BIOLOGY NOTES FOR EXAM 3 Molecular Basis of Inheritance o What is the structure of the genome Chromosome and DNA structure o How is the genome copied DNA replication o What is the genome used for Chromosome Structure Protein synthesis o Eukaryotic chromosome structure DNA linear molecule Histone proteins DNA replication occurs in a semi conservative mechanism Ultimately the information in DNA is used to make proteins DNA structure o Four nucleotides o Complementary base pairing hydrogen bond Adenine bonds to Thymine Guanine bonds to Cytosine o Double helix o Anti parallel backbones held together by covalent sugar phosphate bonds Purine pyrimidine How is DNA Copied o How do you make exact copies o What does the structure of DNA tell you about how to copy it o Replication The parent molecule s strands separate New molecules are added to each piece forming daughter DNA molecules each consisting of one parental strand and one new strand Begins at many origins could be thousands Strands must separate and unwind Helicase untwists at replication fork SSB proteins keeps DNA from re pairing causes strain and tither winding further down strand and topoisomerases relieves strain by breaking swiveling and rejoining DNA strands Add primer RNA chain Synthesized by primase Uses DNA as template Replication DNA polymerase add nucleotides to a preexisting chain Fuse sections fragments of lagging Okazaki fragments DNA ligase New sections built 5 3 and anti parallel What happens if the wrong base is added Proofreading Where does the energy come from From nucleotides themselves before added have three phosphate groups when joined release two phosphate groups releasing energy Why does DNA polymerase only build 5 to 3 It must be important Be able to proofread and nucleotides bring energy Can errors in DNA be repaired after replication Yes nuclease takes it polymerase replaces it and ligase glues it all together o Semi conservative Central Dogma Because the new molecule is a piece of the original DNA and a piece of new backbone o Flow of information within a cell o The flow is largely in one direction DNA DNA replication DNA RNA transcription RNA protein translation RNA DNA reverse transcription retroviruses RNA o Differs from DNA in that Ribose sugar Single stranded Uracil instead of thymine A U C G o Types of RNA Messenger RNA mRNA Transcribed from DNA true for all RNAs Contains the code to build one polypeptide chain Specific Contains exons and codons mRNA nucleotide triplets Specifies the amino acid sequence for a protein Ribosomal RNA rRNA Is the most abundant form of RNA Is a component of ribosomes Transfer RNA tRNA Contains an anticodon base pairs with complementary mRNA sequence at one end of tRNA Has amino acids covalently attached Transcription o RNA polymerase binds to the promoter site TATA box not the strand to be coded o RNA polymerase builds the new strand 5 to 3 with complementary RNA nucleotides o Anti parallel o When RNA polymerase reaches the termination sequence it leaves the DNA and so does the RNA Prokaryotes vs Eukaryotes o Eukaryotes mRNA produced during transcription must be processed prior to translation 3 types of RNA polymerase RNA processing o Capping o Poly A tail pull several hundred adenines in a row o Editing how our genes are structured Editing by reducing and rearranging information Exons final message Introns removed final message is just exons with a cap and a tail Genetic Code o mRNA nucleotides o Triplets codons o Degenerate code Translation o Occurs in the cytoplasm at a ribosome o mRNA to polypeptide nucleotide sequence to amino acid sequence o Steps to Translation Small subunit binds to 5 end of RNA Initiation Moves to start codon AUG tRNA binds and then large subunit Chain elongation Ribosomes binds 2 tRNA molecules o A site o P site o E site Moves 3 nucleotides at a time Termination Reach stop codon Insert releasing factor o Ribosome breaks apart o Polypeptide released Bacterial Genome Organization o Singular circular chromosome o Naked DNA o No introns o Located in the cytoplasm o Plasmids Separate from chromosome Not necessary for survival Do the differences in organization lead to functional differences o Transcription and translation can occur simultaneously o Easy for prokaryotes to take up foreign DNA transformation Gene Regulation o Why regulate Energetics Control Bacterial Operon o Only exists in prokaryotic cells o Promoter o Operator o Structural genes o Regulator produces repressor Wants to attach to the operator Prevents polymerase from transcribing structural genes o Repressible operon Trp operon o Inducible operon Repressor produced in an inactive form Binds with co repressor Complex blocks transcription Lac operon Repressor produced in an active form Blocks transcription Binds with inducer Repressor inducer complex inactive Positive Gene Regulation o cAMP o cAMP Receptor Protein CRP Eukaryotic Gene Regulation o Genome structure genes DNA and chromosomes Complete genome DNA sequence known Exact AGCT base order is known Humans chimps flies worms and plants Genes are known Functions are being determined Human genome Genes are at set positions on the chromosomes o 5000 expressed in each cell type o 1000 housekeeping genes o Prokaryotic gene regulation occurs at the level of transcription o Eukaryotic gene regulation occurs at many levels o Levels of regulation Chromosomal DNA packing DNA Methylation Gene Amplification Transcriptional Promoters enhancers Regulatory proteins Increase rate of transcription of single gene Post transcriptional mRNA processing make many proteins but one gene mRNA degradation message degrades and breaks apart Translational Regulatory proteins Post translational Cleavage and modification Transport and degradation o In a repressible operon the repressor protein is made in an inactive form and does not bind to the operator preventing transcription Cell Cycle o The life of a cell o G1 gap one DNA remains unreplicated o S synthesis of DNA o G2 gap two o Cell division mitosis or meiosis o Interphase G1 S and G2 After twice as much DNA DNA replicated Chromosomes remain replicated through this stage Chromosome structure o DNA and histones o During interphase relaxed extended o During cell division supercoiled condensed o Chromosomes can be unreplicated 1 molecule of DNA o Chromosomes can be replicated 2 identical molecules of DNA held together A cell in G2 of interphase will have how much DNA compared to that same cell when it
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