Flashcards in Chapter 5 flashcards Deck (190):
The collection of controlled biochemical reactions that take place w/in the microbe
Metabolic processes are guided by eight elementary statements
1) Every cell acquires nutrients (the chemicals necessary for metabolism)
2) Metabolism requires energy from light or from the catabolism of acquired nutrients
3) Energy is stored in the chemical bonds of adenosine triphosphate (ATP)
4) Using enzymes, cells catabolize nutrient molecules to form elementary building blocks called precursor metabolites
5) Using precursor metabolites, energy from ATP, & other enzymes, cells construct larger building blocks in anabolic reactions
6) Cells use enzymes & additional energy from ATP to anabolically link building blocks together to form macromolecules in polymerization reactions
7) Cells grow by assembling macromolecules into their cellular structures such as ribosomes, membranes, and cell walls
8) Cells typically reproduce once they have doubled in size
What is the first step of metabolism
The active & passive transport of nutrients into cells
Involves the transfer of electrons between molecules
What are organic catalysts?
Enzymes, they make metabolism possible
Metabolism can be divided into two major classes of reactions
Catabolism, and anabolism. A series of such reactions is called a pathway
Cells have catabolic pathways which?
Break larger molecules into smaller products
Cells have anabolic pathways which?
Synthesis large molecules from the smaller products of catabolism
When catabolic pathways break down large molecules they?
Release energy, that is catabolic pathways are exergonic. Cells store some of this released energy in the bonds of ATP, though much of the energy is lost as heat. Another result of the breakdown of large molecules by catabolic pathways is the production of numerous smaller molecules, some of which are precursor metabolites of anabolism
Some organisms, such as Escherichia coli, can synthesis everything in their cells just from?
Precurser metabolites; other organisms must acquire some anabolic building blocks from outside their cells as nutrients
Catabolic pathways, but not necessarily individual catabolic reactions, produce?
ATP or metabolites or both
The breakdown of lipids into glycerol and fatty acids is an example of
Because building anything requires energy, anabolic pathways are?
Endergonic, that is they require more energy than they release. The energy required for anabolic pathways usually comes from ATP molecules produced during catabolism
The synthesis of lipids for cell membranes from glycerol & fatty acids is an example of?
An anabolic pathway
A cell's metabolism involves both catabolic pathways that _____ _____ macromolecules to supply molecular building blocks & energy in the form of ATP, and anabolic pathways that use the _______ _______ and ATP to synthesis macromolecules needed for growth and reproduction.
What is an electron donor
A molecule that donates an electron
What is an electron acceptor
A molecule that accepts an electron
Many metabolic reactions involve the transfer of electrons from an?
Electron donor to an electron acceptor. These are called oxidation-reduction reactions or redox reactions
An electron acceptor is said to be?
Reduced. They are reduced because their gain in electrons reduces their overall electrical charge (they are more negatively charged)
Molecules that lose electrons are said to be
Oxidized because frequently their electrons are donated to oxygen atoms.
An acronym to help you remember oxidation-reduction reactions in OIL RIG
Reduction & oxidation reactions always happen simultaneously because?
Every electron donated by one chemical is accepted by another chemical
During oxidation-reduction reactions, a chemical may be reduced by?
Gaining either a simple electron or an electron that is part of a hydrogen atom (composed of one proton and one electron)
A molecule may be oxidized in one of three ways
1) By losing a simple electron
2) By losing a hydrogen atom
3) By gaining an oxygen atom
Biological oxidations often involve the loss of hydrogen atoms; such reactions are also called?
Electrons rarely exist freely in cytoplasm; instead, they orbit atomic nuclei. Therefore, cells use electron carrier molecules to?
Carry electrons (often in hydrogen atoms) from one location in a cell to another
Three important electron carrier molecules, which are derived from vitamins, are?
1) nicotinamide adenine dinucleotide (NAD+)
2) nicotinamide adenine dinucleotide phosphate (NADP+)
3) flavin adenine dinucleotide (FAD)
Cells use each of the three electron carrier molecules (NAD, NADP, & FAD) in specific metabolic pathways to carry pairs of electrons. one of the electrons carried by either NAD+ or NADP+ is part of a ______ atom, forming?
Hydrogen atom forming NADH or NADPH.
FAD carries 2 electrons as hydrogen atoms (FADH2).
Many metabolic pathways, including those that synthesis ATP, require such electron carrier molecules
Nutrients contain energy, but that energy is spread throughout their chemical bonds & generally is not concentrated enough for use in anabolic reactions. How do we get this energy?
