3. The cell is the functional unit of
all living organisms.
• Simple organisms - Bacteria and algae
consist of a single cell.
• Multicellular organisms - more complex
consist of many cells as well as
extracellular matrix.
• Cells with great variety of functional and
morphological specializations.
• Differentiation - process by which
cells assume specialised structure and
function.
5. Eukaryotic cells consist of a nucleus and
cytoplasm
• The cytoplasm contains a number of organelles each
with a defined function.
• Organelles bounded by membranes
• Fatty acids and triglycerides are mostly synthesised
within the cytosol.
• The nucleus may be considered the largest organelle.
• its substance - nucleoplasm
• bounded by a membrane system called the nuclear
envelope or membrane.
• contains the genetic material of the cell.
6. Cytoplasm
• Cytosol - fluid medium in the cytoplasm in which the
organelles are suspended and many metabolic reactions
take place.
• Cytoskeleton - a network of minute tubules and
filaments
• provides structural support for the cell and its
organelles
• provides a mechanism for transfer of materials within
the cell and movement of the cell itself.
7. Organelles
• Endoplasmic reticulum - an extensive
system of flattened membrane-bound
tubules, saccules and flattened cisterns.
• Golgi apparatus – another discrete
system of membrane-bound saccules
• typically located close to the nucleus.
• Mitochondria - scattered free in the
cytoplasm are a number of relatively large,
elongated organelles.
• have a smooth outer membrane and a
convoluted inner membrane system.
9. Plasma membrane or plasmalemma
• an external lipid membrane
• serves as a dynamic interface with the external
environment.
• adjacent cells
• extracellular matrix
• Functions:
• transfer of nutrients and metabolites
• attachment of the cell to adjacent cells and
extracellular matrix
• communication with the external environment.
10. Membrane structure
• Permeability to lipid-soluble molecules
• Permeability to non-lipid-soluble molecules
• Singer and Nicholson (early 1970s) - proposed the fluid
mosaic model of membrane structure.
• a lipid bilayer sandwiched between two layers of
protein.
12. Cell membranes consist of a bilayer of phospholipid molecules
that are amphipathic
• polar, hydrophilic (water-loving) head
• derived from glycerol conjugated to a
nitrogenous compound via a phosphate
bridge.
• non-polar, hydrophobic (water-hating)
tail.
• consists of two long-chain fatty acids,
each covalently linked to the glycerol
component of the polar head.
• straight-chain saturated fatty acid
• unsaturated fatty acid which is 'kinked' at
the position of the unsaturated bond.
14. Fluidity and flexibility of the
membrane
• Due to presence of unsaturated fatty acids
• prevent close packing of the
hydrophobic tails.
• Due to cholesterol molecules in the bilayer
• stabilize and regulate the fluidity of the
phospholipid bilayer
• Due to protein molecules incorporated in
the membrane.
• intrinsic or integral proteins
• extrinsic or peripheral proteins
• transmembrane proteins
15.
16. External surface of the plasma membranes
of animal cells
• Glycocalyx - polysaccharide molecules
projecting from the surface of the bilayer forming
an outer coating.
• involved in cell recognition phenomena
• in the formation of intercellular adhesions
• in the adsorption of molecules to the cell
surface
• in some situations, provides mechanical and
chemical protection for the plasma
membrane.
17. GLYCOCALYX
• Glycoproteins -
membrane proteins
conjugated with short
chains of
polysaccharide
• Glycolipids -
membrane lipids
conjugated with short
chains of
polysaccharide
19. NUCLEUS
• the most obvious feature of the cell seen under the light
microscope.
• considered the largest organelle in the cell.
• “Control center” of the cell
• Primarily contains deoxyribonucleic acid (DNA)
arranged in the form of chromosomes - the “blueprint”
from which all the other components of the cell are
constructed.
• When a cell divides, the first step in this process is
replication of the DNA so that a copy of the cell blueprint
goes to each of the daughter cells.
