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Thursday, August 19, 2010

PowerPoint Presentation On Viruses

PPT On Viruses


PowerPoint Presentation On Genomic Library

PPT On Genomic Library


Genomic Library Presentation Transcript:
1. Genome - An Introduction
The total DNA present in the nucleus of each cell of an organism is its Genome. It comes from the terms Gene and Chromosome. It corresponds to all the organism’s bases: A,T,C,G. Our genome is a chain of 3.4 billion ‘pearls’. The genomes of two different people differ on an average by on ‘pearl’ in one thousand. Genes represent only about 5% of the total human genome. The role of all the non-coding sequences that make up the remaining 95% is today unknown, but researches have been able to assign functions to some of those sequences: some regulate DNA replication and transcription; others contribute to the chromosomal structuring. The Human Genome Project, launched in the early 1990s has succeeded in the completing the draft of DNA sequence(2003) of our entire genome. Genome is divided into chromosomes, chromosomes contain genes, and genes are made of DNA.

2. The word “genome” was coined in about 1930, however at that time the scientists had very little information about the real meaning of the word “Genome”. Each one of the earth’s species has its own distinctive genome. Genomes belong to species,& they also belong to individuals. Every Giraffe on the African Savanna has a unique genome, as does every elephant, acacia tree, & ostrich. Unless individuals are identical twins, their genomes are different from each other & every other person on earth-in fact it differs for every single individual who has ever lived. The entire world is full of Genomes. A genome is the information that affects every aspect of our behavior & physiology. Cooking dinner, digesting food talking, sleeping, reading – the genome plays a role in all these things. Thus studying the genome gives us insights into why some people live longer than others, why some die of heart disease and others of cancer, why some people have trouble keeping weight on while others have trouble keeping it off and so on.

3. Gene Library
A gene library is a collection of different DNA sequences from an organism each of which has been cloned into a vector for ease of purification, storage and analysis. There are essentially two types of gene library that can be made depending upon the source of the DNA used. If the DNA is genomic DNA, the library is called a genomic library. If the DNA is a copy of an mRNA population, that is cDNA, then the library is called a cDNA library. Size of the gene library A gene library must contain a certain number of recombinants for there to be a high probability of it containing any particular sequence. This value can be calculated if the genome size and the average size of the insert in the vector are known. Construction of libraries For making libraries, genomic DNA, usually prepared by protease digestion and phase extraction, is fragmented randomly by physical shearing or restriction enzyme digestion to give a size range appropriate for the selected vector. Often combinations of restriction enzymes are used to partially digest the DNA. Vectors Plasmids, Lambda phage, cosmid, BAC or YAC( yeast artificial chromosome) vectors can be used to construct genomic libraries, the choice depending on the genome size. The upper size limit of these vectors is about 10, 23, 45, 350, & 100 kb respectively. The genomic DNA fragments are ligated to the prepared vector molecules using T4 DNA ligase.

4. Genomic DNA Libraries
These libraries are made from genomic DNA (all the DNA found in the organism’s nuclei). Genomic DNA molecules are very large (each chromosome in the nucleus is one such DNA molecule), so they must be fragmented into small pieces to insert into vectors. This is done through digestion using one or more appropriate restriction endonucleases, mechanical shearing, or a combination of the two processes. The DNA is then ligated into the vector, which could be a plasmid, a cosmid (more often) or a viral chromosome. cDNA Libraries These libraries are made from cDNA (complimentary DNA), which are DNA copies of mRNA molecules. To make cDNA, mRNA is isolated from a tissue or whole organism, and DNA is copied from the mRNA template using an enzyme called reverse transcriptase. This enzyme works like a DNA polymerase, except that it uses RNA as a template instead of DNA. The resulting cDNA molecules are then engineered so that they have restriction enzyme recognition sites at each end of every molecule, which allows them to be digested and inserted into a vector.

5. Genomic Libraries
Definitions A library produced when the complete genome of a particular organism is cleaved into thousands of fragments, and all the fragments are cloned by insertion into a cloning vector. A form of gene library containing the complete DNA sequences present in the genome of a given organism. A collection of clones made from a set of randomly generated overlapping DNA fragments representing the entire genome of an organism. A set of thousands of DNA segments from a genome, each carried by a plasmid or a phage.

