BIOL1020 Chap.6 Transcription, Splicing and Translation
Transcription, Splicing and Translation
Gene expression transfers information from DNA into RNA and then changes languages from nucleotide sequence to amino-acid sequence. This chapter establishes template and coding strands, RNA synthesis direction, intron removal, alternative splicing, codon grouping and the roles of mRNA, tRNA and rRNA.
Sequence questions are solved procedurally: label both ends, produce the complementary RNA, process the transcript when appropriate, group codons from the correct start and trace how a mutation changes the reading frame or protein.
What this chapter covers
- 01
Central dogma of molecular biology
- 02
DNA template orientation
- 03
Pre-mRNA and RNA splicing
- 04
Alternative exon combinations
- 05
Codons, anticodons and tRNA
- 06
Frameshift and stop mutations
Worked example · free
Comparing one-base and three-base deletions
- +1A one-base deletion changes the grouping of every downstream triplet.
- +1The frameshift alters later amino acids and often creates a premature stop codon.
- +1A three-base deletion removes one codon while preserving the downstream reading frame.
- +1Either variant can affect function, but the one-base deletion usually changes more of the protein sequence.
Key terms
- Template Strand
- The DNA strand read by RNA polymerase to synthesise a complementary RNA molecule.
- Coding Strand
- The DNA strand matching the RNA sequence except that DNA contains thymine where RNA contains uracil.
- Intron
- A transcribed sequence removed during eukaryotic pre-mRNA splicing.
- Exon
- A sequence retained in mature RNA after splicing.
- Anticodon
- A tRNA triplet that pairs antiparallel with a complementary mRNA codon.
Transcription, Splicing and Translation FAQ
What does the central dogma describe?
It describes cellular information flow from DNA to RNA through transcription and from mRNA to protein through translation. DNA replication copies stored information, while transcription changes the molecule but keeps nucleotide language and translation converts codons into an amino-acid sequence.
Why is RNA splicing important?
Eukaryotic pre-mRNA often contains introns that must be removed before translation. Splicing joins retained exons into mature mRNA. Alternative exon combinations can produce different messages from one genomic region, expanding protein diversity without changing the underlying DNA sequence.
How should codon and anticodon directions be handled?
Write the mRNA codon 5-prime to 3-prime, then align the tRNA anticodon antiparallel and complementary to it. Reading both triplets in the same written direction without reversing one is a common source of incorrect pairing and amino-acid predictions.
How do coding and template DNA strands differ?
RNA polymerase reads the template strand while synthesising RNA in the opposite, antiparallel direction. The coding strand has the same base order as the RNA transcript except that DNA contains thymine where RNA contains uracil. Strand labels matter because only one directly supplies the complementary template.
Why can alternative splicing change protein products?
A single pre-mRNA can be processed with different combinations of exons retained in mature transcripts. Those transcripts may encode proteins with different domains or properties. The DNA locus has not necessarily changed; the variation arises from which RNA segments are joined before translation.
What roles do transfer RNA and ribosomal RNA play?
A transfer RNA carries a specific amino acid and uses its anticodon to recognise a messenger-RNA codon. Ribosomal RNA contributes to ribosome structure and catalysis. Together they connect nucleotide order to peptide synthesis, while messenger RNA supplies the codon sequence being read.
Why is an early frameshift often severe?
An insertion or deletion not divisible by three changes how downstream bases are grouped into codons. Many subsequent amino acids can change, and a premature stop may appear. Earlier changes generally expose more of the coding region to this altered frame, although exact impact depends on location.
How can a non-coding mutation change expression?
A sequence change in a promoter, splice signal or other regulatory site can alter protein binding, transcript processing, timing or expression level without changing an encoded codon. The analysis should identify the affected information-processing step. Non-coding describes the absence of protein coding, not the absence of biological function.
Exam move
Practise sequence problems with a fixed layout: template DNA, coding DNA, pre-mRNA, mature mRNA and protein. Mark 5-prime and 3-prime ends before adding any base. Use a separator between codons and re-establish the frame after each mutation. For splicing, colour introns and exons differently, then compare alternative mature transcripts. Explain the roles of mRNA, tRNA and rRNA without calling every RNA a message.
When reviewing mutation outcomes, classify substitution, insertion or deletion, check whether the site is retained in mature RNA, and translate only after the correct processing step. Finish with original anticodon and frameshift problems. Verify every answer twice: once by complementarity and once by reading the stated strand directions.
Working through Transcription, Splicing and Translation in BIOL1020? Sia is AskSia’s AI Biology tutor — ask any BIOL1020 Transcription, Splicing and Translation question and get a clear, step-by-step explanation grounded in how BIOL1020 is taught and assessed. Read this chapter free, then take your hardest questions to Sia.
