Energy metabolism, enzyme and Cofactors

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Energy metabolism, enzyme and Cofactors
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Forms of Energy

• These forms of energy are important to life
• chemical
• radiant (examples heat, light)
• mechanical
• electrical
• Energy can be transformed from one form to
  another.
• Chemical energy is the energy contained in the
  chemical bonds of molecules.
• Radiant energy travels in waves and is sometimes
  called electromagnetic energy. An example is
  visible light.
• Photosynthesis converts light energy to chemical
  energy.
• Energy that is stored is called potential energy.

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Laws of Thermodynamics

• 1st law Energy cannot be created or destroyed.
• Energy can be converted from one form to another.
  The sum of the energy before the conversion is
  equal to the sum of the energy after the
  conversion.
• Example A light bulb converts electrical energy
  to light energy and heat energy. Fluorescent
  bulbs produce more light energy than incandescent
  bulbs because they produce less heat.
• 2nd law Some usable energy dissipates during
  transformations and is lost.
• During changes from one form of energy to
  another, some usable energy dissipates, usually
  as heat. The amount of usable energy therefore
  decreases.

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Energy is required to form bonds.
Atoms or molecules
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Energy is released when bonds are broken.
The energy is now released. It may be in a form
such as heat or light or it may be transferred to
another molecule.
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ATP (Adenosine Triphosphate)
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ATP Stores Energy
A
ATP
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ATP is Recycled

• ATP (Adenosine Triphosphate) is an energy-rich
  molecule used to supply the cell with energy. The
  energy used to produce ATP comes from glucose or
  other high-energy compounds.
• ATP is continuously produced and consumed as
  illustrated below.
• ADP Pi Energy ? ATP H2O(Note Pi
  phosphate group)

ATP
Energy
Energy (from glucose or other high-energy
compounds)
ADP Pi
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ATP
Energy
Energy release
ATP
ADP Pi
Energy absorbed
Energy
ATP
ADP
Pi
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Catabolic and Anabolic Reactions

• the breakdown of complex organic compounds to
  simpler compounds generally release energy and
  are called catabolic reactions.
• Anabolic reactions are those that consume energy
  while synthesizing compounds.
• ATP produced by catabolic reactions provides the
  energy for anabolic reactions. Anabolic and
  catabolic reactions are therefore coupled (they
  work together) through the use of ATP.

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An anabolic reaction A catabolic
reaction
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Anabolic Reactions
Products
Energy Supplied
Substrates(Reactants)
Energy Released
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Catabolic Reactions
Energy Supplied
Substrate(Reactant)
Energy Released
When bonds are broken, energy is released.
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Energy Supplied
Activation Energy
Energy Released
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Activation energy without enzyme
Energy Supplied
Activation energy with enzyme
Energy Released
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Energy is transferred with electrons
Oxidized atom Electron is donated Energy is
donated
Reduced atom Electron is received Energy is
received
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Energy is transferred with electrons
Oxidized atom Electron is donated Energy is
donated
Reduced atom Electron is received Energy is
received
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Energy is transferred with electrons
Oxidized atom Electron is donated Energy is
donated
Reduced atom Electron is received Energy is
received
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Oxidation and Reduction

• Oxidation is the loss of electrons or hydrogen
  atoms.  Oxidation reactions release energy.
• Reduction is gain of electrons or hydrogen atoms
  and is associated with a gain of energy.
• Oxidation and reduction occur together. When a
  molecule is oxidized, another must be reduced.
• These coupled reactions are called
  oxidation-reduction or redox reactions.
• Food is highly reduced (has many hydrogens). The
  chemical pathways in cells that produce energy
  for the cell oxidize the food (remove hydrogens),
  producing ATP.

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Cofactors

• Many enzymes require a cofactor to assist in the
  reaction.  These "assistants" are nonprotein and
  may be metal ions such as magnesium (Mg),
  potassium (K), and calcium (Ca). 
• The cofactors bind to the enzyme and participate
  in the reaction by removing electrons, protons ,
  or chemical groups from the substrate.

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Coenzymes

• Cofactors that are  organic molecules are
  coenzymes.
• In oxidation-reduction reactions, coenzymes often
  remove electrons from the substrate and pass them
  to different enzymes.
• In this way, coenzymes serve to carry energy in
  the form of electrons (or hydrogen atoms) from
  one compound to another.

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Coenzymes
Coenzyme
Enzyme

• Coenzymes are organic cofactors that are not
  protein.
• They bind to the enzyme and also participate in
  the reaction by carrying electrons or hydrogen
  atoms.

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Vitamins are Coenzymes

• Vitamin Coenzyme Name
• B3 (Niacin) NAD
• B2 (riboflavin) FAD
• B1 (thiamine) Thiamine pyrophosphate
• B5 (Pantothenic acid) Coenzyme A (CoA)
• B12 Cobamide coenzymes

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Electron Carriers

• Some coenzymes are electron carriers function in
  photosynthesis and cellular respiration. Three
  major electron carriers are listed below.
• Respiration
• NAD
• FAD
• Photosynthesis
• NADP

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NAD (Nicotinamide Adenine Dinucleotide)
OrganicMolecule
NAD
NAD


Oxidized OrganicMolecule
NAD 2H ? NADH H

• NAD functions in cellular respiration by
  carrying two electrons. With two electrons, it
  becomes NADH.
• NAD oxidizes its substrate by removing two
  hydrogen atoms. One of the hydrogen atoms bonds
  to the NAD. The electron from the other hydrogen
  atom remains with the NADH molecule but the
  proton (H) is released. 
• NAD 2H NADH H
• NADH can donate two electrons (one of them is a
  hydrogen atom) to another molecule.

