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Organization and Management of Labs
1. Define and characterize various epithelial cells.
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle
tissue and nervous tissue. Epithelial tissues line thecavities and surfaces of structures throughout the
body, and also form many glands. Functions of epithelial cells include secretion, selective absorption,
protection, transcellular transport and detection of sensation. In Greek "Epi" means, "on, upon," and
"Theli" meaning "tissue." Epithelial layers areavascular, so they must receive nourishment via diffusion of
substances from the underlying connective tissue, through the basement membrane.[1][unreliable
source?]
Epithelia can also be organized into clusters of cells that function as exocrine and endocrine
glands. Exocrine and endocrine epithelial cells are highly vascular.
General structure
Cells in epithelium are very densely packed together like bricks in a wall, leaving very little intercellular
space. The cells form continuous sheets which are attached to each other at many locations bytight
junctions and desmosomes.[2] The epithelial tissues cover the interior and exterior part of our skin.
[edit]Basement
membrane
All epithelial cells rest on a basement membrane, which acts as a scaffolding on which epithelium can
grow and regenerate after injuries.[3] Epithelial tissue is innervated, but avascular. This epithelial tissue
must be nourished by substances diffusing from the blood vessels in the underlying tissue. The basement
membrane acts as a selectively permeable membrane that determines which substances will be able to
enter the epithelium.[4][5]
[edit]Cell
junctions
Cell junctions are especially abundant in epithelial tissues. They consist of protein complexes and provide
contact between neighbouring cells, between a cell and the extracellular matrix, or they build up the
paracellular barrier of epithelia and control the paracellular transport.[citation needed]
Cell junctions are the contact points between plasma membrane and tissue cells. There are mainly 5
different types of cell junctions. They are tight junctions, adherens junctions, desmosomes,
hemidesmosomes, and gap junctions. Tight junctions are a pair of trans-membranar protein fused on
outer plasma membrane. Adherens junctions are a plaque (protein layer on the inside plasma membrane)
which attaches both protein and microfilaments. Desmosomes attach to the microfilaments of
cytoskeleton made up of keratin protein. Hemidesmosomes resemble desmosomes on a section. They
are made up of the integrin (a transmembraner protein) instead of cadherin. They attach the epithelial cell
to the basement membrane. Gap junctions connect the cytoplasm of two cells and are made up of
proteins called connexins (six of which come together to make a connexon).
Simple epithelium
Simple epithelium is one cell thick, that is, every cell is in direct contact with the underlying basement
membrane. It is generally found where absorption and filtration occur. The thinness of the epithelial
barrier facilitates these processes.[2]
Simple epithelial tissues are generally classified by the shape of their cells. The four major classes of
simple epithelium are: (1) simple squamous; (2) simple cuboidal; (3) simple columnar; (4)
pseudostratified.[2]
(1) simple squamous; which is found lining areas where passive diffusion of gases occur. e.g. walls of
capillaries, linings of the pericardial, pleural,and peritoneal cavities, as well as the linings of the alveoli of
the lungs.
(2) simple cuboidal: these cells may have secretory, absorptive, or excretory functions. examples include
small collecting ducts of kidney,pancreas and salivary gland.
(3) simple columnar; found in areas with extremely high secretive (as in wall of the stomach), or
absorptive (as in small intestine) areas. they possess cellular extensions (e.g. microvilli in the small
intestine, or cilia found almost exclusively in the female reproductive tract).
(4) pseudostratified epithelia; they are also called respiratory epithelium. this is due to their almost
exclusive confinement to the larger respiratory airways i.e. the nasal cavity, trachea, bronchi e.t.c.
2. Differentiate a prokaryote and an eukaryote.
The prokaryotes (
/proʊˈkæri.oʊts/ or /proʊˈkæriəts/) are a group of organisms that lack a cell
nucleus (= karyon), or any other membrane-bound organelles. The organisms that have a cell nucleus
are called eukaryotes. Most prokaryotes are unicellular, but a few such
asmyxobacteria have multicellular stages in their life cycles.[1] The word prokaryote comes from
the Greek πρό- (pro-) "before" + καρυόν (karyon)"nut or kernel".[2] Prokaryotes do not have a nucleus,
mitochondria, or any other membrane-bound organelles. In other words, neither their DNA nor any of their
other sites of metabolic activity are collected together in a discrete membrane-enclosed area. Instead,
everything is openly accessible within the cell, some of which is free-floating.[3]
Prokaryotes belong to two taxonomic domains: the bacteria and the archaea. Archaea were recognized
as a domain of life in 1990. These organisms were originally thought to live only in inhospitable conditions
such as extremes of temperature, pH, and radiation but have since been found in all types of habitats.
