ethan hack material Flashcards
what are the two mechanisms of cellular control
changing the specific activity of enzymes
changing the concentration of enzymes by synthesis and degradation
discuss 3 methods of changing the specific activity of enzymes
a)non covalent boning. allosteric sites
b)covalent bonding.
usually done by phosphorylation; the phosphate group has a negative charge and therefore changes the structure of the enzyme
c)protein-protein interaction)
enzymes are often phosphorylated to change their specific activity, where does phosphorylation occour and where does the phosphate come from
the phosphate comes from ATP, phosphorylaiton id performed on amino acids with a hydroxyl group (serine, tyrosine)
why are yeast used to study the cell cycle
the genome is small, so cell cycle only takes 2 hours (can take up to 24 in other eukaryotes)
their small haploid genomes are easy to clone and select mutants from
saccharomyces cerevisae is the usual model organism yeast, but another yeast species is used to study the cell cycle, which species is it and why is it used
SCHIZOsaccharomyces pombe. saccharomyces cerevisae is a budding yeast and doesnt divide down the middle
what are the CDC genes
the cell division cycle genes which regulate cell division
why is studying cells with mutant CDC genes hard
these genes control the cell cycle, when they are mutated the cell dies. some mutants can be studied (those that are temperature sensitive)
name the 3 ‘checkpoints’ where the cell commits to certain next steps
in G1 the cell commits to DNA synthesis
in G2 the cell commits to mitosis
in M phase the cell commits to complete mitosis
discuss what Cdk’s are
cyclin dependant kinases are enzymes that initate many important parts of the cell cycle but they only work when cyclin protein is present to activate them
how does the G1 to S phase transition occour
G1-cyclin accumualtes and activates G1-Cdk, which activates transcription of G1/S cycllin.
G1/S cyclin accumualtes, which activates G1/S-Cdk, which increases activity of S-Cdk, which initiates DNA synthesis
the three ways that G1/S-Cdk increases activity of S-Cdk are;
1) activating transcription of S-cyclin
2) inhibiting the S-Cdk inhibitor
3) inhibiting the D-Cdk ubuiquitin ligase which would normally causes S-Cdk to be degraded
how does entry to mitosis occour
M cyclin is synthesised which activates M-Cdk.
initially, M-Cdk is inactivated by Wee1 kinase, but when DNA replication is complete, polo like kinase activates cdc25 phosphatase, which dephosphorylates and activates M-Cdk
M-Cdk activity causes entry to mitosis (nuclear envelope breakdown and chromosome condensation caused). M-Cdk inactivates wee1 kinase and activates more cdc25 phosphatase (positive ffedback)
discuss proteolyis in the cell cycle
degradation of cyclin has massive impacts on weather or not the cell cycle continues
define protein turnover
the balance betweeen protein synthesis and degradation
discuss proteasomes structure
a large hollow cyclinder shaped protease (enzyme that degrades protein)
what structure of a proteasome stops trandom degradation of unwanted proteins and how
the ‘cap’ which stops other proteins entering which dont have a ubiquitin protein attached to them
what is the protein added to a protein which makes it destined for degradation? which enzyme adds the protein? where is the protein added to the protein? how does the enzyme know which proteins to add the protein to
ubuiquitin, ubiquitin ligase, lysin AA side chain; ubuiquitin is added to proteins with degradation signals on them (abnormal structure)
name the chemicals that signal for cell division (entry to cell cycle) and mass increase
mitogens stimualate cell division and growth factors stimulate mass growth
how to mitogens stimulate cells to divide
mitogens bind to the cell surface and cause secondary messenger action which causes transcription of G1-cyclin and transcription of enzymes which inhibit/degrade G1-inhibitor proteins
name two examples of mitogens
platelet derived growth factor (PDGF); stimualtes many cells to divide
erythropoietin; stimulates RBC precursor cells to divide
define cancer and discuss retinoblastoma
cancer in unregulated growth and cell division
retinoblastoma cancer occours when the RB1 gene is mutated (normally would be expressed into RB1 protein which prevents premature cell division by stopping transcription of G1/S-cyclin and S cyclin and therefore blocking entry into the S phase)
what is the RB1 protein
it is a gene that prevents premature entry to mitosis by blocking entry into the s stage (inhibts synthesis of G1/S and S synthesis.
