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The Structure and Function of
DNA
Chapter 10
I. DNA: Structure and Replication
A. DNA and RNA Structure
• DNA=deoxyribonucleic acid
• RNA=ribonucleic acid
A. DNA and RNA Structure
• DNA and RNA are
nucleic acids, made
up of monomers
called nucleotides
• Each nucleotide
consists of 3
components: a
nitrogenous base, a
phosphate group, and
a sugar
A. DNA and RNA Structure
• The sugar in DNA is
deoxyribose
• The 4 bases in DNA
are: Thymine (T),
cytosine (C), adenine
(A), and guanine (G)
A. DNA and RNA Structure
• The sugar in RNA is
ribose
• The 4 bases in RNA
are: Uracil (U),
cytosine (C), adenine
(A), and guanine
(G)—the same as
DNA, except RNA has
uracil instead of
thymine
B. Watson and Crick: The double
helix
• Watson and Crick
proposed that DNA
molecules consisted of 2
individual polymers of
linked nucleotides in the
shape of a double helix
– In each strand the
phosphate of one
nucleotide bonds to the
sugar of the next
– The bases protrude from
the sugar-phosphate
backbone
B. Watson and Crick: The double
helix
• They also discovered that the nitrogenous bases
pair together between strands (like the rung of a
ladder) in a consistent pattern:
– In DNA, A-T, and C-G
– In RNA, A-U and C-G
B. Watson and Crick: The double
helix
• There are no restrictions on the order of
the nucleotides along the length of the
DNA strand, however
•DNA
•REPLICATION
C. DNA replication
• When a cell or whole organism
reproduces, a complete set of genetic
material must pass on from one
generation to the next
• For this to occur, there must be a means
of copying the instructions
• This is referred to as DNA replication
C. DNA replication
• Replication produces
2 identical double
helices which are
passed on to the
daughter cells
DNA Replication
• Base pairing is the
foundation for DNA
replication
• Recall: adenine on one
strand pairs to thymine on
the other, and cytosine on
one strand pairs with
guanine on the other
– ATG pairs with TAC
• Each strand has all the
information to construct
complementary strand
C. DNA replication
• DNA helicase pulls apart
parental DNA double helix at
the replication fork, forming
a replication bubble (next
slide)
• DNA polymerase moves
along each separated
parental DNA, matching
bases on the strand with
complementary free
nucleotides as well as
connects the nucleotide one
with each other to form the
new strand
C. DNA replication
C. DNA replication
• After replication parent
strand and daughter
stand wind together
• Process is called
semiconservative
replication because
result is a parental strand
with a newly formed
daughter strand
Checkpoint
• 1. Compare and contrast the chemical
components of DNA and RNA.
– Both are polymers of nucleotides. A
nucleotide consists of sugar + a nitrogenous
base + a phosphate group. In RNA, the sigar
is ribose; in DNA it is deoxyribose. Both DNA
and RNA have the bases A, G, and C; for a 4th
base, DNA has T and RNA has U
Checkpoint
• 2. Along one strand of a DNA double helix
is a nucleotide sequence GGCATAGGT.
What is the sequence of the other DNA
strand?
– CCGTATCCA
Checkpoint
• 3. How does complimentary base pairing
make the replication of DNA possible?
– When the 2 strands of the double helix
separate, each serves as a template on which
nucleotides can be arranged by specific base
pairing into new complimentary strands
Checkpoint
• 4. What is the function of DNA polymerase
in DNA replication?
– The enzyme covalently connects nucleotides
one at a time to on end of a growing daughter
strand as the nucleotides line up along a
template strand according to the base-pairing
rules
•The Flow of
Genetic
Information from
DNA to RNA to
II. The Flow of Genetic Information
from DNA to RNA to Protein
• What exactly are the instructions carried
by the DNA, and how are these
instructions carried out?
