Transcript 24.5 Nucleic Acids

24.5 Nucleic Acids >
Chapter 24
The Chemistry of Life
24.1 A Basis for Life
24.2 Carbohydrates
24.3 Amino Acids and Their Polymers
24.4 Lipids
24.5 Nucleic Acids
24.6 Metabolism
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24.5 Nucleic Acids >
CHEMISTRY
& YOU
Why do children often look similar to
their parents?
In this lesson, you
will learn about
molecules that are
involved in the
inheritance of
traits from parents.
2
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24.5 Nucleic Acids > DNA and RNA
DNA and RNA
What are the functions of DNA and
RNA?
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24.5 Nucleic Acids > DNA and RNA
More than 100 years ago, a Swiss
biochemist discovered a class of nitrogencontaining compounds in the nuclei of
cells.
• The eventual understanding of the biological
role of the compounds has led to a revolution
in biochemistry.
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24.5 Nucleic Acids > DNA and RNA
These nitrogen-containing compounds,
called nucleic acids, are polymers that
are found primarily in a cell’s nucleus.
• They are indispensable components of
every living thing.
• Two kinds of nucleic acid are in cells—
deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA).
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24.5 Nucleic Acids > DNA and RNA
DNA stores the information needed to
make proteins and governs the
reproduction and growth of cells and new
organisms.
RNA has a key role in the transmission of
the information stored in DNA and in the
synthesis of protein.
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24.5 Nucleic Acids > DNA and RNA
The monomers that make up the DNA
and RNA polymers are called
nucleotides.
• Nucleic acids are therefore
polynucleotides.
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24.5 Nucleic Acids > DNA and RNA
The monomers that make up the DNA
and RNA polymers are called
nucleotides.
• Nucleic acids are therefore
polynucleotides.
• Each nucleotide consists of a
phosphate group, a five-carbon
sugar, and a nitrogen-containing
unit called a nitrogen base.
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24.5 Nucleic Acids > DNA and RNA
There are four different nitrogen bases in
DNA—adenine, guanine, thymine, and
cytosine.
• These four bases are abbreviated A, G, T,
and C, respectively.
Adenine
A
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Guanine
G
Cytosine
C
Thymine (in DNA)
T
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24.5 Nucleic Acids > DNA and RNA
Ribose, which has one more oxygen than
deoxyribose, is the sugar found in the
nucleotide monomers of RNA.
• The base thymine is never found in RNA.
• Instead, it is replaced by a fifth nitrogen
base, called uracil, which is abbreviated U.
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24.5 Nucleic Acids > DNA and RNA
Chemists studying nucleic acids discovered
that the amount of adenine in DNA always
equals the amount of thymine (A = T).
• Similarly, the amount of guanine always equals
the amount of cytosine (G = C).
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24.5 Nucleic Acids > DNA and RNA
James Watson and Francis
Crick proposed that the
structure of DNA consists of
two polynucleotide chains
wrapped into a spiral shape.
• This spiral is the famous
double helix of DNA.
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24.5 Nucleic Acids > DNA and RNA
Every double-ringed base on
one strand must be paired
with a single-ringed base on
the opposing strand.
• The pairing of A with T and
G with C not only provides
the best possible fit; it also
allows the maximum number
of hydrogen bonds to form
between the opposing
bases.
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24.5 Nucleic Acids > DNA and RNA
The pairing of A and T and of G and C makes
for the most stable arrangement
in the double helix.
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24.5 Nucleic Acids >
In DNA, why is A always paired with
T and G with C?
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24.5 Nucleic Acids >
In DNA, why is A always paired with
T and G with C?
These pairings make for the most
stable arrangement of the double helix.
They provide the best fit and allow for
the maximum number of hydrogen
bonds.
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24.5 Nucleic Acids > The Genetic Code
The Genetic Code
How many bases of DNA are
required to specify one amino acid in
a peptide chain?
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24.5 Nucleic Acids > The Genetic Code
An organism contains many proteins that
are characteristic of that particular
organism.
• The proteins of earthworms are different from
the proteins of pine trees, which are different
from the proteins of humans.
• How do cells in a given kind of organism
know which proteins to make?
• Cells use instructions contained in the
organism’s DNA.
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24.5 Nucleic Acids > The Genetic Code
A gene is a segment of DNA that carries the
instructions for making one peptide chain.
