2nd test Flashcards
glycolysis
first step of respiration
starts with glucose ends with pyruvate and 2 molecules of ATP
Harden and Young
dialysis of yeast extract
small molecules diffuse out and big molecules stayed in bag (enzymes) - activity lost when molecules separate
zymaseis the large molecules inactivated by heat
co-zymase is the small molecules which are heat stable
add 2 molecules back together and activity restored so zymase needs cozymase to work
inorganic cofactors
organic
metal ions
NAD
FAD
ATP
respiration vs combustion
respiration is better because it has lots of steps so more controlled and can harvest energy easier
control points
usually at start of pathways
have large negative delta G so are physiologically irreversible
intermediates can be used in other pathways: Glucose-6-P
store E as glycogen and ribose-5-P for DNA and RNA synthesis
oxidation
electron transfer
ligation requiring ATP cleavage
formation of covalent bonds
isomerization
rearrangment of atoms to form isomers
group transfer
transfer of functional group from 1 molecule to another
hydrolytic
cleavage of bonds by addition of water
addition or removal of functional groups
to double bonds or removal from double bonds
major activated carriers: carry energy, electron, carbon
ATP NAD+ FAD NADPH CoA
react slowly in absence of enzymes
difference between NAD and NADP
derived from niacin/vitamin B3
both nicotinamide + ribose + adenosine (but different R groups in adenosine)
R group of NAD is hydrogen
R group of NADP is phosphate
FAD structure
derived from riboflavin/vitamin B2
in vitro approach
like the yeast extract bag
defined conditions and quantitative results
but loss of compartmentation and spatial and temporal organisation
instability of components
in vivo approach
measure process in vivo and modify it and measure results with assays/indicators/labelled compounds
modify with inhibitors/mutations/molecular methods
number of steps in glycolysis
key steps
10
investment (2ATP used)
payout (oxidation, 4ATP produced, 1NADH produced, require NAD- and Pi)
stoichiometry
of glycolysis
using relationships between reactants and/or products in a chemical reaction to determine desired quantitative data
glucose+2ADP+2Pi+2NAD^+ —-> 2 pyruvate + 2ATP+2NADH+2H^+ +2H20
Harden and Young reaction stopped but adding more substrate (sucrose) did nothing, needed to add inorganic phosphate so each part is a limiting factor
regeneration of NAD+
what about anaerobic?
in oxidative phosphorylation, under aerobic
fermentation: organic compounds act as electron donors and acceptors
glucose oxidised to pyruvate
no oxygen as final electron acceptor so pyruvate reduced
makes lactate or ethanol
fate of pyruvate
acetyl CoA
lactate
acetaldehyde to ethanol
energetics of glycolysis
steps 1,3,10 have strong negative delta G so pushes glycolysis forward
these steps have regulatory points because large negative deltaG means irreversible and always forward and energy is released in reaction
regulatory steps
step1: not main regulatory step because other entry points and glucose needed in other pathways
most substrates come in as G6P so don’t need regulation of getting glucose to enter
step3: main regulatory point, phosphofructokinase
step10: not main one, needed as metabolic branch point
hexokinase
phosphofructokinase
pyruvate kinase
feedback inhibition: shut down if G6P accumulating
AMP upregulates it and ATP down regulates it, so responds to energy status of cell
also regulated by metabolic intermediates
feedforward activation, before needed, signals to make it (remember lab)
what happens after HK becomes inactivated
high AMP
control in liver
must regulate blood glucose levels so ATP/AMP regulation occurs but levels not as changeable
citric acid cycle in key regulatory point
allosteric regulator in glycolysis
ATP/AMP
fructose-2,6-bis P
controlling enzymes
allosteric regulatorss
phosphorylation (of pyruvate kinase so inactive)
transcriptional regulation (long term but not energy efficient)
dietary fructose and galactose enter glycolysis
galactose from lactose: converted to UDP-glucose
enters glycolysis at top
fructose: enters glycolysis after main regulatory step by PFK, below cleavage step
turned to fructose-1-phosphate then DHAP and GA
gluconeogenesis share most steps with glycolysis
converts pyruvate to glucose
mostly in liver and kidneys to maintain glucose levels in blood
use ATP and GTP
glycolysis and gluconeogenesis are oppositely regulated
reversible steps shared in 2 opposing pathways can’t be regulatory because don’y know which pathway would be shutting down
3 steps of glycolysis are irreversible so need to get around this
1) glucose-6-p with water cleaves phosphate off so left with glucose and Pi
but no ATP regenerated
3) fructose-1,6-bisP hydrolysed
PPP pathway
generates NADPH and ribose-5-P in response to cellular needs
glucose-6-P degydrogenase
key regulatory enzyme
PPP pathway regulation
availability of substrates
what happens when glucose-6-P accumulates and fructose-6-P accumulates
delta G increases
futile cycles
if glycolysis and gluconeogenesis both happening all time then net reaction is ATP hydrolysed to ADP and Pi so would just lose ATP
malonate
similar to succinate so competitive inhibitor
preparing pyruvate for citric acid cycle
crosses membrane by pyruvate translocase
cotransport using H
TPP
thiamine pyrophosphate
C2 of thiazol ring
H atom dissociates to form carbanion
decarboxylation of pyruvate
pyruvate dehydrogenase complex
lipoamide picks up acetyl group, becomes reduced (E1)
e2 transfers CoA group
e3 regenerates lipoamide
multienzyme complex advantage
rate not limited by diffusion
control of citric acid cycle
atp
nadh
anaplerotic reactions
carboxylation of pyruvate to oxaloacetate
carbon skleletons of amino acids: TCA
glucogenic amino acids can be used for anaplerotic reactions, not ketogenic amino acids
ketogenic
amino acids turn to acetyl CoA
OP respiratory complexes
electrons from FADH go to complex 2,3,4
NADH: 1,3,4
