17_Lecture%20W2011

17_Lecture%20W2011 - Chapter 17 Overview The Flow of...

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1 Chapter 17 From Gene to Protein Overview: The Flow of Genetic Information The information content of DNA is in the form of specific sequences of nucleotides he DNA inherited by an organism leads to specific traits The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins Proteins are the links between genotype and phenotype Gene expression , the process by which DNA directs protein synthesis, includes two stages: transcription and anslation translation Flow of information from gene to protein explained Basic Principles of Transcription and Translation RNA is the intermediate between genes and the proteins for which they code Is single stranded Has ribose instead of deoxyribose and uracil instead of thyamine Transcription is the synthesis of RNA under the direction of DNA produces messenger RNA (mRNA), which carries the genetic material from DNA to the protein synthesis site Translation is the synthesis of a polypeptide, which occurs under the direction of mRNA Ribosomes are the sites of translation Basic Principles of Transcription and Translation Translation the synthesis of a polypeptide which occurs is the synthesis of a polypeptide, which occurs under the direction of mRNA Change in language Ribosomes are the sites of translation from the nucleotide to the amino acid language
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2 In prokaryotes, mRNA produced by transcription is immediately translated without more processing In a eukaryotic cell, the nuclear envelope separates transcription (in nucleus) from translation ( in cytoplasm) Eukaryotic RNA transcripts are modified through NA processing yield finished mRNA RNA processing to yield finished mRNA There is a pre- mRNA stage followed by the mRNA A primary transcript is the initial RNA transcript from any gene Not the whole primary transcript gets translated into protein The central dogma is the concept that cells are governed by a cellular chain of command: DNA RNA protein TRANSCRIPTION TRANSLATION DNA mRNA Ribosome Polypeptide (a) Bacterial cell Nuclear envelope TRANSCRIPTION RNA PROCESSING Pre-mRNA DNA mRNA TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell The Genetic Code How are the instructions for assembling amino acids into proteins encoded into DNA? There are 20 amino acids, but there are only four nucleotide bases in DNA How many bases correspond to an amino acid? If 1 nucleotide would translate into 1 amino acid – 4 2 =16 possible arrangements- not enough for 20 amino acids Therefore triplets of bases needed for 64 possible arrangements
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3 Codons: Triplets of Bases The flow of information from gene to protein is based on a triplet code : a series of nonoverlapping, three-nucleotide words These triplets are the smallest units of uniform length that can code for all the amino acids Example: AGT at a particular position on a DNA strand results in the placement of the
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This note was uploaded on 03/22/2011 for the course MAC AECH111 taught by Professor Cheresres during the Spring '11 term at McGill.

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17_Lecture%20W2011 - Chapter 17 Overview The Flow of...

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