Overview Of Metabolism

OVERVIEW OF METABOLISM By: Muntholib Department of Chemistry State University of Malang

What’s metabolism ? The sum total of the chemical processes that occur in living organisms, resulting in growth, production of energy, elimination of waste material, etc. •Anabolism- build up of complex molecules •Catabolism- break down of complex molecules

Metabolic Pathways

Fats Fats

Glycogen Glycogen

Protein Protein

Pathways of Carbohydrate Breakdown • All organisms (including photoautotrophs) convert chemical energy of organic compounds to chemical energy of ATP • • ATP is a common energy currency that drives metabolic reactions in cells

Pathways of Carbohydrate Breakdown • Start with glycolysis in the cytoplasm – Convert glucose and other sugars to pyruvate

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• Fermentation pathways

– End in cytoplasm, do not use oxygen, yield 2 ATP per molecule of glucose –

• Aerobic respiration

– Ends in mitochondria, uses oxygen, yields up to 36 ATP per glucose molecule

Pathways of Carbohydrate Breakdown

Overview of Aerobic Respiration • Three main stages of aerobic respiration:   

1. Glycolysis 2. Krebs cycle 3. Electron transport chain & oxidative phosphorylation

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Summary equation: C6H12 O6 + 6O2 → 6CO2 + 6 H2O 

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Overview of Aerobic Respiration

Glycolysis;

First Stage of Aerobic Respiration • Enzymes of glycolysis use two ATP to convert one molecule of glucose to two molecules of three-carbon pyruvate • • Reactions transfer electrons and hydrogen atoms to two NAD+ (reduces to NADH) • • 4 ATP form by substrate-level phosphorylation

Products of Glycolysis • Net yield of glycolysis: – 2 pyruvate, 2 ATP, and 2 NADH per glucose

• • Pyruvate may: – Enter fermentation pathways in cytoplasm – Enter mitochondria and be broken down further in aerobic respiration

Krebs Cycle;

Second Stage of Aerobic Respiration • The second stage of aerobic respiration takes place in the inner compartment of mitochondria • • It starts with acetyl-CoA formation and proceeds through the Krebs cycle

Acetyl-CoA Formation • Two pyruvates from glycolysis are converted to two acetyl-CoA • • Two CO2 leave the cell • • Acetyl-CoA enters the Krebs cycle •

Transition Reaction

Krebs Cycle • Each turn of the Krebs cycle, one acetylCoA is converted to two molecules of CO2 • • After two cycles

– Two pyruvates are dismantled – Glucose molecule that entered glycolysis is fully broken down

Energy Products • Reactions transfer electrons and hydrogen atoms to NAD+ and FAD – Reduced to NADH and FADH2

• • ATP forms by substrate-level phosphorylation

– Direct transfer of a phosphate group from a reaction intermediate to ADP

Krebs Cycle (Citric Acid Cycle)

Electron Transport Chains;

Third Stage of Aerobic Respiration • Coenzymes deliver electrons and hydrogen ions to electron transport chains in the inner mitochondrial membrane • • Energy released by electrons flowing through the transfer chains moves H+ from the inner to the outer compartment

Hydrogen Ions and Phosphorylation • H+ ions accumulate in the outer compartment, forming a gradient across the inner membrane • • H+ ions flow by concentration gradient back to the inner compartment through ATP synthases (transport proteins that drive ATP synthesis)

The Aerobic Part of Aerobic Respiration • Oxygen combines with electrons and H+ at the end of the transfer chains, forming water • • Overall, aerobic respiration yields up to 36 ATP for each glucose molecule

Oxidative Phosphorylation

Electrons are transferred from complex to complex and some of their energy is used to pump protons (H+) into the intermembrane space, creating a proton gradient.

Chemiosmosis ATP synthesis is powered by the flow of H+ back across the inner mitochondrial membrane through ATP synthase.

INQUIRY 1.What is the end product in glycolysis? 2.What substance is produced by the oxidation of pyruvate and feeds into the citric acid cycle? 3.Name a product of fermentation ! 4.What role does O2 play in aerobic respiration? 5.What stage during cellular respiration is the most ATP synthesized? 6.What is chemiosmosis? 7.When NAD+ and FAD are reduced what do they form? 8.What are they used for? 9.

RESPIRATION •RESPIRATION is the term applied to a situation when a cell uses an INORGANIC molecule as the terminal H or e- acceptor. •AEROBIC respiration: The final electron acceptor in the electron transport chain is molecule oxygen (O2). •ANAEROBIC respiration: The final electron acceptor in the electron transport chain is not O2. Yields less energy than aerobic respiration because only part of the Krebs cycles operates under anaerobic conditions.

ANAEROBIC respiration Anaerobic respiration uses an inorganic molecule other than O2 as the terminal H or e- acceptor. Electron acceptor

Products

NO3–

NO2–, N2 + H2O

SO4–

H2S + H2O

CO32–

CH4 + H2O

ATP produced in aerobic respiration complete oxidation per glucose molecule 

Pathway

By substrate-level phosphorylation

By oxidative phosphorylation From NADH From FADH

Glycolysis

2

6

0

Intermediate step

0

6

Krebs cycle

2 as GTP

18

4

Total

4

30

4

FERMENTATION •Uses an ORGANIC molecule as the final electron or H acceptor Respiration uses an INORGANIC molecule

FERMENTATION •Releases energy from oxidation of organic molecules Does not require oxygen Does not use the Krebs cycle or ETC 

Fermentation

Lactic Acid

Alcoholic Proprionic Butyric Acid Acid

Mixed Butanediol

FERMENTATION •Alcohol fermentation. Produces ethyl alcohol + CO2. Saccharomyces – YEAST • Lactic acid fermentation. Produces lactic acid.  •Homolactic fermentation. Produces lactic acid only. Streptococcus, Lactobacillus, & Bacillus. •

Heterolactic fermentation. Produces lactic acid and other compounds. Lactobacillus & Leuconostoc (sauerkraut / acar)

Fermentation

OR