BiologyChapter 13: Chromosome and DNA
Transcription and the Code
Transcription: DNA -> mRNA in the nucleus (euk).
Learning objectives
- Explain transcription and the code in clear biological language.
- Distinguish 1. mrna from 2. codons.
- Use the key terms to answer a short Federal Board exam question.
Definition
Transcription: DNA -> mRNA in the nucleus (euk). RNA polymerase named. Promoter named as a start region. Template strand is read; mRNA matches the coding strand except UT. Introns cut out (splicing named) in eukaryotes. Genetic code: triplet codon. AUG start (Met) named. Stop codons named as UAA, UAG, UGA if the book lists them. Degenerate: extra codons for some amino acids. Transcription copies a gene's DNA sequence into mRNA, which carries the message to ribosomes. Eukaryotes process mRNA (splicing, cap, tail) before export from the nucleus.
Important terms
- TRANSCRIPTION AND THE CODE
- Transcription: DNA -> mRNA in the nucleus (euk).
- 1. mRNA
- Only a gene (or a transcription unit) is copied.
- 2. CODONS
- Three bases -> one amino acid.
Overview
Copy a message, not the whole genome:
mRNA
Only a gene (or a transcription unit) is copied. Cap and tail named in euk. mRNA goes to a ribosome. tRNA and rRNA are other RNA jobs. Only the template strand is transcribed. mRNA processed in eukaryotes: 5' cap, 3' poly-A tail, introns spliced out. Exons form the coding sequence.
Examples RNA polymerase · U not T · Splicing named
Codons
Three bases -> one amino acid. Code is nearly universal (school). Start AUG. Stops do not add an amino acid. Reading frame: shift ruins the protein (mutation page).
Examples 64 combinations school · 20 amino acids · Degenerate
WHAT — TRANSCRIPTION AND THE CODE
Transcription: DNA -> mRNA in the nucleus (euk). RNA polymerase named. Promoter named as a start region. Template strand is read; mRNA matches the coding strand except UT. Introns cut out (splicing named) in eukaryotes. Genetic code: triplet codon. AUG start (Met) named. Stop codons named as UAA, UAG, UGA if the book lists them. Degenerate: extra codons for some amino acids. Transcription copies a gene's DNA sequence into mRNA, which carries the message to ribosomes. Eukaryotes process mRNA (splicing, cap, tail) before export from the nucleus.
WHY — Why this topic matters
TRANSCRIPTION AND THE CODE is an independent FBISE learning unit because students must connect its structures and processes with their biological functions and examples.
HOW — How it works
mRNA: Only a gene (or a transcription unit) is copied. Cap and tail named in euk. mRNA goes to a ribosome. tRNA and rRNA are other RNA jobs. Only the template strand is transcribed. mRNA processed in eukaryotes: 5' cap, 3' poly-A tail, introns spliced out. Exons form the coding sequence. Examples: RNA polymerase; U not T; Splicing named. CODONS: Three bases -> one amino acid. Code is nearly universal (school). Start AUG. Stops do not add an amino acid. Reading frame: shift ruins the protein (mutation page). Examples: 64 combinations school; 20 amino acids; Degenerate. Worked: DNA coding: A T G T T T mRNA: A U G U U U AUG is start (Met). UUU is Phe in the usual table.
Worked example
- DNA coding: A T G T T T
- mRNA: A U G U U U
- AUG is start (Met).
- UUU is Phe in the usual table.
In simple words
Code table idea. No gene-construct design.
Key points
- DNA -> mRNA
- AUG start
- nucleus then cytoplasm euk
- triplet
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Transcription and the Code
Sticky Notes · Quick Revision
Core Idea
- Transcription: DNA -> mRNA in the nucleus (euk). RNA polymerase named. Promoter named as a start region. Template strand is read; mRNA matches the coding strand except UT. Introns cut out (splicing named) in eukaryotes. Genetic code: triplet codon. AUG start (Met) named. Stop codons named as UAA, UAG, UGA if the book lists them. Degenerate: extra codons for some amino acids. Transcription copies a gene's DNA sequence into mRNA, which carries the message to ribosomes. Eukaryotes process mRNA (splicing, cap, tail) before export from the nucleus.
1. mRNA
- Only a gene (or a transcription unit) is copied. Cap and tail named in euk. mRNA goes to a ribosome. tRNA and rRNA are other RNA jobs. Only the template strand is transcribed. mRNA processed in eukaryotes: 5' cap, 3' poly-A tail, introns spliced out. Exons form the coding sequence.
2. CODONS
- Three bases -> one amino acid. Code is nearly universal (school). Start AUG. Stops do not add an amino acid. Reading frame: shift ruins the protein (mutation page).
Exam Example
- Worked:
- DNA coding: A T G T T T
- mRNA: A U G U U U
- AUG is start (Met).
- UUU is Phe in the usual table.
Common Misconception
- Do not treat 1. mRNA and 2. CODONS as the same idea; each explains a different part of the topic.
FBISE Exam Check
- Define transcription and the code, explain the two key parts, and use the correct biological terms.
- Exam reminder: Worked: DNA coding: A T G T T T mRNA: A U G U U U AUG is start (Met). UUU is Phe in the usual table.
60-second revision
- Transcription: DNA -> mRNA in the nucleus (euk).
- 1. mRNA: Only a gene (or a transcription unit) is copied.
- 2. CODONS: Three bases -> one amino acid.
- Exam reminder: Worked: DNA coding: A T G T T T mRNA: A U G U U U AUG is start (Met). UUU is Phe in the usual table.
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