Chapter 10 - Structure and Function of DNA
Chapter 10 - Structure and Function of DNA Biology 110 002
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This 3 page Class Notes was uploaded by Kathleen Maris on Thursday October 15, 2015. The Class Notes belongs to Biology 110 002 at University of South Carolina - Columbia taught by Dr. Dhameja in Fall 2015. Since its upload, it has received 76 views. For similar materials see General Biology in Science at University of South Carolina - Columbia.
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Date Created: 10/15/15
Chapter 10 Structure and Function of DNA 0 Genes are made of DNA a nucleic acid The other type of nucleic acid is RNA DNA provides directions for its own replication DNA directs synthesis of messenger RNA mRNA and through it controls protein synthesis which occurs in ribosomes Nucleic acids are polymers called polynucleotides O 0 Each polynucleotide is made of monomers called nucleotides Each nucleotide consists of a nitrogenous base and pentose sugar and a phosphate group 0 In DNA the sugar is deoxyribose In RNA the sugar is ribose 0 There are two families of nitrogenous bases 0 Pyrimidines cytosine thymine and uracil have a single sixmembered ring 0 Purines adenine and guanine have a sixmembered ring fused to a fivemembered ring The portion of a nucleotide without the phosphate group is called a nucleoside Nucleotide nucleoside phosphate group Nucleoside nitrogenous base sugar Nucleotide polymers are linked together to build a polynucleotide 0 Adjacent nucleotides are joined by a phosphodiester linkage which consists of a phosphate group that links the sugar of two nucleotides 0 Two free ends are distinctly different from each other One has phosphate attached to 5 carbon and the other has a hydroxyl group OH on the 3 carbon end 0 The sequence of bases along a DNA or mRNA polymer is unique for each gene A DNA molecule has two polynucleotides spiraling around an imaginary axis forming a double helix 0 In the DNA double helix the two backbones run in opposite 5 I 3 directions from each other an arrangement referred to as antiparallel 0 The nitrogenous bases in DNA pair up and form hydrogen bonds adenine A always with thymine T and guanine G always with cytosine C 0 One DNA molecule includes many genes 0 The information content of DNA is in the form of specific sequences of nucleotides The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins Gene expression the process by which DNA directs protein synthesis includes two stages transcription and translation 0 RNA is the intermediate between genes and the proteins for which they code 0 The central dogma is the concept that cells are governed by a cellular chain of command DNA I RNA El protein 0 There are 20 amino acids but there are only four nucleotide bases in DNA The ow of information from gene to protein is based on a triplet code a series of nonoverlapping threenucleotide words known as CODON These triplets are the smallest units of uniform length that can code for all the amino acids During transcription one of the two DNA strands called the template strand provides a template for ordering the sequence of nucleotides in an RNA transcript During translation the mRNA codons are read in the 5 to 3 direction 0 Each codon specifies the amino acid to be placed at the corresponding position along a polypeptide All 64 codons were deciphered by the mid1960s 0 Of the 64 61 code for amino acids 3 triplets are stop signals to end translation 0 No codon specifies more than one amino acid 0 Codons must be read in the correct reading frame groupings in order for the specified polypeptide to be produced 0 Transcription is the synthesis of RNA under the direction of DNA Transcription produces messenger RNA mRNA In prokaryotes mRNA produced by transcription is immediately translated without more processing Eukaryotic RNA transcripts are modified through RNA processing to yield finished mRNA A primary transcript is the initial RNA transcript from any gene RNA synthesis is catalyzed by RNA polymerase which pries the DNA strands apart and hooks together the RNA nucleotides 0 RNA synthesis follows the same basepairing rules as DNA except uracil U substitutes for thymine 0 The DNA sequence where RNA polymerase attaches is called the promoter In bacteria the sequence signaling the end of transcription is called the terminator The stretch of DNA that is transcribed is called a transcription unit 0 Translation is the synthesis of a polypeptide which occurs under the direction of mRNA Ribosomes are the sites of translation A cell translate an mRNA message into protein with the help of transfer RNA tRNA 0 A tRNA molecule consists of a single RNA strand that is about 80 nucleotides long 0 tRNA molecules are not identical 0 Each carries a specific amino acid on one end 0 Each has an anticodon on the other end The anticodon basepairs with a complementary codon on mRNA 0 For accurate translation there should be a correct match between the tRNA anticodon and an mRNA codon I Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis 0 The two ribosomal subunits large and small are made of proteins and ribosomal RNA rRNA I There are three stages of translation 0 Initiation in which mRNA a tRNA with the first amino acid and the two ribosomal subunits are brought together Initiation begins with the codon AUG 0 Elongation in which amino acids are added one by one to the preceding amino acid 0 Termination in which a stop codon in the mRNA reaches the ribosome 0 Genes can be transcribed and translated after being transplanted from one species to another