Review of Basic Metabolic Principles
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Review of Basic Metabolic Principles. A. Energy Currency of the Cell. Metabolic pathways can be classified as either: energy generating (catabolic) …or energy utilizing (anabolic). The cell also uses two types of energy currency:. 1. Phosphate anhydrides (compounds with high

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Review of Basic Metabolic Principles

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Review of basic metabolic principles

Review of Basic Metabolic Principles

A. Energy Currency of the Cell

  • Metabolic pathways can be classified as either:

    • energy generating (catabolic)…or

    • energy utilizing (anabolic)

The cell also uses two types of energy currency:

  • 1. Phosphate anhydrides(compounds with high

    • phosphate transfer potential)

General: hydrolysis of a phosphate ester

+

+

ATP hydrolysis

ATP

+

+


Review of basic metabolic principles

  • Free Energies of hydrolysis of some phosphorylated

    • compounds

  • ATP is the most commonly used compound with

    • high phosphate transfer potential

    • phosphoenolpyruvate & creatine phosphate

      • have enough energy to synthesize ATP

    • ATP can be used to synthesize glucose 6-

      • phosphate & similar compounds

  • GTP is sometimes used in place of ATP


Review of basic metabolic principles

ATP is called the energy currency of the cell

Catabolism

Anabolism

O2

Work

Heat

ATP

Foods

Biosynthesis

CO2 + H2O

[Energy]

  • Definitions:

    • catabolism is the production of energy from

      • food

    • anabolism is the utilization of energy to provide

      • heat, do work, or drive biosynthetic reactions

  • Reducing equivalents(compounds with high

    • electron transfer potential)

Foods → NADH and FADH2 → ATP for Biosynthesis

  • The reducing equivalents in the foods we eat…

    • are transferred to NADH and FADH2

    • NADH and FADH2 transfer their electrons to

      • the electron transport chain which..

    • uses the energy in those electrons to synthesize

      • ATP


Review of basic metabolic principles

  • Based on what you already know, you might predict

    • that:

    • catabolic pathways produce NADH, FADH2, &

      • ATP

    • anabolic pathways utilize ATP, NADH, & FADH2

  • However, that’s not quite true. In reality:

    • catabolic pathways produce NADH, FADH2, &

      • ATP

    • anabolic pathways utilize ATP, NADPH, & FADH2

B. Coenzymes

1. Definition

  • Coenzymes are small molecular weight

    • compounds that are:

    • necessary for the catalytic activity of

      • one or more enzymes

  • present in very small amounts compared

    • to the substrates of the enzyme

  • used over & over in a catalytic manner

    • most coenzymes exist free in solution

    • some coenzymes are bound to proteins

      • = prosthetic groups


    Review of basic metabolic principles

    • 2. Coenzymes carry some biologically important

      • chemical group in an “activated” (high energy)

      • form so that it can be used in biosynthetic

      • reactions

    Example = coenzyme A (carries acyl groups)

    + CoASH

    + H20

    acetic acid

    acetyl CoA

    G = -7.5 kcal/mole

    + CoASH

    + H20

    acyl CoA

    carboxylic acid


    Review of basic metabolic principles

    3. Coenzymes are sometimes derived from vitamins

    Some activated carriers in metabolism


    Review of basic metabolic principles

    C. What Does a Metabolic Pathway Look Like?

    • many reversible reactions

    • a few irreversible reactions that drive the

      • pathway

    • the irreversible reactions are important!

    A

    B

    C

    D

    E

    F

    E1

    E2

    E3

    E4

    E5

    D. Control of Metabolism

    1. Controls Which Operate at a Cellular Level

    • regulation is by inhibitors & activators in cell

    a. Which metabolites usually regulate pathways?

