Mitosis And Meiosis

Front 1

Term for cytoplasm dividing

Back 1

cytokinesis

Front 2

List the phases of cell division and what happens during each.

Back 2

G(1) – gap phase (“growth phase”) btwn M & S phases

S phase – DNA is replicated

G(2) – gap phase (“growth phase”) btwn S & M phases

M phase – 1.) mitosis: cells nucleus divide, then 2.) cytokinesis occurs.

Front 3

What are CDKs and what function do they serve? What is cyclin?

Back 3

CDK: “Cyclin-Dependent Kinases,” catalytic part of the cell-cycle control system. Activated by Cyclin binding and phosphorylation or dephosphorylation of certain amino acids.

Cyclin: regulatory part of the control system

Different CDKs drive different parts of the cell cycle (i.e. M-CDK drives the cell to Mitosis, G(1)-CDK drives the cell to G(1), etc.)

Front 4

Describe the cell control system

Back 4

**Coordinates the events of the cell cycle by switching on and off the appropriate cellular machinery.
**Key players are Cyclin and CDKs.
**Can halt the cell at specific “checkpoints” to ensure things happen in the right timing and conditions are favorable. (NOTE – cancers often override these checkpoints.)

Front 5

What are the two mechanisms by which the cell cycle can be halted?

Back 5

1.) CDK inhibitor proteins block assembly/activity of cyclin-CDK complex
2.) Components of control system can stop being made [this happens during G(0)]

Front 6

DNA is replicated during the ____ phase. The two copies of chromosomes are called __________. They are bound together by __________.

Back 6

S
Sister chromatids
Cohesins

Front 7

Mitosis is triggered by a phosphorylation, which is initiated by ______. List the phases of mitosis.

Back 7

M-CDK

1.) prophase
2.) prometaphase
3.) metaphase
4.) anaphase
5.) telophase
6.) also … cytokinesis (begins at anaphase, ends at telophase)

Front 8

The cell cycle lasts ____ hours. Mitosis lasts ______. The cell nucleus is visible in ______ phase most of the time.

Back 8

17-18
1-2
Inter(phase)

Front 9

What are the components of interphase?

Back 9

G(1) phase
S phase
G(2) phase

Front 10

What are centrosomes? What are centrioles? Why are they important?

Back 10

Centrosomes are the microtubule organizing center. Microtubules grow out from the centrosome.

Centrioles are the short, cylindrical array of microtubules, found in pairs at the center of the centrosome. (Same thing as basal bodies on cilia and flagella.)

Both are duplicated during S phase.

They are critical for mitotic spindle formation and establish a plane of cell division.

Front 11

What morphological changes occur as mitosis commences?

Back 11

*chromosomes condense
*nuclear envelope breaks down
*reorganization of ER and Golgi apparatus
*cell loosens its attachment to other cells & ECM
*cytoskeleton (microtubules) begins to reorganize for chromosome segregation (formation of spindle)

Front 12

In what phase are centrioles and centrosomes duplicated? What factors initiate their duplication?

Back 12

They are duplicated in S phase (but they don’t move to the poles or separate the sister chromatids until M phase).

G(1)-CDKs and S-CDKs initiate their duplication, same as what initiates chromosomal replication.

Front 13

What are condensins?

Back 13

Sets of protein complexes that help carry out chromosome condensation when the cell is about to enter M phase.

Front 14

What is the aster?

Back 14

Star-shaped system of microtubules emanating from the centrosome.

Front 15

What happens during prophase?

Back 15

*chromosomes condense
*centrosomes separate
*interphase microtubules break down → spindle microtubules assemble

Front 16

What happens during prometaphase?

Back 16

*nuclear envelope breaks down
*chromosomes attach to spindle microtubules
*movement to poles begins

Front 17

The spindle microtubules end up attached to the chromosomes through specialized protein complexes called ____________. These protein complexes first assemble onto the __________ during ______(phase)_____ and the microtubules begin to attach to them during ____(phase)_______.

What important event also occurs during spindle attachment?

Back 17

Kinetochores
Centromere
Late prophase
Prometaphase

One of the key checkpoints occurs during spindle attachment.

Front 18

How do the chromosomes end up along the equator? What two things drive the movement of chromosomes by the spindle?

Back 18

Microtubules from opposite poles each pull in opposite directions on their commonly-attached chromosome, bringing to chromosomes to the center of the mitotic spindle. Sister chromatids will eventually separate, allowing the two daughter chromosomes to be pulled to opposite poles. The poles also begin to move apart.

Movement of chromosomes by spindle is driven by:
1.) microtubule motor proteins
2.) microtubule polymerization and depolymerization (“dynamic instability” -- this occurs much faster and at greater levels during mitosis than during interphase)

Front 19

What happens during metaphase?

Back 19

*Chromosomes align at the spindle equator (“metaphase plate”)
*Bipolar spindle assembly is complete

Front 20

What happens during anaphase?

Back 20

*Sister chromatids separate and move suddenly and synchronously towards opposite poles
*Spindle poles move apart

Front 21

What happens during telophase?

