Chapter 7 Cell Division

Question 1

What are the 2 basic strategies for reproduction?

Answer 1

Asexual and sexual

Question 2

How does diversity occur in asexual reproduction

Answer 2

Asexual reproduction creates clones. Diversity comes from mutations or environmental factors

Question 3

What are different methods of asexual reproduction

Answer 3

Single cell prokaryotes - binary fission
Single cell eukaryotes - mitosis and cytokinesis
*mutlicellular eukaryotes can reproduce asexually too

Question 4

What does Sexual reproduction involve

Answer 4

involves fusion of gametes (form by meiosis which reduces genetic material by half)
leads to genetic variation

Question 5

What are somatic cells

Answer 5

cells not specialized for reproduction

- contain 2 sets of chomosomes in homologous pairs (one from female and one from male parent)

Question 6

How are gametes different to somatic cells

Answer 6

Only have one set of chomosomes - one homolog from each pair of parent cell
Are haploid; number of chom osomes = n

Question 7

What is fertilization

Answer 7

2 haploid gametes form zygote

diploid; number of chomosomes = 2n

Question 8

What are the 4 events in cell division

Answer 8

Reproductive signals
DNA replication
DNA segregation - distribution of DNA into 2 new cells
Cytokinesis - division of cytoplasm and separation of two new cells

Question 9

How do prokaryotes reproduce

Answer 9

Binary fission - results in reproduction of the entire organism
Reproductive signal may be environmental factor such as nutrient availability

Question 10

How does DNA replication occur in prokaryotes

Answer 10

Most prokaryotes have one circular chomosome with 2 important regions
- ori- (replication starts)
- ter - (replication ends)
DNA replicates when threaded through replication complex of proteins in centre of cell

Question 11

How does segregtaion occur in prokaryotes

Answer 11

during replication ori complexes move to opposite end of cell, their adjacent DNA sequences bind proteins for segregation using ATP
- Actin-like protein provides filament for ori and other proteins to move

Question 12

How does cytokinesis occur in prokaryotes

Answer 12

after segregation cell membrane pinches by contraction of ring of protein fibers under surface - new ell wall materials are deposited resulting in 2 separate cells

Question 13

How do eukaryotic cells divide?

Answer 13

Mitosis followed by citokinesis

Question 14

How is cell division different in eukaryotic cells

Answer 14

Signals are usually related to organism function, not individual cell
- most cells in multicellular organisms are specialised and do not divide
DNA replication - DNA replicated as threaded through replication complexes (same) only occurs at specific stage of cell cycle
DNA segregation - more complex due to nuclear envelope and multiple chromosomes
Cytokineses - different in animal cells due to lack of cell wall (same in plant cells)

Question 15

What is the cell cycle

Answer 15

period from 1 cell division to the next

Question 16

What are the 2 main phases of the cell cycle

Answer 16

M phase: Mitosis followed by cytokinesis

Interphase: cell nucleus is visible and cell functions occur (including DNA replication)

Question 17

What are the 3 subphases of interphase

Answer 17

G1 (Gap 1): Specialized cell function, variable duration
S (synthesis): DNA repliction
G2 (Gap 2): cell prepares for mitosis, synthesizing microtubules for segregating chromosomes

Question 18

What are the stages of mitosis

Answer 18

Prophase - metaphase - anaphase - telophase

Question 19

What occurs during prophase

Answer 19

3 structures appear

• Condensed chromosomes (chromosomes after recplicating have 2 dna molecules called ‘sister chromatids’ joinded at the centromere)
• reorient chromosomes (centrosomes determine orientation of spindle. S phase centrosomes duplicate, G2-M phase centrosomes move toward opposite sides of nucleus)
• Spindle (forms between poles formed by centrosomes)

Question 20

What do microtubules do during Spindle part of prophase

Answer 20

Polar microtubules - overlap in middle region, keep poles appart
Astral microtubules - interact with cell membrane proteins, also keep poles apart
Knetochore microtubules - attache to kinetocores on chromatid centromeres, pull sister chromatids to opposite sides

Question 21

what is the difference between chromatids and chromosomes

Answer 21

Chromatids - share centromere

Chromosome - own centromere

Question 22

What are the strops of mitosis between prophase and telophase?

Answer 22

Prometaphase - nuclear envelope breaks down, chromatids attach to kinetochore microtubules
Metaphase - chromosomes line up in middle of cell
Anaphase - chromatids separate towards pole

Question 23

What is the difference between mitosis and meiosis?

