Download Cellular Metabolism - Oklahoma State University–Stillwater

Metabolism
• A cell is a miniature factory
• A large number of Chemical reactions are
occurring
• A (reactants) + B (reactants) ----> C
(products)
• Chemical reactions are either endogonic
(req. energy) or exogonic (release energy)
Enzyme
• Reduce Activation energy
• Contain specific active sites
• Substrates bind to active sites, forming the
enzyme-substrate complex.
• Enzyme-substrate interaction results in
product formation
• For ex. A + B ---> C
Enzymes
• Two types of enzyme-substrate inhibition
• 1.) Competitive – different substrates bind
to the same active site.
• 2.) Allosteric – substrates cause the
protein to change 3-D shape. Thus, the
function changes.
Electron transfer
• Oxidation – when electrons are given up
(donation)
• Reduction – when electrons are taken in
(accepting)
Metabolism
Catabolism
- produce energy (ATP)
- breakdown molecules
(ex. glycolysis)
Anabolism
- use energy (ATP)
- synthesize macromolecules
(ex. DNA, lipids, etc.)
Metabolic Strategies
All are based on energy, electron and
carbon source:
1.) Chemoorganotrophic
(chemoheterotroph)
2.) Chemolithotrophic (chemoautotroph)
3.) Photolithotrophic (photoautotroph)
4.) Photoorganotrophic (photoheterotroph)
Metabolism
Large molecules
Catabolism
Anabolism
Energy (ATP)
Small molecules (precursors)
Catabolism
- ex. Glycolytic pathway (glycolysis)
- Two types of catabolism:
1.) respiration-aerobic( w/ oxygen)
- anaerobic respiration (w/o
oxygen)
2.) fermentation (does not use oxygen)
- Glucose is taken in and broken down in
order to generate energy and to use the
glucose carbons as a source of carbon.
Glycolysis
Respiration
Glycolysis
Fermentation
TCA
Cycle
Organic products
Oxidative phosphorylation
Respiration
- Three phases
- 1.) Glycolysis
- 2.) TCA cycle
- 3.) oxidative phosphorylation
Fermentation
- Two phases
- 1.) Glycolysis
- 2.) Fermentation -high yield of
product, ex. ethanol
Chemical reaction
• Metabolism involves chemical reactions
A+B-->C+D, ex. Glycolysis
• Three events
– 1.) electron flow
– 2.) carbon flow
– 3.) energy production
Metabolism
Flow of
electrons
carbon
Metabolism
Binary fission
energy
Electron flow
eNAD
NADH
Coenzymes NAD-->NADH
Coenzyme NAD -->NADH
NADH
NAD
TCA
eNADH->NAD electrons
NADH
H2O
O2
Oxidative phosphorylation
(electron transport chain)
Fermentation
Reduction/oxidation (redox)
- Electron flow involves redox
reactions.
- Reduction - a molecule accepts an
electron. Reduced. Ex. NADH
- Oxidation - a molecule donates an
electron. Oxidized. Ex. NAD
- H ion transfer is usually accompanied
by electron transfer.
Reduction/Oxidation (Redox)
• Molecules involved in redox reactions
• Ex. Coenzymes:
(oxidized)NAD+
+ H+ + e- --> NADH (reduced) Occurs in glycolysis,
TCA
• Ex. Electron transport chain (electron carriers accept
electrons from NADH)
• Ex. 1/2O2 + H2 + e- ---> H2O
Final
electron acceptor can be oxygen, sulfate, nitrate,
carbonate. (S,N, and C are anaerobic respiration)
• Cycling : If both fermentation and
respiration are possible, the reduced
NADHs are used in the electron transport
systems and fermentation. The oxidized
NADs are used in respiration and/or
fermention.
Glycolysis
Respiration
Fermentation
NADH
NAD
NADH
TCA
Cycle
NADH
NAD
NADH
H2O
Electron transport chain
(chemiosmosis)
Organic products
Carbon Flow
Glucose (6 C molecule)
Intermediates
Biosynthesis
(anabolism)
Pyruvic acid (Two 3 C molecule)
TCA
Intermediates
(3 or2 C)
CO2
Glycolysis
(Breakdown of glucose)
Glycolysis
Respiration
Fermentation
NADH
Pyruvic acid
NADH
TCA
Cycle
NADH
CO2
H2O
Electron transport chain
(chemiosmosis)
Organic products
Carbon flow
• Large molecules are broken into smaller
molecules (catabolism)
• Critical intermediates are generated (ex.
Pyruvic acid, etc.) They are used in the
anabolism process as well as entry back
into the catabolism process.
Energy Production
• 1.) Substrate-level phosphorylation+ P ==> ATP (associated with glycolysis)
ADP
• 2.) Oxidative phosphorylation
Ex.
electron transport chain associated with the
proton motive force.
• 3.) Photophosphorylation – converts light energy
to chemical energy of ATP and NADPH. (Light
+carbon dioxide+wate =>sugar=>glycolysis)
Substrate Level Phosphorylation
- Occurs at certain steps in glycolysis
- Fermentation generates most of its ATP
using this process since no oxidative
phosphorylation is present.
