Microbiology Exam 2 Chapter 7

Photosynthesis

Uses sunlight to create polymers and glucose

Organotrophs

organic molecule donates electrons

Lithotrophs

inorganic molecule to electrons

Importance of energy and entropy for living cells?

• Entropy: increases in favorable reactions

  • In biological systems, entropy decrease as reactions produce more ordered systems

• Energy: conserved

What is the role of enzymes in controlling metabolic biochemistry?

They catalyze chemical reactions by lowering the activation rate as an alternate pathway

Explain catabolism and anabolism

• Catabolism: releases energy; oxidative

  • In hydrolysis reactions

• Anabolism: consumes and stores energy

• Catabolic reactions can be coupled to power anabolic reaction

  • Ex: ATP —> ADP + Pi to power glucose breakdown

Reduction; being reduced

oxidizing agent

GAIN of electron

• ATP, FAD, and NAD accepts electrons

Oxidation; being oxidized

reducing agent

LOSS of electron

• Biomolecules donate electrons

NADH has ___ potential of producing energy than ATP alone

Higher

Because it stores energy in electrons (Hydrogens) that can feed into the electron transport system

Explain glycolysis (EMP pathway) for carb metabolism

1 glucose —> 2 pyruvate —> energy investment & energy payoff

Energy investment:

• cell spends 2 ATP to phosphorylate glucose

• glucose 6-carbon sugar split into two 3-carbon G3Ps

Energy payoff:

• Each of the two 3-carbon G3Ps produces 1 NADH and 2 ATPs on the way to pyruvate

• In total, there are 4 ATP and 2 NADH

• net: 2 ATP and 2 NADH per glucose

Explain alternatives for sugar metabolism

Bacteria can also use the Entner-Doudoroff (ED) and Pentose Phosphate Pathway (PPP) to metabolize sugar

Glycolysis (Again; simplified)

1 glucose —> 2 pyruvate, 2 ATP, and 2 NADH

Entner-Doudoroff (ED) Pathway

Glucose or sugar acids —> 6-P-gluconate, 2 pyruvate, ATP, NADH, NADPH

Pentose Phosphate Pathway (PPP)

6-P-gluconate —> (small) ATP, 2 NADPH, 5-carbon sugar

How is pyruvate further catabolized by fermentation (no oxygen available)

Results in ~2 ATP

• regenerates NAD+ by reduction reaction in absence of oxygen

• NADH reduces pyruvate and forms organic acids/alcohols at the end

• No electron transport chain

How is pyruvate further catabolized by respiration (when oxygen is available)

Results in ~36-38 ATP

• complete breakdown of glucose

• OXYGEN IS FINAL ELECTRON ACCEPTOR

• NADH is a carrier of H atoms

How does a clinical lab use bacterial catabolic reaction in tests to identify a pathogen

Fermentation products allow identification of isolated pathogens

Sorbitol fermentation test in E.Coli

• pass red colonies produced by nonpathogenic E.coli

• fails white colonies produced by pathogenic OH15:H17 E.coli

Explain how the electron transfer system flows generally

Glycolysis —> 2 pyruvate —> 2 Acetyl-CoA —> TCA cycle —> NADH & FADH w/ electron (H) —> drop off electrons to electron transport chain system —> cytoplasmic/mitochondrial membrane (depends on bacteria or eukaryote)

• As these electrons move from one protein to the next, they release a bit of energy that pumps hydrogen across membrane and builds the gradient

Proton flow back through ATP synthase and the energy flow is used to make ATP —> end of chain has terminal electron acceptor —> acceptor picks up electrons in hydrogen to form water

Anaerobic respiration for Pseudomonas Aeruginosa

NO3- + 2e- —> NO2-

N2O + 2e- —> N2

Pseudomonas Aeruginosa is opportunistic pathogen that colonizes lungs of cystic fibrosis patients

Methemoglobin = oxidized hemoglobin

Nitrite can oxidize iron in hemoglobin & high levels of this leads to methemoglobinemia

• lack of oxygen binding and transport —> hypoxia & cyanosis

Why are babies more vulnerable to methemoglobinemia

• They have higher stomach pH, allowing more bacterial growth.

