Quiz 1 - Mitosis & Meiosis

Question 1

Basic steps in cell division?

Answer 1

1) copying of DNA
2) separating DNA copies
3) dividing cytoplasm to create two complete cells

Question 2

What is mitosis and binary fission?

Answer 2

both types are asexual reproduction which is cell division that results in genetically identical daughter cells
mitosis: asexual reproduction in eukaryotes
binary fission: asexual reproduction in prokaryotes

Question 3

What is sexual reproduction called in eukaryotes?

Answer 3

meiosis (involves gametes - sperm/egg cell division)

Question 4

What are the types of sexual reproduction in prokaryotes?

Answer 4

Transformation = prokaryote takes up DNA found within the environment that has originated from other prokaryotes

Transduction = prokaryote is infected by a virus which injects short pieces of chromosomal DNA from one bacterium to another

Conjugation = DNA is transferred between prokaryotes by means of a sex pilus

Question 5

What is chromosomes and chromatin fiber?

Answer 5

• A chromosome is a single long double helix of DNA wrapped around proteins called histones
• When cell is not dividing, chromosome is in form of long, thin chromatin fiber

Question 6

What helps form the chromosome structure?

Answer 6

Chromosomes form almost normally without histones, so it is actually condensin proteins that promote DNA interactions which shape chromosomes, while histones just add compaction and protection

Question 7

What does the cell cycle consist of?

Answer 7

1) Mitotic (M) phase (mitosis and cytokinesis)
2) Interphase (cell growth and copying of chromosomes in preparation for cell division)

Question 8

What is the interphase cycle?

Answer 8

Interphase (about 90% of the cell cycle) can be divided into sub-phases:
– G1 phase (“first gap”): organelles duplicate
– S phase (“synthesis”)
– G2 phase (“second gap”):
** The cell grows during all three phases, but chromosomes are duplicated only during the S phase

Question 9

What are the phases of mitosis?

Answer 9

prophase, prometaphase, metaphase, anaphase, telophase

Question 10

What is the mitotic spindle?

Answer 10

apparatus of microtubules controlling chromosome movement during mitosis (includes the centrosomes, spindle microtubules, and asters)

Question 11

What are centrosomes?

Answer 11

Organelle that serves as a microtubule organizing center (MTOC) (spindle microtubules grow out from them) replication leads to two centrosomes that migrate to opposite ends of cell

Question 12

What are the types of spindle microtubules?

Answer 12

Kinetochore microtubules = capture sister chromatids by binding to kinetochore proteins
Non-kinetochore microtubules (also known as polar microtubules) = do not capture sister chromatids

Question 13

What are asters (astral microtubules)?

Answer 13

A radial array of short microtubules that extends from each centrosome, which connect to proteins on inner surface of cell membrane to anchor the centrosomes

Question 14

What are somatic cells and gametic cells?

Answer 14

Somatic cells (non-reproductive cells) have two sets of chromosomes – mitosis leads to the generation of somatic cells!
Gametic cells (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells – meiosis leads to the generation of gametes!

Question 15

What happens during g2 interphase?

Answer 15

nuclear envelope intact and nucleoli present; centrosome is duplicated; chromatin duplicated during S-phase

Question 16

What happens during early prophase?

Answer 16

nucleolus disappears; chromatin fibers become tightly coiled and condense to form chromosomes (which first become visible using light microscope); centrosomes move away from each other as microtubules lengthen

Question 17

What happens during late prophase (prometaphase)?

Answer 17

nuclear envelope breaks down; chromosomes become completely condensed; microtubules (kinetochore and non-kinetochore) invade nuclear space [kinetochore microtubules attach to chromosomes]

Question 18

What happens during metaphase?

Answer 18

centrosomes at opposite ends of cell (held in place now by astral microtubules); formation of spindle apparatus is now complete; chromosomes settle at metaphase (equatorial) plate

Question 19

What happens during anaphase

Answer 19

sister chromatids move to opposite poles of cell as kinetochore microtubules shorten; non-kinetochore microtubules grow longer which helps elongate cell

Question 20

What happens during telophase?

Answer 20

chromosomes decondense into chromatin; nucleolus and nuclear envelope reappears; spindle microtubules disappear

Question 21

What is cytokinesis and how does it occur in animal vs plant cells?

Answer 21

• Separation of cytoplasm into two daughter cells
• animal: occurs by a process known as cleavage, forming a cleavage furrow on cell surface
• plant: a cell plate forms during cytokinesis (vesicles -containing cell wall materials- from Golgi move along microtubules to middle of cell)

Question 22

How is the cell-cycle controlled?

Answer 22

• Sequential events of the cell cycle are directed by a distinct cell cycle control system driven by specific chemical signals present in the cytoplasm

Question 23

What is the G1 checkpoint?

