Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

b2 > 2_3 > Flashcards

2_3 Flashcards

1
Q

cell cycle

A
  • Multicellular eukaryotes depend on cell division for Development from a fertilized cell, Growth, Repair
  • Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division.
  • Most cell divisions result in daughter cells with identical genetic information.
  • The exception is meiosis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

genome

A
  • All the DNA in a cell constitutes the cell’s genome.
  • A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells).
  • DNA molecules in a cell are packaged into chromosomes.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

binary fission

A
  • Cell Division in a prokaryote
    1. DNA contained in a single circular chromosome with an origin of replication. First step is DNA replication.
    2. Cell gets larger as chromosomes move to opposite ends of the cell.
    3. After replication, cell pinches in two, resulting in two identical daughter cells.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Eukaryotic chromosomes

A
  • Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division.
  • Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Cell division in eukaryotic cells more complicated because

A

because they have…
More than one chromosome
Cell organelles
Cytoskeleton

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

cell cycle phases

A

interphase

  1. G1 (40 percent) - separates M phase from S phase. Cell grows and accumulates substrates needed for DNA replication. Centrioles in centrosome separate.
  2. S (39 percent) - DNA synthesis
  3. G2 (19 percent) - separates S from M. Cell produces molecules needed for mitosis.

M phase
(2 percent); Mitosis (nuclear division) and cytokinesis (division of the cytoplasm)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

G0

A

(variable) The non-dividing (resting) phase in which most cells exist

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

cell cycle differences

A
  • The frequency of cell division varies with the type of cell
  • These cell cycle differences result from regulation at the molecular level
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

cell cycle experiments

A
  • The cell cycle appears to be driven by specific chemical signals present in the cytoplasm
  • Some evidence for this hypothesis comes from experiments in which cultured mammalian cells at different phases of the cell cycle were fused to form a single cell with two nuclei
  • one cell in S; one in G1; G1 nucleus immediately entered S phase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

checkpoints

A
  • In normal cells that divide, the cell cycle does not proceed unchecked. Cells maintain control over the stages of the cell cycle through what are called checkpoints—steps along the cycle that must be completed before the next step is started.
  • Many of these signals are kinases (cyclin-dependent kinases - CDKs) that activate other proteins and allow the next phase to proceed.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

G1 checkpt

A

regulates the entry of the cell into the S-phase of DNA replication.
One of the conditions that must be met is:
Is DNA undamaged?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

G2 checkpt

A

regulates the entry of the cell into the M-phase of mitosis
One of the conditions that must be met is:
Has all of the DNA been replicated?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

M checkpt

A

regulates the entry of the cell from metaphase to anaphase
One of the conditions that must be met is:
Are the chromosomes aligned at the metaphase plate?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Cdk/cyclin concentrations

A
  • Cdks are proteins that activate other proteins and allow the next phase to proceed. Their concentrations do not vary throughout the cell cycle. However, they must be bound to cyclins to be active.
  • Cyclin concentrations do vary during the cell cycle.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Cdk/cyclin compelx and example

A
  • Cyclins and CDK bind together to form complexes that control the progression of the cell cycle.
  • ex: Maturation (or M-phase)-promoting factor (MPF)
  • This protein allows the cell to progress past the G2 checkpoint and enter mitosis. It is formed when a cyclin binds to a CDK.
  • Activated MPF is a kinase and controls some of the processes associated with mitosis, including the breakdown of the nuclear membrane.
  • MPF is only a transiently active molecule - only when it is bound to cyclin.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

MPF concentration

A
  • MPF also initiates a sequence that leads to its separation back into a cyclin and the inactive cyclin-dependent kinase. The cyclin is then broken down, and levels remain low until the correct signal occurs to increase cyclin concentrations.
  • MPF activity tracks (and lags behind) changes in the cyclin concentration
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

internal signal at checkpt

A

An example of an internal signal is that kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

external signal at checkpt

A
  • Some external signals are growth factors, proteins released by certain cells that stimulate other cells to divide
  • Another example of external signals is density-dependent inhibition, in which crowded cells stop dividing
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

