Cell Biology Lecture No. 1: Introduction To Cell Biology
Wednesday January 9 , 2013th
-Cell culturing is the in vitro technique used to grow cells or tissues outside the organism under
strictly controlled conditions. Cells are first isolated from any tissue by breaking down the cell-
cell and cell-matrix interactions. This can be done by mechanical fragmentation (cutting up the
cells), trypsin (a protease enzyme that helps chew apart membrane proteins and make cells
less cohesive) and EDTA (a divalent cation chelator that depletes the medium of free Ca as
calcium is integral in binding to membrane proteins that make cells more cohesive).
-Once dissociated, cells need to be maintained at favourable conditions in a specialized CO 2
incubator that mimics optimal heat and gas conditions (CO and O 2eeded) 2s well as sufficient
nutrients help keep cells alive. Cells are supplied with proper nutrients (amino acids, minerals,
vitamins, salts, glucose, etc.) and serum, a blood product devoid of cells which contains insulin
to help take up sugar and growth (mitogenic) factors that help cells to divide. The liquid tissue
culture media contains a dye known as phenol red, which is specifically added to indicate the
culture’s pH. Acidic cultures arise when too many cells are present, consuming much resources,
resulting in a production of lactic acid that turns the media yellow. Under alkaline conditions, the
media turns purple.
-Cells can grow as adherent cell cultures (require a surface, such as tissue culture plastic or
microcarrier) or suspension cell cultures (without being attached to a surface or cultured in
spinner flasks which cause mechanical agitation). Usually adherent cell cultures have been
coated with something (either an attractive electric charge or extracellular matrix proteins) which
aid cells in adhering to the plastic surface. Roller bottles can also allow for a suspension cell
culture to grow by mechanical agitation.
Two Major Cell Cultures:
A primary cell culture refers to cells taken directly from an organism (normal animal tissues or
whole embryos). As primary cell cultures grow, they move increasingly towards a confluent
model (tightly-packed population of cells), which initiates contact inhibition (a stop in the growth
of cells). When this occurs, the passaging of cells can be performed to enzymatically disrupt cell
adhesiveness and reallocate a portion of the culture to a low-density environment. These cells
usually divide a limited number of times (about 50 generations) until they reach what is called
the Hayflick limit (when cells undergo senescence). In addition to senescence, cells also
undergo contact inhibition (where cell-to-cell contact can stimulate cell cycle arrest, causing
cells to stop dividing) if cell density is high. Senescent cells are related to ageing.
-A cell line refers to cells which are transformed and are able to grow indefinitely. Also known as
immortal cells, these transformed cells, which have lost feedback mechanisms that regulate
growth, are less likely to exhibit contact inhibition. The first human cell line called HeLa was
established from the cervical carcinoma biopsy of Henrietta Lacks. This line grew and doubled
very quickly. Morphology Of Normal Vs. Transformed Fibroblasts:
-Normal cells such as fibroblasts (type of cells that synthesizes the extracellular matrix and
collagen) can be transformed by artificially introducing a gene that disrupts normal contact
inhibition. These once normal, elongated, aligned fibroblast cells are now transformed into a cell
line where fibroblasts rounded, hair-like and grow on top of one another.
Birth, Lineage & Death Of Cells:
-The origin of all bodily cells can be traced back to stem cells (whether embryonic or adult).
When a stem cell divides it gives rise to two genetically identical cells. Each cell can undergo
one of two possible fates: asymmetric division (gives rise two types of differentiated cells with a
finite lifespan) or self-renewal (gives rise to more undefined, identical stem cells with potentially
infinite lifespans). Symmetric division refers to a cell’s maturation that allows