Chapter 12- DNA, RNA, and Proteins

Copyright Pearson Prentice Hall
Biology

12–1 DNA

Griffith and Transformation
In 1928, British scientist Fredrick Griffith
was trying to learn how certain types of
bacteria caused pneumonia.
He isolated two different strains of
pneumonia bacteria from mice and grew
them in his lab.

Griffith made two observations:
(1) The disease-causing strain of bacteria
grew into smooth colonies on culture plates.
(2) The harmless strain grew into colonies
with rough edges.

Griffith's Experiments
Griffith set up four
individual experiments.
Experiment 1:
Mice were injected with
the disease-causing
strain of bacteria. The
mice developed
pneumonia and died.

Experiment 2:
Mice were injected
with the harmless
strain of bacteria.
These mice didn’t
get sick.
Harmless bacteria
(rough colonies)
Lives

Experiment 3:
Griffith heated the
disease-causing
bacteria. He then
injected the heat-killed
bacteria into
the mice. The mice
survived.
Heat-killed disease-causing
bacteria
(smooth colonies)
Lives

Experiment 4:
Griffith mixed his heat-killed,
disease-causing
bacteria with live,
harmless bacteria and
injected the mixture into
the mice. The mice
developed pneumonia
and died.
Live disease-causing
bacteria
(smooth colonies)
bacteria
(smooth colonies)
Harmless bacteria
(rough colonies)
Dies of pneumonia

deadly harmless dead deadly dead deadly
+ harmless
Killed! Survived! Survived! Killed!
Pneumonia Pneumonia

Griffith concluded
that the dead
bacteria
passed their
disease-causing
ability
to the harmless
strain. Live disease-causing
bacteria
(smooth colonies)
bacteria
(smooth colonies)
Harmless bacteria
(rough colonies)
Dies of pneumonia

Transformation
Griffith called this process
transformation because the
harmless strain of bacteria had
changed into the disease-causing
strain.
Griffith hypothesized that a factor must
contain information that could change
harmless bacteria into disease-causing ones.

Avery and DNA
Oswald Avery repeated Griffith’s work to
determine which molecule was most
important for transformation.
Avery and his colleagues made an extract
from the heat-killed bacteria that they
treated with enzymes.

The enzymes destroyed proteins, lipids,
carbohydrates, and other molecules,
including the nucleic acid RNA.
Transformation still occurred.

Avery and other scientists repeated the
experiment using enzymes that would
break down DNA.
When DNA was destroyed,
transformation did not occur.
Therefore, they concluded that
DNA was the transforming factor.

The Hershey-Chase Experiment
Alfred Hershey and Martha Chase studied
viruses—nonliving particles smaller than
a cell that can infect living organisms.

Bacteriophages
A virus that infects bacteria is
known as a bacteriophage.
Bacteriophages are composed of
a DNA or RNA core and a protein
coat.

When a bacteriophage enters a
bacterium, the virus attaches to the
surface of the cell and injects its
genetic information into it.

The viral genes use the
bacteria’s organelles to produce
many new viruses, which eventually
destroy the bacterium.
The cell splits open as hundreds
of new viruses burst out.

If Hershey and Chase could determine which
part of the virus entered an infected cell,
they would learn whether genes were made
of protein or DNA.
They grew viruses in cultures containing
radioactive isotopes of phosphorus-32 (32P)
and sulfur-35 (35S).

If 35S was found in the bacteria, it would
mean that the viruses’ protein had been
injected into the bacteria.
Bacteriophage with
suffur-35 in protein coat
Phage infects
bacterium
No radioactivity
inside bacterium

If 32P was found in the bacteria, then it was
the DNA that had been injected.
Bacteriophage with
phosphorus-32 in DNA
Phage infects
bacterium
Radioactivity
inside bacterium

Nearly all the radioactivity in the
bacteria was from phosphorus (32P).
Hershey and Chase concluded
that the genetic material of the
bacteriophage was DNA.

The nucleic acid DNA stores
and transmits the genetic
information from one
generation of an organism to
the next.

DNA is a polymer made up of
monomers called nucleotides.
A nucleotide contains a five-carbon
sugar, a phosphate group, and a
nitrogenous base.

