Biological Molecules (Edexcel IGCSE Science (Double Award): Biology): Flashcards

• Starch

• Glycogen

• Cellulose

Because they are insoluble.

• A fat is a lipid that is solid at room temperature

• An oil is a lipid that is liquid at room temperature

Because amino acids can be arranged in any order.

Each sequence gives the protein a particular shape, and its shape determines its function.

• Enzymes

• Antibodies

• Haemoglobin, in red blood cells

Add a few drops of Benedict's solution, then heat in a beaker of very hot water for 5 minutes.

A colour change from light blue to orange / brick red.

That the food sample contains a higher concentration of glucose.

Add several drops of iodine solution to the food sample.

No heating is needed.

In the presence of starch, iodine solution changes from yellow-brown to blue-black.

Add a few drops of Biuret solution to the food sample.

A positive Biuret test for protein gives a colour change from blue to purple.

Violet or lilac are also accepted.

Mix the food sample with 4 cm³ of ethanol and shake it vigorously with a bung in the tube.

Allow it to settle, then strain the ethanol solution into another test tube.

Add it to an equal volume of cold distilled water.

A cloudy emulsion forms.

True.

The sample must be heated in a beaker of very hot water for about 5 minutes, or placed in a water bath.

Break up the food using a pestle and mortar.

Transfer it to a test tube, add distilled water and stir with a glass rod.

Filter the mixture using a funnel and filter paper, and collect the solution.

Biuret solution contains copper(II) sulfate and corrosive sodium hydroxide, and iodine solution is an irritant to the eyes.

True.

Ethanol is highly flammable, so it must never be used near an open flame.

• The iodine test — yellow-brown to blue-black

• The Benedict's test — blue to orange

• Glucose

• Starch

• Protein

• Fat

A protein that acts as a biological catalyst, speeding up the rate of a chemical reaction without being changed or used up.

Because they are made in living cells.

They keep all metabolic reactions running at a rate fast enough to sustain life.

Without them, reactions such as digestion would be far too slow.

The region of an enzyme where the substrate attaches. Its shape is complementary to the substrate.

Because the active site is a complementary shape to that substrate, so no other molecule fits into it.

The structure formed when a substrate moves into an enzyme's active site.

1. Enzymes and substrates move about randomly in solution.

2. An enzyme and its complementary substrate collide, an enzyme-substrate complex forms, and the reaction occurs.

3. The products form and are released from the active site. The enzyme is unchanged and goes on to catalyse further reactions.

Because they no longer fit it.

The active site is then free to take up another substrate.

Enzymes are proteins that act as biological catalysts to speed up metabolic reactions.

When a substrate moves into the active site, an enzyme-substrate complex forms.

False.

The enzyme is unchanged by the reaction and goes on to catalyse further reactions.

True.

Both move randomly in solution, and the reaction happens only when a complementary enzyme and substrate collide.

Because only a substrate with a complementary shape can fit into it, which is what makes the reaction possible.

As the reactants for another reaction, so metabolic reactions link together in sequences.

37 °C.

The amino acids that make up the enzyme, held in place by bonds.

The molecules gain more kinetic energy, so they move faster and there are more collisions between enzyme and substrate.

When heating beyond the optimum temperature breaks the bonds holding an enzyme together, so it loses its shape and the substrate can no longer fit its active site.

Because the shape of its active site has been lost, so the substrate cannot fit into it.

False.

Denaturation is irreversible — once denatured, an enzyme cannot regain its proper shape and its activity stops.

False.

Low temperatures do not denature enzymes. They simply work more slowly, because the molecules have less kinetic energy.

Heating an enzyme beyond its optimum temperature breaks the bonds that hold it together.

In the human body, the optimum temperature for enzymes is 37 °C.

Activity rises as temperature increases towards the optimum, peaks at the optimum, then falls sharply to zero as the enzyme denatures.

It falls rapidly and stops, because the enzyme denatures and the substrate can no longer fit the active site.

Because an enzyme is a protein, not a living thing. It loses its shape — it does not die.

Because it is what ensures the substrate fits into the active site, allowing the reaction to proceed.

True.

Their specific shape comes from the amino acids that make them up, held in place by bonds.

Amylase, which digests starch into maltose.

Iodine solution, which is yellow-brown and turns blue-black in the presence of starch.

Add 5 cm³ starch solution to a test tube and bring it to the chosen temperature.

Put a drop of iodine solution in each well of a spotting tile.

Add 2 cm³ amylase, mix, and start the timer.

Every minute, transfer a droplet of the mixture to the next well of iodine.

Stop when the iodine no longer changes colour, and record the time. Repeat at least twice more, then repeat across a range of temperatures.

The iodine stops changing colour and stays yellow-brown, because there is no starch left for it to react with.

The less time it takes for all the starch to be digested into maltose, the faster the enzyme activity.

The iodine stops turning blue-black in the least amount of time, because the enzyme is working at its fastest rate.

The iodine takes longer to stop turning blue-black.

The amylase works slowly because the molecules have low kinetic energy, so there are few collisions with the starch.

The iodine turns blue-black throughout the whole investigation.

The amylase has denatured, so it can no longer bind to the starch or break it down.

Amylase digests starch into maltose.

Before it reacts with starch, iodine solution is yellow-brown in colour.

True.

Heating with a Bunsen burner makes a stable, precise temperature hard to maintain. Water baths set to each temperature are an improvement, allowing about 10 minutes for the solutions to reach temperature.

It relies on subjective visual observation.

A colorimeter would give an objective, numerical reading of colour intensity instead.

• Wear safety goggles — iodine and amylase solutions irritate the eyes

• Wear gloves — amylase solution irritates the skin

• Handle hot equipment with tongs to avoid burns and scalds

The concentration and volume of the starch solution, iodine solution and amylase used.

To give reliable results.

pH 7.

Because they are produced in acidic conditions, so their optimum is about pH 2.

pH 8 or 9, because conditions in the duodenum are alkaline.

The bonds holding the amino acid chain together are disrupted or destroyed.

This changes the shape of the active site, so the substrate can no longer fit, and the rate of activity falls.

The bonds that hold the amino acid chain together to make up the protein.

True.

Moving too far from the optimum pH causes the enzyme to denature, and its activity stops.

False.

Most enzymes have an optimum of pH 7, but stomach enzymes work best at about pH 2 and duodenal enzymes at pH 8–9.

The optimum pH for most enzymes is 7.

Enzymes produced in the stomach have an optimum of about pH 2.

Because the shape of the active site has changed, so it is no longer complementary to the substrate.

Activity peaks at the optimum pH and falls away on either side of it.

Because they work in different conditions — the stomach is acidic (about pH 2), while the duodenum is alkaline (pH 8–9).

It decreases, and stops altogether if the enzyme denatures.