Chapter 8

Question 1

What is binary fission?

Answer 1

The process by which prokaryotic cells divide. The cell replicates its DNA and splits into two genetically identical daughter cells.

Question 2

What is the origin of replication?

Answer 2

The specific site on a prokaryotic chromosome where DNA replication begins.

Question 3

How does a prokaryotic cell divide its DNA between daughter cells?

Answer 3

DNA sequences near the origin of replication attach to the membrane. As the cell elongates the two chromosome copies are pulled to opposite ends before the cell splits.

Question 4

What are the two types of cell division in eukaryotes?

Answer 4

Mitosis (division of somatic cells) and meiosis (division of reproductive germ-line cells).

Question 5

What are somatic cells?

Answer 5

The nonreproductive body cells of an organism - they divide by mitosis.

Question 6

What are the phases of the eukaryotic cell cycle in order?

Answer 6

Interphase (which includes G1 then S then G2) followed by M phase (mitosis) and then C phase (cytokinesis).

Question 7

What happens during G1 phase?

Answer 7

The primary growth phase - the cell grows and carries out its normal functions. It occupies most of the cell’s lifespan.

Question 8

What happens during S phase?

Answer 8

DNA replication - each chromosome is copied producing two identical sister chromatids.

Question 9

What happens during G2 phase?

Answer 9

Final preparations for division - mitochondria replicate then chromosomes condense and microtubules are synthesized.

Question 10

What happens during M phase?

Answer 10

Mitosis - the replicated chromosomes are separated and distributed to opposite ends of the cell.

Question 11

What happens during C phase (cytokinesis)?

Answer 11

The cytoplasm divides producing two separate daughter cells.

Question 12

What are homologous chromosomes?

Answer 12

Pairs of chromosomes that carry information about the same traits at the same locations - one inherited from each parent.

Question 13

What are diploid cells?

Answer 13

Cells that contain two of each type of chromosome - one from each parent.

Question 14

How many chromosomes do human somatic cells have?

Answer 14

46 - or 23 pairs of homologous chromosomes.

Question 15

What are sister chromatids?

Answer 15

The two identical copies of a chromosome produced by DNA replication. They are held together at the centromere.

Question 16

What is the centromere?

Answer 16

The specialized region that joins sister chromatids together after DNA replication and where spindle fibers attach during cell division.

Question 17

How many chromatids does a human somatic cell have after DNA replication?

Answer 17

92 - each of the 46 chromosomes has been duplicated into two sister chromatids.

Question 18

What is a karyotype?

Answer 18

An organized display of all chromosomes in a cell. Homologues are paired by size and shape and centromere location.

Question 19

What is monosomy?

Answer 19

A condition in which a cell is missing one chromosome - usually fatal in humans.

Question 20

What is trisomy?

Answer 20

A condition in which a cell has an extra copy of one chromosome - usually fatal except for a few of the smallest chromosomes.

Question 21

What is chromatin?

Answer 21

The complex of DNA and histone proteins that makes up chromosomes - about 40% DNA and 60% protein.

Question 22

What are histones?

Answer 22

Positively charged proteins around which DNA wraps to form nucleosomes. Their positive charge counteracts the negative charge of DNA.

Question 23

What is a nucleosome?

Answer 23

The basic unit of chromosome packaging - DNA wrapped around a core of eight histone proteins every 200 nucleotides.

Question 24

What are the four phases of mitosis in order?

Answer 24

Prophase then metaphase then anaphase then telophase.

Question 25

What happens during prophase?

Answer 25

Chromosomes condense and become visible. The nuclear envelope breaks down. Centrioles move to opposite poles and form the spindle. Spindle fibers attach to chromosomes at centromeres.

Question 26

What is the spindle?

Answer 26

A network of microtubule fibers that forms between the poles of a dividing cell and moves chromosomes during mitosis.

Question 27

What happens during metaphase?

Answer 27

Chromosomes align along the equatorial plane - the imaginary midline of the cell.

Question 28

What happens during anaphase?

Answer 28

The centromeres split and sister chromatids are separated and pulled to opposite poles by shortening spindle fibers.

Question 29

What happens during telophase?

Answer 29

The spindle disassembles. Nuclear envelopes re-form around each set of chromosomes. Chromosomes begin to uncoil and the nucleolus reappears.

Question 30

What is cytokinesis?

Answer 30

The division of the cytoplasm following mitosis - produces two daughter cells.

Question 31

How does cytokinesis differ between animal and plant cells?

Answer 31

Animal cells pinch inward using a contracting belt of actin filaments forming a cleavage furrow. Plant cells build a cell plate of membrane vesicles that grows outward to divide the cell.

Question 32

What is a cleavage furrow?

Answer 32

The indentation that forms around an animal cell during cytokinesis as actin filaments contract to pinch the cell in two.

Question 33

What is a cell plate?

Answer 33

The expanding membrane partition that forms between dividing plant cells during cytokinesis. It eventually becomes the new cell wall.

Question 34

What is cancer?

Answer 34

A growth disorder of cells in which damage to genes causes cells to divide in an uncontrolled way forming a tumor.

Question 35

What is a tumor?

Answer 35

A mass of cells that results from uncontrolled cell division.

Question 36

What is a malignant tumor?

Answer 36

An invasive tumor whose cells can break away and enter the bloodstream and spread to other parts of the body.

Question 37

What are metastases?

Answer 37

New tumors formed at distant sites when cancer cells spread from the original tumor through the bloodstream.

Question 38

What is a mutation?

Answer 38

A change in DNA - damage to a gene that can alter its function.

Question 39

What are carcinogens?

Answer 39

Cancer-causing agents - most are mutagens that damage DNA.

Question 40

What are growth factors?

Answer 40

Proteins that regulate the cell division cycle - cancer results from mutations in the genes that encode them.

Question 41

What are proto-oncogenes?

Answer 41

Genes that encode proteins that stimulate cell division - mutations that activate them step on the accelerator of division.

Question 42

What are oncogenes?

Answer 42

Mutated proto-oncogenes that cause excessive cell division and contribute to cancer.

Question 43

What are tumor-suppressor genes?

Answer 43

Genes that encode proteins that normally turn off cell division - mutations that disable them release the brakes on cell division.

Question 44

What is the p53 protein?

Answer 44

A tumor-suppressor protein that inspects DNA before cell division. It stops division and activates repair when DNA is damaged or triggers cell death if damage cannot be repaired.

Question 45

What percentage of all cancers have a disabled p53 gene?

Answer 45

50% - and 70 to 80% of lung cancers specifically have a mutant inactive p53.

Question 46

What chemical in cigarette smoke inactivates p53?

Answer 46

Benzo[a]pyrene - it binds to and mutates three specific sites on the p53 gene.

Question 47

What is angiogenesis?

Answer 47

The formation of new blood vessels - tumors promote angiogenesis to obtain the nutrients they need to grow.