RNA & Transcription

Objective

• Explain the function and structure of RNA.• Determine how transcription produces a RNA

copy of DNA.• Analyze the purpose of transcription.

What is RNA?

• RNA is a nucleic acid (like DNA)• RNA differs in three main ways:– Single stranded– Ribose sugar– Thymine (T) is replaced with Uracil (U)• Still pairs with Adenine (A)

The “Big Picture”

The major goal in transcription is to turn DNA into RNA.DNA is transcribed into RNARNA is translated into proteins….this process is known as the CENTRAL DOGMA

Transcription

• There are three types of RNA that help build proteins– mRNA (messenger) brings the message– rRNA (ribosomal) uses instructions from mRNA to

assemble the amino acid– tRNA (transfer) delivers the amino acids to the

ribosome to be assembled into a protein.

– RNA is found in the nucleus and the cytoplasm!

What happens in Transcription?

• Process begins when DNA is “unzipped” by enzymes.

• Free RNA nucleotides form base pairs with their complementary nucleotides on DNA strand.

• mRNA strand is complete when the RNA nucleotides bond together.

• mRNA strand then breaks away and enters to cytoplasm

• Not all nucleotides in the DNA carry instruction.

• Can containing non-coding nucleotide sequences.

• These sequences must be removed from mRNA before it can function to make protein.

• The product (full nucleotide sequence acts as a genetic message (almost like a language)

• Alphabet is the amino acid sequence made by the nucleotide sequence.

Codons

• Scientists began to navigate genetic codes when they discovered that a group of 3 nitrogenous bases coded for 1 amino acid.– ie. Codon CCG results in the amino acid Proline– 64 combinations are possible– Some codons do not code for amino acids; they

provide instruction for protein chain to end.• ie. UAA is a stop codon ; AUG is a start codon

– More than one codon can code for the same amino acid

Knowledge Check1. What is RNA?2. Compare it to DNA3. What’s the big picture for

RNA?4. What’s the central dogma?5. What amino acid would the

codon sequence UCU represent?

6. What are the 3 stop codons?7. What is the start codons?8. What does the start codon

also code for?