6. Construction of Genomic Libraries
The purpose of genomic library construction is to have an organism’s genome cloned as small fragments into separate vectors. Ideally the entire genome is represented: i.e., to say, the sum of the different fragments equals the entire genome. In this way specific groups of genes can be analyzed and isolated. The construction of a genomic library begins with cleaving the genome into small pieces by a restriction endonuclease. These genomic fragments are then either cloned into vectors & introduced into a microbe or packed into phage particles that are used to infect the host. In either case, many thousands of different clones- each with a different genomic DNA insert –are created. Therefore each clone will act as a “book” in this “library” of DNA fragments. If the genomic library has been inserted into a microbe that expresses the foreign gene, it may be possible to assay each clone for a specific protein or phenotype.

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PowerPoint Presentation On RNA Polymerase Enzyme

PPT On RNA Polymerase Enzyme


RNA Polymerase Enzyme Presentation Transcript:
1. 1. The DNA replicates its information in a process that involves many enzymes: replication. 2. The DNA codes for the production of messenger RNA (mRNA) during transcription. 3. In eucaryotic cells, the mRNA is processed (essentially by splicing) and migrates from the nucleus to the cytoplasm. 4. Messenger RNA carries coded information to ribosomes. The ribosomes "read" this information and use it for protein synthesis. This process is called translation. Proteins do not code for the production of protein, RNA or DNA. They are involved in almost all biological activities, structural or enzymatic.

2. Transcription
Transcription is the process by which a single stranded RNA is formed from a single strand of DNA. The process involves : Uncoiling of the 2 strands of DNA in a specific region. It exposes the bases of the DNA strands. One strand of DNA remains dormant & the other one acts as the template for the formation of the new RNA strand. The building blocks the free nucleotides align themselves & form the complementary RNA according to the base pairing rule. The reaction is catalyzed by the enzyme RNA Polymerase. RNA polymerase catalyzes the formation of phosphodiesterase bonds between nucleotides (using tri-phosphate nucleotides). RNA polymerase moves stepwise along the DNA extending the RNA chain as it goes. As RNA polymerase moves it unwinds the next part of the helix, the helix behind closes & the mRNA is displaced

3. RNA polymerase
(RNAP or RNApol) is an enzyme that makes a RNA copy of a DNA or RNA template. In cells, RNAP is needed for constructing RNA chains from DNA genes, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses. In chemical terms, RNAP is a nucleotidyl transferase that polymerizes ribonucleotides at the 3' end of an RNA transcript.

4. History RNA Polymerase
or RNAP was discovered independently by Sam Weiss & Jerard Hurwitz in 1960. In 2006, the Nobel Prize in Chemistry was awarded to Roger Kornberg for creating detailed molecular images of RNA polymerase during various stages of transcription.

5. Structure Of RNA Polymerase
RNA polymerase in Prokaryotes (Bacteria) : In bacteria, the same enzyme catalyzes the synthesis of mRNA RNAP is a relatively large molecule. The core enzyme has 5 subunits (~400 kDa):α2: the two α subunits assemble the enzyme and recognize regulatory factors. Each subunit has two domains: αCTD (C-Terminal domain) binds the UP element of the extended promoter, and αNTD (N-terminal domain) binds the rest of the polymerase. β: this has the polymerase activity (catalyzes the synthesis of RNA) which includes chain initiation and elongation. β': binds to DNA (nonspecifically). ω: restores denatured RNA polymerase to its functional form in vitro.

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PowerPoint Presentation On Quorum Sensing

PPT On Quorum Sensing


Quorum Sensing Presentation Transcript:
1. Introduction To Quorum Sensing
- Cell to cell communication among procaryotes occurs by the exchange of small molecule often termed signal or signaling molecule. The exchanging of signaling molecule is essential in the co-ordination of gene expression of microbial population Quorum sensing is a type of decision-making process used by decentralized groups to coordinate behavior. Many species of bacteria use quorum sensing to coordinate their gene expression according to the local density of their population.

2. Quorum sensing was firstly discovered in the marine bioluminescent bacteria Vibrio fischeri , which produce light only if cells are at high density. It has been discovered that intercellular communication play an essential role in the regulation of gene whose products are needed for establishment of virulence, symbiosis , Biofilm production, plasmid transfer &morphological differentiation in a wide range of microbes.