Answer 23

Meiosis has 2 rounds of cell division and produces 4 haploid cells
Mitosis has one round of cell division and produces 2 genetically identical diploid cells

In both the DNA only replicates Once

Question 24

What is the mechanism for daughter chromosome movement towards the poles in anaphase?

Answer 24

Kinesin and Dyenin (molecule motor proteins) move chromosomes along kinetochore microtubles that also shorten towards the poles

Question 25

What occurs during telophase?

Answer 25

Last phase of mitosis, where nuclear envelope forms around each set of chromosomes and nucelioli appears Spindle breaks and chromosomes become less compact

Question 26

What is the karyotype

Answer 26

Description of condensed chromosome size and centromere position

Question 27

How does cytokinesis occur in animal cells?

Answer 27

Cell membrane pinches in between the nuclei | Actin and Myosin ring forms on inner cell membrane surface

Question 28

How does cytokinesis occur in plant cells?

Answer 28

Vesicles form golgi apparatus appear along plane of cell division - fuse to form new cell membrane - Vesicles contents contribute to cell plate (beginning of new cell wall)

Question 29

What stage of mitosis allows eukaryotic cells to control reproduction?

Answer 29

G1-S transition is the restricted point | growth factors stimulate transition. Passing the S phase usually leads to cell division

Question 30

What is the the trigger substance that allows progression through phases in mitosis?

Answer 30

Cyclin-dependent Kinases (CDKs) | They function at cell cycle checkpoints and signal for cell to proceed to next phase

Question 31

What causes checkpoints in the phases of mitosis?

Answer 31

G1 - triggered by DNA damage S - triggered by DNA damage or incomplete replication G2 - triggered by DNA damage M - triggered by chromasome to spindle attachment failure

Question 32

What triggers the activation of CDKs?

Answer 32

Each CDK has own cyclin to activate it which is broken down into prodease after action. Growth factors and various signals trigger cyclin synthesis

Question 33

Why is meiosis used for producing gametes

Answer 33

Because it produces genetically different cells to the partent cell

Question 34

What is the function of Meiosis

Answer 34

Reduce chromosome numbers form diploid to haploid Ensure haploid cells have full set of chromosomes Promote genetic diversity

Question 35

What is the purpose of crossing over in Meiosis and when does it occur?

Answer 35

Homologous pairs of chromosomes line up along lengths (4 chromatids) They repel at centromeres but remain attached at chiasmata Genetic material is then exchagned between nonsister chromatids at chiasmata -> recombinant chromatids Occurs during prophase 1 (prophase of first meiosis)

Question 36

What are the 2 processes that allow for shuffling of genetic material in meiosis?

Answer 36

Crossing over and Independent assortment

Question 37

What is independent assortment and when does it occur

Answer 37

Occurs during anaphase 1 Chance determines which member of a homologous pair goes into which daughter cell In humans therear e 2^23 possible cominations

Question 38

What are potential errors that can occur in meiosis

Answer 38

Nondisjunction Polyploidy Translocation

Question 39

What is nondisjucntion

Answer 39

When homologous pairs fail to separate at anaphase 1 or sister chromatids don't separate at anaphase 2 - Causes Aneuploidy (abnormal chromosome number)

Question 40

WHat is polyploidy

Answer 40

Organisms with triploid (3n) or tetraploid (4n) or > chromosomes 0 Due to additional DNA replication before meiosis or lack of spindle in meiosis II - occurs naturally for some species

Question 41

What is Translocation

Answer 41

crossing over of nonhomologous chromosomes in Meiosis 1 | Can affect gene expression

Question 42

What is a dangerous case of translocation

Answer 42

Translocation of chromosomes 9 and 22 can cause leukaemia

Question 43

What are the 2 mechanisms of cell death

Answer 43

Apoptosis - programmed | Necrosis - due to damage or nutrient starvation

Question 44

What is the process of apoptosis

Answer 44

Cell detaches from neighbours DNA cut into fragments Membranous loves form, break into fragments

Question 45

What are reasons for apoptosis

Answer 45

cell no longer needed (e.g. connective tissue between fingers of foetus Cell is old and prone to genetic damage Surrounding cells usually ingest dead cells via phagocytosis

Question 46

How is apoptosis controlled

Answer 46

Controlled by signals - Internal signals related to cell age or DA damage -Internal and external signals lead to activation of caspases - which hydrolyze target proteins Cell dies when caspases hydrolyze proteins in nuclear envelope, nucleosomes and cell membrane

Question 47

How does necrosis cause inflammation?

Answer 47

Cell contents are released - triggers inflammatory mediators