Zoey RentzAnthropology 101Test One Extra Credit Essay Questions2. Describe in your own words:a) The steps involved in the process of DNA replication. Include in your answer information on the composition of the DNA molecule and the purpose of replication.b) The steps involved in the process of protein synthesis. Include information on both transcription and translation. c) In what way is DNA different from RNA? What is the result of a change in the DNA code? a) Deoxyribonucleic Acid, or more commonly referred to as, DNA is composed of two polynucleotides that spiral around an imaginary axis, thus forming the double helix structure that we have come to know and love. You may ask, how does this spiral form? Well, once you break it all down it is much easier to understand. As I stated earlier, DNA is made of two polynucleotides wrapped around this imaginary axis. So, lets split the DNA in half and talk about just one of the strands, or a single polynucleotide. Polynucleotides are made up of many nucleotide monomers joined in a chain.Breaking it down even farther, each nucleotide has three parts: a nitrogenous base, afive-carbon sugar, and a phosphate group.The Nitrogenous Base:First off, why are they called bases? They are called bases because the nitrogen atom has a lone pair of electrons, which results in them taking H+ (protons) from the solution they’re in and therefore act as a base. So, there is nitrogen involved? Yes, these bases are made of one or two rings that include nitrogen atoms. There are twofamilies of nitrogenous bases: pyrimidines and purines.- Pyrimidines have one six membered ring of carbon and nitrogen atoms. The members of the pyrimidine family are:o Cytosine (C)o Thymine (T)o Uracil (U)Zoey RentzAnthropology 101- Purines are larger and have a six membered ring fused to a five membered ring. The members of the purine family are:o Adenine (A)o Guanine (G)Adding a sugar:Now that we have thenitrogenous base, we mustadd a sugar. In DNA thesugar is deoxyribose.Deoxyribose sugar lacks anoxygen atom on the secondcarbon ring, giving it thename deoxyribose.In order to distinguish the sugar carbons from the nitrogenous base, the sugar carbon molecules in the nucleotide (at this point a nucleoside, a nitrogenous base plus a sugar is a nucleoside.) have a prime (‘) after them. Hence, the carbon that sticks up from the ring is called the 5’ carbon (five prime carbon.).Zoey RentzAnthropology 101Adding a Phosphate Group: In order to build a nucleotide, a phosphate group needs to be attached to the 5’ carbon of the sugar. Nucleotides are linked together to build a polynucleotide. A phosphodiester linkage (or bond) is aphosphate group that links the sugars oftwo nucleotides that are next to oneanother. This bonding forms abackbone made up of repeating sugarphosphate units. The two ends of the polymer aredifferent from each other. One end is aphosphate attached to a 5’ carbon, andthe other is a hydroxyl group on a 3’carbon. These are referred to as the 5’end and 3’ end. The polynucleotide isbuilt in one direction, from 5’ to 3’.Zoey RentzAnthropology 101The nitrogenous bases are not part of the backbone. The bases stick out from the sugar phosphate backbone. The sequence of these bases is special and unique for every gene; the order of these bases gives specific instructions to the cell. The gene determines the order of the bases, and the order of the bases determines the amino acid sequence. The amino acid sequence is the primary structure, and the primary structure of polypeptides determines a proteins shape.In DNA these two polynucleotides spiral around and form a double helix. Each strand runs in the opposite direction of the other, as shown below. The sugar phosphate backbone runs along the outside of the double helix, thenitrogenous bases are paired up along the interior. The two strands are held together by hydrogen bonds. Only certain bases are compatible with each other. In DNA, Adenine (A) always pairs with Thymine (T), and Guanine (G) always pairs withCytosine (C). Knowing how the bases pair up, looking at one strand of the double helix, you would be able to determine the bases on the other strand. The bases pairing in this specific way is what gives DNA the ability to be copied.DNA Replication:Now that we know the structure of DNA we can apply it to the basic concept of DNA replication. The “parent” DNA has the two complementary strands of nitrogenous bases. When each strand is separated, each strand (polynucleotide) canbe used as a template for a new complementary strand. These new complementary nucleotide bases line up and connect to form the sugar phosphate backbone. From one parent DNA there are now two daughter DNA strands.Zoey RentzAnthropology 101The DNA replication begins at particular sites called origins of replication; these are a specific sequence of nucleotides in the parent DNA. Proteins that start the DNA replication seek out this specific sequence of nucleotides (the ATCG’s), then they and attach to the parent DNA strand. Once attached they separate the two strands of parent DNA and form a bubble. The replication process goes in both directions until the entire parent strand is copied. In the parent DNA morethan one of these bubbleswill form. These replicationbubbles will eventually fusetogether. Having more thanone bubble speeds up thecopying of longer DNA. At each end of thereplication bubble is calleda replication fork. It is the Yshaped region where theparent strand getsunwound. Several proteins are involved in unwinding of DNA:o Helicases: Enzymes that untwist the double helix at replication forks. It makes two template strands by separating the two parent strands.o Single-strand binding proteins: bind to the unpaired parent DNA strands and keep them from matching back up with one another.o Topoisomerase: When the double helix is unwound, it causes tighter twisting and more strain on the DNA ahead of the replication fork. This protein helps relieve the strain by breaking, swiveling, and rejoining DNA strands.Zoey RentzAnthropology 101Now that the parental DNA has been unwound it can be used as a template for new DNA to be created. There is a catch though; the enzyme that creates new DNA cannot start the creation of a polynucleotide. This enzyme can only add nucleotides to the end of an already existing chain. So where do we get the first chain to start DNA?
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