Cytology

1. 1
Cell structure I-Prokaryotic
cells
Dr. S. Mukanganyama
Department of Biochemistry (RM 136)
University of Zimbabwe
MBChB I, BDS I & NS101
2011-2012
Outline
• Introduction to Biochemistry
• Basic Units of life: Cells
• Prokaryote ,eukaryotic cells & viruses
• Role of microbial cells in disease
AIDS, Cholera, Swine Flue, influenza
MBCHB AND BDS 1 2011
BIOCHEMISTRY
COMPONENT MARKS
PRACTICALS/ASSIGNMENT/ECT 200
ORAL EXAMINATION 15 MIN 100
FINAL(PROFESSIONAL)
EXAMINATION 600
TOTAL 900
PASS MARK 450 (50%)
40-49%
FAIL
(SUPPLEMENTARY)
39% and below FAIL (REPEAT)

2. 2
Biochemistry provides
an understanding of:
• how living things are constructed
• what they contain
• how they function and communicate
• how they use food to obtain the building blocks and
energy for growth
• how genetic information is stored, expressed and
passed on to the next generation
• how enzymes catalyse reactions and
• how the cell's chemistry is co-ordinated and
controlled.
• Any aspect of living tissue that can be studied in
terms of chemical and physical principles is a subject
for biochemical investigation.
Biochemistry aims to understand the
structure and function of all living
things at the molecular level

3. 3
• Structure, organization, and functions of living matter in
molecular terms.
• Divided into three principal areas:
1. Structural chemistry of the components of living matter
and the relationship of biological function to chemical
structure.
2. Metabolism - the totality of chemical reactions that occur
in living matter.
3. The chemistry of processes and substances that store
and transmit biological information.
Biochemistry- “the Science
of life”

4. 4
The cell
•Basic Units of life Variable shapes and sizes +
needs energy to perform its specialised functions in
maintaining life.
•Smallest unit in the living organisms capable of
carrying out essential life processes.
Living systems:
•Grow
•Move
•Perform metabolism
•Respond to stimuli
•Replicate (reproduce) with high fidelity
•Life functions are ultimately interpretable in chemical
terms.
The Cell Theory
i) Cells make up all living matter
ii) Cells arise from other cells
iii) Genetic information required during the
maintenance of existing cells and the
production of new cells passes on from
one generation to the next
iv) Chemical reactions of an organism i.e.
metabolism takes place in cells
PROKARYOTIC AND
EUKARYOTIC CELLS
• Prokaryotic cells
"Pro"- Before nucleus.
Lack a definite membrane surrounding the
genetic material.
In various types of bacteria.
Cells invariably unicellular.
• Eukaryotic cells
“Eu”, - true or good and karyon for kernel or
hut. Have a membrane-enclosed nucleus
encapsulating their DNA.

5. 5
Archaebacteria Eubacteria
Progenitor
3.5 billion years
ago
Distinction between prokaryotic cells and eukaryotic cells artificial –
share a common biochemistry
Properties of Living Systems
a) Biological structures serve functional purposes. to
preserve the cell as a living entity.
b) Actively engaged in energy transformation - ability to
extract energy from the environment.
• Upon death an organism at equilibrium with its inanimate
environment.
• steady-state-, energy and material are consumed by the
organism and used to maintain its stability and order.
c) Remarkable capacity for self-replication
Virtually identical copies of deoxyribonucleic acid
(DNA). Sexual versus asexual
Simple molecules - units for
building complex structures
• Organisation of molecules to produce a cell/organisms
• Inorganic precursors e.g. CO2, H2O, Ammonia,
• Metabolites e.g. pyruvate, citrate,
• Building blocks e.g. Amino acids, Nucleotides,
Monosaccharides, Fatty acids, Glycerol
• Macromolecules e.g. proteins, Nucleic acids, polysaccharides
and lipids)
• Supramolecular e.g. ribosomes, structures complexes
cytoskeleton,
• Organelles (Nucleus, Mitochondria,
• The cell e.g. smooth muscle cell, bacterial cell
• Tissues e.g. smooth muscle tissue- similar types of cells
• Organs e.g. blood vessel - Different types of tissues
• Sytems e.g. cardiovascular system- different organs working
together closely
• Organism Many organ systems

6. 6
Cell Structure I -
Prokaryotic Cells
Prokaryotes
• Very small + surrounded by a rigid cell wall
• Single membrane, the plasma membrane or
cell membrane.
• No other membranes + no nucleus or
organelles.
• Distinct nuclear area where a single circular
chromosome is localised
• Internal membranous structure, mesosome,
derived from + continuous with the cell
membrane for cellular respiration activities.
Prokaryotes
• Highly cosmopolitan + varied and highly
adaptable metabolisms.
• Enormous varieties of habitats.
• Thrive in hostile conditions to eukaryotes
e.g. in lack of O2, high temperatures +
unusual chemical environments.
• High reproductive rates (less than 20
min/cell division).
• Resistant spores for survival of adverse
conditions.

7. 7
Cell Wall
• Rigid structures to impart shape.
• Prevents cell from expanding and bursting
• Cell wall structure and synthesis is unique to
prokaryotes.
• Two basic types of bacterial cell wall
structures Gram positive (G+) and Gram
negative (G-).
• Bacterial cells look very different following
staining with the Gram stain.
• G+ cells are Purple and G- cells are red.

