AQA A LEVEL BIOLOGY TOPIC 1 : BIOLOGICAL MOLECULES

Monomer

The smaller units from which larger molecules are made (polymers)

Polymer

Molecules made from a large number of monomers joined together through a condensation reaction

Monosaccharide

The single unit sugars from which larger carbohydrates are made e.g. glucose, fructose, galactose

Disaccharide

Formed by the condensation reaction of two monosaccharides held together by a glycosidic bond e.g. maltose, sucrose, lactose

Polysaccharide

Formed by the condensation of many glucose units held by glycosidic bonds e.g. starch, glycogen, cellulose

Cellulose

Polysaccharide in plant cell walls formed by the condensation of β-glucose

Glycogen

Polysaccharide in animals formed by the condensation of α-glucose

Starch

Polysaccharide in plants formed by the condensation of α-glucose contains two polymers - amylose and amylopectin

Glycosidic bond

C-O-C link between two sugar molecules formed by a condensation reaction it is a covalent bond

Amylose

Polysaccharide in starch made of α-glucose joined by 1,4-glycosidic bonds coils to form a helix

Amylopectin

Polysaccharide in starch made of α-glucose joined by 1,4 and 1,6-glycosidic bonds branched structure

Condensation reaction

A reaction that joins two molecules together with the formation of a chemical bond involves the elimination of a molecule of water

Hydrolysis reaction

A reaction that breaks a chemical bond between two molecules involves the use of a water molecule

Fibrils

Long, straight chains of β-glucose held together by many hydrogen bonds

Triglyceride

Formed by the condensation of one molecule of glycerol and three molecules of fatty acids forming 3 ester bonds

Phospholipid

Formed by the condensation of one molecule of glycerol and two molecules of fatty acid held by two ester bonds a phosphate group is attached to the glycerol

Induced-fit model

The enzyme active site is not initially complementary to the substrate the active site moulds around the substrate this puts tension on bonds lowers the activation energy

Competitive inhibitor

A molecule that is the same/similar shape as the substrate binds to the active site prevents enzyme-substrate complexes from forming

Non-competitive inhibitor

A molecule that binds to an enzyme at the allosteric site causing the active site to change shape preventing enzyme-substrate complexes from forming

Primary structure

The sequence of amino acids on a polypeptide chain

Secondary structure

The folding or coiling to create a β pleated sheet or an α helix held in place by hydrogen bonds

Tertiary structure

The further folding to create a unique 3D shape held in place by hydrogen, ionic and sometimes disulfide bonds

Quaternary structure

More than one polypeptide chain in a protein

Peptide bond

Covalent bond joining amino acids together in proteins C-N link between two amino acid molecules formed by a condensation reaction

What is the effect of temperature on enzyme controlled reaction

At low temperatures, there is not enough kinetic energy for successful collisions between the enzyme and substrate.

Denaturation of enzymes

Occurs at too high a temperature, changing the shape of the active site and preventing enzyme-substrate complexes from forming.

Effect of pH on enzyme reactions

Too high or too low a pH interferes with the charges in the amino acids in the active site, breaking ionic and hydrogen bonds that maintain the tertiary structure, leading to denaturation.

Optimal pH

Different enzymes have different optimal pH levels for their activity.

Effect of substrate concentration on enzyme reactions

At low substrate concentrations, fewer collisions occur between enzyme and substrate; at high concentrations, the reaction rate plateaus as all active sites become saturated.

Effect of enzyme concentration on enzyme reactions

At low enzyme concentrations, there will be fewer collisions between enzyme and substrate; at high concentrations, the rate plateaus because there are more enzymes than substrates, resulting in many empty active sites.

Ester bond

-COO- chemical bond formed between glycerol and fatty acids

Hydrophilic

The ability to mix, interact or attract water

Hydrophobic

The tendency to repel and not mix with water

Glucose

Monosaccharide that exists as two isomers β glucose and α glucose

Galactose

An example of a monosaccharide that forms lactose

Fructose

An example of a monosaccharide that forms sucrose

Isomer

Molecules with the same molecular formula but the atoms are arranged differently

Maltose

Disaccharide formed by the condensation of two glucose molecules

Lactose

Disaccharide formed by the condensation of a glucose molecule and a galactose molecule

Sucrose

Disaccharide formed by the condensation of a glucose molecule and a fructose molecule

Polypeptide

Polymer chain of a protein made up of amino acids bonded together by peptide bonds following condensation reactions

Amino acid

The monomer of a protein formed from C,H,O,N contains a carboxyl group, amine group and an R group

Carboxyl group

COOH group made up of a C with hydroxyl (OH) and carbonyl (double-bonded O) group bonded to it found in amino acids and fatty acids

Amine group

NH2 group found on amino acids

R group on amino acids

The variable group the part of each of the 20 amino acids that is different

α helix

A secondary structure in proteins a coiled shape held in place by hydrogen bonds

β pleated sheet

A secondary structure in proteins a folded, pleated shape held in place by hydrogen bonds

Hydrogen bonds

Weak bond forms between H and O in many biological molecules e.g. proteins, water, DNA, tRNA

Ionic bonds

A bond that forms between the R groups of different amino acids in the tertiary structure of proteins

Disulfide bonds

A strong covalent bond between two sulfur atoms in the R groups of different amino acids in the tertiary structure of proteins

Active site

Unique-shaped part of an enzyme that the substrate binds to

Activation energy

The minimum amount of energy required for a reaction to occur

Enzyme-substrate complex

forms when an enzyme and substrate collide and bind resulting in a lowered activation energy

Denature

When the active site changes shape so the substrate can no longer bind

Enzyme-inhibitor complex

The structure that forms when an enzyme and inhibitor collide and bind prevents enzyme-substrate complexes from forming

Saturated fatty acid

A long hydrocarbon chain with a carboxyl group at one end only single bonds between carbon atoms

Unsaturated fatty acid

A long hydrocarbon chain with a carboxyl group at one end at least one double bond between carbon atoms

Polar molecule

A molecule that has an uneven distribution of charge

Phospholipid bilayer

Phospholipids have two charged regions in water, they are positioned so that the heads are exposed to water and the tails are not

Plasma membrane

Phospholipid bilayer cell surface membranes and organelle membranes

Reducing sugar

sugars that can reduce Cu ions in Benedict's reagent to Cu ions in the form of copper (I) oxide which forms a brick-red precipitate

Test for reducing sugar

Add Benedict's reagent heat observe green/yellow/orange/brick red precipitate

Energy-Storing Bonds

A large ratio of energy-storing carbon-hydrogen bonds compared to the number of carbon atoms; a lot of energy is stored in the molecule.

Metabolic Water Source

High ratio of hydrogen to oxygen atoms; they act as a metabolic water source.

Water Potentials

Do not affect water potentials and osmosis.

Molecular Mass

Have a relatively low mass.

Non-reducing sugar

A sugar unable to reduce Cu; the glycosidic bond must be hydrolysed to expose the reducing group, e.g. sucrose.

Test for nonreducing sugar

Following a negative Benedict's test, boil sample in acid and then neutralise with alkaline, add Benedict's reagent and heat, observe orange/brick red colour.

Test for starch

Add iodine; turns blue/black.

Test for lipids

Add ethanol and shake to dissolve, then add water; white emulsion forms.

Test for protein

Add biuret; turns purple.

Nucleotide

The monomer of DNA and RNA; contains a pentose sugar, a phosphate group and a nitrogenous base.

Nitrogenous base

Part of a nucleotide; adenine, guanine, cytosine, thymine and uracil.

DNA nucleotide

The monomer of DNA; contains a deoxyribose sugar, a phosphate group and a nitrogenous base.

Polynucleotide

DNA polymer; many nucleotides joined together via a condensation reaction, joined by phosphodiester bonds.

Phosphodiester bond

Bond joining two nucleotides together; forms between a phosphate group and the pentose sugar.

Complementary base pairs

The base pairs that align opposite each other and form hydrogen bonds; adenine and thymine/uracil, guanine and cytosine.

Ribose

Pentose sugar found in RNA nucleotide and ATP.

Uracil

Nitrogenous base found in RNA instead of thymine.

mRNA

A copy of a gene; single-strand polymer of RNA.

tRNA

Found only in the cytoplasm; single-stranded but folded to create a shape that looks like a cloverleaf, held in place by hydrogen bonds.

rRNA

rRNA combines with protein to make ribosomes.

DNA template strand

A DNA strand that is used to make a new DNA copy from; both DNA strands in the double helix are used as templates in DNA replication.

DNA polymerase

An enzyme in DNA replication that joins together adjacent nucleotides.

Semi-conservative replication

DNA replication is semi-conservative; one strand is from the parental DNA and one strand is newly synthesised.

DNA helicase

Enzyme that breaks hydrogen bonds between the two chains of DNA in a double helix; causes the two strands to separate, involved in DNA replication and transcription.

Large latent heat of vaporisation

A lot of energy is required to convert water from its liquid state to a gaseous state; this is due to the hydrogen bonds, as energy is needed to break these to turn it into a gas, means water can provide a cooling effect.

High specific heat capacity

A lot of energy is required to raise the temperature of the water because some of the heat energy is used to break the hydrogen bonds between water molecules; important so water can act as a temperature buffer.

Metabolite

Water is involved in many reactions such as photosynthesis, hydrolysis, and condensation reactions.

Solvent

Water is a good solvent, meaning many substances dissolve in it; polar (charged) molecules dissolve readily in water due to the fact water is polar.

Strong cohesion

Water molecules 'stick' together due to hydrogen bonds; results in water moving up the xylem as a continuous column of water, provides surface tension, creating a habitat on the surface of the water for small invertebrates.

ATP synthase

Enzyme that catalyses the synthesis of ATP from ADP + Pi.

ATP hydrolase

Enzyme that catalyses the hydrolysis of ATP into ADP + Pi.

Phosphorylation

The addition of a phosphate group to a molecule, making the molecule more reactive/it gains energy.

Structure of water

Water is a polar molecule; the oxygen atom is slightly negative, the hydrogen atoms are slightly positive.

Dipeptide

Two amino acids bonded together by a peptide bond formed by a condensation reaction.

RNA nucleotide

Monomer of RNA composed of a phosphate group, ribose and a nitrogenous base; has the base uracil instead of thymine.

Role of hydrogen ions

Determine the pH; the more hydrogen ions, the more acidic the conditions are; an important role in chemiosmosis in respiration and photosynthesis.

Role of iron ions

A compound of haemoglobin involved in oxygen transport.

Role of sodium ions in co-transport

Involved in co-transport for absorption of glucose and amino acids in the ileum.