A distinction between prokaryotes and eukaryotes (meaning true kernel, also spelled "eucaryotes") is that
eukaryotes do have "true" nuclei containing their DNA. Unlike prokaryotes, eukaryotic organisms may be
unicellular, as in amoebae, or multicellular, as in plants and animals. The difference between the structure
of prokaryotes and eukaryotes is so great that it is sometimes considered to be the most important
distinction among groups of organisms.
The cell structure of prokaryotes differs greatly from that of eukaryotes. The defining characteristic is the
absence of a nucleus. Also the size of Ribosomes in prokaryotes is smaller than that in eukaryotes, but
two organelles found in eukaryotic cells, the mitochondria and the chloroplast, contain ribosomes similar
in size and makeup to those found in prokaryotes.[4] This is due to the fact that
both mitochondria and chloroplasts are themselves descended from free-living bacteria, and therefore
share the same transcriptional machinery. The genomes of prokaryotes are held within an
irregularDNA/protein complex in the cytosol called the nucleoid, which lacks a nuclear
envelope.[5] Prokaryotes lack distinct mitochondria and chloroplasts. Instead, processes such as oxidative
phosphorylation and photosynthesis take place across the prokaryotic plasma membrane.[6] However,
prokaryotes do possess some internal structures, such as cytoskeletons,[7][8] and the bacterial
order Planctomycetes have a membrane around their nucleoid and contain other membrane-bound
cellular structures.[9] Both eukaryotes and prokaryotes contain large RNA/protein structures
calledribosomes, which produce protein. Prokaryotes are usually much smaller than eukaryotic cells.[2]
Prokaryotes also differ from eukaryotes in that they contain only a single loop of stable chromosomal
DNA stored in an area named the nucleoid, whereas eukaryote DNA is found on tightly bound and
organized chromosomes. Although some eukaryotes have satellite DNA structures called plasmids, in
general these are regarded as a prokaryote feature, and many important genes in prokaryotes are stored
on plasmids.[2]
Prokaryotes have a larger surface-area-to-volume ratio giving them a higher metabolic rate, a higher
growth rate, and, as a consequence, a shorter generation time compared to Eukaryotes. [2]
One criticism of this classification points out that the word "prokaryote" is based on what these organisms
are not (they are not eukaryotic), rather than what they are (either archaea or bacteria). [10]
In 1977, Carl Woese proposed dividing prokaryotes into the Bacteria and Archaea (originally Eubacteria
and Archaebacteria) because of the major differences in the structure and genetics between the two
groups of organisms. This arrangement of Eukaryota (also called "Eukarya"), Bacteria, and Archaea is
called the three-domain system, replacing the traditional two-empire system.[11]
A eukaryote (
/juːˈkæri.oʊt/ ew-KARR-ee-oht or /juːˈkæriət/) is an organism whose cells contain complex
structures enclosed within membranes. Eukaryotes may more formally be referred to as
the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart
from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is
carried.[1][2][3] The presence of a nucleus gives eukaryotes their name, which comes from
the Greek ευ (eu, "good") and κάρυον (karyon, "nut" or "kernel"). Most eukaryotic cells also contain other
membrane-bound organelles such as mitochondria, chloroplasts and the Golgi apparatus. All species of
large complex organisms are eukaryotes, including animals, plants and fungi, although most species of
eukaryote are protist microorganisms.[citation needed]
Cell division in eukaryotes is different from that in organisms without a nucleus (Prokaryote). It involves
separating the duplicated chromosomes, through movements directed by microtubules. There are two
types of division processes. In mitosis, one cell divides to produce two genetically identical cells.
Inmeiosis, which is required in sexual reproduction, one diploid cell (having two instances of each
chromosome, one from each parent) undergoesrecombination of each pair of parental chromosomes, and
then two stages of cell division, resulting in four haploid cells (gametes). Each gamete has just one
complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes.
