26. CELL COMPONENTS
1.1. Cytoskeleton
= cell inclusions
Definition: cellular ‘scaffolding’ or ‘skeleton’ contained
within the cytoplasm
A dynamic structure that maintains cell shape,
structural integrity & cell & organelle motility
Determines the 3 dimensional shape of the animal cells
& give a certain firmness in the plant cells
3 elements of cytoskeleton:
(a) microfilament
(b) microtubule
(c) intermediate filament
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Topics
29. CELL COMPONENTS
1.2 : Microfilament
Structure
- fine filaments made of protein with a diameter of 7 nm & a
length of several µm
- composed of one / two types of protein including actin &
myosin
- dynamic can change their length very quickly depending
on their locations & functions
- each type of protein forms subunits that are arranged
helically
- the subunits can slide over one another causing the
microfilament to contract
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Topics
30. CELL COMPONENTS
1.2.1 Structure, position in cells, functions
Position in cells
- exist in bundles & normally found in layer in cytoplasm
Functions
- cause invagination & evagination of membrane during
endocytosis & exocytosis
- cause protrusion of pseudopodium during amoeboid
movement in white blood cells
- assist in the cleavage process during cytokinesis of
animal cells after nuclear division
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Topics
31. CELL COMPONENTS
1.2.1 Structure, position in cells, functions
Illustrated in Figure 2 is a fluorescence digital image of an Indian Muntjac deer skin
fibroblast cell stained with fluorescent probes targeting the nucleus (blue) and the
actin cytoskeletal network (green).
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32. CELL COMPONENTS
1.3 Microtubule
Structure
- fine unbranched tubules with diameter of 25 nm, a wall of 5 nm
thick & vary in length
- the wall composes 13 rows of globular protein subunits called
tubulin, which arranged helically in the wall
- tubulin can grow from a certain organisation centre, which is made
of dense protein.
- tubulin can be added at the base or at one end of microtubule
causing to increase in length / removed, causing it to decrease in
length
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33. CELL COMPONENTS
1.3.1 Structure, position in cells, functions, centrosome & centriole
(structure, position in cells, functions)
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34. CELL COMPONENTS
1.3.1 Structure, position in cells, functions, centrosome & centriole
(structure, position in cells, functions)
Functions
- form the cytoskeleton that determines the shape of the cell
- divide the cytoplasm into compartments specialized enzyme
system can be isolated from others to function better
- can contract causing movement in the cilia & flagella
- can pull chromosomes / chromatids during mitosis or meiosis
- cause the movement of organelles including mitochondria,
lysosomes & vesicles along them like railway tracks
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35. CELL COMPONENTS
1.3.1 Structure, position in cells, functions, centrosome & centriole
(structure, position in cells, functions)
Centrosome & Centriole
microtubule organizing centre
is an area in the cell where microtubles are produced.
Within an animal cell centrosome there is a pair of small
organelles, the centrioles, each made up of a ring of nine
groups of microtubules.
There are three fused microtubules in each group.
The two centrioles are arranged such that one is
perpendicular (90°) to the other.
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36. CELL COMPONENTS
1.3.1 Structure, position in cells, functions, centrosome & centriole
(structure, position in cells, functions)
During animal cell division, the centrosome divides and the
centrioles replicate (make new copies).
The result is two centrosomes, each with its own pair of centrioles.
The two centrosomes move to opposite ends of the nucleus, and
from each centrosome, microtubules grow into a
"spindle" which is responsible
for separating replicated
chromosomes into the
two daughter cells.
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37. CELL COMPONENTS
1.3.1 Structure, position in cells, functions, centrosome & centriole
(structure, position in cells, functions)
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38. CELL COMPONENTS
1.3.1 Structure, position in cells, functions, centrosome & centriole
(structure, position in cells, functions)
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39. CELL COMPONENTS
1.4 :Intermediate filament
Structure
- filament bigger than the microfilament but smaller than
the microtubule, diameter between 8 to 12 nm, only
found in animal cells
- made up of 4 long stands α-helix coiled fibrous
proteins, each consists of only secondary coiled
polypeptide
- several types; each composes of only one type of
protein, including one with keratin
- very stable
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41. CELL COMPONENTS
1.4.1 Structure, position in cells, functions
Position of cells
- branched & formed a network of cytoskeleton in the cytoplasm &
nucleus
Functions
- maintain the shape of the cell including nucleus
- distribute the organelles & support them in the cytoplasm
- help some specialised cells to perform their functions.
