Catabolic and Anabolic Reactions

     Metabolism: The sum of the chemical reactions in an organism

     Catabolism: Provides energy and building blocks for anabolism.

    Catabolic reactions = exergonic = break-down

     Anabolism: Uses energy and building blocks to build large molecules

    Anabolic reactions = endergonic = synthesis

 

Catabolic and Anabolic Reactions

     A metabolic pathway is a sequence of enzymatically catalyzed chemical reactions in a cell

     Metabolic pathways are determined by enzymes

     Enzymes are encoded by genes

 

Collision Theory

     The collision theory states that chemical reactions can occur when atoms, ions, and molecules collide

     Activation energy is needed to disrupt electronic configurations

     Reaction rate is the frequency of collisions with enough energy to bring about a reaction.

     Reaction rate can be increased by enzymes or by increasing temperature or pressure

 

Enzyme Components

     Biological catalysts

    Specific for a chemical reaction; not used up in that reaction

     Apoenzyme: Protein

     Cofactor: Nonprotein component

    Coenzyme: Organic cofactor

     Holoenzyme: Apoenzyme plus cofactor

 

 

 

Important Coenzymes

     NAD+

     NADP+

     FAD

     Coenzyme A

 

Enzyme Specificity and Efficiency

     The turnover number is generally 1 to 10,000 molecules per second

 

Enzyme Classification

     Oxidoreductase: Oxidation-reduction reactions

     Transferase: Transfer functional groups

     Hydrolase: Hydrolysis

     Lyase: Removal of atoms without hydrolysis

     Isomerase: Rearrangement of atoms

     Ligase: Joining of molecules, uses ATP

 

Factors Influencing Enzyme Activity

     Temperature

     denature proteins

     pH

     denature proteins

     Substrate concentration

     Inhibitors

     Competitive Inhibitors

     Noncompetitive Inhibitors

     Feedback Inhibitors

 

Ribozymes

     RNA that cuts and splices RNA

 

Oxidation-Reduction Reactions

     Oxidation: Removal of electrons

     Reduction: Gain of electrons

     Redox reaction: An oxidation reaction paired with a reduction reaction

 

 

Oxidation-Reduction Reactions

     In biological systems, the electrons are often associated with hydrogen atoms. Biological oxidations are often dehydrogenations.

 

The Generation of ATP

     ATP is generated by the phosphorylation of ADP

 

Substrate-Level Phosphorylation

     Energy from the transfer of a high-energy PO4– to ADP generates ATP

 

Oxidative Phosphorylation

     Energy released from transfer of electrons (oxidation) of one compound to another (reduction) is used to generate ATP in the electron transport chain

 

Photophosphorylation

     Light causes chlorophyll to give up electrons. Energy released from transfer of electrons (oxidation) of chlorophyll through a system of carrier molecules is used to generate ATP.

 

Metabolic Pathways of Energy Production

 

Carbohydrate Catabolism

     The breakdown of carbohydrates to release energy

    Glycolysis

    Krebs cycle

    Electron transport chain

 

Glycolysis

     The oxidation of glucose to pyruvic acid produces ATP and NADH

 

Preparatory Stage of Glycolysis

     2 ATP are used

     Glucose is split to form 2 glucose-3-phosphate

 

Energy-Conserving Stage of Glycolysis

     2 glucose-3-phosphate oxidized to 2 pyruvic acid

     4 ATP produced

     2 NADH produced

 

Glycolysis

           Glucose + 2 ATP + 2 ADP + 2 PO4 + 2 NAD+ 2 pyruvic acid + 4 ATP + 2 NADH + 2H+

 

Alternatives to Glycolysis

     Pentose phosphate pathway

    Uses pentoses and NADPH

    Operates with glycolysis

     Entner-Doudoroff pathway

    Produces NADPH and ATP

    Does not involve glycolysis

    Pseudomonas, Rhizobium, Agrobacterium

 

Cellular Respiration

     Oxidation of molecules liberates electrons for an electron transport chain

     ATP is generated by oxidative phosphorylation

 

Intermediate Step

     Pyruvic acid (from glycolysis) is oxidized and decarboyxlated

 

The Krebs Cycle

     Oxidation of acetyl CoA produces NADH and FADH2

 

The Electron Transport Chain

     A series of carrier molecules that are, in turn, oxidized and reduced as electrons are passed down the chain

     Energy released can be used to produce ATP by chemiosmosis

 

A Summary of Respiration

     Aerobic respiration: The final electron acceptor in the electron transport chain is molecular 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.

 

Carbohydrate Catabolism

     Energy produced from complete oxidation of one glucose using aerobic respiration

     ATP produced from complete oxidation of one glucose using aerobic respiration

     36 ATPs are produced in eukaryotes

 

Fermentation

     Any spoilage of food by microorganisms (general use)

     Any process that produces alcoholic beverages or acidic dairy products (general use)

     Any large-scale microbial process occurring with or without air (common definition used in industry)

     Scientific definition:

    Releases energy from oxidation of organic molecules

    Does not require oxygen

    Does not use the Krebs cycle or ETC

    Uses an organic molecule as the final electron acceptor

 

Fermentation

     Alcohol fermentation: Produces ethanol + CO2

     Lactic acid fermentation: Produces lactic acid

    Homolactic fermentation: Produces lactic acid only

    Heterolactic fermentation: Produces lactic acid and other compounds

 

Biochemical Tests

     Used to identify bacteria.

 

Photosynthesis

     Photo: Conversion of light energy into chemical energy (ATP)

    Light-dependent (light) reactions

     Synthesis:

    Carbon fixation: Fixing carbon into organic molecules

    Light-independent (dark) reaction: Calvin-Benson cycle

     Oxygenic: 

     Anoxygenic:

 

Photosynthesis Compared

Chemotrophs

     Use energy from chemicals

     Chemoheterotroph

     Energy is used in anabolism

     Chemoautotroph, Thiobacillus ferrooxidans

     Energy used in the Calvin-Benson cycle to fix CO2

 

Phototrophs

     Use light energy

     Photoheterotrophs use energy in the Calvin-Benson cycle to fix CO2

 

The Integration of Metabolism

     Amphibolic pathways: Metabolic pathways that have both catabolic and anabolic functions