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?