AP BIO UNIT 3: cellular energetics

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topic 7.

**ENZYMES**

**OVERVIEW:**

* **enzyme structure and function**
* **environmental factors that affect enzyme function**
* **activation energy in chemical reactions**
* **energy and metabolism/coupled reactions**

enzymes

are biological catalyst. most enzymes are made of proteins, which have a three-dimensional tertiary structure that is specific to their function.

*ex.) ribozymes are biological catalysts that are made of RNA.)*

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active site

the **active site** of an enzyme interacts with the **substrate** (or reactant). the shape of the active site on the enzyme is specific to the shape of the substrate.

denaturation

a change to an enzyme’s structure. this can limit the enzyme’s ability to catalyze chemical reactions.

*sometimes, but not always, denaturation can be reversed when the environment returns to more optimum conditions.*

competitive inhibitors

similar in shape to substrates and compete with substrates for the **active site** of an enzyme.

noncompetitive (allosteric) inhibitors

do not bind to the active site but rather bind to a different site on the enzyme (allosteric site).

endergonic reactions

have products with a higher free energy level than its reactants and are considered energetically unfavorable.

exergonic reactions

have products with lower free energy level than its reactants and are considered energetically favorable.

activation energy

the difference between the energy level of the reactants and the transition state of the reaction.

topic 8.

**PHOTOSYNTHESIS**

**OVERVIEW:**

* **light-dependent reactions**
* **light-independent reactions (the calvin cycle)**

heterotrophs

organisms consume other organisms to obtain organic molecules.

autotrophs

organisms that can produce their own organic molecules from inorganic molecules.

PHOTOSYNTHESIS

photosynthesis is divided into two main parts:

* **light-dependent reactions**
* **light-independent reactions (the calvin cycle)**

light-dependent reactions

use energy from sunlight to split water, producing oxygen gas, protons, and high-energy electrons. oxygen gas is released into the atmosphere. the protons and high-energy electrons are used to power the production of ATP and NADPH (which are sent to the light-independent reactions).

light-independent reactions

use this ATP and NADPH, along with carbon dioxide, to produce sugars. the light-independent reactions then send ADP, Pi, and NADP^+ back to the light-dependent reactions so that photosynthesis can continue. in this way, the two parts of photosynthesis are interdependent.