Protein and Gene Manipulation

The One Thing

Protein and gene manipulation uses recombinant DNA methods, protein engineering, genomics, proteomics, and bioinformatics to alter, analyse, and apply biological information. Its success depends on controlling DNA cutting, joining, delivery, selection, expression, and verification while considering safety, environmental, ethical, legal, and social implications.

Reactions, Processes and Experiments

Key Terms

• Recombinant DNA: DNA formed by joining genetic material from two or more different sources.
• Gene cloning: The production of many identical copies of a selected gene or DNA fragment.
• Restriction enzyme: An enzyme that cuts DNA at specific recognition sequences, often producing sticky or blunt ends.
• DNA ligase: An enzyme that joins DNA fragments by forming bonds in the sugar-phosphate backbone.
• Vector: A DNA molecule, such as a plasmid or bacteriophage, used to carry foreign DNA into a host cell.
• Plasmid: A small, circular, independently replicating DNA molecule commonly found in bacteria and widely used as a cloning vector.
• Origin of replication: A DNA sequence in a vector where replication begins, allowing the inserted DNA to be copied.
• Selectable marker: A gene that helps identify host cells that have received the vector, often by providing resistance to a selective substance.
• Insertional inactivation: Identification of recombinant cells because insertion of foreign DNA disrupts the function of a marker gene.
• Polymerase chain reaction: A technique used to amplify a specific DNA sequence through repeated cycles of denaturation, primer binding, and extension.
• Denaturation: Separation of the two DNA strands by heating.
• Annealing: Binding of short primers to complementary sequences on single-stranded DNA templates.
• Extension: Synthesis of new DNA strands by a heat-stable DNA polymerase.
• Complementary DNA: DNA produced from a mature messenger RNA template using reverse transcriptase; it lacks introns.
• Expression vector: A vector designed to produce the protein encoded by an inserted gene in a host cell.
• Transformation: Introduction of foreign DNA into a host cell.
• Protein engineering: Deliberate modification or design of proteins to obtain desired characteristics.
• Site-directed mutagenesis: Introduction of a specific change into the DNA sequence coding for a protein.
• Directed evolution: An artificial process involving repeated mutation and selection to obtain proteins with improved properties.
• Genomics: Study of an organism’s complete genome, including its sequence, organization, functions, and variations.
• Structural genomics: Study of genome sequence, gene organization, and three-dimensional structures of biological molecules.
• Functional genomics: Investigation of gene functions and large-scale patterns of gene expression.
• Comparative genomics: Comparison of genomes from different organisms to identify conserved genes, similarities, and evolutionary relationships.
• Proteomics: Large-scale study of all proteins produced by a cell, tissue, or organism under particular conditions.
• Protein expression profile: The collection and relative amounts of proteins produced by a biological system at a given time.
• Two-dimensional gel electrophoresis: A method that separates proteins first by charge-related isoelectric point and then by molecular mass.
• Mass spectrometry: A technique used to determine the mass and often the sequence or identity of proteins and peptides.
• Bioinformatics: Application of computational methods to collect, store, analyse, and interpret biological information.
• Biological database: An organised digital collection of nucleotide sequences, protein sequences, structures, functions, or scientific information.
• Sequence alignment: Comparison of DNA, RNA, or protein sequences to identify similarities, differences, conserved regions, and possible functions.
• Homology: Similarity between biological sequences or structures resulting from common evolutionary origin.
• Open reading frame: A continuous stretch of DNA or RNA codons that can potentially be translated into a protein.
• Restriction fragment length polymorphism: Variation in DNA fragment lengths produced when restriction enzymes cut different versions of a genome.

Easily Confused

• Genomics vs proteomics: Genomics studies the complete genome, whereas proteomics studies the complete set of proteins produced under particular conditions.
• Structural genomics vs functional genomics: Structural genomics examines genome sequence, gene organisation, and molecular structures, whereas functional genomics investigates gene functions and large-scale expression patterns.
• Comparative genomics vs sequence alignment: Comparative genomics compares whole genomes, whereas sequence alignment compares particular DNA, RNA, or protein sequences.
• Restriction enzymes vs DNA ligase: Restriction enzymes cut DNA at recognition sequences, whereas DNA ligase joins DNA fragments.
• Sticky ends vs blunt ends: Sticky ends contain short single-stranded overhangs that can pair with complementary ends; blunt ends do not have overhangs.
• Transformation vs gene cloning: Transformation introduces foreign DNA into a host cell, whereas gene cloning produces many identical copies of a selected gene or DNA fragment.
• Selectable marker vs insertional inactivation: A selectable marker identifies cells carrying a vector through a selectable trait, whereas insertional inactivation identifies recombinant cells because a marker gene has been disrupted.
• PCR denaturation, annealing, and extension: Denaturation separates DNA strands, annealing binds primers, and extension synthesises new DNA.
• Rational design vs directed evolution: Rational design uses known structural and functional information to guide changes, whereas directed evolution generates variants and selects improved forms experimentally.
• DNA sequence data vs protein expression data: DNA sequence data indicate genetic information, whereas protein expression profiles show which proteins are produced and in what relative amounts under particular conditions.
• Reverse transcription vs transcription: Reverse transcription uses RNA as a template for DNA, whereas transcription generally uses DNA as a template for RNA.
• Protein sequence vs protein structure: The amino acid sequence is the primary order of residues, whereas three-dimensional structure determines how that sequence folds and functions.

What Gets Asked

• Describe the stages of a recombinant DNA process. Marks depend on including isolation of the target gene, cutting of the gene and vector, DNA ligase joining, introduction into a host, selection of transformed cells, and expression or purification.
• Explain the action of EcoRI. The required detail is the recognition of the palindromic sequence 5'-GAATTC-3', cutting between G and A on both strands, and production of sticky ends.
• State and distinguish the three PCR stages. A common error is to confuse the temperatures or processes: denaturation is about 94–98 degrees Celsius, annealing is usually about 50–65 degrees Celsius, and extension is near 72 degrees Celsius.
• Calculate the approximate number of PCR products. The relationship is $2^n$ times the starting number after $n$ efficient cycles; omitting the starting quantity loses accuracy.
• Explain how recombinant cells are identified. Answers should distinguish selectable markers from insertional inactivation rather than treating them as the same method.
• Explain how protein engineering changes protein properties. The relevant links are from altered DNA to amino acid sequence and then to protein structure, stability, activity, or specificity.
• Compare genomics, proteomics, and bioinformatics. The distinction is between studying genomes, studying complete protein outputs, and using computational tools such as databases, genome browsers, alignment programs, motif searches, structure prediction, molecular visualisation, and phylogenetic analysis.