Cell division Flashcards
What are the phases of cell cycle and outline processes
interphase- period of normal functioning, growth and DNA replication in prep for mitotic phase
Mitotic phase- (nucleus and cytoplasm divide), mitosis and cytokinesis=period of cell division
List 3 stages of interphase and outline what happens at each
G1= protein synthesis, organelles replicate, cell increases in size
S= synthesis, DNA is replicated in nucleus
G2=cell increases in size, energy stores increase, duplicated DNA checked for errors
List 2 stages of mitotic phase and outline what happens in both
Mitosis= nucleus divides
Cytokinesis= cytoplasm divides and 2 cells are produced
Describe significance of G0
phase when cell leaves cell cycle temporarily or permanently
- differentiation: cells no longer divide, they carry out their function indefinitely and don’t enter cycle again
- damaged DNA: damaged cells can no longer divide, preventing cancer
- regulates number of cells in tissue
Outline checkpoints role to control cell cycle
ensures a cell only divides once reached correct size
DNA replication is error-free
chromosomes are in correct positions during mitosis
3 examples of checkpoints
G1
G2
M (spindle assembly checkpoint)
when does G1 checkpoint occur
at end of G1 phase before entry to S phase
where does G2 checkpoint occur
end of G2 phase before entry to M phase
where does M checkpoint occur
during metaphase of mitosis
what does G1 checkpoint check
cell size, nutrients, growth factors, DNA damage
what does G2 checkpoint check
cell size, DNA replication, DNA damage
what does M checkpoint check
if all chromatids are correctly attached to spindle fibres
what happens if G1 checkpoint criteria are satisfied
Cell enters S phase and DNA replication begins
what happens if G2 checkpoint criteria are satisfied
molecular processes that signal beginning of mitosis are initiated
what happens if M checkpoint criteria are satisfied
cell continues with mitosis
what happens if G1 checkpoint criteria are not satisfied
cell enters G0
what happens if G2 checkpoint criteria are not satisfied
cell pauses G2 to try and repair, if irreparable then cell undergoes apoptosis
what happens if M checkpoint criteria are not satisfied
mitosis paused, repair attempted
define mitosis
nuclear division stage in mitotic phase of the cell cycle
define chromatids
one of two halves of a replicated chromosome
define sister chromatids
identical copies formed by DNA replication of a chromosome with both copies joined together by a common centromere
define sister chromatids
identical copies formed by DNA replication of a chromosome with both copies joined together by a common centromere
define centromere
region which holds 2 chromatids together
define spindle fibres
structures made of microtubules that organise chromosomes and pull them part to opposite poles during mitosis
define homologous pairs
matching pair of chromosomes, one inherited from each parent
describe how DNA is packaged in a chromosome
tightly packed DNA
found only during cell division
DNA not being used for macromolecule synthesis
describe how DNA is packaged in a chromatid
unwound DNA
found throughout interphase
DNA is being used for macromolecule synthesis
describe formation of chromosomes
- DNA is wrapped around histone proteins (compact)= chromatin
- during interphase, chromatin is decondensed
-during mitosis, chromatin is condensed=chromosomes
list stages of mitosis in order
propase
metaphase
anaphase
telophase
what happens during prophase
-chromatin fibers coil and condense to form chromosomes
-nucleolus disappears
-nuclear membrane breaks down’
-protein microtubules form spindle fibers
-centrioles migrate to opposite poles
-spindle fibers attach to specific areas on centromeres, start moving chromosomes to centre
what happens during metaphase
chromosomes moved by SF and line up along equator of cell
what happens during anaphase
-sister chromatids pulled apart to opposite poles by spindle fibres (contract)
-centromeres divide
what happens during telophase
- nuclear envelope reforms around each chromatid
-chromosomes start to uncoil - nucleolus is formed
-cytokinesis begins
role of centrioles
organise spindle fibers which are attached to them
role of spindle fibers
pull chromatids to opposite poles and ensure even chromosome distribution between daughter cells
describe process of cytokinesis in animal cells
-cleavage furrow forms around middle of cell
-plasma membrane pulled inwards by cytoskeleton until close enough to fuse around middle
-two cells are formed as a result
describe process of cytokinesis in plant cells
- vesicles from golgi begin to assemble in same place along equator where chromosomes aligned (metaphase plate)
-vesicles fuse with eachother and cell surface membrane dividing cell in two. - new sections of cell wall form along new sections of membrane
cleavage furrow cannot form as plants have cell walls
compare animal and plant cytokinesis
-animal cells form cleavage furrow but plants don’t (bc they have a cell wall and internal P)
-plant cells use vesicles, animals don’t
purpose of mitotic cell division
- ensures that both daughter cells produced when a parent cell divides are genetically identical.
