Lecture 11 Flashcards
1
Q
What do cells need to generate ATP, reduced electron carriers, and organic molecules?
A
Cells need energy, electrons, and carbon to generate ATP, reduced electron carriers, and organic molecules.
2
Q
Besides ATP, what else do cells generate during metabolism?
A
Cells also generate reduced electron carriers, such as NADH and FADH2, during metabolism.
2
Q
What is the primary energy currency of the cell?
A
ATP (adenosine triphosphate) is the primary energy currency of the cell.
2
Q
Why is carbon essential for building cells?
A
Carbon is needed to build cells because it serves as the backbone for organic molecules such as carbohydrates, lipids, proteins, and nucleic acids.
2
Q
What are chemotrophs?
A
Chemotrophs are organisms that obtain energy from either organic or inorganic molecules.
2
Q
What are some examples of organic molecules generated during metabolism?
A
Examples of organic molecules generated during metabolism include precursor metabolites, which serve as building blocks for various cellular components.
2
Q
What are phototrophs?
A
Phototrophs are organisms that obtain energy from light.
2
Q
What are the three types of energy-consuming processes that ATP provides energy for?
A
ATP provides energy for chemical work (e.g., making molecules), transport (e.g., importing nutrients), and mechanical work (e.g., flagellar rotation).
2
Q
What is the primary molecule used to conserve energy from the energy source in both chemotrophs and phototrophs?
A
ATP (adenosine triphosphate) is the primary molecule used to conserve energy from the energy source in both chemotrophs and phototrophs.
2
Q
What is the overall purpose of metabolism in cells?
A
The overall purpose of metabolism in cells is to obtain energy, electrons, and carbon from nutrients and use them to sustain cellular functions, growth, and reproduction.
2
Q
Give an example of an energy source for chemotrophs.
A
Examples of energy sources for chemotrophs include glucose (organic) and hydrogen sulfide (inorganic).
2
Q
What are precursor metabolites?
A
Precursor metabolites are simple organic molecules that serve as intermediates in metabolic pathways and are used to synthesize complex biomolecules.
2
Q
How do autotrophs obtain carbon, and what is their electron source?
A
Autotrophs obtain carbon from carbon dioxide (CO2). However, CO2 is not their electron source. They obtain energy from other sources such as sunlight (in phototrophs) or inorganic compounds (in chemotrophs).
2
Q
What are micronutrients, and what are they also known as?
A
Micronutrients, also known as trace elements, are elements required by organisms in small amounts for specific biochemical reactions.
2
Q
What are heterotrophs, and how do they obtain carbon?
A
Heterotrophs are organisms that obtain carbon from organic molecules. These organic molecules often serve as both a carbon source and a source of energy and electrons.
2
Q
Provide examples of micronutrients or trace elements.
A
Examples of micronutrients or trace elements include cobalt (Co), copper (Cu), molybdenum (Mo), manganese (Mn), zinc (Zn), and nickel (Ni). These elements also serve as cations and function as cofactors for enzymes.
2
Q
What role do macronutrients play in cellular processes?
A
Macronutrients serve as building blocks for biomolecules, stabilize cellular structures, and participate in metabolic reactions.
2
Q
Give examples of biomolecules synthesized using precursor metabolites.
A
Biomolecules such as amino acids, nucleotides, and fatty acids are synthesized using precursor metabolites.
3
Q
What are macronutrients?
A
Macronutrients are elements required by organisms in large amounts for various cellular processes.
3
Q
Besides serving as building blocks, what other function do elements like potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe) serve in cells?
A
Elements like potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe) act as cations and serve as cofactors for enzymes, stabilize cellular structures (e.g., cell wall), and are involved in various cellular processes.
3
Q
Name the six macronutrients essential for life.
A
The six macronutrients essential for life are carbon (C), oxygen (O), hydrogen (H), nitrogen (N), sulfur (S), and phosphorus (P).
3
Q
Name two processes that require reducing power (electrons) in cells.
A
Anabolic reactions (e.g., making building blocks) and ATP production through the electron transport chain require reducing power (electrons) in cells.
3
Q
How are organisms classified based on their electron source?
A
Organisms are classified into organotrophs and lithotrophs based on their electron source.
3
Q
What is the role of reducing power (electrons) in cellular processes?
A
Reducing power (electrons) is essential for anabolic reactions, such as synthesizing building blocks, and for producing ATP through the electron transport chain.
3
What are organotrophs, and what is their electron source?
