Cells and proteins - 5 Flashcards
What is a cytoskeleton?
network of protein fibres
what does the cytoskeleton provide for the cell?
gives mechanical support and shape to cell, involved in movement of cellular components
what are the three main components of the cytoskeleton?
microtubules, intermediate filaments, actin filaments
what are actin filaments?
polymers of soluble globular protein actin
what are actin filaments responsible for?
responsible for cellular movements
what are intermediate filaments?
formed from fibrous proteins and are two pairs of monomers wrapped around each other
what to intermediate filaments give to a cell?
high mechanical strength
what are microtubules?
polymers of a dimer made from soluble globular proteins a-tubulin and b-tubulin
what do microtubules govern?
location and movement of membrane bound cell parts
where do microtubules come from?
the microtubule-organising centre (MTOC)
during mitosis, what happens to the microtubules?
disassemble to form spindle fibres
what do the spindle fibres control?
controls the movement of chromosomes
what ensures cells division apparatus is correctly located?
aster at each centromere
what do the spindle fibres attach to?
kinetochore proteins at centromere
what is the purpose of the cell cycle?
regulates growth and replacement of genetically identical cells
what are the three stages of interphase?
G1, S and G2
what happens in G1?
first growth phase - cell makes new proteins and copies of organelles
in what stage in interphase does DNA replication occur?
S phase
what are the 4 stages of the M phase?
prophase, metaphase, anaphase, telophase
what happens in prophase?
- chromosomes condense
- microtubules disassemble
- nuclear membrane disintegrates
what to the microtubules disassemble to produce in prophase?
spindle fibres and asters
what happens in metaphase?
- spindle fibres move chromosomes
- line up on metaphase plate at equator
what happens in anaphase?
spindle fibres pull sister chromatids apart
what happens in telophase?
- separated chromosomes pulled by spindle fibres to opposite poles
- forms daughter nuclei
- chromosomes uncoil
- nuclear membrane made
what pulls the membrane in cytokinesis?
actin and myosin
what are the two phases of the cell cycle?
interphase and M phase
what 2 stages occurs in the M phase?
mitosis and cytokinesis
what happens when the rate of the cell cycle is uncontrollably reduced?
results in a degenerative disease
what happens if there is an uncontrolled increase in the rate of cell cycle?
results in tumour formation
in what parts of the cell cycle is progression regulated by checkpoints?
G1, G2 and metaphase
what is monitored at the G1 checkpoint?
cell size
if the cell fails the checkpoint at G1 what happens?
cell switches to G0 phase
what is the G0 phase?
non-dividing state, cyclin proteins not produced
what is assessed at the G2 checkpoint?
assesses success of DNA replication
what occurs at the M checkpoint?
checks chromosome alignment
what is the role of retinoblastoma protein (Rb)?
- transcription factor inhibitor
- involved in production of proteins required for DNA replication in S phase
what happens when low levels of CDK activity is detected?
Rb binds to transcription factor E2F which inhibits transcription of genes needed to enter S phase
what happens when high levels of D+CDK activity is detected?
Rb is phosphorylated, no longer bind to transcription factors, promotes transcription of genes
where is the p53 protein found?
G1 checkpoint
what is a p53 protein?
transcription factor that stimulates DNA repair, arrest cell cycle or trigger cell death
what is apoptosis?
programmed cell death
what is apoptosis triggered by?
triggered by cell-death signals
what triggers cell death from outside the cell?
ligands binding to surface receptor protein
what happens when a ligand binds to surface receptor protein?
- receptor protein changes conformation of subunits on cytoplasmic side of membrane
- acts as a signal transduction
what is activated by a signal transduction during the extrinsic pathway?
activates protein cascade that produces caspases
inside the cell, how is apoptosis triggered?
- p53 protein activated
- activates caspase cascade
what occurs during a caspase cascade?
involves a series of post-translational modification to proteins in cytoplasm
what does a caspase cascade allow in a cell?
for a rapid response to occur
what happens when inactive caspases become activated?
each inhibitor caspase activates several executioner caspases which destroys cellular components
what engulfs the fragments of cells after apoptosis?
phagocytic white blood cells
