Transcription

Process of copying a gene into RNA form. Similar to DNA replication, except it’s only 1 strand

• DNA strand is template for RNA

• Transcription occurs in the nucleus

• Base pairing rules of RNA

  • G-C

  • A-U

Steps

1. RNA polymerase binds to promoter in DNA. Unwinds small portion of DNA = “transcription bubble”

2. RNA polymerase “reads” DNA strand. Assembles RNA strand with complementary nucleotides. Once strand is read, DNA winds back up.

3. RNA polymerase reaches terminator in transcription bubble. Releases from DNA strand. New RNA strand is released.

Product = different types of RNA

• rRNA - Part of ribosomes

• tRNA - Brings amino acids to ribsomomes

• mRNA - Tells ribosomes what protein to make

Post-transcriptional modifications: finishing touches to new RNA

• Introns

  • Segments of genes that don’t code for proteins

    • These aren’t needed to make proteins so they’re removed from new RNA

• Exons

  • Encode for proteins ; kept

• Alternative splicing

  • Using one copy of RNA (blueprint) to make several different types of proteins

  • Used for efficiency

Translation

Using mRNA to build proteins from amino acids

• Occurs in the cytoplasm

• Amino acids, ribosomes, and RNAs used during translation

• Transcription made 3 types of RNA (rRNA, tRNA, mRNA)

• RNAs exit nucleus into cytoplasm

Steps

1. Initiation

   1. mRNA binds with ribosome. Tells ribosome what protein to make. Initiator tRNA brings the first amino acid to start the process - called start codon

2. Elongation

   1. tRNA brings the amino acids to ribosomes to build the protein. Amino acids are assembled in a specific order for a specific protein.

3. Termination

   1. Last amino acid added to protein chain - called stop codon. Newly made protein is released by the ribosome.