    • The precursor of a pathway usually

      • stimulates the pathway

    +

    A

    B

    C

    D

    E

    • ii. The end product of a pathway usually

      • inhibits the pathway

    -

    A

    B

    C

    D

    E


    Review of basic metabolic principles

    • iii. The end product of a competing pathway

      • often stimulates the other pathway

    A

    B

    C

    D

    E

    +

    G

    H

    I

    • Energy utilizing & producing pathways

      • are often regulated on the basis of

      • ATP supply in the cell

    • Catabolic pathways are inhibited by

      • ATP and/or stimulated by ADP or AMP

    • Anabolic pathways are stimulated by

      • ATP and/or inhibited by ADP or AMP

    b. Where are pathways regulated?

    i. At or near a branch point

    D

    A

    *

    B

    *

    C


    Review of basic metabolic principles

    ii. At 1st committed (irreversible) step

    *

    A

    B

    C

    D

    E

    2. Controls that operate at whole body level

    • sites of regulation similar, but mechanisms different

    • Peptide hormones (glucagon, epinephrine,

      • & insulin)

    • act via second messenger (eg, cAMP)

    • result in phosphorylation or dephosphoryl-

      • ation

    • alter enzyme activity

    • are fast acting

    b. Steroid hormones (cortisol)

    • travel to nucleus & bind to DNA

    • affect amount of enzyme made

    • are slower acting


    Review of basic metabolic principles

    Pi

    O

    +

    OPi

    E. Glossary of Enzyme Names

    • Kinase: catalyzes the phosphorylation of some

      • metabolite, usually with ATP as the donor

    Example = glucokinase or hexokinase

    ATP + glucose → ADP + glucose 6-phosphate

    • Phosphatase: catalyzes the hydrolytic removal

      • of a phosphate group (also called

      • dephosphorylation)

    Example = glucose 6-phosphatase

    glucose 6-phosphate + H2O → glucose + Pi

    • Phosphorylase: catalyzes the phosphorolytic

      • cleavage of a bond (phosphate is the

      • attacking nucleophile)

    Example = glycogen phosphorylase


    Review of basic metabolic principles

    • Hydrolase: catalyzes the hydrolytic cleavage of

      • some bond (water is the attacking nucleophile)

    • Often subclassified according to bond cleaved

      • Esterase: hydrolyzes ester bond

      • Peptidase: hydrolyzes peptide bond

      • Phospholipase: hydrolyses phospholipids

    • Dehydrogenase: catalyses oxidation-reduction

      • reactions by the transfer of hydrogens

      • (electrons). Generally use NAD+/NADH or

      • FAD/FADH2.

    Example = lactate dehydrogenase

    • Synthetase or synthase: catalyzes the joining of

      • two molecules to create a larger molecule

    Example: citrate synthase

    oxaloacetate + acetylCoA + H2O → citrate + CoASH

    (4 carbons) (2 carbons) (6 carbons)


    Review of basic metabolic principles

    • Carboxylase: catalyzes the addition of CO2 to a

      • molecule. Uses biotin as a coenzyme

    Example = pyruvate carboxylase

    OAA + ADP + Pi

    pyruvate + CO2 + ATP + H2O

    • Transferase: catalyzes the transfer of a group from

      • one molecule to another. Subclassified

      • according to group transferred

    • Transaminase: transfers amino groups. Uses

      • pyridoxal phosphate as a coenzyme.

    Example = aspartate transaminase (AST)

    +

    +

    -ketoglutarate

    Aspartate

    Glutamate

    Oxaloacetate


    Review of basic metabolic principles

    • Transaldolase: transfers aldehyde groups. Uses

      • thiaminepyrophosphate as a coenzyme

    aldehyde:

    • Transketolase: transfers ketone groups. Uses

      • thiaminepyrophosphate as a coenzyme

    ketone:

    • Acyltransferase: transfers acyl (carboxylic acid)

      • groups. Uses coenzyme A as a coenzyme

    acyl (carboxylic acid):

    Methyltransferase: transfers methyl groups.

    Decarboxylase: removes carboxyl groups as CO2

    Isomerase: converts from one isomer to another


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