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Transcript of BioEd Online The Molecular Basis of Heredity: Structures and Functions of Nucleic Acids by Raye L....
BioEd Online
The Molecular Basis of Heredity:
Structures and Functions
of Nucleic Acids
by Raye L. Alford, PhD
Baylor College of Medicine
DNA Model by J. Watson and F. Crick© Cold Spring Harbor Laboratory Archives
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The Atomic Components of DNA and RNA
Carbon (C)
Hydrogen (H)
Nitrogen (N)
Oxygen (O)
Phosphorus (P)
Thomas Jefferson National Accelerator Facility, Office of Science Education
The Periodic Table of Elements
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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 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 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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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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The DNA Double Helix
The DNA ladder spirals in a double helix.
There are 10 base pairs per turn.
Each turn is 34 Angstroms high.
The helix is 24 Angstroms wide.
The major groove is the wider of the two grooves.
The other groove is called the minor groove
Redrawn from National Institute of Medical Sciences, NIH
Major groove
Minor groove
Major groove
Minor groove
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DNA Replication
Replication relies on complementary base pairing.
Replication occurs before Mitosis and Meiosis I.
DNA replication is semi-conservative.
DNA is synthesized by DNA polymerase.
DNA is synthesized in a 5’ to 3’ direction. 5‘
5'
3'
3'
5'
Redrawn from National Center for Biotechnology Information
3'
5' 3'
5'
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Transcription
Like replication, transcription relies on base pairing. Instead of DNA, RNA is made.
RNA is synthesized by RNA polymerase II.
3'
3'
5'
NascentRNA
TemplateStrand
5'
5' 3'
CodingStrand
ElongationSiteRNA Polymerase
Unwinding
Rewinding
Movement of polymerase
2005 VisiScience Corporation. All Rights Reserved
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RNA Processing in Eukaryotic Cells
Splicing out of introns,capping with 5' methyl cap,polyadenylation
Exon5' 3'
Intron
RNA
IntronExon Exon
mRNAAAAAAAAn
2005 VisiScience Corporation. All Rights Reserved.
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Translation Ribosomes make proteins from the messages encoded in
mRNA. Three nucleotide groups called codons encode one
amino acid. This is the genetic code.
Adapted from: L. Stryer. Biochemistry, 3rd ed..
5' 3'
Nearly completed protein
Ribosome
Beginning of protein
mRNA
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The Genetic Code
Each 3-nucleotide mRNA codon specifies a particular amino acid.
Each tRNA transfers a particular amino acid.
To use the chart, read from the mRNA.
National Center for Biotechnology Information, National Library of Medicine, NIH
MET-tRNA
codon codon codon
mRNA
anticodon loop
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Summary of DNA
DNA: is a complex macromolecule
made of several basic atomic components.
encodes genes, the instructions needed to make RNA and proteins.
is a double helix. The complementary nature of the DNA helix permits its replication and transcription.
is transcribed into RNA.2005 VisiScience Corporation. All Rights Reserved.
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Summary of RNA
mRNA (messenger RNA) is the template for the production of proteins, the molecules that build and comprise structures and perform enzymatic reactions.
tRNA (transfer RNA) enables the transfer of amino acids into a growing polypeptide chain.
rRNA (ribosomal RNA) is a component of protein-producing ribosomes.