During catabolism, organisms release energy from nutrients that can be concentrated & stored in high-energy phosphate bonds of molecules such as ATP. This happens by a general process called phosphorylation, in which inorganic phosphate is added to a substrate. For example cells phosphorylate adenosine diphosphate (ADP), which has two phosphate groups, to form adenosine triphosphate (ATP), which has three phosphate groups
Cells phosphorylate ADP to form ATP in three specific ways
1) Substrate-level phosphorylation, which involves the transfer of phosphate to ADP from another phosphorylated organic compound
2) Oxidative phosphorylation, in which energy from redox reactions of respiration is used to attach inorganic phosphate to ADP
3) Photophosphorylation, in which light energy is used to phosphorylate ADP with inorganic phosphate
After ADP is phosphorylated to produce ATP, anabolic pathways use some energy of ATP by breaking a?
Phosphate bond (which re-forms ADP)
How does ATP molecules store energy?
ATP stores energy from light (in photosynthetic organisms) & from catabolic reactions & then release stored energy to drive cellular processes (including anabolic reactions, active transport, & movement). ADP molecules can be "recharged" to ATP again & again
In catabolic reactions, a bond must be?
Destabilized before it will break, whereas in anabolic reactions reactants collide with sufficient energy for bonds to form between them
In anabolism, increasing either the concentrations of reactants or ambient temperatures increases the number of collisions & produces more chemical reactions; however in living organisms, neither reactant concentration nor temp. is usually high enough to ensure that bonds will form. Therefore, the chemical reactions of life depend upon?
Catalysts, which are chemicals that increase the likelihood of a reaction but are not permanently changed in the process
The names of enzymes usually end with the suffix "ase", and the name of each enzyme often incorporates the name of that enzymes?
Substrate, which is the molecule the enzyme acts upon.
Based on their mode of action, enzymes can be grouped into six basic categories
3) Ligases, or polymerases
Hydrolases catabolize molecules by?
Adding water in a decomposition process known as hydrolysis. Hydrolases are used primarily in the depolymerization of macromolecules
Isomerases rearrange the atoms within a?
Molecule bu do not add or remove anything (so they are neither catabolic nor anabolic)
Ligases, or polymerases, join?
Two molecules together (and are thus anabolic). They often use energy supplied by ATP.
Large molecules (and are thus catabolic) without using water in the process
Electrons from (oxidize) or add electrons (reduce) various substrates. Used in both catabolic & anabolic pathways
Functional groups, such as an amino group, a phosphate group, or a two-carbon (acetyl) group, between molecules. Can be anabolic
Many protein enzymes are complete in themselves, but others are composed of both protein & nonprotein portions. The proteins, called _______, are inactive if they are not bound to one or more of the nonprotein substances called _______
What are cofactors?
Either organic ions (such as iron, magnesium, zinc, or copper ions) or certain organic molecules called coenzymes.
All coenzymes are either?
Vitamins or contain vitamins, which are organic molecules that are required for metabolism but cannot be synthesized by certain organisms (like mammals)
Some apoenzymes bind with inorganic cofactors, or coenzymes, or both. The binding of an apoenzyme & its cofactor(s) forms an active enzyme, called a?
Not all enzymes are proteinaceous; some are RNA molecules called?
In eukaryotes, ribozymes process other RNA molecules by removing?
Sections of RNA & splicing the remaining pieces together.
Within cells, enzymes catalyze reactions by?
Lowering the activation energy, which is the amount of energy needed to trigger a chemical reaction.
Heat can provide energy to trigger reactions, the temps. needed to reach activation energy for most metabolic reactions are often too high to allow cells to survive, so what is needed?
Enzymes are needed if metabolism is to occur. This is true regardless of whether the enzyme is a protein or RNA, or the chemical reaction is anabolic or catabolic
The activity of enzymes depends on the?
Closeness of fit between functional sites of an enzyme & its substrate
The shape of an enzymes functional site, called its _____ ____, is complementary to the shape of the?
