DNA Structure & Replication Chapter 5

Discovery of DNA as genetic material 1869 a compound found in the nucleus 1920’s the chemical components of nuclein determined 1930’s experiments on single celled algae Experiment 1  stalk removed, and regrew, therefore the DNA can not be in the stalk Experiment 2  foot remove, and did NOT regrow, therefore DNA must be in foot. Foot contained nucleus, so nucleus must contain genetic material1

Watson and Crick James Watson & Francis CrickJames Watson & Francis Crick Described DNA as a double helix in 1953Described DNA as a double helix in 1953 Nobel Prize for Physiology in 1962Nobel Prize for Physiology in 1962

DNA Structure DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix. A molecule of DNA is made up of millions of tiny subunits called Nucleotides. Each nucleotide consists of: 1. Phosphate group 2. Pentose sugar 3. Nitrogenous base

Nucleotide Phosphate Pentose Sugar Nitrogenous Base

Nucleotides The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”. There are four types of nitrogenous bases.

Nucleotides A Adenine T Thymine G Guanine C Cytosine

Nucleotides Each base will only bond with one other specific base. Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Form a base pair.

“The Code of Life” Nitrogenous BasesNitrogenous Bases Purines: Adenine & guanine Double-ringedPurines: Adenine & guanine Double-ringed Pyrimidines: Thymine & cytosine Single-ringedPyrimidines: Thymine & cytosine Single-ringed Triple bonds double bonds

DNA Structure Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

Anti-Parallel Strands

DNA STRUCTURE ?v=qy8dk5iS1f0 ?v=qy8dk5iS1f0 ?v=qy8dk5iS1f0

DNA SEMICONSERVATIVE REPLICATION The process of copying a double-stranded DNA moleculeThe process of copying a double-stranded DNA molecule DNA strands are antiparallel and complementaryDNA strands are antiparallel and complementary Each strand serves as a template for the reproduction of the opposite strandEach strand serves as a template for the reproduction of the opposite strand one strand of the newly formed DNA molecule is “conserved” from the original parent strand. one strand of the newly formed DNA molecule is “conserved” from the original parent strand.

The process of DNA Semiconservative Replication Continued: The 2 nucleotide chains unwind and unzip from each other. Each old chain base pairs with new nucleotides forming 2 identical DNA molecules that are identical to the original DNA molecule. The 2 old chains determine the sequence of the new chains since we know A pairs with T and C pairs with G.

DNA structure and Replication atch?v=8kK2zwjRV0M atch?v=8kK2zwjRV0M

Replication Fork

BIOFACT If extended a single human DNA molecule would be ~ 6 cm long, that is 1000s times longer than the diameter of the nucleus. This chromosome and another 45 chromosomes can fit into the nucleus because of efficient chromatin packing.

ANOTHER BIOFACT !! If you arrange all of the DNA strands in your body end-to-end, their total length would stretch 2 x That is well over 100 times the distance between the earth and the sun !!!!