Cell cycle Flashcards
What is meant by “cells arise from pre-existing cells”
Part of classical cell theory. Mitosis. DNA from parental strand.
Define cell-cycle and cell-division.
(1) to grow and to duplicate the DNA in the
chromosomes
(2) to segregate the DNA
(3) division: 2 identical daughter cells with each a
complete copy of the genome
Cell cycle consists of four phases: G1, S, G2, M
Why are cyclins among the most important cell cycle regulators?
Concentrations of cyclins vary in a cyclical way during the cell cycle, and triggers different transition steps in cell cycle.
Describe how the Cdk-complex works
Cyclin, a regulatory protein, needs to bind to cyclin dependent kinase (Cdk), forms a complex that phosphorylates proteins and trigger transition steps in cell cycle. Acts as an on/off switch to control cell cycle.
Name the stages of a cell-cycle (in chronological order).
G1, S phase, G2 (interphase) M phase (consists of prophase, prometaphase, metaphase, anaphase, telophase and then cytokinesis)
Give 3 functions of the G1 phase
Cell growth, synthesis of organelles, lipids and lipids. Prepare to replicate DNA.
What are mitogens?
Growth factor that bind to receptors to signal about starting mitosis
What is the function of p53 protein? Describe shortly its working mechanism.
DNA damage can stop cell cycle. P53 is a transcription regulator that ensures DNA is not damaged before cycle continues. P53 is needed to activate p21 gene that will allow for mRNA to be produced. If DNA damaged P53 is degraded and does not activate p21 necessary for continuation.
What are the stages of the M-phase, mitosis?
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
CytokinesisWhy is the mitotic spindle a dynamic structure?
array of microtubuli formed at the opposite poles of a
cell during mitosis and pulls duplicated chromosome sets apart, must be able to align chromosomes correctly and pull them apart.
Define kinetochore microtubuli
protein complex that assembles on the centromere of a condensed
chromosome
A human kinetochore binds 20-40 microtubule
Mitotic spindle with its 3 types of microtubuli during the prometaphase of the
mitosis
Interpolar microtubuli: “interacting microtubuli”, motor protein help to cross-link the 2 sets of microtubule Astral microtubuli: grow towards the cell membrane, contribute to cell stability Kinetochore microtubules spindle pole
Define metaphaseplate.
The metaphase plate is the plane on which chromosomes align themselves during metaphase
What is the main function of cohesion rings?
Two copies of DNA remain tightly bound together
by cohesin rings, which is crucial for proper
chromosome segregation
What is the name given to the division of the cytoplasm at the end of mitosis? Describe the
process.
Cytokinesis:
Overlapping interpolar microtubuli of the
mitotic spindle recruit proteins to start
creating a contractile ring
• Position of the contractile ring ensures
equally division
• Contractile ring composed of actin and
myosin filaments
Describe 2 types of cell death.
APOPTOSIS = programmed cell death The cell breaks apart into apoptotic bodies by caspase pathway –phagocytosis NECROSIS Plasma membrane rupture, nuclear and cellular lysis causes inflammation
What is cancer?
Mutations in components of cell-signalling pathway (own
extracellular survival signals, Ras)
•Mutations in genes responsible for cell death (p53→
G1/S-Cdk and S-Cdk)
•Uncontrolled cell proliferation
•Overactive cell metabolism
•Invasive due to lack of adhesion molecules
•Survival and proliferation in abnormal locations
Why is cancer fundamentally a genetic disease?
defects in DNA replication defects in DNA repair defects in cell-cycle checkpoint mechanisms mistakes in mitosis abnormal chromosome numbers genetic instability predisposes the cell to malignant transformation
Define proto-oncogen and tumor-suppressor gene.
Normal gene induce normal cell proliferation
Mutation in proto-oncogene creates oncogene which
accelerates cell growth and division
Act in dominant manner
What is the prometaphase?
Chromosomes attach to the mitotic spindle via kinetochores \+ active movement (chromosome) - Breakdown of nuclear envelope - Kinetochore microtubuli attach to kinetochores - Interpolar microtubuli move the centrosome to opposite directions
What happens in the anaphase?
Sister chromatids split synchronously and are pulled to the opposite
ends of the cell
chromosome segregation by motor proteins dynein and kinesin.
Cohesin rings around the chromatids destroyed by separase (= first
step of the anaphase)
What happens during metaphase?
Chromosomes line up to the centre of the cell (equator) and form
the metaphase plate
The kinetochore microtubules pull the sister chromatids back
and forth until they align along the centre of the cell
What happens during telophase?
Disassembly of mitotic spindle
• Re-assembly of a new nuclear envelope around each set of chromosomes →
2 daughter nuclei
• decondensation of chromosomes →gene transcription possible
• Mitosis is complete at the end of the telophase
What is the mitotic spindle?
array of microtubuli formed at the opposite poles of a
cell during mitosis and pulls duplicated chromosome sets apart. must be able to form two, move and pull
