Chapter 9 Flashcards
How does the hoary marmot (Marmota caligata) obtain energy?
By feeding on plants.
How is chemical energy stored in food used to generate ATP?
Plant/animal cells break down organic molecules by cellular respiration in the mitochondria, and the chemical energy is transformed into chemical energy in ATP while some energy is released to the environment as heat.
What is the catabolic pathway?
Energy enters ecosystems as light and exits as heat, the chemical elements essential to life are recycled.
Photosynthesis uses CO2 and H2O to make organic molecules and H2O.
Cellular respiration uses O2 and organic molecules to make ATP; CO2 and H2O are produced as waste.
How do catabolic pathways produce energy?
Release stored energy by breaking down complex molecules. Electron transfer from food molecules to other molecules plays a major role in these pathways. These processes are central to cellular respiration.
What is fermentation?
A partial degradation of sugars that occurs without oxygen.
What is aerobic respiration?
Consumes organic molecules and oxygen and yields ATP. Anaerobic respiration is similar to aerobic respiration but consumes compounds other than oxygen.
What is cellular respiration?
Includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration.
Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose.
Do catabolic pathways directly power the cell?
No; they are linked to work by ATP. Cells must constantly regenerate their supply of ATP from ADP and phosphate.
What does the transfer of electrons during chemical reactions do?
Releases energy stored in organic molecules. This energy is ultimately used to synthesize ATP.
What are redox reactions?
Chemical reactions that transfer electrons between reactants, also called oxidation reduction reactions.
What is oxidation?
In redox reactions, the loss of electrons from a substance is called oxidation.
What is the addition of electrons to a substance called?
Reduction. (The amount of positive charge is reduced)
In sodium chloride reactions, what becomes reduced and what becomes oxidized?
Sodium becomes oxidized (Na+)
Chlorine becomes reduced (Cl-)
What is a reducing agent?
The electron donor. It reduces the electron acceptor.
What is the oxidizing agent?
The electron acceptor. It oxidizes the electron donor.
What happens when redox reactions don’t fully transfer electrons?
Change electron sharing in covalent bonds.
Oxygen atoms are very electronegative and attract electrons but do not share them equally.
The partial “gain” of electrons by O atoms and the partial “loss” of electrons by their bonding partners constitutes a redox reaction.
When does an electron lose potential energy?
When it shifts from a less electronegative atom toward a more electronegative one.
Redox reactions that move electrons closer to electronegative O atoms release energy.
What molecules are excellent sources of high energy electrons?
Organic molecules with an abundance of hydrogen.
What is cellular respiration considered?
Redox process; energy is released as hydrogen and electrons are transferred to O atoms.
What does the oxidation of glucose do?
Transfers electrons from a higher energy state (in glucose) to a lower energy state with O atoms. This releases energy that is to be used to synthesize ATP.
How are glucose and other organic molecules oxidized in cellular respiration?
In a series of steps; each electron travels with a proton- a hydrogen atom. Hydrogen atoms are usually first passed to electron carries rather than directly to O2.
What is NAD+?
Nicotinamide adenine dinucleotide. A coenzyme that functions as an electron carrier.
As an electron acceptor, NAD+ functions as an oxidizer. Each NADH (reduced form of NAD+) represents stored energy that is tapped to synthesize ATP.
What are dehydrogenases?
Enzymes that remove a pair of hydrogen atoms (2 electrons and 2 protons) from the substrate.
The 2 electrons and 1 proton is transferred to NAD+, forming NADH. The other proton is released as a hydrogen ion (H+) into the surrounding solution.
What happens if NADH transfers electrons directly to oxygen?
Energy would be released in one explosive reaction.
What happens between oxygen and NADH usually?
Cellular respiration uses an electron transport chain to break the fall of electrons to O2 into several energy releasing steps. Each releases a small amount of energy.
What is the electron transport chain?
Consists of a series of molecules built into the inner membrane of the mitochondria (or plasma membrane of prokaryotes).
What are the three stages of cellular respiration with glucose?
- Glycolysis
- Pyruvate oxidation and the citric acid cycle complete the breakdown of glucose to CO2.
- During oxidative phosphorylation, the electron transfer chain and chemiosmosis facilitate synthesis of most of the cell’s ATP.
What process generates almost 90% of the ATP?
Oxidative phosphorylation because it is powered by redox reactions.
What is substrate level phosphorylation?
Occurs when an enzyme transfers a phosphate group directly from a substrate to ADP. From glycolysis and the citric acid cycle.
In terms of money, what are the analogies for cellular respiration?
Glucose- larger denomination bill- worth a lot but hard to spend.
