5-3: Catabolism Flashcards
How is metabolism modular
Set of interconnected modules
Metabolites are shuttled into limited number of pathways for energy generation and key biosynthesis rxns
What are the three ways to generate ATP
- Substrate level phosphorylation
- Oxidative phosphorylation
- Photophosphorylation
What is substrate level phosphorylation?
ATP generated as a product of an exergonic reaction
What is oxidative phosphorylation?
Energy generated from electron transfer reactions generates a PMF, which is then used to make ATP
What is photophosphorylation?
Energy captured from light is used to make a PMF, which is used to generate ATP
What is the preferred energy source of chemoorganotrophs
Sugars like glucose
Is it just glucose that can be used to generate energy?
No, many other organic compounds can also be used. Other sugars can be converted to glucose or intermediate of glycolysis/CAC
Why does direct combustion of glucose in cells not occur?
High activation energy and the reaction would release too much energy all at once
Glycolysis is conserved in what domains?
All domains of life
Does glycolysis require oxygen
NO
What two pathways can glycolysis be followed by?
Respiration or fermentation
What are the energy investment steps of glycolysis
ATP required at steps one and three
What step produces two 3C molecules
Step four
How much ATP is generated during glycolysis
2 in, 4 out = Net 2
What is left at the end of glycolysis
Pyruvate, which still has lots of E
What is the net reaction for glycolysis?
Glucose + 2NAD+ + 2Pi + 2 ADP -> 2 pyruvate + 2NADH + 2ATP + 2H+ + 2H2O
What does glycolysis lack? How is this resolved?
Redox balance
Restored using fermentation or CAC (respiration)
Preferred pathway of chemoorganotrophs
Citric acid cycle (respiration)
What does the CAC require
available external electron acceptor
Citric acid cycle AKA
Kreb’s cycle, Tricarboxylic acid cycle
What is converted to what before entering the CAC
Pyruvate to acetyl-CoA
What can feed into the CAC
Sugars, other organic molecules (lipids, aa, etc)
Where does the CAC take place
mitochondria
Is the CAC only used for catabolic purposes
No, also provides key metabolic intermediates for anabolic rxns
Energy is extracted as what during the CAC via ____________
ATP, GTP
Substrate level phosphorylation
Explain the pyruvate to acetyl-CoA reaction
Pyruvate + NAD+ + CoA = Acetyl-CoA + NADH + CO2
What products are in the CAC
NADH, CO2, NADPH, GTP/ATP, CoA, FADH2
** know where products are made in CAC
ok
How many ATP are generated per pyruvate
1
What goes into the CAC
Acetyl CoA + 2NAD+ + NADP+ + FAD + Pi + ADP + 2H2O
What comes out of the CAC per pyruvate
2CO2 + CoA + 2NADH + NADPH + FADH2 + ATP + 2H+
How many NADH and FADH2 are produced per glucose in the CAC
4 NADH, 2 FADH2
(glycolysis produces 2 pyruvate = 2 CAC cycles)
Did the CAC solve the redox imbalance from glycolysis
No, made it worse
Where does the electron transport chain take place
Cytoplasmic membrane
How does the ETC solve the redox imbalance
Regenerate oxidized forms of electron carriers (NAD+)
What is used to generate ATP in the ETC
Proton motive forces (protons pumped out of cell)
General explanation of ETC
Electrons passed down series of e carriers with increasingly +ve reduction potentials, until terminal e acceptor is reduced
Most efficient respiration? What is the terminal e acceptor?
Aerobic, O2
Key electron carriers in the ETC
NADH dehydrogenase and flavoproteins ->
Iron-sulfur proteins ->
Quinones ->
Cytochromes ->
Explain NADH dehydrogenase & flavoproteins
NADH dehydrogenase take NADH electrons, transfer two e to flavoprotein, which contains FAD/FADH2
Explain quinones
Not proteins - small molecules
Accept 2 e, transfer to next carrier
Often link Fe/S protein to crytochromes
Explain iron-sulfur proteins
Metal cofactors, often multiple in ETC
Explain cytochromes
Proteins containing heme prosthetic groups
Variable reduction potentials
ETC contain multiple, last stop before terminal
Electrons in ETC transferred from _______________ to _______________ to ________________
Lower reduction potential carriers
Higher reduction potential carriers
Final electron acceptor (O2 if aerobic)
ETC needs a continuous source of what
Final electron acceptors, they get used up
Order of complexes the electrons go to
Complex 1 OR 2
to complex 3, to complex 4
Difference between complexes 1 and 2
Complex 1 starts with NADH = 4 more protons pumped per 2e = more E
Complex 2 starts with FADH2 (higher reduction potential) and pumps fewer protons
How many protons are pumped per NADH
10
Is oxygen the only terminal acceptor in the ETC
No, different ones for anaerobic respiration
Examples of other common e acceptors
Nitrate (NO3) and sulfate (SO4 2-)
How is the ETC diverse
Microbe can have multiple different ETC, sometimes simultaneous
Different terminal acceptors
Different energy sources feed into
How does the ETC proton motive force generate ATP
ATP synthase
General overview of ATP synthase
Protons flow back along gradient, generate mechanical energy which powers ADP -> ATP
Parts of ATP synthase
F1 = connected to F0 through stalk
F0 = protons flow through, in membrane
What powers addition of inorganic P to ADP
The conformational change of F1 driven by stalk rotation
How many H+ are pumped to produce an ATP
~3.3
How many ATP are produced by ETC / ATP synthase
ETC = 10 protons pumped
ATP synthasev= 3.3 protons per ATP
= 3 ATP per NADH
Summary on slide 27
ok
What do chemoorganotrophs do when glucose is not present
They are flexible, can use other organic molecules
Pathway called B-oxidation can convert f.a. to acetyl-CoA
A.a can be converted to entry points of CAC
What is catabolite repression
When a better energy source (e.g. glucose) is around, enzymes using other energy sources are inhibited/not expressed
E. coli is a facultative anaerobe, meaning?
Can live/grow with or without O2
Under anaerobic conditions, e. coli respirates using
Nitrate or ferments
How is redox balance restored after glycolysis
Fermentation or respiration
How does fermentation generate ATP and redox balance
Substrate level phosphorylation
Excretion of reduced fermentation products (regenerates NAD+)
Fermentation of glucose occurs under what conditions
Anaerobic
***review fermentation slides (31-37)
ok
Ethanol fermentation used for
Alcoholic beverages, bread
What can microbes ferment
Wide range of organic compounds (glucose, f.a., a.a., purines/pyrimidines)
Common theme of fermentation
Generate energy rich molecule than can be hydrolyzed to produce ATP, donate e to a metabolite (reduce it) and excrete it = redox balance
How many ATP does lactic acid fermentation generate vs how many does aerobic respiration generate
lactic acid = 2
aerobic = 38
