Test 4: Chapter 13

Question 1

cell respiration

Answer 1

• the process whereby all these sugars are broken down to generate energy is very similar in both animals and plants
• the organism’s cells harvest useful energy from the chemical-bond energy locked in sugars as the sugar molecule is broken down and oxidized to carbon dioxide (CO2) and water (H2O)—a process called cell respiration
• The energy released during these reactions is captured in the form of “high-energy” chemical bonds—covalent bonds that release large amounts of energy when hydrolyzed—in activated carriers such as ATP and NADH
  
  • These carriers then serve as portable sources of the chemical groups and electrons needed for biosynthesis

Question 2

The breakdown and uTilizaTion of sugars and faTs

Answer 2

• cells use enzymes to carry out oxidation of sugars in a tightly controlled series of rxns
• cells degrade glucose molecs step by step, paying out energy in small packets to activated carriers by means of coupled rxns
  
  • much of the energy released by the breakdown of glucose is saved in the high-energy bonds of ATP and other activated carriers
    
    • used to do work in cell

Question 3

animal cells making ATP

Answer 3

Two ways:

1. certain energetically favorable, enzyme-catalyzed reactions involved in the breakdown of foods are directly coupled to the energetically unfavorable reaction ADP + Pi → ATP
   
   1. thus, oxidation of food = energy for immediate ATP
2. oxidative phosphorylation
   
   1. energy from activated carriers is used to make ATP
   2. takes place on inner mitochondrial membrane

Question 4

catabolism

Answer 4

• the breakdown process in which enzymes degrade complex organic molecs into simpler one
• three stages:
  
  • 1) breakdown of foods to simple subunits
  • 2) breakdown of simple subunits to acetyl CoA
    
    • limited amounts of ATP and NADH produced
  • 3) complete oxidation of acetyl CoA to H2O and CO2
    
    • large amounts of ATP produced in mitochondria

Question 5

Catabolism Stage 1

Answer 5

• aka digestion
• enzymes convert the large polymeric molecules in food into simpler monomeric subunits:
  
  • proteins into amino acids
  • polysaccharides into sugars
  • fats into fatty acids and glycerol
• occurs either outside cells (in the intestine) or in specialized organelles within cells called lysosomes
• after digestion, small organic molecs derived from food enter cytosol where their gradual oxidative breakdown begins

Question 6

Catabolism Stage 2

Answer 6

• aka glycolysis(takes place in cytosol)
• each glucose molec that enters requires 2 ATP molec
• splits each glucose into two smaller pyruvates and produces smalls amts of ATP(w.o using Oxygen) and NADH
  
  • net gain of 2 ATP and 2 NADH per glucose
    
    • Sugars other than glucose can also be used, after first being converted into one of the intermediates in this sugar-splitting pathway
• The pyruvate is transported from the cytosol into the mitochondrion’s large, internal compartment(matrix)
• There, a giant enzyme complex converts each pyruvate molecule into CO2 plus acetyl CoA(an activated carrier)
• In the same compartment, large amounts of acetyl CoA are also produced by the stepwise oxidative breakdown of fatty acids derived from fats

Question 7

Catabolism Stage 3

Answer 7

• aka citric acid cycle(takes place entirely in mitochondria)
• acetyl group in acetyl CoA is transferred to an oxaloacetate molecule to form citrate –> citric acid cycle
• acetyl group is oxidized to CO2, lots of NADH is produced
• high-energy electrons from NADH are passed along a series of enzymes within the mitochondrial inner membrane called an electron-transport chain
  
  • energy released by their transfer driveS oxidative phosphorylation(a process that produces ATP and consumes O2 gas)
  • In these final steps of catabolism, the majority of the energy released by oxidation is harnessed to produce most of the cell’s ATP

Question 8

Fun ATP facts

Answer 8

• Roughly 10^9 molecules of ATP are in solution in a typical cell at any instant
• In many cells, all of this ATP is turned over (that is, consumed and replaced) every 1–2 minutes
• An average person at rest will hydrolyze his or her weight in ATP molecules every 24 hours
• in anaerobic microorganisms, glycolysis is principle source of ATP

Question 9

Kinase

Answer 9

• glycolysis enzyme
• generally: catalyzes the addition of a phosphate group to molecules
• in glycolysis: a kinase transfers a phosphate group from atp to a substrate in steps 1 and 3; other kinases transfer a phosphate to aDp to form atp in steps 7 and 10

Question 10

isomerase

Answer 10

• glycolysis enzyme
• generally: catalyzes the rearrangement of bonds within a single molecule
• in glycolysis: isomerases in steps 2 and 5 prepare molecules for the chemical alterations to come

