Biochemistry Chapter 7: Non-Aerobic Carbohydrate Metabolism Flashcards
PPP is an aerobic or non-aerobic metabolic pathway?
Non-aerobic. Doesn’t require oxygen
After a meal, is the PPP active?
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.
Goal of Glycolysis
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
When does glycolysis takes place
in the cytosol
Inputs of Glycolysis
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.
Outputs of Glycolysis
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.
Goal of lactic fermentation
Regenerate NAD⁺ from NADH to allow glycolysis to continue under anaerobic conditions.
Provide energy (ATP) when oxygen is unavailable.
location of lactic fermentation
Cytosol of cells (especially in muscle cells during intense exercise and in some microorganisms like lactobacilli).
Inputs and outputs of lactic fermentation
INPUTS
2 Pyruvate (from glycolysis)
2 NADH (from glycolysis)
OUTPUTS
2 Lactate
2 NAD⁺ (recycled for glycolysis)
Goal of Gluconeogenesis
Synthesize glucose from non-carbohydrate precursors (e.g., lactate, glycerol, amino acids) to maintain blood glucose levels during fasting or starvation
Location of Gluconeogenesis
Liver (primarily)
Kidneys (to a lesser extent)
Occurs in the mitochondria, cytosol, and endoplasmic reticulum
Inputs and outputs for Gluconeogenesis
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).
Goal of glycogenolysis
Break down glycogen into glucose-6-phosphate or free glucose to meet energy demands (e.g., during fasting or exercise).
Catabolic
Location of glycogenolysis
Liver (to maintain blood glucose levels).
Skeletal muscle (for energy during muscle contraction).
Inputs and outputs for glycogenolysis
Inputs:
Glycogen
Inorganic phosphate
Outputs:
Glucose-6-phosphate (muscle and liver)
Free glucose (liver, via glucose-6-phosphatase).
Goal of glycogenesis
Store excess glucose as glycogen for future energy needs
Location of glycogenesis
Liver (to regulate blood glucose levels).
Skeletal muscle (to provide energy for muscle activity).
Inputs and outputs of glycogenesis
Inputs:
Glucose-6-phosphate (derived from glucose).
ATP (for glucose phosphorylation).
UTP (to form UDP-glucose).
Outputs:
Glycogen.
ADP.
UDP.
Goals of Pentose Phosphate Pathway
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).
Location of PPP
Cytosol of cells (most active in liver, adipose tissue, and rapidly dividing cells like bone marrow).
Inputs and Outputs of PPP
Inputs:
Glucose-6-phosphate.
NADP⁺.
Outputs:
NADPH.
Ribose-5-phosphate.
Intermediates like fructose-6-phosphate and glyceraldehyde-3-phosphate (non-oxidative phase).
Linkages in Glycogen
linked through alpha(1–>4) linkages (linear chain)
and alpha(1—>6) linkages to form separate branches
Glycogen sythnesis catalyzed by
glycogen synthase, starts from G6P
Glycogen breakdown is catalyzed by
glycogen phosphorylase
main regulation principles
based on energy homeostatsis and negative feedback
⬆️ AMP/ADP = what for glycolysis?
⬆️ Glycolysis (cell needs energy)
⬆️ATP/NADH/Citrate
⬇️ Glycolysis (cell has enough enough)
Excess acetyl-CoA means what for gluconeogenesis?
⬆️ 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
How does glucagon affect gluconeogenesis and glycolysis?
High glucagon:
⬆️ Gluconeogenesis (because blood sugar is low)
⬇️ Glycolysis
How does insulin affect gluconeogenesis and glycolysis?
High insulin:
⬇️ glucoenogenesis
⬆️ Glycolysis
Key points to remember for glycogenesis mechanism
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.
Gluconeogenesis is activated when
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.
PKA’s Role in Metabolism
✅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
critical molecule that promotes glycolysis when present and gluconeogenesis when absent.
F2,6BP
decreased protein kinase A activity would ______________ gluconeogenesis and ________ glycolysis
Decreased PKA activity:
Disfavors gluconeogenesis by reducing F1,6BPase activity
Favors glycolysis by increasing PFK-1 activity (via higher F2,6BP levels).
- Promotes energy utilization and storage.
Hexokinase
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.
Phosphoglycerate mutase
Phosphoglycerate mutase is a non-regulated enzyme common to both glycolysis and gluconeogenesis.
Phosphoglucoisomerase
Phosphoglucoisomerase is a non-regulated enzyme common to both glycolysis and gluconeogenesis.
Glucose 6-phosphatase
he enzyme itself is responsible for the hydrolysis of glucose 6-phosphate to free glucose in the final step of gluconeogenesis,
what does hexokinase do?
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
What are the differences in enzymes between glycolysis and gluconeogenesis?
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)
Which enzyme plays the most direct role in breaking branched linkages during glycogenolysis?
Glycogen debranching enzyme, which breaks α (1→6) linkages
The rate-limiting step of glycolysis involves phosphorylation and the expenditure of ATP. Which enzyme catalyzes this irreversible step?
Phosphofructokinase-1
Is hexokinase involved in a rate-limiting step of glycolysis?
NO
Glucosekinase vs hexokinase
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.
Hexokinase is inhibited by
G6P
Glucokinase is inhibited by
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.
