week 2 - lectures 3,4 Flashcards
describe competitive inhibition
- inhibitor mimics substrate and binds to active site
- Vmax is the same
- overcome by increasing substrate concentration
describe non competitive inhibition
- allosteric inhibition
- inhibitor binds to allosteric site
- inhibitor is structurally different from substrate
- change in enzyme conformation
- reduced ability to form product and sometimes to bind substrate
- Vmax is lowered
describe feedback inhibition and give an ex
non competitive inhibition
ex: citrate inhibits PFK in glycolysis
describe postive feedback
when a product activates an enzyme upstream of the metabolic pathway to continue producing this product in greater amounts
describe allosteric enzymes and give an ex
not an MM enzyme
multiple subunits/polypeptides/active sites per enzyme - quaternary structure
exists in active and inactive forms
substrate binding is cooperative (one substrate binding helps the other too)
ex: phosphofructokinase (PFK)
describe irreversible inhibition and give an ex
chemical capable of reacting covalently with amino acid residues at active site or elsewhere - destroys enzyme
also can occur if non covalent binding is so strong that it is irreversible
ex= penicillin inhibits formation of bacteria cell wall
what type of reaction is cellular respiration
redox reaction
describe redox reactions
catabolic, exergonic
electron donor is oxidized and electron acceptor is reduced
electrons lose energy and become lower energy electrons
describe the components of a redox reaction
reducing agent (e- donor)
oxidizing agent (e- acceptor)
oxidized form (“e- donor”)
reduced form (low energy e-, e- acceptor)
state overall cellular respiration equation
drop in free energy from glucose —> G3P —> pyruvate —> acetylcoA —> CO2
C6H12O6 + 6O2 —> 6CO2 + 6 H2O + energy
describe cellular respiration equation
glucose = high energy electrons, reducing agent
oxygen = electron acceptor, strong oxidizing agent
glucose to CO2 (oxidized) = oxidation
oxygen to water (reduced, low energy electron acceptor) = reduction
how many electrons transferred during CR
24
how many atps produced from cr
30-32 atps
describe the exergonic aspect of cr
ΔG<0
ΔG* = -686kcal/mol glucose
ΔG* = 7.3kcal/mol atp synthesized
much energy lost by heat (should make 93 atps but only makes 30-32), approx 60% energy converted to heat
describe first step of cellular respiration
10 steps linear
complete oxidation of glucose by aerobic respiration
occurs in cytoplasm
converts glucose (6C) to 2 pyruvates (2x3C)
describe step 2 of cellular respiration
acetyl coa formation = pyruvate oxidation
occurs in matrix of mitochondria
oxidative decarboxylation of pyruvate (3C) to form acetyl coa (2C) x2
state net production of acetyl coa formation
2 NADH and 2CO2 (per glucose)
state net production of glycolysis
net production of 2 atp by substrate level phosphorylation (slp) and 2 NADH (per glucose)
what is step 3 of cellular respiration
8 steps circular
citric acid / kreb cycle
multi step reactions
occur in matrix
complete oxidative decarboxylation of acetyl coa
state net production of citric acid cycle
6 NADH and 2 FADH2 and 4CO2 per glucose, 2 GTP (atp) by slp
after what step is glucose completely oxidized to 6CO2
step 3
citric acid cycle
all electrons are carried by 10 NADH and 2FADH2
describe step 4 of cellular respiration
oxidative phosphorylation
has 2 steps
exergonic and endergonic processes are coupled
describe first step of oxidative phosphorylation
electron transport train (ETC)
inner membrane of mitochondria, FADH2—> O2
the electrons move from NADH through complexes to oxygen
electrons lose free energy (exergonic)
energy released creates a proton gradient (endergonic)
describe second step of oxidative phosphorylation
chemiosmosis
diffusion of protons down their electromagnetic gradient is couple to atp synthesis by atp synthase located in inner membrane of mitochondria
proton diffusion = exergonic
atp synthesis = endergonic
what is net synthesis of chemiosmosis
