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Enzymes > Lectures 12-15: Glucose metabolism > Flashcards

Lectures 12-15: Glucose metabolism Flashcards

1
Q

energy containing nutrients broken down by catabolism which are then excreted

A

bond energy transferred

via cofactors fueling anabolic reactions which take simple precursor molecules and make them into macromolecules

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2
Q

metabolism

A

sum of all chemical reactions in the cell

primarily energy producing - catabolism
primary use energy to build complex structures - anabolism or biosynthesis

everything broken down into acetyl coline - converging

cyclic concentration goes up and down i.e. krebs cycle

diverging - anabolic reactions - complex molecules built up i

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3
Q

Entropy (disorder) in a closed system increases

A

increase entropy in order to gain a more stable state

to maintain cellular organisation must be able to extract useable energy from surroundings and release useless energy

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4
Q

when the equilibrium constant is 1 = no net energy

A

when equilibrium constant is
+1 = negative
1 = 0
-1= positive delta G

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5
Q

hydrolysis

A

spontaneous

highly favourable

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6
Q

isomerization

A

same chemical formula at the beginning and end of the reaction
smaller free energy changes
between enantiomers delta g i 0

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7
Q

complete oxidation of reduced compounds

A

strongly favourable
how chemo-trophs obtain energy
reduced fuel with oxygen is stepwise and controlled

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8
Q

delta change depends on

A

the standard change in free energy

actual concentration of products and reactants

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9
Q

spin states

A

reduced fuels are in singlet spin state = all electrons are paired in electron pairs

molecular oxygen is in the triplet spin state = 2 oxygens are unpaired

direct electron transfer from a singlet reduces species to a triplet oxidising species is quantum mechanicaly forbidden

direct oxidation = combustion of biomolecules doesn’t occur readily

NAD, FAD and transition metal ions act as cofactors to catalyse consecutive single electron transfers needed for oxygen utilisation = need to funnel electrons in single or double pairs away from the singlet state so they can react with the triplet state

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10
Q

group transfer reactions

A

proton - ph

methyl

acyl 2C- biosynthesis of fatty acids

glycosyl more than @C- attachment of sugars

phophoryl ATP- activate metabolites = signal transduction

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11
Q

ATP

phosphoryl transfer

A

donor of the phosphate in biosynthesis of phosphate esters

hydrolysis of ATP is highly favourable under standard conditions

better charge separation in products

better solvation of products - hydroxyl group adding in

resonance stabilisation - drives ATP hydrolysis

ADP is more stable

cellular ATP is high above the equilibrium conc. = potent source of chemical energy

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12
Q

NAD and NADP redox cofactors

A

pyridine nucelotides

can dissociate from enzymes after the reaction

oxidation = hydride ion = 2 protons + 2 electrons from an alcohol transferred to NAD+ = NADH = reduced form
electron later injected into electron transport chain to make a proton gradient

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13
Q

FAD

A

shuttles single electron transfers

permits the fate of oxygen as an ultimate electron acceptor

co factors are tightly bound to proteins

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14
Q

fate of glucose

A
  1. stored as glucogen starch or sucrose
  2. synthesis of structural polymers = extracellular matrix and cell wall polysaccharides
  3. make nucleotides - ribose bisphosphate

4 oxidation via glycolysis = pyruvate

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15
Q

important of glucose

A

goodfuel - high bond energy = delta g

can be stored as glycogen

versatile biochemical precursor -carbon skeleton can be rebuilt into many different amino acids + nucleotide bases

survive on glucose only - human brain

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16
Q

glucose entry

A

glucose transporter in membrane = saturable

glucose kept a 2 millimolar in bloodstream

flows down concentration gradient into cell

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17
Q

glycolysis

A

sugar splitting

make ATP and NADH = more ATP in electron transport chain

6C = 2* 3C pyruvates

5 priming + 5 pay off reactions

3 regulated control enzymes

18
Q

gluconeogenesis

A

make glucose for export to brain and muscle

pyruvate back to glucose but not exact reverse of glycolysis

3 regulated control enzymes

19
Q

glycolysis

1. the preparatory phase

A

phosphorylation of glucose using hexokinase = glucose 6 phosphate

1st priming reaction = ATP invested

Phosphohexose isomerase

phosphokinase
1 - second priming reaction

aldolase cleaves 6C into 23C phosphates = glycerldehyde 3phosphate + dihydroxyacetone phosphate

20
Q

payoff phase

A

ATP + NADH out

inorganic phosphate+ NAD = 2NADH

substrate level phosphorylation 2ADP - 2ATP

second atp forming

21
Q

glycolysis

A

glucose + 2 NAD = + 2ADP + 2 phosphates = 2 pyruvates
2 NADH
2H+ + 2 ATP

used 1 glucose invest 2 atps and 2 NADs

made
2 pyruvates
4 ATPs = net gain of 2
2 NADH reoxidised in ETC to make ATP

22
Q

3 stages of regulation

A

stages w a large negative delta G are the best to regulate

in glycolysis hexokinase, fructose 6-phosphate and pyruvate kinase

23
Q

phosphofructokinase

A

tetramer
binds fructose 6 phosphate = fructose 1,6 phosphate

allosteric regulation - sigmoidal curve = activity is regulated

high AP = activity of enzyme decreased

low ATP conc =
enzyme more sensitive - reactivity higher

24
Q

gluconeogenesis

cannot convert fatty acids to sugars
use acetyl CoA as intermediate then pyruvate and back up to glucose 6P