20. Nuclear contents:
• DNA - making up less than 20% of its mass
• Protein called nucleoprotein - synthesised in the
cytoplasm and imported into the nucleus.
• histone proteins - low molecular weight, positively
charged which bind tightly to DNA and control the
coiling and expression of the genes encoded by the
DNA strand.
• non-histone proteins, including enzymes for the
synthesis of DNA and RNA and regulatory proteins.
• Ribonucleic acid (RNA)
• newly synthesised messenger - mRNA
• Transfer - tRNA
• Ribosomal - rRNA
21. Chromatins refers to CHROMOSOMES at
interphase.
Chromatin in the nucleus
forms 2 distinct dispersal
patterns:
•Condensed areas –
heterochomatin; not actively
producing RNA. (INACTIVE)
•Extended areas – (light)
euchromatin; in the process
of producing RNA.
(ACTIVE)
22. NUCLEOLUS
• Spherical, highly basophilic structure that is usually
located eccentrically in the nucleus.
• nuclei of cells highly active in protein synthesis, contain
one or more dense structures called nucleoli
• the sites of ribosomal RNA synthesis and ribosome
assembly.
23. Nuclear envelope (Nuclear membrane)
• Visible in electron micrographs.
• Too thin to be resolved by LM.
• Consists of two unit membranes (outer and inner) 7-8
nm each.
• Separated by 10-30 nm space (perinuclear space)
• Continuous with the rough endoplasmic reticulum (rER).
• Perforated by circular openings (nuclear pores), 70 nm
• Nuclear pores – provide a channel for the exchange of
substances between the cytoplasm and the nucleus.
25. RIBOSOMES
• minute cytoplasmic organelles, each
composed of two subunits of unequal size.
• Each subunit is composed of a strand of
ribosomal RNA (rRNA) with associated
ribosomal proteins forming a globular
structure.
• Ribosomes align mRNA strands so that
transfer RNA (tRNA) molecules may be
brought into position and their amino acids
added sequentially to the growing
polypeptide chain – PROTEIN SYNTHESIS
Polyribosomes - ribosomes that are connected to each other by a fine thread of mRNA.
26. Ribosomes are sites for protein synthesis
Free ribosomes – sites for protein synthesis that are to be used within the cell.
Attached ribosomes - sites for protein synthesis that are to be exported and
also for protein to be used within the cell
27. Endoplasmic reticulum
• A system of interconnecting tubules, vesicles, and
flattened sacs (cisternae).
• The most extensive membranous structure in the cell.
• Membrane units are much thinner than the
plasmalemma; not visible by routine histo stains.
• ER consists of 2 contiguous regions:
• Rough endoplasmic reticulum (rER)
• Smooth endoplasmic reticulum (sER)
28. Rough endoplasmic reticulum
(rER)
• Receives the proteins that are
synthesized by the ribosomes
attached to it.
• Proteins destined for export
and lysosomal proteins
(enzymes) pass through the
membrane into its lumen.
• Proteins are processed into
the form of transfer vesicles
before handing them over to
the Golgi complex.
Smooth endoplasmic reticulum
(sER)
• Continuous with and similar to
rER except that it lacks
ribosomes.
• Principal functions:
• Biosynthesis of cholesterol
and phospholipids
• membrane synthesis and
repair.
29. • Liver cells, sER is rich in cytochrome P450
and plays a major role in the metabolism
of glycogen and detoxification of various
noxious metabolic by-products, drugs and
alcohol.
• Muscle cells: sarcoplasmic reticulum,
sER is involved in the storage and release
of calcium ions that activate the contractile
mechanism
30. Golgi complex
• consists of stacked,
saucer-shaped
membrane-bound
cisternae.
• The outermost
cisternae take the
form of a network of
tubules known as the
cis and trans Golgi
networks.
31. Packaging of proteins in the Golgi complex
(from rER)
1. Proteins synthesised in the rER are transported to the
Golgi apparatus in coated vesicles (transfer vesicle).