What determines the shape of an enzyme's active site
The shapes & locations of only a few amino acids or nucleotides. A change in a single component (mutation) can render an enzyme less effective or even completely nonfunctional
Enzyme-substrate specificity is critical to enzyme activity & has been likened to the fit between a?
lock & key. This analogy is not completely apt, because enzymes change shape slightly when they bind to their substrate, almost as if a lock could grasp its key once it had been inserted. This description is called the induced-fit model
In some cases, several different enzymes possess active sites that are complementary to various portions of a single substrate molecule. For example, the precursor metabolite called phosphoenolpyruvic acid (PEP) is the substrate for at least 5 enzymes, and depending on the enzyme involved, various products are produced from PEP. In one catabolic pathway, PEP is converted to pyruvic acid, whereas in a particular anabolic pathway, PEP is converted to the amino acid ____________
How do enzymes lower activation energy?
The exact ways are not known, it appears that several mechanisms are involved. Some appear to bring reactants into sufficiently close proximity to enable a bond to form, whereas others change the shape of a reactant, including a bond to be broken. Enzymes increase the likelihood that bonds will form or break
Many factors influence the rate of enzymatic reactions, including?
Temperature, pH, enzyme & substrate concentrations, & the presence of inhibitors
Higher temps. tend to do what to most chemical reactions?
What about enzymes?
Increase the rats of most chemical reactions because molecules are moving faster & collide more frequently, which encourages bonds to form or break. This isn't entirely true of enzymatic reactions, because the active site of enzymes change shape as temp. changes. If the temp. rises too high or falls too low, an enzyme is often no longer abel to achieve a fit with its substrate
Each enzyme has an optimal temp. for its activity.
The optimum temperature for the enzymes in the human body is 37 degrees C which is normal body temp.
Organisms that grow best at temperatures above 80 degrees C
If temps. rises beyond a certain critical point, the non covalent bonds within an enzyme (such as the hydrogen bonds between amino acids) will break, & the enzyme will?
Denatured enzymes lose their?
Specific three-dimensional structure, so they are no longer functional
Denaturation is said to be permanent when?
An enzyme cannot regain its original three-dimensional structure once conditions return to normal, much like the irreversible solidification of the protein albumin when egg whites are cooked & then cooled
When is denaturation reversible?
The denatured enzyme's non covalent bonds reform upon the return of normal conditions
Extremes of pH also denature enzymes when?
Ions released from acids & bases interfere with hydrogen bonding and distort and disrupt an enzymes secondary and tertiary structures. Therefore each enzyme has an optimal pH
Changing pH provides a way to control the growth of unwanted microorganisms by?
Denaturing their proteins. For example, vinegar acts as a preservative in dill pickles, and ammonia can be used as a disinfectant
Another factor that determines the rate of enzymatic activity within cells is the concentration of substrate present
As substrate concentration increases, enzymatic activity increases as more & more enzyme active sites bind more and more substrate molecules. When all enzyme active sites have bound substrate, the enzymes have reached their saturation point, and the addition of more substrate will not increase the rate of enzymatic activity
The rate of enzymatic activity is also affected by the concentration of enzyme within cells. One way that organisms regulate their metabolism is by controlling the quantity & timing of enzyme synthesis. Explain
Many enzymes are produced in the amounts & at the times they are needed to maintain metabolic activity.
Eukaryotic cells control some enzymatic activities by?
Compartmentalizing enzymes inside membranes so that certain metabolic reactions proceed physically separated from the rest of the cell. For example, white blood cells catabolize phagocytized pathogens using enzymes packaged within lysosomes
Enzymatic activity can be influenced by a variety of inhibitory substances that block an enzyme's active site. Enzymatic inhibitors, which may be either _________ or _________, do not _______ enzymes
competitive or noncompetitive
What are competitive inhibitors?
They are shaped such that they fit into an enzyme's active site & thus prevent the normal substrate from binding. Such inhibitors do not undergo a chemical reaction to form products. They can bind permanently or reversibly to an active site. Permanent binding results in permanent loss of enzymatic activity; reversible competition can be overcome by an increase in the concentration of substrate molecules, which increases the likelihood that active sites will be filled with substrate instead of inhibitor
What are noncompetitive inhibitors?
Do not bind to the active site but instead prevent enzymatic activity by binding to an allosteric site located elsewhere on the enzyme. Binding at an allosteric site alters the shape of the active site so that substrate cannot bound.
Allosteric control of enzyme activity can take two forms
Inhibitory and excitatory
Excitatory allosteric control, the binding of certain activator molecules (such as a heavy-metal ion cofactor) to an allosteric site causes?
A change in shape of the active site, which activates an otherwise inactive enzyme
Some enzymes have several allosteric sites, both inhibitory and excitatory, which allows?
Their function to be closely regulated
Cells often control the action of enzymes through feedback inhibition (also called negative feedback or end-product inhibition). Allosteric feedback inhibition functions in much the same way a thermostat controls a heater, explain.
