CHEM 153A Final Exam Questions with Correct Answers Latest Update 2025/2026
Glucose to G6P (enzyme and process) - Answers Hexokinase. It adds a phosphate group to the
glucose through metal ion catalysis (Mg2+), stabilizing (shields) the negative charges on the
phosphate and allowing for nucleophilic attack by the hydroxyl, forming a bond between glucose
and phosphate.
G6P to F6P (enzyme and process) - Answers Phosphohexose Isomerase. The substrate (G6P)
enters the enzyme active site and the active site does acid catalysis with the substrate and
opens up the cyclic structure. Then, the active site does base catalysis with the substrate and a
cis-enediolate intermediate is formed. Then, the active site does acid catalysis with the
substrate and a c==o double bond is formed. Lastly, the active site does base catalysis with the
substrate and the bond is removed and reforming the cyclic structure; now F6P.
Describe the pool of Hexoses - Answers Galactose ---> G1P ---> Polysaccharide Biosynthesis
(glycogen formation)
Glucose ---> G6P ---> Pentose Phosphate Pathway (makes NADPH)
Fructose ---> F6P ---> Glycolysis
F6P to F16BP (enzyme and information about the enzyme, and what is does) - Answers
Phosphofructokinase; catalyzes a committed step and commits us to making pyruvate. It is
activated by AMP and inhibited by ATP and Citrate. If it is inhibited, then we will proceed to do
the other pathways in the pool of hexoses, which include the polysaccharide biosynthesis
pathway and the pentose phosphate isomerase pathway. It does the same thing as hexokinase,
adds a phosphate group and uses metal ion catalysis (Mg2+ or K+) to stabilize/shield the
negative charges on the phosphate, allowing for nucleophilic attack by the hydroxyl and
eventually bonding another phosphate group to F6P, creating F16BP.
F16BP to G3P + DHAP (enzyme and its mechanism) - Answers The enzyme is aldolase.
Because F16BP is fructose, it can freely linearize. So first, it linearizes and enters the active site
of the enzyme. From there, the LYSINE residue in the active site of the enzyme does covalent
catalysis with the ANOMERIC CARBON of the substrate and additionally, the ASPARTIC ACID
residue in the active site forms an electrostatic interaction with the substrate. The O- in the
substrate is hydrolyzed and leaves as H2O, and it is replaced with a protonated Schiff Base. The
Aspartic acid residue does base catalysis with the substrate to cleave the carbon carbon bond
between C3 and C4 and give us G3P. Then, the active site (aspartic acid again) does acid
catalysis with the substrate and the protonated Schiff Base returns. Water from the
environment is added and the Schiff Base is replaced with a C==O (its hydrolyzed). DHAP is now
formed and leaves the active site. Now we have G3P and DHAP.
DHAP to G3P process... - Answers Active site does Base catalysis with DHAP, forming and
endiol intermediate, then it does Acid catalysis with the intermediate, and this forms another
, molecule of G3P. Now we have (2) G3P.
(2) G3P to 1,3BPG to 3PG (enzyme and mechanism) - Answers Substrate binds to a CYSTEINE
RESIDUE in the active site and a thiol is added, creating a thiohemiacetal intermediate.
Dehydrogenation then occurs and an Acyl Thioester intermediate is formed. A HIGH ENERGY
Phosphate then binds to this intermediate on the active site and creates 1,3BPG and NADH
(NAD+ is used in this mechanism, and thus when we do lactate fermentation we are using NAD+
and doing glycolysis) 1,3BPG is converted to 3PG through phosphoglycerate kinase--specifically,
the high energy phosphate is removed and added to ADP to form ATP. This is the first time we
see substrate level phosphorylation. These two reactions occur basically at the same time,
making them a coupled reaction.
3GP to 2GP (enzyme and process--brief) - Answers The enzyme is phosphoglycerate mutase.
We now have 2GP.
Cancers often upregulate which types of enzymes - Answers Glycolytic enzymes
2GP to phosphoenolpyruvate (enzyme and brief description of process, and a fun fact---not
really fun, probably should know) - Answers Enolase is the enzyme. Fluoride inhibits it, and if its
inhibited, then basically metabolism is prevented.
Phosphoenolpyruvate to Pyruvate (enzyme and brief information) - Answers Pyruvate Kinase is
the enzyme, and this is the second time we see substrate level phosphorylation. The
mechanism also involves metal ion catalysis (Mg2+ / K+), and phosphates are added to ADP to
form ATP (2ATP). ITS IS UPREGULATED BY F16BP and PEP. IT IS DOWNREGULATED BY
Alanine and ATP.
What are the regulating steps of glycolysis - Answers Hexokinase, phosphofructokinase,
pyruvate kinase.
What are the fates of Pyruvate? - Answers In the absence of Oxygen (anaerobic), pyruvate goes
through homolactic fermentation to create Lactate, which leads to lactic acid buildup. In the
presence of oxygen (aerobic), pyruvate goes through oxidative phosphorylation (TCA cycle) to
form CO2 and H2O. Lastly, in yeast and certain species of fish, it can go through alcoholic
fermentation to create ethanol and CO2.
What is the pasteur effect? - Answers Glucose consumption is higher under anaerobic
conditions, and thus aerobic respiration produces we produce more ATP than anaerobic
glycolysis.
Under Anaerobic conditions, what happens when we do a lot of homolactic fermentation? -
Answers Lactate Dehydrogenase builds up lactic acid, requiring lactic acid fermentation. This
leads to formation of many tumors.
