Transcript chapter 5

Chapter 5
Bacterial Metabolism
• Metabolism is sum total of all biochemical
processes taking place in an organism.
• Two categories
– Anabolism – synthesis of chemical compounds
• Form bonds
• Require energy
• Endergonic
– Catobolism hydrolysis of chemical compounds
• Break bonds
• Release energy
• Exergonic
Enzymes and Energy in Metabolism Pg 163 - 170
• Enzymes – are a group of organic compounds
made of proteins that increase the rate of a
chemical reaction.
• Enzymes are reusable.
• One enzyme is used for one reaction.
• The substance acted on by an enzymes is called
the substrate.
• Product formed is called the product.
Enzyme
• The same enzyme can sometimes act to build
up a product or break it down dependent on the
circumstance.
• Enzymes are usually named for the reaction
they perform and end in “ase”
– Like lactase which breaks down lactose or
sucrase that break downs sucrose.
– There are exceptions lysozyme which lysis
bacterial cell walls.
Enzymes Act Through Enzyme-Substrate Complex
• How an enzyme works is by aligning the
substrate(s) in a specific way to make the
reaction more likely to occur.
• In a hydrolysis reaction, the enzyme forces the
substrate to stretch or weaken causing the bond
to break.
• In a synthesis reaction, the enzyme brings the
substrates together were the chemical bond will
form.
• The area on the enzyme where the substrates
reactions are brought together is called the
active site
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Enzymes
Some enzymes are made up of only proteins like
lysozyme.
Other enzymes need small non-protein
substances that help carry out the reaction.
Some of these are metal ions, Mg2+, Fe2+ or
ZN2+ and are called cofactors.
If the non-protein is a small organic molecule it is
called a coenzyme.
Two important coenzymes are nicotinamide
adenine dinucleotide (NAD+) and flavin adenine
dinucleotide (FAD).
NAD+ and FAD help carry electrons in
metabolism.
Enzymes Often Act In Metabolic
Pathways
• A metabolic pathway is a sequence of
chemical reactions, each reaction is
carried out by a different enzyme, and the
product of one reaction serves as a
substrate for the next reaction
• The pathway starts with a specific
substrate and ends with a final end
product.
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Adenosine Triphosphate Pg 168 – 169
In many enzyme reactions energy is required to
drive the reaction
This energy comes from adenosine triphosphate
Adenosine triphosphate (ATP) is a high energy
molecule and serves as an energy source for cells
The energy is supplied when the covalent bond
between the third and second phosphates of the
ATP molecule is broken
The breaking of this chemical bond releases
12,000 calories of usable energy
In a bacteria cell ATP is formed on the cell
membrane
In a eukaryotic cell it is produced in the
mitochondria
ATP
Catabolism of Glucose p. 170 to 179
• The best studied metabolic activity in a cell is the
breakdown of glucose
• Glucose is the key source of energy for production of
ATP
• A mole of glucose (180 g) contains 686,000 calories of
energy
• Breakdown of glucose is a controlled process that
takes all the energy available in the molecule and
converts it to ATP
• The extraction of the energy of glucose happens down
a metabolic pathway
Glycolysis
• Glycolysis is the first process of energy
extraction from glucose.
• Glycolysis is the chemical breakdown of
glucose.
• Glycolysis occurs in the cytosol of bacteria.