As the room gets warmer, a sensor inside the thermostat changes shape & sends an electrical signal that turns off the heater. Similarly, in metabolic feedback inhibition, the end-product of a series of reactions is an allosteric inhibitor of an enzyme in an earlier part of the pathway. Because the product of each reaction in the pathway is the substrate for the next reaction, inhibition of the first enzyme in the series inhibits the entire pathway, thereby saving the cell energy
Redox reactions & carrier molecules are used to transfer?
Energy from catabolic pathways to an ATP molecule
The three stages of aerobic glucose catabolism
Glycolysis, the Krebs cycle, and an electron transport chain
Many organisms oxidize carbohydrates as their primary energy source for anabolic reactions. What is used most commonly?
Glucose is used most commonly, though other sugars, amino acids, and fats are also utilized, often by first being converted into glucose
Glucose is catabolized via one of two processes
Either via cellular respiration- a process that results in the complete breakdown of glucose to carbon dioxide and water.
Fermentation- which results in organic waste products
Both cellular respiration and fermentation begin with? Then what?
Glycolysis. Respiration then continues via the Krebs cycle and an electron transport chain, which results in a significant amount of ATP production. Fermentation involves the conversion of pyruvic acid into other organic compounds. Because it lacks the Krebs cycle and an electron transport chain, fermentation results in the production of much less ATP than does respiration.
What is glycolysis?
A process that catabolizes a single molecule of glucose to two molecules of pyruvic acid (also called pyruvate) and results in a small amount of ATP production
Glucose catabolism begins with glycolysis, which forms pyruvic acid and two molecules of both?
ATP & NADH
Two pathways branch from pyruvic acid
Respiration and fermentation
In aerobic respiration, the Krebs cycle and the electron transport chain completely?
Oxidize pyruvic acid to carbon dioxide (CO2) and water, in the process synthesizing many molecules of ATP
Fermentation results in?
The incomplete oxidation of pyruvic acid to form organic fermentation products
Glycolysis, also called the?
Embden-Meyerhof pathway after the scientist who discovered it, is the first step in the catabolism of glucose via both respiration and fermentation
In most cells
Glycolysis involves the?
Splitting of a six-carbon glucose molecule into two three-carbon sugar molecules. When these three-carbon molecules are oxidized to pyruvic acid, some of the energy released is stored in molecules of ATP
Where does glycolysis occur?
In the cytosol
Glycolysis, which occurs in the cytosol, can be divided into three stages involving a total of 10 steps, each of which is catabolized by its own enzyme
1) Energy investment stage (steps 1-3). As w/money, one must invest before a profit can be made. In this case, the energy in two molecules of ATP is invested to phosphorylate (add) a six-carbon glucose molecule & rearrange its atoms to form fructose 1,6-bisphosphate
2) Lysis stage (steps 4 & 5)- Fructose 1,6-bisphosphate is cleaved into glyceraldehyde 3-phosphate (G3P) & dihydroxyacetone phosphate (DHAP). Each of these compounds contains 3 carbon atoms & is freely convertible into the other.
3) Energy-conserving stage (steps 6-10)- G3P is oxidized to pyruvic acid, yielding tow ATP molecules. DHAP is converted to G3P & also oxidized to pyruvic acid, yielding another two ATP molecules, for a total of 4 ATP molecules
Each of the two phosphoenolpyruvic acid (PEP) molecules produced in step 9 of glycolysis is a three-carbon compound containing a high-energy phosphate bond. In the presence of a specific holoenzyme (which requires Mg2+ cofactor), the high-energy phosphate in PEP (one substrate) is transferred to an ADP molecule (a second substrate) to form ATP; the direct transfer of the phosphate between the two substrates is the reason the process is called?
Substrate-level phosphorylation. A variety of substrate-level phosphorylations occur in metabolism. Each type has its own enzyme that recognizes both its substrate molecule and ADP
In glycolysis, two ATP molecules are invested by substrate-level phosphorylation to prime glucose for lysis (breakdown), and four molecules of ATP are produced by substrate-level phosphorylation. Therefore, a net gain of?
Two ATP molecules occurs for each molecule of glucose that is oxidized to pyruvic acid. Glycolysis also yield two molecules of NADH
Cellular respiration is a?
Metabolic process that involves the complete oxidation of substrate molecules & then production of ATP by a series of redox reactions
What are the 3 stages of cellular respiration?
