Trace a reading frame from initiation to termination

Mechanism before a label

Translation reads mRNA codons through a ribosome and links amino acids into a polypeptide. A charged tRNA associates a codon with an amino acid through anticodon pairing and prior aminoacyl-tRNA charging; a codon does not chemically transform into an amino acid.

An initiation context establishes the reading frame. Methionine can also occur internally, so finding AUG inside a sequence does not prove that translation starts there. Elongation repeats amino-acid addition and translocation; termination occurs when release machinery recognizes a stop codon in the chosen frame.

The genetic code is degenerate: several codons can specify one amino acid. It is broadly shared but has known exceptions. Stop codons specify termination rather than an additional amino acid. Sequence-derived polypeptide predictions do not establish folding, modification or biological activity.

An alternate information route does not reverse translation

In retroviruses, reverse transcriptase copies an RNA genome into DNA. Viral DNA can integrate into the host genome, after which transcription produces RNA and translation produces viral proteins. The RNA-to-DNA arrow changes the nucleic-acid copying route; it does not mean that a protein sequence is read backward into RNA. This conceptual lifecycle is not a method for handling or modifying viruses. OpenStax viral information pathways, checked 31 October 2026.

Changed case: A hypothetical record shows RNA followed by a complementary DNA copy and later RNA made from that DNA. Label the two copying arrows before naming the protein-making arrow.

Check the information arrows

RNA→DNA is reverse transcription; DNA→RNA is transcription; RNA→polypeptide is translation. An RNA genome alone does not establish that every virus uses a DNA intermediate, and the supplied record does not establish integration unless integration evidence is provided.

Name the frame change before predicting the protein

A substitution changes one base without changing sequence length; it can be synonymous, missense or create a premature stop in a specified coding frame. An insertion or deletion shifts downstream triplet grouping when its length is not a multiple of three. A three-base insertion preserves the downstream frame but can still change the protein. Therefore not every insertion/deletion is a frameshift, and preserving the frame does not guarantee preserved function. Mutation and coding-frame context, checked 31 October 2026.

Changed toy sequence: Start from coding DNA 5′-ATG GCT TTT GGA TAA-3′, with the stipulated first-base frame. Insert one C immediately after ATG, then compare inserting CCC at that same boundary. Write the resulting triplets before using the workbench.

Check the one-base versus three-base changes

One inserted C gives ATG CGC TTT TGG ATA followed by one trailing A; downstream triplets have shifted and the original final stop is no longer in that frame within the short excerpt. Inserting CCC gives ATG CCC GCT TTT GGA TAA: an added proline under the supplied code, with the downstream frame and stop retained. Neither sequence calculation establishes a real protein's activity or the rest of a gene outside the excerpt. These are original toy strings, not a design or manipulation protocol.

Predict, compare and calculate

The following record is an original synthetic teaching dataset. Its assigned conditions are not a claim that an actual organism was measured. Write your prediction before revealing the changed condition.

Supplied coding region	Value (number)
Sense codons before stop	4
Stop codons at termination	1
Predicted amino acids	4

Frame begins at the first AUG in 5′-AUG GCU UUU GGA UAA-3′; codon meanings are supplied in the text.

Your prediction before comparison

This scratch prediction is not saved automatically. Copy it to the lesson notebook to retain it.

Evidence conditionReference comparisonChanged condition / follow-up

Trace a reading frame from initiation to termination

Supplied synthetic evidence: Frame begins at the first AUG in 5′-AUG GCU UUU GGA UAA-3′; codon meanings are supplied in the text.

Supplied coding region: reference condition

Quantity	Value	Unit
Sense codons before stop	4	number
Stop codons at termination	1	number
Predicted amino acids	4	number

Task: Explain why a one-nucleotide insertion early in a coding region can have a broader effect than a three-nucleotide insertion.

No initiation efficiency, protein abundance or functional activity is modeled.

Compare with the conditional interpretation

The predicted peptide is Met–Ala–Phe–Gly, followed by termination.

Using supplied codons AUG=Met, GCU=Ala, UUU=Phe, GGA=Gly and UAA=stop gives four amino acids, not five. The changed third codon ends elongation before Gly in this simple prediction.

Case index for this investigation

0. Use complementary evidence to identify inherited information
1. Trace antiparallel replication and repair limits
2. Predict transcripts and distinguish processing from translation
3. Trace a reading frame from initiation to termination
4. Distinguish transcriptional control from downstream effects
5. Explain differentiated cells with shared genetic information
6. Separate sequence predictions from functional outcomes
7. Interpret gel and expression evidence with controls

No numerical confidence, laboratory credit or independent mastery is inferred from opening a supplied case. Save your first prediction and comparison in the notebook.

Reset this unsaved comparison

Trace a short coding sequence

This original toy sequence is not a real gene, gene-design tool or wet-lab instruction. The supplied DNA is the coding strand, 5′→3′. This exercise deliberately starts its reading frame at the first base, uses the standard genetic code, and stops at the first in-frame stop. It does not infer initiation, splice RNA, process introns or model alternative genetic codes.

Coding DNA (3–60 uppercase bases) Reset toy sequence

Aligned template, 3′→5′

TACCGAAAACCTATT

Same template written 5′→3′

TTATCCAAAAGCCAT

RNA, 5′→3′

AUGGCUUUUGGAUAA

Peptide in one-letter amino-acid symbols

MAFG

Codons in the specified frame (one-letter amino-acid codes)

Triplet	Code	Interpretation
AUG	M	Added in this toy frame
GCU	A	Added in this toy frame
UUU	F	Added in this toy frame
GGA	G	Added in this toy frame
UAA	Stop	First stop: release, not an amino acid

0 trailing base(s) do not form a complete codon. A first in-frame stop is present.

Predict first: change GCT to GCC (both alanine, A), then change it to TAA (stop). Finally insert one C after ATG and compare downstream triplets. Preserve your first prediction in the lesson notebook before editing. This scratch input is not saved or graded.

Worked reasoning

Using supplied codons AUG=Met, GCU=Ala, UUU=Phe, GGA=Gly and UAA=stop gives four amino acids, not five. The changed third codon ends elongation before Gly in this simple prediction.

The predicted peptide is Met–Ala–Phe–Gly, followed by termination.

Apply to a new case

Explain why a one-nucleotide insertion early in a coding region can have a broader effect than a three-nucleotide insertion.

Compare your reasoning with the worked response

A one-nucleotide insertion shifts subsequent triplet grouping until another compensating change or termination. A three-nucleotide insertion preserves the downstream frame but can still affect folding/function. Position and sequence matter.

This public response supplies feedback, not a score for independent reasoning. Record which part of your prediction changed and why.

Evidence and investigation boundary

No initiation efficiency, protein abundance or functional activity is modeled. RNA surveillance and protein degradation can also affect observed abundance.

For a supervised investigation, predeclare the question, biological unit of replication, treatment/comparison assignment, quantities and units, exclusion rules, graph and uncertainty method. Keep the raw records and the first prediction separate from later revisions. A simulated case does not supply laboratory hours or establish AP authorization. No physical manipulation is required by this lesson.

Source and continuation

Detailed mechanism reference, checked 30 October 2026.

Framework topics: 6.4. Current AP Biology framework; supporting scientific reference. Sources checked 30 October 2026; all teaching wording, questions and numbers here are original. Return to AP Biology to compare this mechanism with another scale of organization.