nucleus, mitosis and meiosis Flashcards
What is the nucleus and what does it do
Distinguishes eukaryotic and prokaryotic cells
- Houses genome-genetic info
- Control centre-replication, transcription, RNA processing
- Compartmentalisation
describe the structure of the nuclear envelope
- Two nuclear membranes - nuclear lamina and nuclear pore
complexes - Outer and inner membrane acting as a barrier
- Outer membrane- ribosomes and ER
- Inner membrane- nuclear proteins
what is the nuclear lamina
inner neclear membrane
meshwork of intermediate filaments which bind to inner membrane protiens
what are the 4 different lamins fibrous protiens
A, B1, B2, C
what is the function of the nuclear lamina
fibrous meshwork provides support
what are the nuclear pore complex
channels which small polar molecules, ions and macromolecules travel
what is the transport of molecules in the nuclear pore complex
RNA out, transcription factors in
small molecules - passive diffusion
large molecules - energy dependant mechanism
what do histones do
they bind to DNA and curls them up into a small peice
what are chromatin
complex of DNA and protein
what are the 4 types of chromatin
- Euchromatin- de-condensed and distributed through out the
nucleus - Heterochromatin: 2 types
- Constitutive never transcribed- satellite sequences of
centromeres - Facultative- not transcribed in these cells
why do cells need to divide
- Development
- Growth
- Replacement of cells
- Wound repair
- Cancer
- Sexual reproduction
definition of the cell cycle
A cell reproduces by performing an orderly sequence of events in which it duplicates its contents and then divides in two.
what do the checkpoints do in the cell cycle
act as breaking mechanism to check chromosome damage
cell cycle can be arrested if not right
what happens at each checkpoint
g1 - is environment favourable
g2 - DNA replication and environment
m - chromosomes attached to the spindle
fact
cdk controlled by cyclins for protien kinase activity
what is the role of cdk
Initiate and control major events of cell cycle- DNA replication,
mitosis and cytokinesis
definition of mitosis
the division of the nucleus of a eukaryotic cell, involving condensation of the DNA into visible chromosomes, and separation of the duplicated chromosomes to form two identical sets.
summary of mitosis
- Chromosome condensation
- Formation of mitotic spindle
- Attachment of chromosomes to spindle
- Sister chromatids separate
- Move to opposite poles of spindle
- Formation of new nuclei
what happens during propahse
replicated chromosomes containing 2 sister chromatids condense. the mitotic spindle assembles between centrosome which have replicated, and move apart
what happens during prometaphase
breakdown of nuclear envelope, chromosomes attach to spindle microtubules via kinetochores and undergo active movement
what happens during metaphase
the chromosomes are aligned at equator of spindle, midway between spindle poles. kitetochore microtubules attach sister chromatids to opposite poles of spindle
what happens during anaphase
sister chromatids synchronously separate to form 2 daughter chromosomes and each are pulled towards each spindle pole.
the kinetochore microtubules get shorter and the spindle poles also move apart.
what happens during telophase
2 sets of daughter chromosomes arrive at the poles of the spindle and decondense
new nuclear envelope reassembles around each set, completing formation of 2 nuclei and marking end of mitosis
what happens during cytokenesis
cytoplasm divides in 2 by a contractile ring of actin and myosin filaments, pinching cell in 2 to create 2 daughter cells with a nucleas
what controls the dissolution of nuclear envelop - chromosomes condense then reformation of nuclear envelop
phosphorylation and dephosphorylation under control of CDK1 and cyclin B
What 3 events happen to nucleus during mitosis
- 1) nuclear membrane fragments into vesicles
- 2) nuclear pore complexes dissociate
- 3) nuclear lamina depolymerises
meiosis definition
two successive nuclear divisions
with only one round of DNA replication, which produces four
haploid daughter cells from an initial diploid cell.
when can yeast undergo meiosis
form spores my meiotic division
what does cross over do
increases genetic variation
what is chromosomal crossover
the exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis, which results in new allelic combinations in the daughter cells
