NEW DRUG THAT HELPS IN COLLECTING STEM CELLS FROM BLOOD

Stem cell therapies are used to treat blood cancer patients. Stem cells are collected and reintroduced to a patient after chemotherapy. But doctors have to face difficulty in collecting enough stem cells from one in ten cancer patients to undergo treatment.

The new drug, Plerixafor has allowed doctors to collect stem cells from patients where there had been difficulties previously. This drug has been licensed recently and is being used at Beatson West of Scotland Cancer Centre. Plerixafor has, so far, had a 100% success rate in allowing doctors at the cancer centre to collect enough cells from patients who fall into this category.

Blood specialist, Dr Kenneth Douglas, explained how the drug worked.

"Basically it blocks a chemical scent that stem cells sniff for that tells them they're in the bone marrow," he said.

"If you block that chemical scent they get confused and agitated and they think they are not in the bone marrow any more and they start wandering into the blood stream looking for the bone marrow."

Doctors collect these stem cells for future use when more of them start wandering into the blood. The centre in Glasgow has now treated 13 people with the drug and every one has been able to proceed with stem cell treatment.

STEM CELLS

What is a stem cell?

Stem cells are the cells which have the remarkable potential to develop into different types of cells through mitotic cell division and differentiate into specialized cell types.

Why are they important?

Stem cells are important for many reasons. Embryonic stem cells can give rise to the entire body of the organism. It forms specialized cell types and organs like heart, lung, skin and other tissues. In some adult tissues like bone marrow, muscles and brain, stem cells replace cells that are lost through tear and wear, disease or injury. Due to their regenerative property stem cells have potential to treat diseases like heart disease and diabetes.

Properties of stem cells

Stem cells differ from other kinds of cells in body. They have three general properties: they are capable of dividing and renewing, they are not specialized cells, and they can give rise to specialized cell types.

Stem cells have ability to divide and renew themselves for long period. Cells such as muscle cells don’t normally replicate but stem cells replicate repeatedly. The initial population of stem cells can produce millions of cell within months in the laboratory.

Stem cells are unspecialized. Stem cell does not have certain structures that allow it to perform specialized function. For example, a heart muscle pumps blood and red blood cells carry oxygen. Stem cells cannot perform specialized functions but they can give rise to specialized cells like heart cells, nerve cells, and muscle cells.

Stem cells can give rise to specialized cells. The process by which stem cells give rise to specialized cells is known as differentiation. Cell’s genes, having long DNA, control the internal signals and carry coded instructions to all cellular structures and functions. External signals include chemicals secreted by other cells and physical contact with other cells that help in cell differentiation.

Types of stem cells

Stem cells are classified into three types based on their ability to differentiate.

Totipotent cells

These are the most versatile of the stem cell types. They have the potential to develop into any cell found in the human body or entire organism. In human development, egg cell and sperm cell fuse together to form single cell called zygote. Zygote is totipotent which means it gives rise to all human cells like brain cell, heart cell, liver cell. The first few divisions in embryonic development produce more totipotent cells. After four days of embryonic cell division, the cells begin to develop into specialized pluripotent stem cells.

Pluripotent cells

These are like totipotent cells that can give rise to all tissue types but cannot rise to an entire organism. After four days of fertilization, totipotent cells form a cluster of cells called blastocyst. Blastocyst has small group of cells called inner cell mass. The inner cell mass is pluripotent as it giving rise to all tissues in the human body. The pluripotent cells continue to divide and begin to specialize further.

Multipotent cells

Multipotent stem cells have the same basic features of all stem cells. A multipotent stem cell can give rise to other types of cells but it is limited in its ability to differentiate. These other types of cells are also limited in numbers. Examples of multipotent cells include haematopoietic cells which give rise to blood cells or those in brain that give rise to neural cells. Multipotent stem cells are found in the tissues of adult mammals. It is thought that they are in most body organs, where they replace diseased or aged cells. Thus, they function to replenish the body's cells throughout an individual's life.

Based on the source of stem cells, they are of following types.

