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 Assignment Biology II ( July 12,2010 )

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II-2 Sampaguita

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PostSubject: Assignment Biology II ( July 12,2010 )   Mon Jul 12, 2010 7:04 am

1.What Are The Principles Of Cell Thoery ?
Cells in culture, stained for keratin (red) and DNA (green)

Cell theory states that the cell is the fundamental unit of life, and that all living things are composed of one or more cells or the secreted products of those cells (e.g. shells). All cells arise from other cells through cell division. In multicellular organisms, every cell in the organism's body derives ultimately from a single cell in a fertilized egg. The cell is also considered to be the basic unit in many pathological processes. Additionally, the phenomenon of energy flow occurs in cells in processes that are part of the function known as metabolism. Finally, cells contain hereditary information (DNA) which is passed from cell to cell during cell division.

2.What Is A Cell ?
The cell is the functional basic unit of life. It was discovered by Robert Hooke and is the functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Some organisms, such as most bacteria, are unicellular (consist of a single cell). Other organisms, such as humans, are multicellular. Humans have about 100 trillion or 1014 cells; a typical cell size is 10 µm and a typical cell mass is 1 nanogram. The largest cells are about 135 µm in the anterior horn in the spinal cord while granule cells in the cerebellum, the smallest, can be some 4 µm and the longest cell can reach from the toe to the lower brain stem (Pseudounipolar cells))The largest known cells are unfertilised ostrich egg cells which weigh 3.3 pounds.

In 1835, before the final cell theory was developed, Jan Evangelista Purkyně observed small "granules" while looking at the plant tissue through a microscope. The cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that all cells come from preexisting cells, that vital functions of an organism occur within cells, and that all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.

The word cell comes from the Latin cellula, meaning, a small room. The descriptive term for the smallest living biological structure was coined by Robert Hooke in a book he published in 1665 when he compared the cork cells he saw through his microscope to the small rooms monks lived in.

3.Describe The Following :

a.Cell Membrane -

The cell membrane (also called the plasma membrane or plasmalemma) is one biological membrane separating the interior of a cell from the outside environment

The cell membrane surrounds all cells and it is selectively-permeable, controlling the movement of substances in and out of cells.[2] It contains a wide variety of biological molecules, primarily proteins and lipids, which are involved in a variety of cellular processes such as cell adhesion, ion channel conductance and cell signaling. The plasma membrane also serves as the attachment point for the intracellular cytoskeleton and, if present, the extracellular cell wall.

b.Nucleus -

In cell biology, the nucleus (pl. nuclei; from Latin nucleus or nuculeus, meaning kernel), also sometimes referred to as the "control center", is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these chromosomes are the cell's nuclear genome. The function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression — the nucleus is therefore the control center of the cell. The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and separates its contents from the cellular cytoplasm, and the nuclear lamina, a meshwork within the nucleus that adds mechanical support, much like the cytoskeleton supports the cell as a whole. Because the nuclear membrane is impermeable to most molecules, nuclear pores are required to allow movement of molecules across the envelope. These pores cross both of the membranes, providing a channel that allows free movement of small molecules and ions. The movement of larger molecules such as proteins is carefully controlled, and requires active transport regulated by carrier proteins. Nuclear transport is crucial to cell function, as movement through the pores is required for both gene expression and chromosomal maintenance.

Although the interior of the nucleus does not contain any membrane-bound subcompartments, its contents are not uniform, and a number of subnuclear bodies exist, made up of unique proteins, RNA molecules, and particular parts of the chromosomes. The best known of these is the 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.

c.Cytoplasm -

The cytoplasm is the part of a cell that is enclosed within the cell membrane. In eukaryotic cells, the contents of the cell nucleus are not part of the cytoplasm and are instead called the nucleoplasm. Also in eukaryotic cells, the cytoplasm contains organelles, such as mitochondria, which are filled with liquid that is kept separate from the rest of the cytoplasm by biological membranes. The cytoplasm is the site where most cellular activities occur, such as many metabolic pathways like glycolysis, and processes such as cell division. The inner, granular mass is called the endoplasm and the outer, clear and glassy layer is called the cell cortex or the ectoplasm.

The part of the cytoplasm that is not held within organelles is called the cytosol. The cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell. The cytosol is a gel, with a network of fibers dispersed through water. Due to this network of pores and high concentrations of dissolved macromolecules, such as proteins, an effect called macromolecular crowding occurs and the cytosol does not act as an ideal solution. This crowding effect alters how the components of the cytosol interact with each other.

d.Chromosomes -

A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being very strongly stained by particular dyes.
Diagram of a replicated and condensed metaphase eukaryotic chromosome. (1) Chromatid – one of the two identical parts of the chromosome after S phase. (2) Centromere – the point where the two chromatids touch, and where the microtubules attach. (3) Short arm. (4) Long arm.

