8. The Control of Gene Expression: Definitions (A Level only) (AQA A-Level Biology): Revision Notes

8. The Control of Gene Expression: Definitions (A Level only)

Acetylation: The process of adding acetyl groups to histone proteins. This modification makes genes more accessible for transcription by relaxing chromatin structure, thereby activating gene expression.

Addition: A type of gene mutation where one or more nucleotide bases are inserted into a DNA sequence. This insertion can cause a frameshift mutation, altering the reading frame for subsequent codons.

Benign: A classification for non-cancerous tumours that grow slowly, remain contained within a capsule, and stay localised at their original site. These tumours can typically be surgically removed.

Cancer: A non-communicable disease characterised by the uncontrolled division and spread of tumour cells that undergo metastasis throughout the body.

Cellular proteome: The complete set of proteins that are expressed and produced within a specific cell type at any given time.

Complementary DNA (cDNA): A synthetic DNA strand that is complementary to a specific mRNA template, created using reverse transcriptase enzyme.

Complete proteome: The entire collection of proteins that can potentially be produced by an organism's genome under all possible conditions.

Deletion: A form of gene mutation involving the removal of one or more nucleotide bases from a DNA sequence. This can result in a frameshift mutation that alters subsequent amino acid sequences.

Differentiation: The biological process through which unspecialised cells develop into specialised cells with specific functions and characteristics.

DNA hybridisation: A molecular technique where a single-stranded DNA segment combines with a complementary DNA or RNA fragment to form a double-stranded molecule.

DNA ligase: An enzyme responsible for joining the sugar-phosphate backbones of two separate DNA segments by forming phosphodiester bonds.

DNA polymerase: An enzyme that constructs double-stranded DNA molecules using a single template strand and complementary nucleotides.

DNA probe: A short, single-stranded DNA segment that has been fluorescently or radioactively labelled. These probes are used to identify and locate specific gene sequences or alleles.

DNA sequencing: The laboratory process of determining the complete nucleotide base sequence of an organism's DNA.

Duplication: A type of gene mutation where one or more nucleotide bases are repeated within a DNA sequence, potentially causing frameshift mutations.

Epigenetics: The study of heritable changes in gene expression patterns that occur without alterations to the underlying DNA nucleotide sequence.

Frameshift mutation: A genetic mutation caused by the insertion or deletion of nucleotides that shifts the reading frame of all subsequent triplet codons, often resulting in non-functional protein production.

Gel electrophoresis: A laboratory technique that uses electric current to separate DNA fragments based on their size, with smaller fragments migrating further through the gel matrix.

Gene machine: An automated system that artificially synthesises genes by assembling nucleotides in a predetermined sequence programmed into a computer system.

Gene mutation: Any alteration to at least one nucleotide base in DNA or changes to the arrangement of bases. These mutations occur naturally and may lead to genotype modifications.

Gene therapy: A medical technique involving the introduction of functional genes, typically cloned from healthy individuals, into patients whose cells lack these genes.

Genetically modified organism (GMO): Any organism whose genome has been artificially altered through genetic engineering techniques.

Genetic counselling: A healthcare service providing information and guidance to individuals and families affected by or at risk of inherited genetic conditions, helping them make informed medical decisions.

Genetic fingerprinting: A molecular technique used to identify organisms genetically. This method has practical applications in forensic investigations, paternity determination, medical diagnostics, and agricultural breeding programmes.

Genetic screening: The process of testing individuals to detect the presence of specific faulty or disease-associated alleles.

Genome: The complete collection of genetic material contained within an organism, including all chromosomes and associated DNA sequences.

Hypermethylation: Excessive methylation of DNA sequences, which leads to the silencing of tumour suppressor genes and can contribute to cancer development.

Hypomethylation: Reduced methylation of DNA sequences, resulting in the activation of oncogenes and potential tumour formation.

Induced pluripotent stem (iPS) cells: Unipotent adult cells that have been genetically reprogrammed using specific transcription factors to regain pluripotent stem cell capabilities and self-renewal potential.

Inversion: A chromosomal mutation where a group of nucleotide bases detaches from its original position and reattaches in the reverse orientation.

In vitro: Laboratory procedures conducted outside a living organism in controlled artificial environments, such as PCR amplification in thermocyclers.

In vivo: Biological procedures that occur within living organisms, such as transferring DNA fragments to host cells using vectors for amplification.

Malignant: A classification for cancerous tumours that grow rapidly, lack encapsulation, and can metastasise to distant body regions. Treatment typically involves radiotherapy, chemotherapy, or surgical intervention.