PDGF

A
  • example of growth factor (external signal)
  • platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture
    experiment:
    1. sample of human connective tissue is cut up into small pieces w/ scalpel, pieces placed in petri dish
    2. enzymes digest the ECM, resulting ins uspension of free fibrobasts
    3. cells transferred to culture vessels; PDGF added to half of the vessels
    4. vessels w/ PDGF: many more cells than vessels w/o
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

anchorage dependence

A
  • example of external signal
  • Most animal cells, in addition to density-dependent inhibition, exhibit anchorage dependence, in which they must be attached to a substratum in order to divide
  • Cancer cells exhibit neither density-dependent inhibition nor anchorage dependence
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

density-dependent inhibition

A
  • crowded cells stop dividing

- cells form a single layer; cells divide to fill a gap and then stop

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

S-Cdk

A

S-Cdk controls G1 checkpoint (entry into S-phase)
- if DNA is damaged, S-Cdk is inhibited so cell won’t
enter S-phase and replicate damaged DNA.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Ubiquitylation

A

is the targeting of molecules to be destroyed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

when p53 gene is normal

A
  • Mdm2 binds to the unphosphorylated p53 and directs it to be destroyed. (Ubiquitylation)
  • In response to the presence of damaged DNA, kinases are activated that phosphorylate and thus increase the concentration of p53 (it’s no longer ubiquitylated).
  • Active p53 binds to a regulatory site on the DNA just upstream from a gene that codes for a protein called p21.
  • This stimulates the transcription of the p21 gene and through translation increases the production of the p21 protein.
  • p21 protein is a CDK inhibitor and it binds to and inhibits the activity of the S-cyclin CDK complex.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

when there’s something wrong w/ p53

A
  • Cells that lack the p53 gene or gene product fail to make p21 and thus do not inhibit the S- cyclin CDK complex when their DNA is damaged.
  • As a result, the entry into the S-phase is uninhibited and the damaged DNA is replicated. This can result in the production of cells that have damaged DNA and can become cancerous. In fact many human cancers have been traced to mutants in the p53 gene.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

kinetochores

A

attachment points of microtubules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

M-Cdk

A

allows entry into anaphase (M checkpoint)
by activating APC (anaphase promoting complex)
- Initiates the separation of sister chromatids at the metaphase-anaphase boundary.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

APC

A
  • Cohesin proteins hold sister chromatids together.
    APC (anaphase promoting complex) is activated by phosphorylation by M-Cdk. This activated APC then can bind cdc20.
  • Active APC then ubiquitylates and destroys securin, which had been bound to separase, thus inactivating securin.
  • Freed separase then cleaves the cohesin molecules.
  • Tension on the chromatids exerted by the mitotic spindles (microtubules) pulls chromatids to opposite poles.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

microtubules

A
  • essential for cell division
  • tubulin dimer from alpha and beta monomers
  • 25 nm diameter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

centrosomes

A
  • Centrosomes are the point at which microtubules are formed in some but not all cells. (microtubule-organizing region)
  • In animal cells they contain a pair of centrioles, may contribute to but are not required for microtubule formation.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Nucleolus

A

Consists of ribosomes and RNA. Is well developed in cells that have a lot of active protein synthesis. The nucleolus is the site of synthesis of ribosomal proteins.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Chromatin

A

Consists of DNA and its associated proteins (histones and non-histone proteins) , in particular a group of proteins called histones that are structural proteins are closely associated with DNA. Also many regulatory proteins that have many functions in controlling gene expression.
- in non-dividing cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

packaging of DNA in non-dividing phase

A
  • During the non-dividing phase, DNA is not organized into an easily visible structure within the cell nucleus. Chromosomes, which are the characteristic feature of dividing cells, are not present. Instead, DNA is found in chromatin.
  • Chromatin is distributed throughout the
    nucleus, and in this form would be difficult
    to distribute accurately between the
    daughter cells.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

packaging of DNA in dividing phase

A
  • In dividing cells chromatin is organized into more readily recognizable structures called chromosomes.
  • During cell division a complex of proteins called kinetochores attaches to the centromere. Specialized microtubules attach and pull the chromosome apart.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

chromosomes

A

Each chromosome is comprised of a single strand of DNA. In a somatic cell, the chromosome has two sister chromatids which contain identical strands of DNA. The chromatids are joined at a centromere, which is the point at which the chromosomes are pulled apart during mitosis.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

How is DNA organized within the nucleus?

