Biochemistry Chapter 7: Non-Aerobic Carbohydrate Metabolism

Question 1

PPP is an aerobic or non-aerobic metabolic pathway?

Answer 1

Non-aerobic. Doesn’t require oxygen

Question 2

After a meal, is the PPP active?

Answer 2

YES. Body shifts into an anabolic state. Body wants to produce more biomolecules. The PPP is parallel to glycolysis meaning the run at the same time.

Question 3

Goal of Glycolysis

Answer 3

generate ATP and provide intermediates (pyruvate and NADH). While it can function without oxygen, its products feed into pathways that can maximize energy yield when oxygen is present

Question 4

When does glycolysis takes place

Answer 4

in the cytosol

Question 5

Inputs of Glycolysis

Answer 5

1 Glucose molecule (6 carbons): The starting substrate.

2 ATP molecules: Used during the “investment phase” to phosphorylate glucose and intermediates, making them more reactive.

2 NAD⁺ molecules: Electron carriers that get reduced to NADH during glycolysis.

Question 6

Outputs of Glycolysis

Answer 6

2 Pyruvate molecules (3 carbons each): These are the end products of glucose breakdown.

4 ATP molecules: Produced during the “payoff phase” via substrate-level phosphorylation.
(Since 2 ATP were used in the investment phase, the net gain is 2 ATP.)

2 NADH molecules: These are reduced electron carriers that can feed into oxidative phosphorylation if oxygen is present.

Question 7

Goal of lactic fermentation

Answer 7

Regenerate NAD⁺ from NADH to allow glycolysis to continue under anaerobic conditions.
Provide energy (ATP) when oxygen is unavailable.

Question 8

location of lactic fermentation

Answer 8

Cytosol of cells (especially in muscle cells during intense exercise and in some microorganisms like lactobacilli).

Question 9

Inputs and outputs of lactic fermentation

Answer 9

INPUTS

2 Pyruvate (from glycolysis)

2 NADH (from glycolysis)

OUTPUTS

2 Lactate

2 NAD⁺ (recycled for glycolysis)

Question 10

Goal of Gluconeogenesis

Answer 10

Synthesize glucose from non-carbohydrate precursors (e.g., lactate, glycerol, amino acids) to maintain blood glucose levels during fasting or starvation

Question 11

Location of Gluconeogenesis

Answer 11

Liver (primarily)

Kidneys (to a lesser extent)

Occurs in the mitochondria, cytosol, and endoplasmic reticulum

Question 12

Inputs and outputs for Gluconeogenesis

Answer 12

Inputs:

2 Pyruvate (or precursors like lactate, glycerol, or amino acids).
4 ATP.
2 GTP.
2 NADH.

Outputs:

1 Glucose.
4 ADP.
2 GDP.
2 NAD⁺.
6 Pi (inorganic phosphate).

Question 13

Goal of glycogenolysis

Answer 13

Break down glycogen into glucose-6-phosphate or free glucose to meet energy demands (e.g., during fasting or exercise).

Catabolic

Question 14

Location of glycogenolysis

Answer 14

Liver (to maintain blood glucose levels).

Skeletal muscle (for energy during muscle contraction).

Question 15

Inputs and outputs for glycogenolysis

Answer 15

Inputs:

Glycogen
Inorganic phosphate

Outputs:
Glucose-6-phosphate (muscle and liver)

Free glucose (liver, via glucose-6-phosphatase).

Question 16

Goal of glycogenesis

Answer 16

Store excess glucose as glycogen for future energy needs

Question 17

Location of glycogenesis

Answer 17

Liver (to regulate blood glucose levels).

Skeletal muscle (to provide energy for muscle activity).

Question 18

Inputs and outputs of glycogenesis

Answer 18

Inputs:
Glucose-6-phosphate (derived from glucose).
ATP (for glucose phosphorylation).
UTP (to form UDP-glucose).

Outputs:
Glycogen.
ADP.
UDP.

Question 19

Goals of Pentose Phosphate Pathway

Answer 19

1) Generate NADPH for reductive biosynthesis (e.g., fatty acid synthesis, glutathione reduction).

2) Produce ribose-5-phosphate for nucleotide synthesis.

3) Provide intermediates for glycolysis (via non-oxidative phase).

Question 20

Location of PPP

Answer 20

Cytosol of cells (most active in liver, adipose tissue, and rapidly dividing cells like bone marrow).

Question 21

Inputs and Outputs of PPP

Answer 21

Inputs:

Glucose-6-phosphate.
NADP⁺.

Outputs:
NADPH.
Ribose-5-phosphate.
Intermediates like fructose-6-phosphate and glyceraldehyde-3-phosphate (non-oxidative phase).

Question 22

Linkages in Glycogen

Answer 22

linked through alpha(1–>4) linkages (linear chain)

and alpha(1—>6) linkages to form separate branches

Question 23

Glycogen sythnesis catalyzed by

Answer 23

glycogen synthase, starts from G6P

Question 24

Glycogen breakdown is catalyzed by

Answer 24

glycogen phosphorylase

Question 25

main regulation principles

Answer 25

based on energy homeostatsis and negative feedback

Question 26

⬆️ AMP/ADP = what for glycolysis?

