Name _________________________________________________________________________________Test Date _______________
UNIT VI – DNA AND RNA
I. DNA - THE DISCOVERY OF THE MOLECULE OF INHERITANCE
DNA contains the ______________________ and the __________________________ for a cell. Scientists in the early 1900s realized
that inheritance was dependent on _______________ found on _______________________ and that chromosomes were composed of
______________________ and ___________________________. It wasn’t until the 1940s that scientists established __________ as
the molecule of inheritance, and still another 15 years passed before the structure of DNA was discovered.
A. Structure of DNA
Once scientists discovered the chemical make-up of DNA, there was a race to discover its 3-dimensional structure. It was
__________________ and ___________________ who first proposed the ______________________ structure of DNA after
building possible molecular models and studying a copy of an x-ray of DNA taken by _____________________________________.
DNA is a _________________________, a biomolecule composed of _____________________ called ______________________.
Each nucleotide of DNA consists of:
Draw a DNA nucleotide here:
1. ____________ carbon sugar - _________________________________
2. ________________________ group (PO4)
3. ________________________ base
 Strong, stable __________________________ bonds hold the parts of each
nucleotide together.
 In addition, nucleotides form strong _______________ bonds with other nucleotides, resulting in a long strand of nucleotides.
 Double helix created by weak ________________________ bonds between the _________________________ bases.
 The diameter of DNA is uniform due to specific pairing of nitrogen bases
o Purines – double-ringed nitrogen bases
Pyrimidines – single-ringed nitrogen bases
 ________________________________
- _____________________________________
 ________________________________
- _____________________________________
o _____________________________ always base pairs with a ________________________________, specifically …
 _______________________________ base pairs with ___________________________
 _______________________________ base pairs with ___________________________
o ________________ and _______________ determined this structurally because the ______________ of DNA is uniform.
o _________________________ determined this chemically. His chemical analysis of DNA from many different organisms
always showed that the % of adenine = % _______________ and the % of guanine = the % ____________________.
These findings are known as ______________________________________________________________________.
 The two strands of nucleotides are ________________________________________; that is, they run opposite to each other.
 It is the __________________________ and ___________________________ of nucleotides that makes each gene unique.
Identify the following:
hydrogen bond
covalent bond
cytosine
nucleotide
phosphate group
guanine
purines
pyrimidines
3’ End
5’ End
adenine
nitrogen bases
deoxyribose
thymine
B. DNA Replication
Prior to cell division, the DNA must ___________________________. This occurs in ________ of _________________________.
During this part of the cell cycle, DNA is in the form of ____________________________. DNA can replicate itself exactly due to
______________________________________. Replication occurs in the ________________________ of the cell and requires the
participation of several ___________________________.
Replication may be summarized in the following steps:
 DNA is “unzipped” by the enzyme, ___________________. Helicase breaks the _______________________ bonds between
the _________________________. The point where the unzipping begins is known as the ____________________________.
The continuation of the unzipping is called the _________________________________. This occurs in several places in each
_______________________________, much like a _____________________________________.
 __________________________________________ hold the separated DNA strands apart.
 Another enzyme, ______________________________________________ moves ahead of the ________________________
to relieve tension in the double helix as it is being unzipped.
 The enzyme, ________________________________________ adds nucleotides to both sides of the DNA molecule according
to _____________________________________________________ rules; however, DNA polymerase has two restrictions:
1) It can only add nucleotides in a _____________________ direction.
2) It can only add nucleotides to an existing strand.
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Before DNA polymerase begins moving in nucleotides, a __________________________ must be put in place. Eventually this
primer is removed and replaced with DNA nucleotides.
The two sides of the DNA molecule are replicated differently because nucleotides can only be added in a ___________
direction:
o One side of the DNA molecule is being replicated in the same direction as the ____________________________. This is
known as the _____________________ strand. Nucleotides are moved in by ___________________________________
in a ____________________________________ direction as the DNA is unzipped.
o On the other side of the DNA molecule, nucleotides are added ________________ from the replication fork. This is known
as the __________________________________ strand. Short segments of nucleotides are synthesized, each with a new
___________________________________________, as the DNA is unzipped. These short segments are known as
____________________________________. Eventually, another enzyme known as _______________________ “glues”
together the ___________________________________ fragments to create a continuous strand of nucleotides.