3. Quorum Sensing
Fuqua et al. (1994) introduced the term quorum sensing to describe cell-cell signaling in bacteria Early 1990’s – homologs of LuxI were discovered in different bacterial species V. fischeri LuxI-LuxR signaling system becomes the paradigm for bacterial cell-cell communication

4. Methods & Mechanism
 For a molecule to classed as a quorum sensing signal there are number of important criteria that need to be met → The production of the quorum sensing signal should takes place during specific stage of growth or in response to particular environment changes. The quorum sensing should accumulate in extra cellular environment & be recognized by a specific bacterial receptor.

5. The accumulation of a critical threshold concentration of the quorum sensing signal should be stimulate a response. The cellular response should extend beyond the physiological changes required to metabolized.

For quorum sensing bacteria produce certain signaling compounds called as Auto inducer. Eg. N- acyl homoserin lactos (AHL) They have a receptor that detect AHL. AHL binds with the receptor it activate transcription of certain genes & also those for inducer synthesis.

7. Mechanism
When only few bacterias are present then concentration of AHL decreases or if number of bacteria are present then concentration of AHL increases. When many kinds of bacterias are present concentration of inducer AHL posses the threshold. It causes a +ve feed back loop & receptor become active.

Species of gram –ve bacteria signaling transfer a series of AHL & it’s concentration exceed a threshold i.e. the cell population over a certain no., the promoter plux transcription is activates.

 9. Quorum Sensing in Gram-Positive Bacteria Gram-positive bacteria utilizes modified oligopeptides as signaling molecules – secreted via an ATP-binding cassette (ABC) transporter complex Detectors for these signals are two-component signal transduction systems

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PowerPoint Presentation On Proteins

PPT On Proteins


Proteins Presentation Transcript:
1. Proteins- Introduction
The word protein comes from the Greek ("prota"), meaning "of primary importance" and these molecules were first described and named by the Swedish chemist Jöns Jakob Berzelius in 1838. However, proteins' central role in living organisms was not fully appreciated until 1926, when James B. Sumner showed that the enzyme urease was a protein. The first protein to be sequenced was insulin, by Frederick Sanger, who won the Nobel Prize for this achievement in 1958. The first protein structures to be solved included hemoglobin and myoglobin, by Max Perutz and Sir John Cowdery Kendrew, respectively, in 1958. Both proteins' three-dimensional structures were first determined by x-ray diffraction analysis; the structures of myoglobin and hemoglobin won the 1962 Nobel Prize in Chemistry for their discoverers.

2. Proteins
 Proteins are large complex molecules composed of long chains of amino acids called polypeptides. Proteins are polymers and amino acids are their monomers. C,H,O,S are the elements found in the proteins.

3. Amino Acids
There are 20 amino acids that are common to all life forms. The number and arrangement of these 20 amino acids yields infinite variety of proteins

4. Amino Acids are classified by their “Alkyl” “R” Group: Acidic Amino acid Basic Amino Acids Polar Amino Acids Non-Polar Amino Acids

5. Peptide Bonds Joins two amino acids into a dipeptide Bond forms between carboxyl group of one amino acid and amine group of the second amino acid Peptide bond forms by a condensation reaction losing a molecule of water with each bond

6. Primary Protein Structure

7. Helix
Most abundant 2' structure in proteins Average length = 10 aa's (~10 Angstroms) Length varies from 5-40 aa's Alignment of H-bonds creates dipole moment (positive charge at NH end) Often at surface of core, with hydrophobic residues on inner-facing side, hydrophilic on other side

8. Types of helices
"Standard" helix: 3.6 residues per turn H-bonds between C=0 of residue n and NH of residue n + 4 Helix ends are polar; almost always on surface of protein

9. Certain amino acids are "preferred" & others are rare in helices Ala, Glu, Leu, Met = good helix formers Pro, Gly Tyr, Ser = very poor Amino acid composition & distribution varies, depending on location of helix in 3-D structure

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PowerPoint Presentation On Biosensor

PPT On Biosensor


Biosensor Presentation Transcript:
1. Introduction /Definition
A biosensor is a device for the detection of an analyte that combines a biological component with a physicochemical detector component. OR A biosensor is an analytical devices which employs a biological material to specifically interact with an analyte.

2. Biosensor consists of 3 parts:-
Sensitive biological element & analyte. Transducer or the detector element. Electronic or signal processor / Amplifier.

