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DNA Structure
DNA structure videos are found here. Litlle information about the structure of DNA. The backbone of the DNA strand is made from alternating phosphate and sugar residues.[8] The sugar in DNA is 2-deoxyribose, which is a pentose (five-carbon) sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings. These asymmetric bonds mean a strand of DNA has a direction. In a double helix the direction of the nucleotides in one strand is opposite to their direction in the other strand. This arrangement of DNA strands is called antiparallel. The asymmetric ends of DNA strands are referred to as the 5′ (five prime) and 3′ (three prime) ends, with the 5\' end being that with a terminal phosphate group and the 3\' end that with a terminal hydroxyl group. One of the major differences between DNA and RNA is the sugar, with 2-deoxyribose being replaced by the alternative pentose sugar ribose in RNA. The DNA double helix is stabilized by hydrogen bonds between the bases attached to the two strands. The four bases found in DNA are adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T). These four bases are attached to the sugar/phosphate to form the complete nucleotide, as shown for adenosine monophosphate.
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Created: March 14, 2009, 11:22 pm

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Viruses
Several Videos explaining virus cycle, structure and the way they infect. You are welcome to add videos related to this topic. Wikipedia info: A virus (from the Latin virus meaning toxin or poison) is a sub-microscopic infectious agent that is unable to grow or reproduce outside a host cell. Viruses infect all cellular life. The first known virus, tobacco mosaic virus, was discovered by Martinus Beijerinck in 1899,[1] and now more than 5,000 types of virus have been described.[2] The study of viruses is known as virology, and is a branch of microbiology.
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Created: March 14, 2009, 10:56 pm

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Muscle contraction
Muscle Contraction related Videos. Wikipedia Text info: Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten or remain the same. Though the term \'contraction\' implies shortening, when referring to the muscular system it means muscle fibers generating tension with the help of motor neurons (the terms twitch tension, twitch force and fiber contraction are also used). Locomotion in most animals is possible only through the repeated contraction of many muscles at the correct times. Contraction is controlled by the central nervous system (CNS), which comprises the brain and spinal cord. Voluntary muscle contractions are initiated in the brain, while the spinal cord initiates involuntary reflexes.
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Created: March 16, 2009, 6:21 pm

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Meiosis
Meiosis related videos. Wikipedi text: In biology or life science, meiosis (pronounced IPA:[maɪˈəʊsɪs]) is a process of reductional division in which the number of chromosomes per cell is halved. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores. As with mitosis, before meiosis begins, the DNA in the original cell is replicated during S-phase of the cell cycle. Two cell divisions separate the replicated chromosomes into four haploid gametes or spores. Meiosis is essential for sexual reproduction and therefore occurs in all eukaryotes (including single-celled organisms) that reproduce sexually. A few eukaryotes, notably the Bdelloid rotifers, have lost the ability to carry out meiosis and have acquired the ability to reproduce by parthenogenesis. Meiosis does not occur in archaea or bacteria, which reproduce via asexual processes such as binary fission.
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Created: March 16, 2009, 6:32 pm

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Evolution of the Y Chromosome
All mammals have an XY chromosomal sex determining system, in which a small Y chromosome triggers male development, and contains genes required for spermatogenesis. The X and Y chromosomes were originally homologous, but diverged during evolution as the Y chromosome was degraded progressively. Comparisons among the sex chromosomes of different mammal groups indicate that the X and Y chromosomes received additions of material from other chromosomes. Genes on the Y chromosome originated from the ancient X-Y pair, or from these additions, or were copies of genes on one of the autosomes. Only genes with important male-specific functions, such as sex determination and spermatogenesis, are selected for and retained on the differential region of the Y chromosome. The mammalian sex determining gene, SRY, controls the testis determination pathway, which includes at least one related gene. Several candidate spermatogenesis genes have been identified, but so far the only one that is conserved on the Y chromosome of all therian mammals is RBM (RNA-binding motif gene, Y chromosome).
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Created: March 16, 2009, 6:36 pm

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PCR ( polymerase chain reaction )
The polymerase chain reaction (PCR) is a technique widely used in molecular biology. It derives its name from one of its key components, a DNA polymerase used to amplify a piece of DNA by in vitro enzymatic replication. As PCR progresses, the DNA generated is used as a template for replication. This sets in motion a chain reaction in which the DNA template is exponentially amplified. With PCR it is possible to amplify a single or few copies of a piece of DNA across several orders of magnitude, generating millions or more copies of the DNA piece. PCR can be extensively modified to perform a wide array of genetic manipulations.
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Created: March 18, 2009, 12:45 pm

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HIV (Human immunodeficiency virus )
HIV structure and infection related videos. Wikipedia text: Human immunodeficiency virus (HIV) is a lentivirus (a member of the retrovirus family) that can lead to acquired immunodeficiency syndrome (AIDS), a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections. Previous names for the virus include human T-lymphotropic virus-III (HTLV-III), lymphadenopathy-associated virus (LAV), and AIDS-associated retrovirus (ARV).[1][2] Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk. Within these bodily fluids, HIV is present as both free virus particles and virus within infected immune cells. The four major routes of transmission are unprotected sexual intercourse, contaminated needles, breast milk, and transmission from an infected mother to her baby at birth (Vertical transmission). Screening of blood products for HIV has largely eliminated transmission through blood transfusions or infected blood products in the developed world.
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Created: March 18, 2009, 2:45 pm

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