Embryonic stem cells

Embryonic stem cells are derived from the inner cell mass of blastocyst, an early stage embryo. Human embryos reach the blastocyst stage in 4-5 days after fertilization. These are pluripotent which means they are able to develop into three primary germ layers: ectoderm, endoderm and mesoderm including over 220 types of cells in the human body.

Because of their plasticity and potentially unlimited capacity for self-renewal, ES cell therapies have been proposed for regenerative medicine and tissue replacement after injury or disease. Some of the many diseases that could be treated by transplanting cells harvested from human embryos are: Diabetes, Cardiovascular diseases, Cancer, Parkinson's disease, Spinal injuries.

Adult stem cells

Adult stem cells are undifferentiated cells found throughout the body after embryonic development. The primary roles of adult stem cells in living organisms are to maintain and repair the tissue in which they are found

Adult stem cells have been identified in many organs and tissues, including brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin, teeth, heart, gut, liver, ovarian epithelium, and testis. They are thought to reside in a specific area of each tissue (called a "stem cell niche"). In many tissues, current evidence suggests that some types of stem cells are pericytes, cells that compose the outermost layer of small blood vessels. Stem cells may remain quiescent (non-dividing) for long periods of time until they are activated by a normal need for more cells to maintain tissues, or by disease or tissue injury.

In a living animal, adult stem cells are available to divide, when needed, and can give rise to mature cell types that have characteristic shapes and specialized structures and functions of a particular tissue. The following are examples of differentiation pathways of adult stem cells that have been demonstrated in vitro or in vivo.

• Hematopoietic stem cells give rise to all the types of blood cells: red blood cells, B lymphocytes, T lymphocytes, natural killer cells, neutrophils, basophils, eosinophils, monocytes, and macrophages.
• Mesenchymal stem cells give rise to a variety of cell types: bone cells (osteocytes), cartilage cells (chondrocytes), fat cells (adipocytes), and other kinds of connective tissue cells such as those in tendons.
• Neural stem cells in the brain give rise to its three major cell types: nerve cells (neurons) and two categories of non-neuronal cells—astrocytes and oligodendrocytes.
• Epithelial stem cells in the lining of the digestive tract occur in deep crypts and give rise to several cell types: absorptive cells, goblet cells, paneth cells, and enteroendocrine cells.
• Skin stem cells occur in the basal layer of the epidermis and at the base of hair follicles. The epidermal stem cells give rise to keratinocytes, which migrate to the surface of the skin and form a protective layer. The follicular stem cells can give rise to both the hair follicle and to the epidermis.

Fetal stem cells

Fetal stem cells are primitive cell types found in the organs of fetuses. The classification of fetal stem cells remains unclear and this type of stem cell is currently often grouped into an adult stem cell.

Studying stem cells will help us understand how they transform into the dazzling array of specialized cells that make us what we are. Some of the most serious medical conditions, such as cancer and birth defects, are due to problems that occur somewhere in this process. A better understanding of normal cell development will allow us to understand and perhaps correct the errors that cause these medical conditions.

Another potential application of stem cells is making cells and tissues for medical therapies. Today, donated organs and tissues are often used to replace those that are diseased or destroyed. Unfortunately, the number of people needing a transplant far exceeds the number of organs available for transplantation. Pluripotent stem cells offer the possibility of a renewable source of replacement cells and tissues to treat a myriad of diseases, conditions, and disabilities including Parkinson's disease, amyotrophic lateral sclerosis, spinal cord injury, burns, heart disease, diabetes, and arthritis.

Structure of Eukaryotes

Structure of Eukaryotes

Eukaryotes have a distinct nucleus with a nuclear membrane and other membrane bound organelles. Almost all species of large organisms are eukaryotes, including animals, plants and fungi. The organelles found in eukaryotes are plasma membrane, golgi complex, mitochondria, ribosomes, nucleus, and endoplasmic reticulum. Plant cells have additional components like cell wall, vacuoles and chloroplast.

PLANT CELL

ANIMAL CELL

Plasma membrane

Plasma membrane is a lipid bilayer found in all cells. It separates the interior of the cell with exterior environment. It is composed of lipids and proteins. It is a semi-permeable membrane allowing the passage of substances through it. Protein receptors are present on plasma membrane which communicate with other cells.

