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Frederick Griffith: Bacterial transformation In 1928, British bacteriologist Frederick Griffith conducted a series of experiments using  Streptococcus pneumoniae  bacteria and mice. Griffith wasn't trying to identify the genetic material, but rather, trying to develop a vaccine against pneumonia. In his experiments, Griffith used two related strains of bacteria, known as R and S. R strain.  When grown in a petri dish, the R bacteria formed colonies, or clumps of related bacteria, that had well-defined edges and a rough appearance (hence the abbreviation "R"). The R bacteria were nonvirulent, meaning that they did not cause sickness when injected into a mouse. S strain.  S bacteria formed colonies that were rounded and smooth (hence the abbreviation "S"). The smooth appearance was due to a polysaccharide, or sugar-based, coat produced by the bacteria. This coat protected the S bacteria from the mouse immune system, making them virulent (capable of ...

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HUMAN GENOME PROJECT The Human Genome Project (HGP) was the international, collaborative research program whose goal was the complete mapping and understanding of all the genes of human beings. All our genes together are known as our "genome." Human Genome Project (HGP) was called a mega project. Goals of HGP Identify all the approximately 20,000-25,000 genes in human DNA. Determine the sequences of the 3 billion chemical base pairs that make up human DNA. Store this information in databases; Improve tools for data analysis; Transfer related technologies to other sectors, such as industries; Address the ethical, legal, and social issues (ELSI) that may arise from the project QUIZ HUMAN GENOME PROJECT

Meselson and Stahl’s Experiment Meselson and Stahl’s Experiment was an experimental proof for semiconservative DNA replication. In 1958, Matthew Meselson and Franklin Stahl conducted an experiment on  E.coli  which divides in 20 minutes, to study the replication of DNA. Experiment 15 N (heavy) and  14 N (normal) are two isotopes of nitrogen which can be distinguished based on their densities by centrifugation in cesium chloride (CsCl). Meselson and Stahl cultured E.coli in a medium constituting  15 NH 4 Cl over many generations. As a result,  15 N was integrated into the bacterial DNA. Later, they revised the  15 NH 4 Cl medium to normal  14 NH 4 Cl. At a regular interval of time, they took the sample and checked for the density of DNA. MESELSON AND STAHL INTERACTIVE MESELSON AND STHAL EXPERIMENT

DNA REPLICATION:  It is the process of producing two identical replicas of DNA from the original DNA molecule. This is the basis of inheritance. DNA replication is  semiconservative . Each strand in the double helix acts as a template for synthesis of a new, complementary strand. New DNA is made by enzymes called  DNA polymerases , which require a template and a   primer   (starter) and synthesize DNA in the 5' to 3' direction. During DNA replication, one new strand (the   leading strand ) is made as a continuous piece. The other (the   lagging strand ) is made in small pieces. DNA replication requires other enzymes in addition to DNA polymerase, including   DNA primase ,   DNA helicase ,   DNA ligase , and   topoisomerase . DNA REPLICATION DNA REPLICATION FORK ADDITION OF NUCLEOTIDES IN DNA REPLICATION DNA REPLICATION E.COLI

What is DNA? DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA). The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences. DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. ...

DNA fingerprinting , also called  DNA typing,  DNA profiling,  genetic fingerprinting,  genotyping,  or  identity testing , in genetics  method of isolating and identifying variable elements within the base-pair sequence of DNA  (deoxyribonucleic acid). The technique was developed in 1984 by British geneticist  Alec Jeffreys, after he noticed that certain sequences of highly variable DNA , which do not contribute to the functions of genes  are repeated within genes. Jeffreys recognized that each individual has a unique pattern of minisatellites (the only exceptions being multiple individuals from a single zygote  such as identical twins). DNA FINGERPRINTING

The  lac operon  consists of three structural genes, and a promoter, a terminator, regulator, and an operator. The three structural genes are: lacZ, lacY, and lacA. lacZ encodes β-galactosidase (LacZ), an intracellular enzyme that cleaves the disaccharide  lactose  into glucose and galactose. LAC OPERON INTERACTIVE

Polymerase chain reaction    is a technique used in molecular biology to amplify a single copy or a few copies of a segment of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence. PCR PCR INTERACTIVE PCR

GEL ELECTROPHORESIS: A TECHNIQUE USED TO SEPARATE DNA FRAGMENTS AND OTHER MACROMOLECULES BY SIZE AND CHARGE. GEL ELECTROPHORESIS INTERACTIVE GEL ELECTROPHORESIS TECHNIQUE

HEREDITY AND VARIATION

HARSHE AND CHASE EXPERIMENT HARSHE AND CHASE INTERACTIVE

IMPORTANT QUESTIONS BIOLOGY CLASS XII

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