Organotrophs are organisms that obtain electrons from reduced organic molecules.
3
Name the three main metabolic pathways through which bacteria can generate ATP.
The three main metabolic pathways are aerobic respiration, anaerobic respiration, and fermentation.
3
What are lithotrophs, and what is their electron source?
Lithotrophs are organisms that obtain electrons from reduced inorganic molecules.
3
How do chemoorganoheterotrophs make ATP?
Chemoorganoheterotrophs make ATP by oxidizing organic molecules.
3
What is the primary metabolic strategy employed by most bacteria residing on the human body?
Most bacteria on the human body are chemoorganoheterotrophs.
3
From where do chemoorganoheterotrophs obtain energy, carbon, and electrons?
Chemoorganoheterotrophs obtain energy, carbon, and electrons from organic molecules.
3
What do organisms do with electrons obtained from organic or inorganic molecules?
Organisms funnel electrons to electron carriers such as NAD+ and FAD, which are then reduced to form NADH and FADH2, respectively. These reduced forms serve as carriers of electrons in various cellular processes, including ATP production.
3
How do bacteria utilizing aerobic respiration generate ATP?
Bacteria utilizing aerobic respiration make ATP through the electron transport chain in the presence of oxygen.
4
What distinguishes anaerobic respiration from aerobic respiration in bacteria?
Anaerobic respiration occurs in the absence of oxygen, whereas aerobic respiration requires oxygen.
4
What is fermentation, and how do bacteria make ATP through this process?
Fermentation is an anaerobic process where bacteria generate ATP by converting organic molecules into simpler compounds without using an electron transport chain.
5
What happens during aerobic respiration?
During aerobic respiration, organisms utilize oxygen to break down organic molecules and generate energy in the form of ATP.
5
What occurs during glycolysis in aerobic respiration?
In glycolysis, glucose is oxidized to produce pyruvate. ATP and NADH are generated during this process.
5
How is energy conserved during aerobic respiration?
Energy is conserved as ATP during aerobic respiration.
5
What is the electron transport chain (ETC), and what is its role in aerobic respiration?
The electron transport chain (ETC) is a series of protein complexes located in the inner mitochondrial membrane (in eukaryotes) or the plasma membrane (in prokaryotes). It utilizes electrons from NADH and FADH2 to generate ATP through oxidative phosphorylation.
5
What is the role of the tricarboxylic acid (TCA) cycle in aerobic respiration?
During the TCA cycle, acetyl-CoA is further oxidized to produce carbon dioxide (CO2). ATP, NADH, and FADH2 are also generated.
6
What is the Embden-Meyerhof pathway?
The Embden-Meyerhof pathway, also known as glycolysis, is the most common pathway for glucose metabolism. It occurs in both prokaryotes and eukaryotes, including animals. This pathway converts glucose into pyruvate, generating ATP and NADH.
6
How do electrons move through the electron transport chain?
Electrons move through the electron transport chain, where they are passed from one protein complex to another, ultimately generating a proton gradient that drives ATP synthesis.
6
What is the final electron acceptor in aerobic respiration?
The final electron acceptor in aerobic respiration is oxygen, which combines with protons to form water.
6
Describe the Entner-Doudoroff pathway.
The Entner-Doudoroff pathway is an alternative glucose metabolism pathway found in some bacteria. It converts glucose into glyceraldehyde 3-phosphate (G3P) and pyruvate, producing NADPH instead of NADH. G3P can then enter the Embden-Meyerhof pathway.
6
What is the Pentose Phosphate Pathway (PPP) primarily used for?
The Pentose Phosphate Pathway (PPP), also known as the hexose monophosphate shunt, is primarily used for biosynthesis. It generates NADPH and precursor metabolites for nucleotides and amino acids.
6
What are the main products of the Embden-Meyerhof pathway?
The Embden-Meyerhof pathway (glycolysis) produces pyruvate, ATP, and NADH.
7
What are the main products of the Entner-Doudoroff pathway?
The Entner-Doudoroff pathway produces glyceraldehyde 3-phosphate (G3P), pyruvate, and NADPH.
7
What are the main products of the Pentose Phosphate Pathway (PPP)?
The main products of the Pentose Phosphate Pathway (PPP) are NADPH and precursor metabolites for nucleotides and amino acids.
7
What is the function of the pyruvate dehydrogenase complex?
The pyruvate dehydrogenase complex converts pyruvate into acetyl-CoA, which is a key molecule that enters the tricarboxylic acid (TCA) cycle.
