DAT Cellular Respiration

1. Glycolysis

2. Pyruvate decarboxylation

3. TCA (Krebs cycle)

4. Electron transport chain

• Break down of glucose

• Anaerobic (no O2)

• 1 glucose mol. (6 Carbons) → 2 pyruvate mols. (3 Carbons)

  • 2 ATP input → 4 ATP output & 2 NADH = 2 net ATP mols. & 2 NADH

• Occurs in cytosol (not in organelle)

• Steps:

  1. Hexokinase: phosphorylates glucose → Glucose-6-phosphate → irreversible rxn

  2. Phosphofructokinase (PFK): phosphorylates Glucose-6-phosphate → Fructose-1,6-bisphosphate → rate limiting step

• CO2

• Waste product of cellular respiration (occurs via oxidation)

• ADP + Pi → ATP (oxidized)

• NAD+ + FAD+ → FADH2 + NADH (oxidized)

• Double layered

• Outer membrane

• Intermembrane space: H+ build up

• Matrix:

  • Krebs cycle → produces ATP

  • β-oxidation to break down fatty acids

• Inner membrane: many folds to ↑ surface area → ↑ electron transport chain output

• Occurs in mitochondrial matrix

• Aerobic process

• 2 pyruvate molecules from glycolysis transported into matrix via secondary active transport using protons (doesn’t directly use ATP)

• 1 Pyruvate + Coenzyme A → Acetyl CoA + 1 NADH + 1 CO2

  • Pyruvate decarboxylate complex (PDC) catalyzes rxn

2 CO2 + 2 NADH

• Occurs in mitochondrial matrix

• Aerobic process

• 1 Acetal CoA + oxaloacetate → citrate

  • Citrate further oxidizes until oxaloacetate is formed and the cycle repeats

• Full cycle yields: 3 NADH + 1 FADH2 + 1 GTP (ATP) + 2 CO2

• Occurs in inner membrane / cristae of mitochondria

• Aerobic process

• Removes e- from glucose, pyruvate and Acetyl CoA

• Oxidative phosphorylation occurs here

• Carrier proteins (I, II, III, IV) in inner membrane (electron acceptors): receive electrons from electron transporters (NADH, FADH2) → pump protons against [ ] gradient into intermembrane space to supply energy to ATP synthase

  • Highly acidic environment in intermembrane space

  • CoQ (Ubiquinon): can be fully oxidized and reduced during passing of electrons b/w protein complexes

    • Soluble carrier

  • Cyt C (Cytochrome C): bound to Iron atom which transfers electrons b/w Complex III and Complex IV for redox rxns

    • Protein carrier

    • Used for genetic relations

• Final electron acceptor (after electrons have passed though all proteins): Oxygen → combines w/ H+ to form H2O

• ATP Synthase: drives protons down the gradient towards matrix (high [ ] → low [ ]) to catalyze ADP + Pi → ATP

  • pH + Electrical Gradient: Proton Motive Force

  • If pH of intermembrane space is higher than normal → less H+ → less cellular respiration occurring

• NADH creates more ATP (3x) than FADH2 (2x)

  • NADH pumps more protons to carrier proteins than FADH2 because NADH enters the protein complex earlier than FADH2 and it enters Complex I (FADH2 enters Complex II)

• Total glucose produced = 36 ATP in eukaryotes and 38 in prokaryotes (no mitochondria so don’t need to pump NADH into matrix → saving 2 ATP during glycolysis)

Process of ADP → ATP from NADH and FADH2 via passing of e- through various carrier proteins in the electron transport chain

NADH and FADH2

1 glucose → 2 pyruvate → 2 acetyl CoA → 6 NADH + 2 FADH2 + 2 GTP + 4 CO2

• Occurs when [O2] is too low to carry out aerobic processes in mitochondria

• NAD+ formation prioritized to form NADH

• Alcohol fermentation

• Lactic Acid fermentation

• Fungi (yeast), bacteria, plants

• Reduces pyruvate (from glycolysis) → acetaldehyde + CO2 → ethanol (by product) in a process that oxidizes NADH → NAD+

• Acetaldehyde is the final e- acceptor from NADH

• Occurs in muscle cells

• Use glycolysis to produce 2 pyruvate mols.

