Exam Revision Flashcards
Gene
> A particular sequence of dDNA bases that code for specific polypeptide chain.
It is inherited from parent to offspring
Locus: fixed position on a chromosome where a specific gene is located
Gene expression
> The transcription and translation of gene. The process in which the genetic material (DNA) is converted into a function 3D protein
Gene Expression: Transcription
- Occurs in the nucleus where RNA polymerase binds to the promoter region of the gene to be transcribed on the template of DNA.
- RNA polymerase unwinds the DNA and moves along the template strand ‘reading’ it in the 3’ to 5’ direction whilst synthesising RNA by joining ribonucleotides in the 5’ to 3’ direction.
- RNA polymerase reaches the end of the gene ( termination sequence), the pre-MRNA molecule will be released.
- The pre-MRNA strand is complementary to the template strand and has the same sequence as the coding strand
Gene Expression: RNA processing
> Eukaryotic cells undergo 3 steps
1. Introns (non-coding regions) are removed and exons (coding regions) are spliced together. Where the ‘mature’ mRNA is shorter than pre-mRNA
2. A methyl cap is added to the 5’end of the RNA molecule ( initiate process of translation)
3. A poly-A-tail is added to the 3’end (assist the export from the nucleus)
Once modifications are done, RNA molecule is mature mRNA and will leave the nucleus and move to a ribosome
Gene Expression: Translation
> Once it leaves the nucleus, the mRNA strand migrates to a ribosome entering at the 5’end.
The start codon AUG instructs for translation to begin, directing for the amino acid methionine to start the polypeptide chain
Each successive codon in the mRNA will pair up with the anticodon of a tRNA molecule carrying a specific amino acid within the ribosome
The process continues with more codons and anticodons pairing, resulting in the amino acids being carried by the tRNA molecules being added to the growing polypeptide chain via peptide bonding ( condensation polymerisation)
Once a stop codon is reached, translation will stop and the polypeptide chain will be released
Promoter regions
> Section of gene that RNA polymerase binds to
Where are operator regions found?
> They are found in prokaryotic operons but not in eukaryotic genes
Repressors
> They are transcription factors that can prevent transcription by binding to the promoter or operator region of DNA, preventing DNA polymerase from binding and transcribing the DNA
Regulatory Genes
> Genes that code for the production of proteins that regulate gene expression
Structural Genes
> Genes that produce a protein or product that forms part of the structure or the functioning of an organism (essentially every gene except regulatory gene)
