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New Jersey Center for Teaching and Learning
Progressive Science Initiative
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AP BIOLOGY
GENES
September 2011
Henriquez, Lageman, Satterfield
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Genes Unit Topics
Click on the topic to go to that section
Discovery of DNA
· Discovery of DNA
· DNA Structure & Semi-Conservative Replication
· DNA Replication
· RNA Transcription
· Gene Expression, Central Dogma
· Three Types of RNA, Translation
· Article Discussion Day
Return to
Table of
Contents
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Deoxyribonucleic Acid
Recall that a DNA is a molecule that stores and
transmits genetic information.
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DNA
To understand the "secret of life" scientists had to figure out
the chemical and physical nature of the gene - the factor
passed from parent to offspring that directs the activity of the
cell and determines traits.
By applying basic principles of physics and chemistry and
keeping up on the latest discoveries of their time, a group of
remarkable scientists were able to determine the structure of
DNA.
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DNA and Modern Medicine
The discovery of the structure and function of DNA has led to
astounding leaps in understanding of biology, heredity, and
modern medicine.
"It's impossible to overstate the importance of knowing the
structure of DNA."
- Francis Collins, Director of the Human Genome Project
Click Here to see a
DNA timeline
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"Standing on the Shoulders of Giants"
The proof that DNA is the carrier of genetic information involved
a number of important historical experiments. These include:
Griffith Transformation Experiment
Avery-Macleod-McCarty Experiment
Hershy-Chase Experiment
Contributions of Watson, Crick, Wilkins, and Franklin
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Griffith's Colonies
Griffith and Transformation
In 1928 British Scientist Frederick Griffith was conducting
experiments with mice to determine how bacteria made
people sick.
One strain grew in rough colonies and did not cause disease.
The other strain grew in smooth colonies and caused disease.
Caused
disease
Griffith isolated two different strains of pneumonia bacteria
from mice and grew the bacteria on petri dishes in the lab.
Did not
cause
disease
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S strain
colonies
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Mouse Mortality
Mice and the 2 strains
When he injected the mice with the rough (R) strain, they lived.
When he injected the mice with the smooth (S) strain, they died.
However, when he heated the S strain of bacteria, killing
them, and then injected the heat-killed S strain bacteria into the
mice, they did not die.
R strain
colonies
Heating the S strain
killed the
bacteria and
prevented them
from passing
disease to the
mice.
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Griffith: Part 2
Griffith Experiment Part 2
Griffith then mixed heat-killed disease-causing S strain
bacteria with live, harmless R strain bacteria and injected this
mixture into mice.
Before neither heat-killed S strain or live R strain bacteria
made the mice sick, but the mixture of the two caused the
mice to develop pneumonia and die.
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What was the chemical factor?
What was in the mice lungs?
Griffith examined the lungs of mice that had been infected
with the mixture of dead S strain and live R strain bacteria
and found them filled with disease-causing bacteria.
This indicated that a chemical factor was transferred from the
dead S strain bacteria to the live R strain bacteria that
transformed them into disease-causing bacteria.
He also noted
this factor
was passed
on as the
bacteria
reproduced.
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1 What is bacterial transformation?
A The inheritance of genetic material
B
The exchange of genetic material between
strains of bacteria
C The interaction between strains of bacteria
D
The passage of genetic material from parent
to offpsring
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2 Why was Griffith's experiment significant?
A
It showed that a chemical factor transformed
R strain bacteria into S strain bacteria
B
It proved dead bacteria could still transmit
disease directly to mice
C
It indicated proteins were the source of
genetic material
D None of the above
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Avery's Experiment
Avery, Macleod, MacCarty
Oswald Avery, Colin MacLeod, and Maclyn McCarty were the
first to demonstrate that DNA was the substance that caused
bacterial transformation. Avery's group built on Griffith's work
to determine which chemical was responsible for transforming
the R strain bacteria.
In the 1930s and 1940s, at the
Rockefeller Institute for Medical
Research in New York City, Avery
and his colleagues suggested that
DNA, rather than protein as was
believed at the time, was the
hereditary material in bacteria.
