Chapter 10

Question 1

Bacterial Cell Division

Answer 1

bacteria divide by binary fission
* no sexual life cycle
* reproduction is clonal

Question 2

Replication of Bacteria

Answer 2

• replication begins at the orgin of replication and proceeds bidirectionally to site of termination
• new chromosomes are partitoned to opposite ends of the cell
• septum forms to divide the cell into 2 cells

Question 3

Eukaryotic Chromosomes

Answer 3

• every species has a different # of chromosomes
• humans have 46 chromosomes (23 pairs) sex cells don’t have 46

Question 4

Chromosomes

Answer 4

• composed of chromatin: complex of DNA (40%) and protein (60%)
• DNA of a single chromosome is one long continuous double-stranded fiber
• in the nondividing nucleus:
  Heterochromatin: not expressed
  Euchromatin: expressed
• human chromosome 140 millon nucleotides long

Question 5

Chromosome Structure

Answer 5

• nucleosome: complex of DNA and histone proteins (promotes and guides coiling of DNA) “basic packing”
• DNA duplex coiled around 8 histone proteins every 200 nucleotides
• histones are positively charged, strongly attracted to negative charged phosphate groups in DNA

Question 6

Solenoids

Answer 6

solenoids are nucleosomes wrapped into higher order coils
- leads to a fiber 30 nm in diameter
- usual state nondividing (interphase) chromatin
* during mitosis, chromatin in solenoid arranged around scaffold of protein to achieve maximum compaction
- radical looping aided by condensin proteins

Question 7

Karyotype

Answer 7

a particular array of chromosomes in an individual organism
- arranged according to size, staining properties, location of centromere

Question 8

define Haploid and Diploid

Answer 8

Haploid (n): 1 set of chromosomes (23 in humans)
Diploid (2n): humans (2 compete sets, 46 total)
* pair of chromosomes are homologous

Question 9

Replication

Answer 9

• prior to replication, each chromosome composed of a single DNA molecule
• after replication, each chromosome composed of 2 identical DNA molecules (held together by cohesin proteins)
• visible as 2 stands held together as chromosome become more condensed
• 1 chromosome composed of 2 sister chromatids

Question 10

Eukaryotic Cell Cycle

Answer 10

1. G₁ (gap phase 1): primary growth phase, longest phase
2. S (synthesis): replications of DNA
3. G₂ (gap phase 2:) organelles replicate, microtubules organize
4. M (mitosis): subdivided into 5 phases (seperate DNA)
5. C (cytokinesis): separation of 2 new cells (seperate cell)

Question 11

Cell Cycle Duration

Answer 11

• time it takes to complete varies
• mature cells take longer to grow
• growth occurs during G₁, G₂, and S phase
• most variation in length of G₁
  (resting phase is G₀: brain cells stay here forever)

Question 12

Interphase

Answer 12

G₁: cells undergo major portion of growth
S: replicates DNA
G₂: chromosomes coil more tightly using motor proteins
* Centromere: point of constriction
* kinetochore: attachment site for microtubules
* each sister chromatid has a centromere
* Chromatids stay attched at centromere by cohesin

Question 13

5 Phases of Mitosis

Answer 13

1.Prophase
2.Prometaphase
3.Metaphase
4.Anaphase
5.Telophase

Question 14

Prophse

1st phase in mitosis

Answer 14

• stops making RNA
• chromosomes start to condense (spindle apparatus begins)
• nuclear envelope breaks down
• asters: radial array of microtubulse in animals (not plants)

Question 15

Prometaphase

2nd step in Mitosis

Answer 15

• microtubule attachment (attaches to kinetochores)
• sister chromatids (connected to opposite poles)
  chromosomes (move to center of cell-congression)

Question 16

Metaphase

3rd step in Mitosis

Meta = Midde

Answer 16

• alignment of chromosomes along metaphase plate
• (not an actual structure)
• future axis of cell division

Question 17

Anaphase

4th step in Mitosis

Answer 17

• begins when centromeres split
• removal of cohesin proteins from all chromosomes
• sister chromatids pulled to opposite poles
• Anaphase A: kinetochores pulled toward poles
• Anaphase B: poles move apart

Question 18

Telophase

5th step in Mitosis

Answer 18

• spindle apparatus disassembles
• nuclear envelope forms around each set of sister chromatids (now called chromosomes)
• chromosomes begin to uncoil (RNA genes to be expressed)
• nucleolus reappears in each new nucleus

