Download Unit 4 (ch 10)

Chapter 10
Molecular Biology of the Gene

http://www.pbs.org/wgbh/nova/body/cellula
r-factory.html
Information transfer is from
DNA  RNA  protein
Replication
 What is it?
Copying DNA for division
 Where does it occur? In the nucleus

REPLICATION
Information transfer is from
DNA  RNA  protein
Transcription
 What is it?
Making mRNA from DNA
 Where does it occur? In the nucleus

Information transfer is from
DNA  RNA  protein
Translation
 What is it?
Converting mRNA into a protein
 Where does it occur? In the cytoplasm, at a ribosome
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2.
DNA as source of genetic information
a. Hershey-Chase experiment showed DNA
rather than protein to be the genetic
material passed on from one generation
to the next
DNA
DNA
DNA
DNA
DNA
DNA
2.
DNA as source of genetic information
b. additional evidence – cell doubles DNA
prior to mitosis, and then splits the DNA
evenly among daughter cells
Watson and Crick
3.
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Molecular structure of DNA
a. Watson and Crick described the three
dimensional structure of DNA one year
after Hershey and Chase identified DNA
as the genetic material
3.
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Molecular structure of DNA
b. DNA, along with RNA, are nucleic
acids which are composed of nucleotides
c. Nucleotides consist of a sugar (ribose
or deoxyribose), a nitrogenous base (A,
G, C, T, or U), and a phosphate group
3.

Molecular structure of DNA
d. Structure of single DNA strand
 1. sugar-phosphate backbone
 2. bases covalently attached to sugar
and ‘hang off’ the side
3.

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
Molecular structure of DNA
e. double helical structure
1. double stranded
2. arranged in helix
3.

Molecular structure of DNA
3. hydrogen bonds
between nitrogenous
bases hold strands
together (remember,
hydrogen bonds are weak
chemical bonds)
3.
Molecular structure of DNA
4. the two strands of DNA run
“anti-parallel”; i.e., one strand
runs in 5’-3’ direction while
the other runs in the 3’-5’
direction The primed numbers
refer to the C of the sugar.
The bases are attached to the
1’ carbon and the phosphate
groups are attached at the 5’
sugars. Nucleotides form
covalent bonds between the
3’ carbon of one and the 5’
carbon of the other
nucleotide.
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VIDEO #49
4.
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
DNA replication
a. complementary base pairing governs how
new DNA molecules are synthesized using
existing DNA as templates (fig 10.4)
1. A with T
2. G with C
4.

DNA replication
b. DNA synthesis is semiconservative;
i.e., the two strands are separated and
each strand is used as a separate
template.
4.

DNA replication
c. DNA synthesis occurs along each of
the separated strands thus resulting in
two new double-stranded molecules of
DNA
4.

DNA replication
d. New nucleotides are added to a growing
strand of DNA one at a time, and this
energy-requiring reaction is catalyzed by an
enzyme, DNA polymerase
4.

DNA replication
e. The new strands are synthesized 5’-3’
and anti-parallel with the template
strands (10.5)
4.

DNA replication
f. The two new strands of DNA are
synthesized as the leading and lagging
strand
4.


DNA replication
g. process of replication
1. the enzyme helicase unwinds the
double stranded DNA, while single
stranded binding proteins stabilize the
templates
4.

DNA replication
2. primase adds RNA primers to the
exposed templates because DNA
polymerase must add new nucleotides to
a 3’ end of an existing nucleotide in an
already started strand
5’
3’
3’
5’
4.

DNA replication
3. DNA polymerase adds one nucleotide
at a time in the 5’ – 3’ direction along the
leading strand and lagging strand
(leading strand is synthesized
continuously while the lagging strand is
synthesized in Okazaki fragments)
4.


DNA replication
4. Another DNA polymerase replaces the
RNA primer
5. Ligase seals the Okazaki fragments
Video #50
1. Overview of protein synthesis
Process = DNA to RNA to protein
1. Overview of protein synthesis
Specific sequences of DNA in genes code
for specific sequences of RNA which in
turn code for specific sequences of
amino acids in proteins
1. Overview of protein synthesis
a.
compartmentalization
1.
2.
transcription in nucleus
translation (protein synthesis) in
cytoplasm
2. Genetic Code
a.
mRNA is read 3 nucleotides at a time;
i.e., one amino acid coded for by three
nucleotides
2. Genetic Code
b. each set of three nucleotides is referred to
as a codon
c. use genetic code of RNA codons to
predict amino acid sequence in
synthesized peptide
2. Genetic Code
c. use genetic code of RNA codons to predict
amino acid sequence in synthesized peptide
Using the Chart

