Unit 5: Scientific method, enzymes

Question 1

What is the scientific method?

Answer 1

Specific method by which scientists gain knowledge about the world

Question 2

Steps to a scientific method (5 steps, inductive vs deductive reasoning)

Answer 2

1. Observation: make new observations with your senses and technology, as well as studying previous data
2. Hypothesis: make a testable statement. Involves inductive reasoning – creatively combining facts gained from observation into a cohesive whole.
3. Experiment/Further observation: The hypothesis is tested by experiment or further observations.
   Involves deductive reasoning – Using “if, then” logic on hypothesis. (if the hypothesis is true, then the following should occur)
4. Conclusion: The data (results from experiments) is analyzed, and the hypothesis is either supported or rejected. The rejection of one hypothesis often produces another hypothesis to be tested.
5. Scientific theory: The ultimate goal. These theories are supported by many observations, experiments, and data.

Question 3

What makes a scientific experiment valid?: Experimental variable (cold example)

Answer 3

The factor being tested, should only be one per experiment. (Given the hypothesis “vitamin C reduces cold”, the vitamin C is the experimental variable)

Question 4

What makes a scientific experiment valid?: Dependent variable (cold example)

Answer 4

A dependent variable: The factor being observed, as it responds to the experimental variable. (The cold is the dependent variable)

Question 5

What makes a scientific experiment valid?: Experimental groups (cold example)

Answer 5

Groups being tested, with different levels of experimental variable (Group A & B gets less than the required amount of vitamin C, Group C & D gets more than the required amount, etc)

Question 6

What makes a scientific experiment valid?: Control group (cold example)

Answer 6

The benchmark. The group that provides basis for comparison with the experimental groups. (Group E gets the required amount of vitamin C)

Question 7

What makes a scientific experiment valid?: Constant factors (cold example)

Answer 7

Factors that are held constant throughout the experiment. All factors in the experiment should be constant except the experimental variable. (Intake of all other vitamins/minerals, intake of daily calories, amount of sleep/exercise, exposure to virus, etc)

Question 8

What makes a scientific experiment valid?: Large sample size (cold example)

Answer 8

Ensures the data is valid. Many repetitions of the experiment could be done if sample size is small.

Question 9

What makes a scientific experiment valid?: Repeatable

Answer 9

Must be repeatable by other scientists. The results of the experiment must also be identical in order to check the validity of the experiment.

Question 10

Metabolism

Answer 10

The term that refers to all the chemical reactions that occur in a cell

Question 11

Reactants

Answer 11

The substances that participate in a reaction

Question 12

Products

Answer 12

The substances that form as a result of a reaction

Question 13

Enzyme

Answer 13

Protein molecule that functions as an organic catalyst to speed up chemical reactions

Question 14

Substrate

Answer 14

A reactant that the enzyme acts on

Question 15

Metabolic pathway

Answer 15

Series of linked reactions that begins with a particular reactant and ends with a product.
Represented like:
E1 E2 E3
A->B->C->D
A-C are reactants, B-D are products of each reaction, E1-3 are enzymes, A is the substrate of E1

Question 16

Activation energy

Answer 16

The energy that must be added to cause molecules to react with one another. Many reactions do not occur unless activation energy is added.

Question 17

What effect does enzymes have on chemical reaction?

Answer 17

Enzymes are catalysts that reduce the activation energy of a reaction; less energy is needed for the reaction to proceed.

Question 18

Active site

Answer 18

Usually, only a small portion of the enzyme interact with the substrate to form the ES complex. This portion is called the active site

Question 19

How does the enzyme work? (Described by the induced fit model)

Answer 19

• The substrate enters active site of enzyme
• Enzyme changes shape slightly as substrate binds (induced-fit)
• Enzyme-Substrate (ES) complex is formed
• Chemical reaction, product leaves active site
• Active site returns to its original state

Question 20

Factors that affect the speed of an enzymatic reaction: Substrate concentration

Answer 20

The greater the concentration of substrate, the greater the rate of reaction. More substrate, more collisions between the substrate and the enzyme. However, there is a point where adding substrate does not affect the reaction speed; the enzyme is saturated.

Question 21

Factors that affect the speed of an enzymatic reaction: Enzyme concentration

Answer 21

More enzyme, greater rate of reaction. Adding more catalyst means a faster reaction.

Question 22

Factors that affect the speed of an enzymatic reaction: Temperature

Answer 22

Higher the temperature, greater rate of reaction. Higher temperature causes more collisions between the substrate and the enzyme. However, if temperature rises past a certain point, the reaction rate declines rapidly because the enzyme is denaturing. The enzyme’s shape changes, and it can no longer bind to its substrate effectively.

Question 23

Factors that affect the speed of an enzymatic reaction: pH

Answer 23

Each enzyme has an optimal pH level, and the rate of reaction is fastest at that pH level. Any other pH level can affect the shape and slow down reactions. Like temperature, extreme levels of pH can denature the enzyme and stop the reaction altogether.

Question 24

Factors that affect the speed of an enzymatic reaction: Competitive inhibitors

Answer 24

Certain molecules are shaped like a substrate and ‘competes’ with the actual substrate for the enzyme’s active site. They bind successfully but does not react with the enzyme to produce the desired product. Less or no product is produced. (i.e., cyanide)

Question 25

Factors that affect the speed of an enzymatic reaction: Non-competitive inhibitors

Answer 25

They bond to enzymes at a position other than the active site, called an allosteric site. This changes the shape of the enzyme (denaturation) so it can no longer bind to its substrate. Most common substance is heavy metal such as lead or mercury.

Question 26

Factors that affect the speed of an enzymatic reaction: Cofactors & Coenzymes

Answer 26

Assistors to the enzymes. May accept or contribute atoms to the reactions. Cofactors are inorganic substance such as copper, zinc, iron while coenzymes are organic, non-protein substance such as Vitamin.

Question 27

Factors that affect the speed of an enzymatic reaction: Thyroxin

Answer 27

A special protein hormone produced by the thyroid gland, located in the neck. All cells have receptors for thyroxin, as they regulate the rate that cells consume oxygen, thus affecting the rate of enzyme activity and the body’s metabolism. It usually stimulates the body to metabolize at a faster rate.