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BIOL I > CHAPTER 9 > Flashcards

CHAPTER 9 Flashcards

1
Q

What are the five principles of metabolic pathways?

A
  • COMPLEX TRANSFORMATIONS occur in a SERIES of SEPARATE reactions
  • EACH REACTION is CATALYZED by a SPECIFIC ENZYME
  • Many METABOLIC PATHWAYS are SIMILAR in ALL organisms
  • In eukaryotes, METABOLIC PATHWAYS are COMPARTMENTALIZED in SPECIFIC ORGANELLES
  • KEY ENZYMES can be INHIBITED or ACTIVATED to ALTER the RATE of the pathway
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2
Q

What are the three catabolic processes that harvest energy from glucose?

A
  • GLYCOLYSIS (anaerobic)
  • CELLULAR RESPIRATION (aerobic)
  • FERMENTATION (anaerobic)
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3
Q

oxidation-reduction (redox)

A

reaction where one substance transfers electrons to another substance

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4
Q

reduction

A

gain of electrons

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5
Q

oxidation

A

loss of electrons

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6
Q

What is the relationship between redox reactions and metabolic pathways?

A

in glucose metabolism, glucose gets oxidized and O2 gets reduced; the more reduced a molecule is, the more energy it has; in a redox reaction, some energy is transferred from the reducing agent (glucose) to the reduced product

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7
Q

NAD+

A

coenzyme that is a key electron carrier in redox reactions

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8
Q

glycolysis

A
  • takes place in the CYTOPLASM
  • CONVERTS GLUCOSE into 2 molecules of PYRUVATE
  • PRODUCES 2 ATP and 2 NADH
  • OCCURS in 10 STEPS
    [STEPS 1-5 REQUIRE ATP (ENERGY-INVESTING REACTIONS)]
    [STEPS 6-10 YILED NADH AND ATP (ENERGY-HARVESTING REACTIONS)]
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9
Q

How do oxidation-reduction reactions behave in metabolic pathways?

A

energy released by glucose oxidation is trapped via the reduction of NAD+ to NADH

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10
Q

How does substrate-level phosphorylation behave in metabolic pathways?

A

energy released transfers a phosphate from the substrate to ADP, forming ATP

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11
Q

pyruvate oxidation

A
  • occurs in the MITOCHONDRIAL MATRIX
  • PYRUVATE is OXIDIZED to ACETATE and CO2
  • ACETATE BINDS to COENZYME A to form ACETYL CoA (it donates its acetyl group to oxaloacetate, forming citrate = initiates the citric acid cycle)
  • EXERGONIC; ONE NAD+ is REDUCED to NADH
    catalyzed by pyruvate dehydrogenase complex (three enzymes that catalyze the three intermediate steps in the process)
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12
Q

citric acid cycle

A
  • ACETYL CoA is the STARTING point
  • EIGHT REACTIONS completely OXIDIZES the ACETYL group to 2 molecules of CO2
  • ENERGY RELEASED is CAPTURED by GDP, NAD+, and FAD
  • OXALOACETATE is REGENERATED in the LAST step
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13
Q

What yields when one glucose molecule gets oxidized?

A
  • 6 CO2
  • 10 NADH
  • 2 FADH2
  • 4 ATP
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14
Q

oxidative phosphorylation

A

ATP is synthesized b y reoxidation of electron carriers in the presence of O2
TWO COMPONENTS:
- ELECTRON TRANSPORT
- CHEMIOSMOSIS

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15
Q

respiratory chain

A

where electrons from NADH and FADH2 pass through; electron flow results in a proton concentration gradient across the inner mitochondrial membrane; located in the folded inner mitochondrial membrane; energy is released as electrons are passed between carriers

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16
Q

chemiosmosis

A

electrons flow back across the membrane through a channel protein, ATP synthase, which couples the diffusion with ATP synthesis

17
Q

proton-motive force

A

protons (H+) are actively transported into the intermembrane space during electron transport which creates a concentration gradient and charge difference = potential energy

