Microbiology Metabolism and Genetics Study Guide – Step-by-Step Guidance

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Q1. What are the “net” results of glucose being metabolized by glycolysis? (Consider ATP, NADH, and the final carbon compound.)

Background

Topic: Glycolysis (Central Metabolic Pathway)

This question tests your understanding of the overall products generated when one molecule of glucose undergoes glycolysis, focusing on energy carriers (ATP, NADH) and the fate of carbon atoms.

Key Terms and Formulas

Glycolysis: The metabolic pathway that converts glucose (6 carbons) into two molecules of pyruvate (3 carbons each).
ATP: Adenosine triphosphate, the cell's main energy currency.
NADH: Nicotinamide adenine dinucleotide (reduced form), an electron carrier.
Net yield: The total produced minus what is consumed during the process.

Step-by-Step Guidance

Recall that glycolysis starts with one molecule of glucose (C6H12O6).
During glycolysis, glucose is split into two molecules of pyruvate (each with 3 carbons).
ATP is both consumed and produced in glycolysis. Identify how many ATP are used in the initial steps and how many are produced in the later steps.
Calculate the net ATP gain by subtracting the ATP used from the ATP produced.
Determine how many NAD+ molecules are reduced to NADH during glycolysis.
Summarize the net products: number of ATP, NADH, and the final carbon compound(s) formed.

Try solving on your own before revealing the answer!

Final Answer:

The net results of glycolysis per glucose molecule are:

2 ATP (net gain)
2 NADH
2 pyruvate (3-carbon compounds)

2 ATP are used in the early steps, 4 are produced later, for a net gain of 2. 2 NAD+ are reduced to NADH, and the 6-carbon glucose is split into two 3-carbon pyruvate molecules.

Q2. Pyruvate (3 carbons) is the starting point for the Krebs Cycle but only 2 carbons enter the cycle. What happened to the other carbon?

Background

Topic: Link between Glycolysis and Krebs Cycle (Pyruvate Decarboxylation)

This question examines your understanding of the conversion of pyruvate to acetyl-CoA and the fate of carbon atoms during this process.

Key Terms and Concepts

Pyruvate: 3-carbon product of glycolysis.
Acetyl-CoA: 2-carbon molecule that enters the Krebs cycle.
Decarboxylation: Removal of a carboxyl group, releasing CO2.

Step-by-Step Guidance

Recall that each pyruvate molecule (3 carbons) is converted to acetyl-CoA (2 carbons) before entering the Krebs cycle.
Consider what happens to the third carbon atom during this conversion process.
Identify the byproduct released when pyruvate is converted to acetyl-CoA.
Think about the enzyme complex responsible for this reaction and the fate of the electrons released.

Try solving on your own before revealing the answer!

Final Answer:

The third carbon from pyruvate is released as CO2 during the conversion to acetyl-CoA. This process is called decarboxylation and is catalyzed by the pyruvate dehydrogenase complex.

Q3. During active metabolism, many more carbons enter the Krebs cycle than the number of carbons given off as CO2. What happens to all the carbon that doesn’t become CO2?

Background

Topic: Krebs Cycle and Anabolic Pathways

This question tests your understanding of how intermediates of the Krebs cycle are used for biosynthesis (anabolism) and not just for energy production.

Key Terms and Concepts

Krebs Cycle Intermediates: Molecules like oxaloacetate, α-ketoglutarate, and succinyl-CoA.
Anabolic Pathways: Biosynthetic processes that use intermediates to build amino acids, nucleotides, etc.

Step-by-Step Guidance

Recall that the Krebs cycle is amphibolic, meaning it serves both catabolic and anabolic functions.
Consider how some intermediates are "withdrawn" from the cycle for biosynthetic (anabolic) purposes.
Think about examples of molecules that are synthesized from Krebs cycle intermediates (e.g., amino acids, nucleotides).
Reflect on how the cell replenishes these intermediates to keep the cycle running (anaplerotic reactions).

Try solving on your own before revealing the answer!

Final Answer:

The carbons that do not become CO2 are used as building blocks for biosynthesis. They are withdrawn from the Krebs cycle to make amino acids, nucleotides, and other essential cellular components.

Q4. Electrons cannot run free in the cell. How are they handled by metabolism?

Background

Topic: Electron Carriers in Metabolism

This question is about how cells manage electrons released during metabolic reactions, especially in redox (oxidation-reduction) processes.