In DNA the sugar is deoxyribose.
DNA= deoxyribonucleic acid
In RNA the sugar is ribose.
RNA= ribonucleic acid

There are
four kinds
of bases in
in DNA:
•adenine
•guanine
•cytosine
•thymine

The backbone of a DNA chain is
formed by the sugar and phosphate
groups of each nucleotide.
The nucleotides can be joined together in any
order.

Chargaff's Rules
Erwin Chargaff discovered that:
•The percentages of guanine [G] and
cytosine [C] bases are almost equal in
any sample of DNA.
•The percentages of adenine [A] and
thymine [T] bases are almost equal in
any sample of DNA.

X-Ray Evidence
Rosalind Franklin used
X-ray diffraction to get
information about the
structure of DNA.
She aimed an X-ray
beam at concentrated
DNA samples and
recorded the scattering
pattern of the X-rays on
film.

Using clues from Franklin’s pattern,
James Watson and Francis Crick built a
model that explained how DNA carried
information and could be copied.
Watson and Crick's model of
DNA was a double helix, in
which two strands were wound
around each other.

DNA Double Helix

Watson and Crick discovered that hydrogen
bonds can form only between certain base
pairs—adenine and thymine, and guanine and
cytosine.
This principle is called base pairing.
adenine(A) pairs with thymine(T)
guanine(G) pairs with cytosine(C)

12–2 Chromosomes and DNA Replication
12-2 Chromosomes and DNA Replication

DNA and Chromosomes
• In prokaryotic cells, DNA is located in
the cytoplasm.
•Most prokaryotes have a single DNA
molecule containing nearly all of the
cell’s genetic information.

Chromosome
E. Coli Bacterium
Bases on the
Chromosomes

Many eukaryotes have 1000 times the
amount of DNA as prokaryotes.
Eukaryotic DNA is located in the
cell nucleus inside chromosomes.
The number of chromosomes varies widely
from one species to the next.

Eukaryotic chromosomes contain
DNA and protein, tightly packed
together to form chromatin.
•Chromatin consists of DNA tightly
coiled around proteins called
histones.
•DNA and histone molecules form
nucleosomes.
•Nucleosomes pack together, forming a
thick fiber.

Eukaryotic Chromosome Structure
Chromosome
Nucleosome
Coils
Supercoils
DNA
double
helix
Histones

DNA Replication
•Each strand of the DNA double helix has
all the information needed to
reconstruct the other half by the
mechanism of base pairing.
• In most prokaryotes, DNA replication
begins at a single point and continues in
two directions.

In eukaryotic chromosomes, DNA replication
occurs at hundreds of places. Replication
proceeds in both directions until each
chromosome is completely copied.
The sites where separation and replication
occur are called replication forks.

•Before a cell divides, its DNA is
duplicated in a process called
replication.
•Replication ensures that each resulting
cell will have a complete set of DNA.

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 for the
new strand.

New Strand Original strand
Growth
Growth
Nitrogen Bases
Replication Fork
Replication Fork
DNA Polymerase
Active Art

How Replication Occurs
•DNA replication is carried out by enzymes
that “unzip” a molecule of DNA.
•Hydrogen bonds between base pairs are
broken and the two strands of DNA
unwind.

The main enzyme involved in DNA
replication is DNA polymerase.
DNA polymerase joins individual
nucleotides and then “proofreads”
each new DNA strand.

12-3 RNA and Protein Synthesis 12–3 RNA and Protein Synthesis

Genes are coded DNA instructions
that control the production of
proteins.
Genetic messages can be decoded by copying part
of the nucleotide sequence from DNA into RNA.
RNA contains coded information for
making proteins.

The Structure of RNA
•RNA consists of a long chain of
nucleotides.
•Each nucleotide is made up of a 5-
carbon sugar, a phosphate group, and a
nitrogenous base.

There are three main differences
between RNA and DNA:
•The sugar in RNA is ribose
instead of deoxyribose.
•RNA is generally single-stranded.
•RNA contains uracil in place of
thymine.

There are three main types of RNA:
•messenger RNA
•ribosomal RNA
•transfer RNA

Messenger RNA (mRNA) carries
copies of instructions for assembling
amino acids into proteins.