Answer 26

⬆️ Glycolysis (cell needs energy)

Question 27

⬆️ATP/NADH/Citrate

Answer 27

⬇️ Glycolysis (cell has enough enough)

Question 28

Excess acetyl-CoA means what for gluconeogenesis?

Answer 28

⬆️ gluconeogenesis (cell has enough energy). The cell prioritizes glucose synthesis when energy levels are high because the body doesn't need to break down glucose for more energy

Question 29

How does glucagon affect gluconeogenesis and glycolysis?

Answer 29

High glucagon: ⬆️ Gluconeogenesis (because blood sugar is low) ⬇️ Glycolysis

Question 30

How does insulin affect gluconeogenesis and glycolysis?

Answer 30

High insulin: ⬇️ glucoenogenesis ⬆️ Glycolysis

Question 31

Key points to remember for glycogenesis mechanism

Answer 31

1) glucose is shunted off from the glycolysis/gluconeogenesis pathway and ‘marked’ for glycogenesis by moving the phosphate group and 2) that branching and non-branching enzymes are added via different enzymes.

Question 32

Gluconeogenesis is activated when

Answer 32

1) The body has enough energy and switches to producing glucose for other tissues, such as the brain or red blood cells, which rely heavily on glucose for energy. 2) A state of starvation: During fasting, low-carbohydrate diets, or intense exercise, blood glucose levels drop. The body needs to maintain blood sugar for glucose-dependent tissues like the brain and red blood cells.

Question 33

PKA’s Role in Metabolism

Answer 33

✅Increases glucose availability (glycogen breakdown & gluconeogenesis). ✅ Enhances fat breakdown (lipolysis). ✅ Modulates insulin secretion in the pancreas. ✅ Regulates heart function under stress. PKA is activated by high cAMP levels

Question 34

critical molecule that promotes glycolysis when present and gluconeogenesis when absent.

Answer 34

F2,6BP

Question 35

Hexokinase

Answer 35

catalyzes the reverse of the reaction catalyzed by glucose-6-phosphatase (gluconeogenesis)– the phosphorylation of glucose (or other hexose sugars) to glucose-6-phosphate (or other hexose phosphate sugars) – in the initial step of glycolysis.

Question 36

Phosphoglycerate mutase

Answer 36

Phosphoglycerate mutase is a non-regulated enzyme common to both glycolysis and gluconeogenesis.

Question 37

Phosphoglucoisomerase

Answer 37

Phosphoglucoisomerase is a non-regulated enzyme common to both glycolysis and gluconeogenesis.

Question 38

Glucose 6-phosphatase

Answer 38

he enzyme itself is responsible for the hydrolysis of glucose 6-phosphate to free glucose in the final step of gluconeogenesis,

Question 39

what does hexokinase do?

Answer 39

think hexo and kinase - it ADDS a phosphate group to a 6 carbon sugar. Therefore, it phosphorlates glucose to G6P in the first step of glycolysis

Question 40

What are the differences in enzymes between glycolysis and gluconeogenesis?

Answer 40

Step 1 (glycolysis - hexokinase, gluconeogenesis - glucose phorsphophatase) Step 3: (Glycolysis: phosphofructokinase-1 PFK1, gluconeogenesis - fructose 1,6-biphosphatase) Last step: (glycolysis: pyruvate kinas, gluconeogenesis - PEP carboxykinase and pyruvate carboxylase)

Question 41

Which enzyme plays the most direct role in breaking branched linkages during glycogenolysis?

Answer 41

Glycogen debranching enzyme, which breaks α (1→6) linkages

Question 42

The rate-limiting step of glycolysis involves phosphorylation and the expenditure of ATP. Which enzyme catalyzes this irreversible step?

Answer 42

Phosphofructokinase-1

Question 43

Is hexokinase involved in a rate-limiting step of glycolysis?

Answer 43

NO

Question 44

Glucosekinase vs hexokinase

Answer 44

Isozymes. Both add phosphate to glucose. Hexokinase - in most tissues glucokinase - most in pancreatic B cells and liver cells Hexokinase has low Km (therefore high affinity for glucose) Glucokinase has high Km therefore low affinity for glucose) - because theres SO much glucose in liver etc Hexokinase - inhibited by G6P Glucokinase is NOT directly inhibited by G6P, it's indirectly inhibited by fructose 6-phosphate. Glucokinase, which is active in liver and pancreatic cells, is not inhibited by G6P. Its activity is positively correlated with blood sugar. As a result, when blood sugar is low, glycolysis is slowed, and when blood sugar is high, glycolysis as catalyzed by glucokinase occurs more rapidly.

Question 45

Hexokinase is inhibited by

Answer 45

G6P

Question 46

Glucokinase is inhibited by

Answer 46

Glucokinase is found in the liver (vs hexokinase is found in the tissue) Glucosekinase is indirectly inhibited by low blood sugar glucokinase has a high km (low affinity) for glucose, meaning it only functions when glucose levels are relatively high Whereas hexokinase is active even at low glucose concentrations

Question 47

Can acetyl CoA be used for gluconeogenesis?

