Deoxyribonucleic acid, which is commonly known by its acronym DNA, is the hereditary material in humans and almost all other living organisms. It was discovered by Friedrich Meischer in 1869. It is a linear polymer that is located in the cell nucleus (nuclear DNA) and is protected by the nuclear envelope. However, some of it can be found in the mitochondria (mitochondrial DNA). Nearly every cell in the human body has the same kind of DNA. Its function is to encode information. It encodes all of the sequences of all of the proteins that an organism needs to live. It is an extremely long polymer therefore a single molecule of it encodes all of the information necessary to produce thousands of proteins. Information in DNA is stored as a code made up of four chemical bases: the purine bases, adenine (A) and guanine (G) and the pyrimidine bases, cytosine (C) and thymine (T). It may contain more than 200 million nucleotide base and more than 99% of all these bases are the same in all human beings. 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. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The complementarity of the two strands with strict adherence to the A to T and G to C pairing rules – is the basis for replication of the genes. The two strands separate during replication, and each serves as a template for the synthesis of a new complementary strand.
James Watson, Francis Crick and also Rosalind Franklin are the scientists who discovered that DNA was the carrier of the information needed to make all the proteins in the body. They formulated the ‘central dogma’ that paved way to modern molecular biology. It stated that DNA can be copied to make more DNA, copying all the information in the original. The information in DNA can also be transcribed into RNA, which then directs the production of a protein whose sequence of amino acids is determined by the sequence of nucleotides in the DNA (and RNA). Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. The information flow is always either DNA to DNA or DNA to RNA to protein.
Mitochondrial DNA also plays a very important part in this information flow. It contains thirty seven genes, all of which are essential for normal mitochondrial function. Thirteen of these genes provide instructions for making enzymes involved in oxidative phosphorylation. The twenty four remaining genes provide instructions for making molecules called transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), which are chemically related to DNA. These types of RNA help assemble protein building blocks (amino acids) into functioning proteins.
The discovery of DNA function and structure is one of the most important contributions to science and has enabled scientists and clinicians to better understand the physiology of the human body.
admin January 16th, 2014
Posted In: Handbook
Proteins are very large complex molecules (macromolecules) that have a specific function and sometimes even more than one function. They play a very important role in all aspects of cell structure and function. Although they are complex, they have a simple underlying structure that does not form branches or circles. This is the reason why they are referred to as linear polymers. The simple units that make up proteins are known as amino acids and most organisms have about 20 different kinds. These 20 naturally occurring amino acids are grouped according to criteria such as hydrophobicity, size, aromaticity or charge. They include Glycine (Gly / G), Alanine (Ala / A), Valine (Val / V), Phenylalanine (Phe / F), Proline ( Pro / P), Isoleucine (Ile / I), Leucine (Leu / L), Methionine (Met / M), Aspartic acid / Aspartate (Asp / D), Glutamic acid / Glutamate (Glu / E), Lysine (Lys / K), Arginine (Arg / R), Serine (Ser / S), Threonine (Thr / T),Tyrosine (Tyr / Y), Histidine (His / H), Cysteine (Cys / C), Asparagine (Asn / N), Glutamine (Glu / Q) and Tryptophan (Trp / W). As shown above, they are commonly identified by their three letter abbreviations or one letter symbol. A typical protein, however, is a string of several hundred amino acids. The term amino acid refers to any molecule containing both an amino group and any type of acid group. Thus all amino acids (*except Proline) contain similar structural features such as the amino group, carboxyl group and an alpha carbon. The arrangement in which the amino acids make up a protein chain is known as a protein sequence. The amino acids within these chains are linked by amide bonds and the chains are referred to as peptide chains. These sequences are flexible and determine the characteristic and functional capabilities of the protein.
