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MCAT 2003 Biology (Cellular Metabolism)


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What is the sum of all chemical reactions that take place in a cell called?
Cellular metabolism
What are the two general categories for this.
What type is energy requiring, involving the biosynthesis of complex organic compounds from simple molecules?
Which type releases energy as they breakdown complex organic compounds into smaller molecules.
True or false
The metabolic reactions of cells are coupled so that energy released from catabolic reactions can be harnessed to fuel anabolic reactions.
What is the ultimate energy source for living organisms?
The sun
Green plants that convert sunlight into bond energy stored in the bonds of organic compounds (chiefly glucose) using the process of photosynthesis are considered what type of organism?
They do not need an exogenous supply of organic compounds.
This type of organism obtains their energy catabolically, via breakdown of organic nutrients that must be ingested.
The production of glucose (C₆H₁₂O₆) by autotrophs involves the breakdown of C-O & H-O bonds in CO₂ and H₂O, and the forming of C-H, C-O, C-C and O-H bonds in gluclose. What is teh net reaction of photosynthesis?
6COâ‚‚ + 6 Hâ‚‚O + Energy
C₆H₁₂O₆ (glucose) + 6O₂
Heterotrophs metabolize gluclose and other organic molecules to release the stored bond energies. The net reaction of glucose catabolism is essentially the reversal of what?
C₆H₁₂O₆ (glucose) + 6O₂
6COâ‚‚ + 6 Hâ‚‚O + Energy
What is the cells main energy currency?
Adenosine triphosphate
True or false
ATP is synthesized during glucose catabolism?
ATP is composed of the nitrogenous base adenine and what sugar along with three weekly linked phosphate groups.
The energy of the ATP is stored in what type of bonds attaching the phosphate groups?
Covalent (high energy bonds)
Hydrolysis of ATP breaks it down to what?
ADP and Pi (inorganic phosphate). The stored bond is released for use in the cells metabolic process.
Approximately how many kcals of energy is released per mole of ATP
Release of this energy is used for endergonic (endothermic) reactions for what types of uses?
Muscle contraction
The active transport of substances across the plasma membrane
Can ATP be hydrolyzed into AMP (Adenosine monoposphate)?
Yes, forming AMP and PPi (pyrophosphate). 7 kcal/mole of energy is also used since only one bond is broken.
ADP combines with Pi to form ATP requiring energy. Where is this energy supplied from?
Degradation of glucose. 7 kcal/mole
The second mechanism by which the cells store chemical energy is in the form of what?
High potential energy - Electrons are transfered as hydride ions (H:⁻) or as pairs of hydrogen atoms
During glucose oxidation, are hydrogen atoms added or removed?
Most of these removed hydrogen atoms are accepted by what three carrier enzymes?
NAD⁺ (nicotinamide adenine dinucleotide), FAD (flavin adenine dinucleotide) and NADP⁺ (nicotineamide adenine dinucleotide phosphate)
These molecules transport the high-energy electrons of the hydrogen atoms to a series of carrier molecules on the inner mitochondrical membrane that are collectively known as what?
Electron transport chain
What refers to the loss of an electron?
Why are NAD⁺, FAD and NADP⁺ referred to as oxidizing agents?
They cause other molecules to loose electrons and undergo oxidation.
What happens to NAD⁺, FAD and NADP⁺ in the process (gain electrons)?
What is the result of the following accepting electrons.
NAD⁺ in the presence of hydride ion
FAD in the form of hydrogen atom
NAD is reduced to NADH
FAD is reduced to FADHâ‚‚
NADP⁺ is reduced to NADPH
while all donating molecules are oxidezed.
NADH transfers its electron to another electron acceptor thereby reducing it and in the process, the NADH is oxidized back to what?
Thus the coenzymes temporarily store and release energy in the form of electrons through their successive oxidations and reductions.
The degradative oxidation of glucose occurs in what two stages?
Cellular respiration
What is the first stage of glucose catabolism?
Glycolysis is a series of reactions that lead to the oxidative breakdown of glucose into two molecules of what?
Pyruvate (the ionized for of pyruvic acid)
The production of ATP
And the reduction of NAD⁺ into NADH
All these reactions occur where and are mediated by what?
