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Biology (653)
BIO206H5 (60)
Chapter 7

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University of Toronto Mississauga
George S Espie

Chapter 7 Proteins are principal constituents of cells and determine not only their structure but also their functionThe properties and function of a protein molecule is determined by the sequence of the different amino acid subunits in its polypeptide chainEach type of protein has its own unique amino acid sequenceThe amino acid sequence in a protein dictates how the chain will fold to give the molecule with a distinctive shape and chemistryThese genetic instructions carried by DNA must therefore specify the amino acid sequences of proteinsDNA does not direct protein synthesis but acts like a manager delegating the various tasks to team of workersAll cells from bacteria to eukaryotic cells express their genetic information in this way a principle so fundamental that it has been termed the central dogma of molecular biologyFROM DNA TO RNATranscription and translation are the means by which cells express their genetic instructions genesMany identical RNA copies can be made from the same gene and each RNA molecule can direct the synthesis of many identical protein moleculesEach gene can be transcribed and translated with different efficiency providing the cell with a way to make vast quantities of some proteins and tiny quantities of othersThe production of RNA is the first step in gene expressionPortions of DNA sequence are transcribed to RNA o The first step is to cope the nucleotide sequence of that gene into RNAo The process is called transcription because the information though copied into another chemical form is still written in essentially the same language o RNA is a linear polymer made of different types of nucleotides subunits linked together by phosphodiester bonds like DNA o RNA differs from DNA in two ways RNA nucleotides are ribonucleotides RNA contains Uracil instead of the Thymine o DNA and RNA chemical differences are small but their structural differences differ quite a bit o RNA is single stranded o RNA being single stranded it can fold up into a variety of shapes o Double stranded DNA can not fold in this way o The ability to fold unto a complex 3D shape allows RNA to carry out functions in the cell in addition to conveying information between DNA and proteinstructural and catalyticTranscription produces RNA complementary to one strand of DNAo All of the RNA in a cell is made by transcription o Transcription begins with the opening and unwinding of a small portion of the DNA double helix to expose the bases on each DNA strand
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