs 1.6mm long
– Like packing 300m of rope in your backpack
Eukaryotes and DNA
1000 times more base pairs than bacterial DNA
Smallest human chromosome has 30 million base pairs of DNA
How do eukaryotes fit all that DNA in its nucleus?
Figure 12-10 Chromosome
Structure of Eukaryotes
Section 12-2
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
Go to
Section:
DNA to Chromosomes
Vocabulary
– Chromatin - granular material (uncondensed) within the nucleus;
consists of DNA tightly coiled around proteins
– Chromosomes – condensed chromatin
– Histone - globular protein molecule around which DNA is tightly
coiled in chromatin
DNA Replication
During DNA replication, the DNA molecule separates into two strands, then
produces two new complementary strands following the rules of base
pairing. Each strand of the double helix of DNA serves as a template, or
model, for the new strand.
Enzymes unwind DNA
Enzymes split “unzip” double
helix
The enzyme, DNA polymerase,
finds and attaches the
corresponding N-base
Each “old” stand serves as a
template and is matched up
with a new stand of DNA
New helixes wind back up.
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
DNA Replication
A–C–T–T–G–G–A–C
T–G–A–A–C–C–T -G
Interest Grabber
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.
B.
C.
D.
E.
F.
G.
H.
Go to
Section:
The Structure of RNA
Types of RNA
Transcription
RNA Editing
The Genetic Code
Translation
The Roles of RNA and DNA
Genes and Proteins
Concept Map
Section 12-3
RNA
can be
Messenger RNA
also called
which functions to
mRNA
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Section:
Ribosomal RNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome
RNA and Protein Synthesis
Codon - three-nucleotide sequence on messenger RNA
that codes for a single amino acid
Anticodon - group of three bases on a tRNA molecule
that are complementary to an mRNA codon
Protein Synthesis: Two Parts
Transcription
• Occurs in the nucleus
• Formation of a single strand of messenger RNA from
DNA
Translation
• Occurs on ribosomes
• Cell uses the information on mRNA to assemble
amino acids in the proper order to form specific
proteins
Transcription
Occurs in nucleus
Enzymes unwind DNA
Enzymes split “unzip” double helix
RNA polymerase binds to promoter
sequence (signal) on DNA
RNA polymerase transcribes a single
strand of mRNA
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:
Figure 12–17 The Genetic Code
Section 12-3
Proteins are made by joining
amino acids into long chains
called polypeptides. Each
polypeptide contains a
combination of any or all of the
20 different amino acids.
The genetic code shows the
amino acid to which each of the
64 possible codons
corresponds.
There is one codon, AUG, that
can either specify methionine, or
serve as the initiation, or “start”,
for protein synthesis.
There are three “stop” codons
that do not code for any amino
acid.
Figure 12–18 Translation
Section 12-3
Nucleus
Messenger RNA
Messenger RNA is transcribed in the nucleus.
Phenylalanine
tRNA
The mRNA then enters the cytoplasm and
attaches to a ribosome. Translation begins at
AUG, the start codon. Each transfer RNA has
an anticodon whose bases are complementary
to a codon on the mRNA strand. The ribosome
positions the start codon to attract its
anticodon, which is part of the tRNA that binds
methionine. The ribosome also binds the next
codon and its anticodon.
Ribosome
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Section:
mRNA
Transfer RNA
Methionine
mRNA
Lysine
Start codon
Figure 12–18 Translation
(continued)
Section 12-3
The Polypeptide “Assembly Line”
The ribosome joins the two amino acids—
methionine and phenylalanine—and breaks
the bond between methionine and its tRNA.
The tRNA floats away, allowing the ribosome
to bind to another tRNA. The ribosome moves
along the mRNA, binding new tRNA molecules
and amino acids.
Lysine
Growing polypeptide chain
Ribosome
tRNA
tRNA
mRNA
Completing the Polypeptide
mRNA
Ribosome
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Section:
Translation direction
The process continues until the ribosome reaches
one of the three stop codons. The result is a
growing polypeptide chain.