Specific enzymes
What is obtained from one molecule of glucose?
2 molecules of pyruvate (a three carbon molecule)
What is used in the sequence glycolysis?
2 ATP are used (in steps 1 & 3)
4 ATP are generated (2 in step 6 & 2 in step 9)
There is a net production of how many ATP per glucose molecule?
This type of phosphorylation is called what?
Substrate level phosphorylation
Since ATP is synthesis is directly coupled with the degradation of glucose without the participation of an intermediate molecule such as NAD⁺. One NADH is produced per PGAL giving a total of how many NADH per glucose?
2 NADH per glucose
Does glycolysis occur in both eukaryotes and prokaryotes?
Has all then initial energy of the glucose molecule been released?
No. It is mostly still present in the chemical bonds of Pyruvate.
Where can pryuvate degradation go from here.
Anaerobic conditions (absence of oxygen) Pyruvate is reduced during the process of fermentation
Aerobic conditions (presence of oxygen) pyruvate is further oxidized during cell respiration in the mitochondria.
In fermentation, NAD⁺ must be regenerated for glycolysis to continue in the absence of oxygen. This is accomplished by reducing pyruvate into what two products?
Lactic acid
Fermentation refers to al of the reactions involved in this process. Fermentation produces how many ATPs per glucose molecule?
2 ATPs are porduced.
The pyruvate produced in glycolysis is decarboxylated to become what?
Acetaldehyde is then reduced by the NADH generating step 5 of glycolysis to yield what?
True and false
Fermentation commonly occurs only in yeast and some bacteria.
True or false
Lactic acid fermentation occurs in certain fungi and bacteria and in human muscle cells during strenuous activity.
When the oxygen supply to muscle cells lags behind the rate of glucose catabolism, the pyruvate generated is reduced to what?
Lactic acid
As in alcohol fermentation, the NAD⁺ used in glycolysis is regenerated when pyruvate is what?
The build up of lactic acid in muscle tissue causes a decrease in what that leads to muscle fatigue?
Once oxygen supply has been replenished, the lactic acid is oxidized back to pyruvate and enters what process?
Cellular respiration
The amount of oxygen needed for this conversion is know as what?
Oxygen debt
What is the most efficient catabolic pathway used by organisms to harvest the energy stored in glucose.
Cellular respiration
Whereas glycolysis yields only 2 ATP per molecule of glucose, cellular respiration can yield how many ATP?
3-38 ATP
Cellular respiration is an anaerobic or aerobic process?
What acts as the final acceptor of electrons that are passes from carrier to carrier during the final stage of glucose oxidation?
Where do the metabolic reactions of cellular respiration occur in the eukaryotic organism?
Are these reactions catalyzed by reaction-specific enzymes?
What are the three stages of cellular respiration?
Pyruvate decarboxylation
Citric acid cycle
Electron transport chain
The pyruvate formed during glycolysis is transported from the cytoplasm into the mitochondrial matrix where it is what?
Decarboxlyated - It looses COâ‚‚
The acetyl group that remains from this decarboxylation is transfered to coenzyme A to form what?
Acetyl CoA - In the process, NAD⁺ is reduced to NADH
The citric acid is also known as what other two cycles?
Krebs cycle
Tricarboxylic Acid Cycle (TCA)
The cycle begins when the two carbon acetyl group from acetyl CoA combines with what?
Oxaloacetate (a 4 carbon molecule)
What is formed be the combination of the tow carbon acetyl CoA with Oxaloacetate?
Citrate (6 carbon)
True or false
Through a complicated set of reactions, 2 COâ‚‚ are released, and oxaloacetate is regenerated for use in another turn of the cycle.
For each turn of the citric acid cycle what is produced by a substrate level phosphorylation via a GTP intermediate?
In addition, electrons are transferred to NAD⁺ & FAD, generating what?
These NADH & FADHâ‚‚ coenzymes then transport the electrons to the electron transport chain where more ATP is produced via what?
Oxidative phosphorylation
For each glucose molecule, how many pyruvates are decarboxylated and channeled into the citric acid cycle

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