Question 11

Dehydrogenase

Answer 11

• glycolysis enzyme
• generally: catalyzes the oxidation of a molecule by removing a hydrogen atom plus an electron (a hydride ion, H–)
• in glycolysis: the enzyme glyceraldehyde 3-phosphate dehydrogenase generates NaDh in step 6
  
  • remainder of the energy released during glycolysis is stored in the electrons in thisNADH molec
  • although no molecular oxygen is involved in glycolysis, oxidation does occur: in step 6, a hydrogen atom plus an electron is removed from the sugar intermediate, glyceraldehyde 3-phosphate, and transferred to NAD+, producing NADH

Question 12

Mutase

Answer 12

• glycolysis enzyme
• generally: catalyzes the shifting of a chemical group from one position to another within a molecule
• in glycolysis: the movement of a phosphate by phosphoglycerate mutase in step 8 helps prepare the substrate to transfer this group to aDp to make atp in step 10

Question 13

fermentations

Answer 13

• energy-yielding pathways that break down sugar in the absence of oxygen are called
• In anaerobic conditions, the pyruvate and NADH made by glycolysis remain in the cytosol
• The pyruvate is converted into products that are excreted from the cell: lactate in muscle cells, for example, or ethanol and CO2 in the yeast cells used in brewing and breadmaking
• The NADH gives up its electrons in the cytosol, and is converted back to the NAD+ required to maintain the reactions of glycolysis

*bacteria and archaea can also make ATP w.o O

Question 14

anaerobic respiration vs. fermentation

Answer 14

anaerobic respiration differs from fermentation in that it involves an electron-transport chain embedded in a membrane—in this case, the plasma membrane of the microbe

Question 15

What happens to the pyruvate produced by glycolysis

Answer 15

• In aerobic metabolism in eukaryotic cells, the pyruvate produced by glycolysis is actively pumped into the mitochondrial matrix
• There, it is rapidly decarboxylated by a giant complex of three enzymes, called the pyruvate dehydrogenase complex
• The products of pyruvate decarboxylation are CO2 (a waste product), NADH, and acetyl CoA

Question 16

What happens to fat during glycolysis

Answer 16

• fat is a major source of energy for most nonphotosynthetic organisms
• Like the pyruvate derived from glycolysis, the fatty acids derived from fat are converted into acetyl CoA in the mitochondrial matrix
  
  • Fatty acids are first activated by covalent linkage to CoA
  • then broken down completely by a cycle of reactions that trims two carbons at a time from their carboxyl end, generating one molecule of acetyl CoA for each turn of the cycle.
  • Two activated carriers—NADH and another high-energy electron carrier, FADH2—are also produced in this process

Question 17

several organic molecules are Converted to acetyl Coa in the mitochondrial matrix

Answer 17

• pyruvate
• fatty acids
  
  • Takes place in mitochondrial matrix
  • Fats are covalently linked to CoA
  • With each turn of this cycle
    
    • the energy in the carbon bonds is transferred to activated carriers(FADH2) and NADH + H+
    • Yields 1 molecule of acetyl CoA
• some aa’s transported from cytosol into mitochondrial matrix
  
  • in eukaryotes, the mitochondrion is the center toward which all energy-yielding catabolic processes lead
  • In aerobic bacteria— which have no mitochondria—glycolysis and acetyl CoA production, as well as the citric acid cycle, take place in the cytosol

Question 18

5*citric acid cycle fun facts

Answer 18

• accounts for about 2/3 of the total oxidation of carbon compounds in most cells(takes place in mitochondrial matrix)
• energy is released from carbon bonds
• major end products are CO2(waste) and high-energy electrons in the form of NADH(passed to electron transport chain in inner mitochondrial membrane, at end of chain they combine with O2 to make H2O)
• does not itself use O2, but requires O2 to proceed bc electron transport chain needs it as its final acceptor
• many of its energy-generating rxns are of recent origin
• aka Krebs cycle or tricarboxylic acid cycle
• Completely oxidizes the carbon atoms of acetyl groups in acetyl CoA into CO2
• Yields:
  
  • 3 NADH + H+
  • 1 GTP
  • 1 FADH2

Question 19

5*citric acid cycle steps

Answer 19

• The citric acid cycle catalyzes the complete oxidation of the carbon atoms of the acetyl groups in acetyl CoA, converting them into CO2
• The acetyl group is not oxidized directly, however. Instead, it is transferred from acetyl CoA to a larger four-carbon molecule, oxaloacetate, to form the six-carbon tricarboxylic acid, citric acid
• The citric acid molecule (aka citrate) is then progressively oxidized, and the energy of this oxidation is harnessed to produce activated carriers in much the same manner as we described for glycolysis.
• The chain of eight reactions forms a cycle, because the oxaloacetate that began the process is regenerated at the end

