Unit 2 (Week 6) Cellular Respiration Flashcards
What is the process by which living cells obtain energy from organic molecules and release waste products and was ultimately partly responsible of Carmen running a marathon versus 1 mile?
Cellular respiration
The cells in Carmen’s leg muscles had become more efficient at cellular respiration.
What does metabolism have that fire doesn’t have when using energy or fuel?
Control.
What is the primary aim of cellular respiration?
To make adenosine triphosphate, or ATP.
What is the type of cellular respiration in which O2 is consumed and CO2 is released?
Aerobic respiration
This is completed through the oxidation of organic molecules. Thus, we breath.
What three energy intermediates are created in the oxidation process of glucose within our cells?
ATP
NADH
FADH2
What are the four metabolic pathways involved in breakdown of glucose?
- Glycolysis
- Breakdown of pyruvate
- Citric acid cycle
- Oxidative phosphorylation
What is the metabolic pathway that breaks down glucose (6 carbon atoms) into pyruvate?
Additionally, where does glycolysis occur?
Glycolysis
In eukaryotes, this metabolic pathway occurs in the cytosol.
What are the products of glucose being broken down by glycolysis?
Two molecules of pyruvate (3 carbons each) and 2 molecules of ATP (via substrate-level phosphorylation) and 2 molecules of NADH
Substrate-level phosphorylation, which means the enzyme directly transfers a phosphate from an organic molecule to ADP
Where do the two pyruvate molecules go to be broken down into 2 acetyl groups (two carbons each) and 2 CO2 molecules?
The mitochondrial matrix.
Additionally, two NADH molecule is made by the reduction of NAD+ for each pyruvate broken down via oxidation.
What is the cycle that results in the breakdown of carbohydrates to CO2; also known as the Krebs cycle?
Citric acid cycle; this is where the acetyl groups are completely broken down.
During the citric acid cycle AKA the Krebs cycle, what are the different and total amount of energy intermediates and waste created by the TWO acetyl groups?
Two ATP (via substrate-level phosphorylation), Two FADH2, and six NADH.
Four CO2 molecules
This all occurs in the mitochondrial matrix.
What is present in the six NADH and two FADH2 molecules that is readily transferable in a redox reaction to other molecules?
High-energy electrons
How is the energy harnessed from the high-energy electrons from NADH and FADH2?
Through an electron transport chain producing an H+ electrochemical gradient.
What is the process for harnessed energy to make ATP which is stored in an ion electrochemical gradient (H+) to make ATP from ADP and Pi?
Chemiosmosis
Why do you call the overall process of the electron transport and ATP synthesis, oxidative phosphorylation?
NADH or FADH2 is oxidized (loss of energy)
ADP has become phosphorylated to make ATP
[BONUS] How many ATP molecules can be made via oxidative phosphorylation?
30-34 molecules of ATP via chemiosmosis
Where does the oxidation phosphorylation occur inside the inner mitochondrial membrane or matrix?
The cristae; the projections formed by the invagination of the inner mitochondrial membrane.
Remember: these projections increase surface area and therefore increase the amount of ATP synthesized
[BONUS] Where does oxidative phosphorylation occur in bacteria and archaea?
Along the plasma membrane
[Glycolysis Start] What does the word Glycolysis mean in Greek?
Glykos meaning sweet, lysis meaning splitting.
T/F The metabolic pathway of glycolysis can occur in aerobic and anaerobic conditions.
True
How many steps are involved in glycolysis where different enzymes are needed to catalyze each event in the pathway?
10
An achievement in biochemistry; the study of the chemistry of living things.
[First Phase; Steps 1-3] Energy Investment: What happens in the first three steps of glycolysis?
- Two ATP molecules are hydrolyzed
- Phosphates from ATP are attached to glucose to create fructose-1,6-biphosphate
What does the energy phase raise and thereby allowing?
Raises free energy of glucose allowing future reactions to become exergonic.
[Second Phase; Steps 4-5] Cleavage: What happens to the fructose-1,6-diphosphate molecule?
The six carbon molecule is broken into two molecules of glyceraldehyde-3-phosphate.
[Third Phase; Steps 6-10] Energy Liberation: What is net molecules produced in this phase?
Two ATP, two NADH, and two molecules of pyruvate.
Four molecules are actually produced in this phase but two were used in the energy investment phase.
With regard to oxygen needs, what advantage do glycolytic muscle fibers provide?