Question 19

Cytokinesis

Answer 19

• cuts cells into 2 identical cells
• animal cells: constriction of actin filaments produce a cleavage furrow
• plant cells: cell plate forms between the nuclei
• fungi: nuclear membrane doesn’t dissolve; division of the nucleus occurs with cytokinesis

Question 20

Control of the Cell Cycle

Answer 20

2 concepts:
1. Cell cycle has 2 irreversible points
- replicaiton of DNA (synthesis)
- separation of the sister chromatids
2. Cell cycle can be put on hold at specific points called checkpoints
- process is checked for accuracy and can be halted if there are errors
- allows the cell to respond to internal and external signs

Question 21

3 Cell Cycle Checkpoints

Answer 21

1. G₁/S checkpoint
   - cell “decides” to divide
   - primary point of external signal influence
2. G₂/M checkpoint
   - cell makes a commitment to mitosis
   - assesses success of DNA replication
3. Late metaphase (spindle) checkpoint
   - cell ensures that all chromosomes are attached to the spindle

Question 22

Cyclin-dependent kinases (Cdks)

Answer 22

• enzymes that phosphorylate proteins
• primary mechanism of cell cycle control
• Cdks partner with other cyclins at different points in the cell cycle
• Cdk itself is controlled by phosphorylation

Question 23

Cdk-cyclin complex

Answer 23

• also called mitosis-promoting factor (MPF)
• Activity of Cdk is also controlled by the pattern of phosphorylation
  
  • phosphorylation at one site inactivates Cdk
  • phosphorylation at another site activates Cdk

Question 24

Anaphase-promoting Complex

Answer 24

• aka cyclosome (APC/C)
• function of the APC/C is to trigger anaphase itself
• makes securin for destruction; no inhibition of separase; separase destroys cohesin

Question 25

Control in Multicellular Eukaryotes

Answer 25

* multiple Cdks control the cycle as opposed to 1 Cdk in yeast (eukaryote) * animal cells respond to more external signals * yeast only respond to signals necessary for mating

Question 26

Growth Factors

Answer 26

* act by triggering intracellular signaling systems * platelet-derived growth factor (PDGF) one of the 1st growth factor identified * **growth factors can override cellular controls that otherwise inhibit cell division**

Question 27

Cancer

Answer 27

* unrestrained, uncontrolled growth of cells * failure of cell cycle control 2 kinds of genes can distrub the cycle when they are mutated: 1. Tumor-suppressor genes 2. Proto-oncogenes

Question 28

Tumor-Suppressor Genes

Answer 28

* P₅₃ plays a key role in G₁ checkpoint * P₅₃ protein monitors integrity of DNA - if DNA is damaged, cell divison halted and repair enzymes are stimulated - if DNA damage is irreparable, p₅₃ directs cell to kill itself (apoptosis) * **Prevents the development of mutated cells containing mutations** * P₅₃ is absent/damaged in many cancerous cells * **Both copies of a tumor-suppressor gene must lose function for the cancerous phenotype to develop**

Question 29

Proto-oncogenes

Answer 29

* normal cellular genes that become oncogenes when mutated (oncogenes can cause cancer) * some encode receptors for growth factors - if receptor is mutated in "on", cell no longer depends on growth factors * some encode signal transduction proteins * **Only 1 copy of the proto-oncogene needs to undergo this mutation for uncontrolled division to take place**

Question 30

Metastasis

Answer 30

cells travel to start new tumors | Cancer Cells

Question 31

Angiogenesis

Answer 31

form new blood vessels to nourish themselves | Cancer Cells

Question 32

Benign

Answer 32

contained with a capsule

Question 33

Malignant

Answer 33

invasive and may spread

Question 34

Cancer Cells

Answer 34

* don't undergo apoptosis * form tumors: do not respond to inhibitory signals

Question 35

Cancer Treatment

Answer 35

* remove the tumor * interfere with the ability of the cancer cells to reproduce * Radiation and Chemo because cancer cells are rapidly dividing * Hormone therapy designed to prevent cells from receiving signals for continued growth and division

Question 36

BRCA

Answer 36

* BRCA mutation increases the risk of breast cancer * tumor suppressor gene