1) Synthesis of acetyl-CoA
2) The Krebs cycle
3) A final series of redox reactions called an electron transport chain, that passes electrons to a chemical not derived from the cell's metabolism
Before pyruvic acid (generated by glycolysis for an alternate pathway) can enter the Krebs cycle for respiration, it must first be converted to?
Acetyl-coenzyme A, or acetyl CoA. Enzymes remove one carbon from pyruvic acid as CO2 & join the remaining two-carbon acetate to coenzyme A with a high-energy bond. The removal of CO2 called decarboxylation, requires a coenzyme derived from the vitamin thiamine. One molecule of NADH is also produced during this reaction
Where does the Krebs cycle occur in prokaryotes and eukaryotes
Occurs in the cytosol of prokaryotes and in the matrix of mitochondria in eukaryotes
Also known as the tricarboxylic acid (TCA) cycle
The Krebs cycle because many of its compounds have three carboxyl groups, and as the citric acid cycle for the first compound formed in the cycle
The Krebs cycle is?
A series of eight enzymatically catalyzed reactions that transfer much of this stored energy (stored energy in the bonds of acetyl-CoA) to the coenzymes NAD+ & FAD. The two carbon atoms in acetate are oxidized, and the coenzymes are reduced
There are 6 types of reactions in the Krebs cycle
1) Anabolism of citric acid (step 1)
2) Isomerization reaction (step 2)
3) Redox reactions (steps 3,4,6, & 8)
4) Decarboxylation (steps 3 & 4)
5) Substrate level phosphorylation (step 5)
6) Hydration reaction (step 7)
In the Krebs cycle after isomerization in step 2, the decarboxylation of the Krebs cycle release two molecules of carbon dioxide for each acetyl-CoA that enters. Thus for every two carbon atoms that enter the cycle, two are?
Lost to the environment. At this junction in the respiration of a molecule of glucose, all 6 carbon atoms have been lost to the environment: two as carbon dioxide molecules produced in decarboxylation of two molecules of pyruvic acid and two to form acetyl- CoA molecules, and four in CO2 molecules produced in decarboxylations in the two turns through the Krebs cycle
A small amount of ATP is also produced in the Krebs cycle. For every two molecules of acetyl-CoA that pass through the Krebs cycle, two molecules of?
ATP are generated by substrate-level phosphorylation. A molecule of guanosine triphosphate (GTP), which is similar to ATP, can serve as an intermediary in this process
In the Krebs cycle, redox reactions reduce?
FAD to FADH2 (only in step 6) & NAD to NADH (in steps 3,4, & 8), so for every two molecules of acetyl-CoA that move through the cycle, six molecules of NADH and two of FADH2 are formed.
In the Krebs cycle, little energy is captured directly in high-energy phosphate bonds, but much energy is transferred via?
Electrons to NADH and FADH2. These coenzymes are the most important molecules of respiration because they carry a large amount of energy that is subsequently used to phosphorylate ADP to ATP
Scientists estimate that each day an average human synthesizes his or her own weight in?
ATP molecules & uses them for metabolism, responsiveness, growth, and cell reproduction.
The most significant production of ATP does not occur through glycolysis or the Krebs cycle, but rather through the stepwise release of energy from a?
Series of redox reactions known as an electron transport chain
An electron transport chain consists of?
A series of membrane bound carrier molecules that pass electrons from one to another & ultimately to a final electron acceptor. Typically electrons come from the catabolism of an organic molecule such as glucose, however, microorganisms called lithographs acquire electrons from inorganic sources such as H2, NO2- (nitrogen dioxide), or Fe2+ (iron)
Microorganisms called lithographs acquire electrons from?
Inorganic sources such as H2, NO2- (nitrogen dioxide), or Fe2+ (iron)
Carrier molecules pass electrons down the chain to the?
Final acceptor like firefighters of old, who passed buckets of water from one to another until the last one threw the water on the fire. As with a bucket brigade, the final step of electron transport is irreversible. Energy from the electrons is used to actively transport (pump) protons (H+) across the membrane, establishing a proton gradient that generates ATP via a process called chemiosmosis
Electrons pass sequentially from one membrane bound carrier molecule to another and eventually to?
A final acceptor molecule
The electron's energy is used to?
Pump protons across the membrane
Electron transport chains are located?
In the inner mitochondrial membranes (cristae) of eukaryotes & in the cytoplasmic membranes of prokaryotes
Though NADH & FADH2 donate electrons as hydrogen atoms (electrons & protons), many carrier molecules pass only the?
