Unit 4: The Cell Cycle

Question 1

the cell cycle

Answer 1

important in the growth, repair, and reproduction of cells in living organisms; controlling the rate of the cell cycle ensures that these processes occur in a timely manner while also preventing the development of uncontrolled cell growth or tumors

Question 2

phases of the cell cycle

Answer 2

interphase (G1, S, G2), mitosis (aka M phase), and cytokinesis; nondividing cells will leave the cycle and enter a stage called G0

Question 3

interphase

Answer 3

longest phase of the cell cycle; cell grows so that it has enough material to divide between two daughter cells; cell replicates its genetic material (DNA) during this time; three stages: G1, S, and G2

Question 4

G1 stage

Answer 4

stage of interphase; cell grows and prepares for DNA replication, and some cellular organelles are replicated

Question 5

S stage

Answer 5

stage of interphase; DNA is replicated; when this stage begins, each chromosome consists of one chromatid; after DNA replication is completed, each chromosome has two identical chromatids held together by one centromere; at the end of this stage, the cell contains twice the amount of DNA it had at the end of G1

Question 6

G2 stage

Answer 6

stage of interphase; cell continues to grow and prepares the materials needed for mitosis, like the proteins that will make up the spindle fibers

Question 7

mitosis (M phase)

Answer 7

goal: to make sure there is an accurate transfer of a parent cell’s complete genome to each of the two resulting daughter cells; four stages: prophase, metaphase, anaphase, and telophase

Question 8

prophase

Answer 8

stage of mitosis; nuclear membrane dissolves, chromosomes condense and become visible, spindle fibers begin to form

Question 9

metaphase

Answer 9

stage of mitosis; spindle fibers have fully attached to the centromeres of each chromosome; chromosomes are then aligned along the “equator” of the cell in a single column; center of the mitotic spindle is called the metaphase plate

Question 10

anaphase

Answer 10

stage of mitosis; each chromosome splits at its centromere as opposing spindle fibers begin to shorten; identical chromatids are pulled toward opposite ends of the cell; at this point, each chromatid now has its own centromere and is considered a separate chromosome; at the end of anaphase, the cell has twice the number of chromosomes that it had at the start of the cycle

Question 11

telophase

Answer 11

stage of mitosis; two new nuclear membranes form; each of the two nuclei now contain the same number of chromosomes and the same genetic information as the parent cell

Question 12

cytokinesis

Answer 12

occurs after mitosis; division of the cytoplasm, along with all of its cellular contents, between two daughter cells; animal cells: cleavage furrow forms, partitioning the cytosol and its contents between the two new cells; plant cells: different than animal cells because they have a cell wall, cell plate is built within the dividing cell, providing a new cell wall material for each daughter cell

Question 13

nondividing cells

Answer 13

some cells might stop dividing either temporarily or permanently; cells may stop dividing when they reach their mature, fully differentiated state or when environmental conditions are not favorable for their continued growth; these cells have exited the cell cycle and are in G0; cells may enter G0 at any point in the cell cycle and may reenter the cell cycle if stimulated to do so by appropriate molecular signals

Question 14

regulation of the cell cycle

Answer 14

critical to appropriate growth, repair, and reproduction of cells in living organisms; achieved through the use of checkpoints during the cell cycle

Question 15

checkpoints

Answer 15

found throughout the cell cycle, controlled by the interactions between cyclins and cyclin-dependent kinases

Question 16

cyclin-dependent kinases

Answer 16

present at constant levels throughout the cell cycle; add phosphate groups to other molecules, activating those molecules; inactive until bound to cyclin proteins

Question 17

cyclins

Answer 17

levels of these vary during the cell, reaching their maximum just before mitosis starts; when bound to cyclin-dependent kinases, a complex called mitosis-promoting factor is formed

Question 18

mitosis-promoting factor

Answer 18

formed when cyclins are bond to cyclin-dependent kinases; triggers the start of mitosis

Question 19

somatic cells

Answer 19

all cells not involved with sexual reproduction; division of these cells can also be regulated by density-dependent inhibition; many cells also exhibit anchorage dependence

Question 20

density-dependent inhibition

Answer 20

ex. when cells in tissues become too crowded, they will stop dividing

Question 21

anchorage dependence

Answer 21

when cells need to be attached to a surface in order to divide

Question 22

cancer cells

Answer 22

not regulated by density-dependent inhibition nor anchorage dependence and can continue to grow and divide under conditions that would cause normally functioning somatic cells to stop dividing

Question 23

proto-oncogenes

Answer 23

propel cell division at a specific rate (like how an accelerator propels a car); necessary for regulated and controlled cell growth; if mutated, they may become oncogenes; said to be dominant because a mutation in a single allele can cause a cell to grow out of control

Question 24

oncogenes

Answer 24

promote abnormally high rates of cell division (like how an accelerator stuck in the down position would cause a car to go too fast); can cause tumors to form when cell division occurs too quickly and too often without regard for the neighboring cells

Question 25

tumor suppressor genes

Answer 25

code for proteins that detect mutations in cells that may cause tumors to develop; function like the brakes on a car, preventing cell division from occurring at an abnormally fast rate; if a single mutation in af gene allele occurs, the cell will still possess one remaining unmutated allele that is functional; the tumor suppressor that is not mutated will help the organism identify cells that are dividing at a rate that is too fast; however, if both alleles of the gene are mutated, the growth of a tumor may occur; these genes are said to function in a recessive way because both alleles of the gene must be nonfunctional for a cell to grow out of control

Question 26

apoptosis

Answer 26

programmed cell death; may be triggered when a cell acquires a mutation that could cause cancer; during embryonic development, it may also occur to ensure proper development of various organs or structures; ex. apoptosis removes the webbing between fingers during embryonic development