Biology: Enzymes and Protein Structure

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Questions and Answers

What role do amino acids in an enzyme's active site serve?

They facilitate enzyme breakdown.

They act as a source of activation energy.

They provide structural support for the enzyme.

They bind and interact with specific substrates. (correct)

What can happen to an enzyme at suboptimal temperatures?

The enzyme increases its substrate binding affinity.

The enzyme becomes more efficient.

The enzyme maintains its shape.

The enzyme can denature and lose its shape. (correct)

What occurs when a substrate binds to the active site of an enzyme?

The substrate forms permanent bonds with the enzyme.

The enzyme is destroyed by the substrate.

The substrate becomes inactivated.

Temporary bonds are formed, weakening original substrate bonds. (correct)

What is the function of the enzyme-substrate complex?

It allows new bonds to form between substrates. Signup and view all the answers

What is activation energy?

The energy required for reactants to engage in a reaction. Signup and view all the answers

What role do catalysts play in biochemical reactions?

They enable reactions to occur at lower activation energies. Signup and view all the answers

What happens to the enzyme-substrate complex after the reaction?

It breaks apart to yield the products of the reaction. Signup and view all the answers

Which factor does NOT affect enzyme function?

Substrate shape Signup and view all the answers

What must happen to the energy from exergonic reactions for it to be used in endergonic reactions?

It must be directly transferred to ATP. Signup and view all the answers

Which of the following best describes ATP's role in cells?

It is the universal energy carrier. Signup and view all the answers

What is the outcome when ATP is broken down?

It transforms into ADP and phosphate. Signup and view all the answers

Which statement correctly describes oxidation and reduction?

Oxidation is the loss of electrons, and reduction is the gain of electrons. Signup and view all the answers

What does the acronym OIL RIG stand for?

Oxidation Is Loss, Reduction Is Gain. Signup and view all the answers

In oxidation-reduction reactions, what role does a reducing agent play?

It facilitates the reduction of another substance by being oxidized. Signup and view all the answers

Why is oxygen considered a strong oxidizing agent?

It effectively accepts electrons. Signup and view all the answers

What is the unstable state called when reactants become contorted and able to break or make bonds?

Transition state Signup and view all the answers

What happens during endergonic reactions?

Energy is consumed to form products. Signup and view all the answers

How do enzymes help substrates reach their transition state?

By providing an optimal environment within the active site Signup and view all the answers

Which of the following factors does NOT alter enzyme activity?

Color of the enzyme Signup and view all the answers

Which enzyme is specifically responsible for adding phosphate groups?

Kinase Signup and view all the answers

What effect does increasing temperature have on enzyme activity?

Increases kinetic energy and collision frequency Signup and view all the answers

What suffix do all enzymes end with, indicating their functional role?

–ase Signup and view all the answers

Which statement about the activation energy of a catalyzed reaction is true?

Activation energy decreases. Signup and view all the answers

What best describes the role of cofactors and coenzymes in enzyme activity?

They can affect enzyme activity positively or negatively. Signup and view all the answers

What drives a reversible chemical reaction according to the law of mass action?

The concentration of products and substrates Signup and view all the answers

What results from the phenomenon of end product inhibition?

A decrease in the enzymatic activity at branch points Signup and view all the answers

Which of the following best describes branched metabolic pathways?

They can lead to multiple products from the same substrate Signup and view all the answers

What is a primary function of enzymes in biological reactions?

Lower the activation energy of the reaction Signup and view all the answers

How does allosteric inhibition function within a metabolic pathway?

It prevents the substrate from binding at the active site Signup and view all the answers

What occurs as a result of an inborn error of metabolism?

Deficiency of a specific enzyme in the pathway Signup and view all the answers

Which model describes the initial interaction between an enzyme and its substrate?

Lock-and-key model Signup and view all the answers

According to the first law of thermodynamics, what is true about energy?

Energy can be transformed but not destroyed Signup and view all the answers

How do enzymes facilitate reactions without being consumed?

They are not changed by the reaction Signup and view all the answers

What determines the specific function of an enzyme?

The enzyme's 3D shape Signup and view all the answers

What is the role of carbonic anhydrase in the body?

To facilitate the reversible reaction between carbon dioxide and water Signup and view all the answers

What are the reactants called that enzymes act upon?

Substrates Signup and view all the answers

What is the purpose of negative feedback at branch points in metabolic pathways?

To regulate the flow and balance of metabolic products Signup and view all the answers

Which statement about enzymes is true?

Enzymes do not affect the nature of the reaction Signup and view all the answers

What occurs during the induced-fit model of enzyme activity?

The enzyme changes shape to better fit the substrate after initial binding Signup and view all the answers

What can be concluded about enzyme specificity?

Enzymes are specific for certain substrates Signup and view all the answers

What occurs to an enzyme when the temperature exceeds a few degrees above normal body temperature?

The enzyme becomes denatured. Signup and view all the answers

How does decreasing the temperature affect molecular motion in reactions?

