Exam 2 - Biochemistry

Ch. 7-9

Per glucose molecule, how many ATP are produced?

4

Per glucose molecule, what’s the net number of ATP produced?

2

D glucose + 2 ATP + 2 Pi + 2NAD+

2 pyruvate + 2 ATP + 2 NADH + 2H+ + 2H2O

2 pyruvate + 2 ATP + 2 NADH + 2H+ + 2H2O

D glucose + 2 ATP + 2 Pi + 2NAD+

Which glycolysis steps are irreversible?

1, 3, 10

Which glycolysis steps use up ATP?

1, 3

Which glycolysis step produces ATP?

7, 10

Purpose of Synthesis of Glucose 6 phosphate

• increase reactivity of OH with phosphoryl group

• Make glucose negative

• Keep it in the cell

Enzyme (step 1 glycolysis_

hexokinase

Purpose of isomerization of G6P to F6P

Create primary OH for future phosphorylation

Enzyme (step 2 glycolysis)

Phosphoglucose isomerase

Phosphorylation of F6P purpose

Second phosphorylation makes negative on both halves of hexose when fragmented

Enzyme used for 3rd step glycolysis

Phosphofructokinase-1 (PFK-1)

Cleavage of F-1,6 bisphosphate purpose

Break into 2 3-carbon molecules

Enzyme for 4th step glycolysis

Aldolase

Conversion to DHAP to GAP purpose

Use both fragments for max energy yield

step 5 glycolysis enzyme

triose phosphate isomerase

Oxidation of GAP purpose

• Create high E phosphoanhydride bond

• Produce reduced coenzyme

Enzyme used in 6th step of glycolysis

Glyceraldehyde-3-phosphate dehydrogenase (GAP dehydrogenase)

Phosphoryl Transfer purpose

Create 2x ATP

Enzyme used in 7th step of glycolysis

Phosphoglycerate kinase

Phosphate transfer purpose

Generate higher E bond to produce another molecule of ATP

8th step of glycolysis enzyme

Phosphoglycerate mutase

Purpose of dehydration to phosphoenolpyruvate

Complete preparation of high E bond for ATP synthesis

Enzyme used in 9th step of glycolysis

Enolase

Why is PEP high energy?

Phosphoryl group traps the enol form, squashing the opportunity for tautomerization

Purpose of the synthesis of pyruvate and ATP

Synthesize ATP again

Enzyme used in 10th step of glycolysis

Pyruvate kinase

Irreversible steps of glycolysis

1, 3, 10

1ST STAGE of glycolysis

Phosphorylation and cleavage of glucose

2nd stage of glycolysis

Conversion of GAP to pyruvate, gaining 4 ATP

How many pyruvate are produced at the end of glycolysis?

2

The fate of pyruvate depends on:

• its environmental condition

• organism

If pyruvate is in an aerobic environment,

It is converted to acetyl coA and begins the TCA cycleIf

If pyruvate is in an anaerobic environment, the __________ is not possible and pyruvate is converted to a ______________ compound

Oxidation; reduced

What can be regenerated to keep glycolysis running for a short time?

NAD+

Homolactic fermentation is an example of what kind of process?

Anaerobic

Alcoholic fermentation is an example of what kind of process?

Anaerobic

Homolactic fermentation takes place where?

Muscles and red blood cells

yield what

Enzyme used in homolactic fermentation

Lactate dehydrogenase

Alcoholic fermentation yields what from pyruvate?

CO₂ + EtOH

yields by which enzyme?

Losing what in the process

pyruvate decarboxylate, CO2

yields by which enzyme?

What is converted?

alcohol dehydrogenase

NADH + H+ —→ NAD+

What mechanism is used to break C-C bond (pyruvate decarboxylase, alcoholic fermentation)?

TPP Mechanism

TPP Mechanism

Splits molecule between C=O and alpha carbon

The opposite reaction of glycolysis is considered?

Gluconeogenesis

Net Reaction of gluconeogenesis

2 pyruvate + 4 ATP + 2 GTP + 2NADH + 2H+ + 6H2O —> glucose + 4 ADP + 2GDP + 6 Pi + 2NAD+

2 pyruvate + 4 ATP + 2 GTP + 2NADH + 2H+ + 6H2O —>

glucose + 4 ADP + 2GDP + 6 Pi + 2NAD+

Why is gluconeogenesis more costly than glycolysis?

Far less favorable with a higher delta G

When does gluconeogenesis occur?

