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 htmhttp://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?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?