Cell Biology Flashcards

Question

How would you halt the G1 to S phase? Why does this happen? What does p53 do? How would you halt the G2 to M phase? How would you halt the M to G1 phase?

Answer 1

S-Cdk already formed- so inhibit with p27/p21 proteins to form inactivated p27-cyclin-Cdk complex damaged DNA means protein kinases activate p53 by phosphorylation (tumour suppressor/protoncogene) stimulates transcription p21 gene and induces DNA repair & sometimes activates programmed cell death M-Cdk already assembled- so kinase phosphorylates Cdk enzyme at its inhibitory site Cyclin is degraded with ubiquitylation (adding protein tag) & then destruction in proteosome

Answer 2

1. in G1 origin recognition complex ORC assembled on the origin of replication on the DNA 2. DNA helicase binds so Cdc6 dissociates 3. prereplicative complex preRC is inactive, but is activated when S-Cdk activity is high at end of G1 4. S-Cdk activates helicase, pre-RC & DNA polymerase because it dissociates Cdc6 it prevents re-replication

Answer 3

1. in G1 origin recognition complex ORC assembled on the origin of replication on the DNA 2. DNA helicase binds so Cdc6 dissociates 3. prereplicative complex preRC is inactive, but is activated when S-Cdk activity is high at end of G1 4. S-Cdk activates helicase, pre-RC & DNA polymerase because it dissociates Cdc6 it prevents re-replication

Answer 4

Tie 2 adjacent sister chromatids in each duplicated chromosome- forms large protein rings to prevent chromatids coming apart coil each sister chromatid/DNA double helix into smaller & compact structures- so more easily segregated in mitosis 2 sister chromatids with centromere Microtubules- to separate duplicated chromosomes via pulling chromatids apart as spindles Contractile rings- actin & myosin filaments that form around the spindles for division Microtubules but not contractile rings

Answer 5

1. Microtubules nucleate from centrosomes 2. In interphase (animals G1 S G2) centriole pair in centrosome associate with the centrosome matrix so microtubules grow out 3. Centrosome duplicates at same time as DNA rep in S phase by S-Cdks 4. Early M phase- centrosome starts divide & nucleate own aster microtubules 5. Centrosomes move apart & form bipolar mitotic spindles with aster at each pole 6. Mitotic spindle waits for breakdown of nuclear envelope & then when it does break down- spindle microtubles interact with chromosome

Answer 6

1. Chromosomes condense, mitotic spindles assemble between 2 centrosomes & chromosomes have duplicated and start to move apart 2. Breakdown nuclear envelope so chromosomes attach to spindle microtubules via their kinetochores & move 3. Chromosomes align equator of spindle between spindle poles & kinetochore of each sister chromatid attach to opposite poles of spindle 4. chromatids pulled opposite spindle poles = segregation of chromosomes, kinetochores of microtubules get shorter & spindle poles move apart 5. 2 sets chromosomes arrive poles of spindle & nuclear envelope builds around each set. contractile ring for cytokinesis forms 6. cytoplasm divides in 2- separation of cytosome & daughter cells where the division is due to contractile ring of actin & myosin perpendicular to spindle

Answer 7

+ve aster microtubules, kinetochore microtubules, interpolar (binds to motor proteins)

Answer 8

1. Separase (proteolytic) is inactivated by securin inhibitory protein 2. APC degrades cohesin when chromosomes aligned properly in metaphase 3. Separase's activation means cohesin complex/rings degraded to allow separation chromatids in anaphase (stops this occurring prematurely) Kinetochore microtubules depolarise while attached to chromosomes- shortening & pulling them to opposite poles. loss tubulin subunits on kinetochore microtubules interpolar microtubules slide part eachother & pull poles apart by kinesins dyneins pull poles outwards towards cell cortex

Answer 9

Phosphorylation of nuclear pore proteins & lamin = triggers disassembly of nuclear envelope into small vesicles dephosphorylation of nuclear pore proteins & lamin = vesicles come together around chromosome & reassemble envelope contractile rings (only in animals) cell wall 1. new cell wall forms inside equator of old spindle after telophase (chromosome segregation) 2. interpolar microtubules of spindle form a phragmoplast & golgi-derived vesicles fuse at equator (filled with cell wall materials) to form growing cell wall towards cell wall perpendicularly 3. pre-existing plasma membrane & the membrane surrounding the new cell wall fuse to separate the 2 daughter cells