- Level of ATP generation is less than
oxidative phosphorylation.
- Fermentation:Makes up difference by
metabolizing large amounts of material,
thus generating large amounts of product.
Oxidative Phosphorylation
- Electron transport chain
- Located in the cytoplasmic membrane
- Transfer of electrons also exports H
ions to one side of the membrane,
creating a gradient (Proton motive force).
-The H ions re-enter thru an ATPase,
generating high levels of ATP. This
process is call chemiosmosis
Photophosphorylation
• Light trapping pigments (chlorophylls)
• Sugars are synthesized with energy from
light.
• The sugars are then metabolized
(glycolysis).
Glycolysis
Glucose
Respiration
Fermentation
NADH
ATP
ATP
Pyruvic acid
TCA
Cycle
CO2
ATP
FADH2
NADH
H2O
ATP
Electron transport chain
(chemiosmosis)
Organic products
Respiratory Metabolism
• Conversion of carbohydrates to pyuvate
– end of glycolysis (EM pathway)
• Oxygen is the final electron acceptor =>
water
• Includes the TCA cycle
• Includes Oxidative phosphorylation
Summary of Glycolysis (EM)
• Transfer electrons (oxidation-reduction)
• Generates NADH (oxidized)
• Generates small amounts of ATP
(substrate level phosphosphorylation),
compared to the oxidative
phosphorylation.
• Generates critical intermediates
Summary of TCA
• Generates critical intermediates
• Generates oxidized coenzymes (NADH,
FADH2)
• Release carbon dioxide (reduces size of
molecule)
Summary of ETS (oxidative
phosphorylation)
• Accept electrons from oxidized coenzymes
• Electron carriers transfer electrons to other
carriers.
• Transfer H ions to one side of cytoplasmic
membrane (a gradient is formed)
• H ions move back into cytoplasm by way of the
ATPase. Thus, ATP is generated in large
amounts.
Alternate Glycolytic Pathway
• To supply coenzymes, critical intermediates,
etc., during times of adaptation, absence of EM;
other pathways are needed.
• Entner-Doudoroff pathway - aerobic bacteria
(lack an EM enzyme), certain Archaea
• Less ATP generated
• Generates NADPH, rather than NADH
Alternate Glycolytic Pathway
•
•
•
•
Modified ED pathway
Partially nonphosphorylated
Some Archaea (Halo, Thermo), Eubacteria
Less to no net production of ATP,
compared to EM.
Alternate to glycolysis
• Methylglyoxal pathway
• Eubacteria - during low phosphate
concentrations.
• Less ATP generated, compared to EM.
Pentose Phosphate Pathway
• Directly linked to EM or glycolysis
• Major role is to generate ribose for the
biosynthesis (anabolism) of DNA, RNA,
ATP NAD, NADP.
• Normal process (operates in conjunction
with EM)
Glycolysis supplies energy for
anabolism
Glucose
Respiration
Fermentation
NADH
ATP
ATP
Pyruvic acid
TCA
Cycle
CO2
ATP
NADH
H2O
ATP
Electron transport chain
(chemiosmosis)
Organic products
Metabolism
Large molecules
Catabolism
Anabolism
Energy (ATP)
Small molecules (precursors)
Review Metabolism
• Shared with both respiration and
fermentation
• Three phases of glycolytic pathway 1.)
glycolysis 2.) TCA 3.) electron transport
chain (oxidative phosphorylation)
• Three events during catabolism
1.)electron flow 2.)carbon flow
3.)energy production
Review continued
• 1.) Redox reactions
• Depends on reduction potential, positive
value- more likely to accept electron.
• Participating molecules ex. NAD, NADH
(electron donors or acceptors)
• 2.) 6C molecule to two 3C molecules
• C molecules (intermediates) enter
biosynthesis or is released as CO2
Review continued
• 3.) Three forms 1.) substrate level
phosphorylation 2.) oxidative
phosphorylation 3.) photophosphorylation
• Alternate forms of the glycolytic pathway
exist in order to supply coenzymes, ATP,
etc.
Fermentation
• Variety of products are synthsized.
• Use products to identify specific microoganim.
• Ex. Lactic acid, Ethanolic, Propionic Acid, Mixed
Acid, Butanediol, Butyric acid, Amino acid, Acetic
to methane
• Electron donor (substrate) and acceptor
(product) are internal of the cell, thus less
energy generated.
Mixed acid fermentation
• Methyl Red test - pH based test for acid
production.
• Clinical labs use it to identify E. coli,
urinary tract infections, etc.
• NADH is reoxidized to NAD
Butanediol fermentation
• Enterobacter, Serratia, Klebsiellaassociated with opportunistic infections.
• Voges-Proskauer test - detects an
intermediate metabolite.
• Used with MR test ex. VP-MR test
• Testing water supplies
• E.coli VP(-)MR(+), EnterbacterVP(+)MR(-)
Photoautotrophy
• Absorption of light energy
• Oxygenic photosynthesis- algae,
cyanobacteria, release oxygen, two
photosystems exist
• Anoxygenic photosynthesis-Green and
purple bacteria, no O is released, one
photosystem