Protein Synthesis: Transcription & Translation
Protein synthesis is the two-stage process by which cells build polypeptide chains from the base sequence of DNA. In transcription, RNA polymerase copies a gene in the nucleus to produce messenger RNA (mRNA); in translation, ribosomes read the mRNA codons in the cytoplasm while transfer RNA (tRNA) delivers specific amino acids in sequence.
- Transcription
- The process of synthesizing pre-mRNA from a DNA template.
- Translation
- The synthesis of a polypeptide chain at the ribosome, using the mRNA sequence as a template.
- Splicing
- The removal of introns from pre-mRNA and joining of exons to form mature mRNA.
Mitosis (2n → 2n) vs Meiosis (2n → n) & Ribosome Protein Synthesis
Key Concepts & Exam Definitions (5)
- Transcription
- The process of synthesizing pre-mRNA from a DNA template.
- Translation
- The synthesis of a polypeptide chain at the ribosome, using the mRNA sequence as a template.
- Splicing
- The removal of introns from pre-mRNA and joining of exons to form mature mRNA.
- Codon
- A sequence of three bases on mRNA that codes for a specific amino acid.
- Anticodon
- A sequence of three bases on a tRNA molecule complementary to an mRNA codon.
Quick-Fire Flashcards (5)
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What enzyme catalyzes the formation of pre-mRNA?
Where does translation occur in a eukaryotic cell?
What is the start codon?
What type of bond forms between amino acids during translation?
What is degenerate code?
Exam-Style Questions & Mark Schemes (3)
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- Q1
Describe the process of splicing and explain its significance.
Click “Check Mark Scheme” to compare your answer, Splicing involves removing non-coding introns from pre-mRNA and joining coding exons together to form mature mRNA. It is significant because it allows a single gene to produce multiple different proteins (via alternative splicing) and ensures only coding sequences are translated.
- Q2
Explain how a mutation in a gene can lead to a non-functional enzyme.
Click “Check Mark Scheme” to compare your answer, A mutation changes the DNA base sequence, altering the mRNA codons. This may change the amino acid sequence (primary structure) of the polypeptide. This changes the position of hydrogen, ionic, and disulfide bonds, altering the tertiary structure of the enzyme. The active site shape changes, so it is no longer complementary to the substrate, preventing enzyme-substrate complexes from forming.
- Q3
Compare transcription and DNA replication.
Click “Check Mark Scheme” to compare your answer, Both involve unwinding DNA and complementary base pairing. However, transcription uses RNA polymerase, RNA nucleotides (A, U, C, G), and only copies a single gene into a single-stranded RNA. DNA replication uses DNA polymerase, DNA nucleotides (A, T, C, G), and copies entire chromosomes into double-stranded DNA.
Common Exam Questions (3)
What is the role of RNA polymerase in transcription?
RNA polymerase binds to the start of a gene, breaks the hydrogen bonds between the two DNA strands, and joins free RNA nucleotides along the template strand by complementary base pairing to form a strand of pre-mRNA.
What is the difference between introns and exons?
Introns are non-coding base sequences within a eukaryotic gene that are removed from pre-mRNA during splicing. Exons are the coding sequences that are joined together to form mature mRNA before it leaves the nucleus.
How does tRNA function in translation?
Each tRNA molecule carries a specific amino acid at one end and has a three-base anticodon at the other. During translation, the tRNA anticodon forms temporary hydrogen bonds with the complementary mRNA codon in the ribosome, placing each amino acid in the correct order.
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