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.
-
Anabolic
Catabolic - What type is energy requiring, involving the biosynthesis of complex organic compounds from simple molecules?
- Anabolic
- Which type releases energy as they breakdown complex organic compounds into smaller molecules.
- Catabolic
-
True or false
The metabolic reactions of cells are coupled so that energy released from catabolic reactions can be harnessed to fuel anabolic reactions. - True
- 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?
-
Autotrophic
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.
- Hetrotrophic
- The production of glucose (C₆Hâ‚â‚‚O₆) by autotrophs involves the breakdown of C-O & H-O bonds in COâ‚‚ and Hâ‚‚O, 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
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C₆Hâ‚â‚‚O₆ (glucose) + 6Oâ‚‚ - 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?
-
Photosynthesis
C₆Hâ‚â‚‚O₆ (glucose) + 6Oâ‚‚
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6COâ‚‚ + 6 Hâ‚‚O + Energy - What is the cells main energy currency?
-
ATP
Adenosine triphosphate -
True or false
ATP is synthesized during glucose catabolism? - True
- ATP is composed of the nitrogenous base adenine and what sugar along with three weekly linked phosphate groups.
- Ribose
- 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
- 7
- Release of this energy is used for endergonic (endothermic) reactions for what types of uses?
-
Muscle contraction
Motility
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?
- 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?
- Oxidation
- 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)?
- Reduction
-
What is the result of the following accepting electrons.
NAD⁺ in the presence of hydride ion
FAD in the form of hydrogen atom
NADP⁺ -
NAD is reduced to NADH
FAD is reduced to FADHâ‚‚
NADP⺠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?
-
NAD⁺
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?
-
Glycolysis
Cellular respiration - What is the first stage of glucose catabolism?
- Glycolysis
- 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?
-
Cytoplasm
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?
- 2 ATP
- 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?
- Yes
- 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?
-
Ethanol
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
- Acetaldehyde is then reduced by the NADH generating step 5 of glycolysis to yield what?
- Ethanol
-
True and false
Fermentation commonly occurs only in yeast and some bacteria. - True
-
True or false
Lactic acid fermentation occurs in certain fungi and bacteria and in human muscle cells during strenuous activity. - True
- 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?
- Reduced
- The build up of lactic acid in muscle tissue causes a decrease in what that leads to muscle fatigue?
- pH
- 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?
- Aerobic
- What acts as the final acceptor of electrons that are passes from carrier to carrier during the final stage of glucose oxidation?
- Oxygen
- Where do the metabolic reactions of cellular respiration occur in the eukaryotic organism?
- Mitochondria
- Are these reactions catalyzed by reaction-specific enzymes?
- Yes
- 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. - True
- For each turn of the citric acid cycle what is produced by a substrate level phosphorylation via a GTP intermediate?
- 1 ATP
- In addition, electrons are transferred to NAD⁺ & FAD, generating what?
- NADH & FADHâ‚‚
- 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
- 2