AP Bio - Chapter 3

What are enzymes?

A special class of proteins

Are all proteins enzymes?

All enzymes are proteins but not all proteins are enzymes 

What is an enzyme’s function in a cell?

Enzymes are chemical reaction helpers

WHY are enzymes needed?

They are needed because body temperature is not high enough for spontaneous chemical reactions

What are reactants called in enzyme activity?

Substrates

What is the active site?

The specific spot where reactants bind

What are products in enzyme reactions?

What is released after the reaction

Can enzymes be reused?

Yes, until they are broken down by lysosomes and recycled

What does enzyme specificity mean?

one enzyme is for one specific reaction

What are anabolic enzymes?

Build molecules (ex. DNA polymerase)

What are catabolic enzymes?

break molecules up (ex. Sucrase breaks down sucrose)

What is the induced fit model?

The active sight changes shape to fit the reactant perfectly

How do enzymes speed up reactions?

Enzymes reduce activation energy to make reactions faster

What are enzymes also known as?

Biological catalysts

What is denaturation?

lost function with active site shape change

Why is enzyme shape important?

The shape determines the function of the enzyme (especially the active site)

What factors affect enzyme activity?

temperature and pH

What is optimal temperature and pH?

the range where an enzyme functions best

What happens when all enzymes are busy?

The reaction rate levels off (saturation point)

What is enzyme inhibition?

The off switch to control reactions

What is a competitive inhibitor?

It binds to the active site and blocks the substrate

What is a non-competitive inhibitor?

It binds to a different site and changes the shape of the active site

Why is enzyme inhibition important?

It is useful to control the reaction rates

What is photosynthesis?

the process that converts light energy into chemical energy (glucose) and releases oxygen— it is essential for life

Where does photosynthesis occur?

In plants, algae, and cyanobacteria

What does photosynthesis produce?

Oxygen (O₂) and glucose (C₆H₁₂O₆)

What was the first type of photosynthesis?

Anoxygenic photosynthesis, it produced sulfur gas instead of oxygen gas

What is oxygenic photosynthesis?

a form of photosynthesis that uses water and produces oxygen as a product

What caused the Great Oxygenation Event?

Cyanobacteria releasing oxygen through photosynthesis

What theory explains how chloroplasts evolved?

The Endosymbiotic Theory - cyanobacteria were engulfed by larger cells and became chloroplasts

What is the main function of the chloroplast?

it’s the site of photosynthesis

What are thylakoids?

Thylakoids are disc-shaped membranes

What are granums?

stacks of thylakoids

Where do light-dependent reactions occur?

In the thylakoid membrane

What is the stroma?

The fluid surrounding the thylakoids where the Calvin Cycle occurs

What is the main pigment in photosynthesis?

Chlorophyll a; it absorbs blue and red light, reflecting green

What do accessory pigments like chlorophyll b and carotenoids do?

They absorb extra wavelengths of light, making photosynthesis more efficient

What is the main goal of the light-dependent reactions?

To make ATP and NADPH to power the Calvin Cycle

What happens in Photosystem II (P680)

Light excites electrons, water splits, and releases oxygen, providing electrons and H⁺ ions

What is photolysis?

The splitting of water using light energy; it produces electrons, hydrogen ions, and oxygen gas

What happens in the Electron Transport Chain (ETC)?

Electrons move down the chain, energy pumps H⁺ into the thylakoid, and ATP synthase makes ADP

What happens in Photosystem I (P700)?

Light re-energizes electrons, which helps form NADPH from NADP⁺

What are the end products of the light-dependent reactions?

ATP, NADPH, and O₂ (waste)

What is the goal of the Calvin Cycle?

To use ATP, NADPH, and CO2 to make G3P

What is G3P?

A 3-carbon sugar

Where does the Calvin Cycle occur?

In the stroma of the chloroplast

What happens during carbon fixation?

CO2 combines with RuBP using the enzyme RuBisCO to form 3-carbon molecules

What happens during the reduction phase of the Calvin Cycle?

ATP and NADPH are used to turn 3-carbon molecules into G3P

What happens during regeneration in the Calvin Cycle?

ATP is used to regenerate RuBP so the cycle can continue

What does the Calvin Cycle produce DIRECTLY?

G3P , which can be used to make glucose and other carbohydrates

What is the main problem plants face during photosynthesis?

Opening stomata for CO2 causes water loss through transpiration

How do C3 plants photosynthesize?

CO2 directly enters the Calvin Cycle, the stomata stay open and they need lots of water

How do C4 plants reduce water loss?

They fix CO2 into a 4-carbon compound and move it to bundle sheath cells, keeping the stomata partially closed

How do CAM plants conserve water?

They open the stomata at night to store CO₂, then close them during the day and use the stored CO₂ for the Calvin Cycle

What is the overall photosynthesis equation?

6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂

What happens in the light dependent reactions vs the Calvin Cycle?

Light-dependent reactions make ATP and NADPH; the Calvin Cycle uses them with CO₂ to make G3P

What are the main products and waste of photosynthesis?

Glucose/chemical energy is the product; oxygen is the waste