CAU
• The codon CAU codes for His
3. Transcription
a.
Initiation- RNA polymerase binds to
promoter sequence of DNA, unwinds
DNA and starts transcription at start site
3. Transcription
ATG CAT GTC GAT CAC TAA AGT TTA
ATG CAT
AUG
CAUGTC
GUC GAT
GAUCAC
CACTAA
UAAAGT
AGUTTA
UUA
TAC GTA CAG CTA GTG ATT TCA AAT
b. Elongation – RNA polymerase makes
new strand of RNA in 5’ to 3’ direction;
i.e., it adds new nucleotides to the 3’ end
of the growing RNA strand, DNA reforms
double strand behind polymerase
3. Transcription
c. Termination – RNA polymerase reaches
a terminator sequence of DNA and
polymerase along with the newly
synthesized mRNA are released
3. Transcription
d. Eukaryotic RNA is processed in the
nucleus before final mRNA is sent to
cytoplasm
3. Transcription
e. One gene (DNA) is read at a time by
RNA polymerase in eukaryotes
(monocystronic)
3. Transcription
f. Multiple genes can be read at a time by
RNA polymerase in prokaryotes
(polycystronic)
4. Translation
a.
b.
synthesis of proteins using RNA as a
template
catalyzed by ribosomes in the cytoplasm
What Translation Looks Like
4. Translation
c. involves a variety of other players
1. t RNA transfer
2. m RNA messenger
3. r RNA ribosomal
5. tRNA
a.
b.
interpreters between nucleic acid
language and protein language; i.e.,
translation
single stranded nucleic acid made via
transcription just like mRNA
5. tRNA
c. 3’ end of tRNA binds amino acid
d. anticodon sequence of tRNA base pairs
with corresponding codon on mRNA;
therefore, anitcodon – codon binding
determines which amino acid is added to
the growing peptide
6. Ribosome (fig 10.12)
a.
b.
Catalyze protein synthesis
two ribosomal subunits;
large and small
6. Ribosome
c. mRNA binding site on small ribosomal
subunit
d. two tRNA binding sites known as P and
A on large ribosomal subunit
6. Ribosome (fig 10.12)
e. an anticodon of a tRNA binds to the
ribosome when its anticodon base pairs
with a mRNA codon present in that same
binding site
6. Ribosome (fig 10.12)
f. P site holds the tRNA attached to
growing peptide
g. A sites holds the tRNA attached to the
new (incoming) amino acid
What Translation Looks Like
7. Initiation of translation
a.
b.
small ribosomal subunit binds mRNA
a special initiator tRNA with anticodon
UAC binds to start codon AUG (this
tRNA carries amino acid methionine)
7. Initiation of translation
c. large ribosomal subunit binds with small
ribosomal subunit placing initiator tRNA
in P site and leaving A site empty for the
next tRNA to bind
8. Elongation of translation (fig
10.14)
a.
b.
c.
d.
an incoming tRNA/amino acid binds to
unoccupied A site
ribosome catalyzes formation of peptide bond
between new amino acid and growing peptide,
and the growing peptide is released from the
tRNA in the P site
tRNA in A site is translocated to P site, moving
the mRNA along with it a distance of 3
nucleotides; i.e., one codon
the mRNA moves along the ribosome one
codon at a time
9. Termination of translation
a.
b.
c.
d.
The A site of the ribosome reaches a
stop codon (UAA, UAG, or UGA) in the
mRNA molecule
a releasing factor binds to the stop codon
instead of another tRNA molecule
Releasing factor catalyzes release of
peptide from ribosome
Translation assembly falls apart and can
be used again
10. Overview of translation (fir
10.15)
a.
b.
c.
d.
e.
amino acids  polypeptide (protein)
mRNA carries the “message” of the genetic
code from the nucleus to the cytoplasm
tRNA/amino acid complex in cytoplasm
ribosome brings tRNA/amino acid to mRNA in
a particular order as dictated by mRNA
nucleotide sequence
ribosomes catalyze binding of amino acids into
polypeptide; i.e., formation of peptide bonds
Mutations
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Mutations are random changes in the DNA
sequence.
Gene mutations are relatively small affecting
only one or two genes.
Point mutations are caused by substitutions
and usually result in the change of one amino
acid, and causing no change about 30% of
the time.
Frameshift mutations are usually caused by a
deletion. The affect all of the codons that
follow the deletion. This will change many of
the amino acids in the protein molecule.
Substitution / Point Mutation
AUG CAU GUC GAU CAC UAA AGU UUA
AUG CAU GUC GGU CAC UAA AGU UUA
AUG CAU GUC GAU CAU UAA AGU UUA
AUG CAU GUC GAU CAC GAA AGU UUA
Deletion / Frameshift
AUG CAU GUC GAU CAC UAA AGU UUA
AUG CAU GUC GAU CAC UAA AGU UUA
AUG CAU GUC GUC ACU AAA GUU UAG
Protein Synthesis (Copy)
1st Step
Name of process
2nd step
Transcription
Translation
Nucleus
Cytoplasm
Enzymes or other
DNA, Helicase,
tRNA, amino acids,
substances required
RNA Polymerase
Ribosome
DNA
mRNA
mRNA,
Protein,
Replicated DNA
(polypeptides)
Location
What is read (goes in)
Is Produced