UIUC MCB 150 FINAL STUDY GUIDE Cytoskeleton The Cytoskeleton is a dense and complex network of fibers Provides structural support It moves and changes to alter to cell s shape shift contents and even move the cell itself Actin Filaments Aka microfilaments cytoskeleton w smallest diameter Made of globular protein actin In animal cells actin most abundant two long strands that coil around each other formed through noncovalent bonding between actin subunits Polar Two distinct ends and ends grows faster than structural support and Movement Depends on protein myosin motor protein protein that converts the potential energy in ATP in KE of mechanical work rigor mortis the nucleobinding site is empty ATP Powered interaction between actin and myosin is the basis for an array of cell movements cytokinesis cell moving is the process of cell division In animals this occurs by the use of actin filaments connected to the plasma membrane and arranged in ring around the cell Myosin causes the filaments to slide past one another Cytoplasmic streaming directed flow of cytosol and organelles within plant cells Actin filaments powered by myosin ex Material transport cell crawling actin filaments grow causes plasma membrane to extend and move the cell Intermediate filaments not polar each end identical not involved in movement Only play structural role ex Keratin hair skin ex nuclear lamins form dense mesh under nuclear envelope they help give the cell is shape they also anchor chromosomes they also break up and reassemble the nuclear envelope when cells divide Microtubules The largest cytoskeletal component in terms of diameter consists of two polypeptides a tublin and b tublin exist as stable protein DIMERS a tublins minus end and b tublins plus end grow faster at their plus ends MTOC microtubule organizing center plus ends grow outward plants cells have hundreds of sites where microtubules are growing most animal fungal cells have only ONE site near the nucleus In ANIMALS MTOC has distinct structure called a centrosome contains two bundles of microtubules called centrioles In function microtubules similar to actin filaments provide stability and are involved in movement Microtubules are best known for role in separating chromosomes during mitosis and meiosis kinesin converts the chemical energy in ATP into mechanical energy in form of movement the protein moves along microtubules in a directional manner toward the plus end kinesin has a head with two globular pieces a tail associated with small polypeptides and stalk that connects the head and tail Bacterial flagella are helical rods made of protein called flagellin eukaryotic flagella consist of several microtubules constructed from tubulin dimers bacterial flagella move by rotating rod like propeller eukaryotic flagella move by undulating whip back and forth eukaryotic flagella surrounded by the plasma membrane and are considered organelles bacterial flagella are not flagella much longer than cilia 9 2 structure is called the axoneme axle thread originate from basal body dynein is a motor protein like myosin and kinesin that uses ATP to undergo conformational changes These shape changes move dynein along microtubules toward the MINUS end IF the dynein arms on just one side of the axoneme are activated then the localized movement results in bending Bending of cilia or flagella causes swimming To use lactose E coli must first transport the sugar into the cell Once Lactose is inside the cell the enzyme b galactosidase catalyzes a reaction that breaks down the disaccharide into glucose and galactose Lactose is an inducer small molecule that triggers transcription of a specific gene Transcriptional control when regulatory proteins affect RNA polymerase s ability to bind to a promoter and initiate transcription Slow but efficient in resource use Why Because it stops the process of gene expression at the earliest possible point Translational control When regulatory molecules alter the length of time an mRNA survives or affect translation initiation or elongation Post Translational control Proteins need to be activated by chemical modification Example addition of a phosphate Fast but Energetically Expensive Why Because only one step needed to activate an existing protein Three Types of Lactose Metabolism Mutant in E Coli 1 LacZ Cannot provide B galactoside which breaks down lactose 2 LacY Cannot provide galactoside permease to import lactose 3 LacI Cannot provide repressor continually making B galactoside Negative Control The repressor is the parking brake lactose releases the break when repressor binds to DNA and shuts down transcription The lacI gene produces a repressor protein that exerts negative control over lacZ and lacY gene transcription Lactose acts as an inducer by causing the repressor to release from DNA and end negative control Positive Control regulatory protein called an activator binds to DNA and triggers transcription WITHOUT positive control no or low levels of transcription Lactose is absent repressor present Repressor bound to operator blocks transcription and cannot be removed without lactose Lactose Present Repressor Present Lactose binds to Repressor Repressor releases from DNA Transcription occurs Lactose present repressor absent mutant LacI gene Transcription Occurs Jacob Monod Model of Lac Operon Regulation 1 The LacZ LacY and LacA genes are adjacent and are transcribed into one mRNA initiated from the single promoter of the lac operon AKA cotranscription 2 LacI makes Repressor which binds to DNA and prevents transcription 3 Lactose binds to repressor which causes repressor to release leads to transcription This is known as allosteric regulation When both Glucose and Lactose are present in the environment transport of lactose into cell inhibited This is known as Inducer Exclusion This means the repressor remains bound to DNA and no transcription occurs When glucose levels are low galactoside permease is active which transports lactose into the cell and induces lac operon expression Steps in Mitosis M phase Mitosis nuclear division and Cytokinesis condense chromosomes limit the risk of breaking them when you separate them cytoskeleton reorganizes to form mitotic spindle to send out microtubules to grab onto sister chromatids and facilitate separation nuclear envelope disappears chromosomes move to opposite poles reformation of nuclear envelope cytokinesis Mitosis Interphase two centrosomes in cells centrosomes replicate two