Protein Synthesis

Protein Synthesis

• The process of reading the instructions in the DNA to make a protein.

• Central Dogma of Genetics

• DNA = instructions and is in the nucleus and can’t leave
• But proteins are made in ribosomes
• So protein synthesis takes 2 steps:

• DNA

• RNA

• protein

• transcription

• translation

Three Essential Types of RNA

• mRNA (messenger): copies instructions in DNA and carries these to the ribosomes in the cytoplasm
• tRNA (transfer): carries amino acids to the ribosome and mRNA
• rRNA (ribosomal): composes the ribosome

TRANSCRIPTION

• Purpose: Carry the code/instructions out of the nucleus
• (Remember: DNA never leaves the nucleus, and proteins are made in the cytoplasm by ribosomes.)
• Location: Nucleus
• Starts with: DNA
• Ends with: mRNA

TRANSCRIPTION

• Process:
• Unzip the gene that needs to be copied
• Use complementary base-pairing rules to match RNA nucleotides with the exposed DNA nucleotides (Remember: RNA has uracil instead of thymine, so A binds with U)
• Release the completed mRNA molecule (mRNA = messenger RNA)
• DNA zips back up and the mRNA leave the nucleus and enters the cytoplasm

Transcription: DNA is copied into a complementary strand of mRNA

• DNA

• DNA

• mRNA

• DNA

• mRNA

Transcription – Try it!

• DNA sequence (template):
• TACGCTAGTACGATT
• mRNA sequence:
• AUGCGAUCAUGCUAA

Translation Vocabulary

• Codon: a set of 3 nucleotides on the mRNA

• Anticodon: “complementary” 3 nucleotides on tRNA

• Genetic Code: code of instructions for how to make proteins

• mRNA
• (messenger)

• tRNA
• (transfer)

• Amino acid –monomer (building block) for making proteins, held together by peptide bonds

TRANSLATION

• Purpose: Read/follow the instructions carried on the mRNA to make a protein
• Location: Cytoplasm / Ribosome
• Starts with: mRNA
• Ends with: Protein

TRANSLATION

• Process:
• mRNA attaches to a ribosome.
• Ribosome reads the mRNA codons (3 RNA nucleotides – like a triplet.)
• tRNA (transfer RNA) molecules act like taxis to pick up and drop off the amino acids that match with the current codon.
• tRNA’s continue to drop off amino acids, and the ribosome binds the amino acids together with peptide bonds.
• When the “stop codon” is reached, the ribosome releases the completed protein.

• Translation: interpreting the RNA message into a protein.

The Genetic Code

Transcription and Translation: Try it!

• DNA sequence (template):
• TACGCTAGTACGATT
• mRNA sequence:
• AUGCGAUCAUGCUAA
• Codons:
• AUG CGA UCA UGC UAA
• Amino Acids:
• Met – Arg – Ser – Cys – stop