Genetic material

The genetic material controls the properties and functions of the cell and detcT-mines, for example, whether the cell is a brain cell, a liver cell, a blood cell, or even a cancer cell. The genetic material controls the location of the eyes in the body, how fast we grow and how much we weigh, and, in some cases, personality traits. 

The following paragraphs describe the activities in the cell, which can be summed up by the phrase DNA mates RNA makes protein. Although DNA is only one of many molecules used to make RNA, this terse phrase is accurate, since DNA is the central molecule in the process, and since DNA contains the information needed to formulate the sequence of ribonucleotides in the RNA. The study of aU the steps in the process where DNA makes RNA makes protein, and the study of the process of DNA replication, is called molecular biology. 

The DNA that makes up our genetic material is divided into 46 pieces within the cell These pieces are called chromosomes. People have 22 numbered chromO somes, each of which occurs in duplicate, and 2 sex chromosomes. The sex chromosomes of females consist of two X chromosomes, while the sex chromosomes of males consist of one X chromosome and one Y ebtornosome. Where a cell contains duplicate copies of most, or all, of its chromosomes, the cell is called a diploid cell. Human genetic material contains an estimated 80,000 genes (Collins et aL, 1997). For comparison, the genetic material of the yeast contains 6400 genes. Not counting duplication of all DNA in the cell, which exists because of the occunence of diploid chromosomes, each human cell contains about 3 billion nucleotides in its DNA (Schuler cf ai, 1996). 

Our se chromosomes determine whether we arc male or female. It is interesting to point out that, in human females, one of the two X chromosomes is inactivated, and is not much used to code for mRNA (Migeon, 1994), In human males, the Y chromosome is largely inactive, and is not much used to code for mRNA, while the X chromosome is active (Rice, 1996). An end-result of these inactivation events is that, to some extent, all the cells of human males and females behave as though they contained only one X chromosome (and not two sex chromosomes). 

The inactivation of the genes of the sex chromosomes, and of some of the genes of numbered chromosomes, results, in part, from the attachment of methyl groups (—CHj) to the DNA. Methyl group attachment is thought to be the only type of intentional alteration to the chemistry of human DNA. The methyl groups attached to our DNA reside on residues of cytosine. 

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There are two convenient forms of genetic material, that can be used as vehicles for introducing the new gene into the bacterium a small circular DNA piece, called a plasmid, or a virus that grows in bacteria. The techniques described below apply to both plasmids and viruses. 

It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material... 

The viruses responsible for AIDS are human immunodeficiency virus 1 and 2 (HIV 1 and HIV 2) Both are retroviruses, meaning that their genetic material is RNA rather than DNA HI Vs require a host cell to reproduce and the hosts m humans are the T4 lymphocytes which are the cells primarily responsible for inducing the immune system to respond when provoked The HIV penetrates the cell wall of a T4 lymphocyte and deposits both its RNA and an enzyme called reverse transcriptase inside There the reverse transcriptase catalyzes the formation of a DNA strand that is complementary to the viral RNA The transcribed DNA then serves as the template from which the host lymphocyte produces copies of the virus which then leave the host to infect other T4 cells In the course of HIV reproduction the ability of the T4 lymphocyte to reproduce Itself IS compromised As the number of T4 cells decrease so does the body s ability to combat infections... 

Vaccine development is hampered by the fact that recurrent disease is common. Thus, natural infection does not provide immunity and the best method to induce immunity artificially is not clear. The genome of these vimses is also able to cause transformation of normal cells, thus conferring on them one of the properties attributed to cancerous cells. Vaccine made from herpes vimses must, therefore, be carefully purified and screened to eliminate the possibihty of including any active genetic material. 

Vimses are one of the smallest biological entities (except viroids and prions) that carry all the iaformation necessary for thek own reproduction. They are unique, differing from procaryotes and eucaryotes ia that they carry only one type of nucleic acid as genetic material, which can be transported by the vims from one cell to another. Vimses are composed of a shell of proteki enclosing a core of nucleic acid, either ribonucleic acid (RNA) or deoxyribonucleic acid (DNA), that codes for vkal reproduction. The outer shell serves as a protective coat to keep the nucleic acid kitact and safe from enzymatic destmction. In addition to thek proteki coat, some vimses contain an outer covering known as an outer envelope. This outer envelope consists of a Hpid or polysaccharide material. 

MUTAGEN A chemical or physical agent that can cause a change (mutation) in the genetic material of a living cell. 

Epigenetic carcinogen A substance that causes cancer through a mechanism other than interaction with the genetic material. 

Section 28.13 HIV, which causes AIDS, is a retrovirus. Its genetic material is RNA instead of DNA. HIV contains an enzyme called reverse transcriptase that allows its RNA to serve as a template for DNA synthesis in the host cell. 

Retrovirus (Section 28.13) A virus for which the genetic material is RNA rather than DNA. 

Eukaryotic ceils possess a discrete, membrane-bounded nucleus, the repository of the cell s genetic material, which is distributed among a few or many chromosomes. During ceil division, equivalent copies of this genetic material must be passed to both daughter ceils through duplication and orderly partitioning of the chromosomes by the process known as mitosis. Like prokaryotic... 

FIGURE 1.25 The virus life cycle. Viruses are mobile bits of genetic iuformatiou encapsulated in a protein coat. The genetic material can be either DNA or RNA. Once this genetic material gains entry to its host cell, it takes over the host machinery for macromolecular synthesis and subverts it to the synthesis of viral-specific nucleic acids and proteins. These virus components are then assembled into mature virus particles that are released from the cell. Often, this parasitic cycle of virus infection leads to cell death and disease. 

Compared to bacterial cells, which are identical within a given cell type (except for O antigen variations), animal cells display a wondrous diversity of structure, constitution, and function. Although each animal cell contains, in its genetic material, the instructions to replicate the entire organism, each differentiated... 

Compounds prepared from naturally occurring nucleosides are of course more closely related to genetic material and may have a better chance of interacting with infected cells. Mercu-ration of the 2 -dcoxyuridine 113 leads to the organometallic derivative 114 reaction of that with ethylene in the presence dilithio palladium tetrachloride gives the alkylation product 115 this is reduced catalytically in situ. There is thus obtained the antiviral agent edoxudine (116) [25]. 

Proteins are complex molecules that give cells structure and act as both enzymes and motors within cells. Proteins are long strings of amino acids folded in specific three-dimensional formations. There are twenty different animo acids in our bodies. DNA, the genetic material located in the cell nucleus, carries information for the order of the amino acids in each protein. Indeed, in the simplest sense, a gene is the... 

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