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Lecture 2

Lecture 2 Textbook Readings Notes Detailed and concise notes on the required readings for Lecture 2 with diagrams and panels.

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Kenneth Yip

Chapter 1Introduction to the Cell THE UNIVERSAL FEATURES OF CELLS ON EARTHHeredity is central to the definition of life it distinguishes life from other processesThe single cell is the vehicle for the hereditary information that defines the speciesIt includes the machinery to gather rat materials from the environment and to construct out of them a new cell in its own image complete with a new copy of hereditary information All Cells store their hereditary information in the same linear chemical code DNAAll cells store their heredity information in double stranded DNA long unbranched paired polymer chains All cells replicate their hereditary information by template polymerizationEach nucleotide monomer consists of two parts a deoxyribose sugar with a phosphate group attached and a base ATCGEach sugar is linked with the next phosphate group creating a polymer chainDNA is synthesized from a template formed by a preexisting DNA strandAT 2 H bonds and CG 3 H bondsTwo strands twist to form a double helix Individual sugarphosphate units are asymmetric giving the backbone of the strand a definite directionality or polarity which guides the molecular processes by which the information in DNA is interpreted and copied in cells information is always read in a consistent orderA normal DNA consists of two such complementary strands the nucleotides within each strand are linked by strong covalent chemical bondsBonds between the base pairs are weaker than the sugarphosphate links allowing the 2 DNA strands to be pulled apart without breaking the backboneDNA replication occurs at different rates with different controls to startstop it and different auxiliary molecules to help it alongTemplate polymerization is the way in which this information is copied throughout the living world All cells transcribe portions of their hereditary information into the same intermediary form RNAIn transcription segments of DNA sequence are used as templates for the synthesis of shorter molecules RNAIn translation many of these RNA direct the synthesis of proteinsRNA ribose instead of deoxyribose U instead of TDNA is fixed and sacrosanct RNA transcripts are massproduced and disposable Transcripts mainly serve as an intermediate messenger RNA to guide the synthesis of proteins according to DNABeing single stranded the polymer chain can bend itself to allow one part of the molecule to form weak bonds with another part of the same moleculeAll cells use proteins as catalysts Protein molecules long unbranched polymer chains formed by stringing together monomeric building blocks drawn from a standard repertoire that is the same for all living cellsAmino acids monomers of protein 20 types same core structure with side group that gives each its distinctive chemical characterPolypeptides created by joining aa in a particular sequence folds into a precise 3D form with reactive sites on its surface Bind with high specificity too other molecules and act as enzymes to catalyze reactions that make or break covalent bondsProteins also maintain structures generate movements sense signals put the genetic info into action All cells translate RNA into protein the same waymRNA read 3 nucleotides at a time codon several codons correspond to the same aacode is read out by transfer RNAs each tRNA is attached to an aa with the anticodon displayed at the other end tRNA with the right aa is matched with the mRNA aa have to be linked to extend the chain tRNA is releasedprocess is carried out by the ribosome formed of two chains of RNA called ribosomal RNAs ribosome latches onto the end of mRNA and then trundles along capturing tRNA and stitching together the aa The fragment of genetic information corresponding to one protein is one gene each segment coding for a different proteingeneRNA molecules transcribed can often be processed in more than one way giving rise to a set of alternative versions of a protein A gene is the segment of DNA sequence corresponding to a single protein or setof alternative protein variants or to a single catalytic or structural RNA molecule for those genes that produce RNA but not proteinThe expression of individual genes is regulatedThe cell adjusts the rate of transcription and translation of different genes independently according to needStretches of regulatory DNA are interspersed among the segments that code for protein and these noncoding regions bind to special protein molecules that control the local rate of transcriptionOther noncoding DNA define where the information for an individual protein begins and endsThe quantity and organization of the regulatory and noncoding DNA vary widely from organism to organismGenome the total of its genetic information as embodied in its complete DNA sequenceLife requires free energy
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