Ever wondered how your DNA instructions actually get turned into...
Biology216 views·Updated 7 Sept 2026·2 pagesAQA A-Level Biology: Comprehensive Transcription Notes
Maya A@maya.ah
1
of 2
DNA to RNA: The Transcription Process
Your DNA is locked away in the nucleus, but ribosomes (the protein-making factories) are out in the cytoplasm. This creates a problem - how do you get the genetic instructions from one place to the other?
The solution is brilliant: make an RNA copy that can travel. The DNA strand that gets copied is called the template strand, and it runs in the 3' to 5' direction. The new RNA strand gets built in the 5' to 3' direction - this directional rule is absolutely crucial to remember.
Before transcription kicks off, RNA building blocks (nucleotides) get energised through phosphorylation. These powered-up versions are called ATP, UTP, CTP, and GTP. Think of them as batteries ready to power the copying process.
The process starts when RNA polymerase (the copying enzyme) binds to the promoter region - basically a "start here" sign on the DNA. The DNA then unwinds and unzips, breaking the hydrogen bonds between base pairs but keeping the backbone intact.
Key Point: The template strand has 3' to 5' polarity, whilst the new RNA strand grows 5' to 3' - they're antiparallel!
2
of 2
Building RNA and Making It Functional
Once the DNA is open, RNA nucleotides line up opposite the exposed bases following complementary base pairing rules. Here's the twist: RNA uses uracil (U) instead of thymine, so adenine pairs with uracil, not thymine.
RNA polymerase moves along the template strand, using energy from breaking down those phosphorylated nucleotides to forge phosphodiester bonds between adjacent RNA nucleotides. When it hits the terminator region, transcription stops and the completed RNA chain detaches.
But wait - the story doesn't end there! In eukaryotes, the initial RNA product is called pre-mRNA, and it's not ready for use yet. It contains non-coding sections called introns mixed in with the useful coding bits called exons.
A molecular machine called a spliceosome performs the crucial job of splicing - cutting out the introns and joining the exons together. This creates functional mRNA that can actually be used to make proteins.
Remember: Prokaryotes skip the splicing step entirely - their transcription produces mRNA directly!
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Biology216 views·Updated 7 Sept 2026·2 pagesAQA A-Level Biology: Comprehensive Transcription Notes
Maya A@maya.ah
Ever wondered how your DNA instructions actually get turned into the proteins that run your body? Transcription is the crucial first step where DNA gets copied into RNA - think of it as making a portable photocopy of a recipe...
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of 2
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DNA to RNA: The Transcription Process
Your DNA is locked away in the nucleus, but ribosomes (the protein-making factories) are out in the cytoplasm. This creates a problem - how do you get the genetic instructions from one place to the other?
The solution is brilliant: make an RNA copy that can travel. The DNA strand that gets copied is called the template strand, and it runs in the 3' to 5' direction. The new RNA strand gets built in the 5' to 3' direction - this directional rule is absolutely crucial to remember.
Before transcription kicks off, RNA building blocks (nucleotides) get energised through phosphorylation. These powered-up versions are called ATP, UTP, CTP, and GTP. Think of them as batteries ready to power the copying process.
The process starts when RNA polymerase (the copying enzyme) binds to the promoter region - basically a "start here" sign on the DNA. The DNA then unwinds and unzips, breaking the hydrogen bonds between base pairs but keeping the backbone intact.
Key Point: The template strand has 3' to 5' polarity, whilst the new RNA strand grows 5' to 3' - they're antiparallel!
2
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Building RNA and Making It Functional
Once the DNA is open, RNA nucleotides line up opposite the exposed bases following complementary base pairing rules. Here's the twist: RNA uses uracil (U) instead of thymine, so adenine pairs with uracil, not thymine.
RNA polymerase moves along the template strand, using energy from breaking down those phosphorylated nucleotides to forge phosphodiester bonds between adjacent RNA nucleotides. When it hits the terminator region, transcription stops and the completed RNA chain detaches.
But wait - the story doesn't end there! In eukaryotes, the initial RNA product is called pre-mRNA, and it's not ready for use yet. It contains non-coding sections called introns mixed in with the useful coding bits called exons.
A molecular machine called a spliceosome performs the crucial job of splicing - cutting out the introns and joining the exons together. This creates functional mRNA that can actually be used to make proteins.
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We thought you’d never ask...
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
You can download the app from Google Play Store and Apple App Store.
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