Golgi apparatus

Golgi apparatus is a single membrane bound organelle named after its discoverer, Camillo Golgi, an Italian physician. It is composed of stacks of membrane bound vesicles called cisternae. The main function of Golgi apparatus is to process and package biomolecules like proteins and lipids. The substances are modified by the enzymes present in cisternae by combining with carbohydrates and phosphates. The vesicles that leave the endoplasmic reticulum are transported to cis face and empty their contents in to lumen. Then the contents are moved to trans face where they are sorted and transported to their respective destinations.

Mitochondria

Mitochondria are a double membrane bound organelle. The outer membrane is smooth but inner membrane is convoluted into folds called cristae which increase its surface area. These folds are studded with small round bodies known as F₁ particles or oxysomes. Matrix is a space enclosed by inner membrane. It is important in the production of ATP with the help of ATPase present in inner membrane. Mitochondria are known as power house of the cell as ATP is produced in it. It has its own genetic material and also manufactures its own RNAs and proteins.

Chloroplast

Chloroplasts are found in plants and some protists. Chloroplasts contain chlorophyll, a green pigment that traps solar energy and gives plants their green color. They transform light energy into chemical energy that is stored in food molecules.

Nucleus

Nucleus is also called control center of cell. It is enveloped by double layered nuclear membrane. Nuclear membrane is impermeable to most substances so it has nuclear pores to transport small molecules and ions. Proteins are transported with the help of carrier proteins. Nuclear transport is crucial to cell function, as movement through the pores is required for both gene expression and chromosomal maintenance. Inside the nucleus is nucleolus which is mainly involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA.

The cell nucleus contains the majority of the cell's genetic material, in the form of multiple linear DNA molecules organized into structures called chromosomes. During most of the cell cycle these are organized in a DNA-protein complex known as chromatin, and during cell division the chromatin can be seen to form the well defined chromosomes familiar from a karyotype. A small fraction of the cell's genes are located instead in the mitochondria.

The main function of the cell nucleus is to control gene expression and mediate the replication of DNA during the cell cycle. The nucleus provides a site for genetic transcription that is segregated from the location of translation in the cytoplasm, allowing levels of gene regulation that are not available to prokaryotes.

Endoplasmic reticulum

It forms the interconnected network in cells. The general structure of the endoplasmic reticulum is an extensive membrane network of cisternae held together by the cytoskeleton. The functions of the endoplasmic reticulum vary greatly depending on the exact type of endoplasmic reticulum and the type of cell in which it resides. The three varieties are called rough endoplasmic reticulum, smooth endoplasmic reticulum and sarcoplasmic reticulum.

The surface of the rough endoplasmic reticulum(RER) is studded with protein-manufacturing ribosomes giving it a "rough" appearance.The membrane of the RER is continuous with the outer layer of the nuclear envelop.The smooth endoplasmic reticulum (SER) has functions in several metabolic processes.The sarcoplasmic reticulum (SR) is a special type of smooth ER found in smooth and striated muscle.This fundamental difference is indicative of their functions: the SER synthesizes molecules while the SR stores and pumps calcium ions.The SR contains large stores of calcium, which it sequesters and then releases when the muscle cell is stimulated.

Cytoskeleton

Cytoskeleton is the skeletal system present within the cytoplasm. It maintains the cell’s shape, protects it and helps in its motion. It plays role in cell division and intra cellular transport. Eukaryotic cells contain three main kinds of filaments. They are microfilaments, intermediate filaments and microtubules.

Microfilaments are concentrated just beneath the cell membrane. This filament type is composed of two intertwined chains. These are responsible for resisting tension and maintaining cellular shape and participation in some cell-to-cell or cell-to-matrix junction. They are also important for cytokinesis and, along with myosin, muscular contraction.

Intermediate filaments are more stable than actin filaments. Their function is to maintain cell shape.

Microtubules are hollow cylinders most commonly comprised of 13 protofilaments which, in turn, are polymers of alpha and beta tubulin. They have a very dynamic behavior, binding GTP for polymerization. They are commonly organized by the centrosome.

