Transcription and RNA Processing
Gene transcription, RNA processing in eukaryotes, and gene expression
Written and reviewed by the Study Mondo Education TeamLast updated
🎯⭐ INTERACTIVE LESSON
Try the Interactive Version!
Learn step-by-step with practice exercises built right in.
📝 Transcription and RNA Processing
Overview
Gene expression: DNA → RNA → Protein
Transcription: DNA → RNA (this topic) Translation: RNA → Protein (next topic)
Transcription Process
Purpose: Synthesize RNA from DNA template
Key enzyme: RNA polymerase
- Does NOT need primer (unlike DNA polymerase)
- Synthesizes RNA 5'→3' direction
- Reads template strand 3'→5'
Three Stages
1. Initiation
- Promoter: DNA sequence where RNA polymerase binds
- TATA box: common promoter element in eukaryotes (~25 bp upstream)
- Transcription factors help RNA polymerase bind (eukaryotes)
- RNA polymerase unwinds DNA
2. Elongation
- RNA polymerase moves along DNA (3'→5' on template)
- Adds RNA nucleotides (5'→3')
- Coding strand (non-template) has same sequence as RNA (except T→U)
- Template strand (antisense) used to make RNA
3. Termination
- Prokaryotes: terminator sequence causes hairpin loop
- Eukaryotes: cleavage signal, polyadenylation signal
- RNA polymerase releases
- RNA transcript complete
Prokaryotic vs. Eukaryotic Transcription
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| RNA polymerase | One type | Three types (I, II, III) |
| Promoter | -10, -35 boxes | TATA box, others |
| Processing | None | Extensive |
| Location | Cytoplasm | Nucleus |
| Coupling | Transcription + translation | Separated |
RNA Processing (Eukaryotes Only)
Primary transcript (pre-mRNA) must be processed before translation
1. 5' Cap
- 7-methylguanosine cap added to 5' end
- Functions:
- Protects from degradation
- Helps ribosome recognize mRNA
- Aids in export from nucleus
2. 3' Poly-A Tail
- ~50-250 adenine nucleotides added to 3' end
- Functions:
- Protects from degradation
- Aids in export from nucleus
- Helps ribosome locate start codon
3. RNA Splicing
- Introns (non-coding) removed
- Exons (coding) joined together
- Carried out by spliceosome (snRNPs + proteins)
Alternative splicing:
- Different combinations of exons
- One gene → multiple proteins
- Increases protein diversity
- ~95% of human genes alternatively spliced
Gene Structure (Eukaryotes)
Gene organization:
- Promoter
- 5' UTR (untranslated region)
- Exons (expressed sequences)
- Introns (intervening sequences)
- 3' UTR
- Terminator
Types of RNA
1. mRNA (messenger RNA)
- Carries genetic information DNA → ribosome
- Translated into protein
- ~5% of total RNA
2. rRNA (ribosomal RNA)
- Structural and catalytic component of ribosomes
- Most abundant RNA (~80%)
3. tRNA (transfer RNA)
- Brings amino acids to ribosome
- Has anticodon that pairs with mRNA codon
- ~15% of total RNA
4. Other RNAs
- snRNA: splicing (in snRNPs)
- miRNA: gene regulation (microRNA)
- siRNA: gene silencing (small interfering RNA)
Key Concepts
- RNA polymerase synthesizes RNA 5'→3', reads DNA 3'→5'
- Promoter is where transcription starts
- Template strand is copied; coding strand has same sequence as RNA
- Eukaryotic processing: 5' cap, poly-A tail, splicing
- Introns removed, exons joined
- Alternative splicing increases protein diversity
- Three main RNAs: mRNA (message), tRNA (transfer), rRNA (ribosomal)
📚 Practice Problems
1Problem 1medium
❓ Question:
A gene has the following DNA template strand: 3'-TACGCAATGCGA-5'. (a) Write the mRNA sequence transcribed from this template, (b) identify the start and stop codons, and (c) write the amino acid sequence that would be translated (use the genetic code).
💡 Show Solution
Given: Template strand: 3'-TACGCAATGCGA-5'
(a) mRNA sequence:
Transcription rules:
- RNA polymerase reads template 3' → 5'
- Synthesizes mRNA 5' → 3' (antiparallel)
- Uses complementary base pairing:
- A (DNA) → U (RNA)
- T (DNA) → A (RNA)
- G (DNA) → C (RNA)
- C (DNA) → G (RNA)
Step-by-step:
Template (3'→5'): 3'- T A C G C A A T G C G A -5'
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
mRNA (5'→3'): 5'- A U G C G U U A C G C U -3'
(b) Start and stop codons:
Start codon: AUG
- Position: First codon (nucleotides 1-3)
- Codes for: Methionine (Met)
- Signals: Translation start
- All proteins begin with Met (often removed later)
Looking for stop codons:
- UAA, UAG, UGA = stop codons
- Check the sequence: AUG CGU UAC GCU
- No stop codon present in this sequence!
