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Nucleic Acids
Big Idea 3: Living systems store, retrieve, transmit, and respond to
info essential to life processes.
Essential Knowledge
• 3A1: DNA, and in some cases RNA, is the primary source of heritable information.
Nucleic Acids
• Store and transmit hereditary information• Amino acid sequence of a polypeptide is
programmed by a unit of inheritance called a gene• Genes are found on chromosomes.
Nucleic Acids
•Large, complex molecules composed of C, O, H, N, and P.
•2 types are RNA, ribonucleic acid and DNA, deoxyribonucleic acid.
DNA
RNA
Prokaryotes
• Earliest cells
• Smaller than Eukaryotes!
• No nucleus (home for DNA)
Prokaryotic DNA
• Is housed in a region called the nucleoid
Prok. DNA
• Is usually small and circular
• Has plasmids: small, extra-chromosomal, double stranded, and circular DNA
Viruses and Eukaryotes can have plasmids too…
Herstory• Rosalind Franklin: British
scientist (working in Maurice Wilkins lab) who took an X ray
diffraction image of DNA, 1952
• Led to double helix shape discovery by Watson and Crick
Photo 51
HIStory• Watson and Crick
used Franklin’s image to create the double helix DNA model in 1953.
• Won Nobel Prize in 1962,w/ Wilkins.
Double Helix Structure
Nucleic Acid Structure
• Made of nucleotides; both RNA and DNA.
Each nucleotide contains:
• 1 Phosphate Group
• 1 Sugar
• 1 Nitrogen Base
Phosphate
• PO4
• Makes up a part of the DNA/RNA backbone
Sugar• In DNA, sugar is
deoxyribose• In RNA, sugar is
ribose• Binds to
Nitrogen Base• Is in backbone
of DNA/RNA
Fig. 5-27c-2
Ribose (in RNA)Deoxyribose (in DNA)
Sugars
(c) Nucleoside components: sugars
DNA Nitrogen Bases
• Adenine• Thymine• Guanine• Cytosine
Conserved Through Evolution!
DNA Base Pairing Rules (Chargaff’s Rules)
• A only binds with T• C only binds with G
• H bonds hold Nitrogen bases together
RNA Nitrogen Bases
• Adenine• Cytosine• Guanine• Uracil• NO
Thymine!
Fig. 5-27c-1
(c) Nucleoside components: nitrogenous bases
Purines
Guanine (G)Adenine (A)
Cytosine (C) Thymine (T, in DNA) Uracil (U, in RNA)
Nitrogenous bases
Pyrimidines
Purines: Double Ring Structure, GA
Pyrimidines: Single Ring Structure: CTU
DNA: Double Stranded, RNA Single Stranded
DNA is AntiParallel
Fig. 5-27ab5' end
5'C
3'C
5'C
3'C
3' end
(a) Polynucleotide, or nucleic acid
(b) Nucleotide
Nucleoside
Nitrogenousbase
3'C
5'C
Phosphategroup Sugar
(pentose)
3’ carbon and 5’ carbon bind to PO4 phosphodiester linkage
DNA Replication
• DNA provides directions for its own replication ensure continuous
inheritance of DNA
DNA Replication• Before a cell divides must duplicate its DNA.
• Each strand of DNA will serve as a template/model for a new strand of DNA (semiconservative).
• Enzyme called DNA helicase unzips and unwinds a portion of DNA.
• Enzyme helps breaks apart H connect N bases. (A,T,C,G)
DNA Replication 1st Step
DNA Helicase
DNA Replication: 2nd Step
• 2nd enzyme called DNA polymerase III comes along and begins to add complementary base pairs to nitrogen bases.
• Works in 5’ to 3’ fashion…
• Video Clip!
DNA ReplicationOther Enzymes
Involved:Ligase: Glues back
sugar-phosphate backbone
Topoisomerase: Regulates
overwinding/ underwinding of DNA by cutting
backbone
http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter14/
dna_replication.html
Practice!
• If one side of DNA reads CTCT, what would the
complement side of DNA read? Write down on paper!
GAGA!
Then, The Cell Divides…
• Mitosis: Makes 2 identical diploid (2 copies of chromosomes) cells from 1
parent cell: IPMAT