Protein Control of Cell Division Flashcards
What is the cytoskeleton?
Network of protein fibres that extend throughout the cytoplasm in all eukaryotic cells
Give some functions of the cytoskeleton
Provide mechanical support so cell maintains shape
Provides anchorage for many organelles
Allow the whole cell to move
Enable organelles within the cell to move
What are the three main components of the cytoskeleton?
Microtubules, intermediate filaments, actin filaments
Describe what actin mirofilaments are made up of?
Polymers of the soluble globular protein actin
What is the width of microfilaments?
2 nano metres
What are actin microfilaments responsible for?
Cellular movements, such as contraction during cytokineses
Describe intermediate filaments and give their width
Formed from fibrous proteins
Rope like in structure
10 nano metres in diametes
Consist of two pairs of monomers wrapped around each other
What is the function of intermediate filaments?
Give the cell its mechanical strength/support
What are microtubules made of?
Polymers of a dimer consisting of alpha tubulin and beta tubulin
What is the width of microtubules?
25 nano metres
How is the length of microtubules controlled?
Addition or removal of tubulin at the ends of the microtubules
What is the function of microtubules?
Govern the location and movement of membrane bound organelles
Where do microtubules radiate from?
Microtubules Organising Centre (MTOC)
Where is the MTOC located and what does it contain?
Near the nucleus
Centrosome
What are the three roles of microtubules in cell division?
- The aster at each centrosome ensures that the cell division apparatus is located at the correct position
- Spindle microtubules attach to kinetechore proteins at the centrosomes of each chromatid
- Microtubules attach to microtubules from the opposite centrosome
How are the chromatids seperated during cell division?
Disassembly of the microtubules at the kinetchores
What are the two phases of the cell cycle?
Interphase and Mitosis
What are the three phases of interphase?
G1, S, G2
What happens in the G1 stage of interphase?
First growth stage
Cell makes copies of new proteins and organelles
In what stage of interphase does DNA replication occur?
S
What occurs in the G2 phase of cell division?
Second growth phase
Cell makes more proteins and copies organelles in prep for mitosis
What are the five stages of mitosis?
Prophase Metaphase Anaphase Telophase Cytokenesis
What happens during prophase?
Chromosomes condense
Each chromosomes is composed of two chromatids
Microtubules start to assemble to the spindle fibres
Some spindle fibres attach to the kinetechore
In what stage are the sister chromatids pulled apart?
Anaphase
What happens in Telophase?
Seperated chromosomes are pulled to opposite poles
Chromosomes form daughter nuclei
Chromosomes start to uncoil and nucleur membrane forms
Where do chromosomes line up in metaphase?
Metaphase plate at the equator of the cell
What happens during metaphase?
Chromosomes line up on the metaphase plate at equator of cell
Movement acheived by assembly/diassembly of tubulin dimers
How do spindle fibres contract and expand?
Addition and removal of dimers onto the spindle fibres
What is Cytokenesis?
Division of the cytoplasm to form two daughter cells
What is the mitotic index?
Percentage of cells undergoing mitosis in the sample
What may be indicated from an abnormally high mitotic index in a sample?
Developing tumour
What can an uncontrolled reduction in the rate of the cell cycle cause?
Degenerative diseases
What is one of the causes of cancer?
Uncontrolled increase in the rate of the cell cycle
Where are the checkpoints in the cell cycle?
G1, G2, M
What are checkpoints?
Critical control points where stop and go-ahead signals regulate the cycle
What is checked at the G1 checkpoint?
Cell size is monitored
Which checkpoint regulates entry to G0/S phase?
G1 checkpoint
What is assessed at the G2 checkpoint?
Success of DNA replication
Describe the M checkpoint
occurs during metaphase
monitors chromosome alignment
makes sure each daughter cell receives one chromatid from each chromosome
controls entry to anaphase
what accumulates as cell size increases in the g1 phase?
cyclins
What do cyclins combine with?
Cyclin Dependant Kinases
What does the binding of cyclin and CDKS form?
Mitosis Promoting Factor
What do active CDKs do?
Phosphorylate target proteins that stimulate the cell cycle
What is Rb?
Restinoblastoma protein is a transcription protein important at the G1 checkpoint
What is Rb involved with?
Production of proteins required for DNA replication in the S phase
What phosphorylates Rb?
CDKs
What happens when the activity of CDKs reaches a sufficent threshold?
Each Rb has been phosphorylated 14 times and so can no longer bind to the transcription factors, allowing the cell to progress past the G1 checkpoint into S
What is p53?
A transcription factor
What are the three functions of p53?
Stimulate DNA Repair
Arrest the cell cycle
Trigger apoptosis
What happens if DNA damage has occured?
p53 causes the expression of genes to stimulate DNA repair, arrests the cell cycle
What happens if DNA repair is not successful?
p53 instructs the cell to kill itself
What is apoptosis?
Programmed cell death
What is apoptosis triggered by?
Cell death signals
Where can cell death signals come from?
Outside the cell or inside the cell
Give an example of a cell death signal that originates from outside the cell
Lymphocyte
Natural Killer Cell
What happens in the case of an external cell death signal?
Ligand binds to a receptor protein
Causes a conformational change on the cytoplasmic side
Acts as a signal transduction and activates a protein cascase that produces caspases
When may a cell death signal originate from inside the cell?
When DNA damage is detected
Absence of cell growth factors
How is a caspase cascade initiated?
Caspases must be activated
Inactive proteinases and DNAases are activated
Initiator caspases activate executioner caspases
Degrade cellular components
What is the cause of the fact that the cell breaks into many small vesicles?
Lack of intact cytoskeleton
