Unit 11 Genetics and Genetic Engineering.

Unit 11 Genetics and Genetic Engineering. DNA DNA is the molecule that holds the guidance for growth and development in every living thing. Its structure is described as a double-stranded helix held together by integral base pairs. It contains complementary base pairs in which adenine is always linked by 2 hydrogen bonds to Thymine (A-T). It also contains complementary pairs in which Guanine is always linked by 3 hydrogen bonds to Cytosine (C-G). Complementary base pairs sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=r ja&uact= 8&ved=0ahUKEwi4umKuqnWAhXEfxoKHYzCD6EQjRwIBw&url=https %3A%2F%2F%2Fblog %2F2016%2F05%2F25%2Funderstanding-oncology2016-dna %2F&psig=AFQjCNEg5Q5Zcb0xcR_1T7CgCUuSP BDHvg&ust= sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=r ja&uact= 8&ved=0ahUKEwiD0- L4uqnWAhUC8RQKHUQICdIQjRwIBw&url=http %3A%2F%2Fww %2Fen%2Fvirtuallessons Nana Agyei Unit 11A Task 1 and 2 Ms. Kubasiak Genetics and Genetic Engineering The basic units of DNA are nucleotides. These nucleotides consist of a deoxyribose sugar, phosphate and base. The nucleotides are identical except for the base, which can be an adenine, thymine, guanine or cytosine. DNA is similar to RNA where it consists of adenine, cytosine, guanine and uracil rather than thymine because DNA is believed to have been evolved from RNA due to it being the first to exist. The bases in DNA fall into two classes, purines and pyrimidine. The Purines are adenine and guanine, and the pyrimidine is cytosine and Thymine. The Process of DNA Replication Nana Agyei Unit 11A Task 1 and 2 Ms. Kubasiak Genetics and Genetic Engineering DNA replication constantly duplicates the whole genome of the cell. During DNA replication, a number of different enzymes work together to pull apart the two strands so each strand can be used as a guide to combine new integral strands. Proceeding to replication, the DNA forms and strands separate. A replication fork is formed which serves as a template for replication. Primers bind to the DNA and DNA polymerases add new nucleotide sequences in the 5′ to 3′ direction. This addition is continuous in the leading strand and disintegrated in the lagging strand. Once elongation of the DNA strands is complete, the strands are checked for flaws, repairs are made, and telomere sequences are added to the ends of the DNA. DNA replication occurs at a surprisingly fast rate. Despite this, errors are very rare; occurring at a rate of approx. This is much lower than the expected value of about 1 in every 100 bp. Enzymes involved in DNA replication An enzyme called Helicase breaks the hydrogen bonds between the bases of the 2 antiparallel strands. The strands are initially split apart in areas that are rich in A-T base pairs (only 2 bonds between Adenine and Thymine) forming a replication fork. RNA Polymerase RNA synthetises short RNA nucleotide sequences that act as primers. These essentially provide an early start for DNA replication. Polymerises nucleotide triphosphates in a 5' to 3' direction. The enzyme synthesises RNA primers to act as a template for future Okazaki fragments to build on to. DNA Polymerase III In charge of synthesizing nucleotides onto the leading end in the classic 5' to 3' direction. It synthesises the new DNA strand using free DNA nucleotides. However, DNA polymerase can only read the original template (parent plant) in the 3’-5’ direction (making DNA 5’-3’). This DNA Polymerase I In charge of synthesizing nucleotides onto primers on the lagging strand, forming Okazaki fragments. However, this enzyme cannot completely synthesize all of the nucleotides. It removes the RNA primers and replaces them with DNA. Nana Agyei Unit 11A Task 1 and 2 Ms. Kubasiak Genetics and Genetic Engineering Ligase This enzyme is in charge of "gluing" together Okazaki fragments, an area that DNA Pol I is incapable to synthesize. It joins the DNA fragments of the lagging strand together to form one continuous length of DNA. Telomerase Catalyses the lengthening of telomeres; the enzyme includes a molecule of RNA that serves as an arrangement for new telomere segments. During DNA replication the enzymes (polymerase) that duplicate the chromosome and it continue their replication all the way to the end of the chromosome. At the very ends of the DNA, it has a non-coding region of repeats known as telomeres. Every time the DNA is replicated the telomeres shorten slightly. It is believed that this may be the genetic basis for the aging process. Nuclease this enzyme is in charge of executing, or cutting out, unwanted or defective segments of nucleotides in a DNA sequence. Topoisomerase This enzyme submits a single-strand nick in the DNA, allowing it to rotate and thereby relieve the assembled winding strain developed during the unwinding of the double helix. Single Strand Binding Proteins Responsible for holding the replication fork of DNA open while polymerases read the arrangements and prepare for synthesis. DNA gyrase, or simply gyrase, is an enzyme within the class of topoisomerase (Type II topoisomerase) that relieves strain while double-stranded DNA is being unwound by helicase. The ability of gyrase to relax positive supercoils comes into play during DNA replication and prokaryotic transcription. Single strand binding proteins (SSBs) help to stabilise the single stranded DNA. On the lagging strand DNA polymerase moves away from the replication fork. As the strands continue to unzip more DNA is exposed and new RNA primers must be added. As a result the lagging strand is synthesised in short bursts as DNA polymerase synthesises DNA in-between each of the RNA primers. The newly synthesised lagging strand now consists of both RNA and DNA fragments. The DNA fragments are known as Okazaki fragments, after a Japanese scientist who noticed that heating DNA during replication, which separates the strands, gave many small fragments of DNA. From this he concluded that one stand must be synthesised in short bursts of DNA.