The plasma membrane surrounds eukaryotic cells and is composed of phospholipids, cholesterol, proteins, and carbohydrates. Phospholipids form a double layer with hydrophobic tails facing the center and hydrophilic heads facing out. Cholesterol makes the membrane more fluid. The plasma membrane regulates what passes in and out of the cell. Inside the cell are organelles including the nucleus that contains DNA, endoplasmic reticulum that synthesizes proteins, Golgi apparatus that modifies proteins, mitochondria that generate energy, lysosomes that digest waste, and peroxisomes that break down fatty acids.

1. CYTOLOGY

3. Cell Components
Nucleus
Cytoplasm
Cytoskeleton
Cell surface

4. Plasma Membrane
All eukaryotic cells are enveloped by a
limiting membrane composed of
phospholipids, cholesterol, proteins, and
chains of oligosaccharides covalently
linked to phospholipids and protein
molecules.
The cell, or plasma, membrane functions
as a selective barrier that regulates the
passage of certain materials into and out
of the cell and facilitates the transport of
specific molecules.

5. Membrane phospholipids, such as
lecithin and cephalin, consist of two
long, nonpolar chains linked to a charged
(hydrophilic) head group. Cholesterol is
also a constituent of cell membranes.
Within the membrane, phospholipids are
most stable when organized into a
double layer with their hydrophobic
(nonpolar) chains directed toward the
center of a membrane and their
hydrophilic (charged) heads directed
outward.

6. Cholesterol breaks up the close
packing of the phospholipid long
chains, and disruption makes
membrane more fluid.
The cell controls the fluidity of the
membranes through the amount of
cholesterol present.

7. Plasma membrane
The fluid mosaic model of membrane structure
Main components;
1. Phospholipids
2. Cholesterol
3. Proteins
4. Chains of oligosaccharides

8. Plasma membrane

9. Plasma membrane
Phospholipids
-phosphatidylcholine(lecithin)
-phosphatidylethanolamine(cephalin)
Structure: 2 nonpolar (hydrophobic) hydrocarbon chains
linked to one charged(hydrophilic) head group

10. Cholesterol
-breaks up the close packing of the phospholipid long
chains,and as a consequence plasma membranes become
more fluid

11. Proteins
1. Integral proteins
-directly incorporated within the lipid bilayer
2. Peripheral proteins
-exhibit a looser association with membrane surfaces.They can
be easily removed from the cell membranes with salt
solutions

12. In order to regulate the transport of molecules, there
are two types of proteins in the cell:
- carrier proteins
- transport proteins.
The two types of transport proteins are:
- channel
- carrier protein.
Transport is either active or passive.
Active transport is moving molecules against the
concentration gradient and energy is required in the
form of ATP.

13. Glycocalyx
-a fuzzy carbohydrate-rich region on the external surface of the
cell
-composed of carbohydrate chains linked to a membrane
proteins and lipids and of cell-secreted glycoproteins and
proteoglycans

14. Plasma membrane

15. Plasma membrane-transport
The plasma membrane is the site at which materials are
exchanged between the cell and its environment
Endocytosis-bulk uptake of material through the plasma
membrane

19. Passive transport is moving molecules down the concentration
gradient and no energy is required. Examples of passive
transport are diffusion,
which moves from high concentration to low concentration and
osmosis, which is the diffusion of water molecules.

20. The Nucleus
It’s enclosed by the
nuclear envelope and
contains:
- nuclear lamina
- nucleolus
- chromatin

21. Nucleus
•The nucleus is the site of deoxyribonucleic
acid (DNA) replication and trascription of
DNA into precursor ribonucleic acid (RNA)
molecules.
It contains all of the enzymes required for
replication and repair of newly senthesized
DNA, as well as for trascription and
processing of precursor RNA molecules.

22. Nuclear envelope
-Is double membrane
containing pores
-The outer nuclear
membrane is continuous
with the endoplasmic
reticulum

23. Nucleolus
contains three morphologically
distinc zones:
- granular zone – found at
periphery; contains ribosomal
precursor particles in various stages
of assembly
- fibrillar zone – centrally located;
contains ribonuclear protein fibrils
- fibrillar center- contains DNA that
is not being transcribed

24. Chromatin
Is a complex of:
DNA
histone proteins
and nonhistone proteins

25. DNA
A doublestranded
helical
molecule
that carries
gentic
information
of the cell

26. Histone proteins
Positively charged proteins enriched with
lysine and arginine residues. They are
important in forming two types of
structures in chromatin:
- nucleosomes
- solenoid fibers
The nucleosomes are the basic repeating
units of the chromatin fiber.
Schematic representation of a nucleosome. This
structure consists of a core of 4 types of histones (2
copies of each)—H2A, H2B, H3, and H4—and one
molecule of H1 or H5 located outside the DNA
filament.

