cellular & nuclear division

Question 1

the processess the need it

Answer 1

growth, maintenance, tissue repair, reproduction

Question 2

growth

Answer 2

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

Question 3

maintenance

Answer 3

old cells need to be replaced by new ones

Question 4

tissue repair

Answer 4

wound healing

Question 5

reproduction

Answer 5

organisms produce sex cells with only half the number of chromosomes

Question 6

why is mitosis needed

Answer 6

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)

Question 7

why is meiosis needed

Answer 7

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

Question 8

interphase

Answer 8

a single chromosome will be replicated from 2 sister chromatids

Question 9

sisterchromatid

Answer 9

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

Question 9

cohesin

Answer 9

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

Question 9

the 4 starges

Answer 9

PROPHASE
METAPHASE
ANAPHASE
TELOPHASE

Question 9

centromere

Answer 9

the constricted region, that the sisterchromatids are held by

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

Question 9

chromosome condensation

Answer 9

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

Question 9

chromatin

Answer 9

uncoiled, uncondensed dna

Question 9

condensation

Answer 9

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

Question 10

why is condensation important

Answer 10

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

Question 11

microtubules

Answer 11

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

Question 12

prophase

Answer 12

• 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

Question 13

metaphase

Answer 13

• 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

Question 14

anaphase

Answer 14

• 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

Question 15

telophase

Answer 15

nuclear envelope reappears, the chromosome recondense

Question 16

late telophase // cytokinesis

Answer 16

invagination,

the cell divides into 2 cells

complete separatio of the 2 nucleus by the nuclear envelope

Question 17

cytokinesis

Answer 17

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

Question 18

cytokinesis in plant cells

Answer 18

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

Question 19

animal cell cytokinesis

Answer 19

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

Question 20

equal cytokinesis

Answer 20

- daughter cells of simmilar sizes - each daughter cell receives 1 mitochondrion for cellular respiration - plant cells receive at least 1 chloroplasts

Question 21

examples of unequal cytokinesis

Answer 21

- oogenesis in humans - budding in yeast

Question 22

oogenesis

Answer 22

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

Question 23

purpose of unequal cytokinesis

Answer 23

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.

Question 24

diploid cells

Answer 24

23 homologous pairs of 46 chromosomes

Question 25

haploid

Answer 25

only 1set of genes

Question 26

what is 1 set of chromosomes composed of

Answer 26

centromere, gene loci, alleles

Question 27

what does a pair of homologous chromosomes consist of

Answer 27

same genes different allele variations

Question 28

homologous chromosomes

Answer 28

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

Question 29

tetrad

Answer 29

homologous pair of sister chromatids

Question 30

prophase 1 in meiosis

Answer 30

- 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

Question 31

metaphase 1

Answer 31

- 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

Question 32

anaphase 1

Answer 32

- 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

Question 33

telophase 1

Answer 33

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

Question 34

features common only to mitosis

Answer 34

- 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

Question 35

features common only in meiosis

Answer 35

- 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

Question 36

common features

Answer 36

- microtubules for chromosome movenment - starts as diploid cells - kinetochores shorten the microtubules - nuclear membrane breakdown - all the PMAT phases

Question 37

number of possible haploid combinations in an organism

Answer 37

2^n n= 23 388 608

Question 38

non disjunction

Answer 38

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

Question 39

what leads to trisomy 21

Answer 39

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)