MOLECULAR BIOLOGY: RELICATION, TRANSCITION, AND TRANSLATION Honors Biology 0 IMORTANT EXERIMENTS Frederick Griffith Described a transforming factor that could be transferred into a bacterial cell rocess is called transformation Hershey-Chase IMORTANT EXERIMENTS Head Tail Tail fiber Used bacteriophages to show that is the genetic material hages were labeled with radioactive sulfur (labels proteins) and radioactive phosphorus (labels ) Radioactive hage protein Bacterium Batch Radioactive protein Mix radioactively Agitate in a blender to labeled phages with separate phages bacteria. The phages outside the bacteria infect the bacterial cells. from the cells and their contents. Empty protein shell hage Centrifuge Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. Radioactivity in liquid ellet 4 Measure the radioactivity in the pellet and the liquid. Sulfur-labeled protein stayed outside the cell Batch Radioactive Radioactive Centrifuge ellet Radioactivity in pellet hosphorus-labeled was inside the cell
Monomer of and is called a nucleotide NUCLEOTIDES hosphate group Nitrogenous base Sugar Sugar-phosphate backbone Contains three parts: nitrogenous base, 5-carbon sugar, and phosphate group nucleotide hosphate group Nitrogenous base (A, G, C, or T) Thymine (T) and are called polynucleotides Sugar (deoxyribose) Composed of a sugarphosphate backbone polynucleotide nucleotide Nitrogenous bases point inward Four bases: thymine, cytosine, adenine, and guanine Thymine (T) Cytosine (C) yrimidines Adenine (A) Guanine (G) urines 4 WATSON AND CRICK Credited with discovering the structure of Really took ideas from others and were the first to publish Took X-ray crystallography data from Rosalind Franklin without her knowledge 5 Composed of two polynucleotide chains joined together by hydrogen bonds between bases STRUCTURE Base pair Hydrogen bond A pairs with T, forming two hydrogen bonds Ribbon model artial chemical structure Computer model G pairs with C, forming three hydrogen bonds Twisted as a helical shape Twist 6
RELICATION Semiconservative model Two strands separate Each strand is used as a pattern to produce a complimentary strand Each new helix has one old strand and one new strand arental molecule of Nucleotides Both parental strands serve as templates Two identical daughter molecules of 7 RELICATION Replication occurs in the 5 direction Origin of replication arental strand Daughter strand Leading strand = continuous replication Bubble Lagging strand = segmented replication Two daughter molecules Enzymes important for replication helicase binds to unwind the polymerase adds new base pairs end 4!!! end!! 4! arental polymerase molecule Daughter strand synthesized continuously Daughter strand synthesized in pieces ligase joins fragments together end end ligase Overall direction of replication 8 FROM TO ROTEIN Gene sequence of directs for the synthesis of a protein is transcribed into Transcription Nucleus Cytoplasm Translation rotein strand Transcription is translated into protein Translation Codon olypeptide Amino acid 9
Codons - three nucleotide sequences that correspond to a particular amino acid GENETIC CODE Second base 6 codons code for an amino acid (more than one codon can code for an amino acid) AUG - start codon (codes for the amino acid methionine) First base Third base Three stop codons (UAA, UAG, and UGA) 0 TRANSCRITION strands separate One strand is used as a patter to produce Important change: In thymine (T) is not used; uracil (U) is used instead. polymerase Direction of transcription Newly made nucleotides Template strand of polymerase is the enzyme that complete transcription Three stages: Initiation: polymerase binds to a promoter to unwind the helix Elongation: nucleotides are added to the chain Termination: polymerase reaches a terminator sequence and detaches polymerase of gene romoter Terminator Initiation Area shown in Figure 0.9A Elongation Growing Termination Completed polymerase ROCESSING Messenger () - contains codons for protein sequences Introns - interrupting segments Exons - coding segments rocessing Cap added to the 5 end (guanine nucleotides) Tail added to the end (oly-a tail - 50-50 adenines) Splicing - removal of introns and joining of exons transcript with cap and tail Cap Exon Intron Exon Intron Exon Transcription Addition of cap and tail Coding sequence Introns removed Exons spliced together Nucleus Tail Cytoplasm