• Bacteria reduces nitrate to nitrite

• Nitrite oxidizes hemoglobin

Treatment for methemoglobinemia?

Methylene blue

• reducing agent (donates electrons) for Fe3+ atom in methemoglobin to go back to Fe2+

The class of metabolism most useful for food production because it yields nutrient-rich microbial “waste products” is ____

A) respiration

B) fermentation

C) lithotrophy

D) photosynthesis

B) fermentation

sugar molecules are broken down into ethanol and lactic acid which are nutrient rich

All of the following compounds require energy to build, except ___

A) DNA
B) peptidoglycan

C) fatty acid

D) carbon dioxide

D) carbon dioxide

Which of the following chemical reactions does not require an enzyme?
A) Combustion

B) ATP formation

C) Photosynthesis

D) Sugar catabolism

A) combustion (not biochemical)

Which of these food substrates must first be broken down to sugars in order to enter glycolysis?
A) cellulose

B) lignin

C) lipids

D) proteins

A) Cellulose

Which of these statements is true of NADH?
A) It is a common food substrate for catabolism

B) It is an electron acceptor for catabolite electrons

C) It is an electron donor formed during catabolism

D) It is a waste product of fermentation

C) it is an electron donor formed during catabolism

Which of these kinds of metabolism is not catabolism?

A) glycolysis

B) amino acid conversion to TCA cycle intermediates

C) lipid conversion to glycerol and fatty acids

D) oxidation of ammonia (NH4)

D) oxidation of ammonia (NH4)

Which of the following statements does not describe glycolysis?

C) Glycolysis has a cycle of intermediates that incorporate a carbon skeleton and regenerate the original intermediate

Which molecule from glucose catabolism directly enters the TCA cycle?
A) Acetyl-CoA
B) Fructose

C) Glyceraldehyde

D) Glucose

A) Acetyl-CoA

Which statement is not true of fermentation?

A) fermentation releases all the energy available in a food substrate

B) Fermentation completes sugar catabolism by transferring all the electrons from NADH to pyruvate

A) Fermentation releases all the energy available in a food substrate

Which of the following does not describe an electron transport system (ETS)?

C) The oxidoreductase directly phosphorylates ADP to make ATP

Which of the following metabolic reactions is not an example of lithotrophy?

B) Geobacter catabolizes small organic molecules and donates electrons to an electrode in a fuel cell

Which bacterial metabolism can cause methemoglobinemia?

A) fermentation

B) respiration using oxygen

C) lithotrophy oxidizing iron

D) anaerobic respiration reducing nitrate to nitrite

D) anaerobic respiration reducing nitrate to nitrite

Which part of the Z pathway of photosynthesis releases the oxygen we breathe?

Photosystem II

Which portion of photosynthesis can occur in the dark and also occurs in many lithotrophic bacteria?

A) Chlorophyll electron excitation

B) ATP production from the H+ gradient generated by the ETS

C) NADPH production by electrons from the ETS

D) CO2 fixation via the Calvin cycle

D) CO2 fixation via the Calvin cycle (everything else required light or is organic)

What kind of phototrophs cause food poisoning?

A) Dinoflagellates in ride tide

B) Algal symbionts of coral

C) Marine photosynthetic bacteria producing oxygen

D) Purple sulfur-reducing bacteria

A) Dinoflagellates in ride tide (dinoflagellates produces saxitoxin)

Bacteria synthesize amino acids by obtaining carbon skeletons from ___

A) glycolysis

B) PPP
C) TCA cycle

D) All of the above

D) All of the above

Bacteria incorporate ammonia into a TCA cycle intermediate to form the amino acid ___
A) Cysteine

B) Glutamate

C) Tryptophan

D) Histidine

B) Glutamate