A 
IN:
2 pyruvate
4ATP
2 GTP
2 NADH 
2 H=
4 water
out :
glucose
4 ADP
2 GDP
6 phosphate
2NAD+

brain n nervous sys only use atp from glucose

when glycogen stores are depleted this is our source of glucose

25
Q

glycolysis vs gluconeogenesis

A

both thermodynamically favourable
regulated to prevent futile cycling which is useless to the cell

glycolysis mainly in muscle an brain as require high ATP

gluconeo - occurs in liver site

3 reversible reactions shared in both pathways:

irreversible reaction of glycolysis must be bypasses in gluconeogenesis

glycolysis:
hexokinasw
phosphofructokinase
pyruvate kinase
all kinases - changing phosphorylation state of the product
gluconeogenesis
PEPcarboxykinase
puruvate carboxylase
fructose 1 bisphosphotase
gluce 6 phosphotasease

g;uconeogenesis is expensive - more energy to make a glucose than burning one

26
Q

pyruvate fates

A

yeasts ferment to ethanol

lactate in hypoxic or anaerobic condition
fermentation by lactate dehydrogenase
in contracting muscles

or acetyl-CoA
citric acid cycle

27
Q

pyruvate 3C to acetate 2C

A

pyruvate dehydrogenase

28
Q

citric acid/ krebs cycle catabloic process makes GTP an reduced cofactor to yield ATP but important for Anabolic roles reactions tht take pyruvate into

A

in matrix of mitochondria

more ATp generation than glycolysis

29
Q
  1. acetyl CoA production
A 
pyruvate to acetyl co A
oxidative decarboxylation of pyruvate
first carbons of glucose are fully oxidised
catalysed by the pyruvate dehydrogenase complex found in matrix of mitochondria - requires 5 co enzymes
TPP
lipllysine prosthetic groups
FAD
NAD
CoA co substrate

outL
NADH + CO2 + Acetyl-CoA

30
Q
  1. Acetyl CoA oxidation

3+4 oxidative decarboxylations = 2 NADH *
5 substrate level phosphorylaition ADP = GTP
6 Dehydrogenation = reduced FADH2 electron carrier
7 hydration
8 dehydration rearrangment of hydrogens= NADH

efficient energy storage

A
  1. citrate synthase
    C_C bond formation
  2. aconitase *2
    rehydration = isomerisation via dehydration/rehydration
    large positive delta g = unfavourable reaction so equilibrium is pulled to the right hand side

3 isocitrate dehydrogenase *
second oxidative decarboxylation
NADH produced
oxidation of the alcohol to a ketome transfers hydride 2 electrons to NAD

NADP= used as cofactor by cytosolic isozyme
highly thermodynamically favourable irrivrsible regulated by product inhibition and ATP

4 alpha-ketoglutarate dehydrogenase complex *
3rd oxidative decarboxylation
large negative delta g so regulated

5 succinyl-CoA synthetase
succinyl co A had a GDP attached phosphate added to it becomes GTP
succinate produced CoA lost
substrate level phosphorylation
favourable small delta g eq to the right
6 succinate dehydrogenase
succinate goes to active site of succinate dehydrogenase
FAD - FADh2 electrons removed from succinate go into oxidative phosphorylation pathway
delta g is 0 = when fumarate is used eq pulled to the right
7 fumarate
water in the state of a hydroxl ion aded by fumarate making temporary carbanion transition state
8 malate dehydrogenase * malate converted back to
oxaloacetate for citrate synthase
one NADH out
large positive delta g = unfavourable
[oxaloacetate] low pulling reaction forward

for 1 turn of cycle = 3 NADH
+ 1 FADH2
+ 1 GTP later = ATP

31
Q

why is pyruvate dehydrogenase complex (made up of
pyruvate de hydrogenase E1 + dihydrolipoyl transactylase and dihydrolipoli dehydrogenase E3) efficient

multisubunit
swinging aim
cofactor binding
substrae channelling

intermediates never leave enzyme surface

A
  1. short distance between catalytic sites allows channeling of substrate from one catalytic site to another
  2. channeling minimizes side reactions
    3 regulation of activity of one subunit affects the entire complex
    you only need to modify one of them to modify all of them

regulated my phosphorylation

32
Q

citrate synthase -

Allosterically controlled enzyme
rate imiting step
regulated by {oAA] and product inhibition
MM would be sigmoidal