Eukaryotes appear to be monophyletic, and so make up one of the three domains of life. The two other
domains, Bacteria and Archaea, are prokaryotes and have none of the above features. Eukaryotes
represent a tiny minority of all living things; even in a human body there are 10 times more microbes than
human cells.[4] However, due to their much larger size their collective worldwide biomass is estimated at
about equal to that of prokaryotes
3. Population of cells would double in number with each generation. - Explain.
A population is all the organisms that both belong to the same group or species and live in the
same geographical area. In ecology the population of a certain species in a certain area is estimated
using the Lincoln Index. The area that is used to define a sexualpopulation is such that inter-breeding is
possible between any pair within the area and more probable than cross-breeding with individuals from
other areas. Normally breeding is substantially more common within the area than across the border. [1]
In sociology, population refers to a collection of human beings. Demography is a social science which
entails the statistical study of human populations. This article refers mainly to human population.
Predicted Growth and Decline
Population growth increased significantly as the Industrial Revolution gathered pace from 1700
onwards.[9] The last 50 years have seen a yet more rapid increase in the rate of population growth[9] due
to medical advances and substantial increases in agricultural productivity, particularly beginning in the
1960s,[10] made by the Green Revolution.[11] In 2007 the United Nations Population Divisionprojected that
the world's population will likely surpass 10 billion in 2055. [12]
In the future, world population has been expected to reach a peak of growth, from there it will decline due
to economic reasons, health concerns, land exhaustion and environmental hazards. According to one
report, it is very likely that the world's population will stop growing before the end of the 21st century.
Further, there is some likelihood that population will actually decline before 2100.[13]Population has
already declined in the last decade or two in Eastern Europe, the Baltics and in the Commonwealth of
Independent States.[14]
The population pattern of less-developed regions of the world in recent years has been marked by
gradually declining birth rates following an earlier sharp reduction in death rates. [15] This transition from
high birth and death rates to low birth and death rates is often referred to as the demographic
transition.[15]
[edit]Control
Main article: Human population control
Human population control is the practice of artificially altering the rate of growth of a human population.
Historically, human population control has been implemented by limiting the population's birth rate,
usually by government mandate, and has been undertaken as a response to factors including high or
increasing levels of poverty, environmental concerns, religious reasons, and overpopulation. While
population control can involve measures that improve people's lives by giving them greater control of their
reproduction, some programs have exposed them to exploitation.
Worldwide, the population control movement was active throughout the 1960s and 1970s, driving
many reproductive health and family planning programs. In the 1980s, tension grew between population
control advocates and women's health activists who advanced women's reproductive rights as part of
a human rights-based approach.[16] Growing opposition to the narrow population control focus led to a
significant change in population control policies in the early 1990s. [1
World human population
Main article: World population
As of 3 March 2012, the world population is estimated by the United States Census Bureau to be 6.998
billion.[3] Eurek Alert: World Population to surpass 7 Billion in 2011.[4] Earth’s population will reach seven
billion on 31 October, a milestone that offers unprecedented challenges and opportunities to all of
humanity, according to UNFPA, the United Nations Population Fund.[5]
According to papers published by the United States Census Bureau, the world population hit 6.5 billion
(6,500,000,000) on 24 February 2006. The United Nations Population Fund designated 12 October 1999
as the approximate day on which world population reached 6 billion. This was about 12 years after world
population reached 5 billion in 1987, and 6 years after world population reached 5.5 billion in 1993. The
population of some countries, such as Nigeria, is not even known to the nearest million,[6] so there is a
considerable margin of error in such estimates.[7]
Researcher, Carl Haub, calculated that a total of over 100 billion people have probably been born in the
last 2000 years
4. List out and explain the phases of cell cycle.
In the physical sciences, a phase is a region of space (a thermodynamic system), throughout which all
physical properties of a material are essentially uniform.[1] Examples of physical properties
include density, index of refraction, and chemical composition. A simple description is that a phase is a
region of material that is chemically uniform, physically distinct, and (often) mechanically separable. In a
system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second
phase, and the humid air over the water is a third phase. The glass of the jar is another separate phase.