Marker genes: Additional genes inserted into plasmids that facilitate the identification of host cells containing the desired genetic material. These genes often produce easily detectable characteristics like fluorescence or antibiotic resistance.

Metastasis: The process by which cancer cells detach from primary tumours and spread to distant body locations, establishing secondary tumours.

Methylation: The addition of methyl groups to cytosine bases in DNA sequences. This epigenetic modification inhibits transcription by reducing DNA accessibility to transcription factors, effectively silencing genes.

Multipotent cells: Stem cells found in mature mammals that have limited differentiation potential, capable of developing into only a restricted range of cell types within specific tissues.

Mutagenic agent: Any substance or factor that increases the frequency of gene mutations above normal background levels.

Mutation: A random alteration in DNA structure that may produce genetic variants with different characteristics.

Mutation rate: The frequency at which mutations occur within biological systems, typically measured per cell division or per generation.

Non-coding DNA: DNA sequences that do not encode proteins but instead function to regulate and control gene expression patterns.

Oestrogen: A steroid hormone that initiates transcription by binding to specific receptor sites on transcription factors, activating DNA binding sites and promoting gene expression.

Oncogenes: Mutated versions of proto-oncogenes that remain continuously activated, promoting uncontrolled cell division and tumour development.

Personalised medicine: A medical approach that customises healthcare treatments based on an individual's specific genetic profile and characteristics.

Pluripotent cells: Stem cells found in embryonic tissue that possess the capability to differentiate into virtually any cell type in the body.

Polymerase Chain Reaction (PCR): An in vitro laboratory technique that rapidly amplifies specific DNA fragments through repeated cycles of heating and cooling.

Primers: Short nucleotide sequences that are complementary to one end of target DNA fragments, serving as starting points for DNA replication.

Promoter: A specific DNA region where RNA polymerase attaches and initiates the transcription process.

Proto-oncogenes: Normal genes that promote cell division when activated by growth factor binding to specific cell membrane receptor proteins.

Recognition sequences: Specific nucleotide base sequences in DNA that are identified and cleaved by restriction enzymes.

Recombinant DNA: Genetic material created by combining DNA segments from two or more different organisms.

Recombinant DNA technology: The scientific process of transferring DNA segments between different organisms to create genetically modified entities.

Restriction endonucleases: Enzymes that cleave DNA molecules at specific recognition sequences, producing fragments with sticky ends.

Reverse transcriptase: An enzyme that synthesises DNA molecules using RNA templates as the starting material.

Risk factor: Any variable or characteristic associated with an increased probability of developing a particular disease or infection.

RNA interference (RNAi): A cellular mechanism that controls gene expression by degrading target mRNA molecules, thereby preventing protein translation.

Silent mutation: A type of substitution mutation that produces the same amino acid sequence due to the redundant nature of the genetic code.

Stem cells: Unspecialised cells that maintain the ability to differentiate into various specialised cell types while retaining self-renewal capabilities.

Sticky ends: The staggered cuts produced by restriction endonucleases in double-stranded DNA, creating single-stranded overhangs that can pair with complementary sequences.

Substitution: A gene mutation where one nucleotide base is replaced with a different base at the same position.

Terminator: A DNA region where RNA polymerase detaches and releases the newly synthesised RNA transcript, ending the transcription process.

Thermocycler: A computer-controlled laboratory instrument that precisely regulates temperature changes at predetermined time intervals, essential for PCR reactions.

Totipotent cells: Stem cells present in early mammalian embryos that have the maximum differentiation potential, capable of developing into any cell type in the body.

Transformation: A laboratory procedure involving the reintroduction of plasmids into bacterial cells to create transgenic bacteria, typically performed in calcium ion-containing media.

Transcriptional factors: Regulatory proteins that move from the cytoplasm into the nucleus, where they bind to specific DNA sequences and initiate transcription.

Transgenic organism: Any organism containing recombinant DNA from other species.

Translocation of bases: A chromosomal mutation where nucleotide sequences detach from one chromosome and integrate into a different chromosome.

Tumour: An abnormal cellular mass resulting from uncontrolled and excessive cell division.

Tumour suppressor genes: Regulatory genes that normally slow cell division, facilitate DNA repair, and trigger apoptosis in cells with damaged DNA.

Unipotent cells: Adult stem cells derived from multipotent cells that have the most limited differentiation potential, capable of developing into only one specific cell type.