www.bioedonline.org essential idea the structure of dna allows efficient storage of genetic...
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Essential Idea
The structure of DNA allows efficient storage of genetic information.
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Understandings
The nucleic acids DNA and RNA are polymers of nucleotides.
DNA differs from RNA in the number of strands present, the base composition and the type of pentose.
DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs.
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Discovery of DNA movie
The animation below describes the discovery of the DNA molecule.
http://media.hhmi.org/biointeractive/films/Double_Helix.html
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IB ASSESSMENT STATEMENT
Outline (summarize) DNA nucleotide structure. Include the following terms:
sugar (deoxyribose), base phosphate. Be sure to describe the relative positions of
the above terms.
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www.BioEdOnline.org
Nucleic Acids
Nucleic Acids are information molecules of cells.
They contain the genetic code for all living organisms.
There are two type of nucleic acids:
1. DNA – Deoxyribonucleic acid
2. RNA – Ribonucleic acid
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Nucleic Acids
Nucleic Acids are polymers made of monomers call nucleotides
Nucleotides consist of three substances:
1. Nitrogenous Bases
2. Pentose Sugar
3. Phosphoric Acid
The Animation below shows explains the structure of DNA.
http://www.sumanasinc.com/webcontent/animations/content/DNA_structure.html
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The Molecular Components of DNA and RNA (II)
The Sugar – Phosphate Backbone DNA – Deoxyribose (Pentose) Sugar RNA – Ribose (Pentose) Sugar Phosphate Group
Base + Sugar + Phosphate = Nucleotide
Deoxyribose + Triphosphate Group Ribose + Triphosphate Group
BASE BASE
1’
2’3’
5’1’
2’3’
5’
2005 VisiScience Corporation All Rights Reserved
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The Molecular Components of DNA and RNA (I)
Bases DNA and RNA
Adenine (A) Cytosine (C) Guanine (G)
DNA Only Thymine (T)
RNA Only Uracil (U)
2005 VisiScience Corporation. All Rights Reserved.
Uracil
ThymineGuanine
Adenine Cytosine
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The DNA and RNA Strand
Nucleotide + Nucleotide(n)
= DNA (or RNA) strand
Deoxyribonucleotides = DNA
Ribonucleotides = RNA
2005 VisiScience Corporation. All Rights Reserved.
3'
5'
Base
Base
Base
1'
3'
5'
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RNA vs. DNA
DNA is Double Stranded – Double Helix
RNA is Single Stranded
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IB ASSESSMENT STATEMENT
Identify the names of the four nitrogenous bases in DNA.
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5'
5'
3'
3'
DNA is Double-Stranded
Hydrogen bonds enable the DNA ladder.
A always pairs with T. C always pairs with G.
The sequence of one strand predicts the sequence of the other.
2005 VisiScience Corporation. All Rights Reserved.
3
45
21
4
5
1
6
32
87
96
Thymidine
Two Hydrogen Bonds
Adenosine
93
45
2
4
5
1
6
32
7
6
1
8Cytidine
Guanosine
Three Hydrogen Bonds
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RNA vs. DNA
KEY CONCEPT DNA structure is the same in all organisms.
DNA Animation: https://www.youtube.com/watch?v=8kK2zwjRV0M
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IB ASSESSMENT STATEMENT
Outline (summarize) how DNA nucleotides are linked (bonded) together by covalent bonds into a single strand.
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www.BioEdOnline.org
www.BioEdOnline.org
DNA is composed of two polynucleotides chains.
Nucleotides are covalently bonded between the phosphate of one nucleotide to the C3 of the second nucleotide.
The phosphate group creates a bridge connecting C5 on one pentose with the C3 on the next pentose.
The bond is a phosphodiester bond which indicates that there are two covalent bonds formed between the -OH and the acidic phosphate group
The sugar phosphate backbone which provides the stable backbone of one of the helices.
Covalent bonds that link the nucleotides along the backbone of the molecule.
The bases projecting into the centre.
.
At one end there is pentose with 5' (said "five prime" ) carbon which is free from bonding.
At the other end there is a 3' carbon free from bonding to other nucleotides.
Additional nucleotides are joined to the 3' end of the existing polynucleotide chain.
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www.BioEdOnline.org
IB ASSESSMENT STATEMENT
Explain how a DNA double helix is formed using complementary base pairing and hydrogen bonds.
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Chargaff’s rule Animation
http://www.hhmi.org/biointeractive/chargaffs-ratio
TAC
G
Nucleotides always pair in the same way. The base-pairing rules show
how nucleotides always pair up in DNA.
Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width.
– A pairs with T– C pairs with G
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Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width.
Cytosine always pairs with guanine
Thymine always pairs with Adenine.
hydrogen bond covalent bond
The bases are connected by hydrogen bonds.
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IB Assessment State
Draw and label a simple diagram of the molecular structure of DNA. Be sure to show the following
the complementary base pairs of A–T and G–C, held together by hydrogen bonds
and the sugar–phosphate backbones.
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Two polynucleotide chains.
Two anti-parallel chains.
a)The number followed by the prime (') determined the carbon in deoxyribose free from bonding to another nucleotide.
b) Note that the two chains are in opposite directions 3' to 5' is parallel to 5' to 3' chain.
The anti-parallel chains have a uniform distance (2nm) between the outside of the two sugar phosphate backbones
Complementary base pairs: Inside the double helix bases form one strand hydrogen bond to bases on the opposite strand but always in the following way:
a) Adenine hydrogen binds to Thymine b) Cytosine hydrogen bonds to Guanine
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IB Assessment Statement
Draw & Label a Simple diagram of the molecular structure of DNA
DNA and Chromosomes Eukaryotic Chromosome Structure
Chromosome
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Nature of Science
Using models as representation of the real world—Crick and Watson used model making to discover the structure of DNA. (1.10)
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Application & Skill
Application: Crick and Watson’s elucidation of the structure of DNA using model making.
Skill: Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons and rectangles to represent phosphates, pentoses and bases.
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