TRANSLATION Amino acid attachment site Transfer (t) - match amino acids with the codon Each t carries a specific amino acid Anticodon allows t to bind to the complimentary codon on (A pairs with U; G pairs with C) polynucleotide chain Anticodon Hydrogen bond TRANSLATION Initiator t Met site Met Large ribosomal subunit A site Occurs at the ribosome (r) in the cytoplasm Start codon Small ribosomal subunit Three stages: olypeptide Amino acid Initiation: binds to ribosome and first t at the start codon ( site) site Codons A site Anticodon Codon recognition Elongation: next t binds to at the A site and the two amino acids are joined as the ribosomes moves the molecules over to the next site Termination: stop codon is reached, all of the components are released movement Translocation Stop codon New peptide bond eptide bond formation 4 OVERVIEW OF TRANSCRITION AND TRANSLATION Transcription Amino acid polymerase Translation Enzyme is transcribed from a template. Each amino acid attaches to its proper t with the help of a specific enzyme and AT. Growing polypeptide Codons New peptide bond forming 4 Elongation A succession of ts add their amino acids to the polypeptide chain as the is moved through the ribosome, one codon at a time. t AT olypeptide Anticodon Initiator t Start Codon Large ribosomal subunit Small ribosomal subunit Initiation of polypeptide synthesis The, the first t, and the ribosomal sub-units come together. Stop codon 5 Termination The ribosome recognizes a stop codon. The polypeptide is terminated and released. 5
MUTATIONS Mutation - change in nucleotide sequence Base substitutions: replacement of one nucleotide with another Could have no effect or would effect only one amino acid Deletions or insertions Can alter the reading frame and thus have significant impacts downstream Can be spontaneous (due to errors in replication or recombination) or induced by mutagens (radiation or chemicals) Substitutions Normal hemoglobin Mutant hemoglobin Normal hemoglobin Sickle-cell hemoglobin Glu Val Insertions or Deletions Normal gene rotein Met Lys he Gly Ala Base substitution Met Lys he Ser Ala Base deletion Missing Met Lys Leu Ala His 6 MICROBIAL GENETICS: VIRUSES Two types of reproductive cycles: Lytic: viral particles are produced using host cell components and the host cell dies when the viruses are released Cell lyses, releasing phages 4 hages assemble hage Attaches to cell Bacterial hage chromosome hage injects 7 Lytic cycle Lysogenic cycle hage rophage circularizes 5 OR Many cell divisions Lysogenic bacterium reproduces normally, replicating the prophage at each cell division 6 Lysogenic: viral is inserted into the host by recombination New phage and proteins are synthesized hage inserts into the bacterial chromosome by recombination 7 ENVELOED VIRUSES Viral (genome) VIRUS Glycoprotein spike rotein coat Membranous envelope lasma membrane of host cell Entry Viral (genome) Uncoating synthesis by viral enzyme 4 rotein 5 synthesis synthesis (other strand) Template New viral proteins 6 Assembly New viral genome 7 Exit 8
RETROVIRUSES HIV (human immunodeficiency virus) Envelope Glycoprotein rotein coat (two identical strands) Reverse transcriptase Contains two copies of its genome and an enzyme, reverse transcriptase, which can produce from an template Viral strand Doublestranded Viral and proteins 6 5 CYTOLASM NUCLEUS Chromosomal 4 rovirus 9 VIROIDS AND RIONS Viroid - circular that infects plants rions - infectious proteins that cause nervous system disorders in animals Misfolded forms of normal proteins that can convert other proteins 0 BACTERIA Three ways they transfer Transformation - uptake of from the environment Transduction - gene transfer through bacteriophages Fragment of from another bacterial cell enters cell Bacterial chromosome () Transduction Mating bridge Transformation hage Fragment of from another bacterial cell (former phage host) Conjugation - transfer of from a donor to a recipient through a cytoplasmic bridge Sex pili Donor cell ( male ) Recipient cell ( female ) Conjugation
LASMIDS F factor (plasmid) Male (donor) cell Bacterial chromosome F factor starts replication and transfer Small circular molecules that are separate from the bacterial chromosome lasmid completes transfer and circularizes Cell now male