Answer 23

• For many cells, the G1 checkpoint seems to be the most important one
• pass checkpoint if: cell size adequate, nutrients are sufficient, social signals are presents, DNA is undamaged
• If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide
• If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a non-dividing state called the G0 phase (permanent or temporary)

Question 24

What is the g2 checkpoint?

Answer 24

Second checkpoint between G2 and
M phases
– Chromosomes must be replicated successfully and DNA is not damaged to pass checkpoint
– Activated MPF is present (M phase-promoting factor)

Question 25

What is MPF, Cyclin/Cdk?

Answer 25

Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin-dependent kinases (Cdks) * Level of cyclin fluctuates during the cell cycle while level of Cdk remains fairly constant * MPF (M phase-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past G2 checkpoint into M phase

Question 26

What are the two M checkpoints?

Answer 26

- Between metaphase and anaphase: > Delay occurs as all kinetochores have not yet attached to spindle microtubules > This keeps the anaphase-promoting complex (APC) in an inactive state > When all kinetochores are attached, the APC activates, triggering breakdown of securin and activation of separase to degrade cohesin proteins (hold sister chromatids together) so they can separate during anaphase – Between anaphase and telophase (ensures that chromosomes have fully separated)

Question 27

What are examples of internal cell-cycle control signals?

Answer 27

- production of high levels of MPF: important for passing G2 checkpoint - activation of anaphase promoting complex: important for passing the first M checkpoint (between metaphase and anaphase)

Question 28

What are examples of external cell-cycle control signals?

Answer 28

essential nutrients, growth factors, density-dependent inhibition, anchorage dependence

Question 29

What are growth factors?

Answer 29

proteins released by certain cells that stimulate other cells to divide * For example, platelet-derived growth factor (PDGF) stimulates division of human fibroblast cells in culture – Fibroblast = cell responsible for making extracellular matrix and collagen

Question 30

What is density-dependent inhibition?

Answer 30

crowded cells stop dividing

Question 31

What is anchorage dependence?

Answer 31

in which they must be attached to a substratum for division

Question 32

What is the difference between benign/malignant tumours?

Answer 32

If abnormal cells remain at the original site, the lump is called a benign tumor * Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form secondary tumors

Question 32

How do cancer cells/tumours form?

Answer 32

Cancer cells do not respond normally to the body’s control mechanisms; exhibit NEITHER density-dependent inhibition nor anchorage dependence * Cancer cells may not need growth factors to grow and divide * Cell transforms into cancer cell – cells divide rapidly (proliferate) in uncontrolled manner to form tumor

Question 33

List the differences between cancer cells and normal cells?

Answer 33

- Normal cells exhibit density-dependent inhibition and anchorage dependence but cancer cells do NOT - Normal cells have controlled rate of cell division (NO loss of cell cycle function, so they divide until there are enough cells present) but cancer cells don’t have controlled rate of cell division (loss of cell cycle function which causes cells to divided rapidly before having had a chance to mature) - Either repaired or die (undergo apoptosis) when they are damaged or get old (For example, there is a p53 protein that has the job of checking to see if a cell is too damaged to repair and, if so, advise cell to kill itself), but cancer cells either NOT repaired or DO NOT undergo apoptosis when they are damaged or get old (inactive/mutated p53 protein) - Normal cells have surface adhesion molecules that keep them bonded to neighboring cells but cancer cells do not - Normal cells DO NOT have the ability to metastasize (spread) – they stay in the area of the body where they belong but cancer cells can metastasize to other regions of the body by travelling through blood stream or lymphatic system - Develop into specialized cells (it means they can easily develop into brain cells, heart cells, lung cells or other specific types of cells) but cancer cells DON’T develop into specialized cells - Normal cells undergo angiogenesis only as part of normal growth and development and when new tissue is needed to repair damaged tissue but cancer cells undergo angiogenesis even when growth is not necessary!

Question 34

What is a life cycle?

Answer 34

the generation-to-generation sequence of stages in the reproductive history of an organism • Fertilization and meiosis alternate in sexual life cycles

Question 35

What are homologous chromosomes?

Answer 35

two chromosomes in each pair are called homologous chromosomes, or homologs…one chromosome is from the mother and other chromosome is from the father…homologous chromosomes can exist as unreplicated or replicated Homologous chromosomes are same size (i.e. length), and they have genes which are arranged in same orde

Question 36

How is a karyotype developed?

Answer 36

Karyotypes can be performed using amniotic fluid, blood, bone marrow, placenta • After growing cells, a drug called colchicine is added before karyotype processing – Colchicine arrest the cell at metaphase during cell division – At metaphase, the chromosomes are most condensed

Question 37

What is Down syndrome?

