Protein Control of cell division Flashcards
Complete
Cytoskeleton
- Dynamic Intricate network of thread like filaments that fills cytoplasm
- Consists of different protein structures including microtubules
What gives mechanical support and shape to cells
Cytoskeleton
Microtubules
Hollow cylinders composed of the protein tubulin
Radiate from MTOC/centrosome
Cytoskeleton is responsible for and microtubules control
Movement of organelles and chromosomes within it
Microtubules control cytokinesis
Formation and breakdown of microtubules
Polymeristaion and depolymeristaion
Why does mitosis require remodelling of the cytoskeleton
Because in mitosis microtubules form the spindle fibres which are active during mitosis, to move chromosomes and separate chromatids.
Microtubules must be dissembled and reassembled
Microtubules provide a
Framework for attatching
- organelles
- ribosome subunits
- vesicles
- and even molecules,
Dynamic nature of Cytoskeleton
- Continually changing to provide support and movement within a cell
- ## Microtubules can break and reform(controlled by centrosome)
Centrosome
Structure involved in cell division.
- duplicates in cell division, the two centrosomes move to opposite ends of the cell.
- Micro tubules come from here
- contains centriols
Centriole
Helps to arrange the microtubules that move chromosomes during cell division.
Soeach daughter cell recieves right number of chromosomes
Cell cycle
Consists of
Interphase and Mitosis
Cell grows until it reaches its critical mass, then divides to produce 2
daughter cells
Interphase
Involves growth and DNA synthesis and can be divided into 3 sub phases=
G1
S
G2.
Lasts 80% of the cell cycle
G1
First period of cell growth stage. Cell wont divide until it has doubled in size.
Many extra cell components are also synthesised
S (synthesis)
DNA replication occurs - chromosomes replicate to form two chromatids held together at centromere,
Centrioles duplicate
MTOC in mitosis
what it normally does
Normally controls the cytoskeleton
but during mitosis **cytoskelton breaks down **and Microtubules are reassembled to form spindle
(centrosome)
G2
A further growth phase to prepare for mitosis.
Sufficient reserves of ATP built up to last cell through rest of cycle.
3 active processes taking place during Interphase
- Cell growth
- Replication of DNA
- Protein Synthesis of organelles
Mitosis
consists of
Consists of Prophase Metaphase Anaphase Telophase.
Prophase
- Dna Condenses into chromosomes consisting of two sister chromatids.
- Nuclear membrane breaks down
- Spindle microtubules extend from MTOC by polymerisation
Metaphase
Chromosomes align at the metaphase plate
Anaphase
As spindle microtubules shorten by depolymerisation, sister chromatids are separated, and CHROMOSOMES pulled to opposite poles
Telophase
Chromosomes decondense and nuclear membrane forms around them.
What is mitosis controlled by?
Controlled and regulated by proteins, and checkpoints
what are
Checkpoints
**Mechanisms **within cell cycle that asses condition of cell during cycle
Will halt progression to next phase until requirements are met
When are checkpoints during cell cycle
- near the end of G1
- at the G2/M transition
- and during metaphase
Cyclin Proteins
**Accumulate **during cell growth.
Involved in regulating cell cycle.
They combine with Cdk’s and activate them
Cdk
Cyclin dependent kinases
Respitory enzymes
Active Cdk/cyclin complexes
When sufficient phosphortylation reached
Phosphorylate proteins that regulate cell cycle progression
(so cell cycle can continue)
If sufficient phosphorylation reached, progression occurs
G1 Checkpoint
Cyclin/cdk process
- Increasing cell size accumulates G1 cyclin proteins
- Cdks combine
- active cyclin/cdk complex formed
- phosphorylation of proteins by complex
- Phosphorylation threshold reached
- Pass checkpoint to next stage
G1 Checkpoint
Retinablastoma protein
is a
At G1 checkpoint
Transcription inhibitor factor.
Inhibits transcription of genes that code for proteins needed for DNA replication at G1 checkpoint
(prevents progression of cell cycle, tumour supressor protein)
G1 checkpoint
Phosphorylation of retinablastoma
it can no longer bind to the dna
Allows transcription of genes that code for protein needed for DNA repli
so Cells progress from G1 to S
G1 checkpoint
active RB
- Not phosphorylated, transcription inhibition occurs
- No further growth of cell, so cell cycle halts at G1
G1 checkpoint
Inactive RB
Rb Has been phosphorylated,
- less trancription inhibition
- So growth occurs and progresses to S phase
what is assessed
AT the G2 Checkpoint
sucess of dna replication and any damage to dna is assessed
If dna damage is present during G2 checkpoint
Activation of several proteins including p53 is triggered
p53
Can stimulate DNA repair
Arrest the cell cycle
Or cause cell death
Metaphase checkpoint
controls
Controls progression from metaphase to anaphase
Progression is halted until chromosomes are alligned correctly on the metaphase plate and attatched to the spindle microtubules
Uncrontoled reduction and increase in rate of cell cycle
Reduction= May result in degeerative diseases
Increase= may result in tumour formation
What is a
Proto-oncogene
A normal gene, usually involved in the control of cell growth or divison
It can mutate!!! To form a tumour promoting oncogene
Ccontrol of
Apoptosis
triggered by
Triggered by cell death signals that can be external or internal
Production of cell death signal molecules from
Lymphocytes and Dna damage
lymphocytes= Example of external death signals
DNA damage= Internal
External Death signal molecules
Bind to a surface receptor protein and trigger a protein cascacde within the cytoplasm
What causes activation of p53
tumour supressor protein
Internal death signals
(dnadamage)
All Death signals cause
Activation of caspases
A type of protease enzyme
That cause destruction of the cell
WHat is
Apoptosis essential during
- Development of an organism to remove cells that arent required as development progresses
- or during metamorphosis
What happens in the
ABsence of growth factors
Cells may initiate apoptosis