Decreases molecular movement, slowing down reactions. Signup and view all the answers

What does 'saturation' mean in relation to enzyme activity?

All enzymes in solution are occupied with substrate. Signup and view all the answers

What is the primary role of coenzymes in enzyme activity?

They act as hydrogen carriers between enzymes. Signup and view all the answers

What is the significance of a zymogen in enzymatic activity?

It is an inactive enzyme form activated when needed. Signup and view all the answers

What happens to enzymes when extreme pH changes occur?

Enzymes undergo conformational changes. Signup and view all the answers

Why are co-factors important for enzyme activity?

They assist in forming the active site. Signup and view all the answers

What is true about the pH optimum of enzymes?

It reflects the pH of surrounding fluids. Signup and view all the answers

Study Notes

Enzymes

Enzymes are biological catalysts
Increase the rate of a reaction
Not changed by the reaction (reusable)
Do not change the nature of the reaction
Lower the activation energy of the reaction

Protein Structure Revisited

First level: Amino acids bond to form a chain.
Second level: Attraction between amino acids causes pleated ribbon or coiled rod shapes.
Third level: Pleated ribbons and coiled rods fold into a 3D structure.
Fourth level: Multiple folded proteins connect to form a single protein molecule

Mechanisms of Enzyme Activity

Enzyme function is dictated by structure
Enzymes have a characteristic 3D shape with active sites
Reactants are called substrates
Original model: substrates fit into the active site (lock-and-key model)
Updated model: Substrate fit isn't exact, it changes shape slightly as it enters the active site (induced-fit model)
Enzymes are very specific to their substrates

3D Image of Enzyme Active Site

Protein structure supports and positions active sites.
Binding sites bind and orient substrates.
Catalytic sites reduce activation energy

Metabolic Pathways

Linked chemical Reactions in chains or webs.
Begin with an initial substrate and end with a product.
Involve many enzymatic steps along the way

Branched Metabolic Pathways

Not always linear
Often include branches where multiple products form

Metabolic Pathway Inhibition

End product inhibition occurs when the end product of a metabolic pathway blocks an earlier step in that pathway.
This is a form of negative feedback.
The end products bind to enzymes at a spot away from the active site, which alters the enzyme's shape, preventing binding to the substrate.

Inborn Errors of Metabolism

Gene mutations in DNA lead to flawed enzymes.
This impacts the pathways that follow the defective enzyme.
Leads to product build-up or lack of products as reactions cannot effectively proceed.
Can lead to fatal conditions in the fetus.

Effects of pH

Enzymes work best within a narrow pH range (optimum pH).
Extreme pH changes denature enzymes, altering their shape and function.
Optimum pH typically matches the pH where the enzyme functions (e.g. stomach vs saliva)

Effect of Substrate Concentration

Increasing substrate concentration initially increases the rate of the reaction.
The rate of the reaction plateaus when all enzyme active sites are continuously occupied thus reaching saturation.

Coenzymes and Cofactors

Coenzymes are organic molecules and cofactors are inorganic metal ions that assist enzymes in various reactions often by affecting active site shape, or assisting in temporary bonding between the enzyme and substrates.
Coenzymes often transport small molecules or atoms (like hydrogen)
Cofactors help shape the active sites of enzymes, aid in enzyme substrate bonding

Zymogens

Some enzymes are produced in an inactive form called zymogens.
The suffix -ogen helps identify these enzymes (e.g. pepsinogen).
Zymogens require activation via other enzymes (e.g. phosphorylation) to become active

Law of Mass Action

Some chemical reactions are reversible.
The rate of reaction depends on substrate and product concentrations.
Reactions tend towards the side of the reaction with the lower concentration of products/reactants.

Laws of Thermodynamics

First Law: Energy cannot be created or destroyed, only transferred.
Second Law: Energy is lost as heat, resulting in a decrease in usable energy during transformations.
Energy transfers are inefficient

Endergonic and Exergonic Reactions

Endergonic reactions require energy input to proceed.
Reactants have less free energy than products.
Exergonic reactions release energy to proceed.
Reactants have more free energy than products.

Coupled Reactions: ATP

Cells use energy stored in chemical bonds via ATP, an energy carrier
ATP is synthesized from ADP and phosphate using energy from exergonic reactions.
ATP releases energy when broken down into ADP.

Coupled Reactions: Oxidation and Reduction

Reactions are linked; electrons are transferred or hydrogen atoms.
Reduction is gaining electrons/hydrogen.
Oxidation is losing electrons/hydrogen.
Some molecules are oxidizing/reducing agents, depending on the reaction

Hydrogen Carriers

Coenzymes that accept/donate hydrogen atoms in redox reactions (e.g., NAD, FAD).
These coenzymes (NAD and FAD) play a role in energy production by carrying electrons in coupled reactions.

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Description

Test your knowledge on enzymes, their functions, and the intricacies of protein structures. This quiz covers the characteristics of enzymes, mechanisms of enzyme activity, and the different levels of protein organization. Dive into the world of biological catalysts and learn how they facilitate reactions in living organisms.