Electrons down the chain.
There are 4 categories of carrier molecules in electron transport chains
3) Metal-containing proteins
What are flavoproteins?
Integral membrane proteins, many contain flavin (coenzyme derived from riboflavin, vitamine B2). The familiar FAD is a coenzyme for other flavoproteins. Alternate between the reduced and oxidized states
The initial carrier molecule of electron transport chains of mitochondria
Flavin mononucleotide (FMN)
What are ubiquinones?
Lipid-soluble, nonprotein carriers that are so named because they are ubiquitous in cells. Derived from vitamin K. In mitochondria, the ubiquinone is called coenzyme Q
What are metal-containing proteins?
Mixed group of integral proteins with a wide ranging number of iron, sulfur, & copper atoms, that can alternate between the reduced & oxidized states. Iron-sulfur proteins occur in various places in electron transport chains of various organisms. Copper proteins are found only in electron transport chains involved in photosynthesis
What are cytochromes?
Integral proteins associated with heme, which is the same iron-containing, nonprotein, pigmented molecule found in the hemoglobin of blood. Iron can alternate between a reduced (Fe2+) state and an oxidized state (Fe3+). Identified by letters & numbers based on the order in which they are identified
Describe the carrier molecules of bacteria, archaea, and eukaryotes
Carrier molecules in electron transport chains are diverse, bacteria typically have diff. carrier molecules arranged in diff. sequences from those of archaea or the mitochondria of eukaryotes
Contains two cytochromes
Electrons carried by NADH enter a transport chain at a?
Flavoprotein. More molecules of ATP are generated from NADH
Electrons carried by FADH2 enter the transport chain at?
In some organisms, the final electron acceptors are oxygen atoms, which, with the addition of hydrogen ions, generate water; these organisms conduct?
Aerobic respiration and are called aerobes
Organisms called anaerobes use?
Inorganic molecules (rarely an organic molecule) instead of oxygen as the final electron acceptor & perform anaerobic respiration
A number of redox reactions in glycolysis or alternate pathways & in the Krebs cycle strip electrons, which carry energy, from glucose molecules & transfer them to molecules of NADH & FADH2. In turn, NADH, & FADH2 pass the electrons to an?
Electron transport chain. As the electrons move down the electron transport chain, proton pumps use the electrons energy to actively transport protons (H+) across the membrane, creating a proton concentration gradient.
What is the significance of the electron transport chain?
1) Pumps protons across the membrane
2) Ultimately results in the synthesis of ATP
What is chemiosmosis?
General term used for the use of ion gradients to generate ATP; that is, ATP is synthesized utilizing energy released by the flow of ions down their electrochemical gradient across a membrane.
Chemiosmosis uses the?
Potential energy of an electrochemical gradient to phosphorylate ADP to ATP
Cells use the energy released in the redox reactions of electron transport chains to actively transport?
Protons (H+) across a membrane
An electron transport chain pumps three pairs of protons for each pair of?
Electrons contributed by NADH, and it pumps two pairs of protons for each electron pair delivered by FADH2. This difference results from the fact that FADH2 delivers electrons farther down the chain than does NADH; therefore, energy carried by FADH2 is used to transport one-third fewer protons.
Because lipid bilayers are impermeable to protons, the transport of protons to one side of the membrane creates an?
Electrochemical gradient known as a proton gradient, which has potential energy known as a proton motive force
Protons, propelled by the proton motive force, flow down their?
Electrochemical gradient through protein channels, called ATP synthases (ATPases), that phosphorylate molecules of ADP to ATP. Such phosphorylation is called oxidative phosphorylation because the proton gradient is created by the oxidation of components of an electron transport chain
Cells use proton gradients for other cellular processes, including?
Active transport & bacterial flagellar motion, so not every transported electron results in ATP production
About 34 molecules of ADP per molecule of glucose are oxidatively phosphorylated to ATP via chemiosmosis
Three from each of the 10 molecules of NADH generated from glycolysis, the synthesis of acetyl-CoA, and the Krebs cycle, and two from each of the two molecules of FADH2 generated in the Krebs cycle
Given that glycolysis produces a net two molecules of ATP by substrate-level phosphorylation, and that the Krebs cycle produces two more, the complete aerobic oxidation of one molecule of glucose by a prokaryote can theoretically yield a net total of?
38 Molecules of ATP
The theoretical net maximum for eukaryotic cells is generally given as?
