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“It is one of the most beautiful compensations of this life that no man
can sincerely try to help another without helping himself”
-Ralph Waldo Emerson
Transcription and Translation
Chapters 13, 14 and 15
DNA Structure
DNA Structure
DNA is comprised of nucleotides (adenine, cytosine, guanine, thymine)
that are connected by a sugar (deoxyribose) phosphate backbone.
Phosphate
group
Nitrogenous
Bases
Sugar
deoxyribose
adenine (A)
thymine (T)
Hydrogen
bonds
guanine (G)
cytosine (C)
DNA Replication
1. DNA to be replicated
2. Strands separate
3. Each strand now serves as a template
for the synthesis of a separate DNA
molecule as free nucleotides base-pair
with complementary nucleotides on
the existing strands.
Order of bases encodes
Information for protein
production.
4. This results in two
identical strands of DNA.
DNA Replication
DNA Replication Review
Differences between DNA and RNA
Deoxyribonucleic acid (DNA): primary
information bearing molecule in living things.


Codes for proteins
De-oxy = one less ________ on sugar (ribose)
Ribonucleic acid (RNA): transfers genetic
code from DNA in the nucleus to proteinforming system in the cytoplasm

Uracil instead of Thymine
Differences between DNA and RNA
RNA is single stranded and contains
_______ instead of thymine
DNA is double stranded (double helix)
and contains ________ instead of uracil
Protein Synthesis: Transcription and Translation
Transcription: process by which a
gene’s base sequence is ______ to mRNA
Translation: process by which mRNA
directs the production of a _________
Modified image from What is Life? A Guide to Biology, Third Edition
© 2015 W.H. Freeman and Company
Transcription and Translation
Transcription
1. In transcription, a section of DNA unwinds and
nucleotides on DNA form base pairs with nucleotides
of messenger RNA, creating an strand of mRNA.
2. This segment of mRNA then leaves the cell nucleus,
headed for a ribosome in the cell’s cytoplasm, where
translation takes place.
1
2
Translation
3. mRNA chain attaches to a ribosome, then transfer
RNA molecules transport amino acids to ribosome.
A chain of amino acids is linked together in the
order specified by the mRNA sequence.
4. When the amino acid chain is finished and
folded up, a protein is formed.
3
4
Transcription
RNA polymerase
1. _________________ unwinds a
region of the DNA double helix.
2. RNA polymerase begins assembling
RNA nucleotides on the DNA template.
3. The completed portion of the RNA
transcript separates from the DNA.
4. After the RNA transcript is released
from the DNA, and the DNA is
rewound into its original form.
Transcription is completed.
RNA Polymerase
RNA polymerase: enzyme
that unzips double stranded
DNA and synthesizes the
formation of mRNA
RNA nucleotides
RNA
polymerase
Direction of
transcription
Newly made RNA
Template
strand of DNA
Protein Synthesis
Codon = ____________
sequence of mRNA that
codes for a specific
amino acid
Codons and Amino Acids
 20
amino acids in humans
9
essential
 Multiple
codons code for
same amino acid
 Ex: Codons
UCU, UCC,
UCA, and UCG all code for
Serine
 Start
codon: AUG
 Amino
acid: Methionine
 Stop
codons: UAA, UAG,
and UGA
Modified image from What is Life? A Guide to Biology, Third Edition
© 2015 W.H. Freeman and Company
Check your Understanding
DNA sequence
mRNA sequence
Amino acid sequence
TA C A AT G C G A C G T G C
Check your Understanding
Translation
4. A polypeptide
chain is
produced.
Translation
Ribosomal RNA (rRNA):
organelle that translates mRNA
sequence by binding with tRNA with
appropriate anti-codon and building
polypeptide chain
 Large
and small sub-units
The “START sequence”
of the mRNA (signified by
sequence AUG) is
recognized by a
corresponding tRNA
molecule and the two
ribosomal subunits.
Large subunit
Small subunit
Three binding sites
A
site: site where ribosome
binds with tRNA
P
site: site where amino acids
are ________ together
E
site: site where tRNA
prepares for release from
ribosome
Modified image from What is Life? A Guide to Biology, Third Edition
© 2015 W.H. Freeman and Company
Transfer RNA
Transfer RNA (tRNA): Binds with
amino acids, then transfers amino
acids to ribosome for polypeptide
formation
Anti-codon = set of three
ribonucleotides complementary to a
specific mRNA codon sequence