In the liver during fasting

Viable starting materials for gluconeogenesis

• pyruvate

• lactate

• alpha- keto acids from amino acids

Gluconeogenesis must bypass ____ irreversible reactions

3

Most costly challenge of gluconeogenesis

Synthesis of PEP

PEP general synthesis from gluconeogenesis step 10

Pyruvate + CO2 + H2O —→ oxaloacetate —→ PEP

• what is produced?

• what enzyme facilitates this reaction?

• What are any side reactions taking place?

(oxaloacetate)

pyruvate carboxylase

ATP —> ADP + Pi

Oxaloacetate is membrane ________ because of _______

impermeable; 2- charge

What is the yield?

What enzyme facilitates this reaction?

What are any side reactions taking place?

• PEP carboxykinase

• GTP —> GDP + Pi

  • Loss of CO2

PEP carboxykinase is found where?

In the cytosol

Problem with 1st bypass reaction (gluconeogenesis)

Most organisms only have PEP carboxykinase in the cytoplasm but OAA can’t leave mitochondria

To move OAA to cytosol, what is used?

Malate shuttle

• what reaction is this part of?

• what is the yield?

• what enzyme facilitates this reaction

• what is a side reaction taking place?

• Where does this reaction take place?

• malate shuttle

• malate dehydrogenase

• NADH + H+ —> NAD+

• Mitochrondria

• Where does this reaction go to?

• What is the yield?

• What enzyme?

• What side reaction?

• Cytosol

• OAA

• Malate dehydrogenase

• NAD+ ——> NADH + H+

Malate shuttle provides _________ in cytosol for later reactions

NADH

2nd bypass reaction Step and reaction

“Step 3” —> F 1,6 BP to F6P

What is this reaction?

What is the yield?

What enzyme facilitates it?

Step 3 of gluconeogenesis

Fructose 1,6-bisphosphatase

Difference between Step 3 of glycolysis and “Step 3” of gluconeogenesis

Gluconeogenesis doesn’t generate ATP

Positive modulation

Increases the activity of a metabolic pathway

Citrate ________ modulates Step 3 of gluconeogenesis

Positively

AMP________ modulates Step 3 of gluconeogenesis

Negatively

Fructose 2,6-BP ________ modulates Step 3 of gluconeogenesis

Negatively

• What reaction pathway is this from?

• What is the yield?

• What enzyme facilitates the result?

• “1st” step of gluconeogenesis

• Glucose-6-phosphatase

There is/isn’t ATP made in 3rd bypass reaction of gluconeogenesis

Isn’t

3rd bypass reaction and step 1 of gluconeogenesis

G6P to glucose

This many ATP and GTP were put into the first bypass reaction of gluconeogenesis

ATP 2

GTP 2

Where are 2 more ATP added for gluconeogenesis besides step 10?

Step 7

“Step 7” of gluconeogenesis net reaction

3 phosphoglycerate + ATP ←→ 1,3- BPG + ADP

How fast is allosteric ligand binding?

Fast (usec - msec)

How fast is covalent modification bonding, such as phosphorylation?

Medium (sec)H

How fast is a genetic/transcriptional regulatory mechanism?

Slow (hour to days)

Hexokinase has ______ isoforms

4

1, 2, and 3 isoforms of hexokinase are located?

Tissues, low levels of liver

Km hexokinase 1, 2, 3

0.1 mM for glucose

Activity of isoforms 1, 2, 3 Hexokinase is inhibited by?

G6P, preventing buildup of products

Isoform 4 of hexokinase is found where?

Liver and pancreas K

Km of hexokinase 4

10 mM

is Hexokinase 4 inhibited by G6P?

No

At high concentrations, glucose is diverted where by isoform 4 of hexokinase?

Storage

Most regulated step of glycolysis is

Step 3, enzyme phosphofructokinase 1 (PFK-1)

Inhibitors of PFK-1

• ATP

• Citrate

As the concentration of ATP gets high, it can act as an _______ for this enzyme.

inhibitor for PFK-1

Activators of PFK-1

• AMP/ADP

• F-2,6 BP

F 2,6 BP is controlled by

• Hormone levels

• Blood glucose concentration

Where is F-2,6 BP synthesized and by what?

In the liver by PFK-2

Bifunctional enzyme

Acts as kinase or phosphatase depending on how many of its own phosphoryl groups are added

Kinase

Transfers phosphoryl groups

Phosphatase

removes phosphate groups

How is PFK-2 modified?

Hormone signaling cascades

When PFK-2 is phosphorylated, it acts as a

phosphatase

When PFK-2 is dephosphorylated, it acts as a

kinase