Note: This appears to be partial gene sequence. A real gene would have:
- Promoter (before start)
- Start codon (AUG) ✓
- Coding sequence
- Stop codon (UAA, UAG, or UGA)
- Terminator
(c) Amino acid sequence:
Translation using genetic code:
Divide mRNA into codons (3-nucleotide groups):
mRNA: 5'- AUG CGU UAC GCU -3'
Codons: ↓ ↓ ↓ ↓
Using genetic code table:
| Codon | Amino Acid | Abbreviation |
|---|---|---|
| AUG | Methionine | Met (M) |
| CGU | Arginine | Arg (R) |
| UAC | Tyrosine | Tyr (Y) |
| GCU | Alanine | Ala (A) |
Polypeptide:
Or using single-letter code: MRYA
Complete picture:
DNA coding strand: 5'-ATGCGTTACGCT-3' (not given, but complementary to template)
DNA template strand: 3'-TACGCAATGCGA-5' (given)
↓ Transcription
mRNA: 5'-AUGCGUUACGCU-3'
↓ Translation
Polypeptide: Met-Arg-Tyr-Ala (N-terminus → C-terminus)
Key Concepts:
Genetic Code Properties:
- Triplet code: 3 nucleotides = 1 amino acid
- Degenerate: Multiple codons for same amino acid
- CGU, CGC, CGA, CGG all code for Arg
- Universal: Same code in nearly all organisms
- Unambiguous: Each codon specifies only ONE amino acid
- Non-overlapping: Codons read in sequence, no overlap
Reading frame:
- AUG sets the reading frame
- Must read in correct groups of 3
- Frameshift mutation → wrong amino acids!
Example if we shift by +1:
- Normal: AUG CGU UAC GCU
- +1 shift: A UGC GUU ACG CU → different amino acids!
Why AUG is special:
- Only start codon (in eukaryotes)
- Also codes for Met in middle of protein
- Context determines if it's start or internal Met
Explain using:
📋 AP Biology — Exam Format Guide
⏱ 3 hours📝 66 questions📊 3 sections
| Section | Format | Questions | Time | Weight | Calculator |
|---|---|---|---|---|---|
| Multiple Choice | MCQ | 60 | 90 min | 50% | 🚫 |
| Free Response (Long) | FRQ | 2 | 50 min | 30% | 🚫 |
| Free Response (Short) | FRQ | 4 | 40 min | 20% | 🚫 |
📊 Scoring: 1-5
5
Extremely Qualified
~14%
4
Well Qualified
~22%
3
Qualified
~24%
2
Possibly Qualified
~24%
1
No Recommendation
~16%
💡 Key Test-Day Tips
- ✓Focus on experimental design
- ✓Know data analysis
- ✓Practice graph interpretation
⚠️ Common Mistakes: Transcription and RNA Processing
Avoid these 3 frequent errors
🌍 Real-World Applications: Transcription and RNA Processing
See how this math is used in the real world
🎴
Practice with Flashcards
Rate this topic's cards with spaced repetition. Cards join your deck when you finish a topic's lesson and take its exit quiz.
📖
Browse All Topics
Explore more AP Biology topics
📌 Related Topics in Gene Expression and Regulation
❓ Frequently Asked Questions
What is Transcription and RNA Processing?▾
Gene transcription, RNA processing in eukaryotes, and gene expression
How can I study Transcription and RNA Processing effectively?▾
Start by reading the study notes and working through the examples on this page. Then use the flashcards to test your recall. Practice with the 1 problems provided, checking solutions as you go. Regular review and active practice are key to retention.
Is this Transcription and RNA Processing study guide free?▾
Yes — all study notes, flashcards, and practice problems for Transcription and RNA Processing on Study Mondo are free to access. No account is needed.
What course covers Transcription and RNA Processing?▾
Transcription and RNA Processing is part of the AP Biology course on Study Mondo, specifically in the Gene Expression and Regulation section. You can explore the full course for more related topics and practice resources.
Are there practice problems for Transcription and RNA Processing?▾
Yes, this page includes 1 practice problem with detailed solutions. Each problem includes a step-by-step explanation to help you understand the approach.