Microbial Metabolism Flashcards
Define metabolism
All chemical reactions in an organism
What is a metabolic ‘pathway’?
A sequence of enzyme-catalyzed reactions that lead to the conversion of a substance into a product
What are the 2 major classes of metabolism?
- Catabolism
- Anabolism
Describe catabolic reactions in terms of substrate size and products
The breakdown of larger molecules into smaller ones
Describe anabolic reactions in terms of substrate size and products
The synthesis of larger molecules from smaller products of catabolism
What is the major difference between catabolic and anabolic pathways in terms of energy dynamics?
- Catabolic pathways = exergnoic
- Anabolic pathways = endergonic
Differentiate between exergonic and endergonic reactions
- Exergonic - release energy
- Endergonic - require energy
How do cells temporarily store the energy released during catabolism?
In the bonds of ATP
Where does the energy required for anabolism come from?
From ATP molecules produced during catabolism
What is the difference between an electron donor and an electron acceptor?
- Electron donor - a molecule that donates electrons
- Electron acceptor - a molecule that accepts electrons
What ultimately occurs during ‘oxidation-reduction reactions’ (or ‘redox reactions’)
Electron transfers
Describe the term ‘reduced’ in the context of redox reactions
Gain in electrons reduces the electrical charge (negative charge)
Describe the term ‘oxidized’ in the context of redox reactions
Electrons are donated to oxygen atoms
What are the 2 ways by which an electron acceptor may become reduced?
- Gaining a simple electron
- Gaining an electron from a hydrogen atom
What are the 2 ways by which an electron acceptor may become oxidized?
- Losing a simple electron
- Losing a hydrogen atom
Name 2 important electron carriers derived from vitamins
- Nicotinamide adenine dinucleotide (NAD+)
- Flavin adenine dinucleotide (FAD)
Describe the oxidized and reduced forms of NAD+
- NAD+ + 2 e- + 2 H+ (oxidized form)
- NADH + H+ (reduced form)
Describe the oxidized and reduced forms of FAD
- FAD + 2 e- + 2 H+ (oxidized form)
- FADH₂ (reduced form)
Where is the energy stored in ATP?
In high-energy phosphate bonds
Differentiate among AMP, ADP, and ATP in terms of phosphate groups and charges
- AMP - 1 phosphate group
- ADP - 2 phosphate groups - uncharged
- ATP - 3 phosphate groups - charged (phosphorylation)
Define substrate-level phosphorylation
The transfer of phosphate from a phosphorylated organic compound to form ATP from ADP
Describe oxidative phosphorylation
Use of an inorganic phosphate and a proton motive force to form ATP from ADP
In oxidative phosphorylation, how is the inorganic phosphate and proton motive force generated?
The electron transport chain
What is the function of a catalyst?
Increase reaction rates of chemical reactions
Catalysts are ______ in the process
Not permanently changed
What term is used to describe organic catalysts?
Enzymes
Describe the composition of enzymes (2)
- Apoenzymes
- One or more cofactors
What are apoenzymes?
Protein component
What are cofactors?
Nonprotein component
What are inorganic cofactors?
Ions
What are some examples of inorganic cofactors? (4)
- Iron
- Zinc
- Copper
- Magnesium
What are organic cofactors made from?
Vitamins - NAD+ and FAD
What are coenzymes?
Organic cofactors
Holoenzymes are a combination of …
Apoenzymes and cofactors
What is activation energy?
The amount of energy required to initiate a chemical reaction
What effect do enzymes have upon activation energy?
Enzymes are required to lower the activation energy needed in a biological system
What term is used to describe an enzyme’s functional site?
Active site
What determines enzyme-substrate specificity?
The complementary shapes of active sites and their substrates
What results in an enzyme-substrate complex?
An enzyme binds to a substrate (catabolism)
How do competitive inhibitors prevent normal substrates from binding at an enzyme’s active site? (2)
- Fit into the enzyme’s active site
- Do not undergo chemical reactions to form products
What are the consequences of a competitive inhibitor acting permanently?
Permanent loss of enzymatic activity
What are the consequences of a competitive inhibitor acting reversibly?
Can be overcome by an increase in the concentration of substrate molecules
How do noncompetitive inhibitors prevent normal substrates from binding at an enzyme’s active site?
They bind to an allosteric site
What are allosteric sites?
Sites located somewhere else on the enzyme to prevent enzymatic activity
What role do allosteric sites play in noncompetitive or ‘allosteric’ inhibition? (3)
- Alters the shape of the active site
- Substrates cannot be bound
- Halts enzymatic activity
Describe excitatory allosteric control
The change in the shape of the active site causes an inactive enzyme
Describe the specific conditions under which ‘feedback inhibition’ occurs
When the final product is an allosteric inhibitor
What are the 2 main processes by which glucose is catabolized in microbial cells?
- Cellular respiration
- Fermentation
Which process results in the complete breakdown of glucose to carbon dioxide and water?
Cellular respiration
Describe glycolysis
Catabolizes a single glucose molecule into 2 molecules of pyruvic acid (pyruvate)
Glycolysis results in ______
A small amount of ATP production
Respiration continues via ______
The Krebs cycle
What does fermentation result in?