• Thus, the products of genes are the peptides
and proteins found in an organism.
• You can think of DNA as a reference manual
that stores the instructions for building
proteins.
• The instructions are written in a simple
language that has 4 “letters”—the bases A, T,
G, and C.
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24.5 Nucleic Acids > The Genetic Code
Experimental data show that each “word” in
a DNA manual is exactly three letters in
length.
• Each three-letter base sequence, or triplet,
codes for one of the 20 common amino
acids.
• The code words are strung together in the
DNA molecule to form genes, which
specify the order of amino acids in
peptides and proteins.
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24.5 Nucleic Acids > The Genetic Code
Three bases of DNA arranged in a
specific sequence are required to
specify one amino acid in a peptide or
protein chain.
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24.5 Nucleic Acids >
Interpret Data
Some Three-Letter DNA Code Words for the Amino Acids
A
G
T
C
AAA Phe
AAG Phe
AGA Ser
AGG Ser
ATA Tyr
ATG Tyr
ACA Cys
ACG Cys
A
G
AAT Leu
AAC Leu
AGT Ser
AGC Ser
ATT End
ATC End
ACT End
ACC Trp
T
C
GAA Leu
GAG Leu
GGA Pro
GGG Pro
GTA His
GTG His
GCA Arg
GCG Arg
A
G
GAT Leu
GAC Leu
GGT Pro
GGC Pro
GTT Gln
GTC Gln
GCT Arg
GCC Arg
T
C
CAA Val
CAG Val
CGA Ala
CGG Ala
CTA Asp
CTG Asp
CCA Gly
CCG Gly
A
G
CAT Val
CAC Val
CGT Ala
CGC Ala
CTT Glu
CTC Glu
CCT Gly
CCC Gly
T
C
A
G
C
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Third Letter in Code Word
First Letter in Code Word
Second Letter in Code Word
24.5 Nucleic Acids > The Genetic Code
Note that most amino acids are specified
by more than one code word, but a code
word never specifies more than one amino
acid.
• One of the code words (TAC) signifies the
initiation of a peptide.
• Three code words (ATT, ATC, and ACT) are
reserved as end, or termination, code words.
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24.5 Nucleic Acids > The Genetic Code
The translation of a base sequence of DNA
in a gene into the amino acid sequence of
a peptide begins with the initiation code
word and runs continuously until a
termination code word is reached.
• The termination code word signals a stop to
the addition of amino acids in the production
of the peptide, similarly to what a period
does at the end of a sentence.
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24.5 Nucleic Acids > The Genetic Code
Even with only four bases, the number of possible
sequences of nucleotides in a DNA chain is
enormous.
• The sequence of the nitrogen bases A, T, G, and C in the
DNA of an organism constitutes the genetic plan, or
blueprint, for that organism.
• The genetic plan is inherited from parents and passed to
offspring.
• Differences in the number and sequence of the bases in
DNA ultimately are responsible for the great diversity of
living creatures found on Earth.
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24.5 Nucleic Acids >
CHEMISTRY
& YOU
Why do children often look similar to
their parents?
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24.5 Nucleic Acids >
CHEMISTRY
& YOU
Why do children often look similar to
their parents?
Children often look similar to their
parents because genes are responsible
for the traits that are expressed, and
parents pass their genes on to their
children.
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24.5 Nucleic Acids >
What DNA code words specify the amino
acid leucine (Leu)? What amino acids
does the code word GAG specify?
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24.5 Nucleic Acids >
What DNA code words specify the amino
acid leucine (Leu)? What amino acids
does the code word GAG specify?
AAT, AAC, GAA, GAG, GAT, and GAC
specify the amino acid leucine. GAG
specifies leucine only. It never specifies any
other amino acids.
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24.5 Nucleic Acids > Gene Mutations
Gene Mutations
What are gene mutations?
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24.5 Nucleic Acids > Gene Mutations
When a change occurs in a DNA code
word, the result is a mutation in the DNA.
Substitutions, additions, or deletions of one
or more nucleotides in the DNA molecule
are called gene mutations.
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24.5 Nucleic Acids > Gene Mutations
The effect of the deletion of a single base
from a gene can be illustrated by the
following analogy.
