Biology Exam _3 Study Guide

Biology Exam _3 Study Guide - Biology Exam#3 Study Guide...

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Biology Exam #3 Study Guide Describe the basic model of DNA Structure, including the directionality of the backbones. Bloom 2 DNA Structure o Double Helix : a helix made up of two strands o Each DNA nucleotide monomer consists of: Nitrogenous base: the pairs of nitrogenous bases are held together by hydrogen bonds Complementary base pairing : adenine bonds with thymine; guanine bonds with cytosine Deoxyribose (sugar) Phosphate group o The phosphate group on one nucleotide is attached to the sugar of the next, forming a “backbone of alternating phosphates and sugars from which the bases project. o The polynucleotide strand has directionality 5’ end: with the phosphate group 3’ end: with the –OH group Antiparallel : their subunits run in opposite directions Pages 308-310 Describe how DNA is organized in both eukaryotic and prokaryotic chromosomes. Bloom 2 Eukaryotic o Contain 46 DNA chromosomes (about a thousand times more than in a prokaryote) o One long double-helical molecule per chromosome Prokaryotic o Circular chromosome Pages 312-313 Use the basic process of DNA replication to solve replication problems. Bloom 3 DNA Replication: replication can only occur from 5’ 3’ o Replication begins at particular sites known as origins of replication These sites have a specific sequence of nucleotides that signal that replication must start there o Helicase : enzyme that untwists the double helix and separates the two parental strands of DNA Forms replication “bubble” This bubble separates the DNA strand in both directions In eukaryotic cells there are many replication bubbles o At the end of each bubble is a replication fork A Y-shaped region where the parental strands of DNA are being unwound o Single-strand binding proteins : bind to the unpaired DNA strands, keeping them from repairing o Topoisomerase : helps relieve the strain from the double helix untwisting by breaking, swiveling, and rejoining DNA strands o The unwound sections of parental DNA strands are now available to serve as templates for the synthesis of new complementary DNA strands. However, the enzymes that synthesize DNA cannot initiate the synthesis of a polynucleotide; they can only add nucleotides to the end of anal ready existing chain that is base-paired with the template
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strand. The initial nucleotide chain that is produced during DNA synthesis is actually a short stretch of RNA, not DNA. This RNA chain is called a primer and is synthesized by the enzyme primase. Primase starts a complementary RNA chain from a single RNA nucleotide, adding RNA nucleotides one at a time, using the parental DNA strand as a template. The completed primer, generally 5-10 nucleotides long, is thus base- paired to the template strand. The new DNA strand will start from the 3’ end of the RNA primer. o
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Biology Exam _3 Study Guide - Biology Exam#3 Study Guide...

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