1.3 - Mitosis and Meiosis Flashcards
state of most cells in developed multicellular organisms
G0
when do cells enter cell cycle and divide
during development, growth and wound healing (receive signals from environment)
prophase (2)
- replicated chromosomes condense
- outside nucleus, mitotic spindle assembled between the 2 centrosomes which have begun to move apart
prometaphase (2)
- breakdown of nuclear envelope
- chromosomes can attach o spindle microtubules via kinetochore and undergo active movement
metaphase (2)
- chromosomes aligned at equator of spindle midway between spindle poles
- paired kinetochore microtubules on each chromosome attach to opposite poles of spindle
anaphase (2)
- sister chromatids synchronously seperate and each pulled towards spindle pole
- kinetochore microtubules get shorter and spindle poles move apart
(both contribute to chromosome segregation)
telophase (3)
- Chromosomes arrive at poles of the spindle and start to decondense
- nuclear envelope reassembles following loss of mitotic cyclins
- M-CDK signal absent so molecular signals that establish mitotic state lost, leading to reversion to G1 status
(marks end of mitosis)
cytokenesis
cytoplasm divided by contractile ring of actin and myosin filaments which pinches cell creating 2 daughter cells each with 1 nucleus
condensin (2)
- condensin complexes bind to chromosomes at beginning of mitosis, fold them into consecutive cis-loops until highly compacted and condensed
- activity upregulated by mitotic CDK kinase
SMC complexes
use the power of ATP binding and hydrolyses and manipulate DNA
SMC complex action
Can bring together 2 different regions of DNA to either form DNA loop or cohese them together
SMC complex in eukaryotes (2)
- SMC complex cohesin cohese sister chromatids together from S phase to anaphase
- SMC complex condensin folds chromosomes by looping into their mitotic condensed form
breakdown of nuclear envelope (2)
- phosphorylation of nuclear lamins which coat inner membrane of nucleus inhibits interaction with each other
- causes breakup of nuclear lamina and attached nuclear membrane while mitotic CDK complexes are active
when does nuclear envelope reform
when mitotic CDK complexes are inactivated ay the end of mitosis
what is the mitotic spindle composed of?
microtubules that originate from one of 2 spindle poles at opposite ends of mitotic cell
where do microtubules from spindle pole attach to chromosomes
specialised protein structure (kinetochore)
SMC cohesin complex
enforces sister chromatid cohesion around the kinetochore to keep sister chromatids cohesed until anaphase
how do microtubules find kinetochore?
microtubules from spindle pole grow and shrink across cell until they make contact with kinetochore
when does chromosome segregation take place (kinetochores)
when all kinetochores have 2 kinetochore-microtubule attachments (one connected to each spindle pole)
what monitors connection of kinetochores to microtubules?
spindle checkpoint
what happens to chromosomes in anaphase A
shortening of kinetochore microtubules: forces generated at kinetochores to move chromosomes toward their spindle pole
what happens to chromosomes at anaphase B (2)
- sliding force generated between interpolar microtubules from opposite poles to push poles apart
- pulling force acts directly on poles to move them apart
metaphase to anaphase transition (2)
- when all chromosomes bi-oriented in metaphase, kinetochore microtubules are actively trying to pull chromatids to opposite sides of cell
- chromosome cohesion provided by cohesin prevents this
what does APC promote?
destruction of cyclins allowing telophase to start (and mitotic exit)
cytokineses in plants
plants form new cell wall through fusion of golgi vesicles during cytokineses as well as cell membrane
difference in chromosome condensation in meiosis
chromosomes condense as during mitosis but homologous pairs also synapse (for crossing over)
difference in metaphase 1 in meiosis
synapsed homologous pairs of chromosomes line up at metaphase plate
difference in anaphase in meiosis
one of the homologous sister chromatids goes to one pole and the other to the other pole
producing genetic diversity in meiosis: crossing over during prophase 1
- homologous chromosomes become synapsed with corresponding genes initially lined up along their entire length
- double strand breaks introduced into chromosomes, repaired between homologous chromosomes to produce crossovers (observed as chiasmata)
- resolution of crossover produced recombinant chromosomes composed of parts of both Maternal Paternal chromosomes
sister chromatids
two identical copies of a single chromosome formed during DNA replication
homologous chromosomes
pair of chromosomes (one from the mother and one from the father) that have the same genes at the same loci but may carry different alleles
producing genetic diversity in meiosis: mixing of chromosomes in metaphase 1 (2)
- chromosome pairs randomly oriented across centre of cell
- leads to random sorting of homologous paternal/maternal chromosomes with other chromosomes
what can non-disjunction errors errors during meiosis 1/2 lead to?
both chromatids being segregates into the same gamete -> leads to trisomy in fertilised embryo
aneuploidy
too many or too few chromosomes in a cell