27. Nonhistone proteins
Include enzymes involved in nuclear functions such as:
- replication
- transcription
- DNA repair
- regulation of chromatin function
They are acidic of neutral proteins.

28. Forms of chromatin
- Heterochromatin - highly
condensend, transcriptionally
inactive
- Euchromatin – a more extended
form of DNA, which is potentially
transcriptionally active.

29. Cytoplasm components
-Endoplasmic reticulum
-Golgi Apparatus
-Lysosomes
-Peroxisomes
-Mitochondria

30. Endoplasmatic Reticulum

31. Endoplasmatic Reticulum
Exists in two forms:
-Rough endoplasmatic
reticulum (RER)
-Smooth endoplasmatic
reticulum (SER)

32. Rough endoplasmatic reticulum
- RER is a single, lipid bilayer continuous with
outer nuclear membrane. It’s organized into
stacks of large flattened sacs called cisternae
that are studded with ribosomes on the
cytoplasmic side.
- RER synthesizes proteins that are destined for
the Golgi apparatus, secretion, the plasma
membrane and lysosomes.
- RER is very prominent in cells that are
specialized of proteins destined for secretion
(e.g., pancreatic cells)

33. Smooth endoplasmic reticulum
SER is a network of membranous sacs, vesicles, and
tubules continuous with the RER, but lacking
ribosomes.
SER contains enzymes involved in the biosynthesis of
phospholipids, triglycerides, and sterols.

34. Functions of SER
1.Detoxification Reactions / hepatocytes /
These are reactions that make compounds soluble so that
they can be excreted.
Two types of reactions that increase solubility are:
- Hydroxylation reactions
- conjugation reactions

35. Functions of SER
2.Glycogen Degradation and Gluconeogenesis
3.Steroid synthesis / Leydig cells in testis and adrenal
gland cells /

36. Functions of SER
4.Reactions in Lipid Metabolism
Lipolysis begins in the SER with the release fatty acid
from triglyceride.
The SER is also the site where lipoprotein particles are
assembled

37. Functions of SER
5.Sequesration and Release of Calcium Ions
In striated muscle the SER is known as sarcoplasmic
reticulum (SR).
The sequestration and release of calcium ions takes place
in the SR.

38. Golgi Apparatus

39. Consists of disc-shaped smooth cisternae
that are assembled in stacks
(dictyosomes)
Associated with numerous small
membrane-bound vesicles.

40. The Golgi apparatus has two
distinct faces:
The cis (forming) face
associated with RER
The trans (maturing) face is
often oriented toward the
plasma membrane. The transmost region is a network of
tubular structures known as
the trans-Golgi network.

41. Functions of Golgi apparatus
Proteins and Lipids
AG is the site of posttranslational modification and sorting
of newly synthesized proteins and lipids.
Glycoproteins
Further modification of the carbohydrate moiety of
glycoproteins produces complex and hybrid oligosaccharide
chains. This determines which proteins remain in the Golgi
apparatus or leave the Golgi apparatus to become secretory
proteins, lysosomal proteins, or part of the plasma
membrane.

42. Mitochondria

43. Mitochondria
- two membranes
- synthesizes adenosine
triphosphate (ATP)
- contain their own doublestranded circular DNA, and make
some of their own proteins
- have several compartments

44. Outer membrane
- is smooth, continuous, and
highly permeable
- contains an abundance of porin,
an integral membrane protein
that forms channels in the outer
membrane

45. Inner membrane
Is impermeable to most small ions and small
molecules.
-The inner membrane has numerous infoldings,
called cristae. The cristae greatly increase the
total surface area.
They contain the enzymes for electron transport
and oxidative phosphorylation.
The number of mitochondria and the number of
cristae per mitochondrion are proportional to
the metabolic activity of the cells in which they
reside.

46. Intermembrane compartment
It is the space between the
inner and outer membranes.
Contains enzymes that use ATP
to phosphorylate other
nucleotides.