A
  • The human genome has 6 x 10^9 base pairs, each of which occupies 0.34nm. This means that the DNA in every cell is 2m long. How is this packaged into a nucleus that is often only 10µm in diameter?
  • it’s accomplished by a complex folding process that involves a close association of the DNA with a series of proteins.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

nucleosome

A

a structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histones.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

mitosis

A 
The cell begins mitosis from G2 of interphase.
 Mitosis consists of five phases:
   1) Prophase
   2) Prometaphase
   3) Metaphase
   4) Anaphase
   5) Telophase

Mitosis is just the nuclear division.
It is followed by cytokinesis, which is the separation of the cytoplasm and the formation of the two daughter cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Two key events occur after the cell enters S phase:

A

1) DNA is replicated

2) The centrosome replicates.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

Centrosome replication

A

replication is controlled by a cyclin-cdk complex whose concentration peaks at the G1 checkpoint and is the key event in directing the cell towards mitosis (cell enters S phase).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

centrosome movement

A

During G2-to-M transition, the two new centrosomes separate from each other and move to opposite ends of the nuclear envelope.
The orientation of the centrosomes within the cell determines the cell’s plane of division.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

structures involved in prophase

A

1) Chromosomes

2) Centrosomes and microtubules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

chromosomes in prophase

A
  • During prophase, chromosomes become visible as distinct structures, but are fairly elongated.
  • Prophase chromosomes consist of two sister chromatids held together over much of their length by cohesins.
  • The kinetochore is a structure associated with the centromere and is the site where microtubules attach to the chromatids. They develop in late prophase.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

microtubules in prophase

A
  • Polar microtubules and astral microtubules make up the non-kinetochore microtubules and begin to extend from each centrosome complex in a formation called an aster (‘star’).
  • These tubules will develop into mitotic spindles. Microtubules are formed by addition of tubulin dimers to the end of each microtubule.
45
Q

polar microtubule

A

Each polar microtubule runs from a centrosome to a point where it overlaps and interacts with a microtubule from the other side.

46
Q

astral microtubuel

A

Astral microtubules extend between the centrosome and the cell membrane.

47
Q

prometaphase structures involved

A
  • chromosomes
  • nuclear lamina
  • microtubules
  • kinetochores
48
Q

chromosomes in prometaphse

A
  • The chromosomes become more tightly coiled and appear shorter and fatter. They remain held together by cohesins.
  • Chromosomes move toward the center of the cell—the metaphase plate. At this point, chromosomes often demonstrate a jerky back and forth motion as they line up in the middle of the cell.
49
Q

nuclear structures in prometaphase

A

The nuclear lamina disintegrates (remember MPF?) and the nuclear envelope fragments to permit spindle microtubules to infiltrate the nuclear region.

50
Q

kinetochore vs centromere

A

centromere: The ‘waist’ of a chromosome. The structure where mitotic spindles attach.
kinetochores: Proteins that attach microtubules to centromeres.

51
Q

non-kinetochore microtubules

A

The spindle microtubules ones not attached to kinetochores are called non-kinetochore microtubules: polar microtubules and astral microtubules.

52
Q

microtubules in prometaphase

A
  • Some of the spindle microtubules begin to associate with kinetochores. These are called kinetochore microtubules.
  • The microtubules from one pole associate with the kinetochore of one of the sister chromatids of each chromosome. Microtubules from the other pole associate with the kinetochore of the other chromatid.
53
Q

nuclear structures in metaphase

A

The nuclear membrane and laminar have completely disintegrated.

54
Q

metaphase: ____ begins ____

A

The cohesins begin to be broken down (remember m-Cdk and separase?).

55
Q

microtubules in metaphase

A

Chromosomes held in center by tension of kinetochore microtubules—each is being pulled toward one or the other end, but chromosomes are still attached together so they stay in the center.

