Transcript Control of Gene Activity

Control of Gene Activity
Chapter 17
Controlling gene activity
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Remember to control the cell one must
control protein synthesis.
Protein synthesis can be controlled several
different ways. What are some ways to
potentially control protein synthesis:
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Blocking production of mRNA, tRNA, or rRNA
Blocking ribosome production
Blocking intake of Amino Acids
Bind a substance to the finished protein that
does not allow the protein to function.
4 General methods of controlling
gene expression in Eukaryotes
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1. Transcriptional control: various
mechanisms which control which genes
are transcribed.
Also controls the rate of transcription.
All transcriptional control mechanisms
occur in the nucleus.
Chromatin plays a role in transcriptional
control.
2. Posttranscriptional control
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Occurs in the nucleus after DNA has been
transcribed into primary mRNA.
Causes differences in the processing of
mRNA
Affects the maturation rate of mRNA
Affects the rate which mature mRNA
leaves the nucleus
3. Translational control
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Occurs in the cytoplasm after mRNA
leaves the nucleus.
Affects the “lifespan” of the mRNA
May affect the ability of mRNA to bind to
the ribosome.
4. Posttranslational control
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Occurs in the cytoplasm.
Occurs after the protein is synthesized
Compounds may prevent the protein from
undergoing conformational changes
necessary for its function.
Compounds bind to the completed protein
and limit its ability to function.
Cancer
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Cancer cells seem to have lost the ability
to control gene expression.
Cancer cells lack differentiation. They are
not specialized.
Cancer cells live longer than normal cells.
A normal cell enters the cell cycle about
50 times and then dies.
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In cell culture experiments, a cancer cell
entered the cell cycle repeatedly. It only died
when it ran out of nutrients.
Cancer cells (continued)
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Cancer cells have abnormal nuclei
Cancer cells form tumors.
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Cancer cells lack normal contact inhibition.
Contact inhibition-when a cell comes in contact
with its neighbor, it stops dividing.
Causes normal cells to form layers.
Cancer cells continue to replicate and pile up
on each other in large masses - tumors
tumors
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Angiogenesis- ability of cancer cells to
spur blood vessel formation.
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Some forms of cancer treatment are
investigating methods to suppress blood
vessel growth to tumors and “starving” the
cancer to death.
Metastasis- Ability of tumors to establish
new tumors distant from the primary
tumor. (malignancy)
Vocab (refresher from labs)
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Cancer- a malignant tumor whose nondifferentiated
cells exhibit loss of contact inhibition, uncontrolled
growth, and the ability to invade tissue and
metastasize.
Oncogene- A cancer causing gene through mutation.
Operon- A group of structural and regulating genes
that function as a single unit.
Operator- sequence of DNA that a repressor protein
binds to.
Inducer- A molecule that brings about activity of an
operon by joining with a repressor and preventing it
from binding to the operator.
Vocab (continued)
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Regulator gene- in an operon, a gene that codes
for a repressor
Repressor- A protein molecule that binds to the
operator, prevents polymerase from binding to
the promoter site of an operon.
Promoter- location on an operon where
transcription begins.
Carcinogen- an environmental agent that causes
mutations leading to the development of cancer.
Cancer treatments
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Preventative surgery – removal of tissues at risk of
becoming cancerous (mastectomy)
Chemotherapy – treatment of disease with the use of
chemicals. Adversely affects cancerous cells as well as
healthy tissue.
Radiation therapy – treatment of a disease using radiation.
Targets specific cancer cells, but also affects healthy tissue
as well.
Mastectomy & oophorectomy - Removal of affected tissue
Proton therapy – Firing protons into affected tissue. The
positive charge delivers more energy to the targeted cells
and has shown promise as a cancer treatment.
Cancer Prevention
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Don’t Smoke
Don’t sunbathe
Avoid Alcohol
Avoid Radiation
Get tested for cancer
chemoprevention
Be aware of occupational hazards
Be aware of hormone therapy
Eat a healthy diet
Genetic testing for predisposition to cancer.