RB1 mutation lead to retinoblastoma.
discuss the mechanism by which cells with mutated DNA have replication paused until DNA is repaired
p53 would normally be ubuiquinated and degraded (low concentration exist and replication occours)
when DNA is mutated, phosphorylation of p53 occours and the ubuiquitin protein cant be added; p53 accumualtes, activates transcription of p21 protein which accumulates and inhibits activity of G1/S-Cdk and S-Cdk.
discuss how mutated p53 leads to many human cancers
p53 would normally prevent replication of mutated DNA occouring, if its mutated itself then DNA will be replicated when it shouldnt
state the stages of the cell cycle and which stage takes the longest
G1; protein synthesis S; DNA synthesis (12 hours) G2; checking DNA G0; resting state mitosis; PMAT
describe how sister chromatids are seperated during anaphase
the seperase protease enzyme breaks down the central cohesin protein complex holding the sister chromatids together
M-Cdk activates a ubuiquitin ligase (APC) which ubuiquitinates securin which is then degraded (the enzyme that would normally inhibit sperase)
why does exit from mitosis occour
APC (a ubuiquitin ligase) ubuiquitinates M-cyclin, which is then degraded.
lack of M-cyclin inactivates APC
define necrosis
rapid accidental cell death, usually for cells which are injured
discuss the processes involved in apoptosis
cell shrinkage
nuclear membrane blebbing
cytoskeleton breakdown
phagocytosis by phagocytes
what causes phagocytosis of cells during apoptosis
alteration of the plasma membrane; proteins placed on membrane
what is the principle protease used for apoptosis
what element does it have at its activate site
where does it cleave
what is the name of the inactive precursor that is synthesised before the enzyme is needed
how does this precursor enzyme become activated
caspaces
sulphur at active site
cleaves at aspartic acid amino acids
procaspases are the precursor fort he caspase
1) inhibitor caspases cleave procaspaces between their large and small sub unit as well as cleaving off the prodomain.
2) the large and small subunits rearrange next to eachother
3) dimer formation between two complexes
4) these are known as ‘executionar caspases’ cleave more procaspases and break down proteins
how are DNases activated
an executioner caspase breaks down the DNase inhibitor protein
how is apoptosis initiated via external signals
1) foreign pieces of protein are bound to the MHC (major histocompatibility complex) on the plasma membrane
2) a cytotoxic T lymphocyte binds to MHC by its T cell receptor (TCR), recognises the foreign compound and activates apoptosis
3) the target cells Fas receptor binds to the T cells Fas ligand protein on its surface
4) all fas receptors on the surface aggregate and come together, and so do the associated initator procaspases (8 and10) due to the binding of the FADD adaptor protein
5) when procaspases are brought together they activate eachother which the activate executionar caspases
why does Fas aggregation cause procaspases to come together
Fas receptor has a death domain which FADD adaptor protein binds to, and FADD adaptor protein has a death effector domain which prcaspases 8 and 10 bind to
what is the name of the complex when Fas receptors aggeregate and bring together the procaspases and FADD adaptor proteins
Death inducing signal complex (DISC)
discuss internal initiation of apoptosis
1) mitochondria releases cytochrome C
2) cytochrome C binds to adaptor proteins called Apaf1
3) apaf 1 group together into an apoptosome via CARD domains
4) procaspase 9 come together and bind via their CARD domain and activate eachother
5) procaspase9 activates executionary procaspases
mitochondria release cytochrome C due to an inhibitor inhibiting Bcl2 genes, bax and bak proteins form pores in the membrane
discuss how cytotoxic T cells cause cause internal initation of apoptosis
1) T cell releases perforin which creates holes on plasma membrane
2) granzyme B enters cell and cleaves bid protein
3) tBid enzyme activates bax and bak
3b) granzyme also acitvates procaspase3 and 7
how is apoptosis prevented
survival factors like insulin like growth factor 1 (IGF1) inactivate BH3 which would normally activate bax and bak pore formation by inhibiting their inhibitor
IGF1 activates anti-apoptotic genes; no cytochrome C release
