SBI4U
Eukaryotic Control Mechanisms (7.4)
1. The gene for hemoglobin is methylated (a methyl group (-CH3) is attached to cytosine bases in the promoter
of a gene) in almost all body cells. In bone marrow cells, specific enzymes remove the methyl groups. What
stage of protein synthesis can now occur?
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2. In many unfertilized animal egg cells, masking proteins are bound to mRNA. The masking proteins are
removed by other proteins when the egg is fertilized and the embryo developing. What stage of protein
synthesis do the masking proteins prevent?
3. Proteins are constantly being synthesized and then degraded, and the amino acids are recycled to make
new proteins. Some proteins are tagged with a protein called ubiquitin, which causes them to be degraded at
a faster rate. If these proteins are not tagged with ubiquitin, what happens?
4. An activator molecule binds to a sequence upstream of the promoter, and signals a protein remodelling
complex that separates DNA from the histones and allows the promoter to be exposed. What stage of protein
synthesis can occur now?
5. In normal healthy mice, the agouti gene is methylated (a methyl group (-CH3) is attached to cytosine bases
in the promoter of the gene). Is this gene expressed or not?
SBI4U
Eukaryotic Control Mechanisms (7.4)
1. The gene for hemoglobin is methylated (a methyl group (-CH3) is attached to cytosine bases in the promoter
of a gene) in almost all body cells. In bone marrow cells, specific enzymes remove the methyl groups. What
stage of protein synthesis can now occur?
2. In many unfertilized animal egg cells, masking proteins are bound to mRNA. The masking proteins are
removed by other proteins when the egg is fertilized and the embryo developing. What stage of protein
synthesis do the masking proteins prevent?
3. Proteins are constantly being synthesized and then degraded, and the amino acids are recycled to make
new proteins. Some proteins are tagged with a protein called ubiquitin, which causes them to be degraded at
a faster rate. If these proteins are not tagged with ubiquitin, what happens?
4. An activator molecule binds to a sequence upstream of the promoter, and signals a protein remodelling
complex that separates DNA from the histones and allows the promoter to be exposed. What stage of protein
synthesis can occur now?
5. In normal healthy mice, the agouti gene is methylated (a methyl group (-CH3) is attached to cytosine bases
in the promoter of the gene). Is this gene expressed or not?
6. Certain chemical groups need to be added or deleted to a polypeptide to make it active. At what stage of
protein synthesis is this type of regulation?
7. Alternative splicing of introns results in the production of many different proteins from the same gene. Not
all of the possible proteins are produced each time the gene is expressed. At what stage of protein synthesis
does this control occur?
8. Hormones control the rate at which mRNA is degraded (broken down). Milk production in rats (and in
humans too!) is regulated by the hormone prolactin. Prolactin slows down the rate of degradation of the mRNA
that codes for the milk protein casein. What effect does slowing down the degradation of the mRNA have?
9. The insulin gene is transcribed, then translated as proinsulin (the inactive form of insulin). Certain sections
of proinsulin are removed to form insulin. At what stage of protein synthesis is this type of regulation?
10. A series of proteins called general transcription factors bind to a specific region on the promoter, and
provide a substrate for RNA polymerase to bind to. This allows what stage of protein synthesis to occur?
11. An activator molecule is bound to a regulatory sequence upstream of the gene, which signals an enzyme to
add an acetyl group (CH3COO-) to histones, which separates them from DNA, allowing the promoter to be
exposed. What stage of protein synthesis can occur now?
6. Certain chemical groups need to be added or deleted to a polypeptide to make it active. At what stage of
protein synthesis is this type of regulation?
7. Alternative splicing of introns results in the production of many different proteins from the same gene. Not
all of the possible proteins are produced each time the gene is expressed. At what stage of protein synthesis
does this control occur?
8. Hormones control the rate at which mRNA is degraded (broken down). Milk production in rats (and in
humans too!) is regulated by the hormone prolactin. Prolactin slows down the rate of degradation of the mRNA
that codes for the milk protein casein. What effect does slowing down the degradation of the mRNA have?
9. The insulin gene is transcribed, then translated as proinsulin (the inactive form of insulin). Certain sections
of proinsulin are removed to form insulin. At what stage of protein synthesis is this type of regulation?
10. A series of proteins called general transcription factors bind to a specific region on the promoter, and
provide a substrate for RNA polymerase to bind to. This allows what stage of protein synthesis to occur?
11. An activator molecule is bound to a regulatory sequence upstream of the gene, which signals an enzyme to
add an acetyl group (CH3COO-) to histones, which separates them from DNA, allowing the promoter to be
exposed. What stage of protein synthesis can occur now?