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Cell Division Flashcards

1
Q

Cell cycle

A

controls cell division

Consisting of interphase (G1 phase, S phase, and G2 phase) and M phase (mitosis or meiosis) in cells

  • the life cycle cells must pass through to replicate their DNA and divide

The transition from one phase to the next is controlled by protein-based interactions.

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2
Q

interphase

A

consists of:
G1 phase
S phase
G2 phase

duplicate everything the cell has (if you want to make 2 cells you need 2 ribosomes etx)
increase in cell size
major chunk of cell cycle
does not involve cell division

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3
Q

G1 phase

A

“Gap 1”, Gene expression is high

activity gene expression (genes are actively transcribed and translated while normal cells carry on function) and cell activity preparation for DNA synthesis

4-6 hrs

cell grows increasing in size

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4
Q

s phase

A

Synthesis” phase, DNA replication occurs here

Doubles the DNA content by creating two sister chromatids (chromosomal duplication)

10- 12 hrs- done with high level of accuracy
- if something is recopied wrong this could have major consequences

  • in chromatin phase at the start of s phase at the end each chromosome has 2 sister chromatids
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5
Q

G2 phase

A

“Gap 2”,
cell prepares to divide

Chromosomes are diffuse and not visible (called chromatin)

Chromosomes are duplicated (already went through S-phase)

Nuclear envelope still encloses the nucleus

Two centrosomes are in the cytoplasm

Microtubules begin the to extend

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6
Q

M phase

A

is the short segment during the cell cycle in which cells divide
follows interphase

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7
Q

mitosis

A

is the process that creates two genetically identical daughter cells
Occurs in somatic cells
Responsible for growth and tissue repair, replacing dead cells

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8
Q

meiosis

A

process of cell division that occurs in germ line cells

produces 4 haploid gametes

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9
Q

prophase

A

Chromosomes begin to condense and become visible

Sister chromatids attached via centromeres visible

Pair centrosomes move to the poles

Microtubules extend from centrosomes to form mitotic spindle

Nucleolus disappears

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10
Q

Prometaphase

A

Nuclear envelope breaks down

Mitotic spindle attaches to kinetochores of the sister chromatids

Microtubules begin exerting pulling forces in both directions

Chromosomes begin to move to center of the cell

Cohesion proteins bind sister chromatids together

Resists premature separation

Non kinetochore and astral microtubules stabilize the cell

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11
Q

metaphase

A

Chromosomes fully condensed

Chromosomes align to metaphase plate

Sister chromatids are still attached to kinetochore microtubules extended from centrosomes

Mitotic spindle fully developed

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12
Q

anaphase

A

Sister chromatids separate (disjunction)

Cohesion proteins break down

Kinetochore microtubules depolymerize

Daughter chromosomes move towards opposite poles and congregate at centrosomes

Non kinetochore and astral microtubules polymerize, elongating the cell

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13
Q

telophase

A

Nonkinetochore microtubules continue polymerising, elongating the cell

Nuclear envelope redevelops

Chromosomes decondense

reverse of prophase

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14
Q

cytokinesis

A

divides the cytoplasmic contents equally between the daughter cells

Forms a cell plate in plants

Forms a contractile ring and cleavage furrow in animals

Nucleolus reforms

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15
Q

diploid

A

If organisms have 2 copies of each gene

2n

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16
Q

haploid

A

If organisms only have 1 copy of each gene

n

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17
Q

homologous chromosome

A

Chromosomes that synapse (pair) during meiosis. Chromosomes with the same genes in the same order
Also known as homologs

Each chromosome carries many genes, and homologs carry genes for the same traits in the same order on each member of the pair.

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18
Q

sister chromatids

A

The identical DNA duplexes that are produced by DNA replication (s phase) and are temporarily joined to one another during the early stages of cell division(prophase)

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19
Q

recombination

A

i

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20
Q

crossing over

A

The breakage and reunion of homologous chromosomes that results in reciprocal recombination.

crossing over of genetic material between nonsister chromatids of homologous chromosomes.