Same as _____________ except for
uracil/thymine replacement
Image modified from What is Life? A Guide to Biology, Third Edition
© 2015 W.H. Freeman and Company
Review of RNA Types
Translation: Steps 1 and 2
 Step
1: mRNA strand binds with small
subunit of ribosome. mRNA codon
AUG signifies start point of
polypeptide sequence. tRNA with
Methionine (MET) amino acid (UAC
anti-codon) attaches to codon.
 Step
2: Large ribosomal subunit
connects with small subunit. Second
tRNA arrives with amino acid and
binds with A site within the ribosome
Large subunit
Translation: Steps 3 and 4
 Step
3: Amino acids bond together and
start to form the polypeptide chain.
tRNA molecules shift to the right
leaving A site vacant for next tRNA
molecule
 Step
4: tRNA molecule within E site is
released from the ribosome and a new
tRNA molecule carrying an amino acid
moves into the A site
Termination
Release factor binds to stop
codon (UAA, UAG, UGA),
and initiate hydrolysis the
bond to the polypeptide
Polypeptide is released
Ribosome subunits separate
Mass Production of Proteins

A single mRNA can be translated ____________ by multiple ribosomes
Check your Understanding
1. True or False: DNA replication and RNA synthesis both use the same
polymerase to copy the DNA
2. True or False: Transcription takes places in the nucleus, while translation
occurs in the cytoplasm
3. True or False: Transfer RNA (tRNA) carries the copied DNA out of the
nucleus where it binds with a ribosome
4. True or False: Different codons can code for the same amino acid
Check your Understanding
4. Which of the following contains the anti-codon?
a. Ribosomal RNA
b. Transfer RNA
c. DNA
d. Messenger RNA
Check your Understanding
5. At which of the following binding sites are the amino acids
linked together?
a. A-site
b. E-site
c. P-site
d. T-site
Check your Understanding
6. Which of the following codons would cause the production of
the polypeptide to be terminated?
a. AUG
b. UGA
c. UAG
d. UAA
e. All of the above are stop codons
Check your Understanding
7.Which of the following polypeptides would be made from the
sequence below?
DNA sequence: T A C A A G C G C T G A
a. Tyr-Lys-Arg-stop
b. Met-Phe-Gly-Gly
c. Tyr-Phe-Ala-Gly
d. Met-Phe-Ala-Thr
e. Ine-Edt-Ost-Udy
Check your Understanding
8. A DNA strand is reads A G T T C A . What are the corresponding
anti-codons associated with it?
a. A G T T C A
b. U C A A G U
c. A G U U C A
d. U G A A C U
Mutations
Mutation: a _________
change in the base
sequence of DNA


May result in production
of a nonfunctional protein
Completely ________
Starting DNA
Incorrect base pairing
Mutation
Point
mutation
Types of Mutations
Point mutation: occur when
one base pair in the DNA is
substituted for another, or
when one is inserted or
deleted.
Normal gene
mRNA
Protein
Met
Lys
Phe
Gly
Ala
Lys
Phe
Ser
Ala
Base substitution
Point
mutation
Met
Base deletion
Frame shift
mutation
Met
Missing
Lys
Leu
Ala
His
Different Types of Point Mutations
Name
Definition
Example
Consequence
Original DNA sequence
Original polypeptide
Silent
Missense
Change in nucleotide that
does not change amino acid
specified by codon
Change in nucleotide that
changes amino acid specified
by codon
Change in genetic code but
not the resulting protein
Change in primary structure
of protein
Nonsense
Change in nucleotide that
results in early stop codon
Premature termination,
incomplete polypeptide
Frameshift
Addition or deletion of
nucleotide
Reading frame is shifted,
massive missense
Sickle Cell Anemia
Sickle cell anemia: genetic
disorder caused by a single
point mutation that results in
a change in the structure of
hemoglobin
Gene Regulation
Gene regulation: control of gene
_____________ (protein production)