3. Components of biosensor:-
Analyte. Biological material. Transducer. Amplifier. LED screen/ PC.

4. Sensitive biological element:-
Biological material a biologically derived material or can be created by biological engineering. Biological material is like tissue, cell receptor, enzymes, antibodies, nucleic acid etc. The biological component of biosensor performs the following two key function - It specifically recognizes the analyte . Interacts with it in such a manner , which produces some physical change detectable by the transducer.

5. Transducer or the detector element:-
The biological component interacts specifically to the analyte, which produced a physical change close to the transducer surface. Transducer detects & measures this change and converts it into an electrical signal. Transducer work in a physicochemical way, optical way, piezoelectric way, electrochemical way etc.

6. Analyte:-
An analyte is a compound whose concentration is to be determined by the biosensor. The nature of interaction between the analyte and the biological material used, the biosensor may be of two types – The analyte may be converted into a new chemical molecule , such biosensor are called CATALYTIC BIOSENSOR. The analyte may simply bind to the biological material, these biosensor are known as AFFINITY BIOSENSOR.

7. Immobilization of Biological element:-
A biosensor makes use of a biological molecule (an enzyme ) that is immobilized to detect an analyte. The immobilization permits repeated use of the costly biological molecule.

8. Working principle of biosensor:-
The biosensor convert a chemical information flow, into an electrical information flow, which involves the following steps - 1.The analyte diffuses from the solution to the surface of the biosensor. 2.The analyte react specifically & efficiently with the biological component of the biosensor. 3.This reaction change the physicochemical properties of the transducer surface. 4.This leads to a change in the optical/electronic properties of the transducer surface. 5.The change in optical/electronic properties is measured/ converted into electrical signal, which is amplified, processed and displayed.

9. Features of biosensor:-
A successful biosensor must have at least some of the following features – Highly specific for analyte. Independent of factors like stirring, pH, temp., etc. Linear response, tiny and biocompatible. Cheap, easy to use & durable/repeated use. Cost is lower than that of conventional tests. Require small sample volume. Rapid, accurate, stable, & sterilizable.

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PowerPoint Presentation On DNA

PPT On DNA Repair


PPT On Enzymes And Proteins Required In Eukariotic DNA Replication

PPT On DNA Replication


DNA Replication PPT


Recombinant DNA technology


PowerPoint Presentation On Nitrogen Metabolism

PPT On Nitrogen Metabolism


Nitrogen Metabolism Presentation Transcript:
Nitrogen Fixation can be defined as the conversion of molecular nitrogen into fixed form of nitrogen to make it available for absorption by plants. It is the third most important process after respiration and photosynthesis. It is essential for all living organisms.

Conversion of elemental nitrogen or gaseous nitrogen into nitrogenous compounds or salts by certain microorganisms like bacteria ,blue green algae, fungi etc. is called biological nitrogen fixation. It is carried by two types of micro- organisms. Eg Symbiotic and non-symbiotic.

The Fixation of free nitrogen of the soil by all those micro-organisms living freely or outside the cell is called as non-symbiotic biological N2 fixation.

The Fixation of free nitrogen of the soil by microorganisms living symbiotically inside the plant, is called as symbiotic biological N2-fixation. The term “symbiosis” is coined by De bary in 1879.

Nitrogen Fixation Through Nodule Formation in Leguminous plants. N2 Fixation through Nodule formation in Non-leguminous Plants. N2-Fixation through Non-Nodulation.

In addition to legumes, there are many plants specially trees and shrubs belonging to families other than Leguminosae which produce root-nodules. Eg- Casuarina- Frankia Alnus- Frankia Myrica- Frankia Parasponia- Rhizobium

7. N2 Fixation through Non-nodulation It includes those plants where root nodules are not formed but symbiotic N2-fixation takes place. Examples- Lichens - associated with fungi and algae Azolla- Anabaena azollae. Cycas –Anabaena or Nostoc Gunnera macrophylla- Nostoc

8. Associative Symbiotic N2-Fixation
When the bacteria live in close association with the roots of cereals and grasses and fix nitrogen than the association is of loose mutualism type and is called associative symbiosis whereas this nitrogen Fixation is called associative symbiotic nitrogen fixation. Examples- Azotobactor paspali – Associated with Paspalum notatum Azospirillum brasilense- Cereal roots Beijerinckia- Sugarcane roots

The red pigment of the nodules is called leg-hemoglobin and appears to be a product of the Rhizoboium-legume complex. The pigment is not present in either organism grown alone. It is a reddish pigment found in the cytoplasm of host cells. It is an oxygen carrier & an efficient O2 scavenger

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PowerPoint Presentation On Mutations

PPT On Mutations


Mutations Presentation Transcript:
Mutation are heritable changes in the genetic material. They result from small changes in the genetic material (single gene mutations), rearrangements in chromosome structure (chromosome mutations), or changes in chromosome number( genome mutations).