Ribosome
Ribosomal RNA
Ribosomes are made up of proteins
and ribosomal RNA (rRNA).

Amino acid
Transfer RNA
During protein construction,
transfer RNA (tRNA) transfers
each amino acid to the ribosome.

•RNA molecules are produced by
copying part of a nucleotide sequence
of DNA into a complementary sequence
in RNA. This process is called
transcription.
•Transcription requires the enzyme RNA
polymerase.

During transcription, RNA
polymerase binds to DNA and
separates the DNA strands.
RNA polymerase then uses one
strand of DNA as a template to make
a strand of RNA.

RNA polymerase binds only to regions of
DNA known as promoters.
Promoters are signals in DNA that
tell RNA polymerase where to
bind, so it can start the
transcription of RNA.

Transcription
RNA
RNA polymerase
DNA

RNA Editing
•The DNA of eukaryotic genes contains
sequences of nucleotides, called
introns, that are not involved in coding
for proteins.
•The DNA sequences that code for
proteins are called exons.
•When RNA molecules are
formed, introns and exons are
copied from DNA.

The introns
are cut out of
RNA
molecules.
The exons are
the spliced
together to
form mRNA.
Exon Intron DNA
Pre-mRNA
mRNA
Cap Tail

The Genetic Code
•The genetic code is the “language” of
mRNA instructions.
•The genetic code is written
using four “letters” (the bases:
A, U, C, and G).

A codon consists of three
consecutive nucleotides on mRNA
that specify a particular amino acid.

•Each codon codes for a specific
amino acid.
•Some amino acids have more
than one codon.

The Genetic Code

•Codon AUG is the“start” codon
or it can specify the amino acid
methionine.
•There are three “stop” codons
that do not code for any amino
acid. These “stop” codons signify the
end of a polypeptide.

Translation is the decoding of
an mRNA message into a
polypeptide chain (protein).
Translation takes place on
ribosomes.
During translation, the cell uses
information from messenger RNA to
produce proteins.

Messenger RNA is transcribed and
introns are removed in the nucleus.
Then mRNA enters the cytoplasm
and attaches to a ribosome.
Nucleus
mRNA
Active Art

Translation begins when an mRNA molecule
attaches to a ribosome.
As each codon of the mRNA
molecule moves through the
ribosome, the proper amino acid is
brought in by tRNA.
In the ribosome, the amino acid is
transferred to the growing polypeptide chain.

Each tRNA molecule carries only
one kind of amino acid.
In addition to an amino acid, each tRNA
molecule has three unpaired bases, called
the anticodon.
The anticodon on tRNA is
complementary to one mRNA
codon.

The ribosome binds new tRNA molecules and
amino acids as it moves along the mRNA.
Phenylalanine tRNA Lysine
Methionine
Ribosome
mRNA Start codon

Protein Synthesis
tRNA
Ribosome
mRNA
Lysine
Translation direction

•The process continues until the ribosome
reaches a stop codon.
Polypeptide
Ribosome
tRNA
mRNA

The Roles of RNA and DNA
•The cell uses the DNA “master plan” to
prepare RNA “blueprints.” The DNA
stays in the nucleus.
•The RNA molecules go to the protein
building sites in the cytoplasm—the
ribosomes.

Genes and Proteins
•Genes contain instructions for
assembling proteins.
•Many proteins are enzymes, which
catalyze and regulate chemical
reactions.
• Proteins are each specifically designed
to build or operate a component of a
living cell.

The sequence
of bases in
DNA is used
as a template
for mRNA.
The codons of
mRNA specify
the sequence
of amino acids
in a protein.
Codon Codon Codon
Single strand of DNA
Codon Codon Codon
mRNA
Alanine Arginine Leucine
Amino acids within
a polypeptide

12-4 Mutations
12–4 Mutations

Mutations are changes in the
genetic material.

Kinds of Mutations
•Mutations that produce changes in a
single gene are known as gene
mutations.
•Mutations that produce changes in
whole chromosomes are known as
chromosomal mutations.

Gene Mutations
•Gene mutations involving a
change in one or a few
nucleotides are known as point
mutations because they occur at a
single point in the DNA sequence.
•Point mutations include substitutions,
insertions, and deletions.

