Metabolism quiz,.linte!

Metabolic Pathways and Energy Production

• Metabolism encompasses all chemical reactions within cells, breaking down (catabolism) or building (anabolism) molecules.
• A metabolic pathway is a sequence of linked reactions, each catalyzed by a specific enzyme.
• Pathways can be linear, where a final product is generated, or cyclic, where the first reactant is regenerated.
• Food (polysaccharides, lipids, proteins) is digested into smaller molecules (glucose, fatty acids, amino acids) releasing energy.
• Cells store energy as ATP (adenosine triphosphate); this is then broken down to do work.
• Catabolic reactions involve breaking down large, complex molecules into smaller ones, releasing energy.
• Anabolic reactions use ATP energy to build larger molecules.
• Metabolism's stages are organized into:
  • Stage 1: Digestion and hydrolysis break down large molecules to small ones.
  • Stage 2: Degradation breaks down molecules into two- and three-carbon compounds.
  • Stage 3: Oxidation of small molecules in the citric acid cycle and electron transport provide ATP energy (electrons are carried by NADH and FADH2).

Metabolism and Cell Structure

• Metabolic reactions occur within specific sites in cells, namely organelles.
• Organelles are minute structures in cytoplasm that perform specific cellular functions.
• Organelles are surrounded by cytosol, the fluid part of the cytoplasm.
• The main organelles involved in metabolism are:
  • Nucleus
  • Rough endoplasmic reticulum
  • Smooth endoplasmic reticulum
  • Ribosomes
  • Mitochondria
  • Golgi complex
  • Lysosomes
  • Plasma membrane

Important Nucleotide-Containing Compounds in Metabolic Pathways

• ATP (adenosine triphosphate) is the main energy currency in cells, formed by the oxidation of food.
• ATP consists of adenine, ribose sugar, and three phosphate groups.
• Hydrolysis of ATP to ADP releases energy (7.3 kcal/mol or 31 kJ/mol).
• Hydrolysis of ADP to AMP also releases energy.

Coenzymes in Metabolic Pathways

• Many metabolic reactions, involved in energy extraction, entail oxidation and reduction.
• Oxidation involves the loss of Hydrogen atoms.
• Reduction involves the gain of Hydrogen atoms.
• Coenzymes are necessary to transport hydrogen and electrons.

Oxidation and Reduction

• Oxidation is the loss of electrons or hydrogen or the gain of oxygen.
• Reduction is the gain of electrons or hydrogen or the loss of oxygen.

Coenzyme NAD+

• NAD+ is a coenzyme involved in redox reactions.
• It accepts hydrogen and electrons when an oxidation reaction occurs in metabolic pathways.

Coenzyme FAD

• FAD is a coenzyme involved in redox reactions.
• It accepts hydrogen and electrons during redox reactions by forming a double bond in the substance.

Coenzyme A

• Coenzyme A (CoA) activates acyl groups, especially in the transfer of acetyl groups.
• It has a reactive thiol group (-SH) that forms a high-energy thioester with acyl groups.

High-Energy Phosphate Compounds

• High-energy compounds contain one or more very reactive bonds, often called "strained bonds."
• The energy balance in chemical reactions between breaking and reforming bonds determines whether there's a net gain or loss of energy.

Digestion of Carbohydrates (Glycolysis)

• Stage 1 of carbohydrate digestion: Polysaccharides are broken down into monosaccharides.
• Stage 2: Degradation of monosaccharides (glucose)into smaller molecules.
• Glycolysis involves a series of reactions that degrades glucose (6 carbon atoms) to pyruvate (3 carbon atoms).
• Glycolysis is an anaerobic process that does not require oxygen.

Pathways for Pyruvate

• Depending on oxygen availability, pyruvate has different fates:
  • Aerobic conditions: Pyruvate is decarboxylated to Acetyl CoA, a crucial molecule for the citric acid cycle.
  • Anaerobic conditions (humans, animals, and some microorganisms): Pyruvate is reduced to lactate, an important molecule to regenerate NAD+ and sustain glycolysis.
  • Anaerobic conditions (some microorganisms): Pyruvate is converted to ethanol through decarboxylation and reduction.

The Citric Acid Cycle

• The citric acid cycle, also known as the Krebs cycle, is a crucial aerobic pathway for energy production in mitochondria.
• It involves the oxidation of acetyl CoA into CO2, generating energy-carrying molecules (NADH and FADH2) and ATP.
• This stage of metabolism occurs under aerobic conditions and proceeds in a cycle.

Electron Transport Chain

• The electron transport chain involves a series of protein complexes embedded in the inner mitochondrial membrane.
• Electrons from NADH and FADH2 are passed along the chain to oxygen, generating ATP.
• The flow of protons through ATP synthase, a protein complex also in the membrane, drives ATP synthesis.

Oxidative Phosphorylation and ATP

• Oxidative phosphorylation involves ATP synthase utilizing the proton gradient across the inner mitochondrial membrane to produce ATP.

Fatty Acid Oxidation

• Fatty acids are activated in the cytosol by combining them with coenzyme A (CoA) to form fatty acyl-CoA.
• Fatty acyl-CoA is transported into mitochondria.
• Fatty acyl-CoA undergoes a cycle known as beta-oxidation to produce acetyl-CoA, NADH, and FADH2, while shortening the fatty acid molecule.
• The acetyl-CoA molecules enter the citric acid cycle for further energy production.

Ketogenesis and Ketone Bodies

• Ketogenesis is a process that produces ketone bodies (acetoacetate, 𝛽-hydroxybutyrate, and acetone) from acetyl CoA when carbohydrates aren't available as an energy source.
• Ketone bodies are utilized as alternative energy sources by the brain and other tissues.
• Ketosis, an elevated level of ketone bodies, can result from conditions like uncontrolled diabetes and starvation.

Protein Metabolism

• Protein digestion involves breaking down proteins to individual amino acids.
• In the stomach, HCl activates pepsin to break peptide bonds.
• Trypsin and chymotrypsin, in the small intestine, further break down polypeptides to individual amino acids.
• The amino acids are absorbed into the bloodstream to be used by cells.

Transamination

• Transamination is the process of transferring an amino group from one amino acid to a keto acid, producing a new amino acid and a new keto acid.
• Glutamate is the primary amino acid in transamination reactions.
• Transamination reactions are commonly catalyzed by enzymes called transaminases or aminotransferases.

Oxidative Deamination

• Oxidative deamination is a process where the amino group is removed from glutamate, generating ammonium ion (NH4+).
• This process provides a-ketoglutarate, necessary for transamination reactions and other metabolic processes.

Urea Cycle

• The urea cycle converts harmful ammonium ions (NH4+) into urea in the liver.
• Urea is an excretable waste product that's non-toxic and transported to kidneys for excretion.
• The urea cycle consists of several reactions that convert ammonium with CO2 and aspartate to urea.

Fate of Carbon Atoms from Amino Acids

• Carbon skeletons of different amino acid families (e.g., C-3 family, C-4 family, C-5 family) enter different intermediates via pyruvate, oxaloacetate, or a-ketoglutarate. These intermediates are then used in the citric acid cycle for further energy production.

Glucogenic and Ketogenic Amino Acids

• Glucogenic amino acids can be converted to glucose or intermediates used for glucose synthesis.
• Ketogenic amino acids cannot be converted to glucose, instead they provide carbon skeletons for ketone body synthesis and fatty acid production.

Additional Information (General Overview)

• Anabolic pathways build molecules, requiring ATP.
• Catabolic pathways break down molecules, releasing ATP.