• In this process glucose is converted from a
6 carbon molecule into two 3 carbon
molecules called pyruvate
Cellular Respiration
• The production of ATP through the harvesting
of energy down a metabolic pathway is called
Cellular Respiration
• If a cell uses oxygen in making ATP it is called
Aerobic Respiration
• C6H12O6 + 6O2 + 38 ADP + 38P → 6CO2 + 6H2O +
38ATP
• If no oxygen is used it is called Anaerobic
Respiration
The Steps of
Glycolysis
Glycolysis
• Energy Requiring Steps
– Each step in the breakdown uses a specific enzyme
– The first three steps of gylcolysis requires 2 ATP
molecules
– Glucose is broken down into two 3 carbon molecules
dihydroxyacetone phosphate (DHAP)
• Energy Producing Steps
– The removal of the phosphate groups from these
molecules helps to produce 2 ATP from each of the 3
carbon molecules
– The end product of glycolysis is 2 ATP, 2
Nicotinamide adenine dinucleotide (NADH) and 2
pyruvate molecules
– Note: The 2 NADH molecules will be used in the
production of energy in the electron transport chain
Krebs Cycle (Citric Acid Cycle)
• This metabolic pathway is called a cycle pathway
because the starting product is identical to the finishing
product
• All steps are carried out by enzymes
• All reactions take place along the bacterial cell
membrane
• Eukaryotic cells it occurs in the mitochondria
• The initial product added to the Krebs cycle is not
pyruvate
• Pyruvate first has to loss a carbon in the form of CO2
• The remaining two carbons are attached to a molecule
called coenzyme A
Krebs Cycle (Citric Acid Cycle)
• The new molecule is called acetyl coenzyme A
(Acetyl CoA)
• The removal of the CO2 also produces another
NADH molecule for the electron transport chain
• The remaining 2 carbons from the 3 carbon
pyruvate are now able to enter the Krebs cycle
• This happens when a four carbon oxaloacetate
molecule reacts with the acetyl CoA molecule
and forms citrate (citric acid cycle)
Krebs Cycle (Citric Acid Cycle)
• From each removal of carbon along the cycle an
NADH molecule is produced
• With pyruvate the end product of Kreb’s Cycle is
3 NADH molecules and 1 flavin adenine
dinucleotide (FADH2)
• So all totaled from the breakdown of glucose
through glycolysis and the Krebs cycle 10 NADH
and 2 FADH2 are produced
Electron Transport Chain
(Pg 175 – 179)
• Oxidative Phosphorylation – is a sequence of
reactions were electrons are moved from one
molecule to another (electron transport) and the
energy released is captured in ATP molecules
• Oxidative means the loss of electron pairs from
a molecule
• Reduction means to the gain of a pair of
electron
• Oxidative phosphorylation produces 34
molecules of ATP for each glucose molecule
broken down
Oxidative Phosphorylation in Bacteria
Oxidative Phosphorylation
• Oxidative phosphorylation, like the Krebs cycle,
occurs in the cytoplasmic membrane in bacteria
and mitochondria in eukaryotes
• The NADH and FADH2 molecules produced in
glycolysis and the Kreb’s cycle are used to shunt
electrons to the electron transport chain
• Once at the electron transport chain the
electrons from either NADH and FADH2 are
transferred to the first cytochrome in the cell
membrane
• The oxidized NAD+ and FAD are returned to the
cytosol to be reused in glycolysis and the Kreb’s
cycle
Electron Transport
• The electrons from the first cytochrome are
transported to another cytochrome and then to
the next down the chain
• This is why the process is referred to as the
electron transport chain because it helps
transfer electrons down a chain of cytochromes
to be finally transferred to an oxygen molecule
• The final stage of the electron transport is were
the electron pair is accepted by oxygen
• The oxygen then requires two protons (H+) to
stabilize itself and water is formed water
• O2 is essential in the electron transport chain
• If oxygen is not present the flow of electrons
stops and the whole process stops
ATP Synthesis
• What makes the electron transport chain
so important is that as electrons move
down the cytochromes the energy
released is used at three pumps
• These pumps move protons (H+) out of the
cytosol to the outside of the membrane
• This movement results in build up of
protons (H+) outside the membrane and
creates an electrical potential
• The protons are then moved back into the
cell through a protein channel which has
an enzyme called ATP synthase attached
ATP Synthesis
• As the protons (H+) move back into the cell the
free energy potential is used to synthesize ADP
into ATP
• For each pair of electrons released by a NADH
molecule 3 ATP molecules can be produced
• 2 ATP for each FADH2
• Electron transport chain coupled to ATP
synthesis
ATP Produced By Glycolysis
Anaerobic Respiration and Fermentation (Pg 183)
• Anaerobic respiration oxygen is not used as
the final electron acceptor in electron transport
– NO3- ,SO2= , CO2
• When sulfate is used the final product is H2S
the gas that gives the rotten egg smell
• Fermentation can make ATP in the absence of
cellular respiration
• Krebs and oxidative respiration is shut down
Chapter 5 Summary of Key Concepts
• Enzymes and Energy in Metabolism
– Enzymes Catalyze Chemical Reaction
– Enzymes Act Through Enzyme-Substrate
Complex
– Enzymes Often Act in Metabolic Pathways
– Energy in The Form of ATP Is Required for
Metabolism
The Catabolism of Glucose
• Glucose Contains Stored Energy that Can
Be Extracted
• Cellular Respiration Is a Series of
Catabolic Pathway for the Production of
ATP
• Glycolysis Is the First Stage of Energy
Extraction
• The Kreb’s Cycle Extracts More Energy
from Pyruvate
• Oxidative Phosphorylation Is the Process
by which Most ATP Molecules Form
Other Aspects of Catabolism
• Other Carbohydrates, Proteins and Fats
Can be used to Extract Energy From
• Anaerobic Respiration Produces Using
Other Electron Acceptors
• Fermentation Produces ATP Using an
Organic Final Electron Acceptor