25.4 Control of Gene Expression
Use pp.512-515 to complete the following notes.
1. Cell Specialization
a. Each cell has an _______________ copy of an organism’s _________
b. Cells are _______________ (e.g. _______________ cells, skin cells,
_______________ cells)
c. Only parts of the DNA are _______________ for the cell’s specialized
_______________
d. A s_______________ of DNA (usually many ______________ long)
codes for one _______________ (from a start codon to a stop codon)
e. Every cell expresses “_______________” genes that are required
functions for all cells (e.g. gene that governs glucose
_______________)
f. Other _______________ are only _______________ in some cells
Cell Type
Gene type
expressed
Housekeeping
Hemoglobin
Insulin
Myosin
Red blood cell
Muscle cell
Pancreatic cell
Yes
Yes
No
NO
Yes
No
No
Yes
Yes
No
Yes
No
What does the above chart tell you about the functions of hemoglobin, insulin,
and myosin?
2. Gene Expression Control: the Operon:
a. a cluster of _______________ usually coding for _______________
related to a particular _______________ pathway, along with the
short DNA s_______________ that coordinately control their
_______________
b. Consist of a _______________, sequence of DNA where RNA
polymerase attaches to begin _______________, and an operator (a
sequence of DNA where a _______________ protein can bind)
c. E.g. lac operon: codes for three enzymes needed for
_______________ metabolism
i. Lactose _______________: repressor binds to
_______________ and _______________ enzymes from being
produced
ii. _______________ present: lactose _______________ with
the lac repressor so that the repressor is no longer able to bind
to the operator; _______________ can now _______________
(and the _______________ of these three enzymes)
iii. This operon is _______________ (can be turned on in the
presence of certain molecules), others are _______________
(can be turned off in the presence of certain molecules)
3. Control of Gene Expression in Eukaryotes vs. Prokaryotes
a. Eukaryote: an organism made up of cells that have a
_______________-bound _______________ and organelles
i. Each _______________ has its own _______________ where
RNA polymerase _______________
ii. Employ a variety of _______________ to control gene
expression
iii. Mechanisms can control:
1. whether the gene is _______________
2. The _______________ at which the gene is expresses
3. How _______________ it is expressed
b. Prokaryote: _______________ a membrane-bound nucleus and
organelles; a prokaryotic cell is the cell type within the domains
_______________ and _______________ (live in aquatic
environments that lack oxygen or are too salty, too hot, or too acidic
for most other organisms  may be environments that are more
similar to primitive Earth conditions)
i. Single _______________ serves several genes that make up a
transcription unit
ii. Rely on _______________ control (see below)
4. Gene Expression in Eukaryotes
a. Levels of Gene Control
i. Pretranscriptional control
1. _______________ transcription
2. e.g. Barr bodies in females XX: one X chromosome
becomes darkly stained and _______________
ii. _______________ control
1. After transcription
a. E.g. mRNA is _______________ before it leaves
the _______________
b. E.g. length of time it takes mRNA to be
_______________ out of nucleus
iii. Translational control
1. _______________ translation
a. Lifespan of mRNA can be _______________
(before it is broken down)
b. E.g. mRNA for vitelline, en egg membrane protein,
can last only 15 hours w/o the presence of
estrogen, but for up to 3 weeks in the presence of
estrogen
iv. _______________ control
1. After translation
a. some proteins need to be _______________ after
translation, e.g. insulin
“Check Your Progress” p.515 # 1-3 AND
Draw Figure 25.18 below. Label it and give an example beside each type of the
four gene control types.
5. Explain the main difference between eukaryotes and prokaryotes. Which
domains belong to these classifications? (Use your glossary and index to answer
this if necessary.)
25.4 Control of Gene Expression
1. Cell Specialization
a. Each cell has an ENTIRE copy of an organism’s DNA
b. Cells are specialized (e.g. muscle cells, skin cells, blood cells)
c. Only parts of the DNA are needed for the cell’s specialized function
d. A section of DNA (usually many codons long) codes for one gene
(from a start codon to a stop codon)
e. Every cell expresses “housekeeping” genes that are required
functions for all cells (e.g. gene that governs glucose metabolism)
f. Other genes are only expressed in some cells
Cell Type
Gene type
expressed
Housekeeping
Hemoglobin
Insulin
Myosin
Red blood cell
Muscle cell
Pancreatic cell
Yes
Yes
No
NO
Yes
No
No
Yes
Yes
No
Yes
No
What does the above chart tell you about the functions of hemoglobin, insulin,
and myosin?
2. Operon:
a. a cluster of genes usually coding for proteins related to a particular
metabolic pathway, along with the short DNA sequences that
coordinately control their transcription
b. Consist of a promoter, sequence of DNA where RNA polymerase
attaches to begin transcription, and an operator (a sequence of DNA
where a repressor protein can bind)
c. E.g. lac operon: codes for three enzymes needed for lactose
metabolism
i. Lactose absent: repressor binds to operator and prevents
enzymes from being produced
ii. Lactose present: lactose binds with the lac repressor so that
the repressor is no longer able to bind to the operator;
transcription can now occur (and the synthesis of these three
enzymes)
iii. This operon is inducible (can be turned on in the presence of
certain molecules), others are repressible (can be turned off in
the presence of certain molecules)
3. Control of Gene Expression in Eukaryotes vs. Prokaryotes
a. Eukaryote: an organism made up of cells that have a membranebound nucleus and organelles
i. Each gene has its own promoter where RNA polymerase binds
ii. Employ a variety of mechanisms to control gene expression
iii. Mechanisms can control:
1. whether the gene is expressed
2. The speed at which the gene is expresses
3. How long it is expressed
b. Prokaryote: lacking a membrane-bound nucleus and organelles; a
prokaryotic cell is the cell type within the domains Bacteria and
Archaea (live in aquatic environments that lack oxygen or are too
salty, too hot, or too acidic for most other organisms  may be
environments that are more similar to primitive Earth conditions)
i. Single promoter serves several genes that make up a
transcription unit
ii. Rely on transcriptional control (see below)
4. Gene Expression in Eukaryotes
a. Levels of Gene Control
i. Pretranscriptional control
1. Before transcription
2. e.g. Barr bodies in females XX: one X chromosome
becomes darkly stained and inactive
ii. Posttranscriptional control
1. After transcription
a. E.g. mRNA is processed before it leaves the
nucleus
b. E.g. length of time it takes mRNA to be
transported out of nucleus
iii. Translational control
1. During translation
a. Lifespan of mRNA can be lengthened (before it is
broken down)
b. E.g. mRNA for vitelline, en egg membrane protein,
can last only 15 hours w/o the presence of
estrogen, but for up to 3 weeks in the presence of
estrogen
iv. Posttranslational control
1. After translation
a. some proteins need to be activated after
translation, e.g. insulin
“Check Your Progress” p.515 # 1-3 AND
4. Draw Figure 25.18 in your notes. Label it and give an example beside each type
of the four gene control types.
5. Explain the difference between eukaryotes and prokaryotes. Which domains
belong to these classifications? (Use your glossary and index to answer this if
necessary.)