ATP- a number of smaller denomination bills of equivalent value- can be spent more easily.
Cellular respiration- cashes in a large denomination of energy (glucose) for the small change of many molecules of ATP.
For each molecule of glucose degraded to CO2 and H2O by cellular respiration, how many molecules of ATP are produced?
32 molecules of ATP.
Where does glycolysis occur?
In the cytoplasm.
What are the two phases of glycolysis?
Energy investment phase
Energy payoff phase
What is the energy investment phase?
2 ATP are used to split glucose into 2 three carbon sugar molecules.
What is the energy payoff phase?
4 ATP are synthesized, 2 NAD+ are reduced to NADH, the small sugars are oxidized to form 2 pyruvate and 2 H2O. A net of 2 ATP are produced by substrate level phosphorylation during glycolysis.
Does glycolysis ever release any CO2?
No, whether or not O2 is present does not matter because it does not produce O2.
Where does most of the energy in glucose remain after glycolysis?
In the pyruvate molecules.
What happens in eukaryotic cells if O2 is present?
Pyruvate enters a mitochondrion to complete glucose oxidation.
Where does glycolysis happen in aerobic prokaryotes?
In the cytosol.
What is pyruvate converted to before entering the citric acid cycle?
Acetyl coenzyme A (acetyl CoA).
What does pyruvate dehydrogenase catalyze?
Three reactions:
1. Oxidation of pyruvate’s carboxyl group, releasing the first CO2 of cellular respiration.
2. Reduction of NAD+ to NADH.
3. Combination of the remaining two carbon fragment with coenzyme A to form acetyl CoA.
What is the citric acid cycle called?
Krebs cycle.
What is the Krebs cycle/citric acid cycle?
Oxidizes fuel derived from pyruvate, generating 1 ATP, NADH, and 1 FADH2 per turn. Another 2 CO2 are produced as a waste product.
Because 2 pyruvate are produced per glucose, the cycle runs twice per glucose molecule consumed.
How many steps does the citric acid cycle have?
Eight steps, which are each catalyzed by a specific enzyme.
What are the eight steps of the citric acid cycle?
First, the acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, and forms citrate.
The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle. The NADH and FADH2 produced by the cycle carry electrons to the electron transport chain.
What makes up for most of the energy extracted from glucose during glycolysis?
Molecules of NADH and FADH2. NADH and FADH2 donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation.
Where are the molecules of the electron transport chain located?
Embedded in the inner mitochondrial membrane in eukaryotic cells. The membrane is folded into cristae to increase surface area for electron transport chains.
In prokaryotes, the electron transport chain is embedded in the plasma membrane.
What are most of the molecules in the electron transport chain classified as?
Proteins that exist in multiprotein complexes.
When do NADH and FADH2 donate electrons?
Early in the chain.
What are cytochromes?
Proteins with heme groups containing an iron atom. Electrons are passed through carrier molecules including these cytochromes.
When do electrons drop in free energy?
As they are transferred down the chain, finally passing to O2 to form H2O.
How is the electron transport chain energy managed?
The electron transport chain breaks the large free energy drop from glucose to O2 into smaller steps, releasing energy in manageable amounts. No ATP is produced directly by the chain.
What is the energy released as electrons are passed down used for?
To pump H+ ions from the mitochondrial matrix to the intermembrane space. H+ then moves down its concentration gradient back across the membrane, passing through the protein complex ATP synthase.
What happens when the H+ ions move into the binding sites on the rotor of ATP synthase?
Causes it to spin in a way that catalyzes phosphorylation of ADP to ATP. It is an example of chemiosmosis.
What is chemiosmosis?
The use of energy in an H+ gradient to drive cellular work.
What is proton motive force?
The H+ gradient, emphasizing its capacity to do work.
What is the anglicized cellular respiration model?
Glucose -> NADH -> electron transport chain -> proton motive force -> ATP
What is the percentage of energy in a glucose molecule that is transferred to ATP?
34%, it makes about 32 ATP. The rest of the energy is lost as heat.
What are the three known reasons why the number of ATP produced is not known?
- Photophosphorylation and the redox reactions are not directly coupled; the ratio of NADH to ATP molecules is not a whole number.
- ATP yield varies depending on whether electrons are passed to NAD+ or FAD.
- The proton motive force is also used to drive other kinds of work.
What does most of the cellular respiration depend on?
Electronegative oxygen to pull electrons down the transport chain. Without oxygen, the electron transport chain will cease to operate.
What happens if there is no oxygen during cellular respiration?
Glycolysis couples with anaerobic respiration or fermentation to produce ATP.
What does anaerobic respiration use?
Electron transport chain with a final electron acceptor other than oxygen.
