Karteikarten
Cell Division
Karten in diesem Stapel (41)
- 1G0 phaseQuiescent (inactive) cells
- 2G1 phaseGap phase
Decides if conditions are correct for cell division - 3S phaseSynthesis / replication of DNA
- 4G2 phaseCheck genetic info has been accurately replicated & is ready to move to mitosis
- 52 decisions of M phaseMitosis - nuclear division
Cytokinesis - cytoplasmic divison - 6What is CDK?Cyclin Dependent Kinases (enzyme)
Family of proteins that control the cell cycle - 7How does CDK work?Works as a heterodimer ∴ enzymatic activity is related to the conc. of cyclin subunit
- 8How is CDK activated?Inactive CDK-cyclin complex forms
Phosphorylated at 2 sites by an inhibitory kinase & an activating kinase BUT remains inactive
Activating phosphatase removes the inhibitory phosphate leaving an active CDK-cyclin complex - 9Activity pattern of mitotic cyclinLow activity in the early stages
High activity in the entry to mitosis - 10Cyclin expression patternCyclin D - coupled with CDK4/6 in G1 phase
Cyclin E - coupled with CDK2
Cyclin A - which substitutes its kinase partner for CDC2 on entry to G2 phase
Cyclin B - CDC2 complex - 11What is the R-point?Most important regulatory stage in the cell cycle
- 12Accumulation & destruction of Cyclin BAt end of mitosis it undergoes ubiquitination - creating a polymer ∴ signalling to the cell to destroy the protein
The cyclin part is then destroyed & the CDK is inactivated - 133-step process of Ubiquitination1. Ubiquitin binds E1 (ubiquitin-activating enzyme)
2. Ubiquitin is transferred to E2 (conjugation enzyme)
3. E2 complexes with E3 (ubiquitin protein ligase).E3 recognises which proteins need to be ubiquintated & catalyses the catalyse of the ubiquitination - 14Structure of a proteasomeComplex of many proteins
Core particle in middle forming a channel, with a regulatory particle on top & bottom - 15What do proteasomes do?Destruction happens here
Proteins in the regulatory particle recognises the ubiquitin & start to cleave it off ∴ it can be res-used & unfold the protein so it can move in an energy dependent manner ∴ can move through the core particle in which it will be chopped into amino acids to be lost out the bottom - 16CDK inhibitorsInhibitors transcription can be induced if conditions are incorrect for cell division
They structurally interfere with & inactivate CDK - 17How is S phase gene expression repressed?Retinoblastoma proteins in unphosphorylated ∴ its active & bound to a transcription factor
- 18What happenes when the cell is ready to divide / move into S phase?CDK inhibitor is inactivated contributing to the activation of CDK which phosphorylated the retinoblastoma protein making it inactive ∴ the transcription factor E2F becomes active & synthesis of S phase genes can occur
- 19What is Cdc6?One of a group of proteins which form a pre-replicative complex
- 20Function of the pre-replicative complexBind an ORC (Origin Recognition Site) - when in this form DNA polymerase can't bind ∴ DNA replication can't start
- 21What happens when the cell moves into S phase?CDK phosphorylates it cdc6 ∴ it falls off the pre-replicative complex & a proper replication fork can be assembled at the origin of replication & DNA synthesis can begin
- 22How is recombination of phosphorylated cdc6 avoided?Degradation by ubiquitin specific pathway
- 23What are the 2 main mech. of response to DNA damage?p53 - involved in directing transcription of CDK inhibitors
Activation of checkpoint specific protein CHK2 which inhibits cdc25 (phosphatase responsible for final step in CDK activation - 24Stages of MitosisProphase
↓
Pro-metaphase
↓
Metaphase
↓
Anaphase
↓
Telophase
↓
Cytokinesis - 25ProphaseMitotic spindle begin to form & organise
Nucleolus disappears but membrane is intact - 26PrometaphaseChromosomes finish condensing
Nuclear envelope breaks down - 27MetaphaseChromosome align & attach to central spindle
- 28Important checkpoint in metaphaseSpindle checkpoint
- chromosomes must attach to the spindle in such a way that they are under slight tension & each chromatid is attached to a microtubule from the opposite end of the spindle - 29AnaphaseChromosomes separate out to opposite ends of the spindle
- 30CytokinesisCytoplasm is split into 2 daughter cells
- done via a contractile ring of actin & myosin at the central point - 31How is DNA condensed?Specific proteins form 'handcuffs' around DNA & help them become more condensed
- 32When is max. DNA condensation reached?Metaphase
- 33How is the spindle formed?The centrosome comprises 2 centrioles which are replicated in the cell cycle & start to organise the microtubules even before mitosis is fully underway
- 34How does nuclear envolope break down occur?One of CDKs targets in mitosis is the nuclear lamins - proteins found in nuclear envelope
CDK phosphorylates them ∴ breakdown of the envelope occurs - 35How do chromosomes attach to the spindle?Through constricted regions present at the centromere & require a specific protein called kinetochore
- 36What holds sister chromatids together?Cohesion complex
- 37Example of a defect in cohesionRoberts Syndrome
chromosomes are not held together ∴ are more spread out that desirable - 38Function of separaseTo break cohesins into amino acids so chromosomes can move apart
- 39Function of anaphase promting complexThe activity of APC is regulated to prevent separase activating at the wrong time in the cell cycle
- 40How is separase activated?Separase is normally held inactively as a dimmer by securin and inhibitory protein, BUT at the right time in the cell cycle the APC is an E3 ubiquitin ligase & targets securin for degradation
- 41What can result from a defect in the spindle checkpoint?Aneuploid cells
- cells with the wrong number of chromosomes ∴ long-term abnormalities & prolonged uncontrolled proliferation
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- MD2002 Karteikarten am Cell Division, erstellt von Lareyna Mcmenemy am 26/04/2018.
- Erstellt von
- Lareyna Mcmenemy
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