DO NOW: The picture shows a chemical reaction. 1 DO NOW: The picture shows a chemical reaction. 1. What are the reactants? What is the product? 2. Is it a hydrolysis or dehydration synthesis? Support your answer with a minimum of two reasons.
What did you learn during the DO Now section of the lesson? Write a summary or think about These questions: Describe two characteristics of a dehydration synthesis. What part of a nucleotide is used to identify its specific name? What Parts two nucleotides join together? How will understanding how a dehydration synthesis help learn DNA replication? What are synonyms for Parent strand?
Synthesis of an “exact” copy of the entire genome of the cell DNA Replication Synthesis of an “exact” copy of the entire genome of the cell
The parent molecule has two complementary strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C.
The parent molecule has two complementary strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C. The first step in replication is separation of the two DNA strands.
Semiconservative Replication LE 16-9_3 Semiconservative Replication The parent molecule has two complementary strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C. The first step in replication is separation of the two DNA strands. Each parental strand now serves as a template that determines the order of nucleotides along a new, complementary strand.
Getting Started: Origins of Replication Replication begins at special sites called origins of replication, where the two DNA strands are separated, opening up a replication “bubble” A eukaryotic chromosome may have hundreds or even thousands of origins of replication Replication proceeds in both directions from each origin, until the entire molecule is copied At the end of each replication bubble is a replication fork, a Y- shaped region where new DNA strands are elongating
LE 16-12 Parental (template) strand 0.25 µm Origin of replication Daughter (new) strand Bubble Replication fork Two daughter DNA molecules In eukaryotes, DNA replication begins at may sites along the giant DNA molecule of each chromosome. In this micrograph, three replication bubbles are visible along the DNA of a cultured Chinese hamster cell (TEM).
DNA polymerase Pyrophosphate Nucleoside triphosphate New strand Template strand 5¢ end 3¢ end 5¢ end 3¢ end Sugar Base Phosphate DNA polymerase 3¢ end 3¢ end Pyrophosphate Nucleoside triphosphate 5¢ end 5¢ end
Antiparallel Elongation The antiparallel structure of the double helix (two strands oriented in opposite directions) affects replication DNA polymerases add nucleotides only to the free 3end of a growing strand; therefore, a new DNA strand can elongate only in the 5 to 3direction
The Basic Principle: Base Pairing to a Template Strand Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules Animation: DNA Replication Overview
Along one template strand of DNA, called the leading strand, DNA polymerase can synthesize a complementary strand continuously, moving toward the replication fork To elongate the other new strand, called the lagging strand, DNA polymerase must work in the direction away from the replication fork The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase
LE 16-14 3¢ 5¢ Parental DNA Leading strand 5¢ 3¢ Okazaki fragments Lagging strand 3¢ 5¢ DNA pol III Template strand Leading strand Lagging strand Template strand DNA ligase Overall direction of replication
LE 16-16 Leading strand Lagging strand Origin of replication Lagging Overall direction of replication Leading strand Lagging strand Origin of replication Lagging strand Leading strand OVERVIEW DNA pol III Leading strand DNA ligase Replication fork 5¢ DNA pol I 3¢ Primase Parental DNA DNA pol III Lagging strand Primer 3¢ 5¢