8
What molecule enters the tricarboxylic acid (TCA) cycle?
Acetyl-CoA enters the tricarboxylic acid (TCA) cycle.
9
What happens to acetyl-CoA in the TCA cycle?
In the TCA cycle, acetyl-CoA is oxidized to produce carbon dioxide (CO2). This process generates GTP (which can be converted into ATP), NADH, and FADH2.
9
What are the main products of the TCA cycle?
The main products of the TCA cycle include GTP (which can be converted into ATP), NADH, FADH2, and carbon dioxide (CO2).
10
How are some intermediates of the TCA cycle utilized?
Some intermediates of the TCA cycle are used as precursor metabolites for the synthesis of various biomolecules, including amino acids, nucleotides, and lipids.
10
How are electrons from NADH and FADH2 utilized in the electron transport chain (ETC)?
Electrons from NADH and FADH2 are used in the electron transport chain (ETC) to generate more ATP through oxidative phosphorylation.
11
What are the membrane-bound electron carriers in the electron transport chain (ETC)?
The membrane-bound electron carriers in the electron transport chain (ETC) include ubiquinone (coenzyme Q) and cytochromes, which are proteins with heme co-factors.
11
How do the electron carriers in the electron transport chain (ETC) function?
Each carrier in the electron transport chain (ETC) is reduced by the preceding carrier and oxidized by the following carrier, creating a series of redox reactions.
11
What is the role of ubiquinone (coenzyme Q) in the electron transport chain (ETC)?
Ubiquinone (coenzyme Q) is a mobile electron carrier that shuttles electrons between complex I and complex III of the electron transport chain (ETC).
11
What are cytochromes, and what is their function in the electron transport chain (ETC)?
Cytochromes are proteins with heme co-factors that are involved in electron transport in the electron transport chain (ETC). They play a crucial role in transferring electrons between complexes within the ETC.
12
How does the electron transport chain (ETC) generate ATP?
The electron transport chain (ETC) generates ATP through oxidative phosphorylation, where the energy released from electron transfer is used to pump protons across a membrane, creating a proton gradient. This gradient drives the synthesis of ATP by ATP synthase.
13
What is the initial electron carrier in the electron transport chain (ETC) of E. coli?
The initial electron carrier in the electron transport chain (ETC) of E. coli is NADH.
14
What molecule accepts electrons from NADH in the electron transport chain (ETC) of E. coli?
In the electron transport chain (ETC) of E. coli, electrons from NADH are transferred to ubiquinone (Q).
15
What is the role of cytochromes in the electron transport chain (ETC) of E. coli?
In the electron transport chain (ETC) of E. coli, electrons pass through a series of cytochromes, such as b562 and o.
16
What is the terminal electron acceptor in aerobic respiration in E. coli?
In aerobic respiration in E. coli, the terminal electron acceptor is oxygen (O2).
17
What is the consequence of transferring electrons to oxygen in aerobic respiration in E. coli?
Transferring electrons to oxygen in aerobic respiration in E. coli drives the transport of protons to the periplasm, generating a proton-motive force (PMF).
18
What is the proton-motive force (PMF) used for in E. coli?
The proton-motive force (PMF) generated by the electron transport chain (ETC) in E. coli is used to drive ATP synthesis and perform other energy-requiring processes.
19
What is the proton motive force (PMF)?
The proton motive force (PMF) is the potential energy stored in the form of a proton gradient across a membrane.
20
Describe the charge distribution across the membrane in relation to the cytoplasm.
In relation to the cytoplasm, the cytoplasmic side of the membrane is relatively alkaline and negatively charged.
21
What type of work do protons perform as they flow down their concentration gradient?
As protons flow down their concentration gradient, they perform work, such as driving the synthesis of ATP through ATP synthase.
21
How do protons flow in relation to the proton gradient?
Protons flow down their concentration gradient from areas of high concentration (outside the cell or in the periplasm) to areas of low concentration (inside the cell or in the cytoplasm).
22
Describe the role of ATP synthase in relation to the proton motive force (PMF).
ATP synthase is an enzyme complex that utilizes the energy of the proton motive force (PMF) to synthesize ATP from ADP and inorganic phosphate (Pi). Protons flow through ATP synthase from the outside of the membrane to the inside, and this flow of protons drives the rotation of the ATP synthase complex, leading to the synthesis of ATP.
23
What metabolic pathways are involved in anaerobic respiration?
