AP Biology - Enzymes Quiz 3

What is an enzyme?

• Proteins

• Biological catalysts (to catalyze = “to speed up” a chem. reaction)

• Enzymes make reactions occur more quickly by lowering the activation energy of a reaction

What is activation energy?

The minimum energy required for a chemical reaction to occur.

Do enzymes change the shape/function of the products/reactants?

No. Enzymes do not change the reactants of products of any chemical reaction - they just make the reaction happen faster

How do Enzymes function? 

• Enzymes bind to reactant molecules and hold them together so that chemical processes like bond-breaking and bond-forming can occur more readily

• Enzymes lower the energy of the transition state 

What is the transition state?

The unstable, short-lived point of a chemical reaction where energy is at it’s maximum

Enzyme Graph

graph

• Enzymes aren’t changing the starting reactants or ending products

• The transition state of a reaction is at the top of the energy “hill” - in the reaction w/ enzyme, the hill is smaller because enzymes lower the energy of the transition state

Endothermic Reactions

graph

• absorbs heat/energy from their surroundings

• temperature decreases

• products have more energy because energy is being absorbed

Exothermic reactions

graph

• release heat/energy to their surroundings 

• temperature increases

• products have less energy because energy is being absorbed 

HINT: “exo” → the reaction is releasing outside

What does enzyme function look like?

picture of enzyme substrate complex

Enzymes hold reactants together and stabilize them

• to catalyze (speed up) a reaction, enzymes will bind to reactant molecules 

• these reactant molecules are the enzyme’s substrates 

• the part of the enzyme that the substrate(s) binds to is called the active site

Are enzymes specific or more general?

Enzymes are proteins made of amino acids:

• amino acids found in the enzyme’s active site determine the “target molecules” of the enzyme - a.k.a. which substrates will fit into the enzyme, and which won’t 

• active sites have a specific size, shape, and chemical behavior, so some enzymes will only catalyze certain types of substrates that fit the active site

Lock-and-key Model - how do substrates fit into enzymes?

Image

• substrate fits perfectly into the active site like a puzzle piece fitting together

• now rejected by most scientists 

Induced-fit - how do substrates fit into enzymes?

Image

• enzyme changes shape slightly when it binds to its substrate - called “induced-fit”

• active site conforms to the substrate shape

• scientifically-approved

How do Enzymes lower the activation energy of reactions?

• enzymes bring substrates together in the right orientation

• favorable environmental environments

• temporary covalent bonds with substrate molecules 

• enzymes are NOT altered by the substrates, and vice versa. They release the products and are ready for the next process of catalysis. 

Why are enzymes sensitive to environmental changes?

• enzymes have “optimal conditions” when the reaction occurs the fastest

• active sites are sensitive to change because they are finely tuned to specific substrate(s)

Impact of temp. change on enzymes

• increasing/decreasing the temperature outside of a manageable range can affect the chemical bonds in the active site, making them less suited to binding substrates 

• (ordinarily an increase of temperature would speed up the rate of the reaction, but too large of an increase would denature the protein)

temperature drops → reaction slows down

(large) temperature increase →protein denatures because bonds are breaking and shape is lost

Impact of pH change on enzymes

• active sites have basic/acidic properties that are crucial for catalysis

• enzymes work best at a certain pH range

extreme pH values → protein denatures because bonds are breaking and shape is lost

How can the reaction rate be further increased?

option 1: increase enzyme concentration

• speeds up reaction until there are no longer any substrates for enzymes to bind to, and the reaction no longer speeds up

• more enzymes = “more workers”

option 2: increase substrate concentration

• speeds up reaction until all available enzymes are being used and the reaction will no longer speed up

• more substrate = “more things to work on”

Why do living organisms needs energy?

• energy is necessary for organisms to grow, reproduce, maintain structure, function, and homeostasis 

• cells use ATP - adenosine triphosphate - to power reactions

What is ATP?

image

• a molecule that is the main energy source for all living cells

• holds and transports energy within cells

• releases energy when one of the phosphate bonds is broken through hydrolysis 

What is “energy-coupling”?

• use of exergonic reactions to drive endergonic reactions

• 2 biological reactions are coupled together and linked 

ex. catabolic pathways release energy that is used to power anabolic pathways

image 

What are endergonic reactions?

• require input of energy 

• non-spontaneous 

• cannot occur naturally without input of energy 

• anabolic - builds complex molecules 

What are exergonic reactions?

• releases “free” energy 

• spontaneous 

• can occur without input of energy 

What are metabolic pathways?

• metabolism: sum of chemical reactions that occur throughout the body within each cell that provides the body with energy 

• responsible for both breaking down molecules to release energy (catabolic pathways) and building complex molecules from simpler ones (anabolic pathways)

• Each step in a metabolic pathway is facilitated by a specific enzyme 

• A starting substrate is transformed step-by-step into a final product via a series of intermediate molecules.

What are anabolic pathways?

• small molecules → larger, complex ones

• uses energy 

ex. synthesizing proteins from amino acids

What are catabolic pathways?

• larger molecules → small molecules

• energy is released in the form of ATP

ex. glycolysis, Krebs cycle 

What is the first law of thermodynamics?

Law one: energy can be transformed and transferred but cannot be created or destroyed

ex. water in a series of cups can be moved around to a different cup but the total amount states the same

What is the second law of thermodynamics? 

Law two: every energy transfer/transformation increases the entropy of the universe 

What is entropy?

• randomness in the way molecules are arranged

• measure of “disorder”

• systems move towards more entropy

What are the fundamental qualities of a good experiment?

• 1 independent variable

• clear dependent variable

• control group where conditions remain the same

• multiple trials

• experimental group

• controlled variables

What are the positive and negative control groups?

Positive control: 

• produces the expected result

• confirms the functionality of the experimental design 

Negative control: 

• produces no result, or an expected negative result

• confirms there are no false positives in the experiment or sources of error

• proves there is no outside interference 

ex. testing a denatured enzyme will not yield a result because the enzyme is non-functioning - tested to ensure there are no false positives