2.1.6 Cell Division , Cell Diversity And Cellular Organisation Flashcards
What are the stages of the cell cycle in order?
- interphase (G1, S, G2,)
- mitotic phase (mitosis and cytokinesis)
- (G0) leave cell cyle to enter G0
What happens at each stage (3) of interphase?
3 stages of interphase:
- G1: organelles replicate, cell grows, new proteins made
- Synthesis: cell replicates its DNA (in nucleus)
- G2: cell keeps growing, energy stores (ATP) increased, replicated DNA checked for errors
What happens during mitosis?
- division of the nucleus
- (prophase, metaphase, anaphase, telophase)
What happens during cytokinesis?
division of the cytoplasm producing 2 genetically identical daughter cells.
What happens during G0?
- cell leaves cycle and cell division stopped
- can undergo differentiation and specialisation
What are the 2 stages of the mitotic phase?
- mitosis (PMAT)
- cytokinesis - division of cytoplasm
What are the role of checkpoints to control the cell cycle?
- checkpoints monitor and check if each phase of cell cycle has been accurately completed before moving onto the next
- checkpoibnts insure each division is successful in producing 2 genetically identical daughter cells.
What are the 3 checkpoints in the cell cycle?
- G1 checkpoint
- G2 checkpoint
- metaphase checkpoint
Where does each checkpoint occur?
G1: - end of G1
G2: - end of G2
metaphase/spindle assembly checkpoint: end of metaphase
What is checked at each checkpoint?
- G1 checks: cell size, nutrients growth factors, DNA damage
- G2 checks: cell size, DNA replication, DNA damage
- spindle assembly checkpoint/ metaphase : chromosome attatchement to spindle
What is the link between cell-cycle regulation and cancer?
(s+c)
- cancer caused by unregulated division of cells
- occurs when proteins regulating cell cycle at checkpoints don’t function properly
- division is uncontrolled and tumours form
Define mitosis
- the nuclear division (division of nucleus) stage of the mitotic phase of the cell cycle
- at the end of mitosis there are 2 genetically identical daughter cells (exact copy of parent cell DNA)
Define chromosome
- structure of condensed and coiled DNA made up of two seperate chromatin strands which are joined by a centromere
Define chromatid
the two seperate strands which a chromosome divides into during cell division
Define sister chromatids
2 chromatid strands on the same chromosome
Define centromere
the region at which 2 chromatids are held together
Define centrioles
- component of the cytoskeleton of most eukaryotic cells
- tiny bundles of protein which move to opposite ends of the cell during prophase
- help form spindle
Define spindle fibres
- a network of filaments that form a miotic spindle
- made up of protein microtubules
- attatch to the centromeres and responsable in moving and separating chromosomes
Define homologous pairs
- matching pair of chromosomes, one inherited from each parent
How is DNA packaged in a chromosome?
- double stranded DNA loops around histones forming the nucleosome
- DNA further packaged by forming coils of nucleosomes called chromatin fibres
- these fibres are condensed into chromosomes during mitosis/cell division process
Draw, and annotate, a diagram for each stage of mitosis to show the events occurring at each stage
What are the roles of centrioles and spindle fibres in mitosis?
- centrioles make/form the spindle fibres
- spindle fibres attatch to the centromeres and seperate the chromatids, drawing them to each pole of the cell to form the 2 new nuclei
describe the process of centrioles making the spindle fibres
cetrioles move to opposite poles of the cell and start coordinating the formation of spindle fibres (they come out of the centrioles)
spindle fibres attatch to the centromeres
What is the process of cytokinesis in animal cells?
cytokinesis - division of the cell into 2 separate cells, begins during telophase
1- cleavage furrow forms around the middle of the cell
2- cytoskeleton pulls cell surface membrane inwards until close enough the fuse to form 2 seperate cells
What is the process of cytokinesis in plant cells?
-(have cell wall so not possible for cleavage furrow)
1- vesicles from golgi apparatus line up along centre of cell
2- vesicles fuse together and with cell surface membrane of the cell to form new cell surface membrane down the middle
3- new sections of cell wall then form along the new surface membrane
Compare the process of cytokinesis in animal cells and plant cells?
- in animal cells a cleavage furrow forms but in plant cells this is not possible as the have a cell wall
Is mitosis necessary for sexual or assexual reproduction?
asexual reprodution
What happens during prophase in mitosis?
Prophase:
- chromosomes condense (become shorter and fatter and visible)
- the nucleolus disappears and nuclear envelope breaks down
- centrioles move to opposite poles of cell and form spidle fibres
- spindle fibres attatch to centromeres of each chromosome
What happens during metaphase (mitosis)?
Metaphase:
- chromosomes moved by spindle fibres
- and lined up at the equator of the cell
(metaphase checkpoint- cell checks that all chromosomes are attatched to the spindle)
What happens during anaphase (mitosis)?
anaphase:
- centromeres (holding pair of chromatids) divide
- spindle fibres shorten/contract pulling chromatids to opposite poles of the cell
- (centromere pulled first)
What happens during telophase (mitosis)?
telophase:
- chromatids have reached opposite poles
- chromatids uncoil and long/thin again - now chromosomes
- spindle fibres break down
- nucelar envelope forms around each now group of chromosomes
- 2 nuclei now
(cytokinesis starts and separates cell into 2)
Explain the root tip squash practical to view different stages of the cell cycle.
1) treat the tips of growing roots in HCL
2) cut small thin section from the meristem
3) create a thin layer of cells by squashing tissue onto a microscope slide
4) stain the tissue (toluidine blue)
5) cover with a cover slip
What is the purpose of mitosis?
to create more gentically identical cells
What are 4 roles of mitotic cell division?