8. 8
Structural Composition
• Peptidoglycan (murein) -Polymer of N-
acetylglucosamine (NAG), N-acetyl muramic acid
(NAM), L-alanine, D-alanine, D-glutamate and a
diaamino acid (L-lysine, L-ornithine or L-
daiminobuytric acid).
•  (1-4) glycoside linkage between NAM and NAG.
• Treatment of Gram positive (G+) bacteria with the
enzyme lysozyme degrades their cell walls, which
results in lysis.
• Lysozyme in body secretions, including saliva,
sweat, tears and vaginal secretions.
• Most Gram+ bacteria contain very little lipid, but
those of Mycobacterium , Corynebacterium contain
mycolic acids.
The Gram positive cell wall
• A thick peptidoglycan layer
• Very sensitive to the action of lysozyme
and penicillin, or its derivatives.
• Penicillin is often the antibiotic of choice
for infections caused by G+ organisms.
• E.g. Streptococcus pyogenes which
causes strep throat.
• Always treated with some type of
penicillin
The Gram positive cell wall

9. 9
Penicillin- an antibiotic
• Metabolic product of one micro-organism that in
very small amounts can kill or inhibit growth of
other micro-organisms.
• Inhibiting cell wall biosynthesis
• Penicillin -1929 Sir Alexander Flemming -
Penicillium notatum.
• Binds to and inactivates enzymes (glycopeptide
transpeptidase) that function to cross-link the
peptidoglycan strands of bacterial cell walls
(Reactions?)
• Exposure to penicillin results in bacterial lysis.
Bacterial Capsule
• A viscous substance forming
a layer or envelope around
the cell wall of some
bacteria.
Functions
• i) Against drying by binding
water molecules
• ii) Block attachment of
bacteriophages
• iii) Anti-phagocytic ,
• iv) Promote attachment of
bacteria to surfaces e.g.
Streptococcus mutants, (a
bacterium associated with
producing dental carries)

10. 10
1. Cell wall - Molecular composition: ------
Function: ------
2. The cell membrane- Molecular composition: ------
Function -------
3. Nuclear or nucleoid region- Molecular composition:
----
Function: DNA blue-print of the cell. DNA molecule
replicated to yield two double -helical daughter
molecules. mRNA is made (transcribed) from DNA to
direct the synthesis (translation) of cellular proteins.
Major features of
prokaryotic cells
???
4. Ribosomes: Molecular composition: About
15000 ribosomes. Small (30s) subunit and a larger
(50S) subunit. The total size of a complete unit is
70S. Mass of 2.3 x 106 daltons. 65% RNA and
35% protein.
Function: Protein synthesis.
5. Cytosol-Molecular composition: gelatinous
compartment , 20% protein by weight and rich in
the organic molecules that are the intermediates in
metabolism.
Function: Intermediary metabolism
Major features of
prokaryotic cells

11. 11
7. Flagella-Molecular composition: Threadlike appendages
composed of protein. Made of a single type of protein
subunit called flagellin.
· Function: Locomotion + for chemotaxis.
8. Storage of genetic information
Two forms DNA in bacteria:
i) Chromosomal DNA
ii) Plasmid DNA
• Bacterial Chromosome: Single circular DNA
macromolecule in nucleoid region. replication, transcription,
and regulation of gene expression.
• Plasmids: One or more pieces of circular macromolecules
of extra-chromosomal DNA.
• mating capabilities, resistance to antibiotics, tolerance
to toxic metals
Prokaryotic cells Polar or Monotrichous Lophotrichous Peritrichous
Bacteria are capable of showing simple
behavior that depends upon various
stimuli.
Chemotaxis - towards or away from a
chemical stimulus
Phototaxis - towards or away from light
Aerotaxis - towards or away from
oxygen
Magnetotaxis - orientation in a
magnetic field
Cell properties from plasmid genes
a. Drug Resistance- Plasmid-governed resistance
mediated by enzymatic inactivation of the drug e.g. acetylation
or phosphorylation
b. Virulence
• Genes that code for toxins e.g. the neurotoxin of Clostridium
tetani, the cholera toxin of Vibrio cholerae!!!!
• Genes for invasiveness.
•
c. Production of antimicrobial agents
• E.g antibiotics; bacteriocins.
d. Metabolic Activities
• metabolic pathways e.g. in flavobacterium species, for nylon
degradation
e. Chromosome transfer
• Conjugative plasmids (sex factors).

12. 12
Asexual reproduction
Note the electron-transparent nuclear region (n)
packed with DNA fibrils, the dense distribution of
ribosomal particles in the cytoplasm, and the absence
of intracellular membranous organelles.
Vibrio cholerae
Produces the cholera toxin which causes the release of a
Signalling molecule cAMP. cAMP causes the cells lining
the intestines to secrete large amounts of fluids into the cavity,
causing dehydration and death

13. 13

14. 14
Cholera
• Massive diarrhoea if untreated, massive
dehydration and death.
• Catastrophic loss of body fluid (1litre/hour) = in
response to the toxin produced by the bacteria.
• The toxin -an 87-kDa protein catalyses the
formation of [cAMP].
• 100 fold increment in intracellular [cAMP] induced
by cholera toxin causes the symptoms of cholera
by inducing these epithelial cells to pour out
enormous quantities of digestive fluid.