47. Matrix
Is enclosed by the inner membrane and contains:
-dehydrogenases- oxidize many of the substrates in the cell
, generating reduced NADH (nicotinamide adenine dinucleotid)
and reduced FADH2 (adenine dinucleotide) for use by the
electron transport chain and energy generation.
-a double-stranded circular DNA genome- encodes a few
of the mitochondrial DNA is always inherited from the
mother, resulting in the maternal transmission of diseases
of energy metabolism.
-RNA, proteins, and ribosomes- although there is some
protein synthesis, most mitochondrial proteins are
synthesized in the cytoplasm and are transferred into the
mitochondria.

48. Ribosomes

49. Ribosomes
Composed of RNA and protein
Consist of large (60s) and small (40s)
subunits
Assembled in the nucleus and
transported to the cytoplasm through
the nuclear pores
The large ribosomal subunits are
synthesized in the nucleolus, whereas
the small subunits are synthesized in
the nucleus.

50. Polysomes
Ribosomes often form polysomes,
which consist of a single messenger
RNA (mRNA) that is being
translated by several ribosomes at the
same time.
The ribosomes move on the mRNA
from the 5’ end toward 3’ end. The
two ribosomal subunits associate on
the mRNA with the small subunit
binding first.

51. Forms of ribosomes
-Free polysomes are the site of
synthesis for proteins destined for
the nucleus, peroxisomes, or
mitochondria.
-Membrane-associated polysomes
are the site of secretory proteins,
membrane proteins, and
lyzosomal enzymes.

52. Peroxisomes

53. Peroxisomes are a heterogeneous group of
small, spherical organelles with a single
membrane.
- Contain a number of enzymes that transfer
hydrogen atoms from organic substrates to
molecular oxygen with the formation of
hydrogen peroxide.
Catalase, the major peroxisomal protein,
degrades the hydrogen peroxide to water and
oxygen.
- Peroxisomal enzymes are synthesized on free
polysomes. After translation, the enzymes are
incorporated directly into peroxisomes.

54. Peroxisomes functions
1. synthesis and degradation of hydrogen peroxide
2. β-oxidation of very long chain fatty acids (>C24) starts in
the peroxisomes and proceeds until the carbon chain has
been reduced to length of approximately 10 carbons.
Oxidation of the residual 10 carbons is completed in the
mitochondria.
3. Phospholipid exchange- peroxisomes contain enzymes that
convert phosphatidylserine and phosphatidylethanolamine
4. Bile acid synthesis

55. Lysosomes
Spherical membraneenclosed organelles
Contain enzymes required
for intracellular digestion

56. Lysosomes forms
Primary lysosomes have not yet acquired the
materials to be digested. They are formed by budding
from the trans side of the Golgi apparatus.
Secondary lysosomes are formed by the fusion of the
primary lysosome with the substrate to be degraded and
have contents that are in various stages of degradation.

57. Lysosomes contain approximately 60 hydrolytic enzymes.
These include nulceases for degrading DNA and RNA,
lipases for degrading lipids, glycosidases for degrading
glycoconjugates , proteases and peptidases for degrading
proteins, and a variety of phosphatases
all lysosomal enzymes are acid hydrolases, with optimal
activity at pH of approximately 5.0
the synthesis of the lysosomal hydrolases occurs in the RER;
the hydrolases are transffered to the Golgi apparatus, where
they are modified and packaged into lysosomes.

58. Proteasomes

59. Proteasomes
are multiple-protease complexes that digest
proteins targeted for destruction by attachment
to ubiquitin. Protein degradation is essential to
remove excess enzyme and other proteins that
become unnecessary to the cell after they
perform their normal functions, and also to
remove proteins that were incorrectly folded.
Protein encoded by virus should also be
destroyed.

60. Proteasomes deal primarily with
proteins as individual molecules,
whereas lysosomes digest bulk material
introduced into the cell or whole
organelles and vesicles.

61. The proteasome has a core particle
with the shape of a barrel made of four
rings stacked on each other. At each end
of the core particle is a regulatory
particle that contains ATPase and
recognizes proteins with ubiquitin
molecules attached.

62. Cytoskeleton
Provides a supportive
network of tubules and
filaments in the cytoplasm
of eukaryotic cells. It is
composed of :
- microtubules
- intermediate filaments
- microfilaments.

