Biological molecules – A Level AQA Biology revision notes

What this topic covers

Biological molecules has 8 subtopics, including:

• Monomers and polymers
• Carbohydrates
• Lipids
• Proteins
• Nucleic acids are important information-carrying molecules
• ATP

Biological molecules lessons by subtopic

24 lessons, grouped by subtopic.

Monomers and polymers

• Monomers, Polymers, and Life's Biochemical Basis: An introduction to the fundamental concepts of monomers and polymers, their significance in living organisms, and the underlying biochemical principles.
• Condensation and Hydrolysis Reactions: Exploring condensation and hydrolysis reactions, the two key processes involved in the formation and breakdown of biological polymers.

Carbohydrates

• Monosaccharides and Disaccharides: An introduction to carbohydrates, focusing on monosaccharides (glucose, fructose, galactose) and disaccharides (maltose, sucrose, lactose), their formation through condensation reactions, and the glycosidic bond.
• Polysaccharides: Structure and Function: Explore polysaccharides including glycogen, starch, and cellulose. Focus on their formation from glucose monomers, their distinct structures (alpha and beta glucose linkages), and how their structure relates to their function in energy storage (glycogen and starch) and structural support (cellulose).
• Testing for Sugars and Starch: Learn about the biochemical tests to identify different types of carbohydrates: Benedict's test for reducing and non-reducing sugars, and the iodine/potassium iodide test for starch. Understand the principles behind each test and how to interpret the results.

Lipids

• Introduction to Lipids: Triglycerides: Learn about the structure and formation of triglycerides, including saturated and unsaturated fatty acids.
• Phospholipids and the Emulsion Test: Explore the structure of phospholipids, their unique properties, and how to identify lipids using the emulsion test.

Proteins

• Amino Acids, Dipeptides, and Polypeptides: Explore the basic building blocks of proteins: amino acids, dipeptides, and polypeptides. Learn about condensation reactions and the peptide bond.
• Protein Structure and Function: Delve into the different levels of protein structure (primary, secondary, tertiary, and quaternary) and how they relate to protein function. Learn about the role of hydrogen bonds, ionic bonds, and disulfide bridges.
• The Biuret Test for Proteins: Learn about the Biuret test, a chemical test used for detecting the presence of peptide bonds, and hence of proteins.
• Enzyme Action: Specificity and Mechanisms: Explore enzyme specificity, the induced-fit model, and how enzymes lower activation energy.
• Factors Affecting Enzyme Activity: Investigate the impact of enzyme concentration, substrate concentration, inhibitors, pH, and temperature on enzyme-controlled reactions.

Nucleic acids are important information-carrying molecules

• Nucleotide Structure: DNA vs RNA: Describe the components of a DNA nucleotide, naming the pentose sugar, phosphate group, and four organic bases; Describe the components of an RNA nucleotide, identifying ribose and the four organic bases including uracil; Compare the structures of DNA and RNA nucleotides, identifying key similarities and differences
• DNA and RNA: Structure, Bonding, and Function: Describe the structure of DNA and RNA, including the role of hydrogen bonds and complementary base pairing; Explain how a condensation reaction between nucleotides forms a phosphodiester bond; Compare the structures and functions of DNA and RNA in living cells
• Unwinding and Preparing DNA for Replication: Explore the initial stages of DNA replication, focusing on how the DNA double helix unwinds and the role of DNA helicase.
• Building New DNA Strands: Describe how free DNA nucleotides are attracted to exposed bases on template strands during replication; Explain the role of complementary base pairing in ensuring accurate new strand synthesis; Explain how DNA polymerase catalyses the condensation reaction that joins adjacent nucleotides
• Semi-Conservative Replication and its Validation: Explain why semi-conservative replication ensures genetic continuity between generations of cells; Describe the process of semi-conservative replication of DNA, including the roles of helicase and DNA polymerase; Evaluate the experimental evidence from the Meselson-Stahl experiment that validated the Watson-Crick model of semi-conservative replication

ATP

• ATP: Structure and Hydrolysis: Describe the structure of an ATP molecule, identifying its three components; Explain why ATP is classified as a nucleotide derivative; Explain the hydrolysis of ATP to ADP and inorganic phosphate, including the role of ATP hydrolase
• ATP: Energy Coupling, Phosphorylation and Resynthesis: Explain how the hydrolysis of ATP is coupled to energy-requiring reactions within cells; Describe how inorganic phosphate released during ATP hydrolysis can phosphorylate other compounds, increasing their reactivity; Explain how ATP is resynthesised by the condensation of ADP and inorganic phosphate, catalysed by ATP synthase during photosynthesis and respiration

Water

• Water: Solvent & Metabolite: Explain why water is described as a metabolite, with reference to condensation and hydrolysis reactions; Explain why water is an important solvent for metabolic reactions; Describe the key properties of water that make it biologically important
• Water: Thermal Properties: Explain why water has a relatively high heat capacity and describe its biological significance; Explain why water has a relatively large latent heat of vaporisation and describe its cooling effect; Compare the thermal properties of water with other liquids and evaluate their importance to living organisms
• Water: Cohesion & Transport: Explain how hydrogen bonding between water molecules produces cohesion and surface tension; Describe how cohesion supports the transport of water through the xylem in plants; Explain why water is a major component of cells and how its properties are important in biological systems

Inorganic ions

• Introduction to Inorganic Ions: Explain why inorganic ions are essential to living organisms, with reference to their occurrence in solution in the cytoplasm and body fluids; Describe the specific roles of named inorganic ions, linking each role to the ion's chemical properties; Compare the concentrations at which different inorganic ions occur in biological systems and explain why this variation matters
• Key Inorganic Ions and Their Roles: State the roles of hydrogen ions, iron ions, sodium ions, and phosphate ions in biological systems; Explain how each inorganic ion contributes to a specific biological process or molecule; Compare the structural and functional roles of phosphate ions in DNA and ATP

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