It was in 1953 when Watson and Crick proposed the double-stranded structure for the DNA molecules and it was soon accepted by everyone. They proposed that double-stranded structure has free ends which would enable it to separate the complementary strand. The two complementary strands are hold together by a series of week hydrogen bonds. This bond is between the bases of each strand. In DNA A always bonds with T and C bonds with G (Czepulkowski 2001).
To have the long strand of DNA we need bonds between the carbon atoms in consecutive sugars. These bonds are called phosphodiester bond which is between carbon “3” and “5” (see figure). The two sugars at each side of DNA strand don’t have any bond making them free. So if we have carbon “3” free at one end, we will have carbon 5 free at the other end. The two strands of DNA are anti parallel meaning if we have a free carbon “3” at one end, the other strand would have carbon 5 free at the same end (Czepulkowski 2001).
DNA
Function of human chromosome
DNA Replication
In order to successfully pass a copying of chromosome to the daughter cells we need to replicate DNA. As we know DNA stores the genetics information and the replication of DNA needs to be very accurate. For DNA replication we have to separate the two strands using an enzyme called helicase, this done like zip. After separating each strand, the free bases would bond with a new nucleotide which has the appropriate base. This will be done till we have two double stranded DNA, in each of them we have one original strand and a new strand; as a result DNA replication is called semi-conservative. This replication is very time consuming i.e. human cells would take about 8 hours to complete the DNA replication (Murray 2001).
DNA in protein synthesis
As we mentioned earlier DNA will be used as template for producing RNA and RNA will be used for producing proteins. There are three major steps in this process. In stage one messenger RNA, or mRNA, is build from one strand of DNA and the enzyme controlling this is RNA polymerase. This stage is called “Transcription”. Once the mRNA is successfully built, it would leave the nucleus and move into cytoplasm (Czepulkowski 2001).
In second stage we need a different type of RNA called transfer RNA, or tRNA, which has clover-leaf shape. For all 20 amino acid there is specific tRNA and with the help of specific enzyme, amino acids required for protein production will be attached to one end of tRNA in this stage and to other end there is sequence of three bases called anticodon which will be paired against the mRNA condon (Czepulkowski 2001).
In the last stage mRNA will attach to a ribosome. Ribosome would move along the mRNA and read the codon and than it would attaches the complementary anticodon temporary. The next set of codon would be read and the right tRNA would attach. Amino acids attached to these two tRNA would bond together, this bond is called polypeptide bode. The first tRNA would leave and ribosome would move along the mRNA and read the next set of codon. The freed tRNA would move to cytoplasm for reuse. This process would go on until ribosome read the stop codon. Sometime more than one ribosome would be reading the same mRNA. This stage is called translation (Murray 2001).
As we found out DNA is involve is producing protein and protein is needed for human body for growth or repairing and basically for maintaining the human body, which is one of the most important function of DNA. Although there is only 1.5% of human DNA which code for protein.
Gene
Another important function of chromosomes is being responsible for holding genes; they carry all the genetic information for humans. Gene is specific part of chromosome which establishes a specific characteristic of an organism i.e. their nature and development or the instructions for its cell growth and maintenance. A specific gene would appear always in the same place on the same chromosome and that position is called “locus”.
As we know the chromosomes are always paired and called homologous pairs. Therefore there are two copies of each gene, which line in the same position on the chromosomes or homologous pairs. The different type of genes is called “alleles” and there are two different types for each gene. If the two allele of the gene is the same, they are called “homozygous”. But if the two allele of the gene isn’t the same they are called “heterozygous”. The combination of these alleles that a person has would make up the genotypes. And phenotype is the way which genotypes of person is express for example the way we look like or our eyes colour.
Conclusion
Chromosomes ability to replicate itself exactly and separate accurately enable cells to pass all the genetic information to the daughters cells. As well as this chromosome are involved in producing proteins which is much needed for human body for maintaining human body or growing. So chromosomes are needed to any living species.
Part 2 Sickle cell anemia
Genetic disorder
Genetic disorders, sometimes called genetic disease, are formed by an abnormal expression of one or more genes in person and it would cause a clinical phenotype. Some of the causes for this could be that mutation in gene could affect its function or faulty gene could be inherited from parent, or by having an odd number of chromosomes. If you inherit the faulty gene from your parent than the genetic disorder is called hereditary disease and if healthy couples have a child with genetic disorder is because that couple must be a carrier of defective gene.
