AQA A Level Biology Topic 1: Biological Molecules

Vocabulary practice flashcards covering monomers, polymers, carbohydrates, lipids, proteins, enzymes, nucleic acids, ATP, water, and inorganic ions from AQA A Level Biology Topic 1.

Monomer

Smaller, repeating molecules or units from which larger molecules or polymers are made.

Polymer

Molecules made from many (a large number of) identical or similar monomer molecules joined together.

Condensation Reaction

A chemical reaction that joins two molecules together, forming a chemical bond and releasing a water molecule ($H_2O$).

Hydrolysis Reaction

A chemical reaction that breaks a chemical bond between two molecules, separating them using a water molecule ($H_2O$).

Monosaccharide

The monomer units from which larger carbohydrates are made, such as glucose, fructose, and galactose.

$$\alpha\text{-glucose}$$

An isomer of glucose where the $OH$ group attached to carbon 1 is located below the carbon ring.

$$\beta\text{-glucose}$$

An isomer of glucose where the $OH$ group attached to carbon 1 is located above the carbon ring.

Isomers

Molecules with the same molecular formula but differently arranged atoms in space.

Disaccharide

A molecule formed by joining two monosaccharides together with a glycosidic bond via a condensation reaction, releasing a water molecule.

Maltose

A disaccharide formed by the condensation reaction between two glucose molecules.

Sucrose

A disaccharide formed by the condensation reaction between a glucose molecule and a fructose molecule.

Lactose

A disaccharide formed by the condensation reaction between a glucose molecule and a galactose molecule.

Polysaccharide

A polymer formed by many monosaccharides joined together with glycosidic bonds via many condensation reactions, releasing many water molecules.

Starch

An energy store in plant cells made of polysaccharides of $\alpha\text{-glucose}$, consisting of unbranched amylose ($1,4\text{-glycosidic bonds}$) and branched amylopectin ($1,4\text{-}$ and $1,6\text{-glycosidic bonds}$).

Glycogen

An energy store in animal cells made of a polysaccharide of $\alpha\text{-glucose}$ with $1,4\text{-}$ and $1,6\text{-glycosidic bonds}$ forming a highly branched structure.

Cellulose

A polysaccharide made of $\beta\text{-glucose}$ with $1,4\text{-glycosidic bonds}$ forming straight, unbranched chains linked in parallel by hydrogen bonds to form microfibrils.

Reducing Sugars Test

A biochemical test where Benedict's solution (blue) is added to a sample and heated in a boiling water bath, producing a green, yellow, orange, or red precipitate for a positive result.

Non-Reducing Sugars Test

A test where a sample is heated in a boiling water bath with acid to hydrolyse non-reducing sugars into reducing sugars, neutralised with alkali, then heated with Benedict's solution to form a precipitate.

Iodine Test for Starch

A biochemical test where iodine dissolved in potassium iodide (orange/brown) is added to a sample and shaken/stirred, turning blue-black for a positive result.

Calibration Curve

A graph plotting absorbance on the y-axis against known sugar concentrations on the x-axis, used to read off the concentration of an unknown sample based on its measured light absorbance.

Fatty Acid

A lipid component containing a carboxyl group ($-COOH$) attached to a variable hydrocarbon chain ($R$).

Saturated Fatty Acid

A fatty acid with no $C=C$ double bonds in its hydrocarbon chain, meaning all carbon atoms are fully saturated with hydrogen.

Unsaturated Fatty Acid

A fatty acid with one or more $C=C$ double bonds in its hydrocarbon chain, which creates a bend or kink in the chain.

Triglyceride

A lipid formed by 1 glycerol molecule and 3 fatty acids joined by 3 condensation reactions, forming 3 ester bonds and releasing 3 water molecules.

Phospholipid

A lipid molecule where one of the fatty acids of a triglyceride is substituted by a phosphate-containing group, resulting in a hydrophilic head and two hydrophobic tails.

Emulsion Test for Lipids

A biochemical test where ethanol is added to a sample and shaken to dissolve lipids, followed by adding water, producing a milky white emulsion for a positive result.

Amino Acid

The monomer unit of proteins consisting of a central carbon atom bonded to a carboxyl group ($-COOH$), an amine group ($-NH_2$), a hydrogen atom, and a variable side chain ($R$).

Peptide Bond

A chemical bond formed by a condensation reaction between the carboxyl ($-COOH$) group of one amino acid and the amine ($-NH_2$) group of another.

Dipeptide

A molecule formed when two amino acids are joined together by a peptide bond in a condensation reaction.

Polypeptide

A polymer formed when many amino acids are joined together by peptide bonds in a sequence.

Primary Structure of a Protein

The specific sequence of amino acids in a polypeptide chain, held together by peptide bonds.

Secondary Structure of a Protein

The folding or coiling of a polypeptide chain into repeating patterns, such as an alpha helix or beta pleated sheet, held by hydrogen bonds between $NH$ and $C=O$ groups.

Tertiary Structure of a Protein

The overall 3D folding of a single polypeptide chain held together by hydrogen bonds, ionic bonds, and disulfide bridges formed between amino acid $R$ groups.