Key Terms and Concepts

Electron Carriers: Molecules like NAD+, FAD, and NADP+ that temporarily hold electrons.
Redox Reactions: Chemical reactions involving the transfer of electrons.

Step-by-Step Guidance

Recall that electrons are released during oxidation of substrates (e.g., glucose) in metabolism.
Identify the main electron carriers that accept these electrons (NAD+, FAD).
Consider how these reduced carriers (NADH, FADH2) transport electrons to the electron transport chain (ETC).
Think about the final electron acceptor in aerobic and anaerobic respiration.

Try solving on your own before revealing the answer!

Final Answer:

Electrons are transferred to electron carriers like NAD+ and FAD, which become NADH and FADH2. These carriers then deliver the electrons to the electron transport chain, where they are ultimately transferred to a final electron acceptor (such as O2 in aerobic respiration).

Q5. Describe the role of chemiosmosis/proton motive force in the cell getting energy (ATP) during electron transport. Where is ATPase located in the cell?

Background

Topic: Electron Transport Chain and ATP Synthesis

This question tests your understanding of how the electron transport chain creates a proton gradient and how this gradient is used to generate ATP via ATP synthase (ATPase).

Key Terms and Concepts

Chemiosmosis: The movement of protons (H+) across a membrane, generating a proton motive force.
Proton Motive Force (PMF): The electrochemical gradient of protons across a membrane.
ATP Synthase (ATPase): The enzyme that synthesizes ATP using the energy from PMF.

Step-by-Step Guidance

Recall that as electrons move through the electron transport chain, protons are pumped across the membrane, creating a gradient.
Understand that this gradient (PMF) stores potential energy.
Describe how protons flow back through ATP synthase, driving the synthesis of ATP from ADP and inorganic phosphate.
Identify the location of ATP synthase in prokaryotic and eukaryotic cells.

Try solving on your own before revealing the answer!

Final Answer:

Chemiosmosis uses the proton motive force to drive protons back through ATP synthase, producing ATP. In prokaryotes, ATP synthase is located in the plasma membrane; in eukaryotes, it is in the inner mitochondrial membrane.

Q6. How does anaerobic respiration differ from aerobic respiration in bacteria? (Hint: Where do the electrons end up?)

Background

Topic: Types of Respiration in Bacteria

This question focuses on the differences between aerobic and anaerobic respiration, especially regarding the final electron acceptor.

Key Terms and Concepts

Aerobic Respiration: Uses oxygen (O2) as the final electron acceptor.
Anaerobic Respiration: Uses alternative electron acceptors (e.g., nitrate NO3-, sulfate SO42-).

Step-by-Step Guidance

Recall that both processes use an electron transport chain to generate ATP.
Identify the final electron acceptor in aerobic respiration (O2).
List possible final electron acceptors in anaerobic respiration (e.g., NO3-, SO42-).
Consider how the energy yield (ATP produced) compares between the two processes.

Try solving on your own before revealing the answer!

Final Answer:

In aerobic respiration, electrons end up on oxygen, forming water. In anaerobic respiration, electrons are transferred to alternative acceptors like nitrate or sulfate, resulting in less ATP produced compared to aerobic respiration.

Q7. In fermentation, what is used as the final electron acceptor? What carbon compounds result from this and what does the cell do with these carbon compounds?

Background

Topic: Fermentation Pathways

This question tests your understanding of how cells regenerate NAD+ in the absence of an electron transport chain and what happens to the end products of fermentation.

Key Terms and Concepts

Fermentation: Anaerobic process that regenerates NAD+ by transferring electrons to organic molecules.
Final Electron Acceptor: An organic molecule, often pyruvate or its derivatives.
Fermentation Products: Lactic acid, ethanol, mixed acids, etc.

Step-by-Step Guidance

Recall that fermentation occurs when there is no external electron acceptor (like O2 or NO3-).
Identify the molecule that accepts electrons from NADH during fermentation.
List common fermentation end products (e.g., lactic acid, ethanol).
Consider what the cell does with these end products (excretes them as waste).

Try solving on your own before revealing the answer!

Final Answer:

In fermentation, the final electron acceptor is an organic molecule (often pyruvate or its derivatives). The resulting carbon compounds (like lactic acid or ethanol) are excreted as waste products by the cell.

