Zoology 101 Exam 3 Review OutlineI. Beyond DNA ReplicationA. Expanding Upon DNA Replication1) Proofreading and Repairinga) Mismatch repairi) Mismatched nucleotides corrected by enzymesb) Bases may be damaged by external forces or may spontaneously changec) Nucleotide excision repairi) Nuclease cuts out damaged sectionii) DNA polymerase and ligase refill gap in nucleotides2) Replicating endsa) 5’ end of Okazaki fragment irreparable and irreplaceableb) Telomeresi) Repeated six-nucleotide sequence DNA capii) Becomes shorter after every round of replicationc) Telomerasei) Catalyzes lengthening of telomeres to restore them to original lengthB. Chromosome Packaging1) DNAa) Sugar-phosphate backbone double helix2) Histonesa) Proteins of 100 amino acidsb) Positive charges bind with negative DNA3) Nucleosomesa) Beads on strings of linker DNAb) N-terminus “histone tail” sticks outward from bead4) 30-nm fibera) Interactions between histone tails and linker DNA5) Looped domains (300-nm fiber)a) Attach to chromosome protein scaffolds with topoisomerase6) Metaphase chromosomea) Specific packingi) Same genes at same locationsC. Chromatin1) DNA & protein complex2) Heterochromatina) Irregular clumps of interphase chromosomeb) More dense, unavailable for transcription3) Euchromatina) Less compact, available for transcriptionII. From Gene to ProteinA. Overview of Transcription and Translation1) Transcriptiona) Synthesis of RNA using DNA template in nucleus2) Translationa) Synthesis of polypeptide using mRNA by ribosome in cytosol3) The Genetic Codea) Codonsi) 3-nucleotide groupsii) Written in 5’ -> 3’ directioniii) mRNA codons identical to non-template DNA triplets (with U replacing T)iv) termination codons stop translationv) initiation codons start translationb) 98-99% of genome is non-coding DNAc) Every cell has all genes, but only expresses someB. Transcription1) Molecular Components of Transcriptiona) RNA polymerasei) Pulls apart DNA & attaches complementary RNA towards 3’ endii) Doesn’t need primerb) Transcription uniti) Stretch of DNA transcribed into RNAc) Terminatori) Termination sequence in bacteria onlyd) Promoteri) DNA sequence where RNA initiates transcriptionii) Includes start point and several nucleotides “upstream”iii) i.e. TATA boxiv) Promoter and RNA polymerase bind facilitated by transcription factors2) Synthesis of RNAa) Initiation and RNA Polymerase Bindingi) Transcription initiation complex- Transcription factors and RNA polymeraseb) Elongation of RNAi) RNA polymerase synthesizes pre-mRNA at 3’ endii) Single gene may be transcribed by multiple polymerases simultaneouslyiii) Proteins detach pre-mRNA from DNAiv) Double helix reformsC. RNA Processing1) Alteration of mRNA endsa) 5’ capb) Poly-A tailc) Facilitate export of mRNA from nucleusd) Protect from degradation and provide stability2) RNA Splicinga) Intronsi) Noncoding segments of RNAb) Exonsi) Coding segments of RNAc) Small nuclear ribonucleoproteins (snRNPs)i) Recognize splicing sitesii) Made of snRNAs and proteinsiii) snRNPs and proteins form spliceosomes- cut out introns and join exonsd) importance of intronsi) alternative RNA splicingii) one gene can encode multiple polypeptidesiii) domain- discrete functional regions of proteinsiv) exon shuffling- introns increase likelihood of crossing over3) Ribozymesa) RNA molecules that function as enzymesb) Single-strandedc) Can form H-bonds with other nucleic acid moleculesD. Translation1) Molecular Components of Translationa) tRNAi) complementary tRNA attaches to mRNAii) tRNA deposits amino acid, which ribosome joins into chainiii) shaped like a lowercase tiv) aminoacyl-tRNA synthetases match tRNA and amino acidv) wobble- flexible base-pairing at third codon positionb) ribosomesi) made of 2 subunits of proteins and at least one rRNA moleculeii) P-site- Holds tRNA carrying polypeptide chainiii) A-site- Holds “on deck” tRNAiv) E-site- Exit site for discharged tRNAs2) Building a Polypeptidea) Ribosome Association and Initiation of Translationi) Ribosomal subunit binds to initiator tRNAii) Subunit scans 5’ -> 3’ until tRNA H-bonds with start codoniii) Translation initiation complexiv) Initiation factorsb) Elongation of Polypeptide Chaini) Elongation factorsii) Codons recognized at A-site (energy expended)iii) rRNA catalyzes formation of peptide bond between amino and carboxyl groups of neighboring amino acidsiv) ribosome moves tRNA through sites (energy expended)c) Termination of Translationi) Release factor- Protein that inhabits A-site following stop codon- Prevents other tRNA from entering ribosomeii) Ribosomal units dissociate3) Completing Function Proteinsa) Post-Translational Modificationsi) Chemical modificationsii) Enzymatic cleavage of polypeptide chainiii) Removal of amino acids from leading chainb) Targeting Polypeptidesi) Signal peptide- “ZIP code” moleculeii) Signal-recognition particle (SRP)E. Mutations Affect Protein Structure and Function1) Substitutionsa) Nucleotide-pair substitutionsi) Replacement of one pair with anotherb) Missense mutationsi) Substitute one amino acid for anotherc) Nonsense mutationsi) Substitute amino acid for another which results in formation of a stop codond) Point mutationsi) Affect single nucleotide pair2) Insertions and Deletionsa) Frame shift mutationsi) Inserts or deletes nucleotides in a number that is not a multiple of 3ii) Results in misreading of entire nucleotide sequence3) Mutagensa) Agents that mutate DNAb) i.e. X-rays, carcinogens, UV lightIII. The Cell CycleA. Cell Division Overview1) Organization of Genetic Materiala) Genomeb) Chromosomesi) Contain DNA molecules and proteins- Each DNA molecule has many genesc) Types of cellsi) Somatic cells- Diploid- Bodily cellsii) Gametes- Haploid- Reproductive cells2) Distribution of Chromosomes During Cell Divisiona) Sister chromatidsi) Joined copies of one chromosomeii) Cohesions- Protein complexes that bind sister chromatidsiii) Centromere- DNA sequences that bind sister chromatids together at closest pointB. Mitotic Phase and Interphase Within Cell Cycle1) Phases of Cell Cyclea) Mitotic (M) phaseb) Interphasei) 90% of cell cycleii) G1 phase- Cell growthiii) S phase- Synthesis- Copying of chromosomesiv) G2 phase- Nuclear envelope encloses nucleus- Centrosomes duplicate- Growth and preparation for cell division2) Exploring Mitosis in an Animal Cella) Prophasei) Chromatin fibers condenseii) Centrosomes move away from each other and begin to form mitotic
View Full Document
Unlocking...