UIUC MCB 150 FINAL STUDY GUIDECytoskeletonThe Cytoskeleton is a dense and complex network of fibers. Provides structural support. It movesand 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 DIMERSa-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; bacterialflagella 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. Coli1. 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-galactosideNegative 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 controlPositive Control-regulatory protein called an activator binds to DNA and triggers transcription-WITHOUT positive control, no, or low levels of, transcriptionLactose is absent, repressor present: Repressor bound to operator blocks transcription and cannot be removed without lactoseLactose Present, Repressor Present: Lactose binds to Repressor, Repressor releases from DNA, Transcription occursLactose present, repressor absent(mutant LacI- gene) : Transcription OccursJacob-Monod Model of Lac Operon Regulation1. The LacZ, LacY, and LacA genes are adjacent and are transcribed into one mRNA initiated from the single promoter of the lac operon AKA cotranscription2. 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 regulationWhen 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 MitosisM phase: Mitosis(nuclear division) and Cytokinesis-condense chromosomes, limit the risk of breaking them when you separate