Random Flashcards
Describe the action of the nitrogenase enzyme
Fe protein accepts electrons from ferredoxin and can act as a reductase.
ATP hydrolysis makes confirmational change in that brings the two proteins closer together (2Fe-S clusters and 2Mo-Fe clusters used to reduce N2 to NH3)
How is oxygen reduced around nitrogen fixing bacteria in root nodules?
Leghaemoglobin: has high affinity with oxygen.
How is ammonia aquired in plants without nitrogen fixing bacteria?
Reduction reactions
Nitrate -> Nitrite -> Ammonia
Electrons for reduction come from NADH or NADPH
Enzymes: Nitrate reducase and Nitrite reductase
Both enzymes make use of an Mo cofactor
What is the final product of amino acid biosynthesis from ammonia?
Glutamate - but there is two routes to get to this
2 methods for producing glutamate from ammonia
Animals and fungi: Use glutamate hydrogenase to reduce alpha-ketogluterate using NADH or NADPH
Plants: Synthesise glutamate from itself. Glutamine synthetase enzyme used. Used NADH reducion power.
Glutamate -> Glutamine
Glutamine + Oxoglutarate -> 2 glutamate
2 ways to omake amino acids from glutamate
- Transamination (transfer of amino group between two keto-acids) amino transferases
- Carbon skeleton alteration
Where do carbon skeletons for amino acid synthesis come from?
The TCA cycle: specifically oxoglutarate
How are the carbon skeletons being removed from the TCA cycle replaced?
Carboxylation of C3 intermediates of glycolysis
Pyruvate + HCO3 -> Oxaloacetate
Pyruvate carboxylase
Therefore carbon enters the TCA cycle as OAA or acetyl coA
Describe the action of lysozyme
Cuts the polysaccharide chain in peptidoglycan of bacterial cell walls
Hydrophobic active site is large enough to fit 6 sugar residues. Ring D becomes strained when bound to the enzyme and forced into a half chair structure.
Wall is cut between D and E rings (nucelophillic attack)
Inhibitor of F-type ATPase?
Oligomycin
Evidence for chemiosmosis?
Uncoupling proteins
Inhibiting ATPase with oligomycin stops the electron transport chain.
Detergents stop proton pumping and ATP is not produced.
ATP produced using an artifically generated proton gradient.
What is a haplotype?
A set of SNPs inherited together: can be informative for human disease.
How was the gene causing cystic fibrosis identified? (a monogenic disorder)
- Identifcation of an RFLP that segregated with the disease
- Identify the chromosome: long arm of chromosome 7 (done by fusing with mouse cell - as the mouse cell divides, it looses human chromosomes)
- Chromosome walk narrowed down the region of interest to 500kb
- Used a mixture of northern blots and zoo plots to identify the gene: a gene that codes for a transmembrane chloride channel
66% of CF occurences are due to one mutation: missing phenylalanine.
1525 different mutations in the gene have been idenifed, making diagnostic screening difficult.
How does Dictyostelium aggregate?
Founder cell emits pulses of cAMP
cAMP binds to GCPR activating AC and PLC
cAMP: causes more cAMP to be release
IP3: releases calcium to catalyse chemotaxis (cytoskeletal rearrangement)
Define a secondary messanger
A small molecule that is formed in or released into the cytosol in response to an extracellular signal and helps to relay the signal to the interior of the cell
Describe Tyrosine Kinase Linked Receptors with example
Example: platlet derived growth factor
Binding of PDGF induces dimerisation of 2 receptors
Tyrosine residues phosphoylate each other and these activated residues activate
- PLC
- GAP
- SOS
How does Ras control gene expression?
- A monomeric G protein
- Activated by GTP binding (catalysed by SOS enzyme)
- Initates a phosphoylation cascade that results in MAP kinase activiation
- MAP kinase is able to regulate transcription of proteins involved in the cell cycle (cyclins etc.)
Examples of communication in unicellular organisms
cAMP acting as aggregation stimulus is Dictostelium
Quorum sensing in bacteria (Lux proteins regulate light emission and light is only emitted when a critical population density is reached)
Quroum sensing
Light only expressed at high population densities in Vibro fischeri
LuxI operon expressed during exponecial growth and causes systhesis of OHHL
OHHL can therefore be used as a signal for the popuation density of the bacteria
OHHL concentration sensed by LuxR
At critcal density, LuxR induces LuxL (more OHHL synthesis - positive feedback) and LuxAB which causes light to be emitted.
Protein pairs used in environmental sensing in bacteria
Sensor and response regulator
Sensor: is phosphoylated by input signal
Phosphate is physically transfered to the response regulator
What are the 4 sets of proteins used for chemotaxis in e.coli?
MCPs: Membrane bound signal transducers
Cytoplasmic signal transducers: CheA, CheY, CheW and CheZ
Flagellar switch
Adaptors: CheR and CheB
Adaptation of chemotaxis in bacteria
Results in “random biased walk”
CheR = methylator of the receptor
- methylated receptor is less active leading to cheA to return to phosphoylated state (after dephosphoylation was caused by attractant binding)
CheB = demethylator
- activated by CheA-P (which phosphoylates CheB)
- in the presence of a repellent
Plant communication examples
- ABA causing stomatal closure
- Giberellins and growth gene expression
- Phytochromes
How does ABA cause stomata closure?
ABA inhibits PP2C
PP2C can no longer inhibit OST1
OST1 activates Cl efflux and inhibits K influx
What is photomorphogenesis?
Light dependent determination of plant growth
- Impacted by Phytochromes (increase in the nucleus in the light)
- COP1 increases in the nucleus in the dark
Photomorphogenesis is repressed in the dark.
How does phytochrome impact photomorphogenesis?
Active phytochrome enters the nucleus and phosphoylates PIF3
PIF3 is degraded when phosphoylated
PIF3 usually downregulated photomorphogeneis
Overall: Active phytochrome stimulates photomorphogenesis
How does COP1 negativly regulate photomorphogenesis?
COP1 is an E3 ubiuitin ligase
Targets HY5 for degregation
HY5 activates photomorphogeneis
COP1 accumulates in the dark and is exported from the nucleus in the light.
How does GA target DELLA for degregation?
GA binds to GID1 which recruits E3 ubiquin ligases to target DELLA for degregation