gene expression and regulation. there are 23 pairs of chromosomes in a human body cell. on each...

Gene Expression and Regulation

• There are 23 pairs of CHROMOSOMES in a human body cell.

• On each chromosome, there are thousands of GENES.

• Each gene codes for one type of PROTEIN.

GENE EXPRESSION = DNARNAproteins

GENE EXPRESSION REGULATION

• In a multicellular organism, most of its cells have the same DNA. So how do cells become different? (skin cells, liver cells, etc.)

• An organism begins life as a mass of stem cells (unspecialized cells). These cells can potentially become any type of cell. At some point in development, cells become specialized.

• Although the DNA is the same, genes can be “turned on and off”. For example, the gene that codes for melanin is activated/expressed or “turned on” in skin cells but not for liver cells. This is called gene regulation.

• Because only certain genes are “turned on” in certain cells, this leads to cell differentiation.

• Cell differentiation is irreversible. For example, a heart cell cannot be changed back to a stem cell.

• The cell’s environment can control its gene expression, causing the cell to produce only certain proteins and/or certain amounts of protein. For example, exposure to UV light can cause a skin cell to produce more melanin, resulting in darker skin (a tan).

• If injury occurs, the gene regulation might allow overproduction of certain proteins that speed up healing.

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• However, sometimes things go wrong with gene regulation:– Unintended overproduction of protein (example:

can cause a cell to have uncontrolled cell division leading to tumors which may lead to cancer)

– Underproduction or no production of protein (example: insulin – diabetes)

– Production of protein at the wrong time– these things are usually caused by DNA mutations

Gene Regulation in Prokaryotes• Example – lac operon

An operon is a segment of DNA that contains a promoter, operator, and genes.

http://www.sumanasinc.com/webcontent/animations/content/lacoperon.html