Eg. The nail producing cells to form the nail & neuron to
transmit impulse
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43. CELL COMPONENTS
1.5. Cytoskeletal projection
Cilia & flagella are projections form the cell, have the
same internal structure but with the different length
They are made up of microtubules
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44. CELL COMPONENTS
1.5.1 Definition, example – cilia, flagella, basic structure of cilia &
flagella
Flagellum
A flagellum (plural: flagella) is a long, slender projection from the cell
body
The main differences among these three types of flagella:
(a) Bacterial flagella: helical filaments that rotate like screws. They
provide bacterial motility
(b) Archaeal flagella are superficially similar to bacterial flagella,
but are different in many details & considered non-homologous
(c) Eukaryotic flagella: those of animal, plant & protist cells are
complex cellular projections that lash black & forth
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45. CELL COMPONENTS
1.5.1 Definition, example – cilia, flagella, basic structure of cilia &
flagella
An eukaryotic flagellum is a bundle of nine fused pairs of
microtubule doublets surrounding two central single
microtubules
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47. CELL COMPONENTS
1.5.1 Definition, example – cilia, flagella, basic structure of cilia &
flagella
Cilium
An organelle found in eukaryotic cells
Made up of microtubules
Tail-like projections extending approximately 5-10 µm
outwards from the cell body
Two types of cilia
(a) motile: constantly beat in a single direction
(b) non-motile: typically serve as sensory organelles
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49. CELL COMPONENTS
1.5.1 Definition, example – cilia, flagella, basic structure of cilia &
flagella
The primary purpose of cilia in mammalian cells is to
move fluid, mucous or cells over their surface
In humans, ie. Motile cilia are found in the lining of the
trachea (windpipe), where they sweep mucus & dirt out
of the lungs
In female mammals, the beating of cilia in the Fallopian
tubes moves the ovum from the ovary to the uterus
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50. CELL COMPONENTS
Cytosol
Definition: the liquid medium of the cytoplasm which
is viscous & transparent / soluble part of cytoplasm
= ground substance
Consists of approximately 75 – 90% water plus ions &
many types of organic molecules eg. Enzymes
Cytoplasm minus organelles & insoluble components
e.g mitochondria
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51. CELL COMPONENTS
Functions:
- stores vital chemicals including fats
- as the site for certain metabolic pathways (eg.
glycolysis, synthesis of fatty acids & amino acids)
- as the medium in which many intracellular
chemical reactions occur
- enables organelles (mitochondria, chloroplasts,
ribosomes, lysosomes & vacuole) to move about in it.
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52. CELL COMPONENTS
Organelles
Organelles in cytoplasm include
(a) mitochodria
(b) ribosomes
(c) chloroplasts
(d) lysosomes
(e) vacuoles
(f) Golgi apparatus
(g) endoplasmic reticulum
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53. CELL COMPONENTS
Definition: structures within the cell that are
specialized for particular functions
Basic structure
- most organelles have membranes that are very
similar to the plasma membrane
- the membrane effectively separate the organelle from
the cytosol
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54. CELL COMPONENTS
Mitochondria
Basic structure:
- spherical, filamentous or rod-shaped bodies which
are bound by a double membrane (outer & inner)
- Size: 2 – 8 µm in length
- The outer membrane is smooth in texture &
surrounds the mitochondrion itself
- The inner membrane is arranged in a series of folds
known as cristae
- The central cavity of the mitochondria which is
enclosed by the inner membrane & the cristae is called
the matrix
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55. CELL COMPONENTS
Distribution:
- found in every eukaryotic cell
- the location inside the cell in not fix, they can
move
- protozoa & yeasts have only one mitochondrion
per cell.
