Lecture 2.4 - Metabolism and Enzymes

These flashcards cover key vocabulary related to metabolism and enzymes as discussed in the lecture notes.

Metabolism

The sum of all chemical reactions performed by a cell or organism.

Anabolic pathways

Metabolic pathways that synthesize more complex compounds from simpler ones.

Catabolic pathways

Metabolic pathways that break down complex molecules into simpler ones.

Activation energy

The energy required to initiate a chemical reaction.

Exergonic reactions

Reactions that release energy, usually associated with catabolic processes.

Endergonic reactions

Reactions that require energy input, usually associated with anabolic processes.

Gibbs free energy (G)

The portion of energy stored in a system that can perform work, used to predict reaction spontaneity.

Enzyme

A protein that acts as a catalyst to speed up chemical reactions without being consumed.

Substrate

The initial reactant that an enzyme acts upon.

Co-factor

An inorganic molecule that assists with the chemical transformation of substrates → products

Co-enzyme

A small organic molecule that assists enzymes in chemical transformations.

Feedback inhibition

A regulatory mechanism where the end product of a metabolic pathway inhibits an earlier step.

Induced fit

The alteration of the active site shape of an enzyme to better fit the substrate.

Chemical chaos

The disorder that would occur if all metabolic pathways were active simultaneously.

Optimal temperature

The temperature at which an enzyme operates most efficiently.

Spontaneous reaction

A reaction that occurs naturally without the input of additional energy.

Hydrolysis of ATP

The reaction where ATP is broken down to ADP and inorganic phosphate, releasing energy.

Individual reactions are…

• Catalysed by specific enzymes

• Connected into metabolic pathways, where the products of one pathway become the substrates for others

Two types of metabolic pathways

Anabolic and catabolic

Kinetic energy

Energy associated with the relative movement of objects

Thermal energy is…

Kinetic energy associated with the random movement of atoms or molecules

Potential energy

Energy that an object possesses because of its location or structure

Chemical energy is…

The potential energy available for release in a chemical reaction

Gibbs free energy (G)

The portion of energy stored in a system that can perform work

The change in free energy ΔG can be measured for any reaction can be used to predict…

If a reaction will occur spontaneously or if it requires an input of energy to proceed

What goes a negative ΔG mean?

The reaction will be spontaneous

Catabolic reactions

• Release energy

• Exergonic

• Spontaneous

  • Gproduct < Gsubstrate so ΔG<0

Anabolic reaction

• Require energy

• Endergonic

• Non-spontaneous

  • Gproduct > Gsubstrate so ΔG>0

What does ΔG mean?

Change in system energy

The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of:

A catabolic pathway

Cells perform three kinds of work…

• Chemical

• Transport

  • Mechanical

Chemical work

Endergonic reactions

Transport work

Pumping across membranes against the concentration gradient

Mechanical work

Contraction of muscle cells, movement of chromosomes during cell division, beating of cilia

Energy for this work is paid by…

Harvesting the energy stored in adenosine triphosphate

ATP

Adenosine triphosphate

ATP is composed of…

• Nucleotide base adenine

• Ribose sugar

• 3 linked phosphate groups

Glutamic acid conversion to glutamine

Glutamine synthesis from glutamic acid by itself is endergonic (ΔG is positive) so it is not spontaneous

Glutamic acid conversion to glutamine

Conversion reaction coupled with ATP hydrolysis

In the cell glutamine synthesis occurs in two steps, coupled by a phosphorylated intermediate

Conversion reaction coupled with ATP

Name 1

ATP phosphorylates glutamic acid, making it less stable, with more free energy

Name 2

Ammonia displaces the phosphate group, forming glutamine

Free-energy change for coupled reaction

ΔG for the glutamic acid conversion to glutamine (+14.2 kJ/mol) plus ΔG for ATP hydrolysis (-30.5 kJ/mol) gives the free-energy change for the overall reaction (-16.3 kJ/mol)

Free-energy change for coupled reaction

How to solve free-energy change for coupled reaction

ΔGglu + ΔG ATP = Net ΔG

Name

The ATP cycle

Where does the energy come from?

Energy comes from the breakdown of fuel molecules, primarily glucose, during cellular respiration, which is then stored in ATP.

Which of the following statements about ATP is correct?

1. The hydrolysis of ATP is an endergonic process

2. The hydrolysis of ATP can supply energy needed for catabolic pathways

3. Almost all the free energy released in the hydrolysis of ATP is released as heat

4. The cycling between ATP and ADP + Pi provides an energy coupling between catabolic and anabolic pathways

The cycling between ATP and ADP + Pi provides an energy coupling between catabolic and anabolic pathways

Enzymes are…

Proteins and catalysts

Exception of an enzyme being a protein

Some RNA-based (ribozyme)

What does enzymes do?

Speed up chemical reactions

Catalyst

A substance that increases the rate of a reaction without being consumed by the reaction

What do enzymes do?

Facilitate transformation of initial substances into different molecules

Enzyme names indicate…

Their function

Enzyme - Lipase

Breaks down lipids

Enzymes - Protease

Breaks down proteins

Enzymes - Synthase

Build larger molecules

Enzymes - Isomerase

Rearranges a molecule into its isomer

Types of enzymes

Lipase, protease, synthase, isomerase

Chemical reaction order

Substrate → transition state → product(s)

Transition state is…

Highest energy state

Activation energy

Difference between energy levels of substrate and transition state

How does enzymes speed up chemical reactions?

By lowering energy barriers

Name

Uncatalyzed Reaction

Name

Enzyme-catalyzed Reaction

Why is it important to living systems that chemical reactions show have activation energies?

Activation energies prevent spontaneous reactions, allowing control over metabolic pathways and ensuring that reactions occur under specific physiological conditions.

How to pay the activation energy

by using enzymes as catalysts that lower the activation energy barrier.

How to enzymes work?

Enzymes work by binding substrates at their active sites, facilitating the formation of products while lowering the activation energy needed for the reaction.

Enzymatic reaction does not…

Permanently change the enzyme’s chemistry or structure

Enzymatic reactions changes…

Its shape during the reaction, but reverts to original conformation once the reaction is complete

Chemical chaos would occur if…

All the metabolic pathways of a cell were operating all the time!

Cells regulate enzymes by…

Turning them on and off

Enzymes are described as catalysts, which means that they…

Increase the rate of a reaction without being consumed by the reaction