Click image to open full size
Molecular Biology Central Dogma in Depth Cheat Sheet
A printable reference covering DNA replication, transcription, RNA processing, regulation, translation, and protein fate for college.
Related Tools
Related Labs
Related Worksheets
The central dogma explains how genetic information flows from DNA to RNA to protein, while also showing where cells regulate that flow. This cheat sheet helps college biology students connect replication, transcription, RNA processing, translation, and protein targeting as one integrated system. It is useful for studying molecular genetics, gene expression, biotechnology, and disease mechanisms. The focus is on mechanisms, enzymes, directionality, and checkpoints that determine when and how genes are expressed. DNA replication copies the genome using template strands, primers, DNA polymerases, and proofreading to preserve genetic information. Transcription uses RNA polymerase to synthesize RNA from a DNA template, followed by RNA processing in eukaryotes through capping, splicing, and polyadenylation. Translation converts codons in mRNA into amino acid sequence using ribosomes, tRNAs, and aminoacyl-tRNA synthetases. Protein fate depends on folding, modification, localization signals, and degradation pathways that control final protein function.
Key Facts
- The central dogma is commonly summarized as DNA -> RNA -> protein, but regulation occurs at replication, chromatin access, transcription, RNA processing, translation, and protein stability.
- DNA replication is semiconservative, meaning each daughter DNA molecule contains one parental strand and one newly synthesized strand.
- DNA polymerases synthesize DNA only in the 5' to 3' direction by adding nucleotides to a free 3'-OH group.
- The leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized discontinuously as Okazaki fragments.
- RNA polymerase synthesizes RNA 5' to 3' using the DNA template strand, which is read 3' to 5'.
- In eukaryotes, pre-mRNA is processed by adding a 5' cap, removing introns by splicing, and adding a 3' poly(A) tail.
- During translation, the mRNA codon is read 5' to 3', and the growing polypeptide is synthesized from the N-terminus to the C-terminus.
- The genetic code is read in triplets, where AUG usually serves as the start codon and UAA, UAG, and UGA are stop codons.
Vocabulary
- Semiconservative replication
- A DNA replication mechanism in which each new double helix contains one original strand and one newly synthesized strand.
- Template strand
- The DNA strand read by a polymerase to build a complementary DNA or RNA strand.
- Promoter
- A DNA sequence where RNA polymerase and transcription factors assemble to begin transcription.
- Spliceosome
- A ribonucleoprotein complex that removes introns from pre-mRNA and joins exons together.
- Codon
- A three-nucleotide sequence in mRNA that specifies an amino acid or a translation stop signal.
- Signal peptide
- A short amino acid sequence that directs a newly made protein to a specific cellular location, such as the endoplasmic reticulum.
Common Mistakes to Avoid
- Confusing the coding strand with the template strand is wrong because RNA is complementary to the template strand and nearly identical to the coding strand except U replaces T.
- Writing nucleic acid synthesis in the 3' to 5' direction is wrong because DNA polymerase and RNA polymerase add new nucleotides only to the 3'-OH end.
- Forgetting RNA processing in eukaryotes is wrong because mature mRNA usually requires a 5' cap, splicing, and a poly(A) tail before efficient translation.
- Assuming every mutation changes a protein is wrong because silent mutations, noncoding changes, and some regulatory changes may not alter the amino acid sequence.
- Treating translation as a direct DNA-to-protein process is wrong because ribosomes read mRNA codons, not DNA, and tRNAs deliver the matching amino acids.
Practice Questions
- 1 A DNA template strand reads 3'-TAC GGA CTT ACT-5'. What is the mRNA sequence synthesized from it, written 5' to 3'?
- 2 An mRNA contains 450 nucleotides from start codon through the last sense codon, not including the stop codon. How many amino acids are in the encoded polypeptide?
- 3 If a eukaryotic pre-mRNA has 7 exons and 6 introns, how many introns must be removed to make the mature mRNA?
- 4 A mutation weakens a promoter but does not change the coding sequence of a gene. Explain how this can still reduce the amount of functional protein in the cell.