Another type of __________________________________________ proofreads the replicated DNA to minimize the chance of
___________________________.
The result is two ___________________________ DNA molecules, each new DNA consists of one _____________________
strand and one ____________________ strand. This is known as the ____________________________________________
model of replication.
These two identical DNA molecules are the _______________________________________________ that proceed through
________________________________.
Once replication has been completed, the cell moves into ___________ and then, ________________________________ of
________________________________.
C. A Detailed View of Replication
II. RNA - ______________________________________
The instructions in ____________________ are carried out through the making of _________________. Protein synthesis occurs in
the ___________________________, but DNA is found in the ________________________. DNA cannot leave the nucleus because
it’s _______________________________________, so another molecule is required to take the genetic code from the nucleus to the
____________________________ so protein synthesis can take place. This molecule is __________________________________.
A. RNA Structure – RNA differs from DNA in three ways.
Characteristic
DNA
RNA
Sugar
Base
Structure
RNA is able to leave the nucleus through the _____________________________ because it is a _______________________;
thus, the genetic code can be carried out.
B. Types of RNA – There are three principal forms of RNA involved in carrying out the genetic instructions of DNA:
1. mRNA - ____________________ RNA. Carries instructions from DNA in ___________________ to ___________________.
Known as the “_____________________” for genetic code.
2. tRNA - ______________________ RNA. Carries (transfers) _____________________ to ribosome according to instructions
encoded in _________________________.
3. rRNA - __________________________ RNA. Structural component of _________________; also produces ____________
to bond __________________________together to form _______________________.
III. PROTEIN SYNTHESIS
DNARNAPROTEIN
In protein synthesis, the instructions contained in _____________ are carried out through the making of a protein. Protein synthesis
takes place in two steps:
A. Transcription - Transcription takes place in the __________________ and allows the ______________________ of DNA to be
carried out to the _________________________.
1. First, the enzyme _________________________________________ unzips part of the DNA molecule.
2. RNA nucleotides are moved in according to base pairing rules and ___________________________ is synthesized.
There are 2 important ways that transcription differs from replication:
a. Only ____________________________ of the DNA molecule is copied in transcription.
b. In RNA, the nucleotide that pairs with adenine is _____________. The nitrogen base, ______________, is not found in RNA.
3. When the mRNA is first transcribed, there are long sequences of __________________ that are not required for the synthesis of
the protein called __________________. The DNA sequences that code for the protein are known as _____________. Introns
are edited out (cut out) of the mRNA before it leaves the nucleus and the remaining _________________ are spliced together to
form the final mRNA.
“EX”ONS = “Ex”pressed
“IN”TRONS = “in between” the good stuff
4. mRNA leaves the ________________ through the ______________________ and travels to the __________________, the site
of protein synthesis. When mRNA arrives at the ribosome, the two parts of the ribosome, (small and large ribosomal subunits)
come together and form a functioning ribosome complex.
B. Translation (RNA transferred to Proteins)
Translation - Translation takes place at the ________________. The message in ____________ is read by the ribosome, ______
brings the corresponding ________________________ to make the final product – a polypeptide chain ___________________.
1. Codons
Codon = a codon is a group of 3 nucleotides on mRNA that codes for a specific ____________________________________.
 A codon can be made up of any combination of the 4 RNA nucleotides (A, U, G, C), therefore there are up to 64
possible codons (b/c 4 x 4 x 4). Ex: AAA, AAU, AAG, AAC, etc….
 Many different codons represent the same amino acid b/c there are 64 possible codons, and only 20 amino acids for
which those codons code for.