Quaternary Structure of a Protein

The protein structure that arises when a functional protein is composed of more than one polypeptide chain held together by interactions between polypeptides.

Biuret Test for Proteins

A biochemical test where biuret reagent (sodium hydroxide + copper (II) sulphate) is added to a sample, turning purple/lilac to indicate the presence of peptide bonds.

Enzyme

A globular protein that acts as a biological catalyst by lowering the activation energy of the reaction it catalyses to speed up the rate of reaction.

Activation Energy

The minimum amount of energy required for a chemical reaction to occur.

Induced-Fit Model of Enzyme Action

Model where the substrate binds to an active site that is not initially fully complementary, causing the active site to change shape slightly to fit the substrate, distorting substrate bonds and lowering activation energy.

Denaturation (Enzyme)

The loss of an enzyme's tertiary structure and active site shape caused by broken hydrogen and ionic bonds at high temperatures or extreme pH, preventing enzyme-substrate complexes from forming.

Competitive Inhibitor

A molecule with a similar shape to the substrate that competes for, binds to, and blocks the active site of an enzyme, preventing substrate binding.

Non-Competitive Inhibitor

A molecule that binds to an allosteric site on an enzyme, altering the tertiary structure and active site shape so the substrate can no longer bind.

Initial Rate of Reaction

The rate of a reaction measured at time $t=0$, determined by drawing a tangent line to the initial curve on a graph of product volume/concentration against time and calculating $\text{change in } y / \text{change in } x$.

Buffer Solution

A solution used to maintain a constant pH during an experiment by resisting changes in hydrogen ion concentration.

DNA (Deoxyribonucleic Acid)

A double-stranded polynucleotide made of deoxyribose nucleotides containing adenine, thymine, cytosine, or guanine, which holds genetic information coding for polypeptides.

RNA (Ribonucleic Acid)

A single-stranded polynucleotide made of ribose nucleotides containing adenine, uracil, cytosine, or guanine, which transfers genetic information from DNA to ribosomes.

DNA Nucleotide vs RNA Nucleotide

A DNA nucleotide contains deoxyribose pentose sugar and adenine, thymine, guanine, or cytosine; an RNA nucleotide contains ribose pentose sugar and adenine, uracil, guanine, or cytosine.

Phosphodiester Bond

A strong covalent bond joining adjacent nucleotides in a nucleic acid strand, formed between the phosphate group of one nucleotide and the pentose sugar of another.

Semi-Conservative DNA Replication

The process of DNA duplication where DNA helicase unwinds the double helix, and DNA polymerase joins new nucleotides alongside each template strand, producing two DNA molecules each with one original and one new strand.

DNA Helicase

The enzyme that breaks hydrogen bonds between complementary base pairs to unwind and separate the two strands of the DNA double helix during replication.

DNA Polymerase

The enzyme that joins adjacent DNA nucleotides on a new strand via condensation reactions, forming phosphodiester bonds during DNA replication.

Meselson-Stahl Experiment

An experiment using bacteria grown in heavy ($^{15}N$) and light ($^{14}N$) nitrogen isotopes and centrifugation to validate the semi-conservative model of DNA replication.

Adenosine Triphosphate (ATP)

A nucleotide derivative formed from a molecule of ribose, adenine, and three phosphate groups, acting as an immediate energy source in cells.

ATP Hydrolase

The enzyme that catalyses the hydrolysis of ATP into ADP and inorganic phosphate ($P_i$), releasing energy for cellular processes.

ATP Synthase

The enzyme that catalyses the condensation reaction joining ADP and inorganic phosphate ($P_i$) to resynthesise ATP during respiration and photosynthesis.

Phosphorylation

The addition of an inorganic phosphate group ($P_i$) to a compound, making it more reactive.

Polarity of Water

The uneven charge distribution in a water molecule, where oxygen atoms carry a slight negative charge ($\delta^-$) and hydrogen atoms carry a slight positive charge ($\delta^+$), allowing hydrogen bonds to form.

Specific Heat Capacity of Water

The high amount of heat energy required to raise the temperature of water, which buffers temperature changes in aquatic environments and inside organisms.

Latent Heat of Vaporisation

The large amount of heat energy required to evaporate a given volume of water, allowing effective cooling via evaporation (e.g. sweating).

Cohesion (Water)

The attraction between water molecules due to hydrogen bonding, which supports continuous columns of water in plant xylem tubes and produces surface tension.

Hydrogen Ions ($H^+$)

Inorganic ions that determine pH levels in solution, where high concentrations correspond to low pH/acidic conditions that can cause enzymes to denature.

Iron Ions ($Fe^{2+}$)

Inorganic ions that form a key component of the haem group in haemoglobin, allowing oxygen to bind for transport as oxyhaemoglobin.

Sodium Ions ($Na^+$)

Inorganic ions involved in the co-transport of glucose and amino acids into cells, action potentials in neurons, and controlling water potential.

Phosphate Ions ($PO_4^{3-}$)

Inorganic ions that form key components of nucleotides (DNA/RNA), ATP, and phospholipids, and are used to phosphorylate compounds to increase reactivity.