Chapter 15: Metabolism

Metabolism is composed of..

Many interconnected reactions

Energy is required for

Mechanical work (muscle contraction and cell movement), active transport, and biosynthesis

What are phototrophs?

Capture energy from sunlight

What are examples of phototrophs?

All photosynthetic organisms

What are chemotrophs?

Capture energy through the oxidation of chemicals

What are examples of chemotrophs?

All animals

Cellular processes of extracting energy and synthesizing new material are carried out by?

Metabolism

What is metabolism?

Highly integrated network of chemical reactions that carry out energy extraction and synthesis of new material

What is a metabolic pathway?

A series of linked reactions by which fuels are degraded and large molecules are constructed

Metabolic pathways are interconnected series of 

Enzyme catalyzed reactions

Metabolism is a series of

Reactions in a network

What are common motifs of metabolsim

• Adenosine triphosphate (ATP) is used as an energy
  currency to link energy-releasing (exergonic) and energy-
  requiring (endergonic) pathways.
  – Either sunlight or the oxidation of chemical fuels powers
  ATP formation.
  – ~100 molecules serve as activated intermediates.

Metabolism uses only

A few types of mechanisms

Metabolic reactions are highly

Regulated becase metabolic pathways are interdependent

Many of the enzymes involved in metabolism are

Organized into large complexes

Large complexes does what?

Increases speed and efficiency

Large complexes allows

Efficient processing of unstable or toxic intermediates

What is catabolism?

Reactions that break down complex molecules into simpler ones to capture energy in useful forms

Anabolism

Reactions that construct a more complex molecule from simpler moelcules by using energy

A thermodynamically unfavorable reaction can be driven by

a favorable reaction

A metabolic pathway must meet two criterias

• individual reactions must be specific

• Each of the reactions in the pathway must be thermodynamically favored under real conditions

A reaction can occur spontaneosly onlu if ∆G

is negative

Overall free energy change for a chemically coupled series of reastions equals

The sum of the free-energy changes of the individual steps

Overall free energy change allows for 

The coupling of thermodynamically unfavorable and favorable reactions in an enzyme active sites

ATP is the universal currency of free energy in

Biological systems

Free energy derived from oxidation of frood and from light is transformed into

ATP

What is ATP?

A nucleotide consisting of aadenine,a ribose, and a triphosphate unit

ATP hydrolysis is exergonic

exergonic

ATP is energy rich because its

Triphosphate unit contains two phosphanhydrive linkages

The release of free energy from ATP hydrolysis is by the:

1. formation of new covalent bonds

2. Formation of noncovalent interactions with water

3. Increase in entropy

ATP is the

Primary energy carrier

Phosphoryl-transfer potential is a means of

Comparing the tendency of organic molecules to transfer a phosphoryl group to an acceptor molecule

What is phosphoryl-transfer potential?

The tendency of an organic molecule to transfer its terminal phosphoryl group to water

ATP has a high phosphoryl-transfer potential because of?

• orthophosphate (Pi) has greater resonance stabilization
  than any of the ATP phosphoryl groups
  – electrostatic repulsion of the triphosphate unit
  – the entropy of the products of ATP hydrolysis is greater
  – ADP and Pi are stabilized due to hydration.

Phosphoryl-transfer potential is an important form of

Cellular energy transformation

Creatine phospphate serves as a

Reservoir of high potential phosphoryl groups

What is creatine kinase?

Catalyzes the regeneration of ATP from creatine phosphate and ADP

The sources of ATP change as exercise duration increase,

Even within the frist few seconds

The oxidation of carbon fuels is an important source of 

Cellular energy

APT is the principal immediate donor of

Free energy for biological activites, but ATP is limited

ATP must be constantly regenerated from?

ADP

Oxidation of fuel molecules takes place

One carbon at a time 

Carbon atoms in fuels are oxidized to

Yield CO2

The more reduced a carbon is,

The more free energy is released upon oxidation

Electrons are ultimately accepted by oxygen to form 

H2O

Compounds with high phosphoryl-transfer potential can

Couple carbon oxidation to ATP synthesis

Ion gradients across membranes provide

An important form of cellular energy that can be coupled to ATP synthesis

The oxidation of fuel molecules or phototrophy cserves as

A means of coupling thermodynamically unfavorable and favorable reactions

Energy from food is extracted in 3 stages

• Stage 1: large molecules in food are broken down into smaller units

• Stage 2: small molecules are degraded to a few simple units that play a central role in metabolism

• Stage 3: ATP is produced from the complete oxidation of the acetyl unit of acetyl CoA

Metabolic pathways contain

Many recurring motifs

Activated carriers?

Small molecules to which a chemical group or electrons have been added, which can then be donated to another moelculeA

Activated carriers frequently act as

Coenzymes or cosubstrates

What is an example of activated carriers?

ATP is an activated carrier of phosphoryl groups

NADH is

An activated carrier of electrons for fuel oxidation

Fuel molecules transfer electrons to carriers, which then

Transfer their high potential electrons to O2

What is NAD+?

Accepts a proton and two electrons in the oxidation of a substrate to form NADH

The reactive part of NAD+ is?

Its nicotinamide ring

What is FAD?

Accepts two protons and two electrons in the oxidation of a substrate to form FADH2

What is the reactive part of FAD?

Its isoalloxazine ring

ATP and acetyl CoA are…. in the absence of a catalyst?

Hydrolyzed slowly

Key reactions are reiterated throughout

Metabolism

The thousands of metabolic reactions can be subdivided into

Six types

Hydrolysis cleaves bonds by

The addition of water

Hydrolysis is commonly used to

Degrade large molecules

Isomerization reactions rearranged atoms within

A molecule

Isomerization rearrangment is typically to

Prepare the moelcule for a subsequent reactionW

Ligation reactions forms bonds using

Free energy from ATP hydrolysis

Metabolic processes are regulated in

3 principal waysM

Metabolic pathways must be regulated to

Create homeostasis (a stable biochemical environment)

Metabolism is regulated through by 3 ways:

1. Altering the amount of enzymes

2. Restricting the accessibility of substrate

3. Regulating the catalytic activity of enzymes internally or externally

The amount of particular enzyme depends on both

Its tate of synthesis and its rate of degradation

The level of many enzymes is adjadjusted by

a change in the rate of transcription of the genes encoding them

What is controlling the accesibility of substrates?

Compartmentalization often segregates opposed reactions

What is an example of compartmentalization often segregates opposed reactions?

Fatty acid oxidation occurs in the mitochondrial matric, while fatty acid synthesis occurs in the cytoplasm

Catalytic activity is regulated

Allosterically or by covalent modification

What is an example of allosteric regulation?

Feedback inhibition

Concentrations of allosteric activators and inhibitors can be

Changed

Reversible covalent modification can control

Catalytic rates of enzymes

What is energy charge?

Proportional to the mole fraction of ATP plus half the mole fraction of ADP

Energy charge ranges from

0 (all AMP) to 1 (all ATP)

ATP generating pathways are inhibited, and ATP-utilizing pathways are stimulated under

Conditions of high energy charge

Energy charge is maintained within

Narrow limits (0.90 to 0.95)

Enzymes regulating these pathway are allosterically

Inhibited or activated by binding to ATP or AMP

Energy charge is a useful concept for understanding

How metabolism is regulated