BIO cell division

Question 1

describe DNA, genes and chromosome in prokaryotes?

Answer 1

DNA is circular, short and not associated with any proteins do not make chromosomes

Question 2

describe DNA, genes and chromosomes in eukaryotes?

Answer 2

DNA is long and linear, associated with proteins (histones). chromosomes made up of histones and DNA. mitochondria and chloroplasts have own DNA like DNA of prokaryotes not associated with proteins and no introns

Question 3

what occurs on homologous chromosomes?

Answer 3

1. gene occupies fixed position (LOCUS) on particular DNA/chromosome
2. gene may exists in different forms such as alleles code for different types of same characteristics
3. alleles of particular gene located same locus on homologous chromosomes
4. homologous pair of chromosomes carries genes controlling characteristics but not same alleles
5. homologous pair of chromosome consist of maternal and paternal chromosome

Question 4

what is an allele?

Answer 4

form of DNA codes for different types of same characteristics

Question 5

what is a gene?

Answer 5

sequence of DNA bases coding for specific amino acid of a polypeptide

Question 6

what is mitosis and what does it produce?

Answer 6

type of nuclear division cells are genetically identical so parent cell divides to make 2 daughter cells(having an identical copy to parent gene)

Question 7

mitosis function

Answer 7

-mitosis increases cell number for growth and repair of tissues

Question 8

during mitosis what structures is the nuclear material organised into?

Answer 8

chromosomes

Question 9

what is the diploid number 2n?

Answer 9

total number of chromosomes in normal body cell so 46 in humans 23 pairs

Question 10

what is haploid number?

Answer 10

single set of chromosomes so one member from each homologous pair in humans 23 so number of chromosomes in gamete (sperm/ovum)

Question 11

what are the 3 stages of cell cycle?

Answer 11

1. interphase- non dividing cell when cell growth occur
2. nuclear division- nucleus divides into two (mitosis)
3. cytokinesis- cytoplasm divides into two (mitosis)

Question 12

if interphase is the longest period does it occur same in rapid dividing cells such as lining the intestines?

Answer 12

no it is short enabling rapid multiplication and replacement of cells, not all cells in organism are capable of cell division

Question 13

what happens during late interphase?

Answer 13

prepares for nuclear division by:

1. DNA content double by DNA replication
2. increase in protein synthesis
3. cell organelles replicated eg mitochondria and ATP content increased

Question 14

what are the 4 stages of mitosis?

Answer 14

prophase, metaphase, anaphase
telophase

Question 15

what happens during prophase?

Answer 15

1. due to DNA replication during interphase each chromosome consists of 2 identical sister chromatids joined by centromere
2. each chromosome shortens and thickens (condensation)

3.centrioles move to opposite poles of cell and nuclear membrane breaks down

Question 16

what happens during metaphase?

Answer 16

4. centrioles form spindle across cell, spindle consists of protein microtubles
5. each chromosome moves to equator of spindle and attaches to its centromere
6. sister chromatids are orientated to opposite poles of cell

Question 17

what happens during anaphase?

Answer 17

7. centromere splits and sister chromatids separate
8. sister chromatids PULLED to opposite poles of cell by spindle microtubles

Question 18

what happens during telophase?

Answer 18

9. chromatids at opposite poles of cell and begin to uncoil and nuclear membrane REFORMS
10. 2 cells are genetically identical to each other and to original parent cell

Question 19

what happens during cytokinesis?

Answer 19

follows nuclear division and involves splitting of cytoplasm into 2. 2 new cells form as CELL-SURFACE MEMBRANE and in plants CELLULOSE cell wall forms

Question 20

what is cancer?

Answer 20

group of diseases caused by uncontrolled growth and rapid division of cells. and occurs due to damage to genes that regulate mitosis and cell cycle

Question 21

what does uncontrolled cell division and growth lead to in group of abnormal cells?

Answer 21

tumour and cells may break away and move to other areas of body to spread

Question 22

what is used for cancer treatment?

Answer 22

drugs to stop cancerous cells diving may be used to inhibit enzymes, DNA helices or DNA polymerase or ro inhibit formation of spindle

Question 23

what is meiosis and what does it produce?

Answer 23

type of nuclear division that produces cells that are genetically different, during meiosis single cell divides twice but DNA replication occurs once,
4 cells made and possess half number of chromosomes (haploid) of original cell. these cells are gametes
important in production of haploid gametes

Question 24

what does the production of haploid gametes during meiosis result in?

Answer 24

results in diploid number being restored when gametes fuse at fertilisation to make a zygote

Question 25

does every organism have same life cycle where meiosis occurs?

Answer 25

no some have meiosis after fertilisation so when diploid number has been halved to haploid number

Question 26

how many nuclear divisions occur in meiosis?

Answer 26

2 so during late interphase which starts of first meiotic division DNA replication occurs, build up of ATP and protein synthesis with replication of cells occur

Question 27

after interphase how does meiosis occur?

Answer 27

meiosis 1- separates members of each homologous pair meiosis 2- separates chromatids of each chromosome

Question 28

what's an important feature of meiosis?

Answer 28

variation (genetic diversity) made in haploid cells (gametes).

Question 29

what are 2 processes in meiosis which make cells which are genetically different ?

Answer 29

1. independent segregation of chromosomes - during 1st division separation of each member of homologous pair which enters the gamete, pairing and separation of two members of a pair is completely independent from separation of another pair so chromosomes randomly associate within a gamete eg may be 3 pairs which can make 8 diff combos 2^3 2. crossing over- occurs during prophase of 1st division, 2 members of each homologous pair lie side by side making structure (bivalent) , then intertwine, and some chromatids break and exact portion is exchanged so crossing over happens in CHIASMA results in exchange of alleles of same genes and can make new combos of alleles known as recombinants (genetic recombination) chromosomes then separate however it is low as crossing over rare

Question 30

gametes are made by random fertilisation true or false

Answer 30

true

Question 31

how can mutations occur in chromosomes?

Answer 31

by chromosome NON-DISJUNCTION happens when homologous pair of chromosomes do not separate during 1st division normally during anaphase 1 each member is pulled to opposite poles but during non-disjunction one pair isn't separated and both members move to same side of cell results in gamete with extra chromosome

Question 32

how can downsyndrome occur?

Answer 32

when gametes with 24 chromosomes fuse with gamete with 23 chromosome making individual with 47

Question 33

can non-disjunction also occur if chromatids fail to separate in anaphase 2?

Answer 33

yes and non-disjunction of more than one pair of homologous chromosomes can occur