Microbiology for the Health Sciences
Jan 19, 2016
Microbiology for the Health Sciences
Metabolism: the sum of all chemical reactions that occur in a living
cell in order that the cell sustains its life’s processes
Catabolism: decomposition reactions in a living organism, the breakdown of complex
organic compounds into simpler ones. Catabolic reactions makes ATP
Anabolism: all synthesis reactions in a living organism; the building of complex organic molecules from simpler ones. Anabolic reactions use ATP.
Catabolism and Anabolism coupled
rxns
1. Digestion
2. Movement of nutrients across cell membrane
3. The oxidation of glucose into two pyruvic acid molecules
This is also known as Glycolysis.
4. The complete oxidation of pyruvic acid into carbon dioxide (CO2) and the formation of ATP. This is represented by the Kreb’s Cycle and the Electron Transport system
Enzymes needed to speed up chemical reactions
Exoenzymes: enzymes the cell uses to break down large molecules outside of cell so can be transported across cell membrane
Naming of enzymes substrate/enzyme
Main nutrient groups:◦ Carbohydrates Amylase◦ Proteins Protease◦ Lipids Lipase
Passive Diffusion: moves down concentration gradient (requires No Energy)
Facilitated Diffusion: moves down a concentration gradient
uses carrier molecule (requires No Energy) Active Transport: movement against concentration
gradient (requires Energy)
Endocytosis: (Eukaryotes) substance engulfed by cell membrane
[INSERT FIGURE 5.12]
Beginning of oxidation glucose to two pyruvic acid molecules
1 glucose molecule contains 6 carbons. In glycolysis, glucose is broken down to 2, 3 carbon molecules called pyruvate
Uses 2 ATP
Make 4 ATP Net Energy is 2 ATP
2 ATP added to glucose (6C) to energize it.
Through 10 steps glucose is converted to two
pyruvate (3C), with energy transferred to make 4
ATP (substrate phosphorylation).
Although glycolysis makes 4 ATP, the net ATP
production by this step is 2 ATP (because 2 ATP
were used to start glycolysis). The 2 net ATP are
available for cell use.
If oxygen is available to the cell, the pyruvate will
move into the plasma membrane (P) or the
mitochondria & aerobic respiration will begin.
[INSERT FIGURE 5.18]
Pyruvic acid loses 1 molecule of carbon in form of carbon dioxide in preparatory step for Kreb cycle = 2 carbon compound called acetyl CoA
Kreb cycle results in the complete oxidation of acetyl CoA to carbon dioxide and formation of ATP
Carbon dioxide eventually released from cell
2 ATP equivalents produced
H left with it’s corresponding electron
Requires 2 cycles to metabolize glucose
Acetyl Co-A (2C) enters the Kreb's Cycle & joins with Oxaloacetic Acid (4C) to make Citric Acid (6C)
Citric acid is oxidized releasing CO2 , free H+, & e- and forming ketoglutaric acid (5C)
Free e- reduce the energy carriers NAD+ to NADH and FAD+ to FADH2
Ketoglutaric acid is also oxidized releasing more CO2 , free H+, & e-
The cycle continues oxidizing the carbon compounds formed (succinic acid, fumaric acid, malic acid, etc.) producing more CO2, NADH, FADH2, & ATP
H2O is added to supply more H+
CO2 is a waste product that diffuses out of cells
H’s need to be moved to where can be useful
Carrier molecules NAD+ and FAD+ act as shuttles to move H’s to plasma membrane
NAD can carry 1 H and FAD can carry 2 H
H and corresponding electrons released into plasma membrane
H pumped out of membrane and electron passed down carrier chain inside membrane
Nicotinamide Adenine Dinucleotide
NAD can carry 1 hydrogen
NADH
Flavin Adenine Dinucleotide
FAD can carry 2 hydrogenFADH2
Continuation of Cellular Respiration◦ Electron transport
Most significant production of ATP occurs through stepwise release of energy from series of redox reactions known as an electron transport chain (ETC)
Consists of series of membrane-bound carrier molecules that pass electrons from one to another and ultimately to final electron acceptor
Energy from electrons used to pump protons (H+) across the membrane, establishing a proton gradient
Located in cristae of eukaryotes and in cytoplasmic membrane of prokaryotes
Excess protons outside membrane create potential energy due to high positive charge on one side ofmembrane
Protons used to synthesize ATP
Then protons, electrons and final electron acceptor,
oxygen, combine with oxygen to form water
Oxidative Phosphorylation
NADH and FADH2 carry protons (H+) and electrons (e-) tothe electron transport chain located in the membrane.
The energy from the transfer of electrons along thechain transports protons across the membrane and creates an electrochemical gradient.
As the accumulating protons follow theelectrochemical gradient back across the membrane through an ATP synthase complex, the movement of the protons provides energy for synthesizing ATP from ADP and phosphate.
At the end of the electron transport system, two protons, two electrons, and half of an oxygen molecule combine to form water.
Since oxygen is the final electron acceptor, theprocess is called aerobic respiration.
Net result = 34 ATP from the Electron Transport System
Note:
4 ATP were formed from glycolysis and kreb cycle
Total ATP formed in prokaryotes is 38 for each glucose molecule
ATP synthase, also called complex,
is the final enzyme in the oxidative
phosphorylation pathway.
This enzyme is found in all forms of life and functions in the same way in both prokaryotes and eukaryotes.
The enzyme uses the energy stored
in a proton gradient across a membrane to drive the synthesis
of ATP from ADP and phosphate (Pi).
Found in the inner mitochondrial membrane or cristae
Contains 4 protein-based complexes that work in sequence moving H+ from the matrix across the inner membrane (proton pumps)
A concentration gradient of H+ between the inner & outer mitochondrial membrane occurs
H+ concentration gradient causes the synthesis of ATP by chemosmosis
Process Begin with End with Net EnergyGlycolysis 2 ATP, glucose 4 ATP, 2 pyruvate 2 ATPKreb’s cycle 2 pyruvate 6 carbon dioxide, H+ 2 ATP equivalentsElectronTransport System
H+, correspondingelectrons
Water 34 ATP
[INSERT TABLE 5.3]
Terminal electron acceptor something other than oxygen
Such as: Nitrate, nitrite, sulfate, or carbonate
Releases energy from sugars or other organic molecules (amino acids)
Does not require oxygen
Does not require kreb cycle or electron transport chain
Uses organic molecule as final electron acceptor
Produces only small amounts of ATP
Examples of end products are lactic acid or ethanol
Fermentation◦ Sometimes cells cannot
completely oxidize glucose by cellular respiration
◦ Cells require constant source of NAD+ that cannot be obtained by simply using glycolysis and the Krebs cycle In respiration, electron
transport regenerates NAD+ from NADH
◦ Fermentation pathways provide cells with alternate source of NAD+ Partial oxidation of sugar (or
other metabolites) to release energy using an organic molecule from within the cell as an electron acceptor
[INSERT TABLE 5.4]
[INSERT FIGURE 5.22]