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BIOL 1090 Study Guide - Final Guide: Phosphodiester Bond, Guanosine, Adenosine Monophosphate

Course Code
BIOL 1090
Jaideep Mathur
Study Guide

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Bio Final Exam Notes – Text book content
Lecture #13: text Pg.; 197-214
The structures of DNA and RNA
Nature of the chemical subunits in DNA and RNA
- Nucleic acids are macromolecules composed of repeating subunits called nucleotides
- Each nucleotide is composed of (1) a phosphate group, (2) a five carbon sugar (pentose),
(3) a cyclic nitrogen-containing compound called a base.
- There are four different bases found in DNA; adenine [A], guanine [G], thymine [T],
and cytosine [C].
- In RNA , cytosine [C] is replaced by uracil [U]
- Adenine and guanine are double ringed bases called purines
- Cytosine,thymine,and uracil are single –ring bases called pyrimidine’s
DNA structure: the double helix
- Discovered by Watson and crick in 1953
- DNA goes from 5’ -----------3’
- Base pairing results from hydrogen bonding , purines have 2 hydrogen bonds, while
pyrimidine’s have 3 hydrogen bonds
- The complementarity of the two strands of the double helix ,makes DNA uniquely
suited to store and transmit genetic information from generation to generation
- There are 10 base pairs per turn
- Hydrogen bonds cause stability
DNA structure: alternate forms of the double helix
-B-DNA is the Watson-Crick structure (majority of DNA)
- DNA structure changes due to the environment

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- In high concentrations of salts or in partially dehydrated state , DNA exists as A-DNA
( 11 base pairs per turn)
-Z-DNA is unlike B or A-DNA because it exists in the left handed double helical form
- Occurs when C-G is rich and contain alternating purine and pyrimidine residues
- Function of Z-DNA is not clear
DNA structure: negative supercoils in vivo
- Supercoils: A DNA molecule that contains extra twists as a result of over winding
(positive supercoils) or under winding (negative supercoils)
- Supercoils are introduced into a DNA molecule when one or both strands are cleaved and
when the complementary strands at one end are rotated or twisted each other
- supercoiling only occurs in DNA molecules with fixed ends – ends that are not free to
- DNA molecules in almost all organisms exhibit negative supercoiling
- The DNA molecules in prokaryotic and viral chromosomes are organized into negatively
supercoiled domains
- Bacterial chromosomes contain circular molecules Of DNA segregated into about 50

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- Most eukaryotes are diploid (two complete sets of genes)
-Chromatin : the complex of DNA and proteins in eukaryotic chromosomes
- The proteins in chromatins are from two major classes (1) basic proteins called histones
( +) , (2) heterogeneous largely acidic called nonhistone chromosomal proteins
- Histones play a major structural role in chromatin
- Five major histone types
1) H1
2) H2a
3) H2b
4) H3
5) H4
-Nucleosome, Nucleosome core :
-: the nuclease-resistant subunit of chromatin that consists of about 146 nucleotides of
DNA wrapped as 1.65 turns of negative superhelix around an octamer of histones-two
molecules .
-Linkers: The unprotected DNA double helix that connects adjacent nucleosomes
-Pg. 210
Lecture# 15: text pg. 23-26
Cell division
- All the cells within a clone are identical – barring errors
- Mother Cell : A cell that is about to divide
- Daughter cells: the products of the mother cells division
- Fission:
- Each time a eukaryotic cell divides it goes through a series of phases, known as the cell
cycle. The progression of phases is ;
G1  SG2  M
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