Cellular Respiration & Metabolism- unit 8

bio 1203

Metabolism

sum total of all chem reactions

2 types: anabolic, catabolic

Anabolic Reactions

• chem reactions build up, forming large molecules

• needs energy

Catabolic Reactions

• chemical reactions break large/complex molecules to small building blocks

• releases energy

Carbohydrates

• 1st source of energy

• stored in form of glycogen (in liver/skeletal muscles)

• glycogen easily converted to glucose when blood glucose decreases

• excess converted to fat (stored in adipocytes)

• some cells only use glucose

Lipids

• major energy reservoir

• stored in adipose tissue

• used for energy when glycogen stores start depleting

• provide 2 months supply of energy in starvation

Protein

• potential source of energy

• extensive use to provide energy = undesirable

• not stored in body for en

• structure/functioning

Nucleic Acid

• in food

• digestion= absorption of individual DNA/RNA

• Not stored in body for en

• builds genetic material

Cellular Respiration

• process of nutrient breakdown w accompanying ATP synthesis

• nutrients contain chem en

Uses of Energy in Cells

ATP= universal en currency

• metabolism

• movement

• growth

• cell division

• action potentials

ATP

• nucleotide

• = inorganic phosphate + ADP + energy

ATP from organic molecules

1. Substrate level phosphorylation

   • oxidation of nutrients directly makes ATP

   • en in chem bonds directly transferred to ADP & Pi → produces ATP

2. Oxidative phosphorylation

   • oxidation of nutrients releases high en electrons from nutrients

   • en in high en electrons then used to produce ATP

Redox Reactions

• Reduction: gain in electrons, increases potential energy

• Oxidation: loss of electrons, decreases potential energy

  reactions always coupled

Coenzyme

• molecule used by enzymes to assist in reactions

• use to collect hydrogens during glucose breakdown

Electron Carriers

• molecule oxidized = 2 electrons & 2 hydrogen ions

  2 types: NAD & FAD

• NAD picks up 2 electrons & 1 H ion (remainder becomes part of solvent)

• FAD picks up both electrons & H ions

Glucose Catabolism

• nutrient molecule CHO

• Reactants: ADI, Pi = energy carriers. NAD, FAD= electron carriers. O= needed in last step of cellular resp

• Products: CO2, ATP, NADH, FADH, H2O

Cellular Respiration- Stage 1: Glycolysis

• in cytoplasm

• converts 1 glucose molecule (6 carbons) → 2 pyruvic acid molecules (two, 3 carbon molecules)

Energy Net Totals from Glycolysis

Goes in:

• 1 glucose

Products:

• 2 pyruvic acid

• 2 ATP

• 2 NADH + 2 H

Cellular Respiration- Stage 2: Pyruvic Acid Oxidation/Transition Step

• after glycolysis, pyruvic acid transported to mitochondrial matrix

• further oxidized

• each pyruvic acid oxidized = acetyl-CoA (acetate molecule bound to coenzyme A)

• during process, 1 CO2 & 1 NADH produced

Energy Net Totals from Pyruvate Oxidation

Goes in:

• 1 pyruvic acid

Product:

• 1 acetyl-CoA

• 1 CO2

• NADH + H

(doubled cause 2 pyruvic acids produced during glycolysis)

Cellular Respiration- Stage 3: Krebs Cycle

• metabolic pathway oxidizes nutrients to produce energy

• each step in path catalyzed by separate enzyme

• components of cycle can be taken out to produce other molecules

• in mitochondrial matrix

• begins w oxaloacetic acid

Energy Net total from Krebs Cycle

Goes in:

• 1 acetyl-CoA

Products:

• 2 CO2

• 1 ATP

• 3 NADH + 3 H

• 1 FADH

(doubles as 2 acetyl-CoA produced)

Cellular Respiration- Stage 4: Oxidative Phosphorylation = Electron Transport Chain (ETC) and Chemiosmosis

• occurs on inner mitochondrial membrane

NADH versus FADH

• N: passes electrons to beginning of ETC → yields 2.5 ATP

• F: passes electrons later down chain → 1.5 ATP

less energy releases as electrons are passed along protein chain

Aerobic Respiration

• oxygen is final electron acceptor for ETC

• → production of 32 ATP

• absence of oxygen= system accumulates electrons, saturate & ultimately prevent further formation of NADH/FADH (no more NAD/FAD)

Anaerobic Respiration

• absence of oxygen = organisms convert pyruvate to lactate

• regenerates NAD, glycolysis can continue (pyruvate oxidation/Krebs stop→ not enough NAD)

• anaerobic= 2 ATP produced from 1 glucose

• when oxygen is available, lactate back to pyruvate

Energy Metabolism

• combined process of energy storage/production from nutrient sources

• each process has multiple steps/own enzymes

  includes:

  1. carbs

  2. lipids

  3. proteins

Carb Metabolism

• usual energy source for most tissues

• blood glucose/glycogen sufficient for 1 day

excess glucose:

• glycolysis

• glycogenesis

low glucose:

• gluconeogenesis (liver)

• glycogenolysis

Lipid Metabolism

• triglycerides = primary long term energy storage molecules

• used when glucose levels fall (except for brain, cant use fatty acids)

• some organs preferentially use fatty acids (ex. liver/cardiac muscle)

Processes involved in Lipid Metabolism

Excess Nutrients:

• excess of glucose, AA, lipids can be stored as triglycerides

Glucose levels fall:

• triglycerides broken down to glycerol + individual fatty acids→ lipolysis

• Glycerol converted to pyruvate in glycolysis pathway/used in gluconeogenesis

• fatty acids broken down to acetyl-CoA molecules → beta oxidation

Liver

• also performs gluconegenesis (involves use of oxaloacetate)

• carb restricted diet/fasting = all oxaloacetate in cell → gluconegenesis

• no oxaloacetate = no pickup molecule for Krebs (no Krebs)

• Acetyl-CoA from lipid metabolism accumulates

Ketone Bodies

• access of acetyl-CoA → production of KB by liver

• leave liver, transported to tissues (ex. brain)

• converted back to acetyl-CoA + used for energy there

• KB important to minimize gluconegenesis/save protein catabolism

Accumulation of Ketone Bodies

• acidic

• accumulation can lead to increased blood acidity → ketoacidosis

• ketoacidosis: result of starvation, lack of carbs

Protein Metabolism

• usually broken into AA → structural/enzymatic roles

• fasting: glucose/fatty acids become low → proteins catabolized for energy

  1. converted to acetyl-CoA

  2. used for gluconeogenesis

  3. by product = ammonia

• excess AA = fat storage

Proteins Role in Cellular Respiration

• before AA oxidation for energy, must be deaminated (amino group removed)

• remaining molecule converted to pyruvate, acetyl-CoA, other metabolites → joins cellular respiration at appropriate point