Chapter 4 Basic Molecular Genetic Mechanisms Cell Bio Central Dogma DNA transcription RNA translation Protein Genes molecules that store information in hereditary units 4 1 Structure of Nucleic Acids 1 DNA 2 polynucleic acid strands that are wound together in a stable structure Base Pairing Rules A T 2 hydrogen bonds C G 3 hydrogen bonds Bases held together by hydrogen bonds Backbone made of alternating pattern of a sugar and a phosphate o Phosphates in the backbone are negatively charged 2 strands of the DNA can separate from each other by 1 Melting Temperature Tm increasing the temperature causes hydrogen bonds to 2 break apart Ion Concentration Sugar Phosphate backbone negatively charged o Decrease the cation concentration less shielding of the negative charges between the 2 phosphates near each other in the backbone o Negative charges start to repulse on another which leads to instability of the backbone causes strands to separate o Because DNA and RNA are very similar they can bind to each other Will be important when manipulating things in vitro 2 RNA structure very similar to DNA with 3 exceptions a Sugar molecule structure has an extra hydroxyl OH group at carbon 2 where DNA sugar molecule only has an hydrogen at its carbon 2 refer to slide 4 for structure b Bases DNA has Thymine and RNA has Uracil but both pair with Adenine Thymine has a CH3 group where Uracil does not c Number of strands DNA 2 strands RNA usually single strand 4 2 Transcription of Protein Coding Genes Formation of Functional mRNA RNA synthesize in 5 3 direction Promoter non coding area of the gene designated by negative numbers upstream 1 site start site of transcription Coding Sequence has positive umbers that indicate each base downstream Only 1 strand of DNA is transcribed at a time to make mRNA called the primary RNA transcript o Complementary to the template DNA strand strand that is transcribed o Non template strand is not used during transcription Enhancers Repressors control areas of genes Usually upstream dictate when the mRNA is made and where Cell Bio Chapter 4 Basic Molecular Genetic Mechanisms Eukaryotic RNA Processing primary RNA transcript goes through modifications before it is mature At the 5 end a methlyguanylate cap is added to help protect transcript from degradation and helps start translation At 3 end Poly A Polymerase adds a poly A tail 100 250 adenines added to the end provides stabilization and helps with translation Introns intervening sequences spliced out exons coding sequences ligated together Alternative Splicing Isoforms Fibronectin secreted from cells into extra cellular space and is an adhesive protein that helps hold cells tissues together by forming protein protein connections between cells o But not always good don t want this in the liver o Liver has sinusoids space for blood to travel without being contained in a capillary o If fibronectin present then blood could not pass through the liver From one gene can create several closely related proteins and form isoforms o Amino acid sequences differs slightly but has very similar functions o Can be formed through alternative splicing where exons are spliced together in different combinations
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