4.2.1 Glycolysis: The Initial Steps: Energy Input

Question 1

glycolysis

Answer 1

• glucose, a six-carbon molecule, is split into two pyruvates (three-carbon molecules).
• The first stage of glycolysis involves an energy investment of two ATP
• When studying metabolic pathways, pay attention to the name of the enzyme and what the enzyme did.

Question 2

Glycolysis: The Energy Investment

Answer 2

• Step 1: Glucose is phosphorylated by the enzyme hexokinase to form glucose-6-phosphate. Glucose gains energy by being phosphorylated at the expense of one ATP.
• Step 2: Glucose-6-phosphate is converted into its isomer, fructose-6-phosphate, by an isomerase enzyme. By converting into its isomer, the molecule is further energized.
• Step 3: Fructose 6-phosphate is phosphorylated by the enzyme phosphofructokinase to form fructose-1, 6-bisphosphate. This step adds even more energy to the molecule at the expense of one ATP.
• Step 4: Fructose-1,6-bisphosphate is split into two molecules, dihydroxyacetone phosphate and glyceraldehyde phosphate.
• Step 5: Dihydroxyacetone phosphate is converted into glyceraldehydes-3-phosphate. This reaction runs in both directions, but because the glyceraldehydes-3-phosphate is converted further in glycolysis, the equilibrium favors the formation of glyceraldehydes-3-phosphate.
• Glyceraldehyde-3-phosphate goes on to the next phase of glycolysis, the energy-payoff phase.

Question 3

The role of hexokinase in the first part of glycolysis is:

Answer 3

• The phosphorylation of glucose

Question 4

During two steps in glycolysis, ATP is hydrolyzed in order to form phosphorylated intermediates. Which two enzymes mediate these respective reactions?

Answer 4

• Hexokinase; Phosphofructokinase

Question 5

In the energy investment phase of glycolysis

Answer 5

• two molecules of ATP are invested making glucose and its derivatives more reactive

Question 6

Glycolysis begins in the __________ and ends in the _____________.

Answer 6

• cytoplasm; cytoplasm

Question 7

The pathway in which glucose is broken down to form pyruvate is called

Answer 7

• glycolysis

Question 8

An important goal of the energy investment phase of glycolysis is the

Answer 8

• phosphorylation of a 6-carbon molecule.

Question 9

Which statement regarding the isomerase enzyme in the first half of glycolysis is true?

Answer 9

• Isomerase interconverts glyceraldehyde-3-phosphate to dihydroxyacetone phosphate, and vice versa