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cellular & nuclear division Flashcards

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Biology 101 flashcards
1
Q

the processess the need it

A

growth, maintenance, tissue repair, reproduction

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2
Q

growth

A

when cells grow, they eventually reach the maximum SA: V ratio, hence they divide

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3
Q

maintenance

A

old cells need to be replaced by new ones

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4
Q

tissue repair

A

wound healing

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5
Q

reproduction

A

organisms produce sex cells with only half the number of chromosomes

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6
Q

why is mitosis needed

A

mitosis- maintains chromosome number and genome of cell (producing diploid cells) (continuity) (produces sells with the same genetic material as the parent cells which ensures that all organisms get the genes they need ; allows the genome to be inherited without changes)

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7
Q

why is meiosis needed

A

meiosis- halves the chromosome number (producing haploid cells) + gametes genetic diversity (change);

produces cells that have half as many chromosomes as the parent cell, division of a nucleus with 2 sets of chromosomes (diploid) results in nuclei with only one set (haploid) essential to producing haploid gemetes from diploid germ cells in sexual life cycles

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8
Q

interphase

A

a single chromosome will be replicated from 2 sister chromatids

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9
Q

sisterchromatid

A

to genetically identical chromatids, held together by a centromere, during cell division thay separate and each nucleus gets 1

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9
Q

cohesin

A

loop of protein complext that hold together the sister chromatids, during cell division, they are cut, in order to separate the sisters

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9
Q

the 4 starges

A

PROPHASE
METAPHASE
ANAPHASE
TELOPHASE

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9
Q

centromere

A

the constricted region, that the sisterchromatids are held by

during mitosis//meiosis the microtubule fibres attach to it and pull, to separate the sosterchromatds

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9
Q

chromosome condensation

A

organises the long, thin chromatin into compact, short chromosomes by wrapping double helix of dna around proteins called histones

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9
Q

chromatin

A

uncoiled, uncondensed dna

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9
Q

condensation

A

happens through the process known as SUPERCOILING, where dna wraps itself around histone proteins to produce nucleuses which coils into the chromosome

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10
Q

why is condensation important

A

to separate and move large (50 000um) molecules of DNA without any knots or breaks, as then it dies

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11
Q

microtubules

A

responsible for the movement of chromosomes; hollow cylinders of tubulin proteins that can be rapidly assembled or disassembled pulling interphase, they serve a variety of functions, including cytoskeleton

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12
Q

prophase

A
  • the disintegration of the nuclear envelope 3

-chromatin condenses

chromosomes are sister chromatids with 2 nucleous joined by the centrimere

  • nucleous breaks down
  • centrosomes move to the opposite sides of the nucleous
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13
Q

metaphase

A
  • centrosomes reach opposite sides
  • spindle fibres extend from the centrosomes
  • chromosomes line up at the equator of the spindle (metaphase poles)
  • attach to spindle fibres
14
Q

anaphase

A
  • sister chromatids separate at the centromere, which divides in two

-spindle fibres shorten and pull the chromosomes to the opposite poles the sister chromatids separate as the centromere breaks down

15
Q

telophase

A

nuclear envelope reappears, the chromosome recondense

16
Q

late telophase // cytokinesis

A

invagination,

the cell divides into 2 cells

complete separatio of the 2 nucleus by the nuclear envelope

17
Q

cytokinesis

A

the division of cytoplasm, in animal cells its invagination. a cleavage furrow forms and separates happens at the equator

actin & myosin form a contractile ring under the plasma membrane as the proteins contract they pull the plasma membrane towards the centre, until separation

18
Q

cytokinesis in plant cells

A

a cell plate (formed from vesicles carrying carbohydrates, proteins and lipids from golgi apparatus ) forms at the equator and once it reaches the cell walls of the parent cells, new cell walls are produced (from vesicles carrying pectin and cellulose) separating the two daughter cells

