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Chapter 10: Genes & Chromosomes
10-3: Regulation of Gene Expression
1. Each cell has a complete set of genes
characteristic of
that organism, but not all genes are turned on in all cells at
the same time. Different cells perform different functions
and therefore need different proteins
.
What determines which genes are activated and
therefore which proteins are produced by the cell?
2. In the early
1960s
, a French study revealed that E.
coli bacteria produce 3 enzymes to help digest the sugar
lactose. The bacteria do this only when needed because
enzyme production can be turned on and turned off
by clusters of genes.
3. Describe these genes that were discovered in prokaryotes:
Structural genes (gene clusters) – DNA segment that
codes for the production of a particular protein
Operator gene – Sequence of nucleotides next to the
structural genes that act as an on/off switch
Regulatory gene – Produces the repressor protein which
binds to the operator and turns off the gene
Promoter gene – site where RNA polymerase binds to
the DNA
4. In primitive prokaryotes life bacteria, the promoter and
their associated structural genes are called an operon
(Fig 10-17).
a. Describe what happens if a gene is expressed The gene is transcribed and translated into a protein.
b. In order for a gene to be expressed, RNA Polymerase
must first bind to the promoter. Once this happens,
RNA polymerase can move down the DNA and
transcribe
c. The system is
the gene.
turned off
when a repressor
binds to the operator (see Fig 10.18). This blocks the
RNA polymerase from moving from the
to the
genes
.
promoter
d. The system is turned on when an inducer
to the repressor. The repressor then
lets go
binds
of the
operator and RNA polymerase can move down the DNA
to transcribe the genes.
5. In
eukaryotic
function are not
cells, genes relating to a certain
clustered together
.
a. Related genes may be far apart from one another or
even on different
chromosomes all together.
b. In a process similar to that found in prokaryotes, in
eukaryotic cells RNA Polymerase
transcribes the
entire gene (both introns & exons
), making a type
of RNA called pre-mRNA
(see fig 10.21).
c. Describe the following and explain what happens to
them after the gene is transcribed:
introns – segment of DNA in a gene that does not code
for amino acids. The RNA intron is cut out of the
pre-mRNA.
exons – Segement of DNA in a gene that codes for
amino acids. The exons will be found in functional
mRNA.
d. After the introns have been removed , a cap is put
on one end of the RNA and a tail is put on the other
end. This results in a functional mRNA
molecule.