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Biology 1201A Study Guide - Midterm Guide: Matthew Meselson, Franklin Stahl, Isotopes Of NitrogenPremium

4 pages82 viewsFall 2016

Course Code
Biology 1201A
Vera Tai
Study Guide

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Biology 1201 Test 1 Outcomes Part 2
Basic Structure of Double-Stranded DNA
There are 4 different nucleotides; each of the nucleotide consists of a 5-carbon sugar
deoxyribose, phosphate group and one of the 4 nitrogen bases (Adenine, Guanine, Thymine
and Cytosine)
Adenine and Guanine are purines; thymine and cytosine are pyrimidines
The nucleotides are joined together that forms a polynucleotide chain where it also contains a
sugar-phosphate backbone (sugar-phosphate-sugar-phosphate pattern) PHOSPHODIESTER
BOND holds the nucleotides together (covalent bond); this bond bridges the phosphate group of
the 5 aro of oe sugar to the 3 aro of the et sugar up ahead
The two strands are anti-parallel
Purine and pyrimidine base-pairing in DNA/RNA
As we know that the purines are: Adenine and Guanine; and pyrimidines are: Cytosine and
Thymine; in the double stranded DNA, a purine binds to a pyrimidine (hydrogen bonds) in
between the sugar-phosphate backbone
Adenine binds with Thymine and Guanine binds with Cytosine
A-T has 2 hydrogen bonds and G-C has 3 hydrogen bonds this is known as complimentary
Outcome of the classic Meselson and Stahl experiment
This was a definitive experiment done in 1958 by Matthew Meselson and Franklin Stahl that
showed DNA replication is indeed semi-conservative
Bacteria was grown in a heavy isotope of 15N and then it was mixed in with a 14N medium and
allowed for growth to occur
Extraction occurred initially with 15N and after each generation bacteria grew in 14N
The DNA was mixed with CsCl (forms a density gradient) and spun in a centrifuge for 48 hours
heavy isotopes were located at the bottom and lighter ones at the top
Initially, 15N was at the bottom because it was heavy; and then after one generation there were
2 density lines: 15N and 15N-14N; and then the next generation had 15N-14N and 14N-14N;
This means that when the DNA strands split up for replication, the free floating nucleotides in
14N bind together with the strand so that 2 DNA double-helix are created where you have one
parent/daughter strand in one DNA molecule and another parent/daughter strand in another
Outcome of the classic Avery experiment
Avery and his co-workers showed that DNA was indeed the molecule that was responsible for
transforming Avirulent rough Streptococcus to the Virulent Smooth form
They tried to reproduce the transformation using bacteria growth in culture tubes heat killed
virulent S bacteria and R bacteria were mixed together; however, there were 4 different types
where these macromolecules were treated with enzymes that breakdown either one of these:
protein, DNA, other nucleic acid or RNA
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