(See State of Matter#Glass)
The term phase is sometimes used as a synonym for state of matter. Also, the term phase is sometimes
used to refer to a set of equilibrium states demarcated in terms of state variables such as pressure and
temperature by a phase boundary on a phase diagram. Because phase boundaries relate to changes in
the organization of matter, such as a change from liquid to solid or a more subtle change from one crystal
structure to another, this latter usage is similar to the use of "phase" as a synonym for state of matter.
However, the state of matter and phase diagram usages are not commensurate with the formal definition
given above and the intended meaning must be determined in part from the context in which the term is
used.
Distinct phases may be described as different states of matter such as gas, liquid, solid,plasma or Bose–
Einstein condensate. Useful mesophases between solid and liquid form other states of matter.
Distinct phases may also exist within a given state of matter. As shown in the diagram for iron alloys,
several phases exist for both the solid and liquid states. Phases may also be differentiated based
on solubility as in polar (hydrophilic) or non-polar (hydrophobic). A mixture of water (a polar liquid) and oil
(a non-polar liquid) will spontaneously separate into two phases. Water has a very low solubility(is
insoluble) in oil, and oil has a low solubility in water. Solubility is the maximum amount of a solute that can
dissolve in a solvent before the solute ceases to dissolve and remains in a separate phase. A mixture can
separate into more than two liquid phases and the concept of phase separation extends to solids, i.e.,
solids can form solid solutions or crystallize into distinct crystal phases. Metal pairs that are mutually
soluble can form alloys, whereas metal pairs that are mutually insoluble cannot.
As many as eight immiscible liquid phases have been observed.[2] Mutually immiscible liquid phases are
formed from water (aqueous phase), hydrophobic organic solvents, perfluorocarbons (fluorous phase),
silicones, several different metals, and also from molten phosphorus. Not all organic solvents are
completely miscible, e.g. a mixture of ethylene glycol and toluene may separate into two distinct organic
phases.[3]
Phases do not need to macroscopically separate spontaneously. Emulsions and colloids are examples of
immiscible phase pair combinations that do not physically separate.
Phase equilibrium
Left to equilibration, many compositions will form a uniform single phase, but depending on the
temperature and pressure even a single substance may separate into two or more distinct phases. Within
each phase, the properties are uniform but between the two phases properties differ.
Water in a closed jar with an air space over it forms a two phase system. Most of the water is in the liquid
phase, where it is held by the mutual attraction of water molecules. Even at equilibrium molecules are
constantly in motion and, once in a while, a molecule in the liquid phase gains enough kinetic energy to
break away from the liquid phase and enter the gas phase. Likewise, every once in a while a vapor
molecule collides with the liquid surface and condenses into the liquid. At equilibrium, evaporation and
condensation processes exactly balance and there is no net change in the volume of either phase.
At room temperature and pressure, the water jar reaches equilibrium when the air over the water has a
humidity of about 3%. This percentage increases as the temperature goes up. At 100 °C and atmospheric
pressure, equilibrium is not reached until the air is 100% water. If the liquid is heated a little over 100 °C,
the transition from liquid to gas will occur not only at the surface, but throughout the liquid volume: the
water boils.
5. Define and describe endocytosis.
Endocytosis is a process by which cells absorb molecules (such as proteins) by engulfing them. It is
used by all cells of the body because most substances important to them are large polar molecules that
cannot pass through the hydrophobic plasma or cell membrane. The process which is the opposite to
endocytosis is exocytosis
Principal components of endocytic pathway
The endocytic pathway of mammaliac cells consists of distinct membrane compartments that internalize
molecules from the plasma membrane and recycle them back to the surface (early endosomes and
recycling endosomes) or sort them to degradation (late endosomes and lysosomes). The principal
components of endocytic pathway are:[2]

Early endosomes are the first station on the endocytic pathway. Early endosomes are often located
in the periphery of the cell and receive most of types of vesicles coming from the cell surface. They
have a characteristic tubulo-vesicular morphology (vesicles up to 1 µm in diameter with connected
tubules of approx. 50 nm diameter) and a mildly acid pH. They are principally
sortingorganelles where many ligands dissociate from their receptors in the acid pH of the lumen and
from which many of the receptors recycle to the cell surface (via tubules). [6][7] It is also the site of
sorting into transcytotic pathway to late components (via vesicular component which can form
multivesicular bodies (MVB) or endosomal carrier vesicles (ECVs)).