Spontaneous mutation Induced mutations

Spontaneous mutations can arise from transition, transversion and frameshifts), from dNA lesions (replication errors (apurinic sites, apyrimidinic sites, oxidation ), and from insertions.

The tautomeric shifts changes the hydrogen bonding characteristics of the bases allowing purine for purine, pyrimidine for pyrimidine substitution that eventually leads to a stable alteration of nucleotide sequences. Such alterations are known as transition mutation.

In transversion mutations, a purine is substituted for a pyrimidine, or a pyrimidine for purine. These mutations are rare due to steric problems of pairing purine with purine and pyrimidine with pyrimidine.

Induced mutation are caused by mutagens. Mutations may result from the incorporation of base analogs, specific misparing due to alteration of a base, the presence of intercalating agents, and a by pass of replication because of severe damage.

Base analogs are structurally similar to normal nitrogenous bases and can be incorporated into the growing polynucleotide chain during replication. Once in place, these compounds typically exhibit base pairing properties different from the bases they replace and eventually causes stable mutations.

Specific mispairing is caused when a mutagen changes a base structure and therefore alters its base pairing characteristics. Some mutagens in this category are fairly selective; they preferentially react with some bases and produce a specific kind of DNA damage.

Intercalating agents distort DNA to induce single nucleotide pair insertion and deletion. These mutagens are planar and insert themselves (intercalate) between the stacked bases of the helix.

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PowerPoint Presentation On The Cell Wall

PPT On The Cell Wall


The Cell Wall Presentation Transcript:
The plant cell wall is a remarkable structure. It provides the most significant difference between plant cells and other eukaryotic cells. The cell wall is rigid (up to many micrometers in thickness) and gives plant cells a very defined shape. While most cells have a outer membrane, none is comparable in strength to the plant cell wall. The cell wall is the reason for the difference between plant and animal cell functions. Because the plant has evolved this rigid structure.

2. On the basis of chemical composition of cell wall there are three types of cell wall: 1) Green Plant Cell Wall : which is made up of Cellulose. 2) Cell Wall of Fungi: made up of Chitin. 3) Bacteria Cell Wall: made up of Mucopeptide and Muramic Acid. The cell wall is composed of Cellulose, fibres, polysaccharides and proteins i.e Living Protoplast. It consist of the following: Middle lamella Primary Cell Wall Secondary Cell Wall Tertiary Cell Wall

It is present between two adjacent cells. It is situated outside primary cell wall and is made up of calcium and magnesium pectate. It acts as cement which holds the adjacent cells together.
2. PRIMARY CELL WALL It is present beneath Middle lamella. It is made up of Cellulose, Hemi-cellulose, pectic substances, lipids, proteins, minerals, elements and water.

It is present beneath Primary Cell wall. It is made up of Cellulose, Hemi-cellulose and polysaccharides. Secondary Cell wall is deposited Lignin.
4. TERTIARY CELL WALL Tertiary Cell wall is deposited in few cells. It is considered to be dry residue of protoplast. Besides Cellulose and Hemi-cellulose, Xylan is also present.

5. On the whole, each cell's cell wall interacts with its neighbours to form a tightly bound plant structure. Despite the rigidity of the cell wall, chemical signals and cellular excretions are allowed to pass between cells.

6. The primary wall of cells are capable of expansion. The middle lamella is formed during cell division and grows coordinately during cell expansion. Contact between certain cells is maintained by the middle lamella , and the cell corners are often filled with pectin rich polysaccharides. In older cells the material in the cell corners is sometimes degraded and an air space formes.