Q8. Relative to aerobic respiration, how much energy in ATPs does a cell get from these metabolic processes starting with glucose? (a) Anaerobic respiration (b) Just glycolysis (c) Fermentation

Background

Topic: ATP Yield from Different Metabolic Pathways

This question asks you to compare the ATP yield from various metabolic processes, using aerobic respiration as a reference point.

Key Terms and Concepts

Aerobic Respiration: Highest ATP yield (about 38 ATP per glucose in prokaryotes).
Anaerobic Respiration: Lower ATP yield than aerobic, but more than fermentation.
Glycolysis: Net 2 ATP per glucose.
Fermentation: No additional ATP beyond glycolysis.

Step-by-Step Guidance

Recall the approximate ATP yield for aerobic respiration (use prokaryotic numbers for reference).
Estimate the ATP yield for anaerobic respiration, considering the use of alternative electron acceptors.
State the net ATP produced by glycolysis alone.
Determine if fermentation produces any additional ATP beyond glycolysis.
Compare each process to aerobic respiration (e.g., much less, a little less, actual numbers if possible).

Try solving on your own before revealing the answer!

Final Answer:

(a) Anaerobic respiration: Yields less ATP than aerobic respiration (varies, but typically 2–36 ATP per glucose).
(b) Just glycolysis: Net 2 ATP per glucose.
(c) Fermentation: Also net 2 ATP per glucose (no additional ATP beyond glycolysis).

Aerobic respiration yields the most ATP, while fermentation yields the least.

Q9. How do bacteria ensure that DNA replication is achieved accurately?

Background

Topic: DNA Replication Fidelity

This question tests your understanding of the mechanisms that maintain the accuracy of DNA replication in bacteria.

Key Terms and Concepts

DNA Polymerase: Enzyme that synthesizes new DNA strands and proofreads for errors.
Proofreading: The ability of DNA polymerase to remove incorrectly paired nucleotides.
Mismatch Repair: Additional repair systems that correct errors after replication.

Step-by-Step Guidance

Recall the role of DNA polymerase in adding nucleotides and its proofreading function.
Consider how the enzyme detects and corrects mismatched bases during replication.
Think about additional repair mechanisms that operate after replication is complete.

Try solving on your own before revealing the answer!

Final Answer:

Bacteria ensure accurate DNA replication through the proofreading activity of DNA polymerase and post-replication mismatch repair systems.

Q10. What is “transcription”?

Background

Topic: Central Dogma of Molecular Biology

This question asks you to define transcription and understand its role in gene expression.

Key Terms and Concepts

Transcription: The process of synthesizing RNA from a DNA template.
RNA Polymerase: The enzyme that carries out transcription.

Step-by-Step Guidance

Recall that transcription is the first step in gene expression.
Identify the enzyme responsible for synthesizing RNA from DNA.
Consider the product of transcription (mRNA, tRNA, or rRNA).

Try solving on your own before revealing the answer!

Final Answer:

Transcription is the process by which RNA is synthesized from a DNA template by RNA polymerase.

Q11. What is “translation”?

Background

Topic: Central Dogma of Molecular Biology

This question asks you to define translation and understand its role in protein synthesis.

Key Terms and Concepts

Translation: The process of synthesizing a protein from an mRNA template.
Ribosome: The molecular machine that carries out translation.

Step-by-Step Guidance

Recall that translation is the second step in gene expression, following transcription.
Identify the cellular machinery responsible for translation (ribosome).
Consider the end product of translation (polypeptide/protein).

Try solving on your own before revealing the answer!

Final Answer:

Translation is the process by which a protein is synthesized from an mRNA template by the ribosome.

Q12. What is the difference between genotype and phenotype?

Background

Topic: Genetics – Genotype vs. Phenotype

This question tests your understanding of the distinction between an organism's genetic makeup and its observable traits.

Key Terms and Concepts

Genotype: The genetic constitution of an organism (the DNA sequence).
Phenotype: The observable characteristics or traits of an organism.

Step-by-Step Guidance

Recall that genotype refers to the information encoded in DNA.
Consider how phenotype results from the expression of genes and environmental influences.
Think of examples where genotype and phenotype may differ (e.g., silent mutations).

Try solving on your own before revealing the answer!

Final Answer:

Genotype is the genetic makeup of an organism, while phenotype is the set of observable traits resulting from gene expression and environmental factors.

