Transcript Gene Expression and Regulation

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.
http://www.schremppstudio.com/cutfinger.html
• 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