7. Plant cell walls
Are made of cellulose fibers embedded in other polysaccharides and protein May have multiple layers

8. Cell Wall components
Cellulose Other carbohydrates Lignin (other polyphenolics) Proteins

9. Carbohydrates
Classified by solubilities Pectins – complex carbohydrates extracted in water using Calcium chelators Polyuronic acids Arabinans Glactans Hemicelluloses – soluble in 4M KOH Xylans - common Mannans – abundant in conifers Arabinoglactans Microfibrillar components Cellulose Beta 1,4 mannans - algae Beta 1,3 xylans - algae

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PowerPoint Presentation On Carbohydrates

PPT On Carbohydrates


Carbohydrates Presentation Transcript:
The name Carbohydrates indicates that they are hydrates of Carbon, and contain carbon, hydrogen and oxygen. Most of them contain hydrogen and oxygen in the ratio of 2:1. For that reason, the general empirical formula of carbohydrates is given as [C(H2O)]n e.g,glucose is (C6H12O6) carbohydrates may be defined as Polyhydroxy aldehyde or Ketone or substances that yield these on hydrolysis.e.g.glucose is a polyhydroxy aldehyde and fructose is a polyhydroxy ketone. The names of carbohydrates often end in the suffix-ose.

The carbohydrates often termed as Sugars,are the “staff of life” for most organisms. Carbohydrates are also known as Saccharides(Sakcharon=sugar or sweetness). They are widely distributed molecules in both plant and animal tissues. They are indispensable for living organisms,serving as skeletal structures in plants and also in insects and crustaceans. They also occur as food reserves in the storage organs of plants and in liver and muscles of animals. In addition,they are an important source of energy required for the various metabolic activities of the living organisms;the energy being derived as a result of their oxidation.

The naturally occurring carbohydrates may be classified into three main groups,particularly on the basis of their behaviour towards hydrolysis. Monosaccharides are classified according to three different characteristics: the placement of its carbonyl group,the number of carbon atoms it contains, and its chiral handedness. If the carbonyl group is an aldehyde,the monosaccharide is an aldose; if the carbonyl group is ketone;the monosaccharide is a ketose.Monosaccharide with three carbon atoms are called trioses,those with four are called tetroses,five are called pentoses,six are called hexoses.

4. MONOSACCHARIDES(GK:Mono=one;Sakcharon=sugar)
 They are the simplest sugars and cannot be hydrolysed into simpler compounds. Their general formula is CnH2nOn,where n varies from 3to7.The most important are the pentoses and hexoses.

5. OLIGOSACCHARIDES(GK:oligo=few;Sakcharon=sugar)
On hydrolysis they generally yield 2 to 9 molecules of monosaccharides which are sugars and include di-, tri-tetrasaccharides etc. The monosaccharides are joined together by glycosidic bonds. glycosidic linkage formed via a dehydration reaction, resulting in the loss of a hydrogen atom from one monosaccharide and a hydroxyl group from the other. The most abundant are the disaccharides, which consist of two monosaccharide units.

Polysaccharides are the carbohydrates which yield a large number of monosaccharides on hydrolysis. They contain greater than ten monosaccharide units.

Monosaccharides possess some characteristic properties due to the presence of some specific groups,namely aldehydic,alcoholic,alchol-aldehydic,and α-glycolic. Oxidation with acids: With mild oxidants(like HOBr):-Only the aldehyde group is oxidized to produce monocarbolic acids.Ketoses,however don’t respond to this reaction.Hence reaction is used to distinguish aldoses from ketoses.

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PowerPoint Presentation On Apoptosis

PPT On Apoptosis


Apoptosis Presentation Transcript:
Apoptosis means “programed cell death”. It’s role in cell population control during growth and development suggests that there are inherent cellular mechanisms that lead the cell to destruction. It is a form of cell death which is different from any other form of cell death-necrosis.

Cell death by injury -Mechanical damage -Exposure to toxic chemicals Cell death by suicide -Internal signals -External signals

3. Conted…..
Apoptosis or programmed cell death, is carefully coordinated collapse of cell, protein degradation , DNA fragmentation followed by rapid engulfment of corpses by neighbouring cells. (Tommi, 2002) Essential part of life for every multicellular organism from worms to humans. (Faddy et al.,1992) Apoptosis plays a major role from embryonic development to senescence.