Similar to aerobic respiration, anaerobic respiration involves glycolysis, the tricarboxylic acid (TCA) cycle, and the electron transport chain (ETC).
24
What are the main products of anaerobic respiration?
The main products of anaerobic respiration include ATP, NADH, and FADH2.
25
How does anaerobic respiration differ from aerobic respiration regarding the terminal electron acceptor?
In anaerobic respiration, the terminal electron acceptor is not oxygen (O2). Instead, it can be substances such as nitrate, sulfate, carbon dioxide (CO2), or other molecules depending on the organism.
26
How does the reduction of alternative electron acceptors in anaerobic respiration affect the energy yield compared to aerobic respiration?
The reduction of alternative electron acceptors in anaerobic respiration typically results in a lower energy yield compared to aerobic respiration, as the redox reactions are less energetically favorable.
26
Provide an example of anaerobic respiration involving nitrate as the terminal electron acceptor.
An example of anaerobic respiration involving nitrate as the terminal electron acceptor is seen in Paracoccus denitrificans, which reduces nitrate (NO3-) to nitrogen gas (N2).
27
What is fermentation?
Fermentation is a metabolic pathway in which a substrate is partially oxidized, typically through glycolysis, to produce ATP without the involvement of an electron transport chain (ETC) or exogenous electron acceptors.
28
What is the main purpose of fermentation?
The main purpose of fermentation is to generate ATP in the absence of oxygen or alternative electron acceptors.
29
How does fermentation differ from aerobic or anaerobic respiration?
Fermentation differs from aerobic or anaerobic respiration in that it does not involve an electron transport chain (ETC) or the use of exogenous electron acceptors.
30
What happens to NADH in fermentation?
In fermentation, NADH generated during glycolysis is used to reduce pyruvate or pyruvate derivatives, regenerating NAD+.
31
What is the consequence of regenerating NAD+ in fermentation?
Regenerating NAD+ in fermentation allows glycolysis to continue, ensuring the continued production of ATP through substrate-level phosphorylation.
31
Give an example of a product of fermentation.
An example of a product of fermentation is lactic acid in lactic acid fermentation or ethanol and carbon dioxide in alcoholic fermentation. These are the byproducts of the partial oxidation of substrates such as glucose through glycolysis in the absence of oxygen or an electron transport chain.
32
What is the metabolic classification of humans and many bacteria?
Humans and many bacteria are classified as chemoheterotrophs, meaning they obtain both energy and carbon from organic molecules.
33
Where are many chemoheterotrophic bacteria found?
Many chemoheterotrophic bacteria are found in the human microbiome.
34
How do chemoheterotrophic bacteria utilize nutrients from humans?
Chemoheterotrophic bacteria utilize nutrients from humans, including food consumed by the host, as a source of energy and carbon.
34
What difficulty arises in selectively targeting bacterial metabolic enzymes with antibiotics?
Selective targeting of bacterial metabolic enzymes with antibiotics is difficult due to the similarity of metabolic pathways between bacteria and their host organisms, such as humans. This similarity makes it challenging to develop antibiotics that selectively target bacterial enzymes without affecting host enzymes.
35
What are some challenges associated with targeting bacterial metabolism with antibiotics?
Challenges associated with targeting bacterial metabolism with antibiotics include the potential for toxicity to host cells due to similarities in metabolic pathways, as well as the development of antibiotic resistance by bacteria.
36
Why is the difficulty in selectively targeting bacterial metabolic enzymes a concern in antibiotic therapy?
The difficulty in selectively targeting bacterial metabolic enzymes is a concern in antibiotic therapy because it limits the effectiveness of antibiotics while increasing the risk of side effects and the development of antibiotic resistance.
37
What is the role of tetrahydrofolate as a cofactor?
Tetrahydrofolate serves as a cofactor in various metabolic pathways, including the synthesis of purines and pyrimidines (components of DNA and RNA) and the conversion of methionine (an amino acid).
38
What organisms produce tetrahydrofolate?
Bacteria synthesize tetrahydrofolate as part of their metabolic processes.
39
How do humans obtain folates, including tetrahydrofolate?
Humans acquire folates, including tetrahydrofolate, from their diet, primarily through the consumption of foods rich in vitamin B9.
40
What are the essential roles of tetrahydrofolate in nucleotide and amino acid metabolism?
Tetrahydrofolate is essential for the synthesis of purines and pyrimidines, which are building blocks of DNA and RNA, as well as for the conversion of methionine, an amino acid.
40
Why are biosynthetic enzymes involved in tetrahydrofolate synthesis considered antibiotic targets?