STORAGE ORGANELLES

Vacuoles are a sac of fluid surrounded by a membrane used to store food, fluid or waste products. Lysosymes are membrane bound organelles that contain digestive enzymes. They fuse with vacuoles to digest food or worn out cell parts. Lysozymes are also called ‘suicide sacs’ because they can destroy the whole cell.

Centrioles are membrane bound organelle made of protein. They are found in animals and fungi. They play a role in splitting of the cells into two cells.

Structure of Prokaryotes

Structure and Function

All cells whether prokaryotic or eukaryotic have same basic cell structure. All cells have plasma membrane which envelops it and separates it from exterior being selectively permeable. Inside the cell a large volume of cytoplasm is present which contains genetic material DNA, RNA and other cellular organelles.

Structure of Prokaryotes

Prokaryotes are single celled organisms that are most primitive forms of life on earth. Prokaryotes include bacteria and archeans. Prokaryotic cells have various shapes. The four basic shapes are Cocci (spherical), Bacilli (rod shaped), Spirochaete (spiral) and vibrio (comma shaped).

Taking bacteria as an example the outer most layer is the capsule. It is a layer of polysaccharide that protects the cell against phagocytosis. It also helps bacteria to adhere to surfaces and other cells. Capsular material is used as vaccine against some organisms (e.g., H. influenzae type b and S. pneumonia). Cell wall is composed of peptidoglycan and it gives cell its structural integrity. Its primary function is to protect cell from internal pressure caused by higher concentrations of proteins and other components compared to exterior environment. Plasma membrane is a lipid bilayer surrounding the cytoplasm and regulates the flow of substances in and out of the cell.

Bacteria have appendages like flagella and pilli. Flagella are extra cellular whip like structure protruding from cell wall and responsible for locomotion. Pilli are hollow, hair like structures made of protein. Their function is to facilitate attachment to other organisms and also involve in conjugation.

In the cytoplasm, there is nucleoid which contains the genetic material. Bacteria also have extra chromosomal material called plasmid. Ribosomes are the intracellular multiprotein complexes found in bacteria. This is the site of protein synthesis in living organisms. Bacteria have 70S ribosome which is made up of 50S and 30S subunits

Types of Cells

Types of Cells

There are two types of cells: Eukaryotic and Prokaryotic.

Prokaryotic Cells

The word prokaryote comes from the Greek pro- (before) and karyon (nut or kernel referring to cell nucleus). The prokaryotes are a group of organisms that lack a cell nucleus or any other membrane bound organelle. Most prokaryotes are unicellular but a few like Myxobacteria have multicellular stages in its life cycle.

A prokaryotic cell consists of:

• flagella and pilli, that project out from the cell's surface. These are structures (not present in all prokaryotes) made of proteins that facilitate movement and communication between cells;
• enclosing the cell is the cell envelop - generally consisting of a cell wall covering a plasma membrane though some bacteria also have a further covering layer called a capsule. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, serving as a protective filter.
• inside the cell is the cytoplasm that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. A prokaryotic chromosome is usually a circular molecule. Though not forming a nucleus, the DNA is condensed in a nucleoid. Prokaryotes can carry extra chromosomal DNA elements called Plasmids, which are usually circular. Plasmids enable additional functions such as antibiotic resistance.

Eukaryotic Cell

The word eukaryote comes from Greek eu- (true) and karyon (nut or kenel). A eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus. Most eukaryotic cells contain other membrane-bound organelles such as mitochondria, chloroplasts and the Golgi apparatus.

What is a cell?

What is a cell?

Cell is the basic structural and functional unit of living organisms. It is the building block of life. Some organisms are unicellular (single celled) like bacteria while others are multi-cellular like humans. Human beings have an estimated 100 trillion cells and the typical cell size is 10 micro-meters with cell mass of 1 nanogram. The largest known cell is the unfertilized Ostrich egg cell.

The word ‘cell’ comes from the Latin cellula, meaning ‘a small room’. The cell theory developed by Matthias Jakob Schleiden and Theodor Schwann states that all organisms are composed of one or more cells and all cells arise from preexisting cells. Vital functions of an organism occur within cells, and all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.

A group of cells having similar function constitute to form a tissue. Various tissues having coordinated function form organs which inturn constitute the body system.