First they repeated Griffith's experiment by mixing heat-killed S
strain and R strain bacteria and verifying transformation
occurred.Then they lysed the S cells by adding detergent.
Detergent disrupts the cell membrane and cell wall, causing the
DNA, RNA, proteins and other molecules to spill out.
They mixed the S lysate
with R strain bacteria and
determined that the
contents of cell parts in the
S lysate still allowed
transformation to occur.
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Their Three Mixtures
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3 What does the enzyme RNase do?
Next they mixed heat-killed S strain lysis containing DNA,
RNA, and Protein with R strain bacteria and allocated the
mixture into three test tubes:
A
Breaks down RNA molecules
B
Synthesizes RNA molecules
To tube A they added DNase - an
enzyme that destroys DNA molecules.
C Breaks down proteins
To tube B they added RNase.
D Synthesizes proteins
To tube C they added Protease.
Finally, they injected each mixture
into the mice and waited for results.
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4 If DNA were the molecule being transferred from dead
S strain bacteria to live R strain bacteria, then the mice
injected with DNase treated bacteria would most likely
A
Survive
B Die
C Remain unaffected
D Pass on pneumonia to their offspring
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Avery's Results
The results of the experiment
showed that the mice injected with
both the RNase and Protease
treated bacterial cells died.
However, the mice injected with
the DNase treated bacterial cells
survived.
*Destroying the DNA prevented
transformation of R strain
bacteria.
Lysate
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Hershey and Chase
5 What did Avery's experiment prove?
A
Bacteria can exchange genetic information
B
DNA is the molecule that causes bacterial
transformation
C
RNA and Proteins are the molecules responsible for
transferring genetic information
D
DNase breaks down DNA molecules
Alfred Hershey and Martha Chase conducted a series of
experiments helping to confirm that DNA was the genetic
material in cells.
Hershey and Chase showed that
when viruses (made of proteins
and DNA) infect bacteria, their
DNA enters the host cell but most
of their proteins do not.
Hershey shared the 1969 Nobel
Prize in Physiology for his work
involving the genetic nature of
viruses.
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The Hershey Chase Experment
6 What would you expect to see if protein had been
injected into the cell instead?
A Red-labeled cells
B
Green-labeled cells
C Cells containing phosphorous
D Cells containing oxygen
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DNA Structure & SemiConservative Replication
Structure of DNA
In 1962, the Nobel Prize in Physiology and Medicine was
awarded to James Watson, Francis Crick, and Maurice
Wilkins for their determination of the structure of DNA in 1953.
Unfortunately, the rules of the prize
award state it can only go to the
living. This meant Wilkin's colleague
Rosalind Franklin who collected all
the data they used could not receive
honor.
Return to
Table of
Contents
Franklin died at the age of 37 in 1958
from ovarian cancer which is thought
to be the result of her work with X-ray
radiation incurred while doing the
research.
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X-ray Crystallography
Using information from the work of Wilkins and Franklin,
James Watson and Francis Crick were the first to propose the
double helical nature of DNA.
Franklin and Wilkins used a technique
called X-ray crystallography to
discover more information about the
structure of DNA.
X-ray crystallography is a method of
determining the arrangements of
atoms within a crystal. When X-rays (a
type of electromagnetic wave) strike a
crystal, they diffract around electrons.
The angles and intensities of diffracted
beams can be used to determine the
position of atoms and chemical bonds.
Watson and Crick's Double Helix
Francis Crick is also well known
for coining the term "central
dogma" regarding the flow of
genetic information from DNA to
RNA to protein.
This diffraction pattern
indicated the double
helical shape of DNA
The day they discovered the helix
in 1953, they are said to have left
their lab, walked into a pub in
Cambridge, England and
interrupted the patrons' lunchtime
shouting "we have discovered
the secret to life!"
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Double Helix
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7 The scientists associated with the discovery of the structure of
DNA were:
A
Hershey and Chase
B
Watson, Crick, Wilkins, and Franklin
C
Avery, MacLeod, and McCarty
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8 These scientists showed that DNA was at the root of bacterial
transformation.