2. On arrival at the convex cis Golgi network, the coated
proteins disengage and the vesicles fuse with the
membrane of the forming face.
3. Proteins are passed from cisterna to cisterna.
Glycosylation of proteins is completed by sequential
addition of sugar residues and the proteins are packaged
for transport to their final destination.
4. On arrival at the concave trans Golgi network, the
proteins are accurately sorted into secretory vesicles.
33. Group of plasma cells from inflamed tissue;
• cells are responsible for antibody production as part of the body's immune
defences.
• The plentiful rER is strongly basophilic and the protein is acidophilic so that
there is staining with both eosin and haematoxylin giving a purplish or
amphophilic colour to the cytoplasm.
•The well-developed Golgi complex G consists of lipid (membrane), which is
dissolved out during preparation. Thus the Golgi is unstained and appears as a
pale area (negative image) adjacent to the nucleus
34. Lysosomes
• membranebound organelles containing an amorphous
granular material.
• contain electron-dense particulate material
• have more than 40 different degradative enzymes
including proteases, lipases and nucleases – come from
Golgi complex.
• Lysosomes are the principal organelles involved in:
• Heterophagy – digestion of phagocytosed material from outside.
• Autophagy – digestion of unneeded or senescent cell organelles.
35. Peroxisomes or microbodies
• small, spherical, membrane-bound organelles that
closely resemble lysosomes in size and ultrastructure.
• contain oxidases and catalases
• Oxidases are utilized in catabolic pathways which
form hydrogen peroxide, a potentially cytotoxic by-
product
• Hydrogen peroxide is used by certain phagocytic
cells to kill ingested microorganisms.
• Catalase regulates hydrogen peroxide concentration,
utilising it in the oxidation of a variety of potentially
toxic substances including phenols and alcohol.
36. INCLUSIONS
• Temporary structures (may or may not be
membrane-bound).
• Not all cells contain inclusions.
• Fat droplets, glycogen granules, zymogen
granules, pigment granules, crystals, lipochrome
pigments, lipofuschin pigments and dust
particles.
37. Sympathetic ganglion cells:
contains lipofuscin,
accumulates as brown
granular material in the
cytoplasm (Age pigment)
Nerve cells : contain melanin,
as the substantia nigra
Basal layer of the skin contain
melanin, which is mainly
responsible for skin colour.
Fat droplets in adipocytes
for lipid storage.
PAS stain reveal glycogen,
the storage form of
carbohydrates in lever cells.
Paneth cells in inetstinal
epithelium contain
zymogen granules.
38. Mader: Biology, 9th Ed.
Mitochondria
• Mitochondria are involved in cellular respiration
• Produce most of ATP utilized by the cell
• Cristae – inner membrane that encloses matrix
• Matrix – contains enzymes that break down nutrient
molecules; also contains mitochondrial DNA and
ribosomes
39.
40. MITOCHONDRIA
• the principal organelles involved in
cellular respiration in mammals
• Features: often “hot-dog” shaped, but can
become rod-like, filamentous, spherical,
etc.
• The number in the cell depends on its
energy requirement.
• Liver cell – 2000 M / cell
• Resting lymphocytes – only a few M
• Tend to aggregate in areas within the cell
where energy requirement is high.
• Sperm cell; M conc. at the midpiece of tail.
41. CYTOSKELETON
• Supporting framework of minute filaments and tubules.
• Maintains the shape and polarity of the cell.
• To accommodate the dynamic functions of cells:
• Cells that propel themselves about by amoeboid
movement (e.g. white blood cells)
• Cells that have actively motile membrane
specialisations such as cilia and flagella (tracheal
epithelial cells)
• Cells that are highly specialised for contractility (e.g.
muscle cells)
• Cell division - a process that involves extensive
reorganisation of cellular constituents.