Q13. What is meant by mutation? What is the spontaneous rate of mutation in bacteria compared to our own? Why do bacteria adapt more quickly to a changing environment than higher organisms like us?

Background

Topic: Mutations and Adaptation

This question explores the definition of mutation, mutation rates, and the evolutionary implications for bacteria versus higher organisms.

Key Terms and Concepts

Mutation: A change in the DNA sequence.
Spontaneous Mutation Rate: The natural frequency at which mutations occur.
Adaptation: The process by which organisms become better suited to their environment.

Step-by-Step Guidance

Define what a mutation is in genetic terms.
Recall the typical spontaneous mutation rate in bacteria and compare it to that in humans.
Consider why bacteria can adapt more quickly (e.g., short generation times, high population sizes).

Try solving on your own before revealing the answer!

Final Answer:

A mutation is a change in the DNA sequence. Bacteria have a higher spontaneous mutation rate and reproduce rapidly, allowing them to adapt more quickly to environmental changes than higher organisms.

Q14. What are mutagens? Give some examples of physical, chemical, and biological mutagens.

Background

Topic: Mutagenesis

This question asks you to define mutagens and provide examples from different categories.

Key Terms and Concepts

Mutagen: An agent that increases the rate of mutation.
Physical Mutagens: Radiation (e.g., UV, gamma rays).
Chemical Mutagens: Chemicals that alter DNA (e.g., nitrous acid, base analogs).
Biological Mutagens: Viruses or transposable elements.

Step-by-Step Guidance

Define what a mutagen is.
List examples of physical mutagens (e.g., types of radiation).
List examples of chemical mutagens (e.g., specific chemicals).
List examples of biological mutagens (e.g., viruses).

Try solving on your own before revealing the answer!

Final Answer:

Mutagens are agents that cause mutations. Examples include UV light (physical), nitrous acid (chemical), and certain viruses (biological).

Q15. What are the 3 means of genetic transfer among bacteria? What are their similarities and differences?

Background

Topic: Bacterial Genetic Exchange

This question tests your knowledge of the main mechanisms by which bacteria exchange genetic material.

Key Terms and Concepts

Transformation: Uptake of naked DNA from the environment.
Conjugation: Direct transfer of DNA via cell-to-cell contact, often involving plasmids.
Transduction: Transfer of DNA by bacteriophages (viruses).

Step-by-Step Guidance

List the three main mechanisms: transformation, conjugation, and transduction.
Briefly describe how each mechanism works.
Identify similarities (all involve transfer of genetic material) and differences (mechanism, requirements).

Try solving on your own before revealing the answer!

Final Answer:

The three means are transformation (uptake of naked DNA), conjugation (direct transfer via pilus), and transduction (transfer by bacteriophage). They differ in mechanism and requirements but all result in genetic recombination.

Q16. What is a sex pilus? What are plasmids?

Background

Topic: Bacterial Conjugation and Plasmids

This question asks you to define the structures involved in bacterial conjugation and extra-chromosomal DNA.

Key Terms and Concepts

Sex Pilus: A protein tube used to connect donor and recipient cells during conjugation.
Plasmid: Small, circular DNA molecule independent of the bacterial chromosome.

Step-by-Step Guidance

Define what a sex pilus is and its role in conjugation.
Define what a plasmid is and its significance in bacteria.
Consider how plasmids can carry genes for antibiotic resistance or other traits.

Try solving on your own before revealing the answer!

Final Answer:

A sex pilus is a structure that connects bacterial cells during conjugation. Plasmids are small, circular DNA molecules that can replicate independently and often carry beneficial genes.

Q17. What is the difference between an F-Factor and an R-Factor?

Background

Topic: Plasmids and Genetic Elements in Bacteria

This question tests your understanding of different types of plasmids and their roles in bacterial genetics.

Key Terms and Concepts

F-Factor (Fertility Factor): A plasmid that enables conjugation and transfer of genetic material.
R-Factor (Resistance Factor): A plasmid that carries genes for antibiotic resistance.

Step-by-Step Guidance

Define what an F-Factor is and its function in bacterial conjugation.
Define what an R-Factor is and its significance in antibiotic resistance.
Compare the roles of F-Factor and R-Factor in bacterial genetics.

Try solving on your own before revealing the answer!

Final Answer:

The F-Factor is a plasmid that enables conjugation, while the R-Factor is a plasmid that carries antibiotic resistance genes. Both can be transferred between bacteria, but they have different functions.