Higher National Diploma in Biotechnology
Module Name Number
BIOM 501 (1)
Name of Candidate
Title of Practical
Cell Biology Individual Assignment
Date of Practical
Table of Contents
Task 1. 3
Kingdom Archaea. 3
Cell membrane. 3
Extreme Halophiles. 4
Extreme Thermophiles. 4
Task 2. 5
Translocating signals. 5
Translocators, Transmembrane Receptors and Mechanism.. 6
Mitochondrial Cytopathies. 6
Section of disease. 6
Task 3. 8
Cell division. 8
Cell cycle of meiosis. 9
Genetic variations. 10
Crossing Over. 10
Independent Assortment of Homologues. 10
Joining of Gametes. 10
Task 04. 11
Morphological features of apoptosis. 11
Extrinsic pathway. 11
Intrinsic pathway. 12
Caspase activation pathways. 13
Pathway cross talk. 13
p53 gene. 13
Reference list. 14
All living organisms are included in the
five-kingdom classification: Plantae, Animalia, Fungi, Protista and Monera. Not
so long ago, before 1977, archaea were referred to be a group of anaerobic
bacteria, as well as aerobic prokaryotes. After many disagreements, scientists
found out the variations of 16S rRNA and 18S rRNA sequences, continuously, they
were placed in a separate kingdom called Archaebacteria (Gribaldo and
Archaebacteria are autotrophs and use CO2 as a
source for carbon fixation. They are adapted to survive in extreme
environmental conditions and do not need oxygen or light to survive. There is
no any harmful diseases caused by Archaean besides periodontal (gum) disease
(encourage by some live in the mouth) (Perry, Staley and Lory, 2002).
Cell membranes are made of phospholipid
molecules for each organism. Phospholipids contain a polar phosphate head,
which dissolves in water and a non-polar lipid tail which insoluble in water. A
glycerol group connects these dissimilar ends. Even, the main structure of cell
membranes is a lipid bilayer structure, archaea have different structural
composition. The major difference is that the lipid moieties of the cell membrane
are not glycerol-linked esters, but glycerol-linked ethers. More even, rather
than, fatty acids, most archaea have isoprenoid side chains with repeating
five-carbon unit. Two patterns are found in the archaeal membrane (Perry,
Staley and Lory, 2002).Bilayer
leaflets of glycerol-linked isoprenoid
These organisms produce methane (CH4)
by their metabolic activity (about two billion tons), commonly known as natural
gas. They are adapted to anaerobic conditions and oxygen inhibits their growth
or kills them. Methane assists Archaean to survive in deep oceans, hydrothermal
vents, in soil and ocean sediments. They live in gut of human and grazers (cows
and sheep) for produce gut escapes as belches and flatulence (Perry, Staley and
Methane causes to an important environmental
effect called greenhouse effect (Perry, Staley and Lory, 2002).
They are salt loving
Archaean, which are specialized in living in Dead Sea, Great Salt Lake,
saltwater evaporation ponds, and other highly salty habitats. Some of them have
a purple pigment (bacteriorhodopsin) that allows them to photosynthesis to
produce ATP (Perry, Staley and Lory, 2002).
mainly specialized for life at a very high temperature. They live in hot
springs and near hydrothermal vents, where the temperature can increase 110?C (230?F). Their existence is cited as proofs that
life could have originated on the sea floor (Perry, Staley and Lory, 2002).
two non-homologous chromosomes mutate by exchanging parts, the resulting chromosomal
segments to a different position in the genome relocations are translocation.
The most common type of translocations are reciprocal. Adenine or adenosine
segment from one chromosome is exchange with a segment of another
non-homologous chromosome, thus two translocation chromosomes are generated simultaneously, where the exchanges
establish new linkage relations between chromosome parts and non-homologous. If
the translocated chromosomes are homozygous and heterozygous, these new
linkages are revealed. Furthermore, translocations may sorely alter the size of
a chromosome and the position of its centromere.
Figure 1: Genome restructuring by Translocation
(Griffiths, Miller, Suzuki et al., 2000)
The membrane-bound ribosomes of the
rough endoplasmic reticulum are engaged in the proteins synthesis, resident
luminal proteins of the membrane systems and the majority of cellular integral
membrane proteins. The information responsible for the selective delivery of
ribosomes to the RER is contained in an amino terminal signal sequence.
Ribosomes synthesizing proteins with RER-specific signal sequences are targeted
to a membrane-bound translocation site or “translocon”, which is a
multicomponent protein assembly that mediates the unidirectional transport of
proteins. Nascent polypeptide chains transport across the endoplasmic reticulum
(ER) membrane proposed to occur through a proteinaceous transport site or
channel (Rapiejko and Gilmore, 1993) that may consist of many entire membrane
proteins which identified by cross-linking to initial polypeptides. Gateway
into the RER lumen, the initial polypeptide undergoes modifications and folding
reactions that result in the assembly of mature protein. The roles of
signal recognition particle (SRP) and SRP receptors, two multi subunit GTP-binding
proteins that mediate the nascent phases of the protein translocation reaction.