Answer 10

``` hydrophobic & negative charge polar positive positive positive & 3 AA long ``` gated transport

Answer 11

1. Cargo protein interacts with importers in cytosol with nuclear localisation signal & complex can move in/out pores 2. Complex diffuses into nucleus & interaction of complex disrupted by binding ran-GTP to importer 3. Ran-GTP displaces cargo = release cargo & Ran-GTP free to move in/out pore 4. Ran-GTP enters cytosol- causes conversion to Ran-GDP releasing importer from Ran-GTP so it's free to bind to cargo 1. Ran-GTP binds to exporter allows complex move with nuclear export signal so can diffuse in/out cytoplasm 2. In cytosol: Ran-GTP converted Ran-GDP = disruption & release of cargo 3. Exporter free in cytoplasm diffuse back into nucleus GAP (GTP-ase activating protein) found exclusively in cytoplasm GEF(Guanine nucleotide exchange factor) found in nucleus & bound to chromatin nuclear localisation signal nuclear export signal

Answer 12

Proteins synthesised on free ribosomes in cytoplasm are translocated into mitochondria & peroxisomes with protein channels/transporters Post-translational Travels into ER lumen- co-translational translocation TOM complex- outer membrane Pre-sequence, hydrophobic or beta barrel TIM23 complex in inner membrane & then matrix Electrochemical gradient in inner membrane (+ intermembrane space - matrix from electron transfer chain), activity of TIM chaperones (help proteins fold & pull them into matrix)

Answer 13

Membrane proteins & lipids transport from one cell/organelle to another, mediated by cytoskeleton elements & motor proteins ER to golgi Golgi to plasma membrane/lyosomes/endomes mRNA encoding cytosilic protein is free in cytosol- ribosomal subunits assemble to synthesise the polyribosome from the protein's sequence. If the terminus of mRNA has ER signal sequence (binds to ER membrane) & the ribosome & proteins are recruited to ER & protein is co-translated into the lumen SRP (signal recognition particle) protein SRP binds to ribosome to form complex- which then allows binding to the SRP receptor protein on the RER membrane so nasant protein is translocated with translocators on RER SRP dissociates to be recycled in the RER (its N terminus)- in translation. Mitochondria is during translocation

Answer 14

Chaperones Enter cytosol from ER lumen via an ER protein translocation (sec61 complex). Protein is tagged with ubiquitin (signal for degradation) & will then be degraded in proteasome Multi enzyme complex with lots proteases & peptides Blue sugar tag from ER

Answer 15

Identify the paths that proteins take in the cell Secretory cells e.g from pancreas Label leucine 3H for 3 mins & wash with cold leucine 3 min in ER, 20 mins golgi, 87 mins plasma membrane & vesicles 1. EM autoradiography: image of radioactively labelled proteins 2. Cell fractionation: homogenisation & centrifugation & put supernatant on sucrose gradient allowing separation of organelles by density

Answer 16

1. Vesicles build from ER facing the golgi containing secretory proteins & KDEL receptor 2. Vesicles gain COPII coat 3. Vesicle pinches. off & transported to vesicular tubular cluster 4. Coat removed & vesicle fuses with vesicular tubular structure to release secretory proteins its lumen & present receptor onto membrane 5. both proteins transported to golgi & golgi stacks (orientation of receptor same) 1. Vesicles builds from golgi containing the proteins & gain COPI coat 2. Fuse with vesicular tubular cluster where coat is removed 3. Then fuses with ER KDEL receptor- can bring proteins back to ER

Answer 17

Subunits of COPII coat & their assembly mends the membrane outwards. Exit signals on cargo receptors are packaged into transport vesicles when coat assembles Exit signal, receptor and soluble cargo protein ``` Coat disassembles. V snares (in transmembrane vesicle) and t snares (on target) need to be correctly matched ``` GTP-ase (GAP) of Rab-GTP into Rab-GDP causing change of snare proteins & brings vesicle close to target membrane = fusion disassembled & recycled- v snares need return to ER to be packaged back into vesicles fusion, coat assembly, vesicle budding, transport & cytoskeleton elements

Answer 18

Protein & lipid modifications with glycosylation (covalent addition of sugar group) Golgi apparatus to plasma membrane 1. Constitutive (in all cells & causes secretion proteins destined for extracellular matrix) 2. Regulated (specific cells, not all time & secretion neurotransmitters from synapse to respond to action potential) GTPase (GAP) & snare proteins docking & fusion

Answer 19

Transporting material from outside cell to endosomes & lysosomes binding of LDL to LDL receptors on plasma membrane 1. forms a pit & coat is assembled to form vesicle containing receptor & LDL 2. vesicle then uncoats & fuses with endosome 3. receptor is packed into vesicles & transported back to the membrane 4. LDL is transported from endosome to lysosome containing lots hydrolytic enzymes at low pH 5. LDL is degraded by enzymes into free cholesterol- released into cytosol & recycled causes heart disease- mutations in the gene required in endocytosis can cause conditions increase uptake of LDL to reduce the amt of LDL circulating coat that covers endocytotic vesicles- requires dynamin (type of GTPase) to pinch vesicle off requires an enzyme