Glycolytic muscle fibers rely on glycolysis for their ATP needs. Because glycolysis does not require oxygen, such muscle fibers can function without oxygen.
Why are two NADH molecules formed in the third phase of glycolysis?
Since NAD+ exists, electrons are added through reduction and ADP is phosphorylated into ATP.
Which organic molecules donate a phosphate group to ADP during substrate-level phosphorylation?
The molecules that donate phosphates are 1,3-bisphosphoglycerate and phosphoenolpyruvate.
How is glycolysis regulated?
Availability of substrates, like glucose, and by feedback inhibition of the enzyme, phosphofructokinase.
Phosphofructokinase is the catalyst for the slowest, rate-limiting step in Step 3. When sufficient amount of ATP occurs, feedback inhibition occurs using the allosteric site located on the enzyme causing it to undergo a conformational change rendering the active site inhibited.
What is the Warburg effect in relation to tumors and cancer and is the basis for detection of these disease states via positron-emission tomography (PET)?
The cells use glycolysis for ATP production while healthy cells mainly use oxidative phosphorylation.
How does using fluorodeoxyglucose (FDG) in PET scans help detect cancer cells?
Cancer cells use high amounts of glucose and since these cancer cell’s genome expression involves the encoding of more enzymes involved with glycolysis, high concentrations of the radioactive FDG can be observed.
What percentage of cancers exhibit an overexpression of glycolysis?
Approx 80%
This includes cancers associated with lung, skin, colon, liver, pancreatic, breast, ovarian, and prostate.
All 10 glycolytic enzymes are overexpressed in many of these cases!
Why is FDG radiolabeled?
FDG is radiolabeled so it can be specifically detected by a PET scan.
Why is FDG radiolabeled?
FDG is radiolabeled so it can be specifically detected by a PET scan.
How does the overexpression of glycolytic enzymes affect tumor growth?
The increase in glycolysis favors tumor growth because of the hypoxic , deficient in oxygen, environment within the tumors.
Glycolysis creates ATP without oxygen while oxidative phosphorylation needs oxygen. With this, the increase of glycolytic enzymes is present and favorable to cancer cells since they would have a hard time producing ATP via oxidative phosphorylation.
[Breakdown of Pyruvate] Where is pyruvate produced and where is it transported to?
Made in the cytosol and then sent to the mitochondrial matrix.
What oxidizes pyruvate when it enters the mitochondrial matrix?
Pyruvate hydrogenase
What is removed from pyruvate?
A molecule of CO2 (oxidative decarboxylation)
What is attached to the acetyl group to produce an activated version?
Coenzyme A or CoA
In chemical questions, CoA will be denoted as CoA-SH to emphasize how the -SH group participates in the chemical reaction.
[Rewind] How does pyruvate get into the outer and inner cell membrane of the mitochondria?
It enters a channel through the outer membrane and enters the inner membrane via an H+/pyruvate symporter.
How is NADH produced in this metabolic pathway involving pyruvate?
Two electrons are stripped from pyruvate, reduced to NAD+ with H+ to create NADH.
How is the CoA molecule attached to pyruvate which later produces a large amount free energy when removed?
A sulfur atom
[Citric Acid Cycle aka Krebs cycle] What is a biochemical cycle in which particular molecules enter while others leave; the process is cyclical because it involves a series of organic molecules that are regenerated with each turn of the cycle?
Metabolic cycle
How is citric acid formed?
- Acetyl group (2 carbon atoms) is removed from the CoA
- Acetyl group is then attached to oxaloacetate (four carbon atoms) to create citrate (6 carbon atoms) AKA citric acid.
How many intermediate energy and carbon dioxide molecules are released form the citric acid cycle?
(This is for one molecule of pyruvate and must be doubled for one molecule of glucose)
Three NADH (6)
Two CO2 (4)
One FADH2 (2)
One GTP (guanosine triphosphate) (2 GTP but then 2 ATP)
How is GTP made which will be eventually used to make ATP?
Substrate-level phosphorylation
What happens after these 8 steps of the citric acid cycle are over?
It repeats only provided that acetyl CoA is available
What is significant about the citric acid cycle in regards to continuing in a loop?
The end result of this cycle recreates oxaloacetate (four carbon molecule) from the citric acid (6 carbon molecule) that first bonded with acetyl CoA to recreate the process.
How is the citric acid cycle regulated?
- Availability of substrates such as acetyl-CoA and NAD+
- Feedback Inhibition - In mammals, NADH and ATP act as feedback inhibitors of isocitrate dehydrogenase, whereas NAD+ and ADP act as activators.