- In liver cell 500 – 1400 per cell
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57. CELL COMPONENTS
Functions of mitochondria
(a) carry out Krebs cycle part of cellular respiration within
their matrise
(b) carry out oxidation of fatty acids & amino acids
(c) carry out oxidative phosphorylation, which produces
ATP from ADP & phosphate
principal sites for the generation of cellular energy
(ATP) during cellular respiration; ‘power houses’
(d) produce their own proteins from DNA with the aid of
RNA
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58. CELL COMPONENTS
Definition:
Ribosomes small granules where synthesis of proteins
occurs
Distribution:
- found in all cells particularly cells that produce a lot of
proteins (eg. Glandular cells of the pancreas & liver cells).
- found in the nucleus, cytoplasm freely or attached to
ER, mitochondria & chloroplasts.
- their numbers is not fixed
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60. CELL COMPONENTS
Basic Structure:
- spheroid in shape, consisting of two subunits, one
is larger than the other
- Very small, ~ 20 nm in diameter for 80S (eukaryotic)
& smaller for 70S (prokaryotic)
- The subunits can be attached to form bigger
functional units in the presence of magnesium ion.
Eukaryote: 60S + 40S 80S
Prokaryote: 50S + 30S 70S
- made up of RNA & protein synthesized in the
nucleolus
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61. CELL COMPONENTS
Functions:
- provide site for the formation of peptide bonds
- amino acids are joined together to form
polypeptide / protein.
- the subunits can form complex with mRNA
- two sites are provided on the surface where tRNA
would bring two amino acids to the sites matching
the codon of mRNA to that of anti-codon of the
tRNA.
- ribosomes can ‘read’ the codes on the mRNA &
join specific sequence of amino acids to form
specific protein
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62. CELL COMPONENTS
Endoplasmic Reticulum (ER)
Basic structure:
- formed by a complex system of membranes forming
tubes & branching channels through the cytoplasm
- can be divided into two types
(a) Rough ER – with ribosomal attachments on its
outer surface, found in glandular cells that
produce a lot of protein for secretion (eg.
Digestive system pacrease, stomach)
(b) Smooth ER – lacks ribosomal attachments,
embedded on the inner surface of the membrane,
there are a lot of enzymes catalysing the
synthesis of CHO & lipids
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64. CELL COMPONENTS
Functions:
- differentiated largely based on the presence or
absence of attached ribosomes.
- Rough ER
produce proteins for secretion & also for internal
use. Eg. Digestive enzyme, hormones & antibody.
transports proteins to smooth ER / Golgi apparatus
through sacs pinched off from its surface
membrane. Eg. Protein like mucus has its CHO
component added in the smooth ER or Golgi
apparatus.
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65. CELL COMPONENTS
- Smooth ER
synthesis, secrete & store lipids, CHO & other non-
protein product
participates in the detoxification process of harmful
chemicals
forms lysosomes; vesicles that are used for
internal transport & reactions
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Slide 65 of 10
66. CELL COMPONENTS
Golgi Apparatus
= Golgi body or Golgi complex & found universally in
both plant & animal cells
Basic structure:
- consists of flat vesicular discs structures placed
one on top of the other, which can produce vesicles full
of secretion for internal & external uses
- proteins made within rough ER bud off in vesicles will
be transported to the Golgi where the vesicle fuse with
the membrane
- the components are then modified & packaged by the
time they bud off as vesicle
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68. CELL COMPONENTS
Distribution
- found in large no. in glandular cells, neurones *
muscle cells.
- locations within the cell are not fix, can move &
formed form ER
- usually one per cell
Functions
- modifies, packages & distributes all proteins
(form glycoprotein) & lipids (form glycolipids) for
export & storage
- forms lysosomes through the budding of larger
vesicle or fusion of several smaller ones.
