NRSG 205 Lecture 5 - Microbial Metabolism

Metabolism

he sum of all the chemical changes occurring within a living organism

2 types of metabolism

1. Catabolism

2. Anabolism

Catabolism

breakdown of more complex molecules into simple molecules; energy released

Anabolism

building up of more complex molecules from simple molecules; energy required

Reaction coupling

Catabolic and anabolic reactions are often coupled to supply (catabolic) and utilize (anabolic) energy

4 important molecules for metabolism/chemical reactions

1. ATP

2. Enzymes

3. Cofactors

4. Coenzymes

ATP function

provides energy for anabolic reactions

ATP makeup

Consists of a nitrogenous base (adenosine) with 3 phosphate molecules

How does ATP release its energy?

The last phosphate bond is unstable, giving it high potential energy → one phosphate group is let go, creating ADP (adenosine diphosphate) and releasing energy

Enzymes

proteins produced by living cells that catalyze (speed up) chemical reactions

How do enzymes catalyze reactions?

Enzymes catalyze reactions by decreasing activation energy

Activation energy (Eₐ):

energy that must be surpassed for a reaction to occur (molecules are bumping into each other to increase the energy and suppress the activation energy)

Enzyme substrate complex/reaction

brings two reactants together or puts the molecule in a position where they can be broken down by other molecules

Enzyme specificity

Substrate binds at the active site of the enzyme → specificity

Cofactors

metal ions necessary for the enzyme to perform its function

Coenzymes

organic molecule that is necessary for the enzyme to perform its function

3 main coenzymes

1. NAD+

2. FAD

3. coenzyme K

4 influences on enzymatic activity

1. Temperature

2. pH

3. Substrate concentration

4. Inhibitors

Temperature influence on enzymatic activity

most enzymes have an optimal temperature that they operate at

Effect of decreasing the temperature past the enzyme's optimal temperature

makes activity decrease because molecules are moving too slowly

Effect of increasing the temperature past the enzyme's optimal temperature

can cause denaturation of enzymes

pH influence on enzymatic activity

most enzymes have an optimal pH that they operate at

Enzymes found in the small intestine and mouth have an optimal pH of about _____-

7.4

Enzymes found in the stomach have an optimal pH of about _____

2.0

Substrate concentration influence on enzymatic activity

• increased substrate → increase in activity

• Reaches a plateau eventually because enzymes become saturated, and there is nowhere for the substrate to bind

Inhibitors

molecules that try to stop enzymatic reactions

2 types of inhibitors

1. Competitive

2. Non-competitive

Competitive inhibitors

inhibition is concentration dependent because both the inhibitor and the substrate compete for the same active site

Non-competitive inhibitors

not concentration dependent because they bind to an allosteric site, changing the shape of the enzyme and blocking the substrate

Ribozymes

enzymatic RNAs involved in protein synthesis

Feedback inhibition

end product inhibits the enzyme activity through negative feedback mechanism  (noncompetitive inhibition)

Oxidation-reduction (redox) reactions

one molecule is reduced (gains an electron) and the other is oxidized (loses an electron)

Cellular respiration reaction

C6H12O6 + O2 → CO2 + H2O

In cellular respiration, _____ is oxidized to _____ and _____ is reduced to ____

Glucose, CO2, O2, H2O

When is NAD+/NADH oxidized and reduced in cellular respiration

NAD+ is reduced in the earlier steps of cellular respiration and NADH is oxidized at the electron transport chain

3 forms of ATP synthesis

1. Substrate level phosphorylation

2. Oxidative phosphorylation

3. Photophosphorylation

Substrate level phosphorylation

an inorganic phosphate is added to an ADP molecule by an enzyme

Oxidative phosphorylation

creation of ATP from the electron transport chain that requires oxygen (creates the majority of ATP)

Photophosphorylation

uses light energy to drive ATP synthesis

Steps of aerobic respiration

1. Glycolysis

2. Pyruvate oxidation

3. Citric acid cycle

4. Oxidative phosphorylation

Glycolysis reaction

glucose + 2 ATP +2  NAD+ → 2 pyruvate (3-carbon molecule) + 4 ATP + 2 NADH

____ net ATP are gained from glycolysis and made through __________

2, substrate level phosphorylation

Pyruvate oxidation reaction

2 pyruvate → 2 acetyl-CoA + 2 CO2

Citric acid cycle reaction

 2 acetyl-CoA → 4 CO2 + 6 NADH + 2 FADH2

Where does oxidative phosphorylation take place?

akes place in the electron transport chain in the mitochondria

2 significant locations of the mitochondria in oxidative phosphorylation and their locations

Matrix exists inside of the mitochondria, and the periplasmic space exists between the inner and outer membranes of the mitochondria

Oxidative phosphorylation steps

• NADH and FADH2 molecules donate electrons to the ETC, which releases energy necessary to pump protons into the inner membrane space against their gradient (proton motive force)

• Chemiosmosis: facilitated diffusion of protons through the ATPase enzyme creates a great amount of energy, driving the synthesis of ATP

Oxygen role in oxidative phosphorylation

Oxygen is the final electron acceptor and is reduced to water

Oxidative phosphorylation yields _____-_____ ATP

34, 38

How do organisms produce energy when oxygen isn't presented?

Organisms perform fermentation/anaerobic respiration

2 forms of fermentation

1. Ethanolic

2. Lactic acid

_________ is always the first step of fermentation

Glycolysis

Steps of ethanolic fermentation

• Pyruvate is converted into 2 acetylaldehydes (2-carbon molecule), 2 CO2, and 2 ethanol (2-carbon molecule), and 2 NADH → 2 NAD+

• NAD+ can be used to drive this process over and over again

Ethanolic fermentation produces a net gain of _____ ATP

2

Lactic acid fermentation steps

Pyruvate is converted into 2 lactic acid (3-carbon molecule), and 2 NADH → 2 NAD+

Lactic acid fermentation produces a net gain of _____ ATP

2