Proteins perform specific activities in different forms in our body such as enzymes, hormones, antibodies, haemoglobin (blood) and growth and maintenance proteins. Collagen is the most prevalent protein in human beings. It forms strong sheets that support skin, internal organs and tendons as well as the hard substance that gives shape to the nose and ears. It is one of the largest proteins in the body but it is made up mostly of the same three amino acids that keep repeating over and over again. Proteins can be classified by their functions; structural proteins, enzymatic proteins, transport proteins, contractile proteins, protective proteins, hormonal proteins and toxins. However, sometimes different proteins form stable complexes that work together as a group to perform a specific function. Various techniques have been invented to study the structure and functions of proteins and these include mass spectrometry, nuclear magnetic resonance among others. This is normally done in a modern laboratory. The study of proteins is one of the most important branches of science and there is no clear division between the organic chemistry of proteins and their biochemistry
admin January 16th, 2014
Posted In: Handbook
The gene is the basic functional unit of heredity. Genes are made up of deoxyribonycleic acid (DNA) or in the case of some viruses they are made up of ribonucleic acid (RNA). They contain particular set of instructions as coding for specific proteins or function. They determine an observable trait or characteristic of an organism and the DNA sequence that determines the chemical structure of a specific polypeptide molecule or RNA molecule. The word ‘gene’ was invented by W. Johannsen in 1909 but the modern concept of the gene originated with Gregor Mendel, who in the 1860s studied the inheritance of characteristics that differed sharply and unambiguously among true-breeding varieties of garden peas. Mendel found that a hybrid between two phenotypically distinct varieties resembled one of the two parents – the dominant parent.
In humans, genes vary in size but the Human Genome Project estimated that humans have between 20,000 and 25,000 genes. The entire DNA in the cell makes up the human genome and every person has two copies of each gene, one inherited from each parent. The DNA in the genes makes up only 2% of the genome and most genes are the same in all people but a small number are slightly different between people. Genes contain hundreds of thousands of chemical bases and alleles are forms of the same gene with small differences in their sequence. These small differences contribute to each person’s unique physical features (phenotype). Even though a trait may not be observable, its gene can still be passed on to the next generation. This is known as a recessive gene. A gene that is always exhibiting a trait from one generation to another without suppression is known as a dominant gene. However, some genes are referred to as non-coding genes because they do not appear to contain information that the cells can use and produce. Contrary to popular belief, they are not functionless but their roles are slowly being discovered.
The idea that genes are also responsible for the manufacture of proteins was first proposed in 1902 by Sir Archibald Garrod, who realized that alkaptonuria was an inherited metabolic condition in humans and hypothesized that it was due to the absence of an enzyme (a catalytic protein) required for the breakdown of homogentisic acid. Systematic investigation of the relationship between genes and enzymes did not occur until 1941. It was later realised that in order to make proteins, the gene is copied by each of the chemical bases into the messenger ribonucleic acid (mRNA). The mRNA moves out of the cell nucleus and uses ribosomes to form the polypeptide that configures to form the protein.
All information about the sequences and genes discovered in the human body are carefully recorded and the all the information is placed in a database that is publicly available. Some DNA that have not been sequenced are also available and any scientist can sequence it and post the findings in the same database from anywhere around the world.
admin January 16th, 2014
Posted In: Handbook
To find the position of specific gene, we should first draw a map to locate it, This map can be painted using chemicals to stain chromosomes and then we can see how distinctive patterns appears, this method is called Cytogenetic Location. There is also other way to make this map, a Molecular Location method, it is a sequence of DNA building blocks to precise locate a gene on a chromosome.
A particular band on a stained chromosome normally indicates the position of a gene´s cytogenetic location, for example:
A range of bands can also indicate a gene location when the exact location is less know.
17q12 – q21
An gene´s “address” is written whit letters and numbers and have many parts that help describe it.
· The first part is a letter or a number that indicates the Chromosome number where the gene can be found. from 1 to 22 (the autosomes) or X or Y for sex Chromosomes.
· The second part is the arm where the gene is located, each chromosome has two arms, one longer arm that is called q and the short one is called p, so
if the gene is located in chromosome 1 long arm, we write 1q and if it is located in the short arm of the sex chromosome we write Xp.
· The place where the two arms of the chromosome are narrowed is called the centromere and the position of the gene increase from this point if the stained band (dark or light) is far from it. Example 14q21 is closer to the centromere that 14q22.
When a gene is located almost in the centromere or if it is very close to the end of the chromosome, there are abbreviations like “cen” when is near centromere and “ter” when is at the end.
There are many forms and methods to interpret the sequence of the human genome to find a gene’s molecular address. A sequence of base pairs of each chromosome determinate by the genome project, (an international research effort completed in 2003) is used to locate genes, hence this method is more precise it also gives small variations on the results.
admin January 14th, 2014
Posted In: Handbook