Back 21

*Daughter chromosomes arrive at poles and decondense
*Nuclear envelope reassembles
*Contractile ring assembles

Front 22

During what phase does the nuclear envelope break down? During what phase does it reassemble?

Back 22

Prometaphase
Telophase

Front 23

When does cytokinesis occur? Cytokinesis is not officially over until after the _________ have formed. The process is mediated by the _________, which is made up of ________ filaments and assembles ____(where?)____.

Back 23

Begins at anaphase, ends at telophase

Two daughter nuclei
Contractile ring
Actin and myosin
Midway between the two spindle poles

Front 24

Prophase I is a complex stage further subdivided into what 5 stages?

Back 24

Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis

“Lefty Zebras Probably Don’t Dance”

Front 25

Describe how chromosome number is reduced and then restored.

Back 25

Meiosis reduces the number of chromosomes from diploid (2n=46) to haploid (n=23). The diploid number is restored in the zygote by fertilization. (Two haploid gametes come together to form the zygote.)

Front 26

What are the substages of meiosis I? Which stage is further subdivided?

Back 26

Interphase
Prophase I
Metaphase I
Anaphase I
Telophase I

Prophase I is further subdivided into leptotene, zygotene, pachytene, diplotene, and diakinesis.

Front 27

During what phase (be specific) does crossing over occur? What is another term for crossing over? The points where crossing over has occurred are referred to as what?

Back 27

The pachytene stage of prophase I
recombination
chiasmata

Front 28

Once ______ takes place, the cell is committed to meiosis. What does the cell look like at this stage?

Back 28

Lepotene stage of prophase I

At this stage there are still 46 chromosomes, each comprised of 2 chromatids. They have not yet condensed enough to be seen by light microscopy.

Front 29

During what phase do homologous chromosomes pair? How do they pair? What is the term for this pairing?

Back 29

Zygotene phase of phrophase I

Chromosomes pair by matching locus for locus (can be trouble when there are translocation mutations)

“Synapsis”

Front 30

Give a brief rundown of what happens at each substage in prophase I

Back 30

Lepotene → cell becomes committed to meiosis
Zygotene → synapsis begins (i.e. homologous chromosomes pair)
Pachytene → synapsis is complete; crossing over occurs
Diplotene → homologous chromosomes begin to repel each other (chiasmata are still attached)
Diakinesis → chromosomes reach their greatest contraction (????)

Front 31

During what phase do the homologous chromosomes begin to repel each other? Where are chromosomes attached during this stage?

Back 31

Diplotene stage of prophase I
Chromosomes remain attached at the chiasmata

Front 32

How do sex chromosomes pair during synapsis in males?

Back 32

The X and Y chromosomes only have one point of homology: the “pseudoautosomal regions.” This is where synapsis occurs. This is the only region that have homolgous loci and do not undergo X-inactivation.

Front 33

By the _______ stage, synapsis is complete. Paired homologues form a structure called ________ (a.k.a. _________ because there are ____(#) chromatids).

Back 33

Pachytene
Bivalents
Tetrads
4

Front 34

What are key error points in Meiosis?

Back 34

“Non-disjunction during Metaphase I” (As Metaphase I enters Anaphase I)

and “Non-disjunction during Metaphase II”

Front 35

What one main difference between the metaphase plate in mitosis vs. meiosis?

Back 35

The homologous pairs are not necessarily lined up during mitosis, but they are during meiosis.

Front 36

In going from meiosis I to meiosis II, cells move directly from what phase to what phase? (Skipping what phase?)

Back 36

Move directly from telophase I to metaphase II (skipping prophase II)

Front 37

The net result of meiosis is ____ (#) cells each with _____ (#) chromosomes each consisting of _____.

Back 37

4
23
a single chromatid

**Note: these are gametes

Front 38

What are the key differences between Male and Female meiosis?

Back 38

Male: Meiosis begins at puberty, continues throughout life
Female: Oocytes are formed during fetal life (prophase begins at 14 weeks gestation), then lost throughout life

Male: Each meitotic division results in 4 sperm
Female: Meitotic division results in one large egg and 3 nonfunctional polar bodies

Male: Cycle from spermatocyte to sperm takes about 40 days
Female: Meiosis arrests at diplotene phase of prophase I (during fetal life). Meiosis I completes during ovulation. Meosis II is completed only after fertalization.

Front 39

Spermatocytes are continually replaced by _______. Sperm maturation involves loss of _______ and _______ of the DNA.

Back 39

Mitosis
Histones
Condensation

Front 40

Give the sequence of female meiosis (when in life each stage occurs). What implications does this type of sequence have?

Back 40

Prophase I begins at 14 weeks gestation.
Meiosis is arrested after diplotene phase of Prophase I
Meiosis I resumes and completes during ovulation
Meiosis II is complete only after fertilization

Incidence of chromosome abnormalities (especially non-disjunction) increases with maternal age, but not paternal age. Perhaps because the eggs are really old by the time Meiosis is completed, so they are more prone to stick together.