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BIOL 1090

Cytoskeleton ● dynamic network of interconnected filaments and tubules that extend throughout the cytosol in eukaryotes Functions ● structural support ● intracellular transport ● contractility and motility ● spatial organization within cell Components ● actin microfilaments ● intermediate filaments ● microtubules Microtubules ● LARGEST cytoskeletal element (25nm) ● a polymer of proteins ○ alpha tubulin and beta tubulin ● 2 types ○ AXONEMAL ■ organized and stable ■ axoneme involved in cell movement ○ CYTOPLASMIC ■ loose, dynamic ■ in the cytosol ● STRUCTURE ○ a/b heterodimers form long protofilaments ■ 13 of these protofilaments form a hollow cylinder longitudinally ○ heterodimers aligned in same direction ■ HEAD TO TAIL= structural polarity ● important for growth/shrinkage ● direction of movement of material along MT ● STRUCTURAL POLARITY ○ plus end grows fast ○ minus end grows slow ● UNDERGOASSEMBLY/DISASSEMBLY ○ within the cell,, this leads to rapid turnover of most MT: DYNAMIC INSTABILITY ○ shrinkage may occur rapidly at the plus end: CATASTROPHE ○ formation is controlled, central site of assembly: ■ microtubule organizing center (MTOC) ● CENTROSOME ○ major site of microtubule organization ● MICROTUBULEASSOCIATED PROTEINS (MAPs) ○ several different proteins bind microtubules ○ they mediate assembly and function ○ also mediate interaction with other cell structures ○ help stabilize or stimulate assembly ○ 2 TYPES OF MAPS ■ NON MOTOR ● control organization in cytosol ■ MOTOR ● kinesin : plus ended directed ● Dynein: minus end directed ● useATP to generate force ● moves material along microtubule track ● generates sliding force between MTs Intermediate Filaments ● MIDDLE: 10-12nm ● ONLY in multicellular animals ● structural support, mechanical strength ● most stable cytoskeleton ● are fibrous proteins ○ contain alpha helical domain ● 5 CLASSES ○ keratins ○ neurofilaments ○ lamins ● STRUCTURE ○ alpha helical domain wraps around each other to make rope like dimer ○ IF DIMER IS POLAR ■ monomer aligned parallel with diff n- and c- terminus Microfilaments ● SMALLEST:8nm ● a polymer of actin protein ● polypeptide: 42 kDa, bindsATP ○ individual molecules: G-actin which are globular ○ polymerized microfilament : F-actin ● FUNCTION ○ maintenance of cell shape ○ cell movement ○ cytokinesis ○ muscle contractions ● F-actin ○ g actin monomers are polar ○ monomers are incorporated into filaments in the same orientation ○ polar, has plus and minus ends ○ assembly ■ G actin polymerizes reversible ■ nucleation (slow) ● g-actin>dimers>trimers>short filaments ■ elongation (fast) ● monomers add to both ends ● faster at + ends ○ filaments can be loose arrays/ networks or tight bundles ● Ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) are both polymers ● nucleic acids- macromolecules composed of repeating subunits called nucleotides ● nucleotides have three parts” ○ a phosphate group ○ a pentose (ribose/ 2-deoxyribose,has no hyroxyl) ○ nitrocyclic base DNA ● four nucleotides ○ pyrimidines ■ TC ○ Purines ■ AG ● pyrimidines/purines: connected by phosphodiester bonds ● double stranded ○ strands are antiparallel ○ held together by H bonds ■ between bases ■ mediates base pairing (pyrimidine and purine group to form double helix) ○ hydrophobic interactions ■ between stacked bases ○ strands are polar ■ 5’end: free phosphate group ■ 3’end: free hydroxyl group ○ opposing strands are complementary ■ Ato T, G to C ■ reverse compliment, reverse whole thing ■ when T changed to U, dna>rna ● double helical structure ● right handed ● Most common form of dna- B-DNA ○ has major groove, minor groove ■ both important for protein binding CHROMOSOMES of eukaryotes are composed of proteins, dna and rna 1) first level condensation, packaging DNAinto nucleosomes (11nm) ● dna wrapped around nucleosome core of 8 histone proteins, ● anchored by 9th histone (H1) 2) addition folding, supercoiling of 11nmfiber to create 30nm fiber ● driven by nucleosomal interactions ● called solenoid, or zig zag models ● 30nm fiber= basic structural unit of metaphase chromosome (most condensed form!) 3) Third level condensation ● 30 nmfiber attached to non-histone protein scaffold Chromosome ends are protected by telomeres ● resist degradation by DNases ● prevent fusion of chromosomal ends ● mediate replication of linear DNAends Centromeres (center of chromosome) ● provide a place for mitotic spindles to attach to chromosomes GENETIC MATERIAL Replication: genetic material must accurately store and transmit information from parents to offspring GENOTYPIC FUNCTION Expression: genetic material controls the development of organism: PHENOTYPIC FUNCTION: physical appearance Mutation:genetic material must go through changes to produce variation for evolution/adaptation Griffith- Transforming principle ● used two strains of a disease to infect mice ○ type IIIS: bad ○ type IIR: not so bad ● bacteria from IIIS killed by heat, remains added to IIR ○ neither alone harmed mice, combi killed host ○ genetic material therefore, could be transferred between cells SIA& DAWSON ● conducted griffiths experiment in vitro, mice not element of transformation Avery Mcleod Mccarty ● added DNase, Rnase and Protease to different samples of IIR ○ DNase led to no colonies forming Hershey Chase ● conducted experiment on t2 phage ● labeled DNAwithradioactive phosphorus32, ○ infected phages into E coli ○ DNAtransfers into cytoplasm ● labeled phages withradioactive sulfur ○ infected into E coli ○ put into centrifuge ■ radioactive tracer in protein shell, not bacteria FRAENKEL CONRAT ● reconstituted a tobacco mosaic virus to have the protein coat of a diff. pheno. ○ infected host withthis ● progeny showed protein coat coded withoriginal RNA DOGMA OF MOLECULAR BIOLOGY: ● genetic info stored in DNAtransferred to RNAduring transcription and to proteins during translation RNA ● Messenger RNA(mRNA) ○ synthesized from gene segment of DNA ○ carries code into cytoplasm ■ protein synthesis occurs here ● Ribosomal RNA(rRNA) ○ rRNAand protein combine to make ribosomes ○ ribosomes carries enzymes necessary for protein synthesis ● Transfer RNA(tRNA) ○ reads the code, carries amino acid to be incorporated into developing protein ● small nuclear RNA(snRNA) ○ found in nucleus ○ spices RNA ○ maintenance of telomeres ○ guide chemical modifications of rRNA DNA ● double helix unwinds during transcription ● dna sequences put the RNA polymerase to start transcription at beginning of a gene,
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