Bio 0150 Exam 4: Metabolism

Potential Energy

Chemical energy stored in covalent bonds is released during hydrolysis of polymers

Potential Energy

Electrical gradients across cell membranes help drive the movement of ions through channels

Kinetic Energy

Heat can be released by chemical reactions, and this can alter the internal temperature of an organism

Kinetic Energy

Light energy is captured by pigments in the eye and plant pigments in photosynthesis

Kinetic Energy

Mechanical energy is used in muscle movements within cells

Metabolism

The sum of all chemical reactions in a Biological System

Anabolism

Simple atoms + ATP —> Molecule

Catabolism

Molecule —> ATP + atoms

First Law of Thermodynamics

Energy is Neither Created nor Destroyed

Second Law of Thermodynamics

When energy is converted from one form to another, some energy becomes unavailable for work and lost to disorder

Free energy

Available Energy

Entropy

The measure of disorder in a system

ΔG

Change in free energy (usable energy)

ΔH

Change in enthalpy (Total energy; heat)

TΔS

Change in unable energy = (T);

Change in Entropy = ΔS

Absolute temperature in Kelvin

(temp in celcius + 273k)

What is the change in free energy (ΔG) for a reaction with an enthalpy change (ΔH) of 725 kJ/mol and an entropy (ΔS) change of 5kJ/mol(K) at a physiological temp of 37°C

Equation: ΔG = ΔH - TΔS

-825 kJ/mol

Positive ΔG

• Products have more free energy

• Free energy is required

Negative ΔG

• Reactants have more free energy

• Free energy has to be released

-ΔG

Spontaneous (happens w/o energy input)

Exergonic reaction

+ΔG

Non-spontaneous (Needs energy to occur)

Endergonic Reaction

Chemical reaction that releases energy

Exergonic

Chemical reaction that consumes energy

Endergonic

Endergonic and Exergonic Reactions can be

Coupled

Main Energy Currency of the Cell

ATP

ATP Hydrolysis

ATP + H2O —> ADP + Pi + Free energy

ΔG for ATP Hydrolysis

= 7.3 kcal/mol (-30kJ/mol)

What Couples Endergonic and Exergonic Reactions?

ATP

Exergonic Processes

• Cellular respiration

• Catabolism (think large to small)

Endergonic Processes

• Active transport

• Cell movements

• Anabolism (think small to large)

What is coupled to endergonic (non-spontaneous) reactions?

ATP Hydrolysis

The conversion of glycerol to glycerol 3-phosphate is an endergonic reaction with a ΔG of 2.2 kcal/mol. How can this be coupled to ATP in the cell so that the reaction is spontaneous

Equation: Glycerol + Pi → Glycerol 3-phosphate + 2.2 kcal/mol

Remember: ΔG for ATP Hydrolysis = 7.3 kcal/mol (-30kJ/mol)

-5.1 kcal/mol

The formation of ATP in the cell is an endergonic reaction with a ΔG of +30kJ/mol. How could this be tied to the following reaction to become spontaneous?

Equation: Creatine + Pi → Creatine-phosphate + 43.1kJ/mol

ADP + Pi → ATP + 30 kJ/mol

Remember: We have to adjust one of our reactions to make a -ΔG at the end of coupling

Creatine - Phosphate → Creatine Pi = -43.1 kJ/mol

---

ADP + Pi + Creatine-phosphate → ATP + Creatine + Pi

we have -43.1 + 30 = -13.1 kJ/mol

Explain the characteristics of ATP that account for the high free energy released during is hydrolysis to form ADP and Pi

• ATP has high energy bonds b/w phosphate groups that store significant potential energy. When these bonds are broken during hydrolysis the bonds become stable

• The three phosphate groups of ATP are negatively charged and repel, which creates high energy. When hydrolyzed, the repulsion is revealed and makes more stable products (ADP and Pi)

• The hydrolysis of ATP is reversible, meaning cells can regenerate ATP from ADP and Pi using energy from other metabolic processes. This coupling between exergonic and endergonic reactions is important for cellular function

Catalysts

Speed up chemical reactions without being permanently altered

-Often end in “ase”

-Act as a scaffold for a reaction

Active Site

Where substrates of an Enzyme bind

Activation Energy (E_a)

The amount of energy needed to start a reaction

• Occurs for all reactions

• Puts reactants into a transition state

• Does not impact ΔG

What lowers the activation energy required?

Enzymes

What happens when the E_a has been achieved?

The reaction will proceed

Enzyme-Substrate Complexes

Can use the same enzyme over and over again

Enzymes can lower E_a through

Correct Orientation of Substrates

Enzymes can lower E_a by

Placing Physical Strain on bonds

Enzymes can lower E_a by

Adding Chemical Groups

Acid-Base Chemical Catalysis

Acidic or basic R groups transfer H⁺ to form a substrate

Covalent Chemical Catalysis

R groups form a temporary covalent bond with a substrate

Metal Ion Chemical Catalysis

Metal ions bound to enzyme and gain/lose electrons from the substrate

The active site is specific to the substrates due to

Shape Chemistry

Induced-Fit Model

Active site conforms to it’s substrate’s shape

*Accurate model as opposed tot eh Lock-and-Key

When some enzymes require other molecules to function they are either:

Prosthetic Groups, Inorganic Cofactors, or Coenzymes

Prosthetic groups

Carbon-Based (organic) molecules permanently bound to the enzyme

Ex). Heme, FAD, Retinal

Heme (Prosthetic Group)

Binds ions, O₂, and electrons

FAD (Prosthetic Groups)

Carries electrons/protons

Retinal

Converts light energy

Molecule Y is permanently bound to the enzyme in the active site. It will agin and lose electrons over the course of a chemical reaction

Prosthetic Group

Inorganic Cofactors

Not carbon-based (inorganic), permanently bound to the enzyme.

Iron (Inorganic Cofactors)

Oxidation / reduction

Copper (Inorganic Cofactors)

Oxidation / reduction

Zinc (Inorganic Cofactors)

Stabilizes DNA binding structure

Metal Z is permanently bound to the enzyme in the active site. During a chemical reaction, it will pass electrons between substrate 1 and substrate 2.

Inorganic Cofactor

Coenzymes

Bind to active site only during the reaction, some are organic, non-protein molecules.

Molecule X binds to the active site during a chemical reaction. The enzyme will transfer a phosphate group from molecule X to the substrate

Coenzyme