Regulation of Gene Expression. You Must Know The functions of the three parts of an operon. The role...
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Transcript of Regulation of Gene Expression. You Must Know The functions of the three parts of an operon. The role...
Regulation of Gene Expression
You Must Know
• The functions of the three parts of an operon.
• The role of repressor genes in operons.
• The impact of DNA methylation and histone acetylation on gene expression.
• The role of oncogenes, proto-oncogenes, and tumor suppressor genes in cancer.
Bacteria respond to environmental change by regulating Transcription.• Genes are clustered into units called
operons.
• 3 parts of an operon: – Operator- controls the access of RNA
polymerase to the genes. – Promoter-where the RNA polymerase
attaches. – Genes- The entire stretch of DNA required for
al the enzymes produced by the operon.
General structure of an OPERON
Regulatory Genes
• Produce repressor proteins that may bind to the operator site.
• When they occupy the operator site, RNA polymerase is blocked from the genes of the operon.
• This means the operon is off.
Repressible Operon
• Is normally on but can be inhibited.
• Is Anabolic, building an organic molecule.
• The repressor protein produced by the regulatory gene is inactive.
• If the organic molecule that is produced is provided to the cell, the molecule can act as a corepressor and bind to the repressor protein, activating it.
Inducible Operon
• Normally off, but can be operated.
• Normally catabolic, breaking down food molecules for energy.
• To turn the inducible operon on, an inducer binds to and inactivates the repressor protein.
• Now RNA polymerase can access the genes of the operon.
Regulation of Genes
• The expression of Eukaryotic genes can be turned off and on at any point along the path to becoming a protein.
• Different cell types are due to differential gene expression, the expression of different genes by cells with the same genome.
Packaging of DNA
• A nucleosome is a packaging unit of DNA. – Consists of DNA bound ot small proteins called
histones. – The more tightly bound DNA is to its histones, the
less accessible it is for transcription. – This relationship is governed by 2 chemical reactions.
• DNA methylation- the addition of Methyl groups to DNA – Causes DNA to become more tightly packaged, thus reducing
gene expression.
– Histone acetylation- acetyl groups are added to amino acids of histone proteins, making the chromatin less tightly packaged, encouraging transcription.
Recap
• Methylation- occurs on DNA & reduces gene expression
• Acetylation- occurs on histones & increases gene expression
Other factors of Gene expression
• Transcription initiation is another important control point in gene expression.
• The control of gene expression may also occur prior to translation and just after translation, where proteins are processed.
Connection to real life
• Cardiovascular disease– Gene expression provides valuable, tissue
and cell-specific information about the molecular mechanisms involved in disease processes, allowing a clinician to, for example, evaluate cardiovascular disease state, activity, and/or progression at a point in time.
Links
• http://web.mit.edu/bioedgroup/animations.htm
A program of differential gene expression leads to the different
cell types in a Multicellular organism.
• Zygote undergoes transformation through three interrelated processes. – Cell division– Cell differentiation- cells specialize– Morphogenesis- organization of cells into
tissues and organs.
What controls differentiation & Morphogenesis?
• Cytoplasmic Determinants– Maternal substances in the egg that influence the
course of the early development. – They are unevenly distributed in the early cells of the
embryo and result in different effects.
• Cell-cell signals– Results from molecules, such as growth factors
produced by one cell influencing neighboring cells, a process called induction which causes cells to differentiate.
– Determination• Series of events that lead to observable
differentiation of a cell. • Differentiation is caused by cell-cell signals and is
irreversible.
– Pattern Formation• Sets up the body plan and is a result of
cytoplasmic determinants and inductive signals.• Determines head and tail, left and right, back and
front. • Uneven distribution of morphogens plays a role in
establishing these axes.
• Stem Cell Animation
Cancer Results from genetic changes that affect cell cycle
control.
• Oncogenes- are cancer-causing genes. • Proto-oncogenes- genes that code for
proteins that are responsible for normal cell growth. – Become oncogenes when a mutation occurs that
causes an increase in the product of the proto-oncogene,
Or– an increase in the activity of each protein
molecule produced by the gene.
• Cancer can be caused by a mutation in a gene whose products normally inhibit cell division. – These genes are called tumor-suppressor
genes.
• Cancer development is based on the idea that cancer results from the accumulation of mutations that occur throughout life. – The longer we live, the more mutations that
are accumulated and the more likely that cancer might develop.
Activities
• This weeks CAR:
• What does Stem cell Research Mean to you? – Different types of Stem Cells? – How are they cultured in the lab? – What are some issues in Stem cell research? – What are some issues that you have?