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69. CELL COMPONENTS
Lysosome
Basic structure:
- spherical membrane bound vesicles containing
hydrolytic enzyme that can digest most biological
macromolecules
- size: 0.05 to 0.50 µm in length
- the limiting membrane keeps the digestive enzymes
separated from the cytoplasm (Eg. Protease, lipase)
- contain digestive hydrolases
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70. CELL COMPONENTS
- These enzymes function optimally at pH 5 & inactive
at cytosol pH (pH 7.2)
- together with the limiting membrane, this will protects
the cell from digesting itself
Distribution
- found in cells that carry out endocytosis (eg. WBC &
protozoa)
- found in animal cells, absent in plant cells
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71. CELL COMPONENTS
Functions:
- Carry out intracellular digestion (phagocytosis) in
which plasma membrane engulf substances & pinch off
to form a particle-containing vacuole. Lysosome fuse
with the vacuole & digest with their hydrolytic enzyme
- Carry out program cell destruction (autolysis)
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72. CELL COMPONENTS
< Electron micrograph of
lysosomes
Lysosome in the process
of destroying a membrane
bound mitochondrion >
9/21/2011 72
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74. CELL COMPONENTS
1. Vesicles containing materials from outside the cell are
taken into the cell
2. The vesicle is pinched off from the plasma membrane
& becomes a separate vesicle
3. A lysosome approaches the vesicle
4. The lysosome fuses with the vesicles
5. The enzyme from the lysosome mix with the material
in the vesicle & the enzymes digest the material
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75. CELL COMPONENTS
Nucleus
Largest membrane-enclosed organelle in the eukaryoric
cell, diameter 10 -20 µm
Normally it is spherical or oval in shape; may be
cylindrical or lobed in the WBC. The shape can be
changed
Distribution: found in the centre of the cell but in
matured plant cells, it is pushed one side of the
protoplast by the big sap vacuole. Normally one per cell
Slide 75 of 10
Topics
76. CELL COMPONENTS
1.1.1: Basic structure & Functions
It is found in all cells, except in the red blood cells & sieve tubes
of phloem
Contains most of the cell’s genetic material, organized as
multiple long linear DNA molecules in complex with a large variety
of proteins (eg. histones) to form chromosomes
Function: to control all the activities of the cell by regulating
gene expression and to maintain the integrity of these gene
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Topics
77. CELL COMPONENTS
1.2. Nucleus parts or components
The nucleus can be divided into
(a) nuclear envelope
(b) nucleoplasm
(c) nucleolus
(d) chromosome
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Topics
78. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus,
nucleoplasm, chromatin / chromosome, DNA)
Nuclear envelope
Double lipoprotein membrane that encloses the entire
organelle & keeps its contents separated from the cellular
cytoplasm
Consists of two cellular membranes, an inner & an outer
membrane, arranged parallel to one another & separated by
10 – 50 nm
The inner membrane is smooth; no ribosome is attached to
it & is not folded. This envelope disappears at prophase of
cell division & reappears at the end of it.
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Topics
79. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus,
nucleoplasm, chromatin / chromosome, DNA)
The outer nuclear membrane is continuous with the
membrane of the rough endoplasmic reticulum (RER) & is
similarly studded with ribosomes
Sometimes, it may be continuous right to the plasma
membrane
The space between the membranes (about 10 – 40 nm) is
called the perinuclear space & is continuous with the RER
lumen
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Topics
80. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus,
nucleoplasm, chromatin / chromosome, DNA)
Nuclear pores, which provide aqueous channels through the
envelope, are composed of multiple proteins, collectively referred to
as nucleoporins
The pores are relatively big, 40 -150 nm & covered a surface of 8%
of the envelope
Passage of substances is very controlled allows the free passage
of small water-soluble molecules while preventing larger molecules
(eg. nucleic acids & proteins) from inappropriately entering or
existing the nucleus
These large molecules must be actively transported into the nucleus
instead.
