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 = DNA  RNA  proteins

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.

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.