Notes 18 Flashcards
The cell cycle
Is an ordered set of events that divides a cell into 2 daughter cells
Cell cycle 2 main phases
Interphase & Mphase
Interphase
the stage in development of 2 divisions
G1
First intermediate gap stage in which the cell grows and prepares for DNA replication
S phase
Synthesis stage in which DNA is replicated
G2
Second intermediate gap stage in which the cell finishes growing and prepares for cell division
M phase
The period of the cell cycle in which the cell and contents divide to create two genetically identical daughter cells
Mitosis
nuclear division, where DNA (as condensed chromosomes) is separated into two identical nuclei
Cytokinesis
Cytoplasmic division, whereby cellular contents are segregated and the cell splits into two
Processes of Interphase
DNA replication – DNA is copied during the S phase of interphase
Organelle duplication – Organelles must be duplicated for twin daughter cells
Cell growth – Cytoplasmic volume must increase prior to division
Transcription / translation – Key proteins and enzymes must be synthesised
Obtain nutrients – Vital cellular materials must be present before division
Respiration (cellular) – ATP production is needed to drive the division process
(DOCTOR)
how do chromosomes condense
By supercoiling during mitosis
Chromosome
DNA is temporarily packaged into a tightly wound and condensed chromosome prior to division and is inaccessible to transcriptional machinery (during mitosis)
Chromatin
DNA is usually loosely packed within the nucleus as unravelled chromatin and is DNA is accessible to transcriptional machinery (during interphse)
Centromere
Hold together genetically identical strands called sister chromatids
Mitosis
the process of nuclear division, whereby duplicated DNA molecules are arranged into two separate nuclei
Before mitosis
Interphase- DNA is present as uncondensed chromatin, a clearly defined nucleus
Centrosomes and other organelles have been duplicated, Cell is enlarged in preparation for division
stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
Prophase
-DNA supercoils and chromosomes condense
-Chromosomes are made of genetically identical sister chromatids (joined at a centromere)
-Paired centrosomes move to the opposite poles of the cell and form microtubule spindle fibres
Metaphase
-Microtubule spindle fibres from both centrosomes connect to the centromere of each chromosome
-Microtubule depolymerisation causes spindle fibres to shorten in length and contract
-This causes chromosomes to align along the centre of the cell (equatorial plane or metaphase plate)
anaphase
-Continued contraction of the spindle fibres causes genetically identical sister chromatids to separate
-Once the chromatids separate, they are each considered an individual chromosome in their own right
-The genetically identical chromosomes move to the opposite poles of the cell
telophase
-Once the two chromosome sets arrive at the poles, spindle fibres dissolve
-Chromosomes decondense (no longer visible under light microscope)
-Nuclear membranes reform around each chromosome set
-Cytokinesis occurs concurrently, splitting the cell into two
Prometaphase
-The nuclear membrane breaks down and the nucleus dissolves
-Chromosomes captured
Cytokinesis
final stage of mitosis, the process of cytoplasmic division, where the cell splits into two identical daughter cells
cytokinesis overview
reformation of interphase microtubules array contractile ring forms and forms a cleavage furrow
what controls the progression of the cell cycle
cyclin (regulatory proteins)
cyclin dependent kinases (CDKs)
control cell cycle processes through phosphorylation
regulation of proteins in cell division
phosphorylation: adding Pi=active, remove Pi=inactive
gene expression: genes in nucleus match in protein that orders division
degradation of proteins: Ubiquitin labeled will destroy
CDK are made of
A catalytic subunit and regulatory subunit
when are cdks active
when bound to regulatory subunit
Anaphase-promoting complex
adds ubiquitin tag to proteins to destroy once destroyed, protein is active and can chop up cohesion (holding sisters together)
transcriptional cyclin regulation
ensure proper temporal expression of cyclins
protein degradation cyclin regulation
restricts cyclin to appropriate cell cycle stage by proteosomes
astral microtubules
interacts with cortex and orders spindals to axis of cell division
kinetochore microtubules
attaches to kinetochore on sister pair and transports chromosomes to poles
polar microtubules
attach each spindle pole to opposite side and maintain structure
kinetochore
multilayer protein structures on centromere
function: mediates attachment of chromosomes to kinetochore microtubules during metaphase
Surveillance mechanism
(checkpoint pathways) motoring cell cycle to ensure the previous one is properly completed
how do nuclear envelope reform
segments of ER associate with chromosomes and merge to produce envolope