Receptors and Mechanism
The signal recognition particles and
its receptor adenosine or adenine soluble ribonucleoprotein complex known as
the SRP specifically binds with high affinity to the initial polypeptides
consisting a relevant signal sequence (Walter et al., 1982). The six-polypeptide subunits of SRP (72, 68, 54, 19,
14 and 9kDa) organized into three functional domains as defined by their
binding to separate regions of the 7SL-RNA (SRP-RNA) (Siegel and Walter, 1988).
The 54kDa subunit of SRP (SRP54) binds to the signal sequence of initial
polypeptide shortly after it appears from the large ribosomal subunit (Walter et al., 1982). High affinity binding of
SRP54 to the signal sequence inhibits the rate of elongation of the nascent
polypeptide in vitro (Wolin and Walter, 1989). SRP-ribosome complex is targeted
to the ER membrane via binding of the SRP to the SRP receptor or docking protein.
The SRP receptor is a heterodimeric entire membrane protein composed of a
68-kDa a subunit and a 30-kDa P subunit. Targeting of the SRP-ribosome complex
to its receptor results in the dissociation of the SRP from the signal
sequence, membrane insertion of the initial polypeptide and release of the
elongation arrest of the translation (Rapiejko and Gilmore, 1993).
They are represent a heterogeneous
group of disorders, which preferentially affect the muscle and nervous systems and
caused either by mutations in the maternally inherited mitochondrial genome or
nuclear DNA-mutations (Schmiedel et al.,
several diseases causing mutation of mitochondrial DNA and nuclear, which may
present with a huge variety of symptoms even if the same mutation is involved.
Abnormal mitochondria in muscle tissue and a neurological disorder affect the
cerebrum, cerebellum, extrapyramidal system, vestibular system, retina, upper
motor neuron, lower motor neuron and musculature.
Hypo Plastic Anemia
Renal Tubular Dysfunction.
symptoms may occur even singly or various combinations and the manifestation
may differ even within the same family. ‘Ophthalmoplegia’ is the most common
clinical picture, which occurrence in relatives differs from isolated symptoms
to the complete syndrome with ‘ragged red fibers’ that is inconsistent with an
autosomal dominant mode of inheritance with variable expressivity.
Figure 2: Cardiomyopathies (Elliot et al., 2008)
Arrhythmogenic Right Ventricular Cardiomyopathy
In unicellular organisms, cell
division means of reproduction and in multicellular organisms, it means by cell
growth and maintenance. Survival of the eukaryotes depends upon interactions
between several cell types and it is essential to balance distribution of types
be maintained. The highly regulated process of cell proliferation achieves this.
The growth and division of different cell populations are regulated in
different ways, but the basic mechanisms are similar throughout multicellular
Mitosis is how somatic or
non-reproductive cells divide. Somatic cells can make up most of body tissues
and organs including skin, muscle, lungs, gut and hair cells. Reproductive
cells are not somatic cells. In mitosis, the daughter cells each have the same
chromosomes and DNA as the parental cells. The daughter cells are called
diploid cells. Diploid cells have tow complete sets of chromosomes. Since the
daughter cells have exact copies of their parental cell’s DNA, no genetic
diversity is created through mitosis in healthy cells.
Figure 3: The cell cycle of Mitosis
another main way of cell division, which creates sex cells, like female egg and
male sperm. Each new cell contains a unique set of genetic information. After
meiosis, the sperm and egg cells can join to create new organisms. During this
process, a small portion of each chromosomes break off and reattaches to
another chromosomes. This process is called ‘crossing over’ or ‘genetic
recombination’, which is the reason full siblings made from egg and sperm cells
from same two parents can look very different from one another.
Figure 4: Cell division of Meiosis
cycle of meiosis
two cycle of cell division, called Meiosis I and Meiosis II. Meiosis I halves
the number of chromosomes and when crossing over happens. Meiosis II halves the
amount of genetic information in each chromosome of each cell. The daughter
cells called haploid cells, which have only one set of chromosomes and half
number of chromosomes as the parental cell. Before Meiosis I starts, the cell
goes through interphase. Just like in mitosis, the parental cell uses this time
to prepare for divide by gathering nutrients and energy and making copy of its
DNA. During the next stages of meiosis, this DNA will be switched around during
genetic recombination and then divided between four haploid cells.
During prophase I, non-sister chromatids
begin to exchange their genetic material, making the homologue represent two
parents instead of one.
Assortment of Homologues
In metaphase I, the tetrads of the homologous
chromosomes spilt into chromosomes that separate into different poles. The
chromosome that goes to which pole depends on the where the tetrads are at the
metaphase plate. The placing of the tetrads and the separation is random, not
depending on anything. In some chromosomal pairs, the maternal chromosome will
go to one pole, but for a different pair, the maternal chromosome could go on
the opposite ends of the poles.