 Amino acids are the building blocks (or monomers) of _________________________. Even though there are only 20
amino acids, there are many, many proteins. It is the number and arrangement of the amino acids that makes every
protein unique.
 Start codon: ___________ – __________________ the making of the amino acid chain.
 Stop codon: signal to _________________ the making of the __________________________________________.
 The genetic code is universal, therefore the codons code for the same amino acid in all organisms.
The mRNA message is _____________________by the ribosome using these _____________________.
2. tRNA
The function of tRNA is to transfer the ____________________ specified by the ____________________ to the ______________
for protein synthesis. The __________________ of the cell is stocked with all 20 amino acids required for protein synthesis. The
tRNA molecule carries an ___________________ at one end and at the other end, it has a group of ____ nucleotides known as an
_____________________. The anticodon binds to the mRNA codon according to base pairing rules and insures that the proper
amino acid is brought to the ribosome.
3. Building a Protein
 Initiation
The first tRNA (_____________________ tRNA) comes to the ribosome and its anticodon attaches to the codon of the mRNA
that is located in the _________________________ on the small ribosomal subunit. Next, the large ribosomal subunit comes
down and attaches to the small ribosomal subunit to hold the tRNA and mRNA together. The next tRNA enters and its
anticodon attaches to the mRNA codon in the ___________________________ of the ribosome. The two amino acids form a
_____________________bond with the aid of enzymes & _________________.
 Elongation – Translocation
The initiator tRNA is bumped off, but it leaves its amino acid behind as a part of the growing polypeptide chain.
The _______________ slides through the ribosome (____________________________) so that the next _____________ is in
the A site. As the codon is read, the tRNA with the corresponding ________________________________ (according to basepairing rules) comes to the ribosome carrying its amino acid. That amino acid forms a peptide bond to the last amino acid in
the polypeptide chain. This whole process is known as ________________________________________.
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Termination
Elongation continues until a ____________________ codon on the mRNA is reached. This begins
___________________________. A ________________________________ factor bonds its anticodon to the stop codon on
mRNA. The protein release factor signals the ribosome to release the amino acid chain, which coils & folds to form a
_________________________________. The tRNA, mRNA, and small & large ribosomal subunits disassemble.
IV. Mutations
Mutation is a ________________________ in the DNA sequence.
The mutation may be classified as: _____________________________or ____________________________ mutations.
Some mutations are harmful, but most are beneficial.
A. Gene Mutation
Gene mutation affects only ___________ gene on an individual chromosome. Gene mutations that result in a change to only one
or a few nucleotides are known as ______________ mutations.
There are 2 types of point mutations.
1. Substitutions
 One nucleotide in a gene is _________________________ with a different nucleotide.
 Ex: Codon UGU is changed to UGC. What is the change to the amino acid?
 May have little or no effect, OR
 May have a drastic effect. If UGU is changed to UGA, what would the effect on the protein be?
2. Frameshift Mutations
Frameshift mutations involve the _____________________________ or ________________________________ of a
__________________________________.
 An insertion or deletion of a nucleotide causes a ___________________ in the ________________________ of the
remainder of the codons; therefore, the _________________________________ of the remainder of the mRNA is
__________________. This will usually result in ___________________________changes in the polypeptide chain
and completed_______________________________.
B. Chromosomal Mutation
Chromosomal mutation involves the _______________________ or ___________________ of the _____________________
chromosome. (Affects all genes on that chromosome!)
1. These errors generally occur during meiosis or _____________________________.
2. May result in a __________________________________________ disorder (extra chromosome or deleted chromosome), or
_________________________________of a piece of chromosome and the corresponding genetic information.
3. Examples: Inversion, Translocation, Nondisjunction, duplication
C. Causes of Mutations
Some mutations are chemical mishaps that arise spontaneously, while others are caused by environmental factors.
1. Mutagens – Environmental agents such as _____________________ and ________________________ rays that may cause a
mutation in the DNA sequence.
2. Carcinogens - ____________________ causing agents such as asbestos, ________________________(found in detergents,
plastics, and paints), and other pollutants.