Answer 37

Down syndrome due to three copies of chromosome 21 – Most common chromosome abnormality in humans – Typically associated with a delay in cognitive ability and physical growth

Question 38

What is Klinefelter syndrome

Answer 38

Klinefelter syndrome, an XXY male – Individual has male sex organs, but are sterile – May display feminine characteristics – Intelligence is normal

Question 39

What is turner syndrome?

Answer 39

Turner syndrome, an XO female – Do not mature sexually during puberty (sterile) – Short stature and normal intelligence

Question 40

What is the difference between meiosis I and meiosis II (# of daughter cells, type of division, etc)?

Answer 40

Meiosis I starts with diploid parent cell containing a homologous pair of replicated chromosomes: homologous chromosomes separate into two haploid daughter cells with replicated chromosomes; it is called reductional division Meiosis II starts with haploid cells with just one homologous chromosomes: sister chromatids of each replicated chromosome separate. Results in four haploid daughter cells with unreplicated chromosomes; it is called equational division?

Question 41

What happens during prophase I

Answer 41

Prophase I typically occupies more than 90% of time required for meiosis • Replicated chromosomes condense and spindle microtubules begin to form from centrosomes In synapsis, homologous replicated chromosomes loosely pair up, aligned gene by gene • Each pair of homologs forms a bivalent (each bivalent usually has one or more chiasmata, regions where crossing over occurred) • In crossing over, non-sister chromatids exchange DNA segments to produce chromosomes with a combination of maternal and paternal alleles • Cells in prophase I are diploid

Question 42

What happens during metaphase I

Answer 42

Paired homologs line up at metaphase plate at random (cells in metaphase I are diploid) • Microtubules from one pole are attached to the kinetochore of one replicated chromosome of each bivalent • Microtubules from the other pole are attached to the kinetochore of the other replicated chromosome of each bivalent

Question 43

What happens during anaphase I

Answer 43

paired homologs separate (cells in anaphase I are diploid) • One chromosome moves toward each pole, guided by the spindle microtubules (kinetochore microtubules shorten while non- kinetochore microtubules lengthen) • Sister chromatids remain attached at the centromere

Question 44

What happens during telophase I and cytokinesis

Answer 44

In the beginning of telophase I, the homologs (as replicated chromosomes) finish migrating to the poles of the cell (cells in telophase I are diploid) • Afterwards, cytokinesis occurs, ultimately forming two haploid daughter cells • In animal cells, a cleavage furrow forms; in plant cells, a cell plate forms

Question 45

What happens during prophase II

Answer 45

In prophase II, a spindle microtubules form • In late prophase II, replicated chromosomes (each still composed of two sister chromatids) move toward the metaphase plate

Question 46

What happens during metaphase II?

Answer 46

• Replicated chromosomes are arranged at metaphase plate • Due to crossing over in meiosis I, the two sister chromatids of each replicated chromosome are no longer genetically identical • Kinetochore microtubules attach to sister chromatids

Question 47

What happens during anaphase II?

Answer 47

• In anaphase II, the sister chromatids separate • The sister chromatids of each replicated chromosome now move as two newly individual chromosomes toward opposite poles of cell

Question 48

What happens during telophase II and cytokinesis?

Answer 48

In telophase II, the chromosomes (which appear unreplicated) arrive at opposite poles • Nuclei form, and the chromosomes begin decondensing • Each cell then undergoes cytokinesis • At the end of meiosis, there are four daughter cells, each with a haploid set of unreplicated chromosomes • Each daughter cell is genetically distinct from the others and from the parent cell

Question 49

What three mechanisms contribute to genetic variation?

Answer 49

Independent assortment of chromosomes – Crossing over – Random fertilization

Question 50

What is independent assortment of chromosomes and what are the number of combinations possible?

Answer 50

Homologous pairs of replicated chromosomes (as bivalents) orient randomly at metaphase I of meiosis • Each bivalent sorts maternal and paternal homologs (as replicated chromosomes) into daughter cells independently of each other The number of combinations possible when replicated chromosomes assort independently into gametes is 2n, where n is the haploid number • For humans (n = 23), there are ~ 8.4 million (223) possible haploid combinations of unreplicated chromosomes that gametes can receive

Question 51

How does crossing over contribute to genetic variation?

Answer 51

Crossing over produces recombinant chromosomes, which combine genes inherited from each parent • Crossing over begins very early in prophase I, as homologous replicated chromosomes pair up • In crossing over, homologous portions of two non-sister chromatids trade places • Crossing over contributes to genetic variation by combining DNA from two parents into a single chromosome

Question 52

How does random fertilization contribute to genetic variation and what are the number of possible combinations?

Answer 52

Random fertilization adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg) • The fusion of two gametes (each sperm or egg cell has one of ~ 8.4 million possible haploid chromosome combinations from independent assortment) – 223 = ~ 8.4 million • Zygote can have one of ~ 70 trillion possible diploid combinations – 8.4 million x 8.4 million - ~70 trillion