2.4 Cells Definitions

Enzymes

Proteins that act as biological catalysts to increase the rate of reactions by decreasing the activation energy required. They are globular proteins and are not used up in the reactions. They are specific to the substrate, forming a specific enzyme-substrate complex.

Active site

The enzyme region where the substrate binds, and the shape adjusts slightly (induced fit) to catalyse the reaction.

Denaturing

When an enzyme or protein loses its normal shape due to changes in temperature, pH, or other factors. The hydrogen bonds break, causing the active site to change shape so the substrate can no longer bind and form the enzyme-substrate complex. The enzyme can no longer catalyse the reaction. This is usually irreversible.

Co-enzymes

Alter the shape of the active site so that it can effectively combine with its substrate. E.g., B and C vitamins

Co-factors

Substances that bind with the enzyme to increase its activity, usually by allowing the active site to bind more effectively with the substrate. Without the cofactor, the enzyme won't be able to catalyse the reaction. E.g. inorganic metal ions like magnesium (Mg²⁺), zinc (Zn²⁺), and iron (Fe²⁺)

Inhibitors

Molecules that alter or block the active site of an enzyme, preventing the substrate from binding and stopping enzyme-substrate complexes from forming.

Passive transport

Transport that does not require energy to move substances across the plasma membrane because substances move down their concentration gradient from high to low concentration.

Diffusion

The random movement of particles down a concentration gradient, from a high concentration to a low concentration. It is a passive process, so it does not require energy. Used for small, non-polar or small uncharged molecules (like O₂, CO₂, and water)

Facilitated diffusion

The diffusion of substances through transport proteins in the plasma membrane. It is a passive process because substances move down their concentration gradient and do not require energy.

Osmosis

The movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration. It is a passive process so it does not require energy.

Active transport

Requires energy to move substances across the plasma membrane via carrier proteins because the substances are moved against their concentration gradient from low to high concentration. Useful for larger or charged molecules (e.g. glucose, amino acids, ions) that cannot easily cross the hydrophobic lipid bilayer.

Surface area to volume ratio

A high surface area to volume ratio allows cells to transport materials (like oxygen, nutrients, and wastes) more quickly and efficiently, which is essential for survival of the cell.

Mitosis (purpose)

To produce two new, genetically identical, cells for growth and repair, and to maintain a large surface area to volume ratio of the cell

DNA replication (purpose)

To produce a copy of the DNA in a cell before cell division, so that after cell division each new cell will have a complete set of genetic information and therefore they can function exactly like the original cell

Cellular respiration (purpose)

To produce energy in the form of ATP. ATP is required for all active processes within an organism.

Aerobic respiration

Glucose + Oxygen → water + carbon dioxide + 36 ATP Occurs in the mitochondria

Anaerobic respiration

Glucose → lactic acid + 2 ATP Occurs in the cytoplasm

Photosynthesis

A series of enzyme-controlled chemical reactions that occur in the chloroplasts of plant cells, which use light energy absorbed by chlorophyll as well as carbon dioxide and water to make glucose that can be used in respiration to produce the energy needed for life processes.

Photosynthesis equation

Carbon dioxide + water --> Glucose + oxygen + water

Light dependent phase

In the thylakoid and grana, chlorophyll captures light energy from the sun which is used to split water molecules into the products H+ and waste O2 and creates ATP to drive the light-independent reaction.

Light independent phase

Occurs in the stroma and uses the substrate CO2 and joins the H+ (produced in the light-dependent reactions) with the CO2 to produce glucose.