Name _____________________________________________________________________
Test Date _______________
UNIT 7 – GENE EXPRESSION
I. DNA – A REVIEW (pp 287-294)
 DNA stands for _______________________________________________________.
 DNA contains the _______________________________ and the ________________________________ for a cell.
 DNA is a _____________________________ made up of monomers known as ____________________________
o Each nucleotide contains:
 _____-carbon sugar - ___________________________
 ___________________________ group
 ______________________ base
 ____________________
 ____________________
 ____________________
 ____________________
 The shape of DNA is a ___________________________________.
o ___________________________ bonds hold each nucleotide together
o ___________________________ bonds hold one nucleotide to another to form the backbone of DNA
o ___________________________ bonds form between the nitrogen bases to form the double helix
 _____________________________________________________________
 _____________________________________________________________
II. RNA - _________________________________________ (pp. 300-301)
DNA contains specific sequences of nucleotides known as ______________. The instructions they contain are carried out through the
making of _______________________. Protein synthesis occurs at the _______________ which are located in the ____________,
but DNA is found in the ____________. DNA cannot leave the nucleus because it is ____________________, so another molecule is
required to take the genetic code from the _____________ 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. Provides a __________________ copy of the instructions in DNA so they can be taken
from the _________________ to the _________________; “___________________” for genetic code.
2. tRNA - _____________________ RNA. Carries (transfers) _____________________ to ribosome according to instructions
encoded in _________________.
3. rRNA - _____________________ RNA. Structural component of _______________________. In addition to rRNA,
ribosomes are composed of ___________________ and they are synthesized in the ____________________________.
III. PROTEIN SYNTHESIS
(pp. 301-306)
Protein synthesis requires two steps:
A. Transcription
 Re-writing of the instructions contained in ________ to ____________
 Occurs in the _______________
B. Translation
 Construction of the specified ________________
 Occurs at the ____________________
IV. TRANSCRIPTION
 First, the enzyme ____________________________________, unzips a specific portion of the DNA molecule by breaking the
_________________ bonds between the ____________________________________.
 Specific sequences of DNA nucleotides known as the _____________________ indicate the beginning of a ___________ while
the end of a gene is marked by a _______________________ sequence.
 RNA nucleotides are moved in _____ to ______, according to ____________________________ and ________ is synthesized.
 There are several important ways that transcription differs from replication:
 Only _____________ of the DNA molecule is copied in transcription while in replication, __________ sides are copied.
 In RNA, the nucleotide that pairs with adenine is ____________. The nitrogen base, _______________, is not found in
RNA.
 RNA polymerase does not require a _______________.
 In transcription, only _______________________________ is “unzipped” and copied; in replication, ________________
___________ is unzipped & copied. In addition, in _______________________, all DNA molecules in a cell are
unzipped & copied; this is not true in ________________________.
 In a _____________________ cell, replication occurs during ___________ of the cell cycle while transcription primarily
occurs during _____________.
 All cells carry out ______________________; only cells that are _______________ carry out _____________________


In prokaryotic cells, as mRNA is transcribed, __________________________ begins virtually simulaneously.
In eukaryotic cells,
 When the mRNA is transcribed, there are long sequences of _________________________ that are not used for the
synthesis of the protein. These non-coding nucleotides are known as ______________. The DNA sequences that
actually code for the protein are known as _________________. Before mRNA exits the nucleus, the ______________
are edited (__________) out and the remaining ___________ are spliced together to form the final mRNA.
 mRNA leaves the nucleus via the _______________________ and travels to the __________________, the site of
protein synthesis.
V. TRANSLATION
Translation takes place at the _____________________. The message in ___________________ is read by the ribosome,
________________ brings the corresponding _____________________ to make the final product – a ______________________
chain, that eventually folds into a specific ____________________________ to form the __________________.