• Pyruvate reduced to lactate (by-product) → oxidizes NADH → NAD+

  • Lactate (weak base) → Lactic acid (strong acid)

• Cori Cycle: lactate from muscle cells transported into blood stream → liver → converted to glucose → blood stream → used to generate ATP through glycolysis

Releases energy by breaking down large molecules into smaller molecules

Requires energy to build molecules from smaller molecules

Anabolic & Catabolic rxns

1. Uses other carbohydrates

2. Lipids

3. Proteins (last resort)

• Glycogen (polysacc.): storage for glucose

  • found mainly in muscle and liver cells

• Glycogenesis: formation of glycogen (glucose → glycogen)

• Glycogenolysis: break down of glycogen (glycogen→glucose)

• Glucose-6-phosphate main molecule for rxn

• Regulated by Insulin and glucagon

• First broken down in mouth → stomach → duodenum → small intestine

• Disaccharides hydrolyzed into monosaccharides → converted to glucose or glycolytic intermediates

• All cells can store glycogen but only skeletal muscle and liver cells can store large amounts

• Forming glucose from non-carbs

• Occurs in liver and kidney

To keep the molecule w/n the cell and prevent it from diffusing out of the cell

• Endocrine hormone

• Released by pancreas when glucose ↑

• Triggers cells to:

  • make glycogen from glucose for storage

  • undergo glycolysis to form ATP → activates Phosphofructokinase (R.D.S)

• Released by pancreas when glucose ↓

• Similar to epinephrine (triggers formation of glucose)

• Triggers cells to:

  • Glycogenolysis to form glucose

  • Inhibit glycogenesis to inhibit glycogen production

• Long hydrocarbon chains that are highly reduced → have more energy than carbs

• Triglycerides: 1 glycerol backbone bound to 3 fatty acid chains

• Lipases in adipose tissue are hormone sensitive (e.g., to glucagon)

• Lipolysis: break down of lipids into glycerol and the fatty acids by lipase enzymes

  • Glycerol → Glyceraldehyde 3 Phosphate (DAP/G3P/PGAL) → enters glycolysis

  • Fatty acid chains activated by 2 ATP → β-oxidation of saturated FA in mitochondrial matrix (breaks 2 carbons at the β position) → 1 NADH + 1 FADH2 and 1 Acetyl CoA → citrate in Krebs cycle → 120 ATP generated

  • β-oxidation of unsaturated FA → 1 less FADH2 for each double bond

• Lipids combine w/ soluble proteins → lipoproteins (contain Apoproteins)

  • Classified by density (fat : protein ratio)

  • B/w meals, most lipids in plasma are in the form of lipoproteins

• Lipoproteins large and less dense when ratio is also large

  • Chylomicrons: first fat transporters to leave enterocyte and enter lacteals (small lymphatic vessels)

  • LDL (low protein density): unhealthy due to high fat content

  • HDL (high protein density): healthy cuz transport fat away from tissues → liver → cholesterol for bile → expelled during digestion

Albumin

• Stored as adipose tissue

• Only broken down in duodenum:

1. Bile released from gall bladder to emulsify fats & pancreatic lipase to break down lipids into FA chains and monoacylglycerides

2. Absorbed into enterocytes of small intestine

3. Reassembled into triglycerides, and then, along with cholesterol, proteins or phospholipids → packaged into chylomicrons

4. Chylomicrons move to lymph capillary → circulatory system

• Excess amino acids used for energy

• Oxidative deamination: removal of amino group to form metabolic intermediates (Acetyl CoA, pyruvate, Oxaloacetate)

  • Directly removes ammonia from AA

  • Deamination in liver

  • By-product: NH3 (ammonia) → urea → excreted as urine in mammals

    • Uric acid in insects, birds, reptiles

• Digestion occurs in stomach: pepsin breaks down proteins into polypeptides

• In the small intestine: trypsin breaks down specific polypeptides into amino acids