Biosynthetic enzymes involved in tetrahydrofolate synthesis are considered antibiotic targets because disrupting the synthesis of tetrahydrofolate can impair bacterial growth and proliferation, making these enzymes potential targets for antibiotic therapy.
41
How do sulfa drugs, such as sulfamethoxazole (SMX), exert their antimicrobial effects?
Sulfa drugs, like sulfamethoxazole (SMX), inhibit the enzyme dihydropteroate synthase by resembling p-aminobenzoic acid, a substrate for the enzyme. This inhibition disrupts the synthesis of tetrahydrofolate, an essential precursor for nucleotide synthesis, ultimately inhibiting bacterial growth.
42
What is the mechanism of action of trimethoprim in antimicrobial therapy?
Trimethoprim inhibits the enzyme dihydrofolate reductase by resembling dihydrofolic acid, a substrate for the enzyme. This inhibition blocks the production of tetrahydrofolate, disrupting nucleotide synthesis and inhibiting bacterial growth.
43
How do sulfa drugs and trimethoprim work together synergistically?
Sulfa drugs and trimethoprim can be combined in antimicrobial therapy to achieve synergistic effects. Sulfa drugs inhibit an earlier step in tetrahydrofolate synthesis (dihydropteroate synthase), while trimethoprim inhibits a later step (dihydrofolate reductase). Together, they block tetrahydrofolate production at two different points, leading to enhanced inhibition of bacterial growth.
44
What type of inhibitors are sulfa drugs and trimethoprim?
Sulfa drugs and trimethoprim are both competitive inhibitors, as they compete with the natural substrates of their target enzymes for binding sites.
45
Why is the collection of nutrients from the environment essential for microbial growth?
Microbes must collect nutrients from their environment to sustain their growth and metabolism, as these nutrients serve as essential building blocks for cellular processes.
46
What is a common challenge faced by microbes in collecting nutrients from their environment?
A common challenge faced by microbes is the limited abundance of nutrients in their environment and the competition with other organisms for these resources.
46
How does the cell envelope of microbes contribute to nutrient uptake?
The cell envelope of microbes serves as a barrier that prevents the entry of hydrophilic nutrients into the cell, necessitating the presence of specialized transport systems for nutrient uptake.
47
Why are transporters necessary for nutrient uptake in microbes?
Transporters are necessary for nutrient uptake in microbes because they facilitate the movement of essential nutrients across the cell envelope, allowing microbes to acquire the necessary materials for growth and survival in their environment.
48
What is the characteristic of substances transported via passive diffusion?
Substances transported via passive diffusion move non-concentratively, meaning they do not require the assistance of transport proteins and simply diffuse across the membrane according to their concentration gradient.
49
What type of nutrients typically require transporters for uptake by microbes?
Hydrophilic nutrients, which cannot pass through the hydrophobic cell envelope of microbes, typically require transporters for uptake by microbes. These transporters facilitate the movement of nutrients across the cell membrane to ensure access to essential nutrients for cellular processes.
50
What is passive diffusion?
Passive diffusion is a process in which a substance diffuses across the cytoplasmic membrane of a cell without the input of energy. It occurs when the substance moves down its concentration gradient, from an area of higher concentration to an area of lower concentration.
51
Why is passive diffusion not very useful for nutrient uptake by microbes?
Passive diffusion is not very useful for nutrient uptake by microbes because it relies on concentration gradients, and the concentration of essential nutrients is usually lower outside the cell compared to inside. Therefore, passive diffusion does not efficiently facilitate nutrient uptake.
52
What is the main limitation of passive diffusion in nutrient uptake?
The main limitation of passive diffusion in nutrient uptake is its dependence on concentration gradients. Since essential nutrients are often more concentrated inside the cell, passive diffusion does not effectively facilitate their uptake from the environment.
53
How do transport proteins facilitate the movement of substances in facilitated diffusion?
Transport proteins facilitate the movement of substances in facilitated diffusion by undergoing a conformational change upon binding with the transported molecule. This change allows the molecule to be transported across the membrane.
53
What are energy-independent transport mechanisms?
Energy-independent transport mechanisms are processes that do not require the input of energy for the movement of substances across cellular membranes. Passive diffusion is one example of an energy-independent transport mechanism.
54
What is facilitated diffusion?
Facilitated diffusion is a process in which the passage of substances through a membrane is assisted by transport proteins.
55
Does facilitated diffusion require energy input?
