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Biology Lecture 4

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Western University
Biology 1002B
Tom Haffie

Lecture 4 Biological Function  From a cellular point of view  How do organisms work?  Two approaches o biochemistry looks at proteins to find biological function o genetics: understands the biological function by examining mutants o Molecular Biology: bought the two fields, biochemistry and genetics together Protein Abundance: points of control  Transcriptional Control: DNAmRNA  Translational control: tRNA recruitment and ribosomal level  Post transcriptional control (before translation): mRNA decay- turnover  Abundance Vs Activity: abundance in protein doesn’t mean they are all active and functioning and expressing Gene & Protein Expression Constitutive: gene is always on, contstant level of production, regardless of external changes (housekeeping genes, fundamental aspects of cell need constant supply of these)  Keratin Induced or Repressed: Switched on under conditions/off usually on, but under conditions, they are turned off  Heat shock protiens Measuring Transcript Abundance Northern (RNA) blot analysis  Cell of tissue samples: isolate RNA from each of them  Run RNA on gel electrophoresis o separate RNA based on size o smaller on the bottom o Most abundant RNA= ribosomal RNA (97%), mostvisible on gel o Each lane has 30,000 types of RNA  Transfer to nylon membrane, o thru capillary action, RNA will transfer to membrane  Radioactive probe is a single stranded homologous DNA that corresponds to the gene that you’re looking for o Will bing correctly with the complementary strand of RNA  Incubate probe with the blot, the probe will find the gene (complimentary base pairing) o probe is radio active, once it binds  X-ray film will expose where the genes are  The amount of binding is proportional to the amount of gene there is Western Blot  Isolate proteins instead of RNA  Probe=antibody Measuring transcript and protein abundance  Gene 1 is induced under certain temps  Protein 1 and 2 are induced/repressed according to temp as well Peptides  Made of amino acids o Have amino group o carboxylic acid o R-group  All three make the peptide backbone  Linked together by peptide bond o Formed through dehydration reaction o Incoming amino end and carboxyl end form bond Amino Acids  There are polar and nonpolar amino acids o Nonpolar contribute to the hydrophobic effects o Tendency to stay away from an aqueous environment Protein structure Primary  Typical protein is about 500 amino acids  Unique sequence of amino acids in a polypeptide  It’s the linear ordering of the amino acids Secondary  Depends of carboxyl group  Produced by regular repeated interactions between atoms of the backbone  Alpha helix: classic type of secondary structure  very regular  1 and 5 amino acids interact  hydrogen bond produced  Beta sheet: when one peptide folds over and you have 2 individual peptides Tertiary  Depends on R groups  Peptide Vs. Protein: peptide newly synthesized is unfolded, protein folds into the correct conformation (function requires it to fold)  Gives overall 3D folding of a single polypeptide chain o Protein actually folds into the correct native confirmation (functional
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