Self regulating

Proteins that regulate gene expression are
transcribed and translated
Three forms of gene regulation
Transcription factors
 Promoters and enhancers
2. Micro-RNAs
3. Alternative splicing
1.
Gene Regulation: Transcription Factors
Transcription factors:
proteins that either ________
________ the binding of RNA
polymerase to the template
DNA

Enhancer proteins can increase
rate of transcription
Gene Regulation: Micro-RNAs

Micro-RNAs _______ with mRNA


Slicer enzyme destroys mRNA
Others inhibit translation by locking
up mRNA before it comes in contact
with a ribosome
1. A length of micro-RNA
is transcribed from DNA.
2. Following processing,
the micro-RNA binds to
a protein complex in the
cytoplasm.
3. A messenger RNA (mRNA)
arrives at the micro-RNAprotein complex.
4. mRNA binds to the microRNA through base pairing.
5. The mRNA is cut in two by
the Slicer enzyme within
the protein complex.
Gene Regulation: Alternative Splicing
Introns: ___________ sequences

≈ 90% of gene length
Exons: sequence expressed as
proteins
Alternative slicing: a process of
editing a single primary transcript
in different ways to yield multiple
messenger RNAs
 Made possible by introns
Gene Regulation: Alternative Splicing
ATG TG G T TA AT T G C T TG C T TC C G G A C T TA A
Complementary
DNA Strand
TA C A C C A AT TA A C G A A C G A A G G C C TG A AT T
DNA Template for
RNA Synthesis
Transcription
Unprocessed RNA
Remove introns (bold bases) and splice the exons together before RNA leaves nucleus in the nucleus
Processed RNA in
the cytoplasm
Translation
Amino acid
sequence
Bioengineering
Bioengineering or Biotechnology = using technology to control
biological processes as a means of meeting societal needs

____________ organism = an organism whose genome has incorporated one
or more genes from another species

Genetically Modified Organism (GMO)
+
=
Overview of Bioengineering Process
1. Desired section of DNA is chopped
using ____________ enzymes
2. DNA fragments are amplified using
polymerase chain reaction (PCR)
3. DNA fragments are inserted into
__________ of bacteria or viruses
4. Bacteria or viruses containing
desired DNA replicate and grow
5. Bacteria or viruses with desired
DNA fragment are identified
Chopping of DNA
Restriction enzymes = enzymes from bacteria that are used to cut
DNA into desired fragments
Inserting the DNA
__________ = extra chromosomal
rings of bacterial DNA


Replicate independently of
chromosomes
Move into bacteria cells and
synthesize proteins
Multiplying the Desired DNA

Bacteria or viruses containing
desired DNA fragment multiply
very quickly increasing

Abundance of desired protein is
made by bacterial colony
Genetically Modified Organisms (GMOs)
Genetic engineering: the
manipulation of a species genome in
ways that do not normally occur in
nature
 __________ selection: intentional
reproduction of individuals in a
population with a desired trait
Creating Genetically Modified Organisms
Corn plant destroyed
by butterfly larvae
(caterpillars).
Bacterial gene coding for Bt
crystals, which are poisonous to
the caterpillars, is inserted directly
into the corn plant’s DNA.
Bt crystals—toxic to caterpillars—are now
produced by the corn plant itself and
present in all cells, reducing the amount of
pesticides the farmer must use.
Creating Genetically Modified Organisms

Genes from multiple organisms can
be combined to create a new variety

Golden rice: rice containing gene for
production of beta-carotene
 25 times more vitamin A!
Use of Genetically Modified Organisms (GMOs)
GMO vs non GMO
GMO Controversy

Organisms we want to kill may become
___________

Organisms we don’t want to kill may be
killed inadvertently

GMOs are not tested or regulated
adequately

Loss of _________________ among crops

Escape of GMO animals may impact
natural populations
Check your Understanding
1. True or False: All mutations result in an altered protein
2. True or False: All genes are constantly being transcribed and
translated
3. True or False: A majority of the corn, soybeans, and cotton
grown in the U.S has been genetically modified
Check your Understanding
4. Which of the following is not one of the forms of gene
regulation?
a. Micro-RNA
b. Transcription factors
c. Mutations
d. Alternative splicing
Check your Understanding
5. Which of the following mutations are the result of an addition
or deletion of a nucleotide?
a. Silent mutation
b. Missense mutation
c. Nonsense mutation
d. Frameshift mutation