Chromosomes vary widely between different organisms. The DNA molecule may be circular or linear, and can be composed of 10,000 to 1,000,000,000[1] nucleotides in a long chain. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Furthermore, cells may contain more than one type of chromosome; for example, mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.

In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin. This allows the very long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies through the cell cycle. Chromosomes are the essential unit for cellular division and must be replicated, divided, and passed successfully to their daughter cells so as to ensure the genetic diversity and survival of their progeny. Chromosomes may exist as either duplicated or unduplicated—unduplicated chromosomes are single linear strands, whereas duplicated chromosomes (copied during synthesis phase) contain two copies joined by a centromere. Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure (pictured to the right). Chromosomal recombination plays a vital role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe and die, or it may aberrantly evade apoptosis leading to the progression of cancer.

In practice "chromosome" is a rather loosely defined term. In prokaryotes and viruses, the term genophore is more appropriate when no chromatin is present. However, a large body of work uses the term chromosome regardless of chromatin content. In prokaryotes DNA is usually arranged as a circle, which is tightly coiled in on itself, sometimes accompanied by one or more smaller, circular DNA molecules called plasmids. These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest genophores are found in viruses: these DNA or RNA molecules are short linear or circular genophores that often lack structural proteins.

e.Mitochondria -

In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 10 micrometers (μm) in diameter. Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth. Mitochondria have been implicated in several human diseases, including mitochondrial disorders and cardiac dysfunction, and may play a role in the aging process. The word mitochondrion comes from the Greek μίτος or mitos, thread + χονδρίον or chondrion, granule.

Several characteristics make mitochondria unique. The number of mitochondria in a cell varies widely by organism and tissue type. Many cells have only a single mitochondrion, whereas others can contain several thousand mitochondria. The organelle is composed of compartments that carry out specialized functions. These compartments or regions include the outer membrane, the intermembrane space, the inner membrane, and the cristae and matrix. Mitochondrial proteins vary depending on the tissue and the species. In humans, 615 distinct types of proteins have been identified from cardiac mitochondria; whereas in Murinae (rats), 940 proteins encoded by distinct genes have been reported. The mitochondrial proteome is thought to be dynamically regulated.Although most of a cell's DNA is contained in the cell nucleus, the mitochondrion has its own independent genome. Further, its DNA shows substantial similarity to bacterial genomes.

f.Endoplasmic Reticulum -

The endoplasmic reticulum (ER) is an eukaryotic organelle that forms an interconnected network of tubules, vesicles, and cisternae within cells. Rough endoplasmic reticulums synthesize proteins, while smooth endoplasmic reticulums synthesize lipids and steroids, metabolize carbohydrates and steroids, and regulate calcium concentration, drug detoxification, and attachment of receptors on cell membrane proteins. Sarcoplasmic reticulums solely regulate calcium levels.

The lacey membranes of the endoplasmic reticulum were first seen by Keith R. Porter, Albert Claude, and Ernest F. Fullam in 1945

g.Ribosomes -
Ribosomes are the components of cells that make proteins from amino acids. One of the central tenets of biology, often referred to as the "central dogma," is that DNA is used to make RNA, which, in turn, is used to make protein. The DNA sequence in genes is copied into a messenger RNA (mRNA). Ribosomes then read the information in this RNA and use it to create proteins. This process is known as translation (genetics), i.e. the ribosome "translates" the genetic information from RNA into proteins. Ribosomes do this by binding to an mRNA and using it as a template for the correct sequence of amino acids in a particular protein. The amino acids are attached to transfer RNA (tRNA) molecules, which enter one part of the ribosome and bind to the messenger RNA sequence. The attached amino acids are then joined together by another part of the ribosome. The ribosome moves along the mRNA, "reading" its sequence and producing a chain of amino acids.

Ribosomes are made from complexes of RNAs and proteins. Ribosomes are divided into two subunits, one larger than the other. The smaller subunit binds to the mRNA, while the larger subunit binds to the tRNA and the amino acids. When a ribosome finishes reading a mRNA these two subunits split apart. Ribosomes have been classified as ribozymes, since the ribosomal RNA seems to be most important for the peptidyl transferase activity that links amino acids together.

Ribosomes from bacteria, archaea and eukaryotes (the three domains of life on Earth), have significantly different structure and RNA sequences. These differences in structure allow some antibiotics to kill bacteria by inhibiting their ribosomes, while leaving human ribosomes unaffected. The ribosomes in the mitochondria of eukaryotic cells resemble those in bacteria, reflecting the evolutionary origin of this organelle. The word ribosome comes from ribonucleic acid and the Greek: soma (meaning body).

h.Golgi Bodies -

The Golgi apparatus (also Golgi body or Golgi Complex) is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi and was named after him.

