Lecture_11_Cell Energy II

Cellular Energy II (Ch. 13)

• Focuses on the breakdown and utilization of sugars and fats.

• Regulation of metabolism covered in BIOL 3510: Lecture 11.

Objectives

• General Features of Carbohydrates: Describe their structure and functions.

• Monosaccharides: Recognize the names and general structural features.

• Cellular Respiration: Understand the general formula and detailed features of its three stages:

  • 1) Glycolysis: Conversion of glucose to pyruvate.

  • 2) Citric Acid Cycle: Processing of acetyl-CoA.

  • 3) Respiratory Electron Transport Chain: Energy production and electron carrier regeneration.

• Fates of Pyruvate: Role of oxygen availability.

• Respiration & Carbon Skeletons: Associated production processes.

• Regulation of Glycolysis: Mechanisms of feedback regulation.

• Food Storage in Cells: Mechanisms of how cells store food molecules.

Overview of Carbohydrates

• Abundance: Carbohydrates are the most abundant biomolecules on Earth, comprising sugars and saccharides.

• Structure: Carbon compounds containing many hydroxyl groups. Commonly end in –ose.

• Features:

  • Chiral centers: Carbon atoms with four different groups.

  • Examples of size range: From glyceraldehyde (3C) to amylopectin (>200,000,000 g/mol).

• Glycosidic Bonds: Covalent linkage of sugars with each other or with proteins/lipids.

Functions of Carbohydrates

• Energy Storage: Storage forms include glucose, glycogen, and starch.

• Biological Roles:

  • Building blocks for complex carbohydrates, RNA, DNA, vitamins (e.g., L-ascorbic acid), and amino sugars (e.g., glucosamine).

  • Molecular recognition for the immune system.

  • Structural roles in cellular protection (plant and bacterial cell walls).

  • Cell adhesion through glycoproteins.

  • Biological lubrication and maintenance of structure (e.g., cellulose and chitin).

Common Dietary Carbohydrates

• Sources: Common sugars include fructose, sucrose, lactose, starch, and cellulose (dietary fiber).

• Links: Online resources for further exploration of sugars and starch.

Features of Monosaccharides

• Definition: Cannot be hydrolyzed into simpler carbohydrates.

• Types: Include:

  • Trioses (3C), tetroses (4C), pentoses (5C), hexoses (6C), heptoses (7C).

• Isomers: Molecules with the same formula but different structures; Question example: identifying ketoses.

Cellular Respiration

• Process Overview: Oxidation of food molecules provides energy and carbon skeletons for biosynthesis.

• Energy Release: Controlled release during three stages prevents cell damage.

  • Stages:

    • Glycolysis

    • Tricarboxylic Acid Cycle (TCA)

    • Respiratory Electron Transport Chain

• Reaction Efficiency: ΔGo’ = -2880 kJ/mol; efficient energy conversion from food substrates.

Steps of Cellular Oxidation

• Digestion Stage: Outside cell; conversion of large molecules.

• Glycolysis & Pyruvate Oxidation: Starts in the cytosol and ends in the mitochondrial matrix; production of ATP and NADH.

• Citric Acid Cycle & Oxidative Phosphorylation: Occurs in mitochondria; significant ATP production from NADH in the electron transport chain.

Detailed Steps of Glycolysis

• Energy Investment Phase: First steps include phosphorylation of glucose, isomerization, and further phosphorylation controlled by phosphofructokinase.

• Energy Generation Phase: Conversion of glyceraldehyde 3-phosphate leading to ATP generation and NADH production.

• Irreversible Steps Identified: Steps 1, 3, and 10 are irreversible in glycolysis.

Fate of Pyruvate

• Dependence on Oxygen: Pyruvate enters respiration or fermentation based on oxygen levels.

  • Fermentation Types:

    • Alcoholic: Yeast produces ethanol and CO2.

    • Lactic Acid: Muscle cells produce lactate.

• Function: Both fermentation types regenerate NAD+ for glycolysis continuity.

Acetyl-CoA Production

• Sources: Formed from pyruvate in aerobic metabolism and fatty acid breakdown via β-oxidation.

• Enzyme Complex: Pyruvate dehydrogenase complex facilitates conversion to acetyl-CoA.

Tricarboxylic Acid Cycle Overview

• Functionality: Acetyl-CoA oxidation to CO2; generates NADH and FADH2, crucial for energy production.

• Localization: Most enzymes reside in the mitochondrial matrix except for succinate dehydrogenase, which interacts with the electron transport chain.

• Energy Yield from One Hexose Molecule: Breakdown through glycolysis, TCA, and ATP production.

Oxidative Phosphorylation

• Mechanism: Activated carriers (NADH & FADH2) donate electrons to the electron transport chain, establishing a proton gradient that drives ATP synthesis. True or False: Oxidative phosphorylation requires a proton gradient.

Regulation of Metabolism

• Caloric Pathways: Catabolic pathways deliver substrates to glycolysis and TCA for energy, while anabolic pathways utilize the products for biosynthesis.

• Feedback Regulation Mechanisms: Involve glucose levels impacting glycolytic and gluconeogenesis pathways.

Food Storage in Cells

• Glycogen and Starch: Animal cells utilize glycogen while plant cells utilize starch for glucose storage.

• Fat Storage: Stored as triacylglycerols in adipocytes for animals and in seeds for plants.

• Importance: Stored carbohydrates and fats are primary nutrient sources for animals, including humans.