Substitution–
Switching one
nucleotide for
another,
usually affects
only a single
amino acid.

The effects of insertions or deletions are
more dramatic.
The addition or deletion of a
nucleotide causes a shift in the
grouping of codons.
Changes like these are called frameshift
mutations.

Frameshift mutations may change
every amino acid that follows the
point of the mutation.
Frameshift mutations can alter a protein so
much that it is unable to perform its normal
functions.

Insertion-- An
extra base is
added, so the
reading frame
is shifted.

Deletion-- a single base is lost so
the reading frame is shifted.

Chromosomal Mutations
•Chromosomal mutations involve
changes in the number or
structure of chromosomes.
•Chromosomal mutations include
deletions, duplications, inversions, and
translocations.

Deletions involve the loss of all or
part of a chromosome.

•Duplications produce extra
copies of parts of a chromosome.

Inversions reverse the direction of
parts of chromosomes.

Translocations occurs when part
of one chromosome breaks off
and attaches to another.

Significance of Mutations
Many mutations have little or no effect on
gene expression.
•Some mutations are the cause of genetic
disorders.
•Beneficial mutations may produce
proteins with new or altered activities that
can be useful.

Polyploidy is the
condition in
which an
organism has
extra sets of
chromosomes.

12-5 Gene Regulation
Fruit fly chromosome
12-5 Gene Regulation
Fruit fly embryo
Adult fruit fly
Mouse chromosomes
Mouse embryo
Adult mouse

Gene Regulation: An Example
•E. coli provides an example of how gene
expression can be regulated.
•An operon is a group of genes that
operate together.
•In E. coli, the lac operon genes must
be turned on so the bacterium can
use lactose as food.

The lac genes are turned off by
repressors and turned on by
the presence of lactose.

On one side of the operon's three genes are
two regulatory regions.
• In the promoter (P) region, RNA polymerase
binds and then begins transcription.

•The other region is the operator (O).

When the lac repressor binds to
the O region, transcription is not
possible.

When lactose is added it binds to
the repressor proteins making
them fall off.

The repressor protein changes shape and
falls off the operator and transcription is
made possible.

Many genes are regulated by repressor
proteins.
Some genes use proteins that speed
transcription.
Sometimes regulation occurs at the level of
protein synthesis.

Eukaryotic Gene Regulation
Operons are generally not found in
eukaryotes.
Most eukaryotic genes are
controlled individually and have
regulatory sequences that are
much more complex than those
of the lac operon.

Many eukaryotic genes have a sequence
called the TATA box.
Promoter
sequences
Upstream
enhancer
TATA
box Introns
Exons
Direction of transcription

Eukaryotic Gene Regulation
The TATA box seems to help position RNA
polymerase.
Promoter
sequences
Upstream
enhancer
TATA
box
Introns
Exons

Eukaryotic promoters are usually found just
before the TATA box, and consist of short
DNA sequences.
Promoter
sequences
Upstream
enhancer
TATA
box
Introns
Exons

Genes are regulated in a variety of ways by
enhancer sequences.
Many proteins can bind to different
enhancer sequences.
Some DNA-binding proteins enhance
transcription by:
•opening up tightly packed chromatin
•helping to attract RNA polymerase
•blocking access to genes.

•As cells grow and divide, they
undergo differentiation, meaning
they become specialized in
structure and function.
•Hox genes control the
differentiation of cells and
tissues in the embryo.

Careful control of expression in hox genes
is essential for normal development.
All hox genes are descended from the
genes of common ancestors.

Development and Differentiation
Hox Genes
Fruit fly chromosome
Fruit fly embryo
Adult fruit fly
Mouse chromosomes
Mouse embryo
Adult mouse

12–1
Avery and other scientists discovered that
a. DNA is found in a protein coat.
b. DNA stores and transmits genetic
information from one generation to the
next.
c. transformation does not affect
bacteria.
d. proteins transmit genetic information from
one generation to the next.

