Metabolism - sum off all an organism’s chemical reaction

Metabolic reactions are enzyme catalyzed which means that the product of one reaction is the reactant for the next reaction.

Chemical reaction are either:

• Energy-releasing (exergonic)

• Energy-requiring (endergonic)

What links these processes is the different forms of ATP - made or used

ATP - performs much of the cellular work

• ATP hydrolysis - energy-releasing

• ATP formation - energy requiring

When a negatively charged molecule is broken, it releases energy because it’s unstable and contains a lot of potential energy

ATP on the left side (reactant) is energy-releasing. ADP is one the left side with ATP on the right is energy-requiring.

Catabolism - taking larger, complex molecules and breaking it down to simpler molecules

• energy is released

• ATP formation - catabolism releases the energy needed for the ATP formation

Anabolism - taking simpler molecules and creating larger, complex organic molecules

• energy is used

• ATP hydrolysis because hydrolysis releases energy and the energy released is taken by anabolism process

Heat loss accompanies all energy transfer processes

The energy from catabolism is used to form ATP. The ATP created from catabolism is broken down and hydrolyzes and is used to aid in creating simpler molecules into larger, complex molecules

Energy is stored in the chemical bonds

Molecules are broken down in order to capture energy in the form of electrons. EX: Glucose in Catabolism

• Glucose is broken down in two stages.

  • Glycolysis where it’s broken down into two pyruvates

    • Hydrogen atoms is where energy is captured via electrons

  • Cellular respiration where pyruvate is broken down into CO₂

    • Energy is again captured via electrons as Hydrogen atoms

EX: CO₂ in Anabolism

• Add electrons to CO₂ which requires energy

Oxidation - losing electrons

Reduction - gain of electrons

OILRIG - oxidation is loss, reduction is gain

When looking at which was reduced and oxidized, look at hydrogen atoms and see how they’ve moved

Role of electron carriers: capture and transfer electrons via H atoms

• EX: NAD/NADH & FAD/FADH2

Energy released by redox reactions are captured to form ATP via phosphorylation of ADP: ADP + P₁ + Energy → ATP

• Substrate-level phosphorylation: (fermentation, respiration)

  • Phosphorylated substrate can serve as the phosphate to ADP to create ATP. You need ADP and Phosphate to create ATP

• Oxidative Phosphorylation (respiration)

• Photophosphorylation (photosynthesis)

Both oxidative and photophosphorylation requires electron transfer chains and utilizes process of chemiosmosis to form ATPs

• involves use of proton gradient and ATP synthase

• Photophosphorylation driven by light

Respiration - employes electron transfer chain & terminal electron acceptor; can be aerobic w/ O₂ as terminal acceptor or anaerobic with NO₃- or other terminal acceptor

• Glycolysis where glucose is broken down into pyruvic acid → Pyruvic acid is produced into Acetyl-CoA → Krebs Cycle creates ATP and CO₂ → Electron Transport → H₂O

Fermentation - anaerobic process, incomplete oxidation of carbohydrate

• only takes product of glycolysis or pyruvate acid and breaks it down to acetic acid or lactic acid, etc. Small organic acids

• Fermentation is usually considered incomplete because there is still a lot of energy in the produces of Fermentation

• Fermentation is only producing ATP because of glycolysis

• Glycolysis breaks down glucose into pyruvic acid → pyruvic acid and NADH is used to form fermentation end products

More ATP is created by respiration than fermentation

INSERT PICTURE OF RESPIRATION AND FERMENTATION PROCESS HERE

Glycolysis - oxidation of glucose to pyruvic acid, is usually the first stage in carbohydrate catabolism

• First part is energy investment

  • The 6 carbon in Glucose is broken down by two ATP into two 3 carbon molecules with a phosphate group.

• Second part is Energy Harvest

  • NADH is created

  • substrate phosphorylation occurs from the phosphate attached to the carbon molecules and combines with the ADP which then creates ATP and 2 pyruvates

  • creates 4 ATP and 2 NADH

Entner-Doudoroff pathway: sugar acids catabolism pathway; found in Gram-negative bacteria

Pentose-phosphate shunt: produce pentose sugars used for biosynthesis of:

• Aromatic amino acids

• Nucleotides

• can also form pyruvate

Acetyl CoA Formation and the Krebs Cycle:

Acetyl CoA

• Pyruvate oxidation to acetyl-CoA

• decarboxylation, NADH formed

Two acetyl CoA is created from the two pyruvates

• NADH is created and CO₂

Krebs cycle (citric acid)

• Glucose oxidation is finalized (converted to CO2)

3 NADH, 1 FADH, and 1 ATP per acetyl CoA → 2 Acetyl CoA leads to 6 NADH, 2 FADH, and 2 ATP

End of krebs cycle is when glucose is finally fully oxidized

Processes in the Krebs Cycle serve both catabolism and anabolism

Central point in metabolism

Electron Transport System:

Most of the energy extracted from glucose is contained in the reduced electron carriers, NADH and FADH2

The NADH and FADH2 accumulated would go down the electron transport chain

• Components in an electron transport chain is in a membrane

• Ends in oxygen if it’s aerobic metabolism

• There’s a progressive loss of energy as it flows down because energy transfer is being used to pump out protons out.

• The molecules need to keep providing it electrons to keep the electron transfer train going.

• Oxygen has a high affinity to such electrons. It’s important to have a molecule like that in order to keep the electrons flowing towards it.

Chemiosmotic Mechanism

Has nothing to do with substrate phosphorylation. Involves the oxidative phosphorylation.

• Creating a gradient. Protons are pumped via carriers in the electron transport chain using the energy from electron transfer.

• Excess of H+ on one side of the membrane

  • electrochemical gradient

    • positive charge is attracted to the negative charge on the inside

  • Proton motive force

    • Both of the forces that want to bring the positive protons inside: charge and concentration

  • ATP synthase allows for energy to be harnessed from proton motive force because energy is released as positive protons move through the membrane towards the negative or down the gradient

    • powered by electron transport chain

More ATP is produced with chemiosmotic than substrate phosphorylation

Chemiosmosis is occuring in the cell membrane

Substrate-level phosphorylation creates 4 ATPs

Oxidative phosphorylation creates 10 NADH and 2 FADH2

• 3 ATP per NADH oxidized

• 2 ATP per FADH oxidized

• Total: 30 ATP and 4 ATP

Anaerobic Respiration - The final electron is an inorganic substance other than oxygen

• less yield than aerobic respiration

Substrate phosphorylation: glycolysis, Krebs

Oxidative phosphorylation: Glycolysis, Acetyl CoA, Krebs