63. The cytoskeleton
Microtubules- 25 nm
Microfilaments (actin filaments)-6 nm
Intermediate filaments- 10 nm

64. Microtubules
Tubular structures
Variable in length
Composed of subunits-heterodimers
Each heterodimer is composed of alfa and beta tubulin
molecules
Alfa-tubulin
Beta-tubulin
protofilaments
microtubules

65. Microtubules

66. Microtubules
The main functions of microtubules
-play role in the development and maintenance of cell shape
-participate in the the intracellular transport of organelles and
vesicles
-provide the basis for cytoplasmic components ;centrioles,basal
bodies, cilia,flagella

67. Microtubules-function
chromosomal movement during meiosis and mitosis.
Microtubule assembly is an important event in spindle
formation
intracellular vesicle and organelle transport
ciliary and flagellar movement

68. Microtubules

69. Centrioles
Cylindical structures composed of highly organised
microtubules
Each centriole consists of nine sets of microtubules arranged
in triplets
Centrosome- an important role during cell division

71. Cilia and flagella
-motile processes, covered by cell membrane
Cilia-usually a large number of cilia on one ciliated cell,
play role in sweeping fluid from the surface of cell sheets.
Flagella-in humans only spermatozoa possess a flagellum
(only one)
typical core organisation, contains nine pairs of
microtubules, possesing a 9+2 pattern=AXONEME
Adjacent peripheral pairs are linked to each other by protein
bridges-nexins

72. Cilia
Are apical cell surface of cell membrane
that contain microtubules. They are inserted
on centriole-like basal bodies present below
the membrane surface at the apical pole.
Cilia contain two central microtubules
surrounded by a circle of nine peripheral
microtubule doublets.

74. Cilia and flagella

75. Movement of Cilia
Cilia move back and forth to propel
fluid and particles in one direction.
They are important in clearing mucus
from respiratory tract.

76. Immotile cilia syndrome
Cause; mutations in the proteins of cilia and flagella
Immotile spermatozoa- male infertility
Lack of the cleansing action of cilia in the respiratory tractrespiratory infections

77. Basal body
-at the base of each cillium and flagellum
-Structure; similar to a centriole
-Function; controls the assembly of the axoneme

78. Microfilaments
The thinnest filaments of the cytoskeleton
Found in cytoplasm of all eukaryotic cells
Built up of a protein-ACTIN (actin filaments)
Are formed by the head-to-tail polimerization of actin
monomers (globular G-actin) forming a long filamentous F
actin polymer.
- The polymers are twisted around each other in a double
helical formation

79. Microfilaments

80. Microfilaments
In skeletal muscle they interract with myosin filaments which
is an essential process in the mechanism of contraction.
In most cells actin filaments form a thin sheath just beneath
the plasmalemma, called the cell cortex-associated with
membrane activities like endocytosis,exocytosis and cell
migratory activity
A role in moving and shifting cytoplasmic components

81. Microfilaments
-are
composed of
actin.
Each actin
filament (Factin) consists
of two strands
of actin
twisted into
helical pattern

82. Microvilli
Are apical cell surface evaginations of
cell membranes that function to
increase the cell surface area available
for absorption. A thick glycocalyx
coat covers them. The core of each
microvillus contains actin
microfilaments. It is anchored in the
apical cell cytoplasm to the terminal
web, which itself is anchored to the
zoula adherens of the cell membrane

83. Intermediate filaments
They are intermediate in thickness between microtubules and
microfilaments. They function primarily in structural roles and
contain several types of tissue-specific proteins:
cytokeratins- found in epithelial tissue
desmin- found in smooth muscle; Z disks of skeletal and cardiac
muscle
vimentin- found in cells of mesenchymal origin (endothelial
cells, fibroblasts, chondroblasts, vascular smooth muscle)
neurofilaments- found in neurons
glial fibrillaty acid protein (GFA)- found in astrocytes

84. Intermediate filaments
FILAMENT TYPE
CELL TYPE
EXAMPLES
keratins
epithelium
Both keratinizing and
nonkeratinizing epithelia
vimentin
Mesenchymal cells
Fibroblasts, macrophages
desmin
muscle
Striated and smooth
muscle(except vascular
smooth muscle)
Gilial
Glial cells
Astrocytes
Neurofilaments
neurons
Nerve cell body and
processes