Cell continuity topic 6

Question 1

what is chromatin? and how is it formed?

Answer 1

-the DNA molecule in a human cell that is cut short and wrapped up with histone proteins which forms a complex called chromatin

Question 2

when will chromatin unwind?

Answer 2

-when genes need to be transcribed

Question 3

when does DNA replication take place, why does it take place and how does it occur?

Answer 3

-before cell division DNA is replicated and more histone proteins are synthesized so temporarily there is twice the normal amount of chromatin

Question 4

what is the structure of a chromosome?

Answer 4

-x shaped because it contains two replicated copies of DNA
-each arm of the chromosomes are called chromatin which are joined at the centromere

Question 5

what are the three stages of interphase?

Answer 5

-gap 1
-synthesis
-gap 2
-gap 0

Question 6

what happens during G1?

Answer 6

-just after mitosis
-new cell produces organelles in cytoplasm which increases the size of the cell

Question 7

what happens during the s phase?

Answer 7

-chromosomes are replicated which allows the chromosomes can be passed on to the new cell
-before DNA synthesis chromosomes replicate and produce an x like structure with two chromatids
-histones form

Question 8

what happens during G2?

Answer 8

-period before mitosis and the cell accumulates stores of energy to prepare for cell division
-spindle fibers are synthesized
-chromosomes are checked for error and repaired if necessary

Question 9

what does mitosis used for, where does it occur and how many stages does it have?

Answer 9

-used for growth and asexual reproduction
-occurs in all cells except gametes
-has 5 stages prophase, metaphase, anaphase, telophase, cytokinesis

Question 10

what happens during prophase during mitosis?

Answer 10

-chromosomes condense
-each chromosome consists of two identical sister chromatids connected by a centromere
-centrioles move to opposite poles
-nucleolus disappears and nuclear membrane breakdown

Question 11

what happens during metaphase during mitosis?

Answer 11

-spindle fibers connect centrioles to chromosomes
-chromosomes align along equator of cell and attaches to a spindle fiber by its centromere

Question 12

what happens during anaphase in mitosis?

Answer 12

-centromeres split allowing chromatids to split
-chromatids move towards poles pulled by motor proteins walking along microtubules
-mitochondria provide energy for this

Question 13

what happens during telophase in mitosis?

Answer 13

-spindle fibers disperse
-nuclear membrane form around each set of chromatids
-nucleoli form

Question 14

what happens during cytokinesis in animal cells during mitosis?

Answer 14

-ring of actin filaments form round the equator which tightens to form a cleavage furrow which splits cell in two

Question 15

what happens during cytokinesis in plant cells during mitosis?

Answer 15

-vesicles line up and fuse at equator to form two membrane called the cell plate
-new cell wall is laid down between membranes which fuses with existing cell wall

Question 16

what is cancer?

Answer 16

-uncontrolled cell division

Question 17

how does cancer occur?

Answer 17

-each cell cycle has a checkpoint and during cancer these checkpoints dont work and so dont enter gap 0 which causes uncontrolled cell growth

Question 18

what is a way that some cancers can be treated?

Answer 18

-chemotherapy which invovles drugs that inhibit stages in the cell cycle

Question 19

what are the two types of drugs used in chemotherapy and what happens during them?

Answer 19

-vincristine= stops microtubules forming spindle fibers and so chromatids cannot be pulled apart during anaphase
-fluorouracil= is an antimetabolite which prevents DNA synthesis at s phase

Question 20

how do anti cancer drugs affect normal cells?

Answer 20

-they affect normal cells too which results in unpleasant side effects

Question 21

what is meant by homologous pairs?

Answer 21

-chromosomes that come in pairs
-homologous pairs are a result of sexual reproduction and the homologous pairs are the maternal and paternal versions of the same chromosomes, they have the same sequence of genes

Question 22

how many pairs of chromosomes are different in males and females?

Answer 22

-one pair which are the sex chromosomes meaning they are non homologous
-females have xx males have xy

Question 23

where does meiosis occur and what does it produce?