What needs to be present for the citric acid cycle to be inhibited? What about stimulated?
NADH and ATP levels are high.
NAD+ and ADP levels are high.
[Oxidative Phosphorylation] At this point in the first three stages of glucose metabolism, what is the total yield?
10 molecules of NADH
6 molecules of CO2
4 molecules of ATP
2 molecules of FADH2
What is the process during which NADH and FADH2 are oxidized to make more ATP via the phosphorylation of ADP?
Oxidative phosphorylation
Termed because of the observation that electrons are removed from NADH and FADH2, and ATP is made by the phosphorylation of ADP
What is a group of protein complexes and small organic molecules within the inner membranes of mitochondria and chloroplasts and the plasma membrane of prokaryotes? The components accept and donate electrons to each other in a linear manner and produce a H+ electrochemical gradient.
Electron transport chain (ETC)
A series of redox reactions
What are the small molecules attached to the surface of protein complexes that aid in their function?
Prosthetic groups
What is the role of ubiquinone and iron prosthetic groups in the ETC?
To accept and release electrons
What does the ETC accomplish?
Oxidation or removal of electrons from NADH or FADH2 and pumps H+ across the inner mitochondrial membrane.
Explain the meaning of the name cytochrome oxidase (Protein complex within WTC)
The protein complex is called cytochrome oxidase because it removes electrons from (oxidizes) cytochrome c.
What does ATP synthase transport across its membrane to form ATP from ADP and Pi?
H+ molecule (AKA a proton)
While within the inner mitochondrial membrane, the electrons follow a series of redox reactions and are transferred to components of increasingly higher __________?
Electronegativity
Oxygen is the final electron acceptor and has the highest electronegativity.
What is another name for ETC because of the oxygen we breath is used in this process?
Respiratory chain
T/F NADH and FADH2 donate their electrons at the same point within the ETC.
False
Two high-energy electrons are transferred one at a time to NADH dehydrogenase (complex I)
Then transferred to ubiquinone (Q), cytochrome b-c1 (complex III), cytochrome c, and cytochrome oxidase (complex IV) Final acceptor is O2.
For FADH2, it transfers to succinate reductase (complex II), then to ubiquinone, and the rest of the chain.
What is created in the intermembrane space via the energy released with the movement of the electrons through the inner mitochondrial membrane?
A large H+ electrochemical gradient
How does cyanide effect the ETC?
The lethal effects of cyanide occur by the inhibition of cytochrome oxidase (complex IV) which does not allow the cell to make ATP for survival.
What is the enzyme that synthesizes ATP?
ATP synthase
An enzyme that utilizes the energy stored in a H+ electrochemical gradient for the synthesis of ATP via chemiosmosis.
What type of process is the passive flow of H+ through the enzyme, ATP synthase?
Exergonic
What is the process called by synthesizing ATP as result of pushing H+ across a membrane?
Chemiosmosis (Greek osmos, meaning to push) In other words, chemical push.
How is oxidative phosphorylation regulated? (2)
- Availability of substrates
2. ATP/ADP ratios
When ATP levels are high, what enzyme do they bind to thereby inhibiting the ETC and oxidative phosphorylation?
Cytochrome oxidase (complex IV)
When ADP levels are high, oxidative phosphorylation is stimulated how? (2)
- ADP stimulated cytochrome oxidase
2. ADP is a substrate that is used with Pi to make ATP.
What are the two reasons why maximal ATP is rarely achieved in oxidative phosphorylation?
- Some of the energy intermediates are used for anabolic pathways such as the synthesis of organic molecules such as glycerol (component of phospholipids)
- Some of the energy in the H+ electrochemical gradient will be used for other purposes such as the uptake into the matrix via the H+/pyruvate symporter.
Out of the three metabolic pathways, glycolysis, citric acid cycle, and oxidative phosphorylation, which process has the greater capacity to make ATP?
Oxidative phosphorylation (30-34)
Glycolysis (2)
Citric Acid Cycle (2)
[Review] What are the four processes that drive oxidation of glucose?
Glycolysis, breakdown of pyruvate, citric acid cycle, and oxidative phosphorylation. This process is HIGHLY exergonic that releases free energy.
For the H+ pumps along the ETC, how much free energy is released from each electron which is sampled to power the pumps?
-25 kcal/mol
[ATP Synthase] To study ATP synthase experimentally, this protein was purified. Another protein, bacteriorhodopsin was also purified which is found in Archaea. What did previous research show on bacteriorhodopsin and its relationship with H+?
