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

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.

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