Cell cycle divisions Flashcards
(25 cards)
cell cycle
phases a cell passes through to produce daughter cells by binary fission
four main stages of cell cycle
- cell division signals
- DNA replication
- DNA segregation
- cytokineses
prokaryote cell division signals
usually external forces:
- nutrient concentration
- environmental conditions
binary fission
replication of an entire single celled organism
prokaryote DNA replication
- have one circular chromosome
- ori region = origin of replication
- ter region = termination of replication
prokaryote DNA segregation
after replication, ori regions move to opposite sides of cell
prokaryote cytokinesis
- cell membrane pinches in
- protein fibres form a ring
- new cell wall materials are synthesised
- separation of two cells
eukaryote cell division signals
regulated based on needs of entire organism
eukaryote DNA replication
- have more than one chromosome
- replication starts at many different origins on each
- replication is limited to one part of cell cycle
interphase
- nucleus is visible, cell functions occur
- 3 subphrases: growth 1, synthesis, growth2
growth 1
- chromosomes are single
- duration is variable
- ends at the G1-to-S transition, commitment is made to DNA replication, irreversible
synthesis stage
- DNA replicates
- sister chromatids remain together until mitosis
growth 2
- cell prepares for mitosis
mitosis
- leads to production of 2 genetically identical nuclei, identical to original nuclei
- subdivided into prophase, prometaphase, metaphase, anaphase & telophase
- asexual reproduction = single cell organisms reproduce themselves each cell cycle
meiosis
- sexual reproduction
- gametes offspring not identical to parents
- two nuclear divisions but DNA replicated only once
- reduced chromosomes number from diploid to haploid
= ensures each haploid product has complete set of chromosomes
recombination
generates genetic diversity
crossing over
exchange of genetic material between non-sister chromatids
independent assortment of alleles
a matter of chance how homologous chromosomes line up in anaphase 1
errors in meiosis
- abnormalities in chromosome no.
- chromosome structural rearrangements
- visualised and detected on a karyotype
nondisjunction
pairs of homologous chromosome or sister chromatids fail to separate during mitosis
monosomy
loss of one chromosome
trisomy
having an extra chromosome
sexual life cycles
- involves meiosis to produce haploid cells
- fertilisation and meiosis alternate
- haploid cells or organisms alternate w/ diploid
diploid advantages
- repair DNA damage using other chromosome copy
- recessive mutations can be masked
- more rapid evolution is possible
- greater diversity of immune gene alleles
