Enzymes and metabolism

**All** of the **enzyme-catalysed** chemical reactions that take place inside a living organism.

The reactions that **build larger molecules** from smaller ones. Anabolism **uses (requires) energy**.

The reactions that **break larger molecules** into smaller ones. Catabolism **releases energy**.

Energy is **used (required)** to build the larger molecule.

Energy is **released** as the larger molecule is broken down.

**Condensation** — it joins subunits to build larger molecules.

**Hydrolysis** — it adds water to break larger molecules into subunits.

Making **glycogen** (or starch) from glucose; **protein synthesis**; **photosynthesis**.

**Aerobic respiration**; **digestion**; the **hydrolysis** of macromolecules.

Ask whether the molecule gets **bigger** (anabolic) or **smaller** (catabolic).

**Anabolic** — small glucose subunits are joined into a larger molecule.

**Catabolic** — a large molecule is broken down into smaller subunits.

**Yes** — almost all are **enzyme-catalysed**.

A **globular protein** that acts as a **biological catalyst**.

A substance that **speeds up a reaction** without being used up, so it can be **reused**.

The specific **pocket on an enzyme's surface** where the substrate binds; its shape is **complementary** to the substrate.

The **reactant molecule** that an enzyme acts on.

The temporary structure formed when a **substrate is bound** to an enzyme's **active site**, just before the reaction.

Its **active site is complementary** in shape to **only one substrate**, so only that substrate can fit and bind.

As the substrate binds, the **active site changes shape slightly** to **mould around it**, helping the reaction occur.

Lock-and-key has a **rigid** active site; induced fit has a **flexible** active site that **moulds** around the substrate.

**Induced fit** — the lock-and-key model is older and superseded.

It is **unchanged** — the products leave and the enzyme can be **reused**.

They are **globular proteins**, **biological catalysts**, and each has a **specific active site** (also: specific, reusable/unchanged).

Only that molecule's shape is **complementary** to the **active site**, so only it can bind and react.

The **minimum energy** the reactants must have for a reaction to **start**.

The **height from the reactants level up to the peak** of the curve.

A graph showing how the **energy of a reacting system changes** as the reaction goes from reactants to products.

It **lowers** the activation energy.

A **smaller barrier** means **more reactant particles have enough energy** to react, so the reaction goes faster.

**No** — it lowers only the activation energy; the reactants and products stay at the **same energy levels**.

The one with the **lower peak / smaller activation-energy barrier**.

The energy of the **reactants** (substrate).

The energy of the **products**.

The **drop from the reactants level down to the products level**.

**No** — an enzyme is a catalyst; it is **not used up** and can be used again.

The **transition state** — the most unstable, highest-energy point of the reaction.

**Temperature**, **pH** and **substrate concentration**.

The temperature at which the enzyme works **fastest** — the peak of the rate-versus-temperature graph.

Molecules move **faster**, so the substrate **collides with the active site more often**, increasing the rate.

The enzyme is **denatured** — the **active site changes shape**, so the substrate no longer fits.

A (usually permanent) change to the **shape of the active site**, caused by high temperature or extreme pH, that stops the enzyme working.

A single **peak** at the **optimum pH**; the rate falls either side because the wrong pH **denatures** the enzyme (distorts the active site).

All the **active sites are occupied** (the enzymes are **saturated**), so extra substrate cannot speed up the rate.

The point where **every active site is occupied** by substrate, so adding more substrate does not increase the rate.

The **number of enzyme molecules** (active sites) — not the amount of substrate.

**Denaturation** changes the active-site **shape** (rate falls, enzyme ruined); **saturation** means all sites are **full** (rate plateaus, enzyme unharmed).

Name **denaturation** AND give the mechanism: the **active site changes shape so the substrate no longer fits**.

The **trend** read off the graph **and** the biological **reason** for it.

The **one factor you deliberately change** (e.g. temperature, pH, or substrate concentration).

What you **measure** to see the effect — usually the **rate of reaction**.

A factor **kept constant** in every run so it does not affect the result and the test stays **fair**.

**Temperature, pH, substrate concentration, amount of enzyme and time** — each one affects the rate on its own.

So any change in rate is caused **only** by the factor being tested — this makes the comparison **fair (valid)**.

E.g. **volume of gas released**, **colour change of an indicator**, time for a substrate to disappear, or **amount of product** formed.

To **attach or trap** it on a **solid support** (e.g. gel beads) so it stays in one place instead of mixing freely with the substrate.

An enzyme **dissolved and mixed freely** in solution with its substrate.

It can be **reused** (cheaper), the **product stays pure** (no enzyme contamination), and it is **more stable** over a wider range of conditions.

Immobilized **lactase** is used to make **lactose-free milk** (it breaks lactose into glucose and galactose).

Amino acids are the **product**, so the **more released** per unit time, the **more active** the enzyme — it is proportional to activity.

An immobilized enzyme stays **fixed on its support**, so it can be removed and used again; a free enzyme ends up **mixed into the product** and is lost.

An enzyme that catalyses a reaction **inside** the cell that produced it (e.g. a **respiration** enzyme).

An enzyme that is **secreted** and catalyses a reaction **outside** the cell (e.g. a **digestive** enzyme).

To **release** the enzyme out of the cell, through the membrane, into the surroundings.

A **respiration** enzyme (or catalase breaking down hydrogen peroxide inside the cell).

A **digestive** enzyme such as **amylase, protease or lipase** — or the enzymes a decomposer secretes onto dead matter.

Because a large food molecule (e.g. starch, protein) is **too big to cross the cell membrane**; it must be broken into small soluble subunits first.

It **hydrolyses** it into **small, soluble subunits** (e.g. starch → maltose/glucose) that **can be absorbed**.

They **secrete extracellular enzymes** onto dead matter, digest it **externally**, then **absorb** the small soluble products.

**No** — both intracellular and extracellular enzymes are globular proteins that **lower activation energy**, are **specific** and are **reusable**. Only the location differs.

Its **activity appears outside the cell** (e.g. in the surrounding liquid / culture medium), acting on a substrate the cell has not absorbed.

A linked series of enzyme-controlled reactions where the **product of one reaction is the substrate of the next** — run by intracellular enzymes.

**Intra** = inside; **extra** = outside — so intracellular acts **inside** the cell and extracellular acts **outside** it.