3. Cellular Respiration +

Question 1

Cellular Respiration. Endergonic or Exergonic?

Answer 1

• overall an oxidative, exergonic process (ΔG = -686 kcal/mole)

Question 2

External vs. Internal Respiration

Answer 2

• External respiration: entry of air into lungs and gas exchange between alveoli and blood
• Internal respiration: exchange of gas between blood and cells + intracellular respiration processes

Question 3

Respiration Equation:

Answer 3

C6H12O6 + 6O2 —> 6CO2 + 6 H2O + energy

Question 4

Aerobic Respiration:

Answer 4

• in presence of O2 (glycolysis, pyruvate decarb, krebs cycle, oxidative phosphorylation), water is final product.

Question 5

Glycolysis

Answer 5

• decomposition of glucose into pyruvate in cytosol
• 2 ATP added, 2 NADH produced, 4 ATP produced, 2 pyruvate formed
• Net: 2ATP + 2 NADH + 2 pyruvate (+2 H2O, + 2 H+)
• ATP produced here via substrate-level-phosphorylation ( direct enzymatic transfer of Pi to ADP)
• PFK (enzyme) adds 2nd P, makes fructose 1,6-bisphosphate, this is irreversible and commits to glycolysis, major regulatory point.

Question 6

Pyruvate Decarboxylation

Answer 6

• at this point, we are in mitochondrial matrix
• pyruvate –> acetyl coA, producing 1 NADH and 1 CO2
• net: 2 NADH + 2 CO2
• catalyzed by PDC enzyme (pyruvate dehydrogenase complex)

Question 7

Krebs Cycle/Citric Acid Cycle/Tricarboxylic Acid Cycle

Answer 7

• fate of pyruvate from glycolysis
• in Krebs cycle, acetyl coA merges w/ oxaloacetate to form citrate, cycle goes w/ 7 intermediates.
• 3 NADH, 1 FADH2, 1 ATP (subs level pho), 2 CO2 produced per turn. (2 turns total for one glucose)
• Total for 1 glucose molecule: 6 NADH, 2 FADH2, 2 ATP (technically GTP), 4 CO2
• Place: mitochondrial matrix (like pyruvate decarbox)
• CO2 produced here is CO2 exhaled when animals breathe

Question 8

Electron Transport Chain (ETC)

Answer 8

• Place: inner membrane/cristae(folds that increase SA for more ETC action)
• Oxidative phosphorylation: ADP –> ATP from NADH and FADH2 via passing e- through various carrier proteins.
• NADH makes more energy than FADH2, more H+ pumped across per NADH (both are coenzymes), (3:2 yield)
• O2 if final e- acceptor - combines with native H+ to form H2O
• carriers extract energy from NADH and FADH2 while pumping protons into intermembrane space - ATP synthase uses this gradient (pH and electrical) to make ATP as it shuttles H+ back into inner matrix
• Coenzyme Q(CoQ)/Ubiquinone is a soluble carrier dissolved in membrane that can be fully reduced/oxidized
• Cytochrome C is a protein carrier in ETC, common in many living organisms, used for genetic relation. Cytochromes have nonprotein parts like iron (donat/accept e-, for redox)

Question 9

ATP Yield from 1 glucose

Answer 9

• not actual yield, mitochondrial efficacy varies.
• eukaryotes: 36 ATP
• prokaryotes: 38 ATP. More ATP because prok don’t have mitochonria so they don’t have to transfer pyruvate to mitochondrial matrix (costs ATP).

Question 10

Mitochondria

Answer 10

• outer membrane, intermembrane space (H+), inner membrane (oxid phosph.), mitochondrial matrix (krebs)

Question 11

Chemiosmosis in Mitochondria

Answer 11

• ATP generation from energy stored in form of proton concentration gradient across membrane.
• Krebs produces NADH/FADH2, they are oxidized (lose e-), H+ transported from matrix to intermembrane space, ph and electric charge gradient created, ATP synthase uses energy to create ATP by letting proton flow through the channel.