• Suppose a string of letters of the alphabet
goes as follows:
PATTHEREDCAT
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24.5 Nucleic Acids > Gene Mutations
• Suppose a string of letters of the alphabet
goes as follows:
PATTHEREDCAT
• The letters may not make sense at first
glance. However, if you separate them into
three-letter words, they form a perfectly
sensible statement:
PAT THE RED CAT
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24.5 Nucleic Acids > Gene Mutations
• Suppose a string of letters of the alphabet
goes as follows:
PATTHEREDCAT
• Now delete the first letter and again separate
the string into three-letter segments:
ATT HER EDC AT
• This last sequence is nonsensical.
• Similarly, the deletion of a base in the DNA
base sequence can turn the information into
nonsense.
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24.5 Nucleic Acids > Gene Mutations
Such mutations might result in the
production of a faulty protein or of no
protein at all.
• Diseases that result from gene mutations
are called genetic disorders.
• Thousands of genetic disorders have
been identified.
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24.5 Nucleic Acids > Gene Mutations
Galactosemia is an example of a genetic
disorder that affects about 1 in 55,000
newborn babies.
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• Galactosemia results from a mutation in an
enzyme called GALT (galactose-1phosphate uridyl transferase).
• GALT is needed to break down the sugar
galactose into glucose.
• Without normal GALT, galactose can build
up in the body and cause kidney failure, an
enlarged liver, cataracts, and brain
damage.
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24.5 Nucleic Acids > Gene Mutations
Persons with galactosemia cannot
complete the breakdown of lactose.
• The only treatment is to avoid
foods containing galactose, like
dairy and dried beans.
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24.5 Nucleic Acids > Gene Mutations
Not all gene mutations are harmful.
• Occasionally, a mutation can result in the
synthesis of a protein that is more
efficient than the version that previously
existed.
• Such a mutation could thus be beneficial
to the survival of the affected organism.
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24.5 Nucleic Acids >
Using the sequence PAT THE RED CAT as
the unmutated sequence, what mutations
have occurred in the following
sequences?
ATT HER EDC AT :
PAT THR RED CAT:
PAT STH ERE DCA T:
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24.5 Nucleic Acids >
Using the sequence PAT THE RED CAT as
the unmutated sequence, what mutations
have occurred in the following
sequences?
ATT HER EDC AT : deletion (of p from pat)
PAT THR RED CAT: substitution (of e from the)
PAT STH ERE DCA T: addition (of s after pat)
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24.5 Nucleic Acids > DNA Technologies
DNA Technologies
What are two examples of DNA
technologies used today?
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24.5 Nucleic Acids > DNA Technologies
DNA Typing
The sequences are similar for members
of the same family but are slightly
different for almost every individual.
• Identical twins look similar because they
have identical DNA.
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24.5 Nucleic Acids > DNA Technologies
DNA Typing
DNA typing uses the variation in the
DNA of individuals as a basis for
creating DNA profiles to identify a
person from samples of his or her hair,
skin cells, or body fluid.
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24.5 Nucleic Acids > DNA Technologies
DNA Typing
DNA typing uses the variation in the
DNA of individuals as a basis for
creating DNA profiles to identify a
person from samples of his or her hair,
skin cells, or body fluid.
• Because DNA sequences, like fingerprints,
are unique for each individual, DNA typing
has also been called DNA fingerprinting.
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24.5 Nucleic Acids > DNA Technologies
DNA Typing
To construct a DNA profile, scientists
first isolate the DNA in a sample.
• Only a tiny sample is needed.
• A sample can be anything that contains
DNA, including teeth, fingernails, blood,
hair, saliva, and skin cells.
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24.5 Nucleic Acids > DNA Technologies
DNA Typing
Samples can be typed in several different
ways, but the method used most commonly
is short tandem repeat (STR) analysis.
• A short tandem repeat is a short segment
of DNA that is repeated several times.
• For example, one region of the DNA used
by the FBI contains repeats of the
sequence AGAT.
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24.5 Nucleic Acids > DNA Technologies
DNA Typing
The DNA profile can then be compared
with a sample of DNA from a known
individual.
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24.5 Nucleic Acids > DNA Technologies
DNA Typing
The FBI has a technology system called
the Combined DNA Indexing Systems
(CODIS) that allows laboratories
throughout the country to share and search
DNA profiles.
• The chances of two people (except for
identical twins) having the same DNA profile
for these 13 regions is 1 in 1 billion.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Recombinant DNA technology
consists of methods for cleaving a
DNA chain, inserting a new piece of
DNA into the gap created by the
cleavage, and resealing the chain.
