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  BIOLOGY ASSIGNMENT SB015 SEMESTER 1, SESSION 2018/2019 1. A eukaryotic chromosome may have multiple replication bubbles thus speeding up the copying of the very long DNA molecules. The bubbles expand as replication proceeds in both directions from each srcin. Explain how the process occurs. Firstly, Helicase will unwind the parental DNA double helix at replication fork or we can call it as srcin of replication. This process could happen by breaking the Hydrogen Bond between Nitrogenous bases. Then, Replication Bubble consists of two replication fork formed. We call this process as The Unwinding of Strand. Next, each of the single-strand of Parental DNA will acts as template strands for the new complementary DNA strands. A Protein that we call as Single-Strand Binding Protein will holds the separated DNA strands apart and stabilize them while they act as a template and avoid them from pairing. Then, Topoisomerase or DNA gyrase will make sure that double stranded DNA outside of the replication fork does not super-coil and knot formation during replication. Then Synthesis RNA primer occur by using Primase. Primase will bind the template strands and synthesize RNA to short sequence of RNA at 5’ end of the strand.  After that, DNA Polymerase III will elongate new DNA strand by adding free DNA nucleotides by complementary base pairing. This process is called as Extension where DNA nucleotide will join up to the exposed bases by specific base pairing. The addition of new nucleotide occurs at Fee 3’ -OH. Furthermore, Formation of leading and lagging strands will occur. It starts when DNA Polymerase III synthesize a complementary strands called Leading Strands. This process happens continuously towards the replication fork by using only one RNA primer. Besides, the lagging strand proceed discontinuously contrary to the Leading Strand. A series of segment that known as the Okazaki fragment will be produced. This fragment's direction is away from the replication fork using several RNA primers. While, DNA polymerase I replaces the RNS primer with DNA nucleotides in  both strands. This process occurs before DNA ligase can join the Okazaki fragment together in lagging strands. Lastly, The Formation of new strand from5’ to 3’ will occur when the new lea ding and lagging strands elongates from 5’ to 3’ direction thus resulting in two identical copies of the srcinal DNA. 2. Insulin is a peptide hormone which is synthesized in pancreatic cell. Explain how insulin is produced in the cell. Insulin is produced by protein synthesis. Protein synthesis is a process which amino acids are linearly arranged into proteins through the involvement of ribosomal RNA, transfer RNA, messenger RNA, and various enzymes. Protein synthesis process starts with transcription. It involves 3 main stages. First, elongation where is RNA polymerase recognizes and binds to promoter and then unwind DNA double helix. Second, elongation where is RNA polymerase moves along DNA template to keep unwind the DNA and add free RNA nucleotides. Then, the mRNA is synthesized from 5’ to 3’.Third, transcription ends when the RNA polymerase reaches terminator and mRNA molecule is released from template DNA strand. The process is followed by translation process that involves 3 type of RNA. First, mRNA, it carries genetic information transcript from DNA in nucleus to cytoplasm in form of triplets bases called codon. Second RNA is tRNA. tRNA will bring specific amino acids to the particular codon on the mRNA. Acid amino from tRNA will be determined by specific triplet bases called anticodon.  Anticodon is a region in tRNA that matches with codon in mRNA. This attachment process is known as the activation of amino acids. Third is rRNA, it will combine with protein to form organelles called ribosome. Ribosome facilitates the specific coupling of anticodon and codon during translation. Ribosome have 3 side that are E for exit, P for peptidyl-tRNA binding site where ribosome holds the tRNA that carrying growing polypeptide chain and A for aminoacyl-tRNA binding site where ribosome holds the tRNA that is carrying the next acid amino to be added in the chain.  3. Lac operon is an example of an inducible operon. Explain what is lac operon and the mechanism of operon control in E.coli. Lac Operon means Lactose Operon. It contains genes that encode for enzymes used in the hydrolysis and metabolism of lactose in E.coli bacteria. It has been introduced by Jacob and Monod. Furthermore, only prokaryote ha operon. Next, Lac operon consist of Structural Genes such as Z, Y A, Promoter genes that has a binding site for RNA polymerase, and Regulator gene known as I that is located outside operon and act as a code for repressor protein. Then, if the lactose not present, the repressor protein will bind to operate and this thing makes the RNA polymerase cannot bind with promoter. We can say that Lac operon is inactivated because structural genes are not transcribed then enzymes will not be produced and lactose will not be broken down. However, if we drink Milk, an inducer will present. So, lactose will be converted into allolactose. allolactose will bind repressor protein. Then, the repressor protein changes its shape and cannot bind with operator gene so RNA polymerase can bind with promoter gene. We can say that Lac operon is activated because structural gene are transcribed into tRNA and then ribosome translates tRNA to produce enzymes and the lactose will break down and produce glucose and galactose.
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