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Questions and Answers
What is a primary reason some cells cannot perform respiration?
Which type of fermentation only produces lactic acid?
How many ATP molecules are produced during glycolysis alone in fermentation?
Which of the following roles does lactic acid bacteria (LAB) NOT play?
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What kind of fermentation produces lactic acid, ethanol, acetic acid, and CO2?
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What is a characteristic of prokaryotes that cannot respire at all?
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Which of the following reactions represents alcohol fermentation?
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What conditions enable facultative prokaryotes to switch to respiration?
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Study Notes
Respiration Limitations
- Cells may struggle with respiration due to a lack of the required inorganic final electron acceptors.
- Genetic limitations can prevent cells from synthesizing essential complexes and electron carriers needed for the electron transport system.
- Cells may also lack genes for enzymes necessary for the Krebs cycle, affecting their respiratory capabilities.
- The inability to utilize an electron acceptor can depend on environmental conditions; genetic limitations are permanent.
Prokaryotic Respiration
- Some prokaryotes, such as Streptococcus, are incapable of respiration even in the presence of oxygen.
- Facultative prokaryotes can switch to respiration when conditions permit, allowing for increased ATP production from glucose.
Glycolysis and NADH Recycling
- In the absence of respiration, NADH must be converted back to NAD+ to sustain glycolysis, which is the sole method for ATP production under these circumstances.
Fermentation as an Alternative
- Fermentation uses organic molecules like pyruvate as final electron acceptors, bypassing the electron transport system.
- This process yields only up to 2 ATP per glucose through glycolysis, making it less efficient than respiration.
Microbial Fermentation Applications
- Fermentation is significant in producing food, pharmaceuticals, and for microbial identification.
Lactic Acid Fermentation
- Occurs in low-oxygen environments and involves organisms like yogurt bacteria and human muscle cells.
- Chemical Reaction: Pyruvate + NADH ↔ Lactic Acid + NAD+.
Lactic Acid Bacteria (LAB)
- Includes species like Lactobacillus, Leuconostoc, and Streptococcus, crucial for yogurt and cheese production by coagulating milk proteins through acidity.
- Two types of fermentation:
- Homolactic Fermentation: Produces only lactic acid (e.g., Lactobacillus delbrueckii).
- Heterolactic Fermentation: Generates lactic acid, ethanol, acetic acid, and CO2 (e.g., Leuconostoc mesenteroides used in pickles and sauerkraut).
Medical Importance of LAB
- LAB help inhibit pathogen growth by creating a low pH environment in the body.
- Crucial for maintaining vaginal health, as imbalances can lead to yeast infections.
- LAB are essential components of probiotics, supporting gastrointestinal health.
Alcohol Fermentation
- This process converts pyruvate into ethanol.
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Chemical Reactions:
- Pyruvate → Acetaldehyde + CO2 (via pyruvate decarboxylase).
- Acetaldehyde + NADH → Ethanol + NAD+ (via alcohol dehydrogenase).
- Alcohol fermentation is utilized in the production of alcoholic beverages and baking, with CO2 contributing to the rise of bread.
- It is also important for biofuel generation from plant materials.
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Description
This quiz explores the critical limitations that cells face in performing respiration. It focuses on the lack of necessary electron acceptors and genetic barriers that hinder cellular respiration processes. Test your understanding of these concepts and their implications for cellular energy production.