Answer 47

NO No pathway allows Acetyl-CoA to contribute to glucose synthesis once inside the Krebs cycle. It has no direct exit like other intermediates like oxaloacetate or fumarate

Question 48

Can lactate be used in glyconeogenesis?

Answer 48

Yes under anaerobic conditions The bloodstream carries lactate from muscles (or RBCs) to the liver, where it is converted back into pyruvate. Lactate can be converted back into pyruvate, which is a direct precursor for gluconeogenesis. Pyruvate can become oxaloacetate, which is required for gluconeogenesis.

Question 49

is the enzyme that catalyzes the rate-limiting step in glycogen breakdown (glycogenolysis)

Answer 49

Glycogen phosphorylase

Question 50

Precursors for Gluconeogensis

Answer 50

Lactate – Comes from anaerobic glycolysis in muscles and red blood cells (Cori cycle). Glycerol – Derived from the breakdown of triglycerides in adipose tissue. Amino Acids (Glucogenic Amino Acids) – Especially alanine (via the Cahill cycle) and glutamine. Propionate – Produced from odd-chain fatty acid metabolism and metabolism of certain amino acids. TCA Cycle Intermediates – Such as oxaloacetate and malate, which can be converted into phosphoenolpyruvate (PEP) and enter gluconeogenesis.

Question 51

* Thiamine pyrophosphate (TPP) (Vitamin B1) * Lipoic acid (lipoate) * Coenzyme A (CoA, derived from Vitamin B5 - pantothenic acid) * FAD (Flavin adenine dinucleotide, derived from Vitamin B2 - riboflavin) * NAD⁺ (Nicotinamide adenine dinucleotide, derived from Vitamin B3 - niacin) Are co factors for what reaction?

Answer 51

Co-Factors for pyruvate dehydrogenase complex (PDC) The reaction is highly regulated and requires five cofactors:

Question 52

Pentose pathway is broken into 2 phases:

Answer 52

Oxidative and non-oxidative

Question 53

In the oxidative phase of PPP, _________________ is first converted into __________________ by _______________________

Answer 53

glucose-6-phosphate, 6-phosphoglucono-gamma-lactone, glucose 6-phosphate dehydrogenase

Question 54

PKA Main Priority

Answer 54

To increase glucose release from the liver and increase glucose breakdown in muscles for muscle contraction.

Question 55

PKA Activation Pathway

Answer 55

Glucagon (liver) or Epinephrine (muscle/liver) → GPCR → Gs protein → Adenylyl Cyclase → cAMP → PKA activation

Question 56

PKA Effect in the Liver

Answer 56

Inhibits glycolysis IN THE LIVER by phosphorylating PFK-2, decreasing F2,6BP → slows PFK-1 → decreases glycolysis. Increases gluconeogenesis to generate more glucose for release into the blood. Stimulates glycogenolysis (glycogen breakdown) to release glucose.

Question 57

PKA Effect in the Muscle

Answer 57

Enhances glycolysis by activating PFK-2, increasing F2,6BP → speeds up PFK-1 → increases glycolysis. Stimulates glycogenolysis to provide glucose for ATP production. Does NOT release glucose because muscle lacks glucose-6-phosphatase.

Question 58

Why Does PKA Inhibit Glycolysis in the Liver but Stimulate It in Muscle?

Answer 58

Liver's job = Release glucose into the blood → Inhibits glycolysis and promotes gluconeogenesis. Muscle's job = Use glucose for ATP → Enhances glycolysis for muscle contraction.

Question 59

High NADH signals that the body

Answer 59

has plenty of energy This typically happens after a meal (fed state) when there is plenty of glucose available. The body stores excess glucose as glycogen or fat instead of breaking it down for ATP. Gluconeogenesis is also inhibited because there’s no need to produce more glucose.

Question 60

Conversion of pyruvate into glucose requires PEPCK, an enzyme present in:

Answer 60

both the cytosol and mito Conversion of pyruvate to glucose requires its initial conversion into oxaloacetate, in a reaction catalyzed by pyruvate carboxylase in the mitochondria. Oxaloacetate (OAA) is then decarboxylated and phosphorylated by cytosolic or mitochondrial forms of phosphoenolpyruvate carboxykinase (PEPCK). After transport of either OAA in the form of malate or PEP directly from the mitochondria, the remainder of gluconeogenesis takes place in the cytosol.

Question 61

The conversion between glucose and pyruvate strongly favors the formation of pyruvate, and yet the gluconeogenic pathway is able to utilize several shared enzymes with glycolysis to create glucose from pyruvate. It is able to do this primarily because

Answer 61

the formation of glucose, fructose-6-phosphate, and PEP through gluconeogenesis-specific enzymes push the equilibrium of reactions catalyzed using shared enzymes to favor gluconeogenesis.

Question 62

What does beta oxidation provide during starvation?

Answer 62

Breaks down fatty acids to produce acetyl-CoA for the krebs cycle and Ketogenesis → Produces ketone bodies for brain & muscle

Question 63

fatty acid oxidation takes place in

Answer 63

the mitochondria