56
Q

chromosomes in metaphase

A
  • Chromosomes aligned at metaphase plate in the center of cell, midway between each spindle pole.
  • Chromosomes held in center by tension of kinetochore microtubules.
57
Q

chromosomes in anaphase

A
  • The sister chromatids of each chromosome (now referred to as daughter chromosomes) are pulled apart during anaphase.
  • Cleavage of cohesins is completed.
  • Daughter chromosomes pulled to opposite poles.
58
Q

microtubules in anaphase

A
  • Kinetochore microtubules shorten—pull chromosomes to poles.
  • Polar microtubules lengthen—push spindle poles apart.
  • Astral microtubules shorten—pull spindles apart.
59
Q

At the end of anaphase,

A

each pole of the cell has an identical complement of genetic material.

60
Q

microtubule experiment

A 
- Microtubules labeled with
 yellow fluorescent dye.
- Then, a portion of the dye
 was bleached with a laser.
- Later, when the chromosomes
 were pulled to the poles,
 the bleached area
 was unmoved.
61
Q

conclusion of microtubule experiment

A
  • Kinetochores are microtubule-associated motor proteins.
  • They walk along the kinetochore microtubule pulling the chromosome along. The end of the microtubule then depolymerizes into tubulin subunits.
62
Q

by the end of telophase,

A

telophase is end of mitosis

- Separation of the genetic material is complete.

63
Q

chromosomes in telophase

A

The chromosomes become less tightly coiled and the chromatin again begins to form.

64
Q

nuclear structures in telophase

A

New nuclear membranes and nucleoli begin to form around each group of daughter chromosomes.

65
Q

microtubules in telophase

A

Lengthening of the polar microtubules elongates the cell further.

66
Q

cytokinesis

A
  • The final part of the M phase is cytokinesis where two complete daughter cells are formed.
  • This involves the formation of barrier a between the two new cells.
67
Q

cleavage furrow

A

In animal cells, this forms from a cleavage furrow that requires actin and myosin filaments.

68
Q

cell plate

A

In plant cells, a cell plate forms as vesicles derived from the Golgi fuse to make a new plant cell wall.

69
Q

anaphase microtubule polarity

A

Microtubules have a polarity:
“plus” end is the free end.
“minus” end is the end attached to the centrosome.

70
Q

A closer look at the action of kinetochore microtubules during anaphase

A

During anaphase,

  • kinetochore microtubules shorten
  • daughter chromosomes move toward poles
  • these forces are generated mainly at the kinetochores

Depolymerization of kinetochore microtubules shortens the microtubule, which pulls the kinetochores toward the poles. (the kinetochores walk along the kinetochore microtubules, pulling the chromosomes along.)

71
Q

two forces in anaphase

A

Outward pull: astral microtubules

Outward push: polar microtubules

72
Q

astral microtubules in anaphase

A

outward pull

  • Dyneins are involved (minus-end-directed motor proteins; have “three dots” with two “feet”)
  • one “Dot” is tethered to the cell cortex
  • “Feet” walk along astral microtubules, pulling them toward cell periphery.
73
Q

polar microtubules in anaphase

A

outward push

  • Kinesins (plus-end-directed motor proteins) “carry” (not really carrying) one microtubule as they walk along another polar microtubule, pushing behind them the ones they are walking along.
  • “Walking” is opposite direction of movement of polar microtubules.
74
Q

How kinesin walks along microtubules from minus end to plus end.

A

remember: w/ phosphate group (w/ ATP) means attached to MT
1. starts off: Trailing head (h2) has ADP bound and is unbound to MT. Leading head (h1) is bound to MT
2. ATP binds to leading head, causing trailing head (h2) to step past leading head (h1)
3. ADP released from previously trailing head (t2) (now in the lead), ATP hydrolyzed to ADP on the previously leading head (h1) (now trailing). Phosphate group released and head releases its grip on MT.

Each head spends about 50% of time in bound state and 50% of time in unbound state.

75
Q

what drives chromosomes to the metaphase plate

A

Polar ejection force pushes chromosomes away from the poles toward the equator.