19
Q

animal cell cytokinesis

A

invagination

a contractile ring of ACTIN and MYOSIN protein fragments form around the cell

a contractile sing constricts at the equator of the cell

cleavage furrow reaches the centre

pinched apart to form two daughter cells

20
Q

equal cytokinesis

A
  • daughter cells of simmilar sizes
  • each daughter cell receives 1 mitochondrion for cellular respiration
  • plant cells receive at least 1 chloroplasts
21
Q

examples of unequal cytokinesis

A
  • oogenesis in humans
  • budding in yeast
22
Q

oogenesis

A

the creation of a female gamete (also known as an ovum or oocyte) from primordial germ cell (PGC)

tje production of ova begins in the ovaries of the female fetus

  • germinal epitheial cells divide to form an immature ovum called a primary oocyte and a smaller structure called a polar body as a result of unequal cytokinesis

the secondary oocyte divides again to form an ovum and anoyher polar body

the polar bodies degenrate

23
Q

purpose of unequal cytokinesis

A

the zygote that results from fertilization receives all of its cytoplasm from the egg. So the egg needs to have as much cytoplasm as possible. Maturation of the ovum.

24
Q

diploid cells

A

23 homologous pairs of 46 chromosomes

25
Q

haploid

A

only 1set of genes

26
Q

what is 1 set of chromosomes composed of

A

centromere, gene loci, alleles

27
Q

what does a pair of homologous chromosomes consist of

A

same genes
different allele variations

28
Q

homologous chromosomes

A

a pair of chromosomes that has the exact same genes (in the same order) but they have different variations of alleles

29
Q

tetrad

A

homologous pair of sister chromatids

30
Q

prophase 1 in meiosis

A
  • cwntrosome movenments, spindle formation and nuclear membrane breakdown
  • chromosomes condense and become visible
  • homologous chromosomes pairs with their homologues, aligned gene by gene
  • the sister-chromosomes of non homologous pairs perform crossing over at the chiasmata (X-shaped regions).
  • microtubules attach to kinetochores
31
Q

metaphase 1

A
  • tetrads, bivalent, aligned at the equator of the cell, one chromosome facing one pole
  • random assortment of homologous chromosomes
  • both chrimatids of one homolog attach to microtubules at the kinetochore from one pole, the chromosome from the opposite homolog attach to microtubules from the opposite pole
32
Q

anaphase 1

A
  • spindle microtubules contract and pull the homologous pairs apart
  • the homologs disjunct and move towards opposite poles
  • halves the chromosome number (now = haploud)
  • sister chromatid cohesion persists at the centromere, causing them to move as a unit
33
Q

telophase 1

A
  • the sister chromatids reach the opposite poles and remain together
  • each half of the celll has a complete haploid set of duplicated chromosomes
  • cytokinesis
34
Q

features common only to mitosis

A
  • 2 genetically identical daughter cells are produced
  • only happens in somatic (body cells)
  • only 1 (one) stage of cell division
  • number of chromosomes remains the same
  • no crossing over (genetic mix)
  • the daughter cells are diploid
35
Q

features common only in meiosis

A
  • 2 steps of cell division
  • 4 haploid genetically different daughter cells are produced
  • reproductive cells only
  • tetrads are formed (4 sisterchromatids = 2 pairs)
  • sisterchromatids separate in meiosis 2, in meiosis 1 only the homologous paids separate
  • crossing over (genetic mix)
  • independant assortment
36
Q

common features

A
  • microtubules for chromosome movenment
  • starts as diploid cells
  • kinetochores shorten the microtubules
  • nuclear membrane breakdown
  • all the PMAT phases
37
Q

number of possible haploid combinations in an organism

A

2^n

n= 23

388 608

38
Q

non disjunction

A

sister chromatids or homologous chromosomes fail to separate during meiosis 1 or meiosis 2

thus the produced gametes contain either too many or too few chromosomes

which results in trisomy 21, trisomy 13 or other abnormalities

39
Q

what leads to trisomy 21

A

three copies od chromosome 21 during meiosis the sister chromatids have not been separated (non disjunction) hence the gamete has 24 chromosomes

(23 + extra nr.21 chromosome)

bio (12 decks)

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