Late endosomes receive internalized material en route to lysosomes, usually from early endosomes
in the endocytic pathway, from trans-Golgi network (TGN) in the biosynthetic pathway, and
fromphagosomes in the phagocytic pathway.[8] Late endosomes often contain many membrane
vesicles or membrane lamellae and proteins characteristic of lysosomes, including lysosomal
membrane glycoproteins and acid hydrolases. They are acidic (approx. pH 5.5), and are part of the
trafficking itinerary of mannose-6-phosphate receptors. Late endosomes are thought to mediate a
final set of sorting events prior to delivery of material to lysosomes.

Lysosomes are the last compartment of the endocytic pathway. They are acidic (approx. pH 4.8)
and by EM usually appear as large vacuoles (1-2 µm in diameter) containing electron dense material.
They have a high content of lysosomal membrane proteins and active lysosomal hydrolases, but
no mannose-6-phosphate receptor. They are generally regarded as the principal hydrolytic
compartment of the cell.[9][10]Lysosomes chief function in itself is to break down cellular waste
products, fats, carbohydrates, proteins, and other macromolecules into simple compounds. These
are then returned to the cytoplasm as new cell-building materials. To accomplish the tasks the
lysosomes use some 40 different types of hydrolytic enzymes, all of which are manufactured in the
endoplasmic reticulum and modified in the Golgi Apparatus.[11]
[edit]Clathrin-mediated
endocytosis
The major route for endocytosis in most cells, and the best-understood, is that mediated by the
molecule clathrin. This large protein assists in the formation of a coated pit on the inner surface of
theplasma membrane of the cell. This pit then buds into the cell to form a coated vesicle in the cytoplasm
of the cell. In so doing, it brings into the cell not only a small area of the surface of the cell but also a small
volume of fluid from outside the cell.[12][13][14]
Coats function to deform the donor membrane to produce a vesicle, and they also function in the
selection of the vesicle cargo. Coat complexes have been well characterized so far including: coat
protein-I (COP-I), COP-II, and clathrin.[15][16] Clathrin coats are involved in two crucial transport steps: (i)
receptor-mediated and fluid-phase endocytosis from the plasma membrane to early endosome and (ii)
transport from the TGN to endosomes. In endocytosis, the clathrin coat is assembled on the cytoplasmic
face of the plasma membrane, forming pits that invaginate to pinch off (scission) and become free CCVs.
In cultured cells, the assembly of a CCV takes ~ 1min, and several hundred to a thousand or more can
form every minute.[17] The main scaffold component of clathrin coat is the 190 kD protein called clathrin
heavy chain (CHC) and the 25 kD protein called clathrin light chain (CLC), which form three-legged
trimers, called triskelions.
Vesicles selectively concentrate and exclude certain proteins during formation and are not representative
of the membrane as a whole. AP2 adaptors are multisubunit complexes that perform this function at the
plasma membrane. The best-understood receptors that are found concentrated in coated vesicles of
mammalian cells are the LDL receptor (which removes LDL from circulating blood), the transferrin
receptor (which brings ferric ions bound by transferrin into the cell) and certain hormone receptors (such
as that for EGF).
At any one moment, about 25% of the plasma membrane of a fibroblast is made up of coated pits. As a
coated pit has a life of about a minute before it buds into the cell, a fibroblast takes up its surface by this
route about once every 16 minutes. Coated vesicles formed from the plasma membrane have a diameter
of about 36 nm and a lifetime measured in a few seconds. Once the coat has been shed, the remaining
vesicle fuses with endosomes and proceeds down the endocytic pathway. The actual budding-in process,
whereby a pit is converted to a vesicle, is carried out by clathrin assisted by a set of cytoplasmic proteins,
which includes dynamin and adaptors such as adaptin.
Coated pits and vesicles were first seen in thin sections of tissue in the electron microscope by Matt Lions
and Parker George. The importance of them for the clearance of LDL from blood was discovered by R. G
Anderson, Michael S. Brown and Joseph L. Goldstein in 1976. Coated vesicles were first purified
by Barbara Pearse, who discovered the clathrin coat molecule.