Protein synthesis

- A two part process in which DNA is decoded into corresponding proteins

- The first process is known as transcription

- The second process is translation

- Occurs in the  nucleus and cytoplasm

Transcription

-occurs in the nucleus

- the process in which mRNA is created by transcribing the DNA’s code

-the enzyme RNA polymerase temporarily unzips DNA and adds complementary RNA nucleotides to the growing mRNA strand.

DNA strand:       TAC    CCA   GGA      GCT      TAT      ACT

mRNA strand:  

*mRNA is always complementary to DNA!

mRNA is single stranded so it can simply exit the nucleus via nuclear pores (DNA is too large to exit).

Translation

-a process in which the mRNA that was previously manufactured is translated into an amino acid sequence (proteins)

-occurs in the cytoplasm, on the ribosomes

-involves all types of RNA

mRNA strand:   AUG       GGU         CCU       CGA       AUA        UGA

tRNA strand:    

*tRNA transfers amino acids. The amino acids are attached to the tRNA via a specialized enzyme called tRNA synthetase

-Met is the amino acid methionine

-The ribosome location at which tRNA binds to is known as the P-site (peptidyl-tRNA site)

-The A-site is awaiting the next tRNA + amino acid complex

-As the polypeptide chain grows, the ribsome moves towards the 5’ end of the mRNA, and the tRNA moves to the Exit site, or E-site, where it then detaches itself, leaving the amino acid at the ribosome.

Reading codons

-there are 61 different codons which represent the 20 amino acids as well as start and stop signals (start codons= AUG; stop codons= UAA, UAG, UGA)

-All codons between the start and stop codons are known as “exons”, all codons outside the start and stop codons are called “introns”.