18
Q

ATP synthase

A

the same in all living organisms; molecular motor with TWO parts:
- F0 unit - a transmembrane H+ channel
- F1 unit - projects into the matrix; rotates to expose active sites for ATP synthesis

19
Q

anaerobic respiration

A

many bacteria and archaea use alternate electron acceptors such as SO4-2, Fe3+, and CO2; this allows them to exist where O2 is scarce or absent

20
Q

Anaerobic glycolysis and fermentation

A
  • occurs in the CYTOPLASM
  • GLUCOSE is only PARTIALLY OXIDIZED
  • 2 ATP per GLUCOSE are produced by SUBSTRATE-LEVEL PHOSPHORYLATION
  • in ALL types, NAD+ is REGENERATED to keep GLYCOLYSIS going
21
Q

lactic acid fermentation

A
  • PYRUVATE is the ELECTRON ACCEPTOR; LACTATE is the PRODUCT
  • MICROORGANISMS and some COMPLEX organisms
  • LACTATE DEHYDROGENSASE CATALYSES FERMENTATION; in presence of O2, it CATALYZES OXIDATION of LACTATE to PYRUVATE
22
Q

alcoholic fermentation

A
  • YEASTS and some PLANT CELLS
  • REQUIRES TWO ENZYMES to METABOLIZE PYRUVATE to ETHANOL
  • reactions are REVERSIBLE
  • used to produce ALCOHOLIC beverages
23
Q

catabolic interconversions

A
  • POLYSACCHARIDES are HYDROLYZED to GLUCOSE -> enters GLYCOLYSIS
  • LIPIDS are BROKEN DOWN to
  • glycerol -> DHAP ->
    glycolysis
  • fatty acids -> acetyl CoA
    -> citric acid cycle
  • PROTEINS are HYDROLYZED to AMINO ACIDS -> glycolysis or citric acid cycle
24
Q

anabolic interconversions

A
  • most CATABOLIC reactions are REVERSIBLE
  • GLUCONEOGENESIS
  • ACETYL CoA can be used to form FATTY ACIDS
25
Q

gluconeogenesis

A

citric acid cycle and glycolysis intermediates are reduced to form glucose

26
Q

For what can citric acid cycle intermediates be used?

A

to synthesize nucleic acid components:
- α-ketoglutarate -> purines
- Oxaloacetate -> pyrimidines
(α-ketoglutarate is also a starting point for synthesis of chlorophyll and the amino acid glutamate)

27
Q

How do cells “decide” which pathways to use?

A
  • levels of substances in the metabolic pool are quite constant
  • organisms regulate enzymes to maintain balance between catabolism and anabolism
28
Q

What are the mechanisms that regulate rates of each step in a metabolic pathway?

A
  • CHANGE the AMOUNT of ACTIVE ENZYME by REGULATING GENE EXPRESSION
  • CHANGE ENZYME ACTIVITY by COVALENT modifications, such as PHOSPHORYLATION
  • feedback INHIBITION by ALLOSTERIC ENZYMES
  • SUBSTRATE availability
29
Q

substrate availability

A

if the substrate of a particular enzyme is used up by another pathway, the first enzyme can no longer function and the pathway shuts down

30
Q

What are the main control points in metabolic pathways?

A
  • in GLYCOLYSIS is PHOSPHOFRUCTOKINASE (step 3), which is INHIBITED by ATP
  • in FERMENTATION, PHOSPHOFRUCTOKINASE operates at a high rate to produce ATP; if O2 is present, more ATP is produced, which inhibits the enzyme and slows glycolysis
  • in the CITRIC ACID CYCLE is ISOCITRATE DEHYDROGENASE (step 3); it is INHIBITED by NADH and ATP; if too much of either accumulates, the citric acid cycle shuts down
  • ACETYL CoA is another control point
  • if ATP levels are high and
    the citric acid cycle shuts
    down, the accumulation
    of citrate activates fatty
    acid synthesis from
    acetyl CoA, diverting it to
    storage
  • fatty acids may be
    metabolized later to
    produce more acetyl CoA

BIOL I (12 decks)

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