Questions
1. What happens during DNA replication?
2. List and describe the three main types of RNA.
3. Describe the interactions between DNA, RNA, and
proteins during each part of protein synthesis?
4. Describe the main difference between RNA and
DNA.
Interest Grabber
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:
Interest Grabber continued
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.
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Section:
Section Outline
Section 12-4
12–4
Mutations
A. Gene Mutations
B. Chromosomal Mutations
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Section:
Mutations
Mutation - change in a DNA sequence that affects genetic information
Two Main Types:
– Gene Mutation
• Mutation that causes a change in a single gene
– Chromosomal Mutation
• Mutation that causes a change in an entire chromosome
Gene Mutations:
Substitution, Insertion, and Deletion
Section 12-4
Deletion
Substitution
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Section:
Insertion
Gene Mutations
Point Mutation (substitution)
– mutation that affects a single nucleotide, usually by
substituting one nucleotide for another
Frameshift Mutation (insertion or deletion)
– mutation that shifts the “reading” frame of the genetic
message by inserting or deleting a nucleotide
Figure 12–20 Chromosomal Mutations
Section 12-4
Deletion
Duplication
Inversion
Translocation
Chromosomal mutations involve changes in whole chromosomes.
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Section:
Section Outline
Section 12-5
12–5
Gene Regulation
A. Gene Regulation: An Example
B. Eukaryotic Gene Regulation
C. Regulation and Development
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Section:
Interest Grabber
Section 12-5
Regulation of Protein Synthesis
Every cell in your body, with the exception of gametes, or sex cells,
contains a complete copy of your DNA. Why, then, are some cells nerve
cells with dendrites and axons, while others are red blood cells that have
lost their nuclei and are packed with hemoglobin? Why are cells so
different in structure and function? If the characteristics of a cell depend
upon the proteins that are synthesized, what does this tell you about
protein synthesis? Work with a partner to discuss and answer the
questions that follow.
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Section:
Interest Grabber continued
Section 12-5
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?
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?
3. What type(s) of organic compounds are most likely the ones that help to
regulate protein synthesis? Justify your answer.
Go to
Section:
Typical Gene Structure
Section 12-5
Regulatory
sites
Promoter
(RNA polymerase
binding site)
Start transcription
Regulatory site – places where other proteins, binding directly
to the DNA sequences at those sites, can regulate transcription.
The actions of these proteins help to determine whether a gene
is turned on or turned off.
Promoter - region of DNA that indicates to RNA polymerase
where to bind to make RNA
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Section:
DNA strand
Stop transcription
Lac Operon (E. coli)
Operon – a group of genes that act
together
Operator - region of chromosome in
an operon to which the repressor
binds when the operon is “turned off”
Operator bound – RNA polymerase
can’t transcribe genetic information
(not expressed)
Operator free – gene(s) expressed
Eukaryotic Gene Regulation
mRNA editing before going to transcription
Intron - intervening sequence of DNA; does not code for a protein
(not used)
Exon - expressed sequence of DNA; codes for a protein (used)
TATA box – a short region of DNA about 30 base pairs long;
seems to help position RNA polymerase by marking a point just
before the point at which transcription begins
Eukaryote Gene Regulation
Genes are regulated
in a variety of ways
by enhancer
sequences
DNA region about 30bp long
TATATAAA: help to align
RNA Polymerase
Gene Regulation
Prokaryote Gene Regulation
– Will often have one OPERATOR (regulatory site) controlling the expression
of more than one gene OPERON
Eukaryote Gene Regulation
– Most eukaryotic genes are controlled individually and have regulatory
sequences that are much more complex than those of the lac operon
Gene Reg. and Development
hox genes - series of genes that controls
the organs and tissues that develop in
various parts of an embryo
Mutations affecting the hox genes in the
fruit fly, Drosophila, for example, can
replace the fly’s antennae with a pair of
legs growing right out of its head!