36 molecules of ATP because the energy from two ATP molecules is required to transport NADH generated by glycolysis in the cytoplasm into the mitochondria
What is the pentose phosphate pathway?
Sometimes called the phosphogluconate pathway. Named for the phosphorylated pentose (5-carbon sugars, ribulose, xylulose, & ribose) that are formed from glucose
6-phosphate by enzymes in the pathway. This pathway is used primarily for the production of precursor metabolites used in anabolic reactions, including the synthesis of nucleotides for nucleic acids, of certain amino acids, & of glucose by photosynthesis. Pathway reduces two molecules of NADP to NADPH & nets a single molecule of ATP from each molecule of glucose
NADPH is a necessary coenzyme for?
Anabolic enzymes that synthesis DNA nucelotides, steroids, & fatty acids
Many bacteria use glycolysis and the pentose phosphate pathway, but a few substitute the Entner-Doudoroff pathway for glycolysis. What is this pathway?
Named for its discoverers, is a series of reactions that catabolize glucose to pyruvic acid using different enzymes from those used in either glycolysis or the pentose phosphate pathway. Nets only a single molecule of ATP for each molecule of glucose but it does yield precursor metabolites and NADPH
What are some of the very few bacteria that use the Entner-Doudoroff pathway?
The Gram-negative bacterium Pseudomonas aeruginosa and the Gram-positive bacterium Enterococcus faecalis
Sometimes cells cannot completely oxidize glucose by cellular respiration. For instance, they may lack sufficient final electron acceptors, as is the case of an aerobic bacterium that lacks oxygen in the anaerobic environment of the colon. Electrons cannot flow down an electron transport chain unless oxidized carrier molecules are available to receive them at the end. When there is no final electron acceptor what happens?
All the carrier molecules are forced to remain in their reduced states when there is no final electron acceptor. Without the movement of electrons down the chain, protons cannot be transported, the proton motive force is lost, and oxidative phosphorylation of ADP to ATP ceases. Without sufficient ATP, a cell is unable to anabolize, grow, or divide
ATP could by synthesized in glycolysis and the Krebs cycle by substrate-level phosphorylation. Together these pathways produce four molecules of ATP per molecule of glucose. However, careful consideration reveals that glycolysis, formation of acetyl-CoA, and the Krebs cycle require a continual supply of oxidized NAD+ molecules. Electron transport produces the required NAD+ in respiration, but without a final electron acceptor, this source of NAD+ ceases to be available. A cell in such a predicament must use an alternate source of NAD+ provided by alternative pathways, called?
In everyday language fermentation refers to the?
In microbiology, fermentation refers to?
Production of alcohol from sugar
Micro- The partial oxidation of sugar (or other metabolites) to release energy using an organic molecule from within the cell as the final electron acceptor
Fermentation pathways are?
Metabolic reactions that oxidize NADH to NAD+ while reducing cellular organic molecules. In contrast, respiration reduces externally acquired substances- oxygen is aerobic respiration, and in anaerobic respiration, some other inorganic chemical such as sulfate and nitrate or rarely an organic molecule
The essential function of fermentation is the?
Regeneration of NAD+ for glycolysis, so that ADP molecules can be phosphorylated to ATP
The major benefit of fermentation is?
It allows ATP production to continue in the absence of cellular respiration
Microorganisms produce a variety of fermentation products depending on the enzymes & substrates available to each. Though fermentation products are wastes to the cells that make them, many are useful to humans, including?
Ethanol (drinking alcohol) and lactic acid (used in the production of cheese, sauerkraut, and pickles)
Laboratory personnel routinely use the detection of fermentation products to identify?
Microbes. For example, Proteus ferments glucose but not lactose, whereas Escherichia and Enterobacter ferment both. Further, glucose fermentation by Escherichia produces mixed acids (acetic, lactic, succinc, and formic), whereas Enterobacter produces 2,3-butanediol
Type of phosphorylation for aerobic respiration, anaerobic respiration, and fermentation
Aerobic respiration: Substrate-level and oxidative
Anaerobic respiration: Substrate-level and oxidative
Fermentation: Substrate level
Final electron (hydrogen) acceptor for aerobic respiration, anaerobic respiration, and fermentation
Aerobic respiration: Oxygen
Anaerobic respiration: Nitrate (NO3-), Sulfate (SO42-), Carbonate (CO32-), or externally acquired organic molecules
Fermentation: Cellular organic molecules
Potential molecules of ATP produced per molecule of glucose for aerobic respiration, anaerobic respiration, and fermentation
Aerobic respiration: 38 in prokaryotes, 36 in eukaryotes
Anaerobic respiration: 2-36
Lipid and protein molecules contain abundant energy in their?
