Proteins have a variety of functions within all living organisms.
The general structure of an amino acid (see diagram).
Condensation and the formation of peptide bonds linking together amino acids to form polypeptides.
The relationship between primary, secondary, tertiary and quaternary structure, and protein function.
The biuret test for proteins.
3.1.2 Enzyme action
Enzymes as catalysts lowering activation energy through the formation of enzyme-substrate complexes.
The lock and key and induced fit models of enzyme action.
3.1.2 Enzyme properties
The properties of enzymes relating to their tertiary structure. Description and explanation of the effects of temperature, competitive and non-competitive inhibitors, pH and substrate concentration.
Candidates should be able to use the lock and key model to explain the properties of enzymes. They should recognise its limitations and be able to explain why the induced fit model provides a better explanation of specific enzyme properties.
The role of carrier proteins and protein channels in facilitated diffusion.
3.1.3 Active transport
The role of carrier proteins and the transfer of energy in the transport of substances against a concentration gradient.
The haemoglobins are a group of chemically similar molecules found in many different organisms.
Haemoglobin is a protein with a quaternary structure.
The role of haemoglobin in the transport of oxygen.
The loading, transport and unloading of oxygen in relation to the oxygen dissociation curve.
The effects of carbon dioxide concentration.
Candidates should be aware that different organisms possess different types of haemoglobin with different oxygen transporting properties. They should be able to relate these to the environment and way of life of the organism concerned.
3.2.9 Genetic comparisons
Genetic comparisons can be made between different species by direct examination of their DNA or of the proteins encoded by this DNA.
Comparisons of amino acid sequences in specific proteins can be used to elucidate relationships between organisms.
Energy is transferred through ecosystems and the efficiency of transfer can be measured
3.5.6 Polypeptide synthesis
Transcription as the production of mRNA from DNA. The role of RNA polymerase. The splicing of pre-mRNA to form mRNA in eukaryotic cells.
Translation as the production of polypeptides from the sequence of codons carried by mRNA. The role of ribosomes and tRNA.
Candidates should be able to show understanding of how the base sequences of nucleic acids relate to the amino acid sequence of polypeptides, when provided with suitable data.
3.5.6 Gene mutation
Gene mutations might arise in DNA replication. The deletion and substitution of bases.
Gene mutations occur spontaneously. The mutation rate is increased by mutagenic agents. Some mutations result in a different amino acid sequence in the encoded polypeptide. Due to the degenerate nature of the genetic code, not all mutations result in a change to the amino acid sequence of the encoded polypeptide.
1.1.2 Cell membranes
Describe the roles of the components of the cell membrane; phospholipids, cholesterol, glycolipids, proteins and glycoproteins.
Explain what is meant by passive transport (diffusion and facilitated diffusion including the role of membrane proteins), active transport, endocytosis and exocytosis.
Describe the role of haemoglobin in carrying oxygen and carbon dioxide.
Describe and explain the significance of the dissociation curves of adult oxyhaemoglobin at different carbon dioxide levels (the Bohr effect).
Explain the significance of the different affinities of fetal haemoglobin and adult haemoglobin for oxygen.
2.1.1 Biological molecules
Describe, with the aid of diagrams, the formation and breakage of peptide bonds in the synthesis and hydrolysis of dipeptides and polypeptides.
Explain, with the aid of diagrams, the term primary structure.
Explain, with the aid of diagrams, the term secondary structure, with reference to hydrogen bonding.
Explain, with the aid of diagrams, the term tertiary structure, with reference to hydrophobic and hydrophilic interactions, disulphide bonds and ionic interactions.
Explain, with the aid of diagrams, the term quaternary structure, with reference to the structure of haemoglobin.
Describe, with the aid of diagrams, the structure of a collagen molecule.
Compare the structure and function of haemoglobin (as an example of a globular protein) and collagen (as an example of a fibrous protein).
2.1.2 Nucleic acids
State that a gene is a sequence of DNA nucleotides that codes for a polypeptide.
State that enzymes are globular proteins, with a specific tertiary structure, which catalyse metabolic reactions in living organisms.
5.1.1 Cellular control
State that genes code for polypeptides including enzymes.
Describe, with the aid of diagrams, the way in which a nucleotide sequence codes for the amino acid sequence in a polypeptide.
Describe, with the aid of diagrams, how the sequence of nucleotides within a gene is used to construct a polypeptide, including the roles of messenger RNA, transfer RNA and ribosomes.
State that mutations cause changes to the sequence of nucleotides in DNA molecules.
Explain how mutations can have beneficial, neutral or harmful effects on the way a protein functions.
Explain genetic control of protein production in a prokaryote using the lac operon.
Topic 2: Genes and health
Explain what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP), endocytosis and exocytosis and describe the involvement of carrier and channel proteins in membrane transport.
Describe the basic structure of an amino acid and the formation of polypeptides and proteins (as amino acid monomers linked by peptide bonds in condensation reactions) and explain the significance of a protein’s primary structure and properties (globular and fibrous proteins and types of bonds involved in three-dimensional structure).
Explain the mechanism of action and specificity of enzymes in terms of their three-dimensional structure and explain that enzymes are biological catalysts that reduce activation energy, catalysing a wide range of intracellular and extracellular reactions.
Describe a gene as being a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain.
Outline the process of protein synthesis, including the role of transcription, translation, messenger RNA, transfer RNA and the template (antisense) DNA strand.
