Eukaryotic chromosomes are replicated from multiple origins. Initiation of replication from these origins occurs throughout S phase. Some origins fire in early S, some in late S phase. However, no eukaryotic origin initiates more than once per S phase. S phase continues until replication from multiple origins along the length of each chromosome results in [...]

Checkpoint Overview DNA Damage A Midway through G1, ATM/R activates p53, which activates p21CIP, which blocks Mid-G1-Cyclin+CDK (Cyclin-D+CDK4 & CDK6) if DNA damage is detected. DNA Damage B At the start of S-phase, ATM/R activates: p53, which activates p21CIP, which blocks the late G1 cyclin (Cyclin E) and the S-Phase cyclin (Cyclin A) if DNA [...]

How is the dismantling of the nuclear lamina during prophase and its reassembly during telophase accomplished? Where does the nuclear envelope go during mitosis? Long and fibrous lamin proteins form a layer of structural support for the nuclear envelope. Lamin is phosphorylated in prometaphase, causing a conformational change and the loss of laminal structural properties. [...]

Metaphase Checkpoint How does the metaphase checkpoint prevent sister chromatid separation at the onset of anaphase until every kinetochore has become associated with spindle microtubules? In the spindle assembly checkpoint (aka metaphase checkpoint), mitotic arrest deficient 2 (aka Mad2) blocks metaphase until every single kinetochore has properly attached to spindle microtubules. Mad2 exists in an [...]

Step Overview Growth 1 In a diploid eukaryotic cell, there are two versions of each chromosome, one from the mother and another from the father. The two corresponding chromosomes are called homologous chromosomes. Homologous chromosomes need not be genetically identical. During growth 1 (G1), an interphase, phase is the normal growth phase. Chromosomes are highly [...]

An obvious advantage of proteolysis for controlling passage through these critical points in the cell cycle is that protein degradation is an irreversible process, ensuring that cells proceed irreversibly in one direction through the cycle. Step Initiation Overview Early G1 DNA prepreplication complexes assemble at origins. However, they are not activated. Mitotic cyclin-CDKs activate early [...]

Mitotic Events Process Genomic Cellular Prophase The genome condenses. Visible chromosomes form. Each chromosome has 2 sister chromatids bound at the centromere by cohesin. Spindle fibers (aka spindle poles) emanate from the centromere. The two centrosomes form G2 sprout microtubules by polymerizing free-floating tubulin. The microtubules repel each other, pushing the centrosomes to opposite ends [...]

Mitosis is the division of a parent cell into two daughter cells that are identical to itself. A cell does this to increase population size and to increase genetic diversity. The parent cell duplicates each of its chromosomes before mitosis; these duplicate chromosomes are called sister chromatids, and are attached at their centromere. In animals [...]