Chemical bonds & can also be converted into precursor metabolites. These molecules are first catabolized to produce their constituent monomers, which serve as substrates in glycolysis and the Krebs cycle
The most common lipids involved in ATP and metabolite production are?
Fats, which consist of glycerol and fatty acids
In the first step of fat catabolism, enzymes called lypases hydrolyze the?
Bonds attaching the glycerol to the fatty acid chains. Subsequent reactions further catabolize the glycerol and fatty acid molecules. Glycerol is converted to DHAP, which as one of the substrates of glycolysis is oxidized to pyruvic acid.
For lipid catabolism, the fatty acids are degraded in a catabolic process known as?
What happens in beta-oxidation?
Enzymes repeatedly split off pairs of the hydrogenated carbon atoms that make up a fatty acid and join each pair to coenzyme A to form acetyl-CoA, until the entire fatty acid has been converted to molecules of acetyl-CoA
Beta-oxidation also generates?
NADH & FADH2, and more of these molecules are generated when the acetyl-CoA is utilized in the Krebs cycle to generate ATP
The enzymes involved in beta-oxidation are located in the?
Cytosol of prokaryotes and in the mitochondria of eukaryotes
Most cells catabolize proteins and their constituent amino acids only when?
Carbon sources such as glucose & fat are not available
Generally, proteins are too large to cross cytoplasmic membranes, so prokaryotes typically conduct the?
First step in the process of protein catabolism outside the cell by secreting proteases, enzymes that split proteins into their constituent amino acids. Once released by the action of proteases, amino acids are transported into the cell, where special enzymes split off amino groups in a reaction called deamination
In deamination reaction, the resulting altered molecules enter the Krebs cycle, and the amino groups are either recycled to synthesize other amino acids or excreted as?
Nitrogenous wastes such as ammonia (NH3) , ammonium ion (NH4), or trimethylamine oxide
When acetyl-CoA enters the Krebs cycle by joining with?
Oxaloacetic acid to form citric acid and coenzyme A
What happens if we keep accumulating protons?
pH will go down and whole process will come to a stop
Prokaryote uses oxygen as final acceptor and gets how many ATP? If O2 is not available it uses N,S, & C and gets how many ATP?
O2- 38 ATP
N- 35 ATP
S- 30 ATP
C- 28 ATP
Some microorganisms live where O2 is not readily available so they use N,S, & C. What do they get by combining with them?
By combining N, protons and electrons make ammonia (NH3)
By combining with S, protons and electrons make hydrogen sulfide (H2S)
By combining with C, protons and electrons make Methane (CH4)
a) are types of apoenzymes
b) are proteins
c) are inorganic cofactors
d) are organic cofactors
D) organic cofactors
What best describes ribozymes
Ribozymes process RNA molecules in eukaryotes
Most oxidation reactions in bacteria involve the?
Removal of hydrogen ions and electrons
Under ideal conditions, the fermentation of one glucose molecule by a bacterium allows a net gain of how many ATP molecules?
Which of the following statements about the Entner0Doudoroff pathway is false?
a) It is a series of reactions that synthesis glucose
b) Its products are sometimes used to determine the presence of Pseudomonas
c) It is a pathway of chemical reactions that catabolize glucose
d) It is an alternate pathway to glycolysis
A) It is a series of reactions that synthesize glucose
A major difference between anaerobic respiration and anaerobic fermentation is?
That the latter uses organic molecules within the cell as final electron acceptors
Occurs when energy from a compound containing phosphate reacts with ADP to form ATP
Begins with glycolysis
The final electron acceptor in cyclic photophosphorylation is
The original reaction center, chlorophyll
The initial catabolism of glucose occurs by glycolysis and/or
___________ and _________ pathways
Pentose phosphate and Entner-Doudoroff
_______________ is a cyclic series of eight reactions involved in the catabolism of acetyl-CoA that yields eight molecules of NADH and two molecules of FADH2
The Krebs cycle
Three common inorganic electron acceptors in anaerobic respiration are?
NO3-, SO42-, CO32-
Chemolithotrophs acquire electrons from?
Catabolizes substrate by adding water
Joins two molecules together
Moves functional groups such as an acetyl group
Adds or removes electrons
Splits large molecules
The use of a proton motive force to generate ATP is?