Chapter 12 - Mitosis

Question 1

Roles of Cell Division

Answer 1

• It reproduces giving rise to a new organism
  
  • Plays a function in renewal and repair in multicellular eukaryotes
  • Enables growth and development

Question 2

Chromosomes

Answer 2

consist of one long, linear DNA molecule with many proteins which carry hundred if not thousands of genes
- Associated protein maintains the structure of the chromosome

Question 3

Chromatin

Answer 3

the entire complex of DNA and proteins which are wrapped together to eventually become more compact into chromosomes
○ Vary in its degree of condensation during the process of cell division

Question 4

Process of DNA(chromosome) packing

Answer 4

-Goes from nucleosome to Chromatin to chromosome by;

• 8 histones attach to the DNA molecule
  • Combined tight loop of DNA and protein is called a nucleosome which stacks on top of each other forming chromatin
• Chromatin gets to a thickness of 30nm before looping around other proteins for further packaging into chromosomes

Question 5

DNA Replication and its products

Answer 5

the process of DNA being copied which allows for chromosomal replication

Sister Chromatids: two copies of a duplicated chromosome attached to each other by proteins at the centromere, making up 1 chromosome

Centromere: a region made up of repetitive sequences in chromosomal DNA where the chromatid is most closely attached to its sister chromatid.
- The skinny part of the chromosome due to it being more tightly condensed

Question 6

Mitosis

Answer 6

the division of the genetic material in the nucleus of eukaryotic cells into two complete sets which is divided into stages of prophase, prometaphase, metaphase, anaphase and telophase.
- Equally shares replicated chromosomes
- creates clones

Question 7

Cell Cycle and its 2 phases

Answer 7

the life cycle of the cell

	○ Interphase: 90% of cell cycle and includes division of G1, S phase and G2 phase. 

	○ Mitotic Phase: mitosis(division of nucleus) and cytokinesis(division of cytoplasm)

Question 8

Parts of Interphase

Answer 8

G1: protein synthesis for DNA replication

S phase: Synthesis of copied DNA(DNA replication)

G2: preparation for mitosis

Question 9

Stages of Mitosis

Answer 9

1. Prophase: chromatin condenses into discrete chromosomes, miotic spindles begin to form and nucleolus disappears but nucleus is still intact
   2. Prometaphase: nuclear envelope fragments and spindle microtubules attach to kinetochores of chromosomes
   3. Metaphase: spindle is complete and chromosomes are all aligned at metaphase plate
   4. Anaphase: chromatids have been pulled and separated and daughter chromosomes move to poles of cell

Telophase: daughter cells nuclei begin to form and cytokinesis has begun

Question 10

Mitotic Spindles

Answer 10

an assemblage of microtubules involved in the movement of chromosomes during mitosis
- Can polymerize and depolymerize

Question 11

Centrosomes:

Answer 11

the region containing material that functions throughout the cell cycle to organize microtubules.

Question 12

process of Mitotic Spindles in Cell Division:

Answer 12

• Assembly starts at the centrosome during G2 interphase where the centrosome duplicates and moves apart during anaphase.
• microtubules grow out of them during prometaphase forming an array known as an aster
• microtubules then latch onto the 2 kinetochores facing either side of the sister chromatids and begin to create a tug of war, moving them to the metaphase plate
• when the cohesions holding the sister chromatids is cleaved, the microtubules bring each chromatid to its respective pole

Question 13

Mechanisms for how Kinetochore microtubules function in the poleward movement of chromosomes

Answer 13

1. Motor proteins on kinotechores ‘walk’ chromosomes along the microtubules and depolymerize at the end
2. Chromosomes are reeled in by motor proteins at the spindle poles and that microtubules depolymerize after they pass the motor protein at the pole

Question 14

Cytokinesis

Answer 14

Occurs by a process known as cleavage; the pinching of the plasma membrane and the succession of rapid cell division without significant growth

Question 15

Cytokinesis in Animals

Answer 15

• First sign is the appearance of the cleavage furrow which is the shallow groove in the cell surface near the metaphase plate
• On the cytoplasmic side is a contractile ring of actin and microfilaments associated with myosin which interact and cause the rings to contract which pulls the furrow deeper until the parent cell is pinched in two

