1 | Page
MCAT metabolism Questions and Correct
Answers
Glycolysis Ans: Breakdown of 6-carbon glucose molecule into two
3-carbon molecules of pyruvate
Occurs in cytosol
Can occur with or without oxygen
10 steps
First half of glycolysis Ans: Two phosphate groups from two
different ATP molecules are added to glucose (energy input phase)
AKA 6 carbon phase
Phosphate groups are bulky and charged: trap glucose inside the
cell
They also prime the glucose, allowing the 6-carbon glucose to be
split
Second half of glycolysis Ans: Energy output phase
AKA 3 carbon phase
Two ATP produced per 3-C molecule (4 total)
One NADH produced from NAD per molecule (2 total)
© 2025 All rights reserved
, 2 | Page
Net yield from glycolysis Ans: 2 ATP and 2 NADPH
Substrate-level phosphorylation Ans: Production of ATP by the
transfer of a phosphate molecule from a molecule to an ADP
Fructose and galactose in glycolysis Ans: Fructose and galactose
are also able to feed into glycolysis
Usually converted to glucose by liver first
Fermentation Ans: Metabolism in the absence of oxygen
Glucose undergoing anaerobic respiration
Reduction of pyruvate to ethanol (yeast and some microorganisms)
or lactic acid (human muscles and other microorganisms) in order
to restore NADH back to NAD
Ethanol/lactic acid and CO2 expelled as waste products
Yield: 2 ATP per glucose molecule
Pentose phosphate pathway Ans: Diverges and merges back with
glycolysis
Purpose: to create NADPH and some 5 carbon sugars
First half generates NADPH (various synthetic functions)
Second half (non-oxidative branch): Creates 5 C sugars
Active at all times
© 2025 All rights reserved
MCAT metabolism Questions and Correct
Answers
Glycolysis Ans: Breakdown of 6-carbon glucose molecule into two
3-carbon molecules of pyruvate
Occurs in cytosol
Can occur with or without oxygen
10 steps
First half of glycolysis Ans: Two phosphate groups from two
different ATP molecules are added to glucose (energy input phase)
AKA 6 carbon phase
Phosphate groups are bulky and charged: trap glucose inside the
cell
They also prime the glucose, allowing the 6-carbon glucose to be
split
Second half of glycolysis Ans: Energy output phase
AKA 3 carbon phase
Two ATP produced per 3-C molecule (4 total)
One NADH produced from NAD per molecule (2 total)
© 2025 All rights reserved
, 2 | Page
Net yield from glycolysis Ans: 2 ATP and 2 NADPH
Substrate-level phosphorylation Ans: Production of ATP by the
transfer of a phosphate molecule from a molecule to an ADP
Fructose and galactose in glycolysis Ans: Fructose and galactose
are also able to feed into glycolysis
Usually converted to glucose by liver first
Fermentation Ans: Metabolism in the absence of oxygen
Glucose undergoing anaerobic respiration
Reduction of pyruvate to ethanol (yeast and some microorganisms)
or lactic acid (human muscles and other microorganisms) in order
to restore NADH back to NAD
Ethanol/lactic acid and CO2 expelled as waste products
Yield: 2 ATP per glucose molecule
Pentose phosphate pathway Ans: Diverges and merges back with
glycolysis
Purpose: to create NADPH and some 5 carbon sugars
First half generates NADPH (various synthetic functions)
Second half (non-oxidative branch): Creates 5 C sugars
Active at all times
© 2025 All rights reserved
