While other proteins come and go during the cell cycle, the proteins of the origin

Since there are about 1013 cells in an adult human, and about 1010 cells die and are replaced each day, we become new people every three years.

In order for proliferating cells to maintain a relatively constant size, the length of the cell cycle must match the time it takes for the cell to double in size.

While other proteins come and go during the cell cycle, the proteins of the origin recognition complex remain bound to the DNA throughout.

Chromosomes are positioned on the metaphase plate by equal and opposite forces that pull them toward the two poles of the spindle.

Meiosis segregates the paternal homologs into sperm and the maternal homologs into eggs.

If we could turn on telomerase activity in all our cells, we could prevent aging.

Many cell-cycle genes from human cells function perfectly well when expressed in yeast cells. Why do you suppose that is considered remarkable? After all, many human genes encoding enzymes for metabolic reactions also function in yeast, and no one thinks that is remarkable.

Hoechst 33342 is a membrane-permeant dye that fluoresces when it binds to DNA. When a population of cells is incubated briefly with Hoechst dye and then sorted in a flow cytometer, which measures the fluorescence of each cell, the cells display various levels of fluorescence as shown in Figure Q171. A. Which cells in Figure Q171 are in the G1, S, G2, and M phases of the cell cycle? Explain the basis for your answer. B. Sketch the sorting distributions you would expect for cells that were treated with inhibitors that block the cell cycle in the G1, S, or M phase. Explain your reasoning.

The yeast cohesin subunit Scc1, which is essential for sister-chromatid cohesion, can be artificially regulated for expression at any point in the cell cycle. If expression is turned on at the beginning of S phase, all the cells divide satisfactorily and survive. By contrast, if Scc1 expression is turned on only after S phase is completed, the cells fail to divide and they die, even though Scc1 accumulates in the nucleus and interacts efficiently with chromosomes. Why do you suppose that cohesin must be present during S phase for cells to divide normally?

High doses of caffeine interfere with the DNA damage response in mammalian cells. Why then do you suppose the Surgeon General has not yet issued an appropriate warning to heavy coffee and cola drinkers? A typical cup of coffee (150 mL) contains 100 mg of caffeine (196 g/ mole). How many cups of coffee would you have to drink to reach the dose (10 mM) required to interfere with the DNA damage response? (A typical adult contains about 40 liters of water.)

How many kinetochores are there in a human cell at mitosis?

A living cell from the lung epithelium of a newt is shown at different stages in M phase in Figure Q172. Order these light micrographs into the correct sequence and identify the stage in M phase that each represents.

Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18) are the most common autosomal trisomies seen in human infants. Does this fact mean that these chromosomes are the most difficult to segregate properly during meiosis?

The human genome consists of 23 pairs of chromosomes (22 pairs of autosomes and one pair of sex chromosomes). During meiosis, the maternal and paternal sets of homologs pair, and then are separated into gametes, so that each contains 23 chromosomes. If you assume that the chromosomes in the paired homologs are randomly assorted to daughter cells, how many potential combinations of paternal and maternal homologs can be generated during meiosis? (For the purposes of this calculation, assume that no recombination occurs.)