No, facilitated diffusion does not require energy input. It is an energy-independent process.
56
What is the limitation of facilitated diffusion in terms of nutrient concentration?
Facilitated diffusion cannot concentrate nutrients on its own. It transports molecules down their concentration gradient, from areas of higher concentration to areas of lower concentration.
57
What is the role of transport proteins in facilitated diffusion?
Transport proteins in facilitated diffusion serve as channels or carriers that allow specific molecules to move across the membrane. They facilitate the movement of molecules that are too large, polar, or charged to pass through the lipid bilayer via passive diffusion.
58
What is active transport?
Active transport is a process in which substances are transported across a membrane against their concentration gradient, requiring energy input.
59
What is the primary source of energy for active transport?
The primary source of energy for active transport is ATP hydrolysis. ATP is converted to ADP and inorganic phosphate, releasing energy that is used to drive the transport process.
60
What are ATP-binding cassette (ABC) transporters?
ATP-binding cassette (ABC) transporters are a common type of primary active transporters found in bacteria. They use energy from ATP hydrolysis to transport various substances across the cell membrane.
61
What is the function of importers and exporters in active transport?
Importers are ABC transporters used by bacteria to import sugars, amino acids, vitamins, and other essential nutrients into the cell. Exporters, on the other hand, expel substances such as toxins, antibiotics, and metabolic waste products from the cell.
62
How do ABC transporters couple ATP hydrolysis to substrate transport?
ABC transporters couple ATP hydrolysis to substrate transport by utilizing the energy released from ATP hydrolysis to undergo conformational changes. These conformational changes enable the transporter to alternately bind and release substrates on either side of the membrane, facilitating their transport against the concentration gradient.
63
What role do solute-binding proteins (SBPs) play in ABC transporters?
Solute-binding proteins (SBPs) in ABC transporters are responsible for delivering specific substrates to the transporter for transport across the membrane.
64
Where are solute-binding proteins (SBPs) located in Gram-negative bacteria?
In Gram-negative bacteria, solute-binding proteins (SBPs) are located in the periplasmic space, where they bind to specific substrates and deliver them to the ABC transporter.
65
Where are solute-binding proteins (SBPs) located in Gram-positive bacteria?
In Gram-positive bacteria, solute-binding proteins (SBPs) can be either lipoproteins or associated with the peptidoglycan layer of the cell wall.
66
What is the function of solute-binding proteins (SBPs) in ABC transporters?
The function of solute-binding proteins (SBPs) in ABC transporters is to recognize and bind specific substrates with high affinity, facilitating their delivery to the transporter for transport across the membrane.
67
How do solute-binding proteins (SBPs) contribute to the efficiency and specificity of ABC transporters?
Solute-binding proteins (SBPs) contribute to the efficiency and specificity of ABC transporters by selectively binding to specific substrates and delivering them to the transporter. This ensures that only the desired substrates are transported across the membrane, enhancing the efficiency and specificity of the transport process.
68
What is secondary active transport?
Secondary active transport is a process in which the transport of a substance against its concentration gradient is powered by the potential energy stored in an ion gradient across the cell membrane.
69
How is the ion gradient generated in secondary active transport?
The ion gradient used in secondary active transport can be generated in several ways, including through the action of the electron transport chain, V-type ATPases, or the energy derived from ATP hydrolysis, which creates a gradient of H+ or Na+ ions.
70
What is the role of ion gradients in secondary active transport?
Ion gradients serve as a source of potential energy in secondary active transport. The energy stored in the gradient is utilized to transport substances against their concentration gradients.
71
How is the ion gradient used to transport substances against their concentration gradients?
In secondary active transport, the potential energy stored in the ion gradient is harnessed by transport proteins to move substances against their concentration gradients. This process typically involves the cotransport of ions and the desired substance across the membrane.
72
What is the function of the H+/Na+ antiporter?
The H+/Na+ antiporter is a type of secondary active transporter that utilizes the electrochemical gradient of H+ ions to drive the uphill transport of Na+ ions across the cell membrane.
72
Give an example of an ion gradient utilized in secondary active transport.
An example of an ion gradient utilized in secondary active transport is the H+/Na+ antiporter, which uses the energy from the electrochemical gradient of H+ or Na+ ions to transport other substances against their concentration gradients.
73
How is the electrochemical gradient of H+ ions generated?
The electrochemical gradient of H+ ions is generated by the electron transport chain (ETC), which pumps H+ ions across the membrane, creating a proton motive force (PMF).