Question 20

5*FADH2 and GTP

Answer 20

• tytpes of activated carriers
• In addition to 3 molecules of NADH, each turn of the cycle also produces 1 molecule of FADH2 (reduced flavin adenine dinucleotide) from FAD and 1 molecule of the ribonucleoside triphosphate GTP (guanosine triphosphate) from GDP
  
  • GTP is a close relative of ATP
• Like NADH, FADH2 is a carrier of highenergy electrons and hydrogen

Question 21

5*A common misconception about the citric acid cycle

Answer 21

• misconception: atmospheric O2 required for the process to proceed is converted into the CO2 that is released as a waste product
• reality: the oxygen atoms required to make CO2 from the acetyl groups entering the citric acid cycle are supplied not by O2 but by water
  
  • three molecules of water are split in each cycle, and the oxygen atoms of some of them are ultimately used to make CO2

Question 22

anabolic pathways

Answer 22

• Many of the intermediates formed in glycolysis and the citric acid cycle are siphoned off by such anabolic pathways, in which they are converted by series of enzyme-catalyzed reactions into amino acids, nucleotides, lipids, and other small organic molecules that the cell needs

Question 23

oxidative phosphorylation

Answer 23

• final stage in the oxidation of food molecs
• chemical energy captured by the activated carriers produced during glycolysis and the citric acid cycle is used to generate ATP
• 1)NADH and FADH2 transfer their high-energy electrons to the electron-transport chain(a series of electron carriers in the inner mitochondrial membrane in eukaryotic cells/plasma membrane of aerobic bacteria)
• 2)as e- pass thru, they move into lower energy states
• 3) the energy released is used to drive H+ (protons) across the inner membrane, from the mitochondrial matrix to the intermembrane space
• 4)This movement generates a proton gradient across the inner membrane, which serves as a source of energy that can be used to driveenergy-requiring reactions
  
  • EX: phosphorylation of ADP to generate ATP on the matrix side of the inner membrane
• 5) At the end of the transport chain, the electrons are added to molecules of O2 that have diffused into the mitochondrion, and the resulting reduced oxygen molecules immediately combine with protons (H+) from the surrounding solution to produce water

Question 24

Oxidative phosphorylation fun facts

Answer 24

• complete oxidation of a molecule of glucose to H2O and CO2 produces 30 molecules of ATP. BUT only two molecules of ATP are produced per molecule of glucose by glycolysis alone.
• Oxidative phosphorylation occurs in both eukaryotic cells and in aerobic bacteria
• It represents a remarkable evolutionary achievement, and the ability to extract energy from food with such great efficiency has shaped the entire character of life on Earth

Question 25

Enery Utilization

Answer 25

• If a fuel molecule (glucose) was oxidized all in one step, more energy than can be captured is release
  
  • SO Cells break down fuel molecules in a series of steps to capture the free energy and store it in activated carriers (ATP, NADH)

Question 26

Pyruvate Dehydrogenase Complex(PDC)

Answer 26

• Produces of pyruvate decarboxylation are CO2, NADH, and acetyl CoA
• Reaction intermediates passed from one to another
• Acetyl CoA enters the Citric Acid Cycle

Question 27

2 types of anaerobic fermentation

Answer 27

• pyruvate is broken down in the absence of oxygen by fermentation
• 1 glucose enters glycolysis, 2 pyruvate exit
  
  • fermentation of 2 pyruvate yields 2 lactate(2 CO2 and ethanol) and 2 NAD+
• A: fermentation in an active muscle cell
  
  • When inadequate oxygen is present, for example, in a muscle cell undergoing vigorous contraction, the pyruvate produced by glycolysis is converted to lactate in the cytosol. this reaction restores the NaD+ consumed in step 6 of glycolysis, but the whole pathway yields much less energy overall than if the pyruvate were oxidized in mitochondria
• B: fermentation in yeast
  
  • In microorganisms that can grow anaerobically, pyruvate is converted into carbon dioxide and ethanol. again, this pathway regenerates NaD+ from NaDh, as required to enable glycolysis to continue

Question 28

pyruvate dehydrogenase complex(PDC)

Answer 28

• PDC is larger than a ribosome
• PDC is a complex of 3 enzymes
• pyruvate is converted into acetyl Coa and CO2 by the pyruvate dehydrogenase complex in the mitochondrial matrix
• without PDC
  
  • pyruvate from glycolysis would stay in mitochondrial matrix and not be decarboxylated