Topic 3: The voice of the genome
Explain the role of the rough endoplasmic reticulum (rER) and the Golgi apparatus in protein transport within cells and including its role in formation of extracellular enzymes.
Topic 6: Infection, immunity and forensics
Explain the process of protein synthesis (transcription, translation messenger RNA, transfer RNA, ribosomes and the role of start and stop codons) and explain the roles of the template (antisense) DNA strand in transcription, codons on messenger RNA, anticodons on transfer RNA.
Explain how one gene can give rise to more than one protein through post-transcriptional changes to messenger RNA.
Unit BY1: Basic Biochemistry and Cell Structure
Structure and role of amino acids and proteins. The peptide link.
Relation of molecular structure to function.
Primary, secondary, tertiary and quaternary structure of proteins.
Globular and fibrous proteins.
Unit BY5: Environment, Genetics and Evolution
The two major functions of DNA: replication and protein synthesis.
The transcription of DNA to produce messenger RNA.
Translation by ribosomes and transfer RNA, which has an anticodon and a specific amino acid binding site, to synthesize proteins
Polypeptides may be further modified and combined.
SQA Advanced Higher Biology
Biology: Cells and Proteins
The proteome is larger than the genome due to RNA splicing and post-translational modification. As a result of gene expression not all genes are expressed as proteins in a particular cell.
(b) Protein structure, binding and conformational change
(i) Amino acid sequence determines protein structure
Primary sequence. The main classes of R groups and interactions in secondary and tertiary structure. Influence of temperature and pH on R group interactions. Prosthetic groups. Quarternary structure.
(ii) Hydrophobic and hydrophilic interactions influence the location of cellular proteins
The fluid mosaic model. The role of R groups in determining the distribution of soluble, globular, integral membrane and peripheral membrane proteins.
(iii) Binding to ligands
Involvement of R groups in ligand binding. Proteins and DNA binding interactions including nucleosomes and transcription regulation.globular, integral membrane and peripheral membrane proteins.
(iv) Ligand binding changes the conformation of a protein
Change in conformation causes a functional change in the protein. Substrate binding and induced fit. Activation energy, allosteric enzymes, positive and negative modulators and cooperativity in the binding and release of oxygen in haemoglobin.
(v) Reversible binding of phosphate and control of conformation
The addition or removal of phosphate from R groups, reversible conformational changes and the regulation of the activity of proteins.
Protein kinases, protein phosphatases and ATPases. Phosphorylation of myosin and its interaction with actin.
(c) Membrane proteins
Movement of molecules across membranes.
Phospholipid bilayer as a barrier to ions and most uncharged polar molecules. Transmembrane proteins including channel proteins, and transporter proteins. Gated channels, ligand gated channels and voltage gated channels. Substrate transport including facilitated and active transport.
International Baccalaureate Diploma Biology
Topic 2: Cells
2.4 Membranes (Core)
2.4.3 Membrane proteins
2.4.5 Facilitated diffusion
2.4.6 Active transport
Topic 3: The Chemistry of Life
3.2 Carbohydrates, lipids and proteins (Core)
3.2.4 Condensation and hydrolysis reactions in amino acids and dipeptides
3.2.2 Diagrams of amino acids
3.6 Enzymes (Core)
3.6.1 Enzymes and active site
3.6.2 Enzyme-substrate specificity
3.6.3 Effect of temperature, pH and [substrate]
Topic 6: Human Health and Physiology
6.1 Digestion (Core)
6.1.2 Digestive enzymes
6.1.3 Amylases, proteases and lipases
6.3 Defence against infectious disease (Core)
6.3.6 Antibody production
Topic 7: Nucleic Acids and Proteins
7.5 Proteins (AHL) and C1 (SL option identical to 7.5)
7.5.1 and C1.1 Primary, secondary, tertiary and quaternary protein structure
7.5.2 and C1.2 Fibrous and globular proteins
7.5.3 and C1.3 Polar and non-polar amino acids
7.5.4 and C1.4 Protein functions
7.6 Enzymes (AHL) and C2 (SL option identical to 7.6)
7.6.1 and C.2.1 Metabolic pathways
7.6.2 and C.2.2 Induced fit
7.6.3 and C.2.3 Activation energy and catalysis
7.6.4 and C.2.4 Inhibition
7.6.5 and C.2.5 Allosteric sites
Topic 8: Cell Respiration and Photosynthesis
8.1 Respiration (AHL) and C3 (SL option identical to parts of 8.1)
8.1.5 and C.3.5 ATP synthase in chemiosmosis
Topic 11: Human Health and Physiology
11.1 Defence against infectious disease (AHL)
11.1.4 Antibody production
11.2 Muscles and movement (AHL) and B1(SL option identical to 11.2)
11.2.5/6 and B.1.6/7 Actin and myosin
Option A1: Components of the Human Diet (SL)
A.1.2 Essential amino acids
A.1.3 Non-essential amino acids
Option A2: Energy in Human Diets (SL)
A.2.1 Energy value of protein
A.2.3 Health consequence of high protein diet
Option B4: Exercise and Respiration (SL)
B.4.2 Glycogen and myoglobin
Option F6: Microbes and Disease (HL)
Option H1: Hormonal Control (HL)
H.1.2/3 Protein hormones
Option H2: Digestion (HL)
H.2.5 Membrane-bound digestive enzymes
H.2.7 Pepsin and trypsin
Option H6: Gas Exchange (HL)
H.6.2 Adult and foetal haemoglobin, myoglobin
About this resource
This resource was first published in ‘Proteins’.