A. Ribosomes
 Synthesized in the __________________________ of eukaryotic cells
 Composed of _________________ and ____________________
 Prokaryotic ribosomes are ____________________ than eukaryotic ribosomes
 Composed of two _______________________________ that come together when translation begins

Two locations for eukaryotic ribosomes
o Bound
 Attached to ________________________________________________________________________
 Synthesize proteins __________________________________________________________________
o Free
 Found suspended in the ________________________
 Synthesize proteins __________________________________________________________________
B. Codons - A Mechanism to “Read” mRNA
The monomers of proteins are ________________________. There are ________ amino acids used in building the proteins
essential for life yet there are only _____________ different nucleotides DNA and RNA. In order to have a different code for
each of the 20 amino acids, nucleotides are read in groups of ___________ known as _______________. The codons
collectively make up the ________________________.
 The genetic code is __________________________; in other words, a ___________ codes for the same amino acid in all
_________________________.
 The genetic code is ________________________________. Since there are ______ possibilities for each nucleotide,
and ________ nucleotides represent a codon, this allows for _____ x ______ x _______ = _____________ variations.
There are only ___________ amino acids, so many different codons represent the same amino acid.
 There is one codon that designates “start” - ______________ which codes for ___________________.
 There are three “stop” codons:
o _______________
o _______________
o _______________
For the following codons, identify the corresponding amino acid:
a. UAC - ______________________________
b. AGA - ______________________________
c. GCA - ______________________________
d. CCU - ______________________________
For the following amino acids, give all possible codons:
a. arginine - ______________________________________________
b. glycine - _______________________________________________
C. tRNA
The function of tRNA is to transfer the _________________________ specified by the _____________________ to the
_______________ for protein synthesis. The _______________________ of every cell is stocked with all _________ amino
acids required for protein synthesis. tRNA forms _____________________ bonds with itself, resulting in a folded molecule with
an __________________ at one end that is specific for that tRNA. At the other end, there is a group of three nucleotides known
as the ________________________.
The anticodon binds to the ____________________ according to _______________________________. This insures that the
proper amino acid is brought to the ribosome.
D. The Steps of Translation
 mRNA joins with a _________ subunit of a ribosome and the start codon, ___________, is read.
 The large subunit attaches to the complex forming a complete ____________.
 A tRNA carrying a _______________________ arrives at the ______ site of the ribosome.
 Base pairing occurs between the __________________ and ______________, insuring the proper amino acid has been
delivered.
 The mRNA & ribosome slide against each other, moving the tRNA and its amino acid from the A site to the ______ site.
 The next codon is read, and the tRNA with the corresponding ______________________ arrives at the _____ site of the
ribosome carrying its amino acid.
 The methionine that had been shifted to the P site forms a ____________________ bond known as a _________________
bond with the next amino acid.
 Everything shifts ______ places. The “empty” tRNA departs the ribosome, and the next codon is read. This process is
known as ___________________________, results in a growing chain of amino acids known as a
____________________________ chain.
 Elongation continues until a _________ codon is reached.
 At this point, the ribosome releases the _______________________ chain, which coils and folds to form a ______________.
o The “empty” tRNAs will be re-charged by binding another amino acid.
o The mRNA will be ____________________________ or translated again.
o The protein may be modified, and used in the cell; for example, _______________, or packaged in a ______________,
sent to the ______________________________, and transported out of the cell via ___________________________.
PROTEIN SYNTHESIS – A SUMMARY
VI. MUTATIONS
A mutation is a _______________________________________. Most mutations are harmful but they may also be
___________________ or __________________. Mutations are classified according to the scope of the change:
A. Chromosomal Mutations
 Involve the number or structure of the entire chromosome.
 Generally occur during ________________________________.
 Very serious consequences; usually results in death of cell.
 Types of chromosomal mutations:
B. Gene Mutations
 Affect one gene on a chromosome
 Usually due to a mistake in ____________________________
 Consequences are variable
 Known as point mutations; 2 main categories
o Substitution
 One nucleotide is exchanged for another
 May or may not affect resulting amino acid sequence
o Frameshift
 Caused by addition or deletion of nucleotide(s)
 Results in a different number of nucleotides, shifts the reading of the remainder of mRNA codons
following mutation
 Typically more serious