cell cycle Flashcards
name the different stafes of the cell cycle
- interphase:
G1 = cell increases in size
S = DNA replicated semi conservatively
G2 = cell ready for division, new organelles synthesised - nuclear vision: mitosis or meiosis
- cell division/ cytokinesis: division of cytoplasm
define a gene
section of DNA that codes for a specific polypeptide
what is a chromosome?
independent DNA molecule (chromatid) supercoiled into a condensed form
- when duplicated, are attached at the centromere; producing identical sister chromatids
homologous chromosomes
same genes
same loci
dofferent alleles of the gene (one maternal, one paternal)
diploid
somatic (body) cels in homologous pairs
2n = 46
two copies of each chromosome
haploid cells
one copy of each chromosome
gametes
what is mitosis used for?
- repairs damaged tissues
- increasing cell numbers/growth of organism
- replacement of worn out cells
- produces genetically identical daughter cells
describe the features of prophase
- nuclear membrane begins to breakdown
- centrioles move to opposite poles of the cell
- chromatins supercoils and condense in chromosomes
describe the features of metaphase
- spindle fibres form
- spindle fibres attach to the centromere of chromosomes
- chromosomes align in the equator
describe the features of anaphase
- spindle fibres shorten and contract
- centromere splits
- sister chromatids are separated to opposite ends of the pole
describe the features of telophase
- nuclear membrane reforms
- chromosomes unwind
describe the appearance and behaviour of chromosomes during mitosis
- during prophase, chromosomes supercoil and condense to become visible
- chromosomes appear as 2 identical sister chromatids joined by centromere
- metaphase, chromosomes align in the middle/equator of the cell
- chromosomes attach to spindle fibres
- by centromeres
- anaphase, centromere splits
- sister chromatids are pulled to oppsoite poles of cell, making a V-shape
- during telophase, chromatids uncoil and become thinner
tumour suppressor genes
code for proteins that slow down cell cycle
proto-onco genes
code for proteins that speed up cell cycle
One method of treating cancer (AO2)
- drugs that inhibit cell division
- stop DNA replication/spindle formation/cytokinesis
BINARY FISSION
- NOT mitosis
- replication of circular DNA
- replication of plasmids
- cytokinesis (division of cytoplasm) to produce 2 daughter cells
mitotic index
number of cells with visible chromosomes divided by total number of cells
greater value = faster rate of CD
where does mitosis occur in plants?
meristem
why must a plant sample be soaked in HCl
breaks cellulose cell wall so stain can enter
OR
tissue squashed to one cell thick so light can pass through
calculating length of time each stage of mitosis occurs
total numver of visible chromosomes divied by total number of cells
multiplied by time of one cycle (minutes)
serial dilution
M1V1 = M2V2
M1 = DESIRED CONC
V1 = DESIRED VOL
M2 = ORIGINAL CONC
V2 = UNKNOWN VOL
meiosis
- produces haploid gametes
- four genetically different daughter cells produced
in first division, homologous chromosomes pair up and are separated
in second division, chromatids are separated
describe and explain what the student should have done when counting cells to make sure the mitotic index he obtained for the root tip was accurate
- repeat count to ensure figures are correct
OR - examine many cells to ensure representative sample
meiosis results in cells with haploid number of chromosomes and show genetic variation. Explain how.
- homologous chromosomes pair up
- chromosomes are arranged in any order
- independent segregation
- crossing over
- equal sections of genes are swapped between chromosomes
- produces a new combination of alleles
- chromatids separated at meiosis
describe the process of crossing over and explain how it increases genetic diversity
- homologous chromosomes form a bivalent pair
- chiasmata form
- equal lengths of the allele are exchanged
- produces new combination of alleles
give 2 diferences between mitosis and meiosis
mitosis vs meiosis
- one division vs 2 divisions
- daughter cells genetically identical vs different
- 2 cells produced vs 4 cells produced
- diploid to diploid/haploid to haploid vs diploid to haploid
- separation of homologous chromosomes only in meiosis
- crossing over only in meiosis
- independent segregation only in meiosis
calculaing the number of different chromosome combinations with meiosis wthout crossing over
2n
n = number of chromosomes
eg: if n=2 then 4
n=3 then 8
