DNA

İnsan Genom Projesi

İnsan Genom Projesinin son hali, ‘İnsanlığın Kitabı’nın daha önce düşünülenden daha harika, muhteşem ve sırlarla dolu olduğunu göstermektedir. İnsanın DNA dizi analizini yapmak için yaklaşık 20 laboratuvarda yüzlerce bilim adamı 10 yıldan fazla çalışıyorlar. Bu proje için 16 kurumdan oluşan uluslararası bir konsorsiyum ile Dr. Craig Venter’in başkanlık ettiği Celera Genomics firması çalışıyor. Haziran 2000 yılında uluslararası İnsan Genome Projesinin liderleri bir yıl sonra insan genomunun  ilk müsvedde halini tamamlayacaklarını açıkladılar. Şubat 2001’de ise Science ve Nature dergilerinin özel sayılarında projede ulaştıkları son durum ve analizleri yayınladılar.

İnsan Genom Projesinin amaçlarından bazıları şu şekilde özetlenebilir1:

§         İnsan genomunda bulunan genleri belirlemek

§         DNA’yı oluşturan yaklaşık 3 milyar baz çiftinin dizisini belirlemek

§         Elde edilen bilgiyi databanklarda saklamak

§         Data analizleri metod ve araçlarını geliştirmek

§         Genler ve fonksiyonları arasındaki bağlantıların bulunması

§         Genlerin kromozomlarda nasıl bir bütün halinde çalıştıklarının tesbiti

§         Genetik hastalıkların temeli ve sebeplerinin tesbiti

Dr. Venter’in takımının Science dergisinde yayınlanan yazısında, insanların düştüğü iki hatadan bahsediliyor. Birincisi determinizim, yani  insandaki bütün özelliklerin genlerine bağlı olduğu fikri; diğeri ise indirgeme; yani şimdi bütün insan genlerinin bilindiği düşüncesi. Bilim adamları genlerin fonksiyonlarının ve aralarındaki ilişkilerin anlaşılması aşamasının daha başında olduklarını belirtiyorlar.

DNA, CHROMOSOMES AND GENES

DNA? Chromosomes? Genes? Aren't these just different terms for the same thing? Well, yes and no. To begin to figure out the difference between these terms, we'll have to learn a little bit about the life of a cell and it's nucleus.
When a cell is not actively dividing, its nucleus contains chromatin, a tangle of fibers composed of protein and DNA. When the time comes for the cell to divide into two new cells, the DNA is duplicated via Mitosis so that each new cell can receive a complete copy of all the genetic material in the "parent" cell. This makes perfect sense if you think of it in practical terms. What if you and another person were both in charge of putting together a bicycle. As part of the deal, you and your friend would each have a bike in your own separate room without being able to contact each other. But the person asking you and your friend to put the bicycles together only had one set of directions, so the directions were torn in half and each of you received one half. It's pretty obvious that, unless you're a whiz at putting bicycles together, there's going to be some trouble unless each of you has your own complete set of directions!
During cell division chromatin organizes itself into chromosomes. Each chromosome contains a DNA molecule, and each DNA molecule is made up of many genes-individual segments of DNA that contain the instructions needed to direct the synthesis of a protein with a specific ********.
Different organisms differ in their complexity and therefore have different numbers of chromosomes and genes. Up to a certain point (and there are some exceptions), the more complex an organism is, the more chromosomes it has. A frog, for example, has 26 chromosomes (13 pairs), whereas a human has 46 chromosomes (23 pairs). Why do we make a reference to there being 23 pairs? Why don't we just say 46 chromosomes? This is because the 46 chromosomes in human somatic cells are actually 23 matched pairs of homologous chromosomes! A good analogy is a pair of socks...with one exception. Each member of the pair comes from one parent; so they may be the same size and shape, but they don't carry exactly the same information.
There are two categories of cells in multicellular organisms based on their chromosomes: Somatic (another word for "body" cells) and Gametes (reproductive cells). In human gametes, each sperm cell has 23 chromosomes, and each egg cell has 23 chromosomes through the process of Meiosis. This is called the haploid number and is represented by the letter n. When these two gametes get together, they form a complete human whose somatic cells have 46 chromosomes. This is the diploid number and is represented by 2n. So, since the frog has a diploid number of 26 (2n=26), its haploid chromosome number is 13 (n=13). A fruit fly has a diploid number of 8. So what is the number of chromosomes in its gametes (the haploid number)?……4! Check out this site if you need a review of genetics.

Deoxyribonucleic acid, or DNA is a nucleic acid molecule that contains the genetic instructions used in the development and ********ing of all living organisms. The main role of DNA is the long-term storage of information and it is often compared to a set of blueprints, since DNA contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.

Chemically, DNA is a long polymer of simple units called nucleotides, which are held together by a backbone made of alternating sugars and phosphate groups. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called tran******ion. Most of these RNA molecules are used to synthesize proteins, but others are used directly in structures such as ribosomes and spliceosomes.

Within cells, DNA is organized into structures called chromosomes and the set of chromosomes within a cell make up a genome. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms such as animals, plants, and fungi store their DNA inside the cell nucleus, while in prokaryotes such as bacteria it is found in the cell's cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA, which helps control its interactions with other proteins and thereby control which genes are transcribed.