Possible Q's To Look Out For Flashcards
Role of Myosin in Cytokinesis
- Starfish egg incubated with myosin antibody which inhibits cytokinesis
- Mitosis continues in absence of cytokinesis
- Experiment illustrates how you can separate mitosis from cytokinesis. Starfish egg has multiple mitotic events. Done by inhibiting myosin II. won’t progress to cytokines just keeps going through mitotic events.
how to plants assemble a spindle fibre apparatus with the presents of a centrosome?’
- centrosomes are unique to animals, none in plants. Different mechanisum, uses 2 headed motor proetins. Jumble of cspindle fibres but there’s these motor proteins present. M.Tubules have plus and minus end. When the proteins grab them they \d then start moving towards the minus end and as they move they pull the m.Tubules togtheretr like a drawstring. Create the equivalent of a centrosome.Plant cells set up the spindle apparatus without the centrosome.
- SUMMARY: Use 2 headed minus directed motor proteins and associated micro tubules that move towards the minus end and [ ] the minus ends together at the pole of the cell.
Cell Cycle Regulation in Yeast
Two groups of cyclins Cdc2 kinase works with different classes of kinease. The first class of kinase is G1/S that promotes cell to go from G1 to S. Different cyclins can regulate kinase for what it targets, in this case the target is the ORC. Mitotic cyclase, will change the specificity of the enxyme. One target is lamin proteins which help form the nuclear membrane. Memebrane breaks down due to phosphorylation of the lamin. More than one type of cyclin.
3 Regulation of cdks
Cyclin Concentration -Differential transcription of cyclins at stages of cell cycle
Controlled proteolysis -Cyclin concentration regulated by controlled synthesis and degradation -SCF and APC complexes link cyclins to polyubiquitin chain (degradation signal)
Cdk phosphorylation state -Kinases CAK and Wee1 Phosphatase Cdc25
cdk Phosphorylation State
1) cdc2K interacts with mitotic cyclin but remains inactive because phosphorylation of a tyrosine residue Tyr15 by Wee1.
2) CAK trasferì a phosphate to Thr161, needed for cdc2K activity. When cell reaches critical size, Cdc25 phosphatase enzyme active and removes inhibitory phosphate of Tye 15. Cdc2K active so drives cell into mitosis.
3) End of mtiosos. phosphate group removed from Thr161 by a phosphatase. Free cyclin degraded. Cell begins another cycle Cdc2K is effected by 2 kinases CAK and Wee1
Yeast Cell Cycle Mutants
- Wild Type: Cell through G2 grows and gets bigger then M divides into 2
- Wee1- mutant: doesn’t become doubly phosphorylated so skips through and doesn’t grow. Very short G2 so very little time to grow. It divides early.
- Cdc25- mutant: never switches from inactive to active. So continues to grow and will never divide. Turns into a giant cell that will never divide.
Eukaryotic Replication Fork comparison to PROkaryotes
PCNA = sliding clamp RFC = clamp loader (like gamma clamp loader in E.Coli) RPA = SSB proteins
Meselson-Stahl Experiment
Meselson and Stahl found that DNA employs semi-conservative replication. They put the bacteria in an environment with a Nitrogen isotope. They first used N14. The bacteria then integrated this isotope into their DNA. Later they used an environment that contained N15. They then looked at which of the isotopes the bacterial DNA contained. They found that it contained both isotopes of nitrogen, which implies that conservative replication is not the correct conclusion. By having a closer look they could then also rule out disperse replication. Some helix strands were all N14. Other helix strands from the time in the N15 environment had N15.
Semiconservative Replication in Eukaryotes
•experiment where cells transferred from thymidine medium to BRdU and completed 2 rounds of replication. •resulted in one chromatid of each chromosome contains thymidine
descipbe 4 ways that miRNAs are involved with the lblocking of translation. Which structure in the cell does this occur?
Occurs in P Bodies
1) Deadenylation (followed by recapping and degradation)
2) Proteolysis (degradation of nascent peptide)
3) Initiation Block (repressed cap recognition or 60s joining)
4) Elongation Block (slow elongation or ribosome ‘drop -off’
4 alternative actions of Chromatin Remodeling Complex SW1/SNF
- remodelling complex remodel the nucleotide core so that it’s accessible to the RNA pol? -at step some RNApol can’t gain access to TATA because DNA is wound around Nucleosome core.
1) Sliding exposes TATA site
2) Reorganization of histone octamer provides access to promoter
3) Histone variants exchanged for H2A/H2B
4) Histone octamer disassembled
Long Noncoding RNAs as Transcriptional Repressors
- lncRNAs guide protein complexes to specific sites on chromatin
- HOTAir lncRNA transcribed from HOXC locus
- 3’ end of HOTAir interacts with CoREST complex -Demethylates H3 K4 residues
- 5’ end of HOTAir interacts with PRC2 complex -Methylates H3 K27 residues
- Results in transcriptional repression of HOXD locus
the 3 main classes of trasciption factor:
- zinc finger motif
- helix loop motif
- Leucine Zipper Motif
Zinc Finger
largest class of TF -cis and histone form the finger -Zinc ion coordinated between two cysteine and two histidine residues -common to have multiple fingers 1
Helix Loop Motif
- Two alpha helical segments separated by an intervening loop. Domain is often preceded by a stretch of highly basic amino acids whose positively charged side chains contact the DNA and determine sequence specificity of the transcription factor. Always occur as dimers
- 2 helices that form a loop.
- 2 helix proefins dimerizing togehter to form an active TF
- example is MyoD NB for differentiating into muscle cells
- Myogenein is turned on my MyoD -Heterodimerization increases diversity of regulatory factors. -can either be homo or heterodimer
- home = 2 identical proteins dimerizing together
- hetero = 2 die pretiös dimerizing together
- gert’s lots of diversity due to dif things dimerizing together