12–1
The Hershey-Chase experiment was based on
the fact that
a. DNA has both sulfur and phosphorus in its
structure.
b. protein has both sulfur and phosphorus in
its structure.
c. both DNA and protein have no phosphorus
or sulfur in their structure.
d. DNA has phosphorus, while protein has
sulfur in its structure.

12–1
DNA is a long molecule made of monomers
called
a. nucleotides.
b. purines.
c. pyrimidines.
d. sugars.

12–1
Chargaff's rules state that the number of guanine
nucleotides must equal the number of
a. cytosine nucleotides.
b. adenine nucleotides.
c. thymine nucleotides.
d. thymine plus adenine nucleotides.

12–1
In DNA, the following base pairs occur:
a. A with C, and G with T.
b. A with T, and C with G.
c. A with G, and C with T.
d. A with T, and C with T.

12–2
In prokaryotic cells, DNA is found in the
a. cytoplasm.
b. nucleus.
c. ribosome.
d. cell membrane.

12–2
The first step in DNA replication is
a. producing two new strands.
b. separating the strands.
c. producing DNA polymerase.
d. correctly pairing bases.

12–2
A DNA molecule separates, and the sequence
GCGAATTCG occurs in one strand. What is the
base sequence on the other strand?
a. GCGAATTCG
b. CGCTTAAGC
c. TATCCGGAT
d. GATGGCCAG

12–2
In addition to carrying out the replication of DNA,
the enzyme DNA polymerase also functions to
a. unzip the DNA molecule.
b. regulate the time copying occurs in the cell
cycle.
c. “proofread” the new copies to minimize the
number of mistakes.
d. wrap the new strands onto histone
proteins.

12–2
The structure that may play a role in regulating
how genes are “read” to make a protein is the
a. coil.
b. histone.
c. nucleosome.
d. chromatin.

12–3
The role of a master plan in a building is similar
to the role of which molecule?
a. messenger RNA
b. DNA
c. transfer RNA
d. ribosomal RNA

12–3
A base that is present in RNA but NOT in DNA is
a. thymine.
b. uracil.
c. cytosine.
d. adenine.

12–3
The nucleic acid responsible for bringing
individual amino acids to the ribosome is
a. transfer RNA.
b. DNA.
c. messenger RNA.
d. ribosomal RNA.

12–3
A region of a DNA molecule that indicates to an
enzyme where to bind to make RNA is the
a. intron.
b. exon.
c. promoter.
d. codon.

12–3
A codon typically carries sufficient information to
specify a(an)
a. single base pair in RNA.
b. single amino acid.
c. entire protein.
d. single base pair in DNA.

12–4
A mutation in which all or part of a chromosome
is lost is called a(an)
a. duplication.
b. deletion.
c. inversion.
d. point mutation.

12–4
A mutation that affects every amino acid
following an insertion or deletion is called a(an)
a. frameshift mutation.
b. point mutation.
c. chromosomal mutation.
d. inversion.

12–4
A mutation in which a segment of a chromosome
is repeated is called a(an)
a. deletion.
b. inversion.
c. duplication.
d. point mutation.

12–4
The type of point mutation that usually affects
only a single amino acid is called
a. a deletion.
b. a frameshift mutation.
c. an insertion.
d. a substitution.

12–4
When two different chromosomes exchange
some of their material, the mutation is called
a(an)
a. inversion.
b. deletion.
c. substitution.
d. translocation.

12–5
Which sequence shows the typical organization
of a single gene site on a DNA strand?
a. start codon, regulatory site, promoter, stop
codon
b. regulatory site, promoter, start codon, stop
codon
c. start codon, promoter, regulatory site, stop
codon
d. promoter, regulatory site, start codon, stop
codon

12–5
A group of genes that operates together is a(an)
a. promoter.
b. operon.
c. operator.
d. intron.

12–5
Repressors function to
a. turn genes off.
b. produce lactose.
c. turn genes on.
d. slow cell division.

12–5
Which of the following is unique to the regulation
of eukaryotic genes?
a. promoter sequences
b. TATA box
c. different start codons
d. regulatory proteins

12–5
Organs and tissues that develop in various parts
of embryos are controlled by
a. regulation sites.
b. RNA polymerase.
c. hox genes.
d. DNA polymerase.

Chapter 12- DNA, RNA, and Proteins

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