The primary function of the Golgi apparatus is to process and package macromolecules, such as proteins and lipids, after their synthesis and before they make their way to their destination; it is particularly important in the processing of proteins for secretion. The Golgi apparatus forms a part of the cellular endomembrane system.

i.Lysosome -

Lysosomes are spherical organelles that contain enzymes (acid hydrolases) that break up endocytized materials and cellular debris. They are found in animal cells, while in yeast and plants the same roles are performed by lytic vacuoles.[1] Lysosomes digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. The membrane around a lysosome allows the digestive enzymes to work at the 4.5 pH they require. Lysosomes fuse with vacuoles and dispense their enzymes into the vacuoles, digesting their contents. They are created by the addition of hydrolytic enzymes to early endosomes from the Golgi apparatus. The name lysosome derives from the Greek words lysis, which means to separate; and soma, which means body. They are frequently nicknamed "suicide-bags" or "suicide-sacs" by cell biologists due to their role in autolysis. Lysosomes were discovered by the Belgian cytologist Christian de Duve in 1949.

The size of lysosomes varies from 0.1–1.2 μm. At pH 4.8, the interior of the lysosomes is acidic compared to the slightly alkaline cytosol (pH 7.2). The lysosome maintains this pH differential by pumping protons (H+ ions) from the cytosol across the membrane via proton pumps and chloride ion channels. The lysosomal membrane protects the cytosol, and therefore the rest of the cell, from the degradative enzymes within the lysosome. The cell is additionally protected from any lysosomal acid hydrolases that leak into the cytosol as these enzymes are pH-sensitive and function less well in the alkaline environment of the cytosol.

j.vacuoles -

A vacuole is a membrane bound organelle which is present in all plant and fungal cells and some protist, animal[1] and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain cases they may contain solids which have been engulfed. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these. The organelle has no basic shape or size, its structure varies according to the needs of the cell.

The function and importance of vacuoles varies greatly according to the type of cell in which they are present, having much greater prominence in the cells of plants, fungi and certain protists than those of animals and bacteria. In general, the functions of the vacuole include:

* Isolating materials that might be harmful or a threat to the cell
* Containing waste products
* Maintaining internal hydrostatic pressure or turgor within the cell
* Maintaining an acidic internal pH
* Containing small molecules
* Exporting unwanted substances from the cell
* Allows plants to support structures such as leaves and flowers due to the pressure of the central vacuole

Vacuoles also play a major role in autophagy, maintaining a balance between biogenesis (production) and degradation (or turnover), of many substances and cell structures in certain organisms. They also aid in destruction of invading bacteria or of misfolded proteins that have begun to build up within the cell. In protists, vacuoles have the additional function of storing food which has been absorbed by the organism, and assist in the digestive and waste management process for the cell.

l.chloroplast -

Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.

The word chloroplast is derived from the Greek words chloros, which means green, and plast, which means form or entity. Chloroplasts are members of a class of organelles known as plastids.

m.DNA -

Deoxyribonucleic acid (en-us-Deoxyribonucleic_acid.ogg /diːˌɒksɨˌraɪbɵ.n(j)uːˈkleɪ.ɪk ˈæsɪd/ (help·info)) (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints, like a recipe or a code, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.

Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called bases. 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 long structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.

4.Give The Following Contributiors Of The Following Scientist :

a.Robert Hooke -

Robert Hooke FRS (18 July 1635 – 3 March 1703) was an English natural philosopher, architect and polymath who played an important role in the scientific revolution, through both experimental and theoretical work.

b.Francesco Redi -

Francesco Redi (Arezzo, February 18, 1626 – Pisa, March 1, 1697) was an Italian physician, naturalist, and poet.

c.Anton Van Leeuwenhoek -

Antonie Philips van Leeuwenhoek (in Dutch also Anthonie, Antoni, or Theunis, in English, Antony or Anton) [1] (born on October 24, 1632 and died on August 26, 1723 – buried on August 30) was a Dutch tradesman and scientist from Delft, Netherlands. He is commonly known as "the Father of Microbiology", and considered to be the first microbiologist. He is best known for his work on the improvement of the microscope and for his contributions towards the establishment of microbiology. Using his handcrafted microscopes he was the first to observe and describe single celled organisms, which he originally referred to as animalcules, and which we now refer to as microorganisms. He was also the first to record microscopic observations of muscle fibers, bacteria, spermatozoa and blood flow in capillaries (small blood vessels). Van Leeuwenhoek never authored any books, but wrote many letters.

d.Caspar Wolff -

Caspar Friedrich Wolff (January 18, 1733 – February 22, 1794) was a German physiologist and one of the founders of embryology.

e.Felice Fontana -

Felice Fontana (15 April 1730 – 10 March 1805) was an Italian physicist who discovered the water gas shift reaction in 1780. He is also credited with launching modern toxicology and investigating the human eye.

f.Henri Dutrochet-

René Joachim Henri Dutrochet (November 14, 1776 – February 4, 1847) was a French physician, botanist and physiologist.

