1.6 PROTEIN CONTROL OF CELL DIVISION Flashcards
What is the main requirement of cell division?
Remodelling of the cell’s cytoskeleton
What is the cytoskeleton?
Microscopic network of protein filaments and tubules in the cytoplasm
What is the purpose of the cytoskeleton?
To give mechanical support and shape to cells
What does the cytoskeleton consist of?
Different types of proteins extending throughout the cytoplasm
What are microtubules composed of?
Hollow straight rods
What are the rods that make up microtubules made of?
Globular proteins known as tubulins
What is the purpose of microtubules?
To govern location and movement of membrane-bound organelles and other cell components
Where are microtubules found?
All eukaryotic cells
Where do microtubules radiate from?
The microtubule organising centre (MTOC)
What is the MTOC also known as?
The centrosome
Which necessary structure do microtubules form during cell division?
Spindle fibres
What does the cell cycle regulate?
Growth and replacement of genetically identical cells
Over what time period does the cell cycle regulate growth and replacement of cells?
The entire life of the organism
Unconrolled reduction in rate of cell cycle could result in?
A degenerative disease
Unconrolled increase in rate of cell cycle could result in?
Tumour formation
What are the three stages of the cell cycle?
Interphase, mitosis, cytokinesis
What is interphase?
Cell growth divided into three further stages
What are the three sub-phases of interphase?
G1, S phase, G2 phase
What occurs during G1 phase?
Proteins and organelles synthesised
What occurs during S phase?
Cell continues to grow, DNA replication
What occurs during G2 phase?
More growth - more proteins and organelles synthesised
What follows interphase?
Mitotic phase
What are the four stages of mitosis?
PMAT - prophase, metaphase, anaphase, telophase
What happens to chromosomes during prophase?
Each duplicated chromosome appears as two identical sister chromatids joined at the centromere
What happens in the cytoplasm during prophase?
Mitotic spindle begins to form
Where does mitotic spindle begin to form during prophase?
Between two centrosomes
What happens to chromosomes during metaphase?
They line up on metaphase plate in centre of cell
What attaches to chromatids during metaphase?
Microtubules from opposite ends of parent cell
Where do microtubules join to chromatids?
At the kinetochore
What happens during anaphase?
Spindle fibres shorten
What is the result of spindle fibres shortening?
Sister chromatids move apart as paired centromeres separate
What happens to the cell during telophase?
Lengthens and nuclear membranes form around each set of chromosomes
What happens to chromosomes during telophase?
Begin to uncoil
Which stage of the cell cycle also takes place during telophase?
Cytokinesis
What does cytokinesis involve?
Separation of cytoplasm into two daughter cells
What regulates progression through the cell cycle?
Checkpoints
What are checkpoints?
Critical control points which signal stop and go ahead
Where are the three checkpoints in the cell cycle?
G1, G2, Metaphase
Which is the most important checkpoint for many cells?
G1 checkpoint
What is the result of a go ahead signal not being reached at G1 checkpoint?
Cell may switch to G0 phase
What is G0 phase?
Non-dividing state
What happens as cell size increases during G1 phase?
Cyclin proteins accumulate
What do cyclin proteins combine with?
Cyclin-dependant kinases (Cdks)
What are cyclin-dependant kinases?
Regulatory proteins
What is the result of cyclin proteins combining with Cdks?
Cyclin-dependant kinases are activated
What do activated Cdks do?
Cause phosphorylation of proteins that stimulate cell cycle
What results in a go ahead signal at G1 checkpoint?
Threshold of phosphorylation of cell cycle-stimulating proteins by Cdks is surpassed
What results in a stop signal at G1 checkpoint?
Insufficent phosphorylation of cell cycle-stimulating proteins by Cdks
What does the G1 Cdk do?
Phosphorylates retinoblastoma (Rb)
What is a retinoblastoma protein?
A transcription factor inhibitor
What is the phosphorylation of Rb protein allow?
DNA replication in S phase
What does DNA damage trigger?
Activation of several proteins including p53
What can p53 do?
Stimulate DNA repair, arrest the cell cycle, cause cell death
What must be carefully controlled in a multicellular organism?
Cell destruction
What is apoptosis?
Programmed cell death
What is apoptosis triggered by?
Cell death signals
What do cell death signals activate?
Inactive forms of DNAase and proteinases (caspases)
What do activated DNAases and proteinases (caspases) do?
Destroy the cell
Where may cell death signals come from?
May originate outwith the cell
Name a possible source of extracellular cell death signals.
Lymphocytes
Where are receptors for extracellular cell death signals found?
Cell surface
What is the result of an extracellular cell death signal binding to its receptor?
Activation of caspase-producing protein cascade
Name a possible source of intracellular cell death signals.
p53 protein
How does p53 protein trigger cell death?
Activation of caspase cascade
Name one other reason cells may initaite apoptosis.
Absence of cell growth factors
