DNA, RNA & Protein Synthesis: From Genes to Proteins

Inside nearly every cell is a complete set of instructions for building and running an organism, written in DNA. But DNA itself doesn't do the work — proteins do. So the cell needs a way to turn the stored instructions into functional proteins. That process, summarized as the "central dogma," moves information from DNA to RNA to protein in two clear steps. Once you see those steps, the molecular machinery stops being intimidating.

This guide covers DNA and RNA structure, base pairing, and the transcription/translation pathway, with worked and practice questions matched to the level seen in ACT Science and biology at Northside Tutoring.

Why This Matters

Molecular biology underlies genetics, biotechnology, and many ACT Science passages. Knowing the central dogma helps you follow experiments about genes and proteins quickly. It's central to high-school and AP Biology. (The SAT has no science section.)

DNA Structure & Base Pairing

DNA is a double helix — two strands twisted together like a spiral ladder. The rungs are pairs of bases, and the pairing is strict: adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). So if one strand reads A-G-C-T, the matching strand reads T-C-G-A.

DNA vs. RNA

	DNA	RNA
Strands	double	single
Sugar	deoxyribose	ribose
Bases	A, T, G, C	A, U, G, C

The key swap: RNA uses uracil (U) wherever DNA would use thymine (T). So in RNA, adenine pairs with uracil.

The Central Dogma

The flow of genetic information goes one main direction:

Two steps: first copy the gene from DNA into messenger RNA (mRNA), then use that mRNA to assemble a protein.

Transcription

Transcription happens in the nucleus. An enzyme reads a DNA gene and builds a complementary strand of mRNA, following the base-pairing rules (with U replacing T). The mRNA is a portable copy of the gene that can leave the nucleus and travel to a ribosome.

Translation

Translation happens at the ribosome. The mRNA is read in three-base groups called codons; each codon specifies one amino acid. Transfer RNA (tRNA) brings the matching amino acids, which link together into a protein chain.

Where You'll See This — Test by Test

Molecular biology supports ACT Science genetics and biology passages; the SAT has no science section and the SSAT doesn't test it. It's core high-school and AP Biology.

Watch the Lesson

Sometimes a diagram needs a voice. In the short video below, one of our Northside tutors walks through the core idea and works through test-style problems in real time.

Worked Example Problems

These problems are calibrated to the difficulty you'll actually see on test day. Try each one before opening the solution.

Common Mistakes to Avoid

Practice Problems — You Try

Three problems below. Work each before checking the solution.

The Northside Method — How We Teach This 1-on-1

Reading a blog is a great starting point. But there's a meaningful gap between understanding a concept and reflexively applying it under timed conditions. That gap is exactly what our tutors close.

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