4. History of cell death / apoptosis
research 1800s Numerous observation of cell death 1908 Mechnikov wins Nobel prize (phagocytosis) 1930-40 Studies of metamorphosis 1948-49 Cell death in chick limb & exploration of NGF 1955 Beginning of studies of lysomes 1964-66 Necrosis & PCD described 1971 Term apoptosis coined 1977 Cell death genes in C. elegans 1980-82 DNA ladder observed & ced-3 identified 1989-91 Apoptosis genes identified, including bcl-2, fas/apo1 & p53, ced-3 sequenced (Richerd, 2001)

5. Why should a cell commit suicide?
Apoptosis is needed for proper development Examples: The resorption of the tadpole tail The formation of the fingers and toes of the fetus The sloughing off of the inner lining of the uterus The formation of the proper connections between neurons in the brain Apoptosis is needed to destroy cells Examples: Cells infected with viruses Cells of the immune system Cells with DNA damage Cancer cells

6. What makes a cell decide to commit suicide?
Withdrawal of positive signals examples : growth factors for neurons Interleukin-2 (IL-2) Receipt of negative signals examples : increased levels of oxidants within the cell damage to DNA by oxidants death activators : Tumor necrosis factor alpha (TNF-) Lymphotoxin (TNF-β) Fas ligand (FasL)

7. Necrosis vs. Apoptosis
Cellular swelling Membranes are broken ATP is depleted Cell lyses, eliciting an inflammatory reaction DNA fragmentation is random, or smeared In vivo, whole areas of the tissue are affected Cellular condensation Membranes remain intact Requires ATP Cell is phagocytosed, no tissue reaction Ladder-like DNA fragmentation In vivo, individual cells appear affected

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PowerPoint Presentation On Genetic Recombination

PPT On Genetic Recombination


Genetic Recombination Presentation Transcript:
1. Genetic Recombination
INTRODUCTION : Genetic recombination is the process by which a strand of DNA is broken and then joined to the end of a different DNA molecule. In eukaryotes recombination commonly occurs during meiosis as chromosomal crossover between paired chromosomes. This process leads to offspring having different combinations of genes from their parents and can produce new chimeric alleles. In evolutionary biology this shuffling of genes is thought to have many advantages

2. A recombination pathway in DNA is any way by which a broken DNA molecule is reconnected to form a whole DNA strand. In molecular biology "recombination" can also refer to artificial and deliberate recombination of disparate pieces of DNA, often from different organisms, creating what is called recombinant DNA.

When crossing over occurs between sister chromatids its called sister chromatid exchange . sister chromatid are genetically identical to each other, wit,sce does not produce a recombination of alleles. Therefore it is not considered a form of recombination .By comparison , it is also common for homologous chromosomes to cross over.

4. Perry and wolf produced harlequin chromosomes to reveal recombination between sister chromatid. In 1970s, The Russian cytogeneticist A.F ZAKHROV AND COLLEAGUES spent much more effort developing methods that inproved our ability to identify chromoes.They mode the intresting observation that chromes labled with the nucleotide analogue 5- bromo deoxyurinide become more fluorescent when stained with giemsa and then visualized microscopically.

5. Perry and wolff, grew eukaryotic cells in a laboratory and exposed them to BrdU for two rounds of DNA replication . after the second round of DNA replication , one of the sister chromatid contained one normal strand and one BrdU labled strand. The other sister chronatid have two BrdU –labled strands . when treated with two dyes , Hoechst33258 and giemsa , the sister chromatid containing two strands with BrdU stains very weakly and appears light, whereas the sister chromatid with only one strand containing BrdU stains much more strongly and appears very dark. In this way , the two sister chromatid can be distinguished microscopically . chromosomes stained in this way have been regerred to as harlequin chromosomes , because they are reminiscent of a harlequin characters costumes with its variegated pattern of light and dark patches.

Refers to recombination between the paired chromosomes inherited from each of one's parents, generally occurring during meiosis. During prophase I the four available chromatids are in tight formation with one another. While in this formation, homologous sites on two chromatids can mesh with one another, and may exchange genetic information. Because recombination can occur with small probability at any location along chromosome, the frequency of recombination between two locations depends on their distance. Chromosomes are expected to cross over at many points along their length; independently.

7. The Holliday Model of Genetic Recombination
This model of recombination was first proposed by Robin Holliday in 1964 and re-established by David Dressler and Huntington Potter in 1976 who demonstrated that the proposed physical intermediates existed. Alignment two homologous DNA molecules. Nick the DNA at the same place on the two molecules. This must happen in strands with the same polarity.

8. Exchange strands and ligate.
The intermediate that is formed is called a Holliday intermediate or Holliday structure. The shape of this intermediate in vivo is similar to that of the greek letter chi, hence this is also called a chi form.

9. Resolution of the structure.
There are two ways in which this can happen: If the same strands are cleaved a second time then the original two DNA molecules are generated: If the other strands are cleaved, then recombinant molecules are generated:

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