Genomes, genes and alleles Flashcards
Gene expression
The process by which functional products, such as proteins, are produced through two stages: Transcription and Translation.
Gene regulation
The process by which cells can either turn on or off gene expression.
RNA polymerase
An enzyme that is responsible for producing a transcript (pre-mRNA) of a gene by joining free RNA nucleotides via complementary base pairing.
Coding strand
A strand of DNA that codes for a protein. It is complementary to the template strand, so when a pre-mRNA is formed using the template strand, the sequence of pre-mRNA is similar to that of the coding strand, except Uracils replace Thymines in the pre-mRNA sequence.
template strand
It is the strand of DNA that is copied into a pre-mRNA transcript during transcription.
Genome
All the genetic information (DNA) in an individual or cell.
Transcription followed by RNA processing.
The first stage of gene expression. It occurs in the nucleus in eukaryotic cells where a gene is copied into pre-mRNA transcript. Step 1: DNA unwinds and RNA polymerase attaches to the promoter region (+ context). Step 2: DNA template strand is copied into pre-mRNA via complementary base pairing using RNA polymerase.
Step 3: pre mRNA undergoes RNA processing. Introns are removed, a 5’ methyl cap and 3’ poly-A tail are added to form mRNA.
Step 4: mRNA from the _________ gene leaves the nucleus and goes to a ribosome.
RNA processing
the process during which a pre-mRNA transcript undergoes several changes for it to become a mature mRNA. This process is unique to eukaryotic cells. The mature mRNA then leaves the nucleus and goes to a ribosome.
Splicing
One of the main modfications that occurs to a pre-mRNA transcript during RNA processing. Introns (non-coding sections of a gene) are cut out, and exons (coding sections of a gene) are joined together to form a mature mRNA.
5’ methyl cap and 3’ poly A tail
Structures that are added to the ends of a pre-mRNA transcript. Methyl cap (which is added to the 5’ end) protects the mRNA from enzyme degradation and allows the ribosome to bind to the mRNA to begin translation. Poly-A tail (added to the 3’ end) also protects the mRNA from enzyme degradation and allows the mRNA to leave the nucleus.
Translation
The second stage of gene expression where the mRNA code is read by the ribosome to produce a particular polypeptide molecule.
Step 1: Ribosomes read the mRNA molecule (+ context). Step 2: tRNA brings the correct and specific amino acid to the ribosome. Step 3: tRNA anticodons are complementary and specific to mRNA codons. Step 4: Amino acids are joined together by peptide bond in a condensation polymerisation reaction to form a specific polypeptide.
Ribosome
An organelle found in both eukaryotic and prokaryotic cells. It consists of two protein subunits and is responsible for producing proteins for the cell.
mRNA codons
Groups of three RNA bases that code for specific amino acids or represent “End” of Translation.
tRNA anticodon
A group of three RNA bases found in a tRNA. It is complementary to a particular mRNA codon, allowing the tRNA molecule to bind to its complementary mRNA codon in the mRNA molecule.
Degenerate code
It refers to the fact that some codons can code for the same amino acid, while others may signal the end of translation.
Post-translational modification
The process in which polypeptides produced by the ribosome undergo structural changes in different parts of the cell: the rough endoplasmic reticulum, cytosol (using chaperone proteins), and Golgi apparatus. An example of post-translational modification can be addition of carbohydrate chains to existing polypeptide molecules. Post-translation modification can influence the folding of a polypeptide.
Mutation
A change in the genetic code (in the DNA sequence).
Point mutations
Mutations that involve a single base change in the DNA sequence.
Examples: Substitution, Insertion, and Deletion.
Silent mutation
the mutated codon codes for the same amino acid as the original codon.
Missense mutation
the mutated codon codes for a different amino acid than the original codon.
Nonsense mutation
the mutated codon becomes a stop codon.
Frameshift mutation
A deletion or addition of bases in the DNA sequence that changes the reading frame of the DNA. It often results in multiple changes in the amino acid sequence, as any codon that comes after where the mutation is introduced can be altered to produce different amino acids or become stop codons, resulting in a premature production of the polypeptide chain.
Gene
The hereditary unit, which is a section of DNA occupying a specific location on a chromosome. It determines the characteristic of an organism by directing the formation of a protein.
Allele
Variation of a gene at a particular gene locus.
Genotype
The allele combination of an individual
Homologous chromosomes
Chromosomes that have identical gene loci.
Homozygous
having two of the same allele for a gene at a specific gene locus.
Heterozygous
having two different alleles for a gene at a specific gene locus.
Dominant trait
A trait that is expressed in a heterozygous genotype.
Recessive trait
A trait that is only expressed when the genotype is homozygous.
Phenotype
The physical, behavioural or physiological characteristics of an organism which are a result of the combination of the genotype and environment.
Epigenetic changes
Unlike genetic changes,epigeneticchanges are reversible and do not change your DNA sequence, but they can change how your body reads a DNA sequence.