Roughly the ratio of energy for Anaerobic to Aerobic processes (think delta G) - Answers about
Glucose to G6P (enzyme and process) - Answers Hexokinase. It adds a phosphate group to the
glucose through metal ion catalysis (Mg2+), stabilizing (shields) the negative charges on the
phosphate and allowing for nucleophilic attack by the hydroxyl, forming a bond between glucose
and phosphate.
G6P to F6P (enzyme and process) - Answers Phosphohexose Isomerase. The substrate (G6P)
enters the enzyme active site and the active site does acid catalysis with the substrate and
opens up the cyclic structure. Then, the active site does base catalysis with the substrate and a
cis-enediolate intermediate is formed. Then, the active site does acid catalysis with the
substrate and a c==o double bond is formed. Lastly, the active site does base catalysis with the
substrate and the bond is removed and reforming the cyclic structure; now F6P.
Describe the pool of Hexoses - Answers Galactose ---> G1P ---> Polysaccharide Biosynthesis
(glycogen formation)
Glucose ---> G6P ---> Pentose Phosphate Pathway (makes NADPH)
Fructose ---> F6P ---> Glycolysis
F6P to F16BP (enzyme and information about the enzyme, and what is does) - Answers
Phosphofructokinase; catalyzes a committed step and commits us to making pyruvate. It is
activated by AMP and inhibited by ATP and Citrate. If it is inhibited, then we will proceed to do
the other pathways in the pool of hexoses, which include the polysaccharide biosynthesis
pathway and the pentose phosphate isomerase pathway. It does the same thing as hexokinase,
adds a phosphate group and uses metal ion catalysis (Mg2+ or K+) to stabilize/shield the
negative charges on the phosphate, allowing for nucleophilic attack by the hydroxyl and
eventually bonding another phosphate group to F6P, creating F16BP.
F16BP to G3P + DHAP (enzyme and its mechanism) - Answers The enzyme is aldolase.
Because F16BP is fructose, it can freely linearize. So first, it linearizes and enters the active site
of the enzyme. From there, the LYSINE residue in the active site of the enzyme does covalent
catalysis with the ANOMERIC CARBON of the substrate and additionally, the ASPARTIC ACID
residue in the active site forms an electrostatic interaction with the substrate. The O- in the
substrate is hydrolyzed and leaves as H2O, and it is replaced with a protonated Schiff Base. The
Aspartic acid residue does base catalysis with the substrate to cleave the carbon carbon bond
between C3 and C4 and give us G3P. Then, the active site (aspartic acid again) does acid
catalysis with the substrate and the protonated Schiff Base returns. Water from the
environment is added and the Schiff Base is replaced with a C==O (its hydrolyzed). DHAP is now
formed and leaves the active site. Now we have G3P and DHAP.
DHAP to G3P process... - Answers Active site does Base catalysis with DHAP, forming and
endiol intermediate, then it does Acid catalysis with the intermediate, and this forms another
, molecule of G3P. Now we have (2) G3P.
(2) G3P to 1,3BPG to 3PG (enzyme and mechanism) - Answers Substrate binds to a CYSTEINE
RESIDUE in the active site and a thiol is added, creating a thiohemiacetal intermediate.
Dehydrogenation then occurs and an Acyl Thioester intermediate is formed. A HIGH ENERGY
Phosphate then binds to this intermediate on the active site and creates 1,3BPG and NADH
(NAD+ is used in this mechanism, and thus when we do lactate fermentation we are using NAD+
and doing glycolysis) 1,3BPG is converted to 3PG through phosphoglycerate kinase--specifically,
the high energy phosphate is removed and added to ADP to form ATP. This is the first time we
see substrate level phosphorylation. These two reactions occur basically at the same time,
making them a coupled reaction.
3GP to 2GP (enzyme and process--brief) - Answers The enzyme is phosphoglycerate mutase.
We now have 2GP.
Cancers often upregulate which types of enzymes - Answers Glycolytic enzymes
2GP to phosphoenolpyruvate (enzyme and brief description of process, and a fun fact---not
really fun, probably should know) - Answers Enolase is the enzyme. Fluoride inhibits it, and if its
inhibited, then basically metabolism is prevented.
Phosphoenolpyruvate to Pyruvate (enzyme and brief information) - Answers Pyruvate Kinase is
the enzyme, and this is the second time we see substrate level phosphorylation. The
mechanism also involves metal ion catalysis (Mg2+ / K+), and phosphates are added to ADP to
form ATP (2ATP). ITS IS UPREGULATED BY F16BP and PEP. IT IS DOWNREGULATED BY
Alanine and ATP.
What are the regulating steps of glycolysis - Answers Hexokinase, phosphofructokinase,
pyruvate kinase.
What are the fates of Pyruvate? - Answers In the absence of Oxygen (anaerobic), pyruvate goes
through homolactic fermentation to create Lactate, which leads to lactic acid buildup. In the
presence of oxygen (aerobic), pyruvate goes through oxidative phosphorylation (TCA cycle) to
form CO2 and H2O. Lastly, in yeast and certain species of fish, it can go through alcoholic
fermentation to create ethanol and CO2.
What is the pasteur effect? - Answers Glucose consumption is higher under anaerobic
conditions, and thus aerobic respiration produces we produce more ATP than anaerobic
glycolysis.
Under Anaerobic conditions, what happens when we do a lot of homolactic fermentation? -
Answers Lactate Dehydrogenase builds up lactic acid, requiring lactic acid fermentation. This
leads to formation of many tumors.
Roughly the ratio of energy for Anaerobic to Aerobic processes (think delta G) - Answers about
