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Chapter 4

chapter 4.docx

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Gillian Goward

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KEY POINTS:  protein sequences are typically read from amino-terminus to carboxy-terminus  When nucleotide polymerize to form a nucleic acid: a hydrogen bond forms between the sugars of one nucleotide and the phosphate of the second  Franklin and Wilkins analyzed DNA by bombarding DNA crystals and X - rays. Their analysis yielded two numbers that sparked interest, 3.4nm and 0.34nm. These numbers tell us there are 10 rungs, or steps, on the DNA ladder for every turn of the helix  Phosphodiester bonds connect nucleotides NUCLEOTIDE Structure How is structure formed? Function + Sig  Is the monomer of nucleic acids Formed by phosphodiester linkage between -C-O-P-O-C  DNA and RNA are  Consists of phosphate group + a pentose C3 - C5 bond polynucleotides sugar + nitrogenous base.  There is a strong  Nitrogenous base is attached to C1 consensus that if  Phosphate group at C5 ribonucleotides  C3 OH is involved in bonding with the next and nucleotide deoxyribonucleotid  Lipid zones are recognized by receptor es were able to form during chemical evolution, they would be able to polymerize and form RNA and DNA NUCLEIC ACIDS Structure How is structure formed? Function  Nucleic acids are polymers  Via polymerization Nucleic acids allow organisms to transfer genetic information just like proteins. from one generation to the next. There are two types of  Monomer of nucleic acid: nucleic acids: deoxyribonucleic acid, better known as DNA nucleotide and ribonucleic acid, better known as RNA.  Contains a sugar - phosphate spine: this backbone is directional DNA Structure How is structure formed?  Sugar - phosphate backbone created by phosphodiester linkages + sequence of 4 nitrogenous bases that extend from it.  Has a secondary structure  Has 2 anti - parallel strands twisted into double helix  Model of secondary structure was presented by Watson and Crick. Observation they used to create the model: o Sugar - phosphate backbone o 2 rules by Chargaff:  The total number of purines = pyrimidmines  Number of A = T and number of C = G o Distances by rosalindfranklin and Maurice Wilkins using X - ray crystallography: in which the crystallineatomscause a beam of X- raysto diffracinto many specific directions. By measuring the angles and intensities of these diffracted beams, a crystallographecan produce a three-dimensional picture of the density of electronswithin the crystal 3 repeating distances were found: 0.34nm (distance between bases stacked in a spiral), 2.00 nm width of the helix and 3.4nm (distance between every turn)  Using this created a double helix structure.  Inside the double helix, the bases lined up in a way that allowed hydrogen bonding to form between certain purines and pyrimidines. Complementary base pairing: A-T and G-C. this phenomenon of Complementary base pairing was discovered by
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