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SUFFOLK UNIVERSITY / Science / Sci 111 / why is a nitrogen label good for studying dna

why is a nitrogen label good for studying dna

why is a nitrogen label good for studying dna

Description

School: Suffolk University
Department: Science
Course: Introduction to the Cell
Professor: Professor mcgee
Term: Spring 2016
Tags:
Cost: 25
Name: DNA- Case study
Description: This includes the full case study with the answers done in class
Uploaded: 03/11/2016
3 Pages 1116 Views 0 Unlocks
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NATIONAL CENTER FOR CASE STUDY TEACHING IN SCIENCE We also discuss several other topics like general steel macon

CLASSIC EXPERIMENTS IN MOLECULAR BIOLOGY

Meselson and Stahl Experiment: The Nature of DNA Replication Don't forget about the age old question of Enumerate the functions of osteoclasts.

by

Robin Pals-Rylaarsdam

Department of Biological Science

Benedictine University, Lisle, IL

Don't forget about the age old question of chemisthesis

Part 1 - Three Possibilities

How did you spend New Year's Day this year? In 1958, Matthew Meselson and Frank Stahl celebrated the first day of the new year by having breakfast with college friends in Chicago and passing a photograph around the table, not of a girlfriend or a new baby, but of the data behind what is sometimes called the “most elegant experiment in molecular biology--the experiment that first demonstrated how DNA replication occurs (Judson 1996, p612). Others followed (and won Nobel prizes too) by giving us details about the enzymes involved, but Meselson and Stahl's experiment is so important and well designed that it has become necessary knowledge for one to be called an educated biologist. We also discuss several other topics like What is the use of a buffer solution?

Here are three different possibilities for DNA replication. Only one really happens, but until Meselson & Stahl conducted their experiment, each of these was plausible.

To the right of each diagram below, write two or three sentences describing how the starting DNA molecule differs from the molecule after replication. Do this for each of the three postulated methods of replication. We also discuss several other topics like let r be the distance between the cylinder and the center of the turntable. now assume that the cylinder is moved to a new location r/2 from the center of the turntable. which of the following statements accurately describe the motion of the cylinder at t

Three postulated methods of DNA Replication

Don't forget about the age old question of Whatare the key strategies from the Dietary Guidelines?

Semi-conservative                 The DNA templaris made into two new copies and 

Conservative                         second strand doesn't have any of the DNA, or template.

Dispersive                        Two strands are dispersively copied but both copies are identical 

        Newly, synthesized strand

Original template strand

* not found to be biologically significant

Credit: Original uploader was Adenosine at en.wikipedia; used in accordance with CC-BY-SA-2.5 license. http://commons.wikimedia. org/wiki/File:DNAreplicationModes.png

"Classic Experiments in Molecular Biology" by Robin Pals-Rylaarsdam

Part II - Nitrogen

Meselson and Stahl had tools like Avery, McCarty, and McLeed: 14N and 15N.

Questions

  1. Why is a nitrogen label a good tool for studying DNA?
  • Because DNA has nitrogen (nitrogenous bases)
  1. What other molecules in a cell have nitrogen in them?
  • Protein (amino acids) and RNA
  1. What's the difference between 14N and 15N at the atomic level?
  • Amount of Neurons, more dense (15N)
  1. What's the term for two atoms of the same element with different molecular masses?
  • Isotopes
  1. Give an example of another element that has atoms of more than one molecular mass.
  • Hydrogen, carbon

Bacteria in the laboratory can grow on plates or in broth cultures composed of precisely defined mixtures of chemicals. Meselson and Stahl grew bacteria in cultures containing only 15N nitrogen for many generations so that the DNA was almost entirely composed of 15N-containing nucleotides. These chromosomes are more dense than 14N chromosomes, and by spinning chromosomes at very high speeds in a density gradient tube, Meselson & Stahl could tell the difference between the two kinds of chromosomes. Heavy chromosomes sank farther to the bottom of the tube, where the liquid was more dense. Lighter chromosomes floated in the less dense liquid toward the top of the tube. This can be represented by the diagram below. The blue lines represent the location of chromosomes in the tubes after centrifugation.

Part IV - Second Generation

The diagram below shows the result from the experiment of the 2nd generation of cells grown in 14N.

                                                        First Generation        2nd Generation

                Controls                                Incubation of heavy cells in 14N

Questions

  1. Which model has now been ruled out by these results? Dispersive
  2. What would the data look like if this model was actually happening? Include a diagram of a test tube as part of your answer.

First Generation        Second Generation

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