• This can be broken down into 2 stages:
TRANSCRIPTION (the transfer of genetic
info from DNA into an RNA molecule); and
TRANSLATION (the transfer of the info in
the RNA into a protein)
A. Transcription, a closer look:
From DNA to RNA
• Transcription is the transfer of genetic
information from DNA to RNA
A. Transcription: From DNA to RNA
• The DNA strands
separate (as in
replication)
• Only one strand serves
as a template
• The RNA bases then take
their appropriate place
along the DNA template
(A-U, C-G)
• The enzyme that links
these nucleotides is
called RNA polymerase
A. Transcription, a closer look:
From DNA to RNA
• The RNA strand that is synthesized on the
DNA template PEELS OFF the template,
and then goes on for TRANSLATION
A. Transcription, a closer look:
From DNA to RNA
• This RNA that is sent to the cytoplasm is
called messenger RNA, or mRNA
A. Transcription, a closer look:
From DNA to RNA
• 1. the RNA transcript
has a tail and a cap
added; this helps
keep the strand from
attack and helps
ribosomes recognize
the RNA
A. Transcription, a closer look:
From DNA to RNA
• 2. Introns—those
noncoding regions of
the RNA—are
removed
A. Transcription, a closer look:
From DNA to RNA
• 3. Exons—those
regions that code—
are spliced together
(called RNA splicing)
A. Transcription, a closer look:
From DNA to RNA
• 4. Now the RNA,
called mRNA, is sent
to the cytoplasm,
where the coding
sequence on the
mRNA is ready for
translation
B. TRANSLATION: the transfer of
the info in the RNA into a protein
• TRANSLATION is the 2nd step of the
process: the transfer of this information
into a protein
B. TRANSLATION (the transfer of
the info in the RNA into a protein)
• Remember that the RNA strand is made
up of a series of nucleotides, for example,
UUUAGACCG
B. TRANSLATION (the transfer of
the info in the RNA into a protein)
• The nucleotides actually exist as
TRIPLETS of bases/nucleotides called
codons
• ex. AAA, AGG, ATC
B. TRANSLATION (the transfer of
the info in the RNA into a protein)
• These codons each correspond to, or
code for, a specific amino acid
• This is called the GENETIC CODE
B. TRANSLATION (the transfer of
the info in the RNA into a protein)
• The GENETIC CODE
is a set of rules
relating nucleotide
sequence/codons to
amino acid sequence
B. TRANSLATION (the transfer of
the info in the RNA into a protein)
• Almost all of the genetic code is shared by
ALL organisms—from bacteria to plants to
animals: it is UNIVERSAL
B. TRANSLATION (the transfer of
the info in the RNA into a protein)
• In review:
– One DNA codon (three nucleotides)  one
RNA codon (three nucleotides)  one amino
acid
Checkpoint
• 2. How many nucleotides are necessary to
code for a polypeptide that is 100 amino
acids long?
– 300
Checkpoint
• 3. An RNA molecule contains the
nucleotide sequence CCAUUUACG.
Using the Genetic Code, translate this
sequence into corresponding amino acids
– Pro-Phe-Thr
B. TRANSLATION (the transfer of
the info in the RNA into a protein)
• There are 3 “players” in translation:
messenger RNA (mRNA), transfer RNA
(tRNA), and ribosomes
B. TRANSLATION (the transfer of
the info in the RNA into a protein)
• mRNA:
– This is produced first by transcription and sent
to the cytoplasm
– Next, it needs to be translated by tRNA and
ribosomes
B. TRANSLATION (the transfer of
the info in the RNA into a protein)
• tRNA:
– This RNA serves to translate, or convert, the 3 letter
words (codons) of nucleic acids to the one-letter,
amino acid words of proteins
– tRNA molecules match amino acids to the appropriate
codons to form the new polypeptides
– The anticodon is a special triplet of bases at one end
of the RNA. It recognizes a codon on the mRNA. At
the other end of the tRNA is a site where an amino
acid can attach
B. TRANSLATION (the transfer of
the info in the RNA into a protein)
• Ribosomes
– Ribosomes are the organelles that coordinate
the functioning of the mRNA and tRNA and
actually make polypeptides
– The ribosome connects the amino acids to the
growing polypeptide
II. Viruses: Genes in Packages
• A virus is a bit of nucleic acid with a
protein coat
• They can only survive by infecting a living
cell with genetic material, and therefore
making more viruses
A. Bacteriophages
• Bacteriophages are
viruses that infect
bacteria
• A bacteriophage
latches onto a
bacteria cell and
inserts its DNA into
the bacteria
• Then the bacteria go
to reproduce, all with
this viral DNA inside
B. Plant viruses
• Viruses that infect plant cells can stunt
plant growth and diminish crop yields
• Generally, a plant must be damaged for a
virus to enter
C. Animal viruses
• Viruses are common in animals
• Many viruses have RNA instead of DNA as
their genetic material
• RNA viruses include the common cold,
measles, mumps, and polio
• DNA viruses include hepatitis, chicken
pox, and herpes
D. HIV, the AIDS virus
• HIV is a retrovirus, an RNA virus that
reproduces by means of a DNA molecule;
that is, it synthesizes DNA on an RNA
template