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NAD 2H ? NADH H
NADH H
Energy 2H
Energy 2H
NAD
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NADP 2H ? NADPH H
NADPH H
Energy 2H
Energy 2H
NADP
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NADP (Nicotinamide Adenine Dinucleotide
Phosphate)

• NADP 2H NADPH H
• NADP is similar to NAD in that it can carry two
  electrons, one of them in a hydrogen atom, the
  other one comes from a hydrogen that is released
  as a hydrogen ion. (Click here to review NAD.)
• Electrons carried by NADPH in photosynthesis are
  ultimately used to reduce CO2 to carbohydrate.

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Phosphorylation

• ATP is synthesized from ADP Pi. The process of
  synthesizing ATP is called phosphorylation.
• Two kinds of phosphorylation are illustrated on
  the next several slides.
• Substrate-Level Phosphorylation
• Chemiosmotic Phosphorylation

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Substrate-Level Phosphorylation
A high-energy molecule (substrate) is used to
transfer a phosphate group to ADP to form ATP.
ADP
High-energy molecule
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Substrate-Level Phosphorylation
A high-energy molecule (substrate) is used to
transfer a phosphate group to ADP to form ATP.
ADP
High-energy molecule
This bond will be broken, releasing energy.
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Substrate-Level Phosphorylation
A high-energy molecule (substrate) is used to
transfer a phosphate group to ADP to form ATP.
ADP
High-energy molecule
The energy released will be used to bond the
phosphate group to ADP, forming ATP.
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Substrate-Level Phosphorylation
A high-energy molecule (substrate) is used to
transfer a phosphate group to ADP to form ATP.
ADP
High-energy molecule
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Substrate-Level Phosphorylation
Enzyme
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Substrate-Level Phosphorylation
The energy has been transferred from the
high-energy molecule to ADP to produce ATP.
Low-energy molecule
ATP
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Mitochondrion Structure

• This drawing shows a mitochondrion cut lengthwise
  to reveal its internal membrane.

Intermembrane Space
Cristae Matrix
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ChemiosmoticPhosphorylation
This drawing shows a close-up of a section of a
mitochondrion.
H
H
H
Matrix (inside)
H
Outside Intermembrane Space Matrix
H
H
H
H
H
H
H
H
H
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00
Pumps within the membrane moves hydrogen ions
from the matrix to the intermembrane space
creating a concentration gradient.
H
This process requires energy -- cellular
respiration.
H
H
Matrix (inside)
H
Outside Intermembrane Space Matrix
H
H
H
H
H
H
H
H
H
H
H
H
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ChemiosmoticPhosphorylation
A high concentration of hydrogen ions in the
intermembrane space creates a gradient for
diffusion of H back to the matrix.
H
H
Matrix (inside)
H
Outside Intermembrane Space Matrix
H
H
H
H
H
H
H
H
H
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ChemiosmoticPhosphorylation
H
H
H
Matrix (inside)
H
Outside Intermembrane Space Matrix
H
H
H
H
H
H
H
H
H
H
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ChemiosmoticPhosphorylation
H
H
H
Matrix (inside)
H
Outside Intermembrane Space
H
H
H
H
H
ADP Pi
H
ATP
H
H
ATP synthase produces ATP by phosphorylating ADP.
The energy needed to produce ATP comes from
hydrogen ions forcing their way into the matrix
as they pass through the ATP synthase.
H
H
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Chemiosmotic Phosphorylation

• Chemiosmotic phosphorylation is used by the
  mitochondrion to produce ATP. The energy needed
  to initially pump H ions into the intermembrane
  space comes from glucose. The entire process is
  called cellular respiration.
• The chloroplast also produces ATP by chemiosmotic
  phosphorylation. The energy needed to produce ATP
  comes from sunlight.

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Chloroplast Structure

• The chloroplast is surrounded by a double
  membrane.
• Molecules that absorb light energy
  (photosynthetic pigments) are located on
  disk-shaped structures called thylakoids.
• The interior portion is the stroma.

Double membrane
Stroma
Thylakoids
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A Thylakoid
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
In order to synthesize ATP, hydrogen ions must
first be pumped into the thylakoid. This process
requires energy.
H
A concentration gradient of hydrogen ions is
established. The chemical gradient can be used as
an energy source for producing ATP.
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Chemiosmotic Phosphorylation
H
hydrogen ions force through this protein (ATP
synthase) as they return to the stroma.
H
H
H
H
H
H
H
H
H
H
H
H
H
H
ADP Pi ATP
H
H
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Phosphorylation

• We have just discussed two different forms of
  phosphorylation
• Substrate-level phosphorylation
• Chemiosmotic phosphorylation
• We saw that chemiosmotic phosphorylation occurred
  in both the mitochondria (during cellular
  respiration) and in the chloroplast (during
  photosynthesis). These two processes are
  sometimes given separate names
• Oxidative phosphorylation (in mitochondria)
• Photophosphorylation (in chloroplast)

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• Chemiosmosis Chloroplasts vs. Mitochondria
• Similarities In both organelles
• Redox reactions of electron transport chains
  generate a H gradient across a membrane
• Involves ATP synthase which uses this
  proton-motive force to make ATP
• Difference
• use different sources of energy to accomplish
  this (proton gradient). Chloroplasts use light
  energy (photophosphorylation) and mitochondria
  use the chemical energy in organic molecules
  (oxidative phosphorylation).