Question 12

ATP

Answer 12

• RNA nucleotide (due to ribose sugar)
• unstable because 3 phosphates in ATP are negatively charged and repel one another
• when one phosphate group removed via hydrolysis, more stable molecule ADP results
• change from less stable molecule to more stable always releases energy
• provides energy for all cells by transferring phosphate from ATP to another molecule

Question 13

Anaerobic Respiration

Answer 13

• Cytosol
• glycolysis + fermentation
• aerobic respiration regenerates NAD+ via O2, which is required for continuation of glycolysis, without O2, there would be no replenishing - NADH accumulates, cell would die w/ no new ATP, so fermentation occurs.
• Alcohol Fermentaion
• Lactic Acid Fermentation

Question 14

Alcohol Fermentation

Answer 14

• occurs in plants, fungi (yeasts), and bacteria (botulinum)
• pyruvate -> acetaldehyde + CO2, then acetaldehyde —> ethanol (and NADH -> NAD+)
• acetaldehyde is final e- acceptor (forming ethanol)

Question 15

Lactic Acid Fermentation

Answer 15

• occurs in human muscle cells, other microorganisms
• pyruvate -> lactate (NADH -> NAD+)
• lactate is transported to liver for conversion back to glucose once surplus ATP is available

Question 16

Facultative Anaerobes

Answer 16

• can use O2 when it’s present (more efficient) but switch to fermentation/anaerobic respiration if it isn’t

Question 17

Obligate Anaerobes

Answer 17

• cannot live in presence of oxygen

Question 18

Other Energy Sources

Answer 18

When glucose supply is low, body uses other energy sources, in priority of: others carbs, fats, and proteins. First converted to glucose or glucose intermediates, then degraded in glycolysis or CAC

Question 19

Alternate Energy Sources (other Carbohydrates)

Answer 19

• disaccharides are hydrolyzed into monosaccharides, most of which can be converted to glucose or glycolytic intermediates.

*** random: all cells capable of producing and storing glycogen but only muscle cells and especially liver cells have large amounts

Question 20

Insulin…..PFK enzyme.

Answer 20

• activates
• insulin means “hey, we got too much glucose around, so lets chew it up”
• glucagon inhibits PFK enzyme

Question 21

Alternate Energy Sources (Fats)

Answer 21

• fats store more energy than carbohydrates per C, their carbons are in a more reduced state
• fats are 10 cals/g, whereas carbs and protein are 4
• triglycerides in lumen of small intestine broken down via lipases into monoacylglycerides + fatty acids which are then absorbed into the enterocytes (cell lining of small intestine). There, they are reassembled into triglycerides and then (along with cholesterol/proteins/phospholipids) packaged into chylomicrons which move to lymph capillary for transport to rest of body where they are stored as adipose tissue.
• glycerol -> PGAL, enters glycolysis
• when fatty acid –> acetyl coA, every 2 carbon from fatty acid chain makes an acetyl coA. fatty acids in blood are carried by albumin
• fatty acids broken down via beta oxidation (mitochondrial matrix). 2 ATP spend activating entire chain. Saturated fatty acids produce 1 NADH and 1 FADH2 for every cut into 2 carbons. 18 C chain is 9 2C pieces but only cut 8 times, each cut is beta oxidation step. unsaturated fatty acids produce 1 less FADH2 for each double bond
• Fats more ATP yield than carbohydrates or proteins

Question 22

Alternate Energy Sources (Protein)

Answer 22

• least desirable source of energy, only when carbs and fats are unavailable.
• most amino acids are deaminated in liver, then converted to pyruvate or acetyl coA or other CAC intermediates, enter cellular respiration at these various points (varies by AA). Oxidative deamination removes ammonia molecule directly from AA. ammonia is toxic to vertebrates: fish excrete, insects and birds convert to uric acid, mammals convert to urea for excretion.