BCH110B_Key_Concepts

Key Enzymes and Intermediates
- Key enzymes involved in glycolysis include aldolase, dihydroxyacetone phosphate, and hexokinase.
- Triose phosphate isomerase is also significant as it interconverts dihydroxyacetone phosphate and glyceraldehyde-3-phosphate (GAP).
Glycolysis Definition
- Represents the process of splitting sugars to generate energy, specifically through the oxidative breakdown of glucose to pyruvate.
- It is a key step in cellular respiration, providing energy for cellular functions.
Relevance to Starvation
- Under starvation conditions, gluconeogenesis occurs which is making glucose from precursors.

Definition of Metabolism
- Refers to a series of linked chemical reactions that convert substrates into products, encompassing both the breakdown and synthesis of molecules.
Categories of Metabolism
- Catabolism: Breakdown of larger molecules into smaller ones, yielding energy (ATP).
- Anabolism: Synthesis of larger molecules from smaller ones, requiring energy (using ATP).
Role of Glucose
- A fundamental sugar molecule, crucial for energy production.
- Acts as a precursor for various biomolecules like amino acids, lipids, and nucleotides.
- Primary Uses of Glucose:
  1. Storage (as starch in plants or glycogen in humans)
  2. Structural polysaccharides (e.g., cellulose)
  3. Energy production via glycolysis
  4. Pentose Phosphate Pathway (for reducing power and ribose sugars).
Glycolysis Details
- An oxidative anaerobic process occurring in the cytosol, resulting in the net production of 2 ATP and 2 NADH from glucose.
- Key Phases:
  - Investment Phase: Uses 2 ATP to modify glucose.
  - Cleavage: Glucose is split into two 3-carbon molecules.
  - Payoff Phase: Produces 4 ATP, resulting in a net gain of 2 ATP and 2 NADH, culminating in the production of pyruvate.

Purpose of Gluconeogenesis
- Synthesizes glucose from non-carbohydrate precursors like pyruvate or lactate, especially during fasting.
Relationship Between Glycolysis and Gluconeogenesis
- Glycolysis is energetically favorable (releases ATP and NADH), while gluconeogenesis consumes ATP and GTP.
Regulation Factors
- Allosteric and energy signal molecules regulate gluconeogenesis; primarily activated by ATP and citrate, inhibited by AMP.
- Example: The Cori Cycle describes the recycling of lactate produced in muscles back to glucose in the liver.
- Irreversible steps differ: Important enzymes like hexokinase and pyruvate kinase in glycolysis vs. glucose-6-phosphatase in gluconeogenesis.

Gluconeogenesis Cost
- Requires significant energy: 4 ATP, 2 GTP, and 2 NADH to generate one glucose molecule, indicating its physiological importance during periods of low blood sugar.
Sources of Glucose Synthesis
- Animals can produce glucose from several sources, including pyruvate and lactate, but not from fatty acids.
Fermentation Insights
- Anaerobic fermentation primarily regenerates NAD+ for glycolysis to continue under low-oxygen conditions; humans primarily undergo lactic acid fermentation, not ethanol.

Cori Cycle Overview
- Associate with the interconversion of glucose and lactate between muscles and liver, crucial for maintaining energy supply during anaerobic conditions.
Lactate Recycling
- Lactate produced in muscles is transported to the liver, where it is converted back to glucose through gluconeogenesis.

Importance of Regulation
- Critical to maintain metabolic homeostasis.
Regulatory Mechanisms
- Substrate Accessibility: Determines the availability of starting materials for reactions.
- Allosteric Binding: Activation or inhibition via metabolite binding.
- Covalent Modifications: Enzyme activity is altered by modifications such as phosphorylation.
- Feedback Inhibition: End products inhibit their own biosynthetic pathways to maintain balance.

Function of Glycogen
- Acts as a short-term energy storage molecule primarily in the liver and muscle.
- About 12-36 hours of glucose supply can be mobilized from glycogen stores.
Key Enzymes for Glycogen Metabolism
- Glycogen Synthase: Main enzyme for glycogen synthesis.
- Glycogen Phosphorylase: Primarily involved in glycogen breakdown.

Insulin and Glucagon Regulation
- Hormones like insulin promote glycogen synthesis, while glucagon stimulates glycogen breakdown to release glucose into the blood.

Glycogen Formation
- Involves branching and elongation processes through enzymes such as glycogen synthase and branching enzyme.
Key Metabolic Intermediates
- Understand the conversion between different forms of glucose and glycogen intermediates such as UDP-glucose and glucose-1 phosphate.

Oxidative Phase
- G6P dehydrogenase is the rate-limiting step, producing NADPH and ribose phosphate.
Non-oxidative Phase
- Involves the conversion of sugars for the synthesis of nucleotides and amino acids via transketolase and transaldolase reactions.

Functionality Overview
- The TCA cycle is vital for energy production through oxidative phosphorylation, generating NADH, FADH2, and GTP.
- Key enzymes include citrate synthase, aconitase, and various dehydrogenases overseeing the cycle's progression.