Protein Synthesis · Remember Proteins?? •Proteinsare the most versatile macromolecules in living systems and serve crucial functions in essentially all biological processes such

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 proteintranscription translation

Remember Proteins??• Proteins are the most versatile

macromolecules in living systems and serve crucial functions in essentially all biological processes such as: - Function as catalysts- Transport and store other molecules such as oxygen- Provide mechanical support and immune protection- Generate movement- Transmit nerve impulses- Control growth and differentiation.

• #proteinsmatter

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

TRANSCRIPTIONPurpose: 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

TRANSCRIPTIONProcess:1.RNA Polymerase binds to the DNA promoter where transcription is to begin and unzips the gene that needs to be copied. (looks for “TATA box” as a signal)

2.RNA Polymerase uses 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)

3.Release the completed mRNA molecule 4.DNA zips back up and the mRNA leave the nucleus and enters the cytoplasm

Transcription: DNA is copied into a complementary strand of mRNA

RNA is made in the 5’-3’ directionThe DNA template read in the 3’-5’ direction

DNADNA

mRNADNAmRNA

3’

3’

3’

3’3’

5’

5’ 5’

5’ 5’

Transcription – Try it!• DNA sequence (template):

3’ TACGCTAGTACGATT 5’

• mRNA sequence: 5’ AUGCGAUCAUGCUAA 3’

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

TRANSLATIONPurpose: Read/follow the instructions carried on the mRNA to make a protein

Location: Cytoplasm / Ribosome

Starts with: mRNA

Ends with: Protein

TRANSLATIONProcess:1.mRNA attaches to the small subunit of the ribosome2.Ribosome reads the mRNA codons (3 mRNA nucleotides – like a triplet) ALWAYS in the 5’ to 3’ direction; starting at codon AUG.3.tRNA (transfer RNA) molecules act like taxis to pick up and drop off the amino acids that match with the current codon being read off the mRNA.4. tRNA’s continue to drop off amino acids, and the ribosome binds the amino acids together with peptide bonds5.When the “stop codon” is reached, the ribosome releases the completed protein.

Translation: interpreting the RNA message into a protein.

The Genetic Code

• DNA sequence (template): 3’ TACGCTAGTACGATT 5’

• mRNA sequence: 5’ AUGCGAUCAUGCUAA 3’

• Codons: AUG CGA UCA UGC UAA

• Amino Acids: Met – Arg – Ser – Cys – stop

Transcription and Translation: Try it!