BIO 1140: Lecture 2
What is a cell?
•The smallest unit of life that is alive and it must have all the basic units of life.
•The building block of life.
•Bounded by a membrane, and contains genetic information.
The Cell theory:
1) All organisms consist of one or more cells.
2) The cell is the basic unit of structure for all organisms.
•Theodor Schwann, 1839 (Matthias Schleiden, 1838)
3) All cells arise only from pre-existing cells (i.e. the cell is the basic unit of
•Rudolf Virchow, 1855
•There is an enormous diversity in form, function, and size of cells.
•The shapes of cells can be very simple, to very complex.
•The size of cells differs greatly as well. (Some cells can be up to a meter long
as in motor cells in very large animals.)
•Share common characteristics: similar chemical composition, metabolism, use
of ATP as the cellular energy currency, and the use of DNA for genetic
Size in Biology:
•Micron: 1 um = 10^-6 m (most cells, and cell parts)
•Nanometre: 1 nm = 10^-9 m (viruses, small cell organelles, larger macro
•Most cells are between 1 and 100 um.
Why are cells small?
•Surface area to volume ratio.
oThe surface area of the cell must be matched to the volume of the cell
so that the cell is able to get rid of the waste it produces, as well as take
in enough nutrients to support itself. E.g. if the volume of a cell is very
large, but the surface area is not big enough, it will not be able to expel
all of its waste and therefore poison itself, and it will not be able to take
in enough nutrients to live.
oTo solve this problem, the cell can divide, or it can have a folded
membrane, which increases the surface area dramatically, but not the
•Rates of diffusion.
oBrownian motion: the random movement of molecules from an area
where they are very abundant to an area where they are less abundant.
oCells need a certain concentration of molecules to survive and to carry
out reactions, if cells are too big then the concentrations needed also
grow and therefore it is harder to maintain the same concentration of
oCytoplasm can be partitioned so that a certain part of the cell needs
certain molecules and therefore it is easier to maintain the molecule
•Simple structure: cell wall, plasma membrane, cytoplasm that lacks organelles,
ribosomes, nucleoid, flagellum.
•No nucleus or membrane bound organelles. No protein associated with the
•Very simple interior, no internal transport system, not partitions within the cell.
•Because these cells are not utilizing any of the tricks, they tend to be very
small in size (1-5 um).
•Two different types: bacteria and archaea. Not very similar to each other even
though they share some similar structural characteristics.
Bio 1140: lecture 2: the smallest unit of life that is alive and it must have all the basic units of life, the building block of life, bounded by a membrane, and contains genetic information. Size in biology: micron: 1 um = 10^-6 m (most cells, and cell parts, nanometre: 1 nm = 10^-9 m (viruses, small cell organelles, larger macro molecules, most cells are between 1 and 100 um. Prokaryotic cells: simple structure: cell wall, plasma membrane, cytoplasm that lacks organelles, ribosomes, nucleoid, flagellum, no nucleus or membrane bound organelles. Many do not cause any harm to humans, but many others do. We are most familiar with the bacteria that cause illness: there are many different uses for bacteria. Include protists (single-celled organisms), fungi, animals, plants (multicellular: utilize the compartmentalization of cellular functions. Therefore they are able to be much bigger than prokaryotes: purple pages of text book for animal examples.