Ex. some organisms use a sulfate ion (SO4 2-) as a final electron acceptor. In this reaction, H2S (hydrogen sulfide) is made as a by product instead of H2O.
During anaerobic respiration, how does glycolysis oxidize?
Without O2 or electron transport chain, NAD+ is the oxidizing agent used in glycolysis. Glycolysis produces 2 ATP (net) by substrate level phosphorylation whether O2 is present or not.
Is NAD+ regenerated?
Under aerobic conditions, it is regenerated from NADH by transferring electrons to the electron transport chain. Fermentation must use alternate mechanisms to regenerate NAD+.
What are two common types of fermentation?
Alcohol fermentation and lactic acid fermentation.
What is fermentation?
An extension of glycolysis that oxidizes NADH by transferring electrons to pyruvate or its derivatives.
What is alcohol fermentation?
Pyruvate is converted to ethanol in two steps.
1. The first step releases CO2 from pyruvate.
2. Produces NAD+ and ethanol.
What is alcohol fermentation utilized to make?
Alcohol fermentation by yeast is used in brewing, winemaking, and baking.
What is lactic acid fermentation?
Pyruvate is reduced directly by NADH to form lactate. There is no release of CO2 in lactic acid fermentation.
What is lactic acid utilized to make?
Lactic acid fermentation by fungi and bacteria is used to make cheese and yogurt.
How is chocolate produced?
A complex series of fermentation and aerobic respiration carried out by yeasts and bacteria on cacao beans.
When do human muscle cells produce lactate?
One type of skeletal muscle (red) oxidizes glucose completely to CO2; the other (white) produces lactate even under aerobic conditions.
What is a now incorrect way to refer to lactate production in muscles?
Fermentation. Because lactate production is not anaerobic, but the result of glycolysis in white muscle cells, physiologists prefer to now use a term other than fermentation to describe lactate production.
What are the similarities of fermentation, anaerobic and aerobic respiration?
All use glycolysis (net 2 ATP) to oxidize glucose and harvest the chemical energy of food.
In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis.
What is the major difference between fermentation, aerobic and anaerobic respiration?
The mechanisms used to oxidize NADH to NAD+.
In fermentation, an organic molecule (pyruvate or acetaldehyde) acts as a final electron acceptor.
In cellular respiration, electrons are transferred to the electron transport chain.
What is another difference between fermentation, aerobic and anaerobic respiration?
Fermentation produces 2 ATP by substrate level phosphorylation.
Cellular respiration harvests much more ATP by oxidative phosphorylation- up to 32 ATP in aerobic respiration.
What are obligate anaerobes?
Carry out fermentation or anaerobic respiration and cannot survive in the presence of O2.
What are facultative anaerobes?
Yeast and many bacteria, meaning that they can survive using either fermentation or cellular respiration. For facultative anaerobes, pyruvate is a fork in the metabolic road leading to alternative catabolic routes.
What did early prokaryotes use?
Most likely used glycolysis to produce ATP before oxygen accumulated in the atmosphere.
What is the most widespread metabolic pathway?
Glycolysis; used in both cellular respiration and fermentation.
What is a metabolic heirloom from early cells?
Glycolysis.
What are major intersections to various catabolic and anabolic pathways?
Glycolysis and the citric acid cycle.
What funnels electrons from many organic molecules into cellular respiration?
Catabolic pathways.
What can glycolysis utilize?
Many carbohydrates, including starch, glycogen, and several disaccharides.
What is deamination?
Proteins used for fuel must be digested to amino acids and their amino groups must be removed.
How is nitrogenous waste excreted as?
As ammonia (NH3), urea, or other products.
What are fats digested to?
Glycerol and fatty acids.
What is glycerol used for?
To produce compounds needed for glycolysis.
What are fatty acids broken down by?
Beta oxidation, and yield acetyl CoA, NADH, and FADH2.
How much does an oxidized gram of fat produce?
More than twice as much ATP as an oxidized gram of carbohydrate.
How are macromolecules made? (Biosynthesis)
Organisms use small molecules from food to build them, like proteins from amino acids. The small molecules can come directly from food, glycolysis, or from the citric acid cycle.
What is feedback inhibition?
The most common mechanism for metabolic control because it prevents wasteful production.
What happens if ATP concentration drops?
Respiration speeds up; if there is plenty of ATP, respiration slows down.
How is catabolism controlled?
By regulating the activity of enzymes at strategic points in the pathway.
What is the relationship between phosphofructokinase activity and fructose 6 phosphate concentration?
As phosphofructokinase increases, the fructose 6 phosphate slowly increases, but increases faster after the fructokinase plataeus.