Answer 23

-occurs in ovaries and testes and produces gametes with half the number of chromosomes
-meiosis results in 4 haploid genetically different daughter cells

Question 24

what does diploid and haploid mean?

Answer 24

-diploid means the full number of cells which is 46 (2n)
-haploid means half the number of cells which is 23 (n)

Question 25

how does mitosis and meiosis differ?

Answer 25

-meiosis results in haploid numbers because it allows the chromosome number to remain constant from generation to generation. Haploid cells have one copy of each chromosome and diploid have homologous pairs -chromosomes are rearranged during meiosis which results in genetic variation

Question 26

how many stages occur during meiosis and what are each of their steps?

Answer 26

-two stages -first stage has 4 phases and results in the exchange of genetic material -second stage has 5 phases

Question 27

what happens during prophase 1 in meiosis?

Answer 27

-chromosomes condense -homologous chromosomes join to form a bivalent -chromatids cross over to exchange genetic material known as chiasmata formation

Question 28

what happens during metaphase 1 during meiosis?

Answer 28

-bivalents line up at equator -nuclear membrane disappears

Question 29

what happens during anaphase 1 during meiosis?

Answer 29

-chromosomes separate and are pulled apart -not the chromatids as the centromere doesnt split

Question 30

what happens during telophase 1 during meiosis?

Answer 30

-nuclear membrane reforms -cell divides into two -each cell has 2 chromosomes not 4 chromatids because the chromatids are still joined by the centromere

Question 31

what happens during prophase 2 during meiosis?

Answer 31

-centrioles move to poles

Question 32

what happens during metaphase 2 during meiosis?

Answer 32

-nuclear membrane disappears -chromosomes line up on equator

Question 33

what happens during anaphase 2 during meiosis?

Answer 33

-centromeres split -chromatids separate and pulled to opposite ends of cell -once they are separated each chromatid is known as a chromosome

Question 34

what happens during telophase 2 during meiosis?

Answer 34

-nuclear membrane reforms

Question 35

what happens during cytokinesis during meiosis?

Answer 35

-cell membrane forms which divides the cells into 4 daughter cells -there four haploid cells contain two chromosomes

Question 36

what are the 2 stages of sexual reproduction and what happens?

Answer 36

-meiosis happens first which is the type of cell division that results in haploid gametes -fertilization the occurs which is the fusion of two gametes forming a diploid zygote

Question 37

what are 5 differences between mitosis and meiosis?

Answer 37

-mitosis produces two diploid daughter cells and meiosis results in 4 haploid cells -mitosis is one cell division and meiosis is 2 -in mitosis chromosomes do not pair up and in meiosis they do pair up and exchange genetic material -mitosis is asexual reproduction which results in clones and meiosis is sexual reproduction which results in genetic variation -mitosis occurs in all cells except testes and ovaries and meiosis occurs only in testes and ovaries

Question 38

what are the three ways that meiosis results in genetic variation?

Answer 38

-independent assortment -random fertilization -crossing over in meiosis

Question 39

how does independent assortment result in genetic variation?

Answer 39

-happens at metaphase 1 in meiosis when bivalents line up at equator -they can line up in any order, the maternal and paternal versions of the different chromosomes can be mixed up in the final gametes

Question 40

how does random fertilization result in genetic variation?

Answer 40

-takes place when two gametes fuse to form a zygote -each gamete has a unique combination of genes and any of the numerous male gametes can fertilize any of the numerous female gametes

Question 41

how does crossing over result in genetic variation?

Answer 41

-at prophase 1 homologous chromosomes come together to form bivalents -chiasmata formation results in genes from one chromosome are exchanges with the corresponding genes of the other chromosome

Question 42

what are chiasmata?

Answer 42

-the point where chromosomes actually cross over, they involve large multi enzyme that cut and join DNA -equal amounts of chromosomes cross over so they stay the same length -chiasmata therefore results in different allele combinations