Dutrochet was born in Poitou. In 1799 he entered the military marine at Rochefort, but soon left it to join the Vendean army. In 1802 he began the study of medicine at Paris; and he was subsequently appointed chief physician to the hospital at Burgos. After an attack of typhus he returned in 1809 to France, where he devoted himself to the study of the natural sciences. His scientific publications were numerous, and covered a wide field, but his most noteworthy work was embryological. His Recherches sur l'accroissement et la reproduction des végétaux, published in the Mémoires du museum d'histoire naturelle for 1821, procured him in that year the French Academys prize for experimental physiology. In 1837 appeared his Mémoires pour servir a l'histoire anatomique et physiologique des végétaux et des animaux, a collection of all his more important biological papers.

He investigated and described osmosis, respiration, embryology, and the effect of light on plants. He has been given credit for discovering cell biology and cells in plants and the actual discovery of the process of osmosis.

He died in Paris.

The Mauritian plant genus Trochetia was named in his honour.

g.Pierre Turpin -

Pierre Jean François Turpin (1775-1840) was a French botanist and illustrator. He is considered one of the greatest floral and botanical illustrators during the Napoleonic Era and afterwards. As an artist, Turpin was largely self-taught.

In 1794 Turpin was stationed in Haiti as a member of the French Army. Here he met botanist Pierre Antoine Poiteau (1766-1854), with whom he would have a working relationship throughout his career. Through Poiteau, Turpin learned botany, and he created many botanical field drawings that became a basis of further study when the two men returned to France. Concerning their work in Haiti, they were able to describe around 800 species of plants.

Through his collaboration with Poiteau and other naturalists, Turpin created some of the finest watercolors and illustrations of plants that are known to exist. The following are some of the works in which Turpin contributed his illustrative work:

* He did much of the illustrated work in Jules Paul Benjamin Delessert's (1773-1847) Icones selectae plantarum.
* With Pierre Poiteau, he produced an updated version of Henri Louis Duhamel du Monceau's (1700-1782) Traité des arbres fruitiers (Treatise of the Fruit Trees).
* Contributed the illustrative work for Alexander von Humboldt (1769-1859) and Aimé Bonpland's (1773-1858) Plantes Equinoxales (1808).
* Provided the illustrations to Jean Louis Marie Poiret's (1755-1834) Leçons de flore: Cours complet de botanique (1819-1820).

h.Robert Brown -

i.Matthias Jakob Schleidenr -

Matthias Jakob Schleiden (5 April 1804 - 23 June 1881) was a German botanist and co-founder of the cell theory, along with Theodor Schwann and Rudolf Virchow.

Born in Hamburg, Schleiden was educated at Heidelberg and practiced law in Hamburg, but soon developed his hobby of botany into a full-time pursuit. Schleiden preferred to study plant structure under the microscope. While a professor of botany at the University of Jena, he wrote Contributions to Phytogenesis (1838), in which he stated that the different parts of the plant organism are composed of cells. Thus, Schleiden and Theodor Schwann became the first to formulate what was then an informal belief as a principle of biology equal in importance to the atomic theory of chemistry. He also recognized the importance of the cell nucleus, discovered in 1831 by the Scottish botanist Robert Brown, and sensed its connection with cell division.

Schleiden was one of the first German biologists to accept Charles Darwin's theory of evolution. He became professor of botany at the University of Dorpat in 1863. He concluded that all plant parts are made of cells. He died in Frankfurt am Main on 23 June 1881.

j.Hugo von Mohl -

Hugo von Mohl (8 April 1805 – 1 April 1872) was a German botanist from Stuttgart.

He was a son of the Württemberg statesman Benjamin Ferdinand von Mohl (1766–1845), the family being connected on both sides with the higher class of state officials of Württemberg. While a pupil at the gymnasium he pursued botany and mineralogy in his leisure time, till in 1823 he entered the University of Tübingen. After graduating with distinction in medicine he went to Munich, where he met a distinguished circle of botanists, and found ample material for research.

k.Theodor Schwann -

Theodor Schwann (7 December 1810, Neuss – 11 January 1882) was a German physiologist. His many contributions to biology include the development of cell theory, the discovery of Schwann cells in the peripheral nervous system, the discovery and study of pepsin, the discovery of the organic nature of yeast, and the invention of the term metabolism.

l.Rudolf Virchow -

Rudolf Ludwig Karl Virchow (13 October 1821 – 5 September 1902) was a German doctor, anthropologist, pathologist, prehistorian, biologist and politician, known for his advancement of public health. Referred to as "the father of modern pathology," he is considered one of the founders of social medicine.

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