76
Q

what drives chromosomes to the metaphase plate: experiment

A
  • using laser, cut chromosome in prometaphase when only one of its sister chromatids is attached to a kinetochore MT (before a second MT attaches to the other sister chromatid’s kinetochore)
  • result: unattached arm moves (pushed) away from pole; attached arm is pulled by MT towards pole
77
Q

meta vs anaphase movements

A
  • Kinesin “walks” on a polar microtubule and “carries” the chromosome arms
    pushing them toward the metaphase plate.
  • Meanwhile, kinetochore “walks” along kinetochore microtubule
    pulling the chromosomes toward the spindle pole.
78
Q

microtubules

A
  • long, hollow cylinders made of tubulin
  • 25 nm outer diameter
  • more rigid than actin or intermediate filaments
  • long and straight
  • typically have one end attached to a single microtubule-organizing center (centrosome)
  • They constantly change shape (and length) through cycles of polymerization / depolymerization.
79
Q

protofilaments

A

microtubules
- There are thirteen strands or protofilaments arranged in a circle around a hollow lumen.
- Each protofilament is made of chains of heterodimers.
There is a plus end and a minus end.
These correspond to the two polypeptides, α and β tubulin
that make up each dimer: “plus” end is β, “minus” end is α .

80
Q

microtubules and GTP

A
  • Each monomer (the α/β tubulin dimer) has a bound GTP.
  • When it is added to the polymer the GTP (T) is hydrolyzed to GDP (D).
  • Hydrolysis of the bound nucleotide reduces the binding affinity of the newly added subunit for neighboring subunits and makes it more likely to dissociate from the end.
  • Therefore, it is the T form that adds and the D form that leaves.
81
Q

monomer concentrations

A

(remember monomer is alpha+beta dimer)
The higher the monomer concentration (T form) the more likely addition will be greater than subtraction and the microtubule will grow.

Therefore, the “on” rate will be dependent upon the concentration (availability) of free monomers.

At lower monomer concentrations, subtraction will be faster than addition and it will shrink.
At higher monomer concentrations, addition will be faster than subtraction and it will grow.
The concentration where addition and subtraction are equal is called…
the critical concentration.

82
Q

Plus end vs minus end

A

Monomers add more easily to the plus end than they do to the minus end. Therefore, the critical concentration is lower for the plus end (monomers add more easily to that end) than it is for the minus end.

83
Q

GTP cap

A

If monomer addition (T-on) is faster than hydrolysis of nucleotide (D-off), a GTP CAP will form at the growing end.

De-polymerization will be inhibited and the growing end will be stabilized.

This will occur when the concentration of T-form monomers is higher than the critical concentration for that end.

84
Q

Another way of looking at the critical concentration.

A

At any given concentration of monomer, addition at the minus end is slower, so hydrolysis predominates, and the minus end will more likely have a subunit with a “D” nucleotide.
On the other hand, plus end addition is faster, so the plus end will have a “T” nucleotide.
Thus, Cc(T) (plus) is lower than Cc(D) (minus).

In other words, since the monomers are being added to the plus end faster, the concentration where they are added and removed at the same rate (the critical concentration) for the plus end is lower (fewer are needed to add on more monomers).

85
Q

graphical way of looking at criticial concentration

A
  • Graph of subunit concentration (x) vs. elongation rate (y) for plus and minus ends.
  • Slope is steeper for plus end because subunits add added more easily there.
  • x-int is where the monomers are being added and removed at the same rate to that end—this is the critical concentrations (Cc).
  • More subunits are needed to grow the minus end since they are added more slowly there—therefore the Cc(D) is higher.
  • A lower monomer concentration is needed to grow the plus end since they are added more easily there—therefore the Cc(T) is lower.
  • When the actual concentration is in between Cc(T) and Cc(D), the monomers are being added to the plus end but removed from the minus end—this is the treadmilling range (xD - xT)
86
Q

treadmilling

A
  • When the free monomer concentration is above the Cc for the plus end
    but below the Cc for the minus end, subunits undergo a net assembly at
    the plus end and net disassembly at the minus end at an identical rate.
  • The polymer maintains a constant length, even though there is a net flux
    of subunits through the polymer.
87
Q

treadmilling MT diagram

A
  • Tubulin monomers labeled with green fluorescent dye.
  • Filament seems to slide from left to right, but adding subunits to the right (plus end) and losing subunits from the left (minus end).
  • plus end is “dynamically
    unstable”; it grows, shrinks
    then grows again.
88
Q

asexual reprod

A

Asexual reproduction
Generates a new individual that is essentially genetically identical to the parent. It involves a cell or cells that were generated by mitosis.
Genetic variation is generated from random mutations or environmental effects.
This can be efficient for environmental adaptation if offspring
production is rapid, e.g. bacterial reproduction.

