THE ROLE OF COENZYMES IN BIOCHEMICAL PATHWAYS

ATP, NADH, NADPH, CoA AND FADH2 roles

- ATP: Carries useable energy

- NADH: Electron carrier; transfers electrons to electron transport chain.

- NADPH: Reducing agent; used in biosynthesis of molecules.

- CoA (Coenzyme A): Carrier of acetyl groups

- FADH2: To transfer protons/electrons to the site of the ETC Or accepts ions during Krebs cycle

Define cofactors

• additional non-protein molecules needed for enzyme activity and stability

Define coenzymes

• organic cofactors needed for enzyme activity and stability, such as those used in cellular respiration and photosynthesis

What are the major coenzymes involved in photosynthesis and cellular respiration?

• NAD (nicotinamide adenine dinucleotide) 

• NADP (nicotinamide adenine dinucleotide phosphate) 

• FAD (flavin adenine dinucleotide) 

• ATP (adenosine triphosphate) 

• CoenzymeA (CoA)

What can cofactors also be other than organic?

• Inorganic

Define inorganic

• Do not contain carbon

• Include metal ions

What do some enzymes include to aid the substrates binding?

What does this do?

• Many enzymes include a metal cofactor

• Form bonds at the active site of their enzyme and also bond with the substrate

• As a result, the substrate is temporarily held (with help from the cofactor) in the position required for enzyme action

Diagram with cofactor?

Define organic factors?

• Small non-protein organic molecules that are essential for the function of particular enzymes.

What do organic cofactors comprise of?

• Prosthetic groups

• Coenzymes

Define prosthetic groups

• cofactors that are tightly bound to an enzyme and are essential for it to function as a catalyst

Define coenzymes

•  cofactors that are loosely bound to their enzymes only when the enzyme is acting on a substrate

What is the role of coenzymes in biochemical pathways?

• Assist some enzymes to perform their catalytic actions

What are the specific roles of coenzymes in biochemical pathways?

• Transferring of atoms or groups of atoms, such as hydrogens, phosphate groups and acetyl groups. 

• Energy transfers.

What two forms do coenzymes exist in?

• a high energy form that is loaded with a group that can be transferred 

• a lower energy form that is unloaded

Unloaded vs unloaded form of nicotinamide adenine dinucleotide (NAD) - which assists other enzymes crucial for cellular respiration

UNLOADED FORM:

• NAD+

• It accepts hydrogen ions and their associated electrons (receiver)

• Energy level is low

• Its redox state is oxidised

LOADED FORM:

• NADH

• It can donate hydrogen ions and electrons and transfer energy

• Energy level is high - Unloads electrons so that the energy released is used in the production of ATP

• Its redox state is reduced

What is the role of coenzymes involved in cellular respiration (ATP)?

• transferring energy within cells

• transfer of its energy to drive endergonic reactions in biochemical pathways

How is ATP removed/used in cellular respiration?

• The third phosphate group is removed creating ADP (lower energy level). 

How is ATP regenerated from cellular respiration?

• ATP can be regenerated from ADP with the addition of a phosphate (Pi).

Endergonic reactions and ATP interaction

• Coenzyme ATP transfers both energy and a phosphate group to assist the action of the hexokinase enzyme on its substrate

• Glucose to form glucose-6-phosphate

Exergonic reactions and ATP interaction

• Pyruvate kinase enzyme is assisted by an ADP coenzyme that accepts a phosphate group and energy from PEP, allowing pyruvate and ATP to be formed

What is a coenzyme involved in cellular respiration and what are its two forms?

• FAD⁺ (flavin adenine)

• An unloaded FAD⁺ and a loaded FADH2

What does FAD⁺ do?

• Carries protons and electrons from one location to another within the mitochondria

What is the coenzyme involved in photosynthesis? What is its two forms?

• NADP (nicotinamide adenine dinucleotide phosphate)

• An unloaded NADP+ and a loaded NADPH.

  
  

Coenzyme use for cellular respiration vs photosynthesis

CELLULAR RESPIRATION

• NAD+

• FAD+

PHOTOSYNTHESIS

• NADP+

Both

• ATP

What does the photosynthesis pathway involve?

• Adding hydrogen to form glucose

How is NADPH formed?

• Formed from NADP+ using high-energy electrons produced by uptake of the radiant energy of sunlight.

NADPH formation equation

• NADP+ + H+ + 2e- (double squiggle) NADPH

Each coenzyme exists in…

• two forms