AQA A-LEVEL BIOLOGY - BIOLOGICAL MOLECULES

Smaller units from which larger molecules are made.

Monomers

Molecules made from a large number of monomers joined together.

Polymers

Monosaccharides

amino acids

Two molecules joining

forming a chemical bond and eliminating a water molecule.

Breaking of a chemical bond between two molecules

using a water molecule.

Monomers from which larger carbohydrates are made.

Monosaccharides definition

Glucose

galactose

Glycosidic bond.

Bond between two monosaccharides

Maltose

Glucose + Glucose -\>

Sucrose

Glucose + Fructose -\>

Lactose

Glucose + Galactose -\>

α-glucose and β-glucose

Two isomers of glucose

Alpha glucose has its hydrogens on the same side as well as its hydroxides

whilst in beta-glucose

Formed by the condensation of many glucose units.

Polysaccharides definition

alpha

Glycogen and starch are formed by the condensation of \___ glucose.

beta

Cellulose is formed by the condensation of \___ glucose.

Storage molecule

energy source

Starch has glycosidic bonds.

Bonds in starch

Either branched or unbranched

Shape of starch chains

The unbranched chain is wound into a tight coil

making the molecule very compact.

chains of alpha glucose

some chains are branched\= amylopetcin

some chains are coiled\= amylose

Describe the structure of starch

Add equal volumes (around 2cm^3) of benedicts reagant (alkaline copper (II) sulfate) and a liquid food sample.

Heat for 5 minutes in a water bath.

Brick red copper (I) oxide precipitate forms.

Describe the chemical test for reducing sugars

Add equal volumes of benedicts reagant and liquid food sample

heat for 5 minutes. (water bath)

No brick red precipitate.

Add hydrochloric acid to hydrolyse the disaccharide into (reducing) monosaccharides.

Add sodium hydrogencarbonate to neutralise the acid.

Re-do benedicts test - brick red precipitate forms.

Describe the chemical test for non-reducing sugars:

- Insoluble

doesn't affect water potential and doesn't diffuse out of cells.

- Forms alpha glucose when hydrolysed

which is easily transported and used in respiration.

- Branched form has many ends

can be acted on by enzymes to glucose is released quickly.

- Insoluble so doesn't draw water in by osmosis

doesn't diffuse out of cells.

- Compact

stored in small space.

- More branched

broken down rapidly as animals have higher metabolic rate and need more energy.

- Made of long beta glucose chain forming long unbranched chains.

- Cellulose chains run parallel and are cross-linked by hydrogen bonds

strength.

- Molecules form microfibrils which form fibres - strength.

How is cellulose suited to its function?

20

How many amino acids are there?

Amine group (NH2)

carboxyl group (COOH)

Condensation reaction

What reaction forms a peptide bond?

Peptide bond.

What bond forms in proteins?

Amino acids join via polymerisation

forming a polypeptide.

Amino acid sequence in primary sequence

What determines the protein's 3D shape?

Proteins

What is formed by the joining of multiple polypeptide chains?

Joining of hydrogen from amine group and oxygen from C\=O in carboxyl

twisting polypeptide chains into 3-D shapes.

Alpha helix and beta pleated sheet

What are the two secondary protein structures?

Hydrogen bonds

What bond forms in the secondary structure of proteins?

Disulfide bridges

ionic bonds

Fairly strong and not easily broken

Describe disulfide bridges

Formed between carboxyl Nd amino groups that aren't involved in forming peptide bonds. Weaker than disulfide bridge and broken by change in pH.

Describe ionic bonds in proteins

Numerous but easily broken

Describe hydrogen bonds in proteins

3-D shape of proteins

and the interaction of the secondary structures together. Bending and twisting of polypeptide helix into compact structure.

Combination of a number oc polypeptide chains and prosthetic groups into a large complex protein molecule. Such as iron in the haem group. This is where it gains its function.

Describe the quaternary structure of proteins

Place sample into test tube

add equal vol of sodium hydroxide at room temp.

Add few drops of dilute (0.05%) of copper(II) sulfate and mix gently.

Purple coloratiom shows peptide bonds

showing protein. No protein \= stays blue.

Globular proteins that act as catalysts.

What are enzymes?

Lower activation energy.

How do enzymes speed up reactions?

Molecules must collide with sufficient energy in order to form their products.

Why does a reaction have activation energy?

Globular proteins with specific 3D shapes. Active site is the functional part

made up of a small number of amino acids.

Substrate

What is the molecule that acts on an enzyme?

Enzyme-substrate complex

What forms when an enzyme and substrate join?

Active site forms when the enzyme and substrate interact

causing a change in the enzyme as it moulds around the substrate. Changing shape causes strain on the substrate

A site that is elsewhere to the active site

where proteins can attach to

- Coming into contact with the substrate.

- Having an active site that fits the substrate.

What 2 things are required for an enzyme to work?

Rise in temp \= rise in kinetic energy. Molecules move quicker

collide more often

Around 60

enzyme denatures as it is really disrupted - too much kinetic energy so bonds in tertiary structure are broken

pH is measured by the concentration of hydrogen ions. Every enzyme has optimum pH. Any change away from the optimum reduces action. Above a certain pH

enzyme denatures

pH \= -log[H+]

How do you calculate the pH of a solution?

Change in pH alters charges of amino acids making up active site. Substrate no longer bonds - no enzyme-substrate complexes.

Can cause tertiary bonds to break

changing shape of active site.

Hydrogen and ionic bomds between amine and carboxyl groups in polypeptides. Change in H+ affects this bonding.

How is the arrangement of the active site determined?

Enzymes are re-used constantly and so are efficient at low concentratiions

however as long as there is excess substrate

If substrate is limiting

it eventually runs out so an increase in enzyme means it doesn't change. Rate of reaction eventually levels off.

Rate increases proportionate to substrate

because at low substrate conc

Substances directly interfering with the functioning of the active site

reducing its activity.

Competitve and non-competitive.

What are the two types of enzyme inhibitors?

Binding to the active site of the enzyme.

What is a competitive inhibitor?

Binding to the enzyme at a position other than the active site.

What is a non-competitive inhibitor?

Simple shape to substrate - binds to active site instead. Doesn't stay there permanently - it depends on the conc of inhibitor and of substrate. If inhibitor conc is higher

it stays for longer. Only slows down enzyme action.

Attach to the allosteric site

and alters the shape of the enzyme

Because they aren't competing for the same site.

Why doesn't an increase in substrate conc decrease the effect of a non-competitive inhibitor?

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

What are two nucleic acids?

Double helix

What type of structure does DNA have?

- Pentose sugar (5 carbons)

- Phosphate group

- Nitrogenous base (A

T

Condensation reaction

What type of reaction forms a nucleotide?

Mononucleotide

What is a single nucleotide called?

Phosphodiester bond

What bond forms between two nucleotides?

Dinucleotide

What is the name of 2 nucleotides joined together?

Polynucleotide

What is a long chain of nucleotides?

Single

Is RNA single or double stranded?

Shorter

Is RNA longer or shorter than DNA?

Ribose

What type of pentose sugar is in RNA?

Adenine

guanine