89
Q

sexual reprod

A

Sexual reproduction mixes and shuffles genes from two parents to form a new individual.
- new genetic combinations are created.
- these new combinations produce genetic variation.
- this allows for the potential for greater adaptation of
organisms to their environment.

90
Q

Homologous chromosomes

A

come from the two parents

91
Q

Like mitosis, meiosis

A

is preceded by the replication of chromosomes.

92
Q

unlike mitosis, meiosis

A
  • Unlike mitosis, meiosis takes place in two consecutive cell divisions, called meiosis I and meiosis II.
  • The two cell divisions result in four daughter cells, rather than the two daughter cells in mitosis.
  • Each daughter cell has only half as many chromosomes as the parent cell.
93
Q

prophase I

A

In early prophase I (after chromosome duplication in interphase) each chromosome pairs with its homologue and crossing over occurs.
- The result is that gene alleles are swapped between homologous
chromosomes. This swapping is a source of genetic variation
among offspring because these new combinations will be sorted
out into different gametes.

94
Q

chiasmata

A

X-shaped regions called chiasmata are sites of crossover between non-sister chromatids.

95
Q

metaphase I

A
  • In metaphase I, pairs of homologues line up at the metaphase plate, with one chromosome facing each pole.
  • Each pair of duplicated homologous chromosomes is called a tetrad.
96
Q

synapsis

A

(tetrads in metaphase I)
when synapsing occurs, the chromosomes don’t lie side by side but rather on top of each other w/ a protein called the synaptonemal complex holding them together

97
Q

microtubules in metaphase I

A

Microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad; microtubules from the other pole are attached to the kinetochore of the other chromosome.

98
Q

anaphase I

A
  • In anaphase I, pairs of homologous chromosomes separate.
  • One chromosome of each pair moves toward opposite poles, guided by the spindle apparatus.
  • Sister chromatids remain attached at the centromere and move as one unit toward the pole.
99
Q

Telophase I and Cytokinesis

A
  • In the beginning of telophase I, each half of the cell has a haploid set of chromosomes; each chromosome still consists of two (non-identical due to prophase I crossover) sister chromatids.
  • Cytokinesis usually occurs simultaneously, forming two haploid daughter cells.
100
Q

prophase II

A

In prophase II, a spindle apparatus forms in each cell.

In late prophase II, chromosomes (each still composed of two chromatids) move toward the metaphase plates.

101
Q

metaphase II

A
  • In metaphase II, the (non-identical due to prophase I crossover) sister chromatids are arranged at the metaphase plate.
  • The kinetochores of sister chromatids attach to microtubules extending from opposite poles.
102
Q

anaphase II

A
  • In anaphase II, the sister chromatids separate.
  • The cohesin molecules keeping the sister chromatids attached are cleaved.
  • The sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles.
103
Q

Telophase II and Cytokinesis

A

In telophase II, the chromosomes arrive at opposite poles.

Nuclear membrane reforms.

Cytokinesis separates the cytoplasm.

104
Q

mitosis vs meiosis: chromosome sets

A
  • Mitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell
  • Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell
105
Q

mitosis and meiosis similarity

A

The mechanism for separating sister chromatids is virtually identical in meiosis II and mitosis

106
Q

events are unique to meiosis

A

Three events are unique to meiosis, and all three occur in meiosis l:
- Synapsis and crossing over in prophase I.
- At the metaphase plate, there are paired homologous chromosomes (tetrads) instead of individual replicated chromosomes
- At anaphase I, it is homologous chromosomes
instead of sister chromatids, that separate

107
Q

Three Sources of Genetic Variation

A

1) Distribution of genetic material between chromosomes during “crossing over” of prophase I.
2) Random arrangement of chromosomes at Metaphase I (Independent Assortment).
3) The random nature of fertilization.

108
Q

possible combo numbers

A
  • Random fertilization adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg).
  • Independent assortment can generate 2^23 or 8.4 million possible chromosome combinations in each gamete.
  • Random fertilization (any egg can theoretically combine with any sperm) will then produce a zygote with any of about 2^23 X 2^23 or 70 trillion diploid combinations.
  • These calculations don’t even account for the variability coming from crossing over events.

b2 (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions