AQA AS BIOLOGY STUDY EXAM GUIDE 2025/2026
QUESTIONS AND ANSWERS GRADED A+
✔✔Quaternary protein structure - ✔✔A number of polypeptide chains linked together,
and sometimes associated with non-protein groups to form a protein.
✔✔Biuret test - ✔✔A simple biochemical reaction to detect the presence of protein, if
the Biuret's solution turns purple then protein is present.
✔✔Enzyme - ✔✔A protein that acts as a catalyst and so lowers the activation energy
needed for a reaction.
✔✔Activation energy - ✔✔Energy required to bring about a reaction.
✔✔Active Site - ✔✔A group of amino acids that makes up the region of an enzyme into
which the substrate fits in order to catalyse a reaction.
✔✔Substrate - ✔✔A substance that is acted on or used by another substance or
process. Fits into the active site of an enzyme.
✔✔Enzyme-substrate complex - ✔✔The intermediate formed when a substrate
molecule interacts with the active site of an enzyme.
✔✔Complimentary - ✔✔Describes the relationship between the active site of an
enzyme and the substrate molecule - the way in which they fit together.
✔✔Specific - ✔✔Describes how enzymes catalyse a certain chemical reaction.
✔✔Induced fit - ✔✔A mechanism of interaction between an enzyme and a substrate. As
the substrate fits into the active site the active site of the enzyme changes shape in
order to allow an enzyme-substrate complex to be formed.
✔✔Lock and key - ✔✔An analogy for how enzymes work - only the correctly sized key
(substrate) fits into the key hole (active site) of the lock (enzyme)
✔✔Rate of reaction - ✔✔The speed of a chemical reaction - can be worked out by
looking at the decrease in concentration of a reactant over time or increase in
concentration of a product over time.
✔✔Kinetic Energy - ✔✔The energy of motion, observable as the movement of an
object, particle or set of partices.
, ✔✔pH - ✔✔A figure expressing the acidity or alkalinity of a solution on a logarithmic
scale on which 7 is neutral, lower values are more acidic and higher values are more
alkaline. Equivalent to -log10[H+].
✔✔Inhibitor - ✔✔A substance which reduces the activity of an enzyme.
✔✔Competitive inhibitor - ✔✔A form of inhibitor which binds to the active site of the
enzyme preventing the binding of substrate.
✔✔Non-competitive inhibitor - ✔✔A form of inhibitor which does not bind at the active
site of the enzyme which prevents the binding of substrate.
✔✔DNA - ✔✔Deoxyribonucleic acid which is present in nearly all living organisms as
the carrier of genetic information. A double helix made up of two polynucleotide chains,
running antiparallel to each other, with the sugar-phosphate backbone on the outside
and organic bases bonded together by Hydrogen bonds in the centre of the helix. The
nucleotides have a deoxyribose sugar and the bases adenine, thymine, guanine or
cytosine.
✔✔Nucleotide - ✔✔Complex chemicals made up of an organic base, a sugar and a
phosphate. They are the basic units of which the nucleic acids DNA and RNA are made.
✔✔Polynucleotide - ✔✔A polymer of monomers called nucleotides.
✔✔Phosphodiester bond - ✔✔The bond formed by a condensation reaction between
the phosphate group of one nucleotide and the pentose sugar of another nucleotide.
✔✔RNA - ✔✔A polynucleotide which contains nucleotides that have the pentose sugar
ribose rather than deoxyribose and contains the bases adenine, uracil, guanine or
cytosine. Can be either mRNA, tRNA or rRNA.
✔✔Complimentary base pairing - ✔✔Specific rules for how the bases pair together.
Adenine pairs with thymine with 2 hydrogen bonds. Guanine binds with cytosine with 3
hydrogen bonds.
✔✔Double helix - ✔✔Structure of DNA made up of 2 strands of nucleotides running in
opposite directions.
✔✔Semiconservative replication - ✔✔The process in which the double helix of a DNA
molecule unwinds and each strand acts as a template on which a new strand is
constructed.
QUESTIONS AND ANSWERS GRADED A+
✔✔Quaternary protein structure - ✔✔A number of polypeptide chains linked together,
and sometimes associated with non-protein groups to form a protein.
✔✔Biuret test - ✔✔A simple biochemical reaction to detect the presence of protein, if
the Biuret's solution turns purple then protein is present.
✔✔Enzyme - ✔✔A protein that acts as a catalyst and so lowers the activation energy
needed for a reaction.
✔✔Activation energy - ✔✔Energy required to bring about a reaction.
✔✔Active Site - ✔✔A group of amino acids that makes up the region of an enzyme into
which the substrate fits in order to catalyse a reaction.
✔✔Substrate - ✔✔A substance that is acted on or used by another substance or
process. Fits into the active site of an enzyme.
✔✔Enzyme-substrate complex - ✔✔The intermediate formed when a substrate
molecule interacts with the active site of an enzyme.
✔✔Complimentary - ✔✔Describes the relationship between the active site of an
enzyme and the substrate molecule - the way in which they fit together.
✔✔Specific - ✔✔Describes how enzymes catalyse a certain chemical reaction.
✔✔Induced fit - ✔✔A mechanism of interaction between an enzyme and a substrate. As
the substrate fits into the active site the active site of the enzyme changes shape in
order to allow an enzyme-substrate complex to be formed.
✔✔Lock and key - ✔✔An analogy for how enzymes work - only the correctly sized key
(substrate) fits into the key hole (active site) of the lock (enzyme)
✔✔Rate of reaction - ✔✔The speed of a chemical reaction - can be worked out by
looking at the decrease in concentration of a reactant over time or increase in
concentration of a product over time.
✔✔Kinetic Energy - ✔✔The energy of motion, observable as the movement of an
object, particle or set of partices.
, ✔✔pH - ✔✔A figure expressing the acidity or alkalinity of a solution on a logarithmic
scale on which 7 is neutral, lower values are more acidic and higher values are more
alkaline. Equivalent to -log10[H+].
✔✔Inhibitor - ✔✔A substance which reduces the activity of an enzyme.
✔✔Competitive inhibitor - ✔✔A form of inhibitor which binds to the active site of the
enzyme preventing the binding of substrate.
✔✔Non-competitive inhibitor - ✔✔A form of inhibitor which does not bind at the active
site of the enzyme which prevents the binding of substrate.
✔✔DNA - ✔✔Deoxyribonucleic acid which is present in nearly all living organisms as
the carrier of genetic information. A double helix made up of two polynucleotide chains,
running antiparallel to each other, with the sugar-phosphate backbone on the outside
and organic bases bonded together by Hydrogen bonds in the centre of the helix. The
nucleotides have a deoxyribose sugar and the bases adenine, thymine, guanine or
cytosine.
✔✔Nucleotide - ✔✔Complex chemicals made up of an organic base, a sugar and a
phosphate. They are the basic units of which the nucleic acids DNA and RNA are made.
✔✔Polynucleotide - ✔✔A polymer of monomers called nucleotides.
✔✔Phosphodiester bond - ✔✔The bond formed by a condensation reaction between
the phosphate group of one nucleotide and the pentose sugar of another nucleotide.
✔✔RNA - ✔✔A polynucleotide which contains nucleotides that have the pentose sugar
ribose rather than deoxyribose and contains the bases adenine, uracil, guanine or
cytosine. Can be either mRNA, tRNA or rRNA.
✔✔Complimentary base pairing - ✔✔Specific rules for how the bases pair together.
Adenine pairs with thymine with 2 hydrogen bonds. Guanine binds with cytosine with 3
hydrogen bonds.
✔✔Double helix - ✔✔Structure of DNA made up of 2 strands of nucleotides running in
opposite directions.
✔✔Semiconservative replication - ✔✔The process in which the double helix of a DNA
molecule unwinds and each strand acts as a template on which a new strand is
constructed.