Sickle Cell Disease is one of the three most common hereditary diseases and affects 15,000 people in England alone.
Genetic Bases
Sickle cell anemia is a hereditary type of genetic disorder and mostly affects people from area that malaria is very common, so you’ll see mostly it affects African people. This disorder happens when you inherit two abnormal genes and these faulty genes would make the red blood cell to change shape, from round and flexible shape to a more firm and with a shape of a farm tool “sickle”. So to have sickle cell anemia you need to inherit the sickle cell gene from both parent and not from one parent. You need the presence of two defective genes (SS) for sickle cell anemia. If each parent carries one sickle cell gene (S) and one normal gene (A), each child has a 25% chance of inheriting two defective genes and having sickle cell anemia; a 25% chance of inheriting two normal genes and not having the disease; and a 50% chance of being an unaffected carrier like the parents and could pass it to next generation. As carrier of this genetic disorder may never discover that they carry the gene it is always recommended to test for and make sure your child isn’t in danger.
Molecules Bases
So this genetic disorder is blood related and it affects haemoglobin which is protein in red blood cells. Haemoglobin job is to help red blood cells carry oxygen throughout the body. A normal person’s red blood cell would move freely in blood stream and transferring oxygen to human body cells but they have donut shape. But when faulty haemoglobin (Hbs) is created than sickle cell anemia happen, Hbs molecules are likely to clump tighter and changing the structure of red blood cell from a flexible to hard and stiff and changing their shape. A red blood cell with Hbs could change shape from sickle shape to normal shape at the start of its life but eventually it would stay in sickle shape permanently. Unlike normal blood cells, sickle cells can’t move feely in blood stream and they could block blood stream and stopping different part of body from receiving blood; which means they won’t get oxygen needed. Sickle cells have a much short life as well; they would break down after only 10 to 20 day. As for normal cells they last up to 4 month. The short life long of sickle cells would cause in anemia or not having enough red blood cells.
Signs and Symptoms
One of the main signs is when the skin and the white part of eyes change colour to a yellow. This is called juandic.
Another sign of this genetic disorder is when you get short-term pain in any part of your body. As we mentioned before sickle cells could block the blood vessels and stopping the blood reaching its destination and causing these short term pains. Period of pains are called crises and they could differ from person to another person. Another sign is feeling tired and having trouble combating infections. This genetic disorder could affect the rate of growth in teenagers and it would slow down the process.
Treatment
Although there is no cure for sickle cell anemia, doctors can do a great deal to help patients to improve the quality of patient life, and there are always research going on to improve the treatments. A simple treatment for painful crises is painkilling drugs and oral and intravenous fluids to reduce pain and prevent complications. Another treatment is to try to balance the number of healthy red blood cells by blood transfusion.
To stop the pneumococcal infection and early death, taking oral penicillin twice a day from early age of two month old till the child is 5 years old has proven to be helpful.
There are things that patient could do to maintain a good health like nutrition, good hygiene, bed rest, protection against infections, and avoidance of other stresses. And regular visit to clinics that help people with sickle cell anemia problem is absolutely necessary for finding any problem at early stage and making sure that right action is taken.
It was in 1995 that the first helpful drug for adult with sickle cell anemia was reported. This drug was a result of research conducted by the National Heart, Lung, and Blood Institute and it was found out that if patient take a daily does of this drug, it would cut down the number of crisis and chest infection.
Another research which has started in April 2005 at Nottingham University is to try to develop a new detector which it should allow doctors to accurately assess the severity of the disease. This detector would take images red blood cells from blood vessel under surface of skin. This should help doctors and give them the best and most accurate method to examine the patient.
Conclusion
Today, with good health care, many people with sickle cell anemia are living a better and much more productive lives and their quality of life have improved. In fact, in the past 30 years, the life expectancy of people with sickle cell anemia has increased.
Reference:
Electronic references:
Online books:
James Eckman, M.D. and Allan Platt (2002), “Problem Oriented management of syndromes”
Books:
Barbara Czepulkowski (2001) “Analyzing chromosomes”
John Murray (2001), “Introduction to advanced biology”
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