44. Cytoskeletons:
1. Microfilaments
• Extremely fine protein filament (5-7 nm)
• Made up of F-actin filament – undergo frequent
assembly and disassembly to accommodate changes in
cell shape and cell movement.
• Abundant in the peripheral areas of the cell just beneath
the cell membrane.
• Involved in the activities of the cell membrane such as
exocytosis and endocytosis.
• Less abundant in the central portion of the cell.
• Probably involved in the movement of cell organelles.
• Involved in the locomotion of certain cells.
45. Cytoskeletons:
2. Intermediate filaments
• Intermediate in size between microfilaments and
microtubules (10-15 nm in diameter).
• Intermediate filaments have 5 types (morph. similar) but
differ in protein contents:
1. Keratin – in keratinocytes of skin cells; for cell-to-cell
attachment.
2. Desmin – skeletin; in muscle cells; more numerous
in smooth than in striated muscles .
3. Vimentin – scattered all over cytoplasm of fibroblasts
and muscle cell.
4. Neurofilament - provide internal support for neurons
5. Glial filament - provide internal support for glial cells.
46. Cytoskeletons:
3. Microtubules
• Tubules that are much thicker than microfilaments or
intermediate filaments (25 nm).
• Formed in the centrosomes (microtubule organizing
center; MTOC).
• Attached to organelles – for movement
• Scattered in the cytoplasm – internal support to cell
• Comprise centrioles – sources of mitotic spindles,
the cilia of ciliated cells and flagellum of sperm cells.
47. References:
• Young B. 2009. WHEATER’S FUNCTIONAL
HISTOLOGY. 5TH
Edition. UK: Churchill Livingstone.
Distributor: Phils: C & E Publishing, Inc.
• Gonzales E. 2009. ESTEBAN and GONZALES’
TEXTBOOK OF HISTOLOGY. 4TH
Edition. PHILS: C & E
Publishing, Inc.
Editor's Notes
inner and outer nuclear membranes have the typical phospholipid bilayer structure but contain different integral proteins. outer lipid bilayer is continuous with the endoplasmic reticulum ER and has ribosomes R on its cytoplasmic face. inner aspect of the inner nuclear membrane, there is an electron-dense layer of intermediate filaments, the nuclear lamina , consisting of polypeptides called lamins that link inner membrane proteins and heterochromatin
Cells with numerous ribosomes have intensely basophilic cytoplasm. This basophilia is due to the numerous phosphate groups in the RNA of the ribosomes.
Every cell contains within its DNA the code for every protein that individual could produce. Production or expression of selected proteins only is characteristic of differentiated cells. The presence of a particular protein within a cell is one possible method of identifying different cell types, e.g. the presence of actin and myosin in muscle cells. Thus the DNA code is converted first into RNA and then into a specific protein. First, the DNA template is copied to form a complementary messenger RNA ( mRNA ) copy, a process known as transcription . A fairly recent discovery is that the DNA template contains non-coding sequences or introns I which are cut or spliced out of the mRNA before it passes through the nuclear pore complex NPC into the cytoplasm. Here the mRNA binds to ribosomes R , organelles that read the mRNA sequence and translate it into the specific sequence of amino acids which characterises a particular protein.
Fatty acids and triglycerides are mostly synthesised within the cytosol, whereas cholesterol and phospholipids are synthesised in areas of smooth endoplasmic reticulum
In the Golgi apparatus the glycosylation of proteins, begun in the rER, is completed by sequential addition of sugar residues and the proteins are packaged for transport to their final destination. There are two current theories as to how this happens. The most accepted theory postulates that each cisterna is enriched for the specific enzyme to add a specific sugar and that proteins are passed from cisterna to cisterna by formation of a series of coat protein complex I (COP I) coated vesicles which then fuse with the next cisterna in the stack. Alternatively, there is now some evidence to show that the medial cisternae mature, with specific enzymes being moved backwards to less mature cisternae by means of coated vesicles. It is possible that both mechanisms operate depending on circumstances.
