Gene Expression Flashcards
Allele
Different forms of a gene due to slightly different order of bases e.g. brown eyes and blue eyes
Amino acids
Building blocks of proteins. Carried by the tRNA molecule. There are 20 different types.
Anticodon
A sequence of three nucleotides/bases on a tRNA molecule that complementary bonds with a specific codon on a strand of mRNA during translation.
Block Mutation
A mutation resulting in a change in the number or arrangement of genes on chromosomes.
Chromosome
A threadlike structure made of DNA and (in eukaryotes) associated histone proteins on which the genetic information of an individual is stored.
Codon
A triplet of nucleotides within a molecule of messenger RNA that specifies a particular amino acid during the synthesis of proteins in a cell.
Complementary base pairing rules
These state that the nitrogenous bases Adenine and Thymine will always pair together (Uracil replaces Thymine in RNA) and Cytosine and Guanine will always pair together.
Degeneracy
Degeneracy in the code is that if you change the third position of a triplet you often code for the same amino acid.
Degeneracy leads to redundancy in that two or more codons can specify for the same amino acid. For example, codons GAA and GAG both specify glutamic acid (GLU). Because an amino acid may be coded for by more than one codon, this can buffer the effect of any mutations as a change in one base may not alter the amino acid coded for.
Deletion Mutation
A base is removed from the DNA and this results in a reading frame shift with each triplet after that being different.
DNA
Deoxyribonucleic acid. The genetic material of most living organisms. It plays a central role in the determination of hereditary characteristics by controlling protein synthesis in cells. It has a double helix shape.
Enzymes
A protein that is a biological catalyst that helps increase the rate reactions of the cell.
Exons
Remaining coding sequences on the mRNA strand which are then translated (introns are non-coding and are removed)
Frame Shift
Since mRNA is read in codons (groups of 3 bases) a change in ONE nucleotide by either inserting or deleting will result in a change in the reading frame. The change will affect all the codons, and therefore amino acid sequence from this point onward.
Gametes
A reproductive cell that fuses with another to form a zygote - eg. eggs (ova) and sperm (spermatozoa). Mutations in these cells will be inherited by offspring.
Gene
A length of DNA that codes for a particular polypeptide/protein/enzyme
Genetic code
A triplet code where each 3 bases codes for a specific amino acid
Genotype
The genetic make-up of an organism for a feature
Homologous Chromosomes
Chromosomes that have the same genes at the same location. In diploid cells, one chromosome comes from the female parent, the other from the male parent.
Insertion
A base is inserted into the DNA, resulting in a frame shift and all the other bases move down one
Meiosis
Meiosis is cell division that produces gametes/sex cells with a haploid/ (half the number of chromosomes) as the parent cell / somatic cells
Metabolism
The sum of all the physical and chemical reactions that are controlled by enzymes and take place within cells
Metabolic Pathways
A series of enzyme-controlled reactions, where the product of one reaction becomes the substrate of the next
Missense mutation
The altered codon still codes for an amino acid – but not the correct amino acid
Mitosis
A type of cell division that results in two daughter cells, each having a nucleus containing the same number and kind of chromosomes as the parent cell
mRNA
Messenger RNA, RNA that carries the genetic code transcribed from DNA to the ribosomes.
Mutagen
Physical or chemical agents that interact with DNA increasing the chance of mutations (e.g. environmental factors, UV light, X-rays,)
Mutation
A change in the base sequence of DNA. Can occur randomly or as a result of a mutagen.
Nonsense Mutation
A change of the base on the DNA which changes the instructions, so a STOP codon occurs in the wrong place. Protein is greatly affected. In most cases a short, non-functional protein is formed
Nucleotide
An organic compound consisting of a nitrogen-containing purine or pyrimidine base linked to a sugar and a phosphate group
Peptide bond
Bond formed between 2 amino acids during translation
Phenotype
The observable characteristics of an organism
Point Mutation
Mutations that involve a single nucleotide (1 base)
Polypeptide chain
Formed as amino acids are bonded to one another with a peptide bond during translation. It will eventually fold and form a functional protein.
Primary Protein Structure
The sequence of amino acids as coded for by the DNA
Protein synthesis
The process by which living cells assemble amino acids into proteins based on the genetic information carried in the DNA of the chromosomes
Redundancy
The fact that multiple codons code for the same amino acid, e.g. CCU, CCC, CCA and CCG all code for the same amino acid
RNA
Ribonucleic acid. It plays a role in transferring information from DNA to form a protein. It is single stranded and contains the base uracil instead of thymine
rRNA
A type of RNA that is present in the ribosomes (ribosomal RNA)
Ribosome
A cellular unit made up of two sub-units (rRNA and protein) which are the site of translation. They can be free floating in the cytoplasm or attached to Endoplasmic Reticulum
Silent mutation
Base pair mutation with no impact on the sequence of the proteins produced (no change in amino acid) (due to redundancy)
Somatic cells
All cells in the body other than the reproductive cells
Start codon
Translation begins when the Ribosome binds to the AUG codon on the mRNA. AUG codes for the amino acid Methionine (Met) brought by the tRNA molecule.
Stop codon
UAA, UGA and UAG are STOP codons and signal the end of the polypeptide chain. These codons do NOT code for an amino acid. They act like a bookend, completing the translation process.
Substitution mutation
One base is replaced by another. Single base mutations can alter a codon but may or may not have an effect.
Trait
Feature whose appearance is determined by genes (inherited)
Transcription
The process in of making mRNA by RNA polymerase reading the DNA template strand
Translation
The process in which a sequence of mRNA triplets (codons) is read by a ribosome and allows the tRNA to drop specific amino acids which the ribosome joins by catalysing a peptide bond to make polypeptide chain during protein synthesis
Triplet
A sequence of three bases on a DNA strand
tRNA
Transfer RNA, RNA that carries/transports specific amino acids to the site of translation on the ribosome where they are bonded together by the ribosome to form a polypeptide chain
Variation
Differences between organisms created by their different genetic make-up. Variation can be discrete (either/or), where a trait is controlled by a single gene; or continuous (e.g. height), where a trait is influenced by several genes