• The altered DNA formed by this
method is known as recombinant DNA.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
In this experiment, DNA from one organism is
inserted into the DNA of a different organism.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Applications in Medicine
The first practical application of recombinant
DNA technology was to insert the gene for
making human insulin into bacteria.
• Insufficient insulin production results in
diabetes.
• The symptoms of diabetes can often be
controlled by insulin injections.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Applications in Medicine
In the past, human insulin was not available
for this purpose. Pig insulin, which is quite
similar, was used as a substitute.
• Today, diabetic patients use the human form of
insulin produced by bacteria that have been
altered by recombinant DNA technology.
• Use of this insulin removes the need for the
potentially dangerous use of pig insulin.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Applications in Medicine
Other proteins produced by recombinant
DNA technology are used as medicinal
drugs.
• An enzyme called tissue plasminogen activator
(TPA) is used to dissolve blood clots in patients
who have suffered heart attacks.
• Interferon is thought to relieve or delay some of
the debilitating effects of multiple sclerosis.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Applications in Medicine
Recombinant DNA technology is also being
applied to the cure of genetic disorders in an
experimental treatment known as gene
therapy.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Applications in Agriculture
New recombinant DNA techniques can make
plants resistant to pests and weed killers and
produce fruits and vegetables that are better
suited for shipping and storage.
• The most common traits in genetically modified
crops are herbicide resistance and insect
resistance in corn, cotton, soybean, and canola.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Applications in Agriculture
Crops have also been genetically modified
for pharmaceutical purposes.
• These so-called pharma crops are genetically
modified to produce drugs to treat or prevent
diseases such as cancer or AIDS.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Applications in Agriculture
Genetically altered organisms have many
potential benefits, but some people have
concerns about their safety.
• There is also concern that genetically modified
crops could contaminate other crops if they are
grown and processed in close proximity to them.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Cloning
Ethical concerns were raised
in 1997 when Scottish
scientists announced the birth
of a lamb named Dolly.
• In normal animal reproduction,
an offspring is a genetic mixture of the
characteristics of both parents.
– Dolly was a clone—an offspring of a single individual.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Cloning
Polly and
Dolly had
no fathers.
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24.5 Nucleic Acids > DNA Technologies
Recombinant DNA Technology
Cloning
The birth of cloned animals has raised the
question of whether humans might
eventually be cloned.
• Many people are concerned about some of the
possible outcomes of cloning identical individuals.
• These situations are one aspect of more general
concerns about the uniqueness of life.
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24.5 Nucleic Acids >
Which of the following is not an
example of DNA technology?
A. Blood typing
B. DNA typing
C. Cloning
D. Genetically modified crops
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24.5 Nucleic Acids >
Which of the following is not an
example of DNA technology?
A. Blood typing
B. DNA typing
C. Cloning
D. Genetically modified crops
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24.5 Nucleic Acids > Key Concepts
DNA stores information needed to make
proteins and governs the reproduction
of cells. RNA transmits information
stored in DNA during protein synthesis.
A sequence of three bases of DNA is
required to specify one amino acid in a
peptide.
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24.5 Nucleic Acids > Key Concepts
Gene mutations occur when one or
more nucleotides in DNA are
substituted, added, or deleted.
Examples of DNA technology include
DNA typing, producing bacteria that
make human proteins, genetically
modifying foods and animals, and
cloning.
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24.5 Nucleic Acids > Glossary Terms
• nucleic acid: a polymer of ribonucleotides
(RNA) or deoxyribonuclotides (DNA) found
primarily in cell nuclei; nucleic acids play
an important role in the transmission of
hereditary characteristics, protein
synthesis, and the control of cell activities
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24.5 Nucleic Acids > Glossary Terms
• nucleotide: one of the monomers that
make up DNA and RNA; it consists of a
nitrogen-containing base (a purine or
pyrimidine), a sugar (ribose or
deoxyribose), and a phosphate group
• gene: a segment of DNA that codes for a
single peptide chain
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24.5 Nucleic Acids >
BIG IDEA
Chemistry as the Central Science
• Nucleic acids are polymers of
nucleotides.
• The nucleic acid DNA carries the
instructions for a cell.
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24.5 Nucleic Acids >
END OF 24.5
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