A

changes conformation once binds oxaloacetate
open conformation = no binding site for acetyl CoA
closed conformation = binding of oxaloacetate creates binding site = induced fit
avoid unnecessary hydrolysis of thioester

33
Q

regulation of citric acid cycle

A 
enzymes that are reuglated
PDH
citrate synthase
IDH and aKDH
= sigmoidal MM curve

activated by substrate availablity
inhibity by product accumulation

NADH and ATP
affect all regulated enzymes in cycle

inhibitor NADH and ATP

activators NAD+ and AMp

34
Q

regulation of citric acid cycle

A 
enzymes that are regulated
PDH
citrate synthase
IDH and aKDH
= sigmoidal MM curve

activated by substrate availability
inhibity by product accumulation

NADH and ATP
affect all regulated enzymes in cycle

inhibitor NADH and ATP

activators NAD+ and AMp

35
Q
  1. Electron transfer + oxidative phophorylation
A

proton motive force built up across inner membrane
=synthesis of atp

protons flow back through from inter membrane space into a matrix of the mitochondria

electrons from reduced cofactors NADH and FADh2are passed to proteins in respiratory chain

oxygen final electron acceptor = water

energy of oxidation by flow of protons own the electrochemical gradient used to phosphorylate ADP = ATP

energy released by electron transport used to transport protons against electrochemical gradient

outer membrane of mitochondria porous permeable to metabolites

inter membrane space similar to cytosol high [proton] =low pH

inner membrane
large surface area due to cristae convolutions
location of ETC complexes

matrix
location of krebs cycle lipid/acid metbaolism
low [h+]

electrons taken from matrix into inter membrane space
protons pumped through by complex 1 and 3 and 4

complex 2 passed though series of electron carriers into inter membrane space and meets oxygen in complex 4

36
Q

each complex contains multiple redox centers

A 
1. flavin mononucleotiode
(FMN) or flavin ADEnine (FAD)
initial electron acceptors for complax 1 n 2
carry 2 e by tranferring 1 at a time
2. iron-sulfur cluster carry 1
co ordinated by cysteines in the protein
3 coenzyme ubiquinone 
carry 2 - proton is added so 2 OH groups added
ubiquinol reduced result
2 cytochromes a b or c carry 1 e

1.
NADH dehydrogenase
succinate dehydrogenase
ubiquinon cytochrome c

37
Q

COMPLEX 1 proton pump

A

transfer or. 2 electron from NADH to ubiquinone carrier that can carry 2
per NADH 4 protons from matirx (N) into intermembrane space (P)

conenzyme Q picks up 2 protons transported by proton wires

=reduced ubiquinone = only soluble in the membrane

2 electrons from NAD+ passed down and meet protons make QH2

38
Q

complex 2

succinate dehydrogenase

A

delta g 0

2 electrons stripped off of succinate
transferred to FADH2 one at a time via iron sulfur centers in ubiquinone
added to protons = QH2

doesn’t transport protons

reduce [proton] in matrix

39
Q

complex 3

buiquionen:cytochrome C oxidoreductase

A

shunts electrons from ubiquinol onto cytochrome and cytochrome moves it onto final complex
into inter membrane space
moving electrons

used 3 electrons from QH2 to reduce t molecules of cytochrome c
contains iron sulfur clusters and haem grops

Q cycle causes 4 additional protons transported to IMS

40
Q

complex 4

A

cytochrome released into inter membrane space

hydrophiic
bump into complex 4
cytochrome oxidase
4 electrons used to reduce one oxygen molecule to 2 waters
4 protons picked up from matrix in this process
4 additional protons passed from matrix to inter membrane space

electrons injected via a series of coppor centres to produce water

oxygen reduced 1 at time = 2 waters
polar but uncharged diffuse out of cell =maintain hypertonic sate

huge positive change in intermambrane space made up of protons
ATP synthase part of respiratome complex

electron transport sets up a proton motive force

FoF1 ATP synthase has amembrane binding portion in inner membrane
Fo =and head group in matrix

protons flow through and spin inner spindle in head at high speed by protons flowing in and back into matrix to meet OH groups

f1 soluble in matric
making ATP

Fo intergral membrane complex
tramsports protons back to matrix dissipating the proton gradient
energy transferred to F1 to catalyse phosphorylation of ADP

hexamer arranged in 3 alpha beta dimers
arranged in 3 conformations
open = empty
loose = binding to ADP and pi 
tight = catalyses ATP formation and binds product

proton translocation causes a rotation of the Fo subunit and the central shaft gamma = conformational change by the gamme subunit rotating inside
within all the 3 alpha beta pairs

promotes condensation of ADP into ATP

41
Q

binding change model

A

alpha and beta subunits from dimer release and ATP molecule the gamma spindle pushes ATP off
ADP and PI come in to bind and spindle moves to next position
particular position inside head required pushing against the beta conformation

ATP is churned off

ADP + Pi bound state
ATP form
ATP exclusion from binding site

Enzymes (9 decks)

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