Making Proteins

From DNA to Protein

What is transcription?

• Transcription = The process of making RNA from DNA’s instructions

Process of transcription

1. Enzymes unzip the molecule of DNA by breaking what special bond??????

2. Free RNA nucleotides attach to one exposed strand of DNA

3. The sugar-phosphate backbone bonds. This time is uses which sugar? (think R instead of D)

Process of transcription

4. The mRNA breaks away as the DNA strands rejoin. The DNA re-bonds into its original state

Process of transcription

5. mRNA leaves the nucleus and enters the cytoplasm.

What is the genetic code?

• mRNA carries a genetic message• Uhhh…so what is a genetic message?– a sequence of nucleotides that instruct how to

build proteins

Genetic Code (cont)

• amino acids make up what macromolecule?– PROTEINS

• there are only 20 common amino acids in the world; they are the same 20 amino acids for all living organisms. The difference comes from the coding sequence.

Codons

• Codon - A sequence of 3 nitrogenous bases that match with a specific amino acid. – Ex: ATG

Codons

• The RNA strand AUGUAAAUU is actually the following three codons:– AUG UAA AUU

Codons

• The order of the nitrogenous bases in the mRNA determines the type of the amino acids in a protein.

Codons

• There are 64 possible codons but only 20 Possible Amino Acids

Start and Stop codons

• Start codon = AUG (Methionine or Met)

• Stop codons = UAA UAG UGA

Tidbits to Remember!

• More than one codon can code for the same amino acid BUT for any one codon, there can only by one amino acid!!!

• The genetic code is UNIVERSAL. (i.e. all organisms use this code for making proteins)

Translation

• Translation = The process of making proteins from amino acids using the instructions written on mRNA.

Translation location

• Translation happens in the cytoplasm

Translation steps

1. The strand of mRNA attaches to the ribosome

Translation steps

2. A tRNA molecule brings the first amino acid to the mRNA strand that is attached to the ribosome.

Translation steps

3. A tRNA anticodon pairs with the first mRNA codon temporarily.

What is the first mRNA codon? – AUG

Anticodon = Region of tRNA that is complimentary (or reverse) to the codon of the mRNA. This is where it attaches.

Translation steps

4. AUG signals the start of protein production.

Translation steps

5. The ribosome slides along the mRNA to the next codon.

Translation steps

6. A new t RNA carrying an amino acid pairs with the second mRNA codon.

Translation steps

7. the first and second amino bond together in a peptide bond.

Translation steps

8. This process continues joining amino acids until the ribosome reaches a stop codon on the mRNA strand.

Translation steps

9. The amino acid strand (now an amino acid chain) released from the ribosome.

Translation steps

10. Once released the Amino Acid Chain folds into a protein (tertiary structure!)

DNA replication vs. transcriptionDNA Replication 1. DNA to DNA2. DNA is permanently split and now has a parent and daughter strand3. Final product prepares cell for division but remains in the nucleus (b/c DNA never leaves!)

DNA Transcription 1. DNA to RNA2. DNA returns to original state3. Final product shoots out of the nucleus into the cytoplasm to make proteins at the Ribosome!