Molecular BiologyFoundational~12 min

Central Dogma Engine

DNA → mRNA → protein, and what happens when you break it

Transcribe and translate a real gene, shift the reading frame, then mutate any base and watch the tool classify the damage.

The takeaway

The same physical event — one base changing — can be harmless or catastrophic. The genetic code's structure, not the mutation itself, decides which.

TranscriptionTranslationReading framesSilent / missense / nonsenseFrameshiftCodon degeneracy
Read the theory: The Central Dogma, Precisely
DNA coding sequence (5' → 3')
69 bpGC 55%length is a multiple of 3β-globin, codons 1–22. Home of the sickle-cell mutation.
Step 1 — Transcription
Coding strand (5'→3')
Same sequence as the mRNA, with T instead of U
ATGGTGCACCTGACTCCTGAGGAGAAGTCTGCCGTTACTGCCCTGTGGGGCAAGGTGAACGTGGATTAA
Template strand (3'→5')
The strand RNA polymerase actually reads
TACCACGTGGACTGAGGACTCCTCTTCAGACGGCAATGACGGGACACCCCGTTCCACTTGCACCTAATT
mRNA (5'→3')
Complement of the template = coding strand with T→U
AUGGUGCACCUGACUCCUGAGGAGAAGUCUGCCGUUACUGCCCUGUGGGGCAAGGUGAACGUGGAUUAA

RNA polymerase reads the template strand 3'→5' and builds the mRNA 5'→3'. Because the mRNA is the complement of the template, it ends up identical to the coding strand — just with uracil in place of thymine.

Step 2 — Reading frame

The ribosome reads three bases at a time, but where it starts decides everything. Shift the start by one base and every downstream codon is re-sliced into a different triplet — a completely different protein. Translation begins at the first AUG.

No mutation

Unmutated sequence

Click any base below to substitute it, or use Insert / Delete to shift the reading frame. The verdict will update instantly.

Mutation simulator

Click a base to select it, then substitute, insert, or delete. Codon boundaries follow frame +1. The start codon is green, the stop codon red, and mutated bases are ringed in amber.

1
31
61
Step 3 — Translation (frame +1)

Ribosome starts at codon 1 (AUG) and produces a 22 aa peptide, terminating at the stop codon.

HydrophobicPolarAcidic (−)Basic (+)Special (Gly / Pro)Stop
1
AUG
Met
M
2
GUG
Val
V
3
CAC
His
H
4
CUG
Leu
L
5
ACU
Thr
T
6
CCU
Pro
P
7
GAG
Glu
E
8
GAG
Glu
E
9
AAG
Lys
K
10
UCU
Ser
S
11
GCC
Ala
A
12
GUU
Val
V
13
ACU
Thr
T
14
GCC
Ala
A
15
CUG
Leu
L
16
UGG
Trp
W
17
GGC
Gly
G
18
AAG
Lys
K
19
GUG
Val
V
20
AAC
Asn
N
21
GUG
Val
V
22
GAU
Asp
D
23
UAA
Stop
stop
Polypeptide (N → C)
MVHLTPEEKSAVTALWGKVNVD
Why this matters in biotech

Reading the variant, not the gene

Clinical genomics is mostly this exercise at scale: a patient variant is classified as silent, missense, nonsense or frameshift, and that class is the first evidence for whether it is benign or pathogenic. One base — HBB codon 7 — is the difference between healthy haemoglobin and sickle-cell disease.

Frameshifts are the knockout tool

CRISPR cuts DNA and the cell repairs it sloppily by NHEJ, inserting or deleting a base or two. If the indel is not a multiple of three, the frame shifts, a premature stop appears, and the gene is dead. That is how most gene knockouts and most functional-genomics screens actually work.

Codon choice is engineering

Because the code is degenerate, the same protein can be encoded many ways. Codon optimisation — choosing synonymous codons the host cell translates fastest — is standard practice for protein manufacture and for mRNA vaccines, where it changes yield by orders of magnitude without touching the protein.
Next lab →

CRISPR Guide RNA Designer