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21
Q

disjunction

A

Sister chromatids separate

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22
Q

nondisjunction

A

failed chromosomal separation

Chromosomes pulled to the wrong pole

Occurs in meiosis I or meiosis II

Leads to aneuploidy

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23
Q

aneuploidy

A

missing or extra chromosomes
Extra chromosomes result in excessive gene product

Causes miscarriage since most aneuploid cells are inviable  Trisomy 21 (Down Syndrome) occurs in 1 of 1000 births

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24
Q

Genes

A

are the physical units of heredity, that collectively control gene transcription of DNA to RNA and therefore translation to proteins

-code for various functions within cells

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25
what is the central dogma of biology?
(DNA -> RNA -> protein) 
26
chromosomes
- consisting of single long molecules of double-stranded DNA contained within the nucleus and is inherited through cell division - contain genes
27
polyploid
Some organism have more than 2 copies
28
Cytoplasmic inheritance
used to identify the random distribution of the mitochondria and chloroplasts among daughter cells during cytokinesis
29
Where else can genetic info be carried in?
Genetic information (DNA and RNA) can also be contained within chloroplasts (plants) and mitochondria (plants and animals)
30
Genotype
is the genetic make-up of the organism 
31
Phenotype
is the observable traits dictated by the genotype  | Controlled by variations in genes called alleles
32
What are the 3 main subdisciplines of genetics?
Transmission genetics Evolutionary genetics Molecular genetics
33
Transmission genetics
“Mendelian” genetics -> transmission of traits and characteristics between successive generations (inheritance)
34
Evolutionary genetics
Studies the origins of and genetic relationships between organisms and the evolution of traits and genes/genomes
35
Molecular genetics
Studies inheritance and variation in nucleic acids (DNA and RNA), proteins, and genomes and connects them to inherited variation and evolution in organisms
36
somatic cells
structural cells of the body  ex- liver nervous muslce skin cells 23 homologous pairs of chromosomes- 22 autosomal and 23rd is sex linked
37
G0
some cells enter after G1 Some specialized cells enter this phase and do not go on to cell division Gene expression continues No longer progress through the cell cycle - very rarely leave and resume cell cycle most G0 cells maintain their specialized function until they enter programmed cell death Ex. Bone cells, eye cells
38
Describe the movement of eukaryotic chromosomes during the cell cycle.
Kinetochore microtubules move chromosomes Non kinetochore microtubules elongate and stabilize the cell Astral microtubules stabilize the cell
39
What are the 4 main checkpoints in cell division?
G1 checkpoint: Pass if cell size is adequate, nutrients availability is good, presence of growth factors S-phase checkpoint: Pass if DNA replication is complete and base-pair mismatches/errors are removed G2 checkpoint: Pass if cell size is adequate, chromosome replication is complete Metaphase checkpoint: Pass if all chromosomes are attached to the mitotic spindle Mutations that alter the cell cycle or checkpoints can lead to cancer, and other diseases
40
daughter cells
The genetically identical cells produced by mitotic cell division
41
What are somatic cells in humans? How many chromosomes are in human cells?
Each somatic cell within a typical mammal is 2N (diploid) Human cells contain 23 unique chromosomes, so in the diploid state 2N = 46 chromosomes
42
What are gametes in human cells?
Human gametes are 1N (haploid), so N = 23 chromosomes
43
germ-line cells
produce gametes- egg and sperm divide by meiosis 23 in total (not pairs) 1-22 are autosomal and 23rd= X or Y
44
what happens if mitosis doesn't occur? or if too much occurs
an organism may fail to develop at all or have morphological abnormalities growth of structures beyond the boundaries leading to morphological abnormalities even death
45
What are the 5 stages of mitosis?
``` prophase prometaphase metaphase anaphase telophase and cytokinesis ```
46
chromatin
The complex of nucleic acids and proteins that compose eukaryotic chromosomes DNA + protein
47
karyokinesis
Part of telophase, the process of nuclear division between daughter cells. equal partitioning of the chromosomal material in the nucleus of the parental cell between the nuclei of the 2 daughter cells
48
when cells enter mitosis are they diploid of haploid?
diploid
49
centromere
A specialized DNA sequence on eukaryotic chromosomes that is the site of kinetochore protein and microtubule binding.
50
centrosomes
A cytoplasmic region, containing a pair of centrioles (90 degrees to each other) in many eukaryotic species, from which the growth of microtubules forms the spindle apparatus during cell division site of spindle assembly
51
kinetochore
The site of attachment of multiple proteins that connects a spindle fiber microtubule to the centromeric region of a chromosome Forms during M phase of cell division
52
List the basic similarities presented in the notes between meiosis and mitosis
Germ-line cells have identical interphase as somatic cells Structures such as centrosomes, spindle fibres are the same Germ-line cells are replenished via mitosis, but undergo meiosis to produce gametes