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81. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
Nuclear pore
1. Nuclear envelope.
2. Outer ring.
3. Spokes.
4. Basket.
5. Filaments.
(Drawing is based on electron microscopy
images)
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82. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
Functions of nuclear envelope
It protects the inner structures of the nucleus
It separates the nucleus from the cytoplasm / separates the cell’s
genetic material from the surrounding cytoplasm reactions occur
in the nucleus are not affected
It controls the shape of nucleus
It controls the passage of substances from & to nucleus / serving as
a barrier to prevent macromolecules from diffusing freely between
the nucleoplasm & the cytoplasm
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83. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
Nucleoplasm
Nuclear sap / karyoplasm
Part of protoplasm that is inside the nucleus
Its composition – same as cytoplasm consisting
mainly water with crystalloids & colloids dissolved in it
Has DNA, histone & pentoses that are not found in the
cytoplasm
Easily stained with acidic eosin to form purple colour
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84. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
Crystalloids: monosaccharides, amino acids, organic
acids, nucleotides & mineral ions
Colloids: DNA, RNA & proteins particularly histone that
mixed with DNA forming chromatins
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85. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
Functions of nucleoplasm
Contains various enzymes for metabolism including that
for glycolysis, Krebs cycle, phosphorylation & synthesis
of NAD, replication & transcription of DNA
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86. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
Chromatin
Describes nuclear material that contains the genetic code
The code is stored in individual units called ‘chromosomes’
The complex of DNA & protein that makes up chromosomes
It is found inside the nuclei of eukaryotic cells, & within the nucleoid
in prokaryotic cells
The major proteins involved in chromatin are histone proteins,
although many other chromosomal proteins have prominent roles
too
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87. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
Changes in chromatin structure are affected mainly by
methylation (DNA & proteins) & acetylation (proteins)
The functions of chromatin are to package DNA into a
smaller volume to fit in the cell, to strengthen the DNA to
allow mitosis & meiosis & to serve as a mechanism to
control expression
Chromatin structure is also relevant to DNA replication &
DNA repair
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88. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
Two types of chromatin can be describes:
(a) Heterochromatin
(b) Euchromatin
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89. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus,
nucleoplasm, chromatin / chromosome, DNA)
Slide 89 of 10
90. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus,
nucleoplasm, chromatin / chromosome, DNA)
Nucleolus
Spherical structure that is the site of ribosome synthesis
in interphase nucleus
It is not surrounded by a membrane & is sometimes
called suborganelle
It forms around tandem repeats of rDNA, DNA coding for
ribosomal RNA (rRNA)
The main roles of the nucleolus are to synthesize rRNA
& assemble ribosomes
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91. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus,
nucleoplasm, chromatin / chromosome, DNA)
The transcription, post-transcriptional processing &
assembly of rRNA occurs in the nucleolus
The assembled ribosomal subunits are the largest
structures passes through the nuclear pores
Nucleolus disappears during cell division but reappears
in the final stage of mitosis
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92. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus,
nucleoplasm, chromatin / chromosome, DNA)
Chromosome
Functions:
- control the production of RNA & proteins in cells. Through these
RNA & proteins (enzymes), chromosomes control all the activities of
the cell & inheritable characters of an organism
- compact chromosomes enable mitosis & meiosis. Such forms
can move easily compared to untidy long slender DNA enable
genes to be passed down from one mother cell to daughter cells &
one generation to the next generation
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93. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
Slide 93 of 10
94. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
DNA
A nucleic acid that contains the genetic
instructions used in the development &
functioning of all known living organisms
Main role: long term storage of information
Long polymere of simple units called
nucleotides, with a backbone made of
sugars & phosphate groups joined by
ester bonds
Attached to each sugar is one of four types of
molecules calles bases
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95. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
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96. CELL COMPONENTS
1.2.1 Structure and functions (nuclear envelope, nucleolus, nucleoplasm,
chromatin / chromosome, DNA)
It is the sequence of these four bases along the
backbone that encodes information
This information is read using the genetic code, which
specifies the sequence of the amino acids within proteins
The code is read by copying stretches of DNA into the
related nucleic acid RNA, in a process called
transcription
Within cells, DNA is organized into structures called
chromosomes
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