chapter 11

Question 1

4 main event in all organisms

Answer 1

cell division
DNA replication
DNA segregation
Cytokinesis

Question 2

cell division is prokaryotes

Answer 2

Cell division (binary fission) results in reproduction of the entire single-celled organism

Cell division signals are usually external factors such as nutrient concentration and environmental conditions

Question 3

replication - prokaryotes

Answer 3

• One chromosome
• a single molecules of DNA
• often circular, but folded
  2 important regions:
• ori - where replicaiton starts (origion)
• ter - where replication ends (terminus)
• in a replication fork

Question 4

DNA segregation

Answer 4

• replication is complete
• ori regions move to the opposite ends of the cell
• segregation of the daughter chromosomes

Question 5

cytokinesis

Answer 5

• cell membrane pinches in
• protein fibers form a ring
• new cell wall materials are synthesized
• separation of the two cells

Question 6

DNA replication (eukaryotes)

Answer 6

• eukaryotes have more than one chromosome
• replication starts are many origins on the chromosome

Question 7

DNA segregation

Answer 7

Mitosis
- separates chromosomes into 2 new nuclei
- ends up in each daughter cell

Question 8

cytokinesis

Answer 8

splitting of cells into 2 cells

Question 9

cell cycle

Answer 9

phases a cell passes through to produce daughter cells by cell division

Question 10

interphase

Answer 10

nucleus is visible and cell functions occur
- duration of interphase is highly variable
- interphase has 3 subphases: G1(Chromosomes are single (unreplicated)
- duration is variable, from mins to yrs, some enter resting phase (G0)), S (DNA replicates, sister chromatids remain together until mitosis)
, G2 (cell prepares for mitosis, e.g. by synthesizing the structures that move the chromatids; sister chromatids are held tg during G2 by proteins called cohesins)

M phase includes mitosis and cytokinesis

Question 11

Cell cycle is controlled by

Answer 11

• cyclin-dependent kinases (CDKs)
• Protein kinases catalyze transfer of a phosphate group from ATP to a protein (phosphorylation)
• changes the shape and function of the protein
• growth factors activate signal transduction

Question 12

chromatin

Answer 12

DNA molecules are bound to proteins to chromatin

Question 13

Mitosis

Answer 13

all cells except sex cells

production of 2 nuclei that are genetically identical

subdivided into:
prophase
prometaphase
metaphase
anaphase
telophase

at mitosis cohesin is removed, except at the centromere. condensins coat the DNA molecules and make them more compact

during mitosis chromosomes are so compact, they are inaccessible to replication and transcription factors

Question 14

asexual reproduction is based on mitosis

Answer 14

a single-celled organism reproduces itself with each cell cycle; some multicellular organisms also reproduce asexually

Question 15

sexual reproduction

Answer 15

• offspring are not identical to the parents
• deals with gametes

Question 16

gametes

Answer 16

Gametes (eggs or sperm cells) are created by meiosis; each parent contributes one gamete to an offspring
- Gametes and offspring differ genetically from each other and from the parents.
- gametes contain only one set of chromosomes—one homolog of each pair

Question 17

Meiosis

Answer 17

Meiosis generates genetic diversity that is the raw material of evolution

Question 18

somatic cells

Answer 18

• body cells other than sex cells, not specialized for reproduction
• each somatic cell has homologous pairs of chromosomes

Question 19

haploid

Answer 19

chromosome number haploid

Question 20

fertilization

Answer 20

2 haploid gametes fuse to form a diploid zygote

Question 21

meiosis

Answer 21

2 nuclear divisions, but DNA is replicated only once
- reduces chromosomes # from diploid (2n) to haploid (n)
- ensures each haploid product has a complete set of chromosomes
- generates genetic diversity among the products
- can occur only in diploid cells

Question 22

meiosis I

Answer 22

• preceded by DNA replication in S phase
• homologous chromosome pairs separate but individual chromosomes (sister chromatids) stay together
• 2 haploid nuclei result, each with half of the original chromosomes (one member of each homologous pair)

Question 23

prophase I (of meiosis I)

Answer 23

Homologous chromosomes pair by adhering along their lengths (synapsis)

the 4 chromatids of each homologous pair form a bivalent

Question 24

chiasmata

Answer 24

regions of attachment that form between nonsister chromatids

Question 25

crossing over

Answer 25

exchange of genetic material between nonsister chromatids at the chiasmata results in recombinant chromatids and increases genetic variability of products one reason for genetic diversity in meiosis I products

Question 26

independent assortment

Answer 26

also allows for chance combinations matter of chance how they line up in anaphase I (meeting in middle)

Question 27

Meiosis II

Answer 27

- not preceded by DNA replication - sister chromatids are separated - chance assortment of chromatids contributes to genetic diversity - final products are 4 haploid daughter cells (n)

Question 28

errors in meiosis

Answer 28

Nondisjunction - homologous pairs may fail to separate at anaphase I - in meiosis II, sister chromatids may fail to separate - results in aneuploidy---chromosomes are either lacking or present in excess aneuploidy - may be caused by lack of cohesins that hold the homologous pairs tg - without cohesins both homologos may go to the same pole - resulting gametes will have 2 of the same chromosome or none

Question 29

down syndrome

Answer 29

results from a gamete with 2 copies of chromocome 21. after fertilization there are three copies (trisomic) a fertilized egg that did not receive a copy of chromosome 21 will be monosomic, which is lethal

Question 30

translocation

Answer 30

a piece of chromosome may break away and attach to another chromosome an individual with a translocated piece of chromosome 21 plus 2 normal copies will have down syndrome

Question 31

karyotype

Answer 31

display of chromosomes-number, shape, and sizes of all chromosomes of a cell can be used to diagnose abnormalities such as trisomies - branch of medicine called cytogenetics

Question 32

polyploid

Answer 32

- organisms w complete extra sets of chromosomes are called polypoid - triploid (3n, sterile and cannot undergo meiosis) - tetraploid (4n) and higher levels are possible if there is nondisjunction of all chromosomes during meiosis I, diploid gametes will form, leading to autopolyploidy after fertilization

Question 33

cell death

Answer 33

occurs in 2 ways Necrosis: cell is damaged or starved of oxygen or nutrients - the cell swells and bursts, cell contents are released to the extracellular environment and can cause inflammation Apoptosis: programmed cell death - cells may no longer be needed (e.g. fetus finger tissue) - old cells are prone to genetic damage that can lead to cancer Events of apoptosis - cell detaches from neighbors - chromatic is digested by enzymes that cut DNA between nucleosomes - the cell forms membranous lobes called "blebs" that break into fragments - surrounding living cells ingest remains of the dead cell and recycle the contents

Question 34

cancer cells

Answer 34

lose control over cell division and can migrate to other parts of the body, divide continuously, forming tumors (large masses of cells) - benign tumors grow slowly, resemble the tissue they grow from, and remain localized - malignant tumors do not resemble the parent tissue metastasis: cancer cells invade surrounding tissue and travel through bloodstream or lymph system to lodge and continue dividing to form new tumors surgical removal of tumors in the optimal treatment, but sometimes not all cancer cells can be removed other treatments target the cell cycle: - drugs that prevent cell division 5-fluorouracil blocks synthesis of thymine paclitaxel prevents functioning of microtubules in the mitotic spindle radiation treatment causes DNA damage in tumor cells

Question 35

cell regulation

Answer 35

in normal cells, the cell cycle is regulated - positive regulators such a growth factors stimulate cell division - negative regulators such as retinoblastoma protein (RB) inhibit the cell cycle the 2 regulator systems ensure that cells divide only when needed