It is a light-driven H+ pump.
What is the process of taking purified proteins and inserting them into membrane vesicles?
Reconstitution
Is the functioning of the electron transport chain always needed to make ATP via ATP synthase?
No. The role of the electron transport chain is to produce an H+ electrochemical gradient, which is what drives ATP synthase. If the H+ electrochemical is made another way, such as by bacteriorhodopsin, ATP synthase can still make ATP.
T/F ATP Synthase does not spin when it makes ATP.
True.
The y subunit rotates when a H+ flows between a c subunit and the a subunit causes the y subunit to rotate 120 degrees.
What subunit, after the y subunit rotates, undergoes a series of 3 conformational changes that lead to the synthesis of ATP from ADP and Pi?
B subunit
What subunits does the H+ move between when entering from the intermembrane electrochemical gradient?
c and a subunits
What are the three conformational changes the B subunit undergoes?
Conformation 1: ADP and Pi bind with good affinity
Conformation 2: ADP and Pi bind very tightly, which strains chemical bonds so that ATP is made
Conformation 3: ATP binds very weakly and is released.
At any given time, what is going on with the three B subunits?
One is ADP bound, one with ATP bound, and one without any nucleotide bound.
What advantage does integrating protein, carbohydrate, and fat metabolism have for cells?
The advantage is that cells can use the same enzymes to metabolize different kinds of organic molecules. This saves energy because it would require a lot of energy to make many different enzymes, which are composed of proteins.
DING: This is why proteins, fats, and carbohydrates are all sources of energy or calories.
Breakdown products of proteins and fats are used as fuel for cellular respiration, entering the same pathways used to break down carbohydrates.
What refers to an environment that lacks oxygen or a process that occurs in the absence of oxygen; a form of metabolism that does not require oxygen?
Anaerobic
Bacteria and archaea oxidize organic molecules to obtain sufficient amounts of energy in these environments.
What is the breakdown of organic molecules in the absence of oxygen by using a final electron acceptor that is something other than oxygen?
Anaerobic respiration
What is the breakdown of organic molecules to produce energy without any net oxidation of an organic molecule?
Fermentation.
This produces ATP via substrate-level phosphorylation only, without any net oxidation.
What bacterial species within the human body uses an enzyme, nitrate reductase, and recognizes nitrate (NO3-) as the final electron acceptor instead of O2 in the absence of O2?
Escherichia coli or E. coli
What organisms, among many others, use only O2 as the final electron acceptor of their ETC?
Animals and yeast.
What happens when animals and yeast do not have an oxygen source even though they can create ATP from glycolysis, a reaction that does not need oxygen? (2 reasons why this is a problem)
NADH builds up and NAD+ decreases (NADH cannot be oxidized without the help of oxygen)
First, at high concentrations, NADH haphazardly donates its electrons to other molecules and promotes the formation of free radicals, highly reactive chemicals that damage DNA and cellular proteins. For this reason, yeast and animal cells exposed to anaerobic conditions must have a way to remove the excess NADH generated from the breakdown of glucose.
The second problem is the decrease in NAD+. Cells need to regenerate NAD+ to keep glycolysis running and make ATP via substrate-level phosphorylation.
How do muscle cells cope with the buildup of NADH and accompanying decrease in NAD+?
When the environment for the muscle cells become anaerobic, as in high-intensity exercise, the pyruvate from the glycolysis is reduced to make lactate or lactic acid)
With this, the electrons used to reduce pyruvate are from NADH which is then oxidized to NAD+ This effectively reduces NADH and provides NAD+ for glycolysis to continue.
With yeast, how does it cope with anaerobic conditions?
Pyruvate is broken down to CO2 and a two-carbon molecule called acetaldehyde.
Acetaldehyde is then reduced by NADH to make ethanol, which NADH is oxidized to NAD+.
T/F The term fermentation is used to describe the breakdown of organic molecules to harness energy without any net oxidation (that is, without any removal of electrons). The pathways for breaking down glucose to lactate or ethanol are examples of fermentation.
True
How are electrons not removed in this process?
Electrons are donated back to an organic molecule in the production of lactate or ethanol.
T/F Fermentation produces less ATP than oxidative phosphorylation.
True
T/F Overall, the complete breakdown of glucose in the presence of oxygen yields 34–38 ATP molecules. By comparison, the anaerobic breakdown of glucose to lactate or ethanol yields only 2 ATP molecules.
True