- growth, repair, replace, asexual reproduction
Define diploid
a cell with 2n chromosomes (2 copies of each chromosome, one from each parent)
Define haploid
a cell with n chromosomes (one copy of each chromosome)
Define gamete
haploid sex cell
Define gamete
haploid sex cell
Define zygote
- fertilised egg cell
-cell produced when haploid egg cell (gamete) is fertilised by haploid sperm cell (gamete)
Define meiosis
- nuclear division that results in production of haploid (gametes) nuclei from a diploid nucleus
(cell division that halves the original genetic material in cells to make haploid cells for sexual reproduction)
Define reduction division
any form of nuclear division where the chromosome number is reduced
Explain the role of meiosis in life cycles
- needed for sexual reproduction
- it halves the number of chromosomes so the diploid number of chromosomes is restored at fertilisation
- produces genetic variation in offspring
What are 2 ways in which meiosis produces variation?
- independant assortment
- crossing over
What is the importance of the creation of different allele combinations in populations?
- different allele combinations = genetic variation
- genetic variation is important in populations
- less vulnerability to disease/change in conditions as some more suited to new environment
Define homologous chromosomes
- matching pair of chromosomes, one inherited from each parent (same size, same genes)
Define bivalent
name for 2 homologous chromosomes that have paired up
(in prophase I of meiosis)
Define crossing over
the exchange of a part of a chromosome between chromatids of homologous pairs (happens at chiasmata)
Define chiasmata
- point of breakage
- sections of DNA that became entangled during crossing over, break and rejoin - point that they break is chiasmata
Define recombinant chromatid
- chromatids with a combination of DNA from both homologous chromosomes
- formed by crossing over and chiasmata in meiosis
Define random independent assortment
- which daughter cell a chromosome ends up in after meiosis I
- or a chromatid ends up in after meiosis II is random and independent of the fate of chromsomes from other homologous pairs
Describe the 2 stages of meiosis
snaprevise for diagrams
- Meiosis I - pairs of homologous chromosomes separated into 2 cells
- each intermediate cell contails 1 full set of chromosomes instead of 2, so haploid
- Meiosis II - same mechanism as mitosisi but fewer chromosomes
- pairs of chromatids in 2 daughter cells separated forming 2 more cells
- 4 haploid cell in total
What are the stages of meiosis in order
interphase - PMAT I, cytokinesis I , PMAT II, cytokinesis II
What happens during prophase I ?
Prophase I:
- chromosomes condense (shorter+fatter)
- nuclear envelope breaks down
- centrioles move to opposite poles forming spindle fibres
- homologous chromosomes pair up (1+1, 2+2 etc) forming bivalents
- crossing over occurs
What happens during metaphse I ?
Metaphase I:
- homologous pairs line up at equator of cell
- attatch to spindle fibres by their centromeres
(independant assortment as maternal/paternal chromosomes randomly get pulled to each pole)
What happens during Anaphase I ?
Anaphase I:
- spindles contract
- homologous pairs pulled apart (1 chromosome to each end of cell)
What happens during Telophase I ?
Telophase I:
- nuclear envelope forms around each group of chromosomes
- spindle fibres broken down
- chromosomes uncoil
- cell undergoes cytokinesis
How many cells are there at the end of meiosis I ?
2 haploid cells
What happens during Prophase II ?
Prophase II:
- chromosomes condense (shorter+fatter+visible)
- nuclear envelope breaks down
- centrioles move to opposite poles forming spindle fibres
What happens during Metaphase II ?
Metaphase II:
- homologous pairs of chromosomes assemble along the equator of the cell
- crossing over (chromatids not identical anymore) so independent assortment again bc
What happens during Anaphase II ?
Anaphase II:
- centrioles divide and spindle fibres contract
- chromatids of individual chromsomes pulled to opposite poles
What happens during Telophase II ?
Telophase II:
- chromatids have reached opposite poles in cell
- chromotids uncoil and long again - become chromosomes
- nuclear envelope reforms and nucleolus visible again
- cytokinesis happens = 4 haploid daughter cells (genetically different)
How many cells are there at the end of meiosis II ?
4 haploid daughter cells
- haploid bc of reduction division
- genetically different from each other and from parent cell bc of crossing over and independant assortment
Describe the process of crossing over
- homologous pairs of chromosomes come together and pair up
- chromatids become entangled/twist over at the chiasmata
- sections of chromatids break off and are exchanged
- now have a different combination of alleles
During which stage of meiosis does crossing over occur?
Prophase I of meiosis I
How does crossing over produce genetic variation?
- after crossing over chromatids no longer contain just maternal or paternal DNA
- so each of the 4 daughter cells are different (contain chromatids with different alleles) and there are infinite possibilities for different combinations of DNA
Define allele
different versions of the same gene
Describe the process of random independent assortment
- when bivalents (2 paired up homologous chromosomes) line up in meiosis I/ when chromosomes line up in meiosis II
- it is random which chromosome goes to which pole of the cell
- so random which chromosome from each pair ends up in which daughter cell
How does independent assortment produces genetic variation?
- the pole that the maternal or paternal homologous chromsomes face is due to random assortment and can result in many different combinations of alleles on either side of equator
- produces different daughter cells
Explain (given the chromosome number of the species)
How to calculate the total number of possible genetically different gametes that could be produced through independent assortment only
the number of chromosomes squared
When in meiosis does independent assortment occur?
metaphase I
Compare meiosis I, meiosis II, mitosis
paper flashcard
compare meiosis and mitosis
paper flashcard
