AQA A Level Biology Topic 8: Control of Gene Expression

Comprehensive vocabulary flashcards for AQA A Level Biology Topic 8, covering gene mutations, stem cells, transcription/translation regulation, cancer, and gene technologies.

Gene mutation

A change in the base sequence of DNA which can arise spontaneously during DNA replication in interphase.

Mutagenic agent

A factor that increases the rate of mutation, such as ultraviolet (UV) light or alpha particles.

Substitution mutation

A type of gene mutation where a base or nucleotide is replaced by a different base or nucleotide in DNA.

Addition mutation

A type of gene mutation where one or more bases or nucleotides are added to the DNA base sequence.

Deletion mutation

A type of gene mutation where one or more bases or nucleotides are lost from the DNA base sequence.

Duplication mutation

A mutation in which a sequence of DNA bases or nucleotides is repeated or copied.

Inversion mutation

A mutation where a sequence of bases or nucleotides detaches from the DNA sequence, then rejoins at the same position in the reverse order.

Translocation mutation

A mutation where a sequence of DNA bases or nucleotides detaches and is inserted at a different location within the same or a different chromosome.

Degenerate code

A feature of the genetic code where an amino acid can be coded for by more than one triplet code or codon.

Frameshift

Occurs when gene mutations (e.g. addition, deletion, duplication, or translocation) change the number of nucleotides or bases by any number not divisible by $3$, shifting how the genetic code is read downstream.

Stem cells

Undifferentiated or unspecialised cells capable of dividing by mitosis to replace themselves indefinitely and differentiating into other types of specialised cells.

Totipotent cells

Stem cells occurring for a limited time in early mammalian embryos that can divide and differentiate into any type of body cell, including extra-embryonic cells like the placenta.

Pluripotent cells

Stem cells found in mammalian embryos after the first few cell divisions that can divide and differentiate into most cell types, excluding placental cells.

Multipotent cells

Stem cells found in mature mammals that can divide and differentiate into a limited number of cell types, such as blood cell types from bone marrow.

Unipotent cells

Stem cells found in mature mammals that can divide and differentiate into just one cell type, such as cardiomyocytes in the heart.

Induced pluripotent stem (iPS) cells

Pluripotent cells produced from adult somatic cells (e.g. fibroblasts) by adding specific protein transcription factors to reprogram the cells.

Transcription factors

Proteins which regulate (stimulate or inhibit) transcription by binding to a specific DNA base sequence on a promoter region.

Epigenetics

Heritable changes in gene function or expression without changes to the base sequence of DNA, caused by environmental changes such as diet, stress, or toxins.

Epigenome

All chemical modification of DNA and histone proteins, specifically methyl groups on DNA and acetyl groups on histones.

Methylation of DNA

The addition of methyl groups to cytosine bases in DNA; increased methylation inhibits transcription by causing nucleosomes to pack tightly, preventing RNA polymerase binding.

Acetylation of histones

The addition of acetyl groups to histones; decreased acetylation increases the positive charge of histones, causing them to bind DNA more tightly and inhibit transcription.

RNA interference (RNAi)

The inhibition of translation of mRNA produced from target genes by RNA molecules such as siRNA or miRNA.

RNA-induced silencing complex (RISC)

A protein-RNA complex where single-stranded siRNA or miRNA binds to target mRNA with a complementary base sequence, leading to mRNA hydrolysis or prevented translation.

Malignant tumour

A cancerous mass of abnormal cells that grows fast, can invade surrounding tissues, and spread through the body by metastasis.

Benign tumour

A non-cancerous mass of abnormal cells that grows slowly, is well differentiated, has well-defined borders, and does not spread by metastasis.

Metastasis

The process where cells break off from a malignant tumour and spread to other parts of the body to form secondary tumours.

Tumour suppressor genes

Genes that code for proteins that inhibit or slow the cell cycle if DNA damage is detected or cause apoptosis of potential tumour cells.

Proto-oncogenes

Genes that code for proteins that stimulate cell division through signalling pathways controlling growth factors.

Oncogenes

Mutated or abnormally expressed forms of proto-oncogenes that lead to uncontrolled cell division via overproduction or permanent activation of proteins.

Genome

The complete set of genes in a cell.

Proteome

The full range of proteins that a cell can produce, coded for by the cell's DNA.

Recombinant DNA technology

The transfer of DNA fragments from one organism or species to another.

Restriction enzymes

Enzymes that cut DNA at specific base ‘recognition sequences,’ often in a staggered fashion to form single-stranded ‘sticky ends.’

Reverse transcriptase

An enzyme used to synthesise a single strand of complementary DNA (cDNA) using isolated mRNA as a template.

Gene machine

A technology that synthesises fragments of DNA quickly and accurately from scratch based on a determined amino acid sequence, without needing a DNA template.

Polymerase chain reaction (PCR)

An in vitro technique used to amplify DNA fragments in a cycle of heating ($95^\text{o}C$) to separate strands, cooling ($55^\text{o}C$) for primer binding, and heating ($72^\text{o}C$) for DNA polymerase action.

Primers

Short, single-stranded DNA fragments complementary to the base sequence at the start of a desired gene, allowing DNA polymerase to bind and start synthesis at the $3'$ end.

Vector

A tool used to transfer DNA into host cells or organisms, such as a plasmid or bacteriophage (virus).

DNA ligase

An enzyme used in recombinant DNA technology to join a DNA fragment to vector DNA by forming phosphodiester bonds.

Marker genes

Genes inserted into vectors alongside desired DNA fragments to detect genetically modified cells, such as genes for antibiotic resistance or fluorescent proteins.

Promoter and terminator regions

DNA sequences added to fragments to ensure transcription starts (allowing RNA polymerase to bind) and stops at the intended locations.

Gene therapy

The introduction of new DNA containing functional alleles into cells to overcome the effects of faulty alleles in genetic disorders.

DNA probes

Short, single-stranded pieces of DNA with a base sequence complementary to a target allele or region, usually labelled with fluorescent or radioactive tags.

DNA hybridisation

The process in which a single-stranded DNA probe binds to a complementary single strand of DNA by forming hydrogen bonds.

Gel electrophoresis

A method used to separate DNA, RNA, or protein fragments according to their length or mass and their electrical charge.

Personalised medicine

Medical treatment tailored to an individual’s genotype, such as identifying specific mutations causing cancer to use specific tailored drugs.

Variable number tandem repeats (VNTRs)

Repeating sequences of nucleotides found within non-coding sections of DNA that vary in length between individuals.

Genetic fingerprinting

A diagnostic technique that uses PCR and gel electrophoresis to compare patterns of VNTRs for identification, paternity testing, or forensic science.