Cell Biology and Molecular Biology
Lectures.
( First year medics )
Professor Dr. Zuhair Radhi Zahid
2011-2o12
( Lectures 1 and 2 )
Cell biology is the study of different cell types from which the
organisms are made up. A cell is the smallest unit of living matter. On
the other hand molecular biology of the cell is chiefly concerned with
eukaryotic cells. The later that form multi-cellular animals are social
organisms to an extreme degree: they live by coordination and
specialization. To understand how they function, one must study how
they function , one must study the ways of cells in multi-cellular
communities , as well as the internal workings of cells in isolation.
Biological macromolecules are composed of many thousandssometimes millions- of atoms linked together in precisely defined
spatial arrangement.
Cells contain 4 major types of giant molecules ( macromolecules) or
(polymers) such as proteins, polysaccharides, lipids and nucleic acids.
Proteins differ from one another in two ways : size ( number of amino
acids) and sequence of amino acids. Incorporated in its structure is a
series of biological messages that can be " read" in its interaction with
other molecules, enabling it to perform a precise functions for example
reception of signals.
Two major types of nucleic acids ( DNA and RNA ). A helix is a
common structural motive in biological molecules ( e.g. DNA and actin
filament ). The significance of polarity of the two DNA strands ,
complementary base pairing , linear arrangement of nucleotides , its
ability to replicate and coiling and super-coiling is of great biomedical
value. For these reasons DNA molecule is the archival copy of genetics
whereas RNA is the working copy ( codes, used to translate a specific
gene into proteins.
Elasticity of connective tissues and receptors ( including their
conformational changes ) inform us why biological molecules are able
to perform these vital and complex functions.
Cell theory: All organisms are made up of cells, and a cell is the
structural and functional unit of organs and , ultimately,
organisms. Cells are capable of self-reproduction; they come
from preexisting cells.
Cells are small most cells are smaller than one millimeter; some are
even as small as one micrometer (Um). Human egg is large enough to
be seen by the human eye (100 Um). Birds egg is the largest.
Cells exhibit variable shape; the following is a summary on the
subject:
1.Cuboidal cells lining kidney tubules.
2.Columnar cells lining the digestive tract.
3.Spherical cells, e.g. female ovum.
4.Monopolar neurons of the DRG.
5.Bipolar neurons of the retina.
6.Multi-polar neurons in the CNS.
7.The peculiar shape of spermatozoa.
According to their function cells perform different types of
activities such as:
1. Digestion.
2. Reproduction.
3. Glandular.
4. Nervous ( both sensory and motor ).
5.Excretion.
6. Muscular for contraction.
7. BVS.
8. Immunity.
MICROSCOPY: Tissues are usually fixed and sectioned for
microscopy. In chemical terms fixation makes cells permeable to
staining reagents. Most tissue samples are usually cut into very thin
slices (sections) with a microtome. Tissues need to be embedded in a
supporting medium before sectioning. The usual embedding media are
waxes and resins.
Specific molecules (e.g. specific proteins) can be located in cells by
fluorescence microscopy using fluorescent dye. Living cells are seen
clearly in phase-contrast. Fixed cells (dead) are examined by ordinary
light microscope.
IMAGE can be enhanced and analyzed by electronic techniques ( TEM
and SEM). Imaging of complete 3-dimensional objects is possible with
con-focal scanning light microscope using thick slice.
TABLE: Comparison between prokaryotic and eukaryotic cells:
Description
Prokaryote
( blue green algae, bacteria,
and mycoplasma )
Eukaryote
( other algae,protozoa,
metaphyte and metazoan )
--------------------------------------------------------------------------------------------------------------------------------------------Nuclear envelope
Absent
Present
--------------------------------------------------------------------------------------------------------------------------------------------DNA
Naked
nuclear membrane,
combined with protein
--------------------------------------------------------------------------------------------------------------------------------------------Chromosome
Single
Multiple
---------------------------------------------------------------------------------------------------------------------------------------------Nucleolus
Absent
Present
------------------------------------------------------------------------------------------------------------------------------------------ ----Ribosomes
70S
80S
-----------------------------------------------------------------------------------------------------------------------------------------------Endomembranes
Absent
Present
------------------------------------------------------------------------------------------------------------------------------------------------Mitochondria
Absent
Present
-------------------------------------------------------------------------------------------------------------------------------------------------Exocytosis and endocytosis
Absent
Present
--------------------------------------------------------------------------------------------------------------------------------------------------