74
Describe the mechanism of the H+/Na+ antiporter.
In the H+/Na+ antiporter mechanism, the transport of H+ ions down their electrochemical gradient through the antiporter powers the export of Na+ ions up their concentration gradient across the membrane.
74
How does the H+/Na+ antiporter contribute to secondary active transport?
The H+/Na+ antiporter contributes to secondary active transport by utilizing the energy stored in the electrochemical gradient of H+ ions to transport Na+ ions against their concentration gradient. This process is an example of cotransport, where the movement of one ion down its gradient drives the movement of another ion against its gradient.
75
What is an example of a transporter that could be powered by the new Na+ gradient generated by the H+/Na+ antiporter?
An example of a transporter that could be powered by the new Na+ gradient generated by the H+/Na+ antiporter is a Na+/nutrient symporter, which transports nutrients into the cell using the energy of the Na+ gradient. This process represents another instance of secondary active transport, where the movement of Na+ ions down their gradient drives the uptake of nutrients into the cell.
76
What is group translocation?
Group translocation is a type of active transport in which the transported substrate is chemically modified during transport across the membrane.
77
What is the sugar phosphotransferase system (PTS)?
The sugar phosphotransferase system (PTS) is a group translocation system used by bacteria to transport sugars across the cytoplasmic membrane.
78
What happens to the sugar during transport by the PTS (phosphotransferase system)?
During transport by the PTS, the transported sugar is phosphorylated. This phosphorylation occurs as part of the transport process.
79
How does the PTS function as a phosphorelay?
The PTS functions as a phosphorelay by transferring a phosphate group from phosphoenolpyruvate (PEP) to PTS components, and then to the transported sugar. This sequential transfer of phosphate groups allows for the phosphorylation of the sugar during transport.
80
What is the source of the phosphate group used in the PTS?
The phosphate group used in the PTS is derived from phosphoenolpyruvate (PEP), a high-energy phosphate compound involved in glycolysis. The phosphate group is transferred from PEP to the PTS components and ultimately to the transported sugar during the transport process.
81
What are porins in the outer membrane of Gram-negative bacteria?
Porins are β-barrel proteins located in the outer membrane of Gram-negative bacteria. They form channels that allow solutes to pass through the outer membrane and reach the periplasm.
82
What is the function of porins in the outer membrane?
Porins facilitate the diffusion of solutes across the outer membrane of Gram-negative bacteria. They create channels through which solutes can pass, allowing for the exchange of molecules between the external environment and the periplasm.
82
What determines which substrates can pass through porins?
The size of the channel in porins determines which substrates can pass through. General porins allow molecules of a certain size or smaller to diffuse through, while substrate-specific porins have specific binding sites that attract particular molecules.
82
Can porins directly concentrate substrates?
No, porins cannot directly concentrate substrates. They facilitate the diffusion of molecules across the outer membrane but do not actively concentrate substrates. Their role is primarily to allow molecules to passively diffuse into or out of the bacterial cell.
82
How do general porins differ from substrate-specific porins?
General porins have channels of varying sizes that determine which substrates can enter. They allow for the passive diffusion of a wide range of molecules. In contrast, substrate-specific porins have substrate-binding sites that attract specific molecules to the porin, and their channel size impacts the selectivity of substrates they transport.
82
How do mutations in porin genes contribute to antibiotic resistance?
Mutations in porin genes can confer antibiotic resistance by altering the number or structure of porins. These mutations may reduce the ability of antibiotics to penetrate the bacterial cell, reducing their effectiveness and contributing to antibiotic resistance.
82
How do TonB-dependent receptors transport substrates?
TonB-dependent receptors transport substrates by a mechanism involving energy from the proton motive force (PMF). When a substrate binds to the receptor, it exposes a TonB box. The TonB protein then binds to the TonB box and uses energy from the PMF to pull out the plug, allowing the substrate to be transported through the channel.
82
How does porin loss affect nutrient uptake?
Porin loss decreases nutrient uptake by reducing the ability of molecules to pass through the outer membrane. This can lead to nutrient limitation and affect the growth and survival of bacteria.
82
What are TonB-dependent receptors?
TonB-dependent receptors are active transporters located in the outer membrane of Gram-negative bacteria. They facilitate the uptake of specific substrates into the cell.
82
What role does the TonB protein play in the transport process?
The TonB protein is essential for the transport process mediated by TonB-dependent receptors. It binds to the TonB box exposed when a substrate binds to the receptor and uses energy from the proton motive force (PMF) to remove the plug blocking the channel, allowing the substrate to be transported into the cell.
