Cell Cycle Flashcards

Question

Cyclin-Cdk complex pairs

Answer 1

Activation of cyclin-Cdk complex A. In absence of cyclin, the active site in CdK is partly obscured by a protein loop(like a stone blocking the entrance to a cave) B. Cyclin binding cause the loop to move away from the active site – partial activation of Cdk enzyme C. Cdk-activating kinase (CAK) phosphylate an amino acid near the entrance of Cdk active site – conformational change that increase the activity

Answer 2

Cdk activity can be suppressed by inhibitory phosphorylation and Cdk inhibitor proteins (CKIs)

Answer 3

Replication must occur with extreme accuracy to minimise the risk of mutations * Every nucleotide (A, T, G, C) must be copied once, and only once

Answer 4

* DNA replication begins at origin of replication – numerous locations in every chromosomes * Licensing of replication origins – when inactive DNA helicases loaded onto the replication origin forming prereplicative complexes * S-Cdk – activate DNA replication with other proteins

Answer 5

The size of an organ depends on its total cell mass – number of cells and their size Tightly controlled cell growth, division and survival By intracellular programs and by extracellular signal * Mitogens – primarily by triggering a wave of G1/S-Cdk (removing of blocking cell cycle) * Growth factors – promoting synthesis of proteins and macromolecules by inhibiting degradation * Survival factors – suppressing apoptosis

Answer 6

In the absence of a mitogenic signal to proliferate, Cdk inhibition in G1 is maintained and progression into a new cell cycle is blocked. Specialised nondividing state, G0

Answer 7

Upon mitogen binding to the receptor on the surface of plasma membrane, GTPase RAS activate mitogen-activated protein kinase (MAP kinase) cascade. * Myc (transcription regulatory protein) activate G1-Cdk which phosphorylate Rb (retinoblastoma) proteins leading activation of E2F proteins (promoting transcription activity – key for DNA replication). * With following positive feedback loops, DNA synthesis can be efficiently accomplished.

Answer 8

* G1/S-Cdk and S-Cdk need to be activated to pass G1/S checkpoint but if DNA is damaged, cell cycle should not proceed to S phase * When DNA damage phosphorylate p53, activation of p53 transcribe p21 gene * Translation of p21 mRNA to p21 protein (repressor protein) inhibit activity of G1/S-Cdk and S-Cdk * When DNA damage is repaired, p53 level drops (degradation), cyclin-Cdk is no longer inhibited and blocked G1/S checkpoint is removed

Answer 9

Meiosis * Generation of gametes (e.g., Egg and sperms) to carry only a single copy of parent’s chromosome * Diploid (carrying chromosome pairs) to haploid (carrying only 1 chromosome of pairs) * Sexual reproduction cycle ends when 2 haploids (a sperm and egg) fuse to form a diploid zygote, which can from a new individual * 2 cell divisions

Answer 10

Mitosis * Generation of 2 identical daughter cells * 2 daughter cells will have the same number of chromosomes as a parent cell (diploid to diploid) * A single cell division * For multicellular eukaryotic organism – tissue growth and replacement of cells * For single cell eukaryotic organism – asexual reproduction

Answer 11

Crossing over * Only in meiosis * Same type of chromosomes lined up during prophase I * Chiasma forms between a pair of homologous chromosomes by crossover of non-sister chromatids * Switch (exchange of genetic materials) can happen in non-sister chromatids of a homologous chromosomes * Allows new combinations of genetic materials – genetic variation