5-3: Catabolism Flashcards by Emily Liu

How is metabolism modular

Set of interconnected modules
Metabolites are shuttled into limited number of pathways for energy generation and key biosynthesis rxns

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What are the three ways to generate ATP

Substrate level phosphorylation
Oxidative phosphorylation
Photophosphorylation

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What is substrate level phosphorylation?

ATP generated as a product of an exergonic reaction

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What is oxidative phosphorylation?

Energy generated from electron transfer reactions generates a PMF, which is then used to make ATP

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What is photophosphorylation?

Energy captured from light is used to make a PMF, which is used to generate ATP

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What is the preferred energy source of chemoorganotrophs

Sugars like glucose

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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

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Why does direct combustion of glucose in cells not occur?

High activation energy and the reaction would release too much energy all at once

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Glycolysis is conserved in what domains?

All domains of life

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Does glycolysis require oxygen

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What two pathways can glycolysis be followed by?

Respiration or fermentation

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What are the energy investment steps of glycolysis

ATP required at steps one and three

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What step produces two 3C molecules

Step four

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How much ATP is generated during glycolysis

2 in, 4 out = Net 2

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What is left at the end of glycolysis

Pyruvate, which still has lots of E

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What is the net reaction for glycolysis?

Glucose + 2NAD+ + 2Pi + 2 ADP -> 2 pyruvate + 2NADH + 2ATP + 2H+ + 2H2O

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What does glycolysis lack? How is this resolved?

Redox balance
Restored using fermentation or CAC (respiration)

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Preferred pathway of chemoorganotrophs

Citric acid cycle (respiration)

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What does the CAC require

available external electron acceptor

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Citric acid cycle AKA

Kreb’s cycle, Tricarboxylic acid cycle

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What is converted to what before entering the CAC

Pyruvate to acetyl-CoA

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What can feed into the CAC

Sugars, other organic molecules (lipids, aa, etc)

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Where does the CAC take place

mitochondria

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Is the CAC only used for catabolic purposes

No, also provides key metabolic intermediates for anabolic rxns

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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

How many ATP are generated per pyruvate

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

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

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)

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