82
What are the consequences of impaired membrane structure due to porin loss?
Impaired membrane structure due to porin loss can lead to increased membrane permeability and susceptibility to environmental stresses. It may also affect the integrity of the cell envelope and compromise bacterial survival.
82
What is the structure of TonB-dependent receptors?
TonB-dependent receptors are β-barrel proteins with a channel that is typically blocked by a plug. This plug prevents the passive diffusion of substrates through the channel.
82
What is the fitness cost associated with porin loss?
Porin loss exerts a fitness cost on bacteria, as it decreases nutrient uptake and impairs membrane structure. While porin loss may confer resistance to antibiotics, it can also reduce the overall fitness and viability of the bacterial population.
82
What provides the energy for substrate transport by TonB-dependent receptors?
The energy for substrate transport by TonB-dependent receptors is provided by the proton motive force (PMF), which is generated by the electron transport chain. The energy from the PMF is used by the TonB protein to remove the plug blocking the channel, enabling substrate transport.
82
How do bacteria scavenge iron from their environment?
Bacteria scavenge iron from their environment using siderophores, which are small molecules that bind very tightly to ferric iron (Fe3+). Siderophores help bacteria acquire iron even when it is present in low concentrations.
82
How can the lack of specificity of porins be detrimental?
The lack of specificity of porins can be detrimental because it allows various molecules, including antibiotics, to pass through. This can lead to antibiotic resistance, as mutations in porin genes can confer resistance by altering the number or structure of porins.
82
Why is ferric iron (Fe3+) limited in availability to bacteria?
Ferric iron (Fe3+) is very insoluble and forms complexes that are not readily available to bacteria. As a result, its availability in the environment is limited, posing a challenge for bacterial growth and survival.
82
Why do bacteria need iron?
Bacteria need iron for various essential functions, including as a component of cytochromes involved in the electron transport chain and as a cofactor for enzymes.
83
What are siderophores?
Siderophores are small molecules produced by bacteria that have a high affinity for ferric iron (Fe3+). They act as iron chelators, binding tightly to ferric iron and solubilizing it, making it available for uptake by the bacteria.
83
Can you provide an example of a siderophore produced by bacteria?
One example of a siderophore produced by bacteria is enterobactin. Enterobactin is secreted into the environment by bacteria and competes for ferric iron, facilitating its uptake by the bacteria for use in essential metabolic processes.
83
What is the final destination of Fe3+ once it is scavenged by siderophores?
The final destination of Fe3+ once it is scavenged by siderophores is the bacterial cytoplasm, where it is utilized for various metabolic processes.
84
Describe the pathway of Fe3+ uptake by bacteria using siderophores.
The pathway of Fe3+ uptake by bacteria using siderophores involves several steps:
1. Secreted siderophores bind to Fe3+ in the environment.
2. The siderophore-Fe3+ complex is transported to the periplasmic space by TonB-dependent receptors.
3. In the periplasm, the siderophore-Fe3+ complex binds to a periplasmic solute-binding protein (SBP).
4. The SBP delivers the siderophore-Fe3+ complex to an ATP-binding cassette (ABC) transporter located in the cytoplasmic membrane.
5. The siderophore-Fe3+ complex is transported across the cytoplasmic membrane into the bacterial cytoplasm, where Fe3+ is released and made available for metabolic processes.
85
Why is the uptake of Fe3+ by bacteria through siderophores considered a highly regulated process?
The uptake of Fe3+ by bacteria through siderophores is considered a highly regulated process because iron is essential for bacterial growth and survival, but its availability in the environment is often limited. Bacteria must tightly regulate the expression and activity of siderophore biosynthesis and uptake pathways to ensure efficient iron acquisition while avoiding toxicity from excess iron.
85
How is the siderophore-Fe3+ complex transported across the cytoplasmic membrane?
The siderophore-Fe3+ complex is transported across the cytoplasmic membrane by an ATP-binding cassette (ABC) transporter. This transporter uses energy from ATP hydrolysis to move the siderophore-Fe3+ complex into the bacterial cytoplasm.
85
What is the role of TonB-dependent receptors in the Fe3+ uptake pathway?
TonB-dependent receptors facilitate the transport of the siderophore-Fe3+ complex from the outer membrane to the periplasmic space. They use energy from the proton motive force (PMF) to pull the siderophore-Fe3+ complex into the periplasmic space through the outer membrane.