Random Joining of Gametes
When the sperm fertilizes an egg, the pick of
the egg is completely random. With the random pick of the egg, it can affect
the genetic composition of the gametes. If some sperm are faster swimmers, they
will reach the egg earlier. Therefore, the one that reaches the egg first will
fertilize the egg, giving it its genetic material.
Mutations increase genetic variation as it
introduces alternative genes, beneficial or not. There are several types of
mutations such as frame-shift mutations, which is when a DNA base is inserted
or deleted, changing a gene’s reading frame. The resulting protein is different
and usually nonfunctional. It is the major source of genetic variation in
Word count: 615
The term of apoptosis describes a
morphologically distinct form of cell death. Apoptosis occurs normally during
development and aging and as a homeostatic mechanism to maintain cell
populations in tissues and as a defense mechanism such as immune responses and
when diseases or noxious agents damage cell. There are several variety of
stimuli and conditions; both physiological and pathological that can trigger
apoptosis (Elmore, 2007).
features of apoptosis
With cell shrinkage, the cells are
very smaller, the cytoplasm is dense and the organelles are more tightly
packed. Pyknosis is the result of chromatin condensation and this the most
characteristic feature of cell death. Extensive plasma membrane blebbing occurs
followed by karyorrhexis and separation of cell segments into apoptotic bodied
during a process called “budding”, consist of cytoplasm with organelles with or
without a nuclear fragment. The tangible bodies are the bits of nuclear debris.
There is no essential inflammatory reaction associated with the removal of
apoptotic cells, because,
Apoptotic cells do not release their cellular
constituents into the surrounding interstitial tissue
They are quickly phagocytosed by surrounding cells thus
likely preventing secondary necrosis
The engulfing cells do not produce anti-inflammatory
cytokines (Elmore, 2007).
Apoptosis signaling pathways
Apoptosis is triggered by
multi-signaling pathways and regulated by multi complicated extrinsic and
intrinsic ligands. The apoptosis is controlled by diversity cell signals
pathway and involved in regulation of cell survival. The mitochondria, as the
cross-talk organelles can connect the different apoptosis pathway.
This triggers apoptosis in response
to external stimuli, namely by ligand binding at ‘death’ receptors of the cell
surface. These receptors are typically members of the tumor necrosis factor
receptor (TNFR) gene family, such as TNFR1 or FAS. Binding at these receptors
leads to receptor molecules grouping up on the cell surface to initiate
downstream caspase activation.
intrinsic pathway mainly triggers apoptosis in response to internal
DNA damage (this activates the p53 gene – which halts the cell
cycle and initiates DNA repair. If this repair attempt is
unsuccessful, apoptosis can be induced)
Lack of growth factors
intrinsic pathway is modulated by Bcl-2 and Bax. Activation of Bax leads to the
formation of Bax-Bax dimers,
which in turn enhances the action of a variety of apoptotic stimuli –
increasing a cell’s susceptibility to apoptosis. The Bcl-2 family consists of
both pro- and anti-apoptotic members, and it is the balance between these that
determines how susceptible a cell may be to apoptosis.
balance between these groups of molecules establishes a ‘molecular
which determines whether a cell will survive or undergo apoptosis in response
to internal stimuli.
Figure 5: extrinsic and intrinsic pathways of Apoptosis
Caspase activation pathways
The initiation of apoptosis by
either pathway result in a cascade activation of caspases. Specialized protease
normally reside as inactive precursors within cell. Apoptosis first activates caspase
8 to cleave other pro caspase into active “executioner” caspases, which cause
degradation of a variety of cellular structures, such as the cytoskeleton and
nucleus. This process leads to several morphological changes within cells, such
as nuclear shrinkage (pyknosis) and fragmentation (karyorrhexis).
A pro-apoptotic member of the BcI2
family is directly cleaved by caspase 8 and the C0terminal fragments acts on
mitochondria to trigger cytochrome c release. Depletion of Bid from cytosolic
extracts disrupts the ability of caspase-8 to trigger cytochrome c release in
vitro. In Xenopus cytosolic
extracts, the ability of small amounts of caspase-8 to trigger activation of a
caspase-3-like activity was dependent on the presence of mitochondria. This
suggests the possibility that caspase-8 cleaves and activates Bid more
efficiently than procaspase-3, and in doing so enlists the cytochrome c/Apaf1
pathway to amplify the caspase-8 function. In the absence of mitochondria,
caspase-8 processes procaspase-3 and thus other caspases do not effectively
serve as amplifiers of caspase-8 activity. It is only in those cells where the
mitochondrial amplification loop is important that antiapoptotic Bcl2 family
members can suppress Fas/TNFR-induced apoptosis.
The most frequently inactivated
tumor suppressor gene is the p53 gene, which encodes a protein with a 53-kilo
Dalton molecular mass or gene. The human p53 signaling pathway RT² Profiler™ PCR Array profiles the expression of 84 genes
related to p53 mediated signal transduction. The array includes p53-related
genes involved in the process of apoptosis, the cell cycle, cell growth,
proliferation, differentiation and DNA repair.
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