53
How does meiosis differ than mitosis?
2 main divisions, with no DNA replication in between Meiosis I – homologous chromosomes separate, ploidy level reduces by half Ie. 2N -> 1N Meiosis II – sister chromatids separate Duplicated chromosomes reduce to single chromosomes (ie no sister chromatids)
54
What are the 3 hallmark events during meiosis 1?
1. Homologous chromosome pairing Chromosome synapsis 2. Crossing over between homologous chromosomes results in recombination at cross-over sites called chiasmata 3. Segregation (separation) of homologous chromosomes (ploidy level reduced by half)
55
What are the stages of meiosis 1?
Prophase I -> homologous pairing and cross-over Metaphase I -> aligning to the centre of the cell Anaphase I -> separation of homologous chromosomes Telophase I and cytokinesis -> end of first division
56
what are the stages within prophase 1?
``` Leptotene Zygotene Pachytene Diplotene Diakinesis ```
57
Leptotene
Chromosomes are duplicated (having passed Sphase) Chromosomes condense, but not visible Centrosomes migrate to poles Spindle fibers produced from each centrosome
58
 Zygotene
Chromosomes continue condensing Homologous pairs enter synapsis, forming the synaptonemal complex Meiotic spindle forms Nuclear envelope beings to break down
59
synaptonemal complex
3 layer structure that forms during prophase I Tightly binds non-sister chromatids of homologous chromosomes The function is to properly align homologous chromosomes before their separation and then to facilitate recombination between homologous chromosomes.
60
Pachytene
Chromosome condensation partially complete Synapsed homologs are seen as bivalents (tetrads) Crossing over occurs between non-sister chromatids, formation of chiasmata Kinetochore microtubules attach to the kinetochores Nuclear envelope breakdown continue
61
Diplotene
Crossing over is complete Synaptonemal complex dissolves but chiasmata remain Tetrads completely visible Nuclear envelope fully dissolved
62
Diakinesis
Meiotic spindle established Homologous chromosomes tethered to poles via spindle fibres Nuclear envelope fully degraded Tetrads move to cell middle
63
Metaphase I
Tetrads align to metaphase plate Homologous pairs tethered to opposite poles Kinetochores od sister chromatids are attached to the same centromere, joined by cohesion proteins to prevent premature separation Chiasmata linking non -sister chromatids broken Allows recombination via independent assortment 2 (n -1) possible combinations, where n = number of homologous pairs
64
 Anaphase I
segregation of alleles)  Kinetochore microtubules depolymerise Disjunction occurs, pulling homologs to opposite poles Sister chromatids remain attached by cohesion Ploidy level has now been reduced by half
65
Telophase I
Nuclear membrane re-form around chromosomes Chromosomes partially decondense
66
Cytokinesis 
Cytokinesis divides the cytoplasmic contents, which may be unequal Progeny cells are now haploid (n)
67
Prophase II
Nuclear envelope breaks down Centrosomes duplicate and migrate to poles Microtubules form Chromosomes recondense
68
Metaphase II
Sister chromatids attached to kinetochore Align at metaphase plate
69
Anaphase II
Sister chromatids separate, breakdown of cohesion proteins Kinetochore microtubules depolymerize Sister chromatids move to opposite poles Non kinetochore microtubules elongate the cell
70
Telophase II and Cytokinesis
Chromosome migration complete Chromosomes decondense Nuclear envelope reforms Cytokinesis divides the cytoplasm
71
synapsis
The close approach and contact between homologous chromosomes during early prophase I in meiosis.
72
Nonsister chromatids
are chromatids belonging to different members of a homologous pair of chromosomes.
73
chiasmata
they are located along chromosomes where crossing over has occurred mark the locations of DNA-strand exchange between nonsister chromatids of homologous chromosomes.
74
Which part of meiosis is similar to mitosis and how?
meiosis II kinetochore microtubules from opposite centrosomes attach to the kinetochores of sister chromatids the chromosomes align randomly along the metaphase plate sister chromatid separation is accompanied by cohesin breakdown, the action of motor proteins, and depolymerization of microtubules Cytokinesis takes place at the end of telophase II
75
What are the different stages within interphase?
G1 S and G2
76
metaphase plate
the cell midline along which chromosomes align in the middle of the cell
77
Describe how DNA content changes or stays the same throughout mitosis
if we start with 2 ng of DNA in 2N=46 at G1 then: After S phase, the DNA content doubles: 4 ng DNA content After anaphase (M phase), the DNA content is halved: 2ng DNA content
78
Describe DNA content during meiosis
If we start with 2 ng of DNA in 2N=46 at G1 then: After S phase, the DNA content doubles: 4 ng DNA content, with duplicated chromosomes Ie 2 chromatids per chromosome After anaphase I, the DNA content is halved: 2 ng DNA content, but chromosomes are still duplicated Twice the number of chromatids still After anaphase II, the DNA content is halved again, and chromatids no longer doubled
79
Why does aneuploidy occur?
Reduced cohesion of sister chromatids Reduced connection between homologous chromosomes Reduced recombination Environmental factors: Maternal age Smoking, oral contraceptives, radiation exposure

Genetics (12 decks)

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