A Hershey and Chase
B
Watson, Crick, Wilkins, and Franklin
C Avery, MacLeod, and McCarty
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9 Four of the following terms all involve the experiment of Hershey
and Chase. Choose the one which does not belong.
A
helix structure
B DNA
C virus
D host
E bacteriophage
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DNA
DNA
DNA is made up of two chains of repeating nucleotides.
1 Nucleotide
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Deoxyribonucleic Acid
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10 If one strand of DNA is CGGTAC, the complementary strand
would be:
A
DNA is a good archive for
genetic information since
the bases are protected on
the inside of the helix.
GCCTAG
B CGGTAC
C TAACGT
D GCCATG
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11 Four of the following are associated with DNA. Choose
the one which is not.
A uracil
B
thyamine
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12 If one strand of DNA is AGCTGA, the complementary strand
would be:
A
TCGACU
B TCGACT
C adenine
C AGCTGA
D guanine
D AGTCGA
E cytosine
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Replication
Replication
The functions of a cell are determined by its DNA.
Consider these three facts:
Cells have to reproduce many times. In complex organisms,
trillions of copies are made from one original cell.
· Each individual strand of DNA is held together by strong
covalent bonds.
But when cells reproduce, their DNA has to reproduce as
well.
· The two strands are held to one another by weaker hydrogen
bonds.
The structure of DNA reveals how trillions of copies of the
DNA in one of your cells can be made, and be nearly
identical each time.
· Each base (ACGT) attracts only its complementary base
(TGCA)
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DNA Molecule as Template
Each molecule of DNA is made
of a template strand and a new
strand.
Replication
template
strand
The template is used to make
the new strand.
The template strand is also
known as the parent strand
since it came from the original
DNA molecule.
The new strand is also known
as the daughter strand.
DNA nucleotide monomers are made ahead of time and stored in
the cell.
When it is time for the DNA to replicate itself, the nucleotides are
ready to be added to the new growing strand of DNA.
DNA polymerase is the
enzyme responsible for
adding each new nucleotide
to the growing strand.
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Replication
DNA is anti-parallel. Each strand has two ends: a 5' end and a 3'
end. Nucleotides can only be added to the -OH end (3`), not the 5`
so all strands grow from the 5' end to the 3' end.
Each molecule of
DNA is made of
one "old" and one
"new" strand.
The "old" strand is
used as a template
to make the "new"
strand.
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Semi-Conservative DNA Replication
The template strands
of the DNA molecule
separate and the new
strands are made on
the inside.
The new strands
are made in the 5' 3' direction.
The result of this process is 2 new DNA molecules
each having an old template strand and new strand.
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Semi-Conservative DNA Replication
Semi-Conservative Replication
DNA replication is said to be a Semi-Conservative process. This
means that the template DNA strand is partially saved and reused
throughout the process.
Two parent strands
The base sequence on the template strand will allow for the
creation of the base sequence on the new strand.
One parent and
one daughter
strand
One parent and
one daughter
strand
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15 If the parent DNA strand is 5' ATCGATACTAC 3', what will the
daughter stand be
5'
5'
______________________
3'
template strand
new strand
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14 Why does a DNA strand only "grow" in the 5' to 3' direction?
True
False
ATCGGGTTAACGCGTAAA
What is the sequence of
the new strand?
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13 The 3' end of a DNA strand has a phosphate at the end.
3'
A
because DNA can only add nucleotides to the 3'
end of the molecule
B
because DNA can only add nucleotides to the 5'
end of the molecule
C
because mRNA can only read a DNA molecule
from 5' to 3'
D
because mRNA can only read a DNA molecule
from 3' to 5'
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16 "Semi-conservative" means:
A the DNA is used slowly
A
5' TAGCTATGATG 3'
B the DNA is sometimes reused
B 3' ATCGATACTAC 5'
C the DNA is partially saved and reused in the process
C 5' UAGCUAUGAUG 3'
D only part of the DNA is used
D 3' TAGCTATGATG 5'
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17 Which of the following is a nucleotide unit found in DNA?
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DNA Replication
A ribose + phosphate + thymine
B deoxyribose + phosphate + uracil
C deoxyribose + phosphate + cytosine
D ribose + phosphate + uracil
Return to
Table of
Contents
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DNA Replication In-Depth
In order for DNA replication to occur, DNA strands, which are
naturally twisted in the shape of a double helix, must be
relaxed, unwound, and opened-up to allow each strand to be
copied. Then nucleotides must be added to each strand.
DNA Replication In-Depth
Topoisomerase binds to the DNA strand and cuts the
double helix, causing the molecule to untwist and relax.
Many enzymes are involved in this process.
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DNA Replication In-Depth
Helicase breaks
hydrogen bonds
between nucleotide
base pairs causing the
two strands to
separate and form a
replication fork.
Small proteins called
single-stranded
binding proteins
stabilize each strand.
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18 Which enzyme causes the double helix to unwind by
breaking hydrogen bonds?
A Topoisomerase
B
Helicase
C Polymerase
D RNAse
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DNA Replication In-Depth
DNA Replication In-Depth
Recall in a DNA molecule, DNA strands are antiparallel, meaning
that one strand runs from the 3' OH group at one end of the
molecule to 5' phosphate group at the other end of the molecule.
The other strand runs in the opposite direction from 5' to 3'.
At the replication fork, the new strand added in the 5' to 3'
direction is referred to as the leading strand. The new strand
added in the 3' to 5' direction is called the lagging strand.
On the leading strand, new complementary nucleotides are
added continuously by the enzyme DNA polymerase.
*DNA polymerase can only add nucleotides to the 3' end of a
parent strand, so the leading strand elongates toward the
replication fork in the 5' to 3' direction.
3'
5'
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19 DNA Polymerase adds nucleotides in which direction?
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DNA Replication In-Depth
The lagging strand elongates away from the replication fork.
A 3' to 5'
DNA polymerase cannot add nucleotides to the end of this
parent strand continuously, and the process of adding
nucleotides discontinuously becomes a bit more complicated.
B 5' to 3'
C 3' to 5' and 5' to 3'
D 5' to 5'
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DNA Replication In-Depth
DNA Replication In-Depth
First an enzyme called DNA primase synthesizes a short RNA
primer - a complimentary sequence of RNA that binds to the
DNA on the lagging strand.
The RNA primer allows DNA polymerase to bind and add short
segments of nucleotides called Okazaki fragments. Okazaki
fragments are between 100-200 nucleotides long in eukaryotes
and about 1000-2000 nucleotides long in prokaryotes.
5'
3'
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DNA Replication In-Depth
The short Okazaki fragments are joined together by the enzyme
DNA ligase to produce a continuous strand.
20 In this diagram, the highlighted arrows are pointing to
A The leading strand
B
DNA Polymerase
C Okazaki Fragments
D DNA Ligase
5'
3'
Click Here for
Animation
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21 The green dot represents which enzyme?
A
Helicase
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22 The highlighted arrow is pointing to the
A Parent strand
Leading strand
B Ligase
B
C DNA Primase
C Lagging strand
D DNA Polymerase
D Okazaki fragment
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23 The highlighted arrow is pointing to the
A
Lagging strand
B
Leading strand
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DNA Replication In-Depth
Lagging and leading strands grow simultaneously resulting in
the formation of two new DNA molecules.
C Replication fork
D Replication bubble
Click Here for
Animation
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DNA Replication In-Depth
Write the name of the enzyme that matches the description.
Cuts double helix to
prepare for replication
Breaks H bonds,
unwinding DNA strands
Adds nucleotides to
parent strand
Synthesizes RNA
Primer
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DNA Replication In-Depth
DNA replication begins at specific sites on a chromosome
called origins of replication and can occur at many different
places on a chromosome simultaneously.
Short pieces of nucleotides
added to lagging strand
Brings together
Okazaki fragments
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24 DNA replication is initiated at
A
The origin of replication
B
One site at a time
Click Here for
Animation
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RNA Transcription
C The edges of a chromosome
D The lagging strand
Return to
Table of
Contents
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RNA
DNA to RNA
We stated earlier in this chapter that the functions of a cell
are determined by DNA, and this is true.
But DNA cannot function by itself...it needs the help of RNA.
RNA is essential for bringing the genetic
information stored in the DNA to where it
can be used in the cell.
Recall that RNA is made up of a sugar molecule
and phosphate group "backbone" and a
sequence of nitrogen bases:
Adenine (A)
Uracil (U)
Guanine (G)
Citosine (C)
These bases hydrogen bond in pairs: A bonds to U and G bonds to C.
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Transcription
25 RNA is more stable than DNA.
True
Transcription is the process by which RNA strands are
synthesized from DNA strands. This is the first step in the
transport of the genetic information contained in DNA.
False
The process of making RNA from DNA is called transcription
because the DNA sequence of nucleotides is being rewritten
into the RNA sequence of nucleotides, which differ only
slightly. The process of transcription is very similar to that of
DNA replication.
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Transcription
Transcription: DNA Strands
In DNA replication both strands are used as templates.
One of the DNA strands has the code for the protein that will
be made from RNA; that code is called the gene.
Which DNA strand is used to make RNA?
The strand with the genes is called the "non-template
strand." This IS NOT the strand that is transcribed.
The other strand is the mirror image of the first, it carries the
mirror image of the gene, not the gene itself. It is called the
"template strand." This IS the strand that gets transcribed
into RNA.
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Transcription: DNA Strands
DNA Strands
This makes sense in that the RNA will be the mirror image
of the DNA it is transcribed from. And the non-coding strand
is the mirror image of the gene.
template strand
non-template strand of DNA
template strand of DNA
transcription of template strand
RNA
Note:
the non-template strand of DNA (the gene)
matches the new RNA strand
non-template strand
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Transcription
Transcription
Transcription is made possible by the fact that the different bases
are attracted to one another in pairs.
Transcription proceeds along the
DNA molecule, coding an RNA
molecule. The RNA molecule is
always made from the end with a
phosphate group towards the end
with a hydroxyl group.
RNA
Just like in DNA replication, RNA is made from the 5'
end to the 3' end.
DNA
A
bonds with
T
U
bonds with
A
G
bonds with
C
C
bonds with
G
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Replication vs Transcription
DNA Replication
Transcription
Two new double-stranded One new single-stranded
DNA are produced
RNA is produced
Adenine from the parent
Adenine on the DNA
strand bonds with thymine
strand bonds with uracil on
on the new daughter
the new RNA strand.
strand of DNA
The whole DNA molecule
is replicated
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26 What was the first genetic storage molecule?
A DNA
B protein
C RNA
D
amino acid
Only the strand with the
code for the gene is
transcribed.
Synthesis of both occur in the 5' to 3' direction
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27 What molecule is now used to store genetic information?
A
DNA
B
protein
C
RNA
D
amino acid
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28 The strand that is transcribed into RNA is called the
A
Template Strand
B
Non Template Strand
C
RNA Strand
D
Amino Acid Strand
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29 The strand that is NOT transcribed into RNA is called the
30 Genes are located on the
A
Template Strand
A
Template Strand
B
Non Template Strand
B
Non Template Strand
C
RNA Strand
C
RNA Strand
D
Amino Acid Strand
D
Amino Acid Strand
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Step 1 - Initiation
Steps of Transcription
An enzyme called RNA Polymerase attaches to the promoter
sequence on the DNA. The Promoter is a specific sequence
of bases that the RNA polymerase recognizes.
Initiation
Elongation
Termination
olymerase
NonTemplate
Promotor
Region
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Step 3 - Termination
Step 2- Elongation
RNA Polymerase synthesizes the new RNA by moving down
the DNA template strand reading the bases and bringing in the
new RNA nucleotides with the proper complementary bases.
RNA Polymerase gets to a sequence on the DNA called a
Termination Sequence. This sequence signals the RNA
Polymerase to STOP transcription.
As the RNA Polymerase runs down the DNA, it actually
unwinds the DNA!
NonTemplate
new
mRNA
olymerase
NonTemplate
Termination
Sequence
The RNA Polymerase falls off the DNA. The new RNA strand
separates from the DNA and the DNA recoils into a helix.
Click Here to
see an animation
of Transcription
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31 The transfer of genetic material from DNA to RNA is called:
A
32 What is the function of the promoter sequence on the DNA?
A
translation
it is where the RNA polymerase recognizes and binds
to initiate transcription
B it is where the RNA gets copied
B transcription
C elongation
C
it is where the RNA polymerase binds to on the 5' end
of the DNA initiating transcription
D promotion
D
it is where the RNA polymerase binds to on the 3' end
of the DNA initiating transcription
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33 If the template strand of DNA is 5' ATAGATACCATG 3', which is
the RNA strand produced from transcription
34 If the non-template strand of DNA is 3' ACGATTACT 5', which is
the RNA strand produced through transcription
A 5' UAUCUAUGGUAC 3'
A
B 5' TATCTATGGTAC 3'
B 3' UGCUAAUGA 5'
C 3' UAUCUAUGGUAC 5'
C 5' UGCUAAUGA 3'
D 3' TATCTATGGTAC 5'
D 5' ACGAUUAGU 3'
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3' TGCTAATGA 5'
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Gene Expression,
Central Dogma
Evolution
Remember that back in time, the functions performed directly by
RNA were taken over by proteins.
The shapes of proteins are determined by the sequence of their
amino acids. Proteins must be coded with the correct sequence
of amino acids to have the right shape.
Return to
Table of
Contents
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Transcription and Genes
Transcription and Genes
The first step in specifying the amino acids to create a protein is
to transcribe the DNA code into RNA code.
Each DNA molecule is very long, and contains codes for a very
large number of proteins. The code for a single protein is
transcribed into a single strand of mRNA or messenger RNA.
The DNA code necessary to specify a single protein is called a
gene.
The gene is coded, on the DNA, with the bases A,T,C and G.
Transcribing that code into a strand of mRNA requires
converting that DNA code into RNA code with the bases
A,U,C and G. It also requires knowing where each gene
starts and stops on those very long DNA molecules.
This process is the beginning of gene expression.
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Gene Expression
Gene expression is the process of taking the code in the
nucleic acid and making into the protein.
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36 What is meant by "gene expression"?
A
making the protein or RNA coded in the nucleic acid
B
making amino acids so they can be made into protein
C
making tRNA only
D
folding of the protein
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35 What is a gene?
A
segment on the amino acid
B
segment on the protein
C
segment on the DNA that codes for a protein or RNA
D
segment on the RNA that codes for codons
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DNA to RNA to Protein
Expressing the information stored on a gene into a protein
requires translating:
· First from the 4 letter language of DNA to RNA
· Then from the 4 letter language of RNA to the 20 letter
language of proteins.
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Codons
The Universal Genetic Code
If one letter in the DNA codes one amino acid, there'd be 16
amino acids that couldn't be specified, since DNA only uses 4
letters.
If a 2 letter code were used, we could specify up to 16 different
amino acids (4 x 4); we'd still be short.
A codon is a 3 base sequence on either
DNA or mRNA that "codes" for an amino
acid.
So, each amino acid is specified by a 3 letter DNA code; this 3
letter code is called a codon.
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Codons
There are two main roles for the additional codons:
punctuation and protection.
Codons specify instructions for transcribing from DNA to RNA.
For example, the beginning and end of each gene on a strand
of DNA are specified by codons. Since there are hundreds of
genes on each DNA strand, punctuation is essential.
While a codon can only
specify a single amino acid,
there is more than one
codon that can specify that
amino acid.
Redundant Genetic Code
The Universal Genetic Code
This is called a "universal" code because ALL LIFE uses the
same genetic code... If there were alternative codes that could
work, they would have appeared in nature.
This tells us that this code goes back billions of years,
beyond LUCA in the first cell... even before that.
While we speak of the translation of these codes from those
used in DNA, mRNA and proteins; recognize that these
translations occur due to very basic properties of the nucleotides
and amino acids.
All 4 codons above code for the
same amino acid - Leucine.
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The 64 Codons
61 of the codons code for an amino acid
1 codon that codes for the
amino acid methionine is also
the START codon. This codon
signals the beginning of the
translation process.
3 of the remaining codons are
STOP codons that do not
code for an amino acid. They
just signal that translation is
over.
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37 Each nucleotide triplet in mRNA that specifies an amino
acid is called a(n)?
A
mutagen
B
codon
C anticodon
D intron
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38 The codon UAG specifies:
39 The codon GUG specifies:
A Adenine
A Adenine
B Glycine (Gly)
B Glycine
C STOP
C STOP
Second Position
D Arginine
D Arginine
E Valine
E Valine
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40 The codon GAG specifies:
41 Which of the following amino acid sequences corresponds to this
mRNA strand? CUCAAGUGCUUC
A Adenine
B Glycine
A
ser-tyr-arg-gly
C STOP
B
val-asp-pro-his
D Arginine
C leu-lys-cys-phe
E
Second Position
D pro-glu-leu-val
Aspartic Acid
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The Central Dogma of Biology
To be used by the cell the DNA
information must be transcribed
into mRNA strands; then it can be
translated into proteins.
DNA
RNA
Protein
(Francis Crick)
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42 Which one of the following sequences best describes the flow of
information when a gene directs synthesis of a cellular
component?
A
43 The transfer of genetic material from DNA to RNA is called:
A
RNA to DNA to RNA to Protein
translation
B transcription
B DNA to RNA to Protein
C elongation
C Protein to RNA to DNA
D promotion
D DNA to Amino Acid to RNA to Protein
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Three Types of RNA,
Translation
Three Types of RNA
mRNA or messenger RNA : carries the information for
protein synthesis. This type of RNA is key to The Central
Dogma.
rRNA or ribosomal RNA : a catalyst for protein synthesis
tRNA or transfer RNA : helps in the assembly of amino
acids during protein synthesis
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tRNA
Messenger RNA (mRNA)
The specific RNA that transcribes information from DNA
is called Messenger RNA (mRNA); it carries the genetic
message to ribosomes, where it is translated.
transcription
DNA
mRNA
translation
Protein
tRNAs transfer amino
acids to the ribosome
so that the ribosome
can covalently bond
them together to form
the protein.
RNA, being single
stranded, can fold in
on itself. In tRNA, the
RNA folds into a tshape.
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Active sites of tRNA
tRNA
The Amino Acid
Attachment Site is
where the amino acid
will attach to the tRNA.
Notice the hydrogen
bonds between the
complementary bases.
This is an example of
how the sequence of
nucleotides in RNA
results in a very specific
shape.
The Anticodon Loop is a
3 base sequence on the
tip that is complementary
to the codon on the
mRNA.
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tRNA
Wobble Position
One side of tRNA binds to the correct amino acid.
The other side binds to the appropriate location on the mRNA
strand, by binding to the complementary codon.
Since there are 61 mRNA codes for amino acids, this would
seem to require 61 different types of tRNA, one to match each
code at one end, and the appropriate amino acid at the other.
There are actually 30 - 40 types of tRNA in bacteria and about 50
types in animals. This is possible because of the wobble
position on tRNA's anticodon site.
This allows the last letter of
the mRNA code to violate the
complementary pairing rule.
In general, the first two letters
specify the amino acid, so
this works.
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44 Why does tRNA fold into its specific shape?
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45 The result of tRNA not working would be:
A
The sequence and bonding of its amino acids
A
B
The sequence of and bonding of nucleotides
C
Its protein structure
B mRNA errors
D
A and B
E
A and C
ribosomal cell death
C creation of faulty proteins
D the synthesis of DNA
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Translation - An Overview
46 Which type of RNA functions as a blueprint for the genetic code?
A rRNA
B
tRNAs bond to the amino acid specified by their anti-codon.
tRNA
The opposite side of each tRNA, the anti-codon, bonds to the
matching codon on the mRNA, creating a string of amino acids
in the proper sequence.
C mRNA
D RNA polymerase
The ribosome makes covalent bonds between the amino acids.
The result is a protein chain with the specified sequence of
amino acids.
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Translation Step 1- Initiation
Translation Step 1- Initiation
The ribosome goes to the 5' end of the mRNA because the 5' end is
the beginning of where the gene on the DNA was transcribed into
mRNA.
The small subunit of
the ribosome attaches
to the mRNA at the
bottom of the start
codon (at the 5' end).
Then the large subunit
of the ribosome comes
in over the top.
Also notice that there are 2
sites within the large
subunit:
3'
3'
5'
5'
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The tRNAs, hydrogen bonded to their specific amino acids, surround
the ribosome.
Translation Step 1- Initiation
The methonine is removed from the tRNA and stays in the ribosome to
be bonded with the next amino acid. The tRNA leaves the ribosome so
another tRNA can enter.
Each tRNA will carry the appropriate amino acid into the ribosome to
be bonded in the proper sequence, since each tRNA anticoding site
matches the coding site on the mRNA, which is located at the A site of
the ribosome.
C
Met
UA
tRNA with the code
UAC enters the site
and hydrogen bonds
with it, carrying
methionine into the
ribosome.
The A-site where the
Amino Acids are delivered
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Translation Step 1- Initiation
As the leading edge of
the mRNA, with the
start code AUG, is
exposed in the A site,
The P-site where the new
protein will emerge
A UG
Because each tRNA has an anticoding sequence it complimentary
base pairs with the codon on the mRNA.
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47 How does the anticodon on the tRNA and the codon on the
mRNA match up?
A
by hydrogen bonding/complimentary base pairing
B
by ionic bonding
C
by peptide bonds
D
none of the above
48 Why is Methionine the very first amino acid in all proteins?
A
because it is coded by the stop codon
B
because it is coded for by AUG which is the start codon
C
Methionine is coded for by more than one codon
D
none of te above
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Translation Step 2 - Elongation
Translation Step 2 - Elongation
The ribosome moves the mRNA using ATP
The 2nd tRNA with its
amino acid is delivered
into the A-site in the
ribosome.
The tRNA that was in
the A-site moves to the
P-site and the tRNA that
was in the P-site
separates from its
amino acid and the
protein emerges from
the P-site
The ribosome
catalyzes a covalent
bond between the
amino acids.
Elongation continues by adding one amino acid after another.
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Translation Step 3 - Termination
The ribosome reaches a STOP codon. This signals the end of
translation, the completion of the protein.The 2 subunits separate
from each other.
Translation Step 3- Termination
The Result- A protein in its "primary sequence".
UAA is 1 of the 3
possible STOP codons.
Click Here to
see animation
of Translation
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49 What is the first event of translation?
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50 During translation, the ribosome binds to a:
A
the tRNA comes in
A DNA
B
the small subunit of the ribosome and the 1st tRNA brings in
Methionine to the start codon
B mRNA
C
elongation happens
D
the large subunit of the ribosome comes in
C protein
D peptide bond
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51 What is the first step of translation called?
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52 What is the P site of the ribosome?
A
transcription
A
it is where the amino acids are delivered in
B
elongation
B
it is where the protein or peptide will emerge
C
termination
D
initiation
C
it where the tRNA's will deliver in the next amino acid after
each translocation
D
it is where the proteins fold into their 3-d shape
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53 What is the function of the ribosome in translation?
A
it makes a peptide/covalent bond using the energy
from translocation
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54 What does termination in translation involve?
A translocation of the ribosome
B
the ribosome gets to a stop codon and the small
and large subunits of the ribosome separate
C it makes covalent/peptide bonds between the codons
C
RNA polymerase falls off the DNA
D
D
a tRNA brings in an amino acid
B it makes hydrogen bonds between the codons
none of the above
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55 What is transcription?
The Central Dogma
DNA
transcription
RNA
translation
A
the making of DNA from protein
B
the making of RNA from amino acids
C
the assembly of the protein
D
the making of mRNA from the DNA code/gene
PROTEIN
replication
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56 What is translation?
A the assembly of the amino acids from the protein code
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Article Discussion
B assembly of amino acids coded for by the mRNA codons
C
the making of mRNA
D
assembly of codons from DNA template
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Contents
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