Organic waste products
Fermentation results in ______ than cellular respiration
Less ATP production
Of the 2 main processes by which glucose is catabolized in microbial cells, which one involves the Krebs cycle and an electron transport chain?
Cellular respiration
Why does fermentation result in the production of much less ATP than respiration?
It does not use oxygen or the electron transport chain
What is the name of the initial substrate in glycolysis, and how many carbon atoms does it possess?
- Glucose
- 6 carbon atoms
What is the name of the final substrate in glycolysis, and how many carbon atoms does it possess?
- Pyruvate
- 2 separate intermediates of 3 carbon atoms
How many ATP molecules are invested in the conversion of one molecule of glucose to one molecule of fructose 1,6-bisphosphate?
2 ATP
How many NAD+ molecules are reduced to NADH in the oxidation of two molecules of glyceraldehyde 3-phosphate (G3P)?
2 NAD+
Per initial glucose molecule, how many ATP molecules are ultimately generated via substrate-level phosphorylation along the pathway to the end products of glycolysis?
2 ATP
What is the name of the end-product of glycolysis, how many of these molecules are generated per initial molecule of glucose, and how many carbon atoms does each contain?
2 molecules of pyruvate - each containing 3 carbon atoms
What is the net amount of ATP generated via glycolysis per original molecule of glucose?
2 ATP
In preparation for the Krebs cycle (the transition step), 2 pyruvate molecules per molecule of glucose are decarboxylated and oxidized to yield 2 molecules of acetyl-CoA.
- How many carbon atoms does each acetyl-CoA molecule possess?
- How many carbon dioxide molecules are liberated per initial molecule of glucose?
- How many molecules of NAD+ are reduced to NADH per initial molecule of glucose?
- Each acetyl-CoA molecule - 2 carbons
- 2 CO₂ molecules liberated
- A single molecule of NAD+
In the Krebs cycle, what is the relationship among acetyl-CoA, oxaloacetic acid, and citric acid, and how many carbon atoms are found in each of these molecules?
- Acetyl-coA enters the cycle by joining with oxaloacetic acid, forming citric acid
- Acetyl-coA - 2 carbons
- Oxaloacetic acid - 4 carbons
- Citric acid - 6 carbons
How many CO2 molecules are generated per acetyl-CoA molecule that enters the Krebs cycle?
2 CO2 molecules
For every molecule of acetyl-CoA that passes through the Krebs cycle, how many molecules of NADH and FADH2 are formed?
- 3 NADH
- 1 FADH₂
What is the fate of the NADH and FADH2 generated via the Krebs cycle? (2)
- Regeneration of oxaloacetic acid
- Large amount of ATP production
______ is needed for the electron transport chain to function
An electron acceptor
What would result in a lack of oxidative phosphorylation?
No electron acceptor
What is a proton gradient?
An electrochemical gradient of protons that has potential energy
What is the relationship between electron transport and the establishment of a proton gradient?
As electrons move down the transport chain, proton pumps use the electrons’ energy to actively transport protons (H+) across the membrane
What is the final electron acceptor in aerobic respiration, and what molecule is formed as the final electron acceptor is reduced?
- Final electron acceptor - oxygen
- Forms H₂O molecule
What is the difference between aerobic respiration and anaerobic respiration?
- Aerobic respiration - requires oxygen
- Anaerobic respiration - does not require oxygen
Describe chemiosmosis
ATP is synthesized utilizing energy released by the flow of ions down their concentration gradient
What is the term used to describe the potential energy in a proton gradient?
Proton motive force
What is the relationship between a proton motive force and protein channels (ATPases)?
As proteins flow through a channel, the movement spins the protein
Cellular respiration generates an estimated 34 molecules of ATP via oxidative phosphorylation. Indicate the number and kind of reducing power (and the equivalent ATP molecules) produced during:
- Glycolysis
- Synthesis of acetyl-Co-A
- Krebs cycle
- Glycolysis - 2 NADH (6 ATP)
- Synthesis of acetyl-coA - 2 NADH (6 ATP)
- Krebs cycle - 6 NADH (18 ATP) and 2 FADH₂ (4 ATP)
Cellular respiration generates an estimated 4 molecules of ATP via substrate-level phosphorylation. Indicate from where these ATP molecules originate
- Glycolysis - 2 ATP
- Krebs cycle - 2 ATP
What is the theoretical yield of ATP per molecule of glucose via aerobic respiration?
38 ATP
What is the theoretical yield of ATP per molecule of glucose via fermentation?
2 ATP
What are the functions of fermentation in terms of facilitating substrate-level phosphorylation during glycolysis? (2)
- Regeneration of NAD+ for glycolysis
- Ensures that ADP molecules can be phosphorylated to ATP
Name 2 types of fermentation
- Lactic acid fermentation
- Alcoholic fermentation
Describe lactic acid fermentation
NADH reduces pyruvic acid from glycolysis to form lactic acid
Describe alcoholic fermentation
Pyruvic acid undergoes decarboxylation and reduction by NADH to form ethanol
What is decarboxylation?
CO₂ is given off