-necessary when all DC have to be identical
list 4 roles of mitosis
-growth of organisms
-repair/replacement of tissues
-embryo development
-asexual reproduction
what is mitotic index
ratio between number of cells in mitosis and total number of cells
what is mitotic index
ratio between number of cells in mitosis and total number of cells
define diploid
containing homologous chromosome pairs- two complete sets of chromosomes, one from each parent
define haploid
containing one chromosome from each homologous pair
define gamete
haploid sex cells produced by meiosis in organisms that reproduce sexually
define zygote
initial diploid cell formed when 2 gametes are joined by sexual reproduction
-earliest stage of embryonic development
define meiosis
nuclear division for the purpose of gamete production
-nucleus divides twice resulting in forming four haploid cells from one diploid cell
define reduction division
where the chromosome number is halved from diploid to haploid (first meiotic division)
role of meiosis in life cycles
-production of gametes which allow sexual reproduction
-ensures all organisms produces via sexual reproduction contain the correct number of chromosomes would double with every round of reproduction
-produces genetic variation
how does meiosis produce variation
-crossing over during prophase 1
- independent assortment of chromosomes in metaphase 1
-independent assortment of chromatids in metaphase 2
importance of different allele combinations
-this means that different phenotypes will be produced
-this reduces the chances of a population going extinct as it is more likely that some individuals possess advantageous characteristics to help them survive and adapt
define homologous chromosomes
matching pair of chomosomes, one inherited from each parent
define bivalent
a pair of homologous chromosomes during crossing over
define crossing over
exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring
define chiasmata
points at which chromatids break and rejoin
define recombinant chromatid
chromatid with a combination of DNA from both homologous chromosomes
-formed from crossing over and chiasmata in meiosis
state stages of meiosis in order
prophase 1
metaphase 1
anaphase 1
telophase 1
prophase 2
metaphase 2
anaphase 2
telophase 2
what happens at P1
-chromosomes condense
-nuclear envelope disintegrate
-nucleolus disappears
-spindle formation begins
-homologous chromosomes pair up, forming bivalents & crossing over occurs
what happens at M1
-homologous pairs assemble along metaphase plate
-independent assortment occurs
what happens at A1
-homologous chromosomes pulled to opposite poles and chromatids stay joined to each other
-entangles sections of DNA on non-sister chromatids that became entangled during crossing over break off and rejoin at chiasmata, resulting in recombinant chromatids
what happens at T1
-chromosomes assemble at each pole, nuclear membrane reforms
-chromosomes uncoil
-cytokinesis occurs, cell divides into 2
-reduction of chromosome number from diploid to haploid is complete
what happens at P2
-chromosomes condense and become visible.
-nuclear envelope breaks down, spindle formation begins
what happens at M2
-individual chromosomes assemble on metaphase plate
-due to crossing over, chromatids are not identical= independent assortment occurs
what happens at A2
chromatids of individual chromosomes are pulled to opposite poles after division of centromeres.
what happens at T2
-chromatids assemble at poles, uncoil and form chromatin.
-nuclear envelope reforms, nucleolus is visible again.
describe process of crossing over
-HC pair up=bivalent
-non-sister chromatids become entangled at points called chiasmata
-they break off and reform, sometimes resulting in the exchange of DNA=recombinant chromatids with diff combinations of alleles and therefore gen variation
describe process of random independent assortment
-orientation of each HP on metaphase plate is random and independent of any other HP
-maternal/paternal chromosomes can end up with any combination of maternal and paternal chromosomes hence why it produces genetic variation
similarities between meiosis and mitosis
-begin with 1 diploid parent cell
-end with cytokinesis
-both stages duplicate DNA
-both stages condense DNA
-both require chromosomes to be pulled apart by a centrosome
-both pulled apart by spindle fibres formed from centrosome
-require nuclear membrane to go away
differences between meiosis and mitosis
-mitosis is used in asexual reproduction and meiosis in sexual
-crossing over occurs in meiosis not mitosis
-cells produced in mitosis are genetically identical, meiosis is gen diff
-mitosis used for growth and repair, meiosis used for genetic diversity through sexual reproduction
-cells divide once in mitosis but twice in meiosis
-2 diploid cells produced in mitosis and 4 haploid in meiosis
-n. chromosomes stays same in mitosis but in meiosis is halved
-mitosis used to create any cell (except gamete), meiosis used only to create sex cells
define specialised
having particular structure to serve a specific function
define differentiated
specialised to carry out a very specific funtion