26-28 atp per glucose
describe atp synthase
molecular mill
multiple subunits (rotor)
quaternary structure
atp is synthesized from adp and inorganic phosphate Pi
describe energy transformations of atp synthase
electrochemical potential energy of the proton gradient —> kinetic energy (turning of rotor)
—> chemical energy (bond formation in synthesis of atp)
name the 3 enzymes involved with cellular respiration
kinase
dehydrogenase - oxireductase
isomerase
describe kinase
transfers a phosphate onto an OH group of a molecule
kinase = transferase (functional group of molecule is transferred to another)
slp (substrate-p + adp —> product + atp catalysed by kinase
overall exergonic
describe dehydrogenase-oxireductase
catalyses redox reactions by transferring electrons
NAD+ and FAD are oxidizing agents (accept electrons), become reduced to NADH & FADH2, each carry 2 high energy electrons
describe isomerase (ex)
ketose sugar converted to aldose by isomerase
describe step 3 of glycolysis and the types of inhibition/activation
- first real committed step of glycolysis - phosphofructokinase - allosteric enzyme
- pfk is inhibited by high levels of atp (allosteric enzyme)
- pfk is stimulated by high levels of AMP-ADP (allosteric activation)
- pfk is inhibited by high levels of citrate which accumulates if krebs cycle functions too slow relative to glycolysis (feedback inhibition, negative feedback)
name the two situations of fate of pyruvate
aerobic conditions = converted to acetyl coa and enters kreb cycle
anaerobic conditions = fermentation
describe the mitochondrial electron transport chain (carriers)
two mobile electron carriers (UQ and cytochrome (cyt c))
state overall redox for op (NADH)
NADH + 1/2 O2 —> NAD+ + H2O
describe deficiencies
vitamin b are coenzymes of important metabolic enzymes
affect energy metabolism, causes fatigue, anemia, skin disorders, muscle and nervous system malfunction
describe alternative catabolic pathways
fatty acids, glycerol and amino acids can also be oxidized
fats are hydrolyzed to glycerol and fatty acids
glycerol is converted to G3P by phosphorylation
fatty acids are converted to acetyl coa by beta-oxidation
describe fermentation under anaerobic conditions
pyruvate réduction to lactate or alcohol is coupled to oxidation of NADH
goal = recycle NADH to NAD+ allowing continued synthesis of atp by glycolysis
what is oxidative decarboxylation (in terms of dehydrogenase-oxireductase)
release of CO2
occurs at the same time as electron transfer reactions (redox)
if primary electron donor is NADH give equation order (ETC)
NADH —>complex i —> UQ —> complex iii —> cyt c —> complex iv (cytochrome c oxidase) —> O2
if primary electron donor is FADH2 state equation order
FADH2 —> complex ii —> UQ —> complex iii —> cyt c —> complex iv —> O2
describe carrying capacity of FADH2
carries lower energy electrons than NADH
produces less atp than NADH
H+ gradient is not as steep when FADH2 is electron donor
when are fats oxidized
glucose is limiting
fasting
dieting
sleeping
exercising for a long time
explain when proteins are oxidized
only under extreme starvation or disease
proteins are hydrolyzed to amino acids
amino acids are deaminated and converted into intermediates of kreb cycle (pyruvate and acetyl coa)
what products does fermentation produce (yeast and muscles)
total of 2 atp per glucose
occurs in cytoplasm
1 glucose produces
- yeast = 2 CO2 + 2 ethanol + 2 atp (glycolysis)
- muscle = 2 lactate + 2atp (glycolysis)
what happens to a cell when there is no NAD+
no glycolysis (no acetylcoa formation, no citric acid cycle), no atp = CELL DEATH
step 3 of glycolysis equation
fructose 6P + atp —> fructose biphosphate + adp
name the 3 steps that converts pyruvate into acetyl coa (fate of pyruvate, aerobic conditions
- pyruvate dehydrogenase (in matrix, allosteric enzyme)
decarboxylation
redox
thioesther bond (unstable, makes acetyl coa more reactive
conversion factors of cr
cytoplasmic NADH = 1.5-2.5 atp (1.5 = FADH2)
matrix FADH2 = 1.5 atp
matrix NADH = 2.5 atp