Question 16

Cytokinesis in Plants

Answer 16

• No cleavage and instead during telophase, vesicles from GA move along microtubules to the middle of the cell where they coalesce and create a cell plate
• Cell wall materials gather and collect inside the cell plate which grows until its surround membrane fuses with the plasma membrane resulting in two daughter cells

Question 17

Binary Fission

Answer 17

asexual reproduction occurring in single celled organisms in which cells grow to roughly double their size before splitting in two

- In prokaryotes, BF does not require mitosis but in single celled eukaryotes it does

Question 18

Process of Binary Fission

Answer 18

• Cell division occurs when bacterial DNA begins to replicate at the origin of replication where the newly replicated DNA begins to move towards an opposite end of the cell
  • As the DNA is replicating the cell is elongating until it reaches double the size and all DNA is copied
  • Proteins cause the plasma membrane to pinch inward dividing it into two daughter cells.

Question 19

Evidence of Evolution in Mitosis

Answer 19

• The fact that some proteins involved in bacterial binary fission relate to eukaryotic proteins functioning in mitosis support the hypothesis that mitosis evolved from simple prokaryote cell division
  • Intermediate stages in cell reproduction seen in unicellular eukaryotes such as dinoflagellates and diatoms are seen as cases where ancestral mechanisms of cell reproduction have remained unchanged over time

Question 20

Cell Cycle Checkpoint System

Answer 20

a cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell

- Proceeds on its own according to a built in clock but can also be regulated at certain checkpoints

Question 21

Checkpoints and each type

Answer 21

a control point where stop and go ahead signals can regulate the cycle

- Found in G1: 
- G2: checks DNA replication occurred correctly 
- Metaphase: checks the accuracy of mitosis

Question 22

Function of G2 Specific Checkpoint(all checkpoints function in same pattern but with different proteins)

Answer 22

• Cyclin Dependent Kinase is present in the cell always as an inactive model and is only active when cyclin binds to it forming Maturation Promoting Factor
  • MPF in sufficient quantity then allows the cell to cross the G2 checkpoint
  • Cyclin accumulates in population when the cell cycle requires it
  • Another protein accumulating during metaphase then breaks cyclin and leaves Cdk as a stand alone once the cell reaches anaphase, recycling it to be used again

Question 23

Internal Checkpoints in the Cell

Answer 23

M, G1, G2 checkpoints are considered internal as within the cell determines to go ahead or not
- if not it can switch into G0 phase; a nondividing state

Question 24

External Factors Affecting Cell Division

Answer 24

• Cells fail to divide if an essential nutrient is lacking in the culture medium
  • Most mammal cells divide only if the growth medium includes specific growth factors: a protein released by cells to stimulate cell division

Question 25

Example of Growth Factors affecting cell division

Answer 25

• Platelet derived growth factors(PDGF) are made by blood cell fragments and when an injury occurs they are released in the vicinity
  
  • This allows for the division of cultured fibroblasts: cells loose in connective tissue which secretes protein ingredients of extracellular fibers and have PDGF receptors
  • When PDGF binds to these molecules it triggers a signal transduction pathway allowing cells to pass the G1 checkpoint and divide, stimulating fibroblast division in the animals body and allowing healing of the wound

Question 26

External Processes regulating cells division

Answer 26

Density Dependent(contact) inhibition is a phenomenon in which crowded cells stop dividing when they physically touch, which is why cultured cells divide until they form a single layer of cells on the surface of an object.
- This regulation occurs as a result of cell surface proteins binding to its counterpart on adjoining cells which sends a signal to both cells to inhibit cell division

Anchorage Dependence: the requirement a cell to divide is that it must be attached to a substratum in order to initiate cell division
- Most animal cells exhibit this and in order to divide they must be attached to something e.g. extracellular matrix of a tissue

Question 27

Cancer Cells:

Answer 27

cells with unregulated cell growth and reproduction

don’t stop dividing when growth factors are depleted because;
○ This may be due to them making their own required growth factors
○ they have an abnormality in signaling pathways conveying a growth factors signal to the cell cycle control system

Question 28

Types of Cancer Cells

Answer 28

Benign tumor: if the abnormal cells remain at the original site and their genetic and cellular changes don’t allow them to move or survive at another site.

Malignant tumor: cells whose genetic and cellular damages enable them to spread to new tissues which impairs the function of one or more organs
- Can result in cells with unusual number of chromosomes, altered metabolism and the inability to function in constructive ways