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]