Chapter 13 Section 2 Protein Synthesis (“the making of protein”) Starring – DNA MAN

“LOOK! Up in the nucleus! It’s a double helix! It’s a spiral staircase! No….. It’s DNA MAN!!!”

(Part II of our continuing saga…..) When we last left our Superhero, he was in the nucleus, all twisted up with no place to go….

“Unzip, copy, rezip. Unzip, copy, rezip. Day in and day out. That’s all I seem to do around here.” sighs DNA MAN. “Is replication all there is to life?”

Just at that moment, a collective call arises from somewhere out in the distant cytoplasm… “We need protein! We want protein! Where’s our protein?”

“AHA!” exclaims our superhero, “There’s trouble in paradise. They need my secret plans for making protein. This is a job for ….da da ta da... DNA MAN!”

Quick as a flash, DNA MAN races toward the nuclear membrane. But, alas, he finds himself too large to squeeze through the small nuclear pores. What’s a superhero to do?

“Of course!” shouts DNA MAN, “I know what I’ll do. I’ve got the perfect solution!”

Can DNA MAN solve this problem? Will he be able to smuggle the secret plans for making proteins from his impenetrable fortress to the needed destination? Can he? Will he? What will DNA MAN do????????

STEP 1 (X-rated) DNA unzips its genes and exposes its bases…. DNA strand “unzipping”

Step 2 Free-floating nucleotides, in the nucleus, join to one side (the coding side) of DNA’s exposed bases,

This creates a messenger and transfers the genetic code (mRNA = messenger RNA).

Characteristics of mRNA Is composed of ribose sugar Is only 1/2 of a ladder in size Has nitrogen bases: A, G, C, and U (uracil)

Example : If the DNA code was: ATGCGAAAGTTC Then the transcribed RNA code would be: UACGCUUUCAAG

The process of DNA making RNA is called: TRANSCRIPTION

The “code” that DNA gives to mRNA is arranged in groups of 3 nitrogen bases called a “codon”. EXAMPLE DNA Code: ATT - CCG - GAT mRNA Code: UAA - GGC - CUA

Step 3 mRNA leaves the nucleus, carrying “the code”, and travels to the ribosomes.

Step 4 At the ribosomes, mRNA makes a complimentary copy of itself (tRNA = transfer RNA). mRNA passes the “code” onto tRNA.

The tRNA “code” is a group of three nitrogen bases called an anticodon. EXAMPLE mRNA = UAC - CGG - AUA - CGA tRNA = AUG - GCC - UAU - GCU

Step 5 tRNA leaves the ribosomes and travels out into the cytoplasm. There, tRNA collects amino acids that match its anticodons. tRNA takes the amino acids back to the ribosomes.

The ribosomes read the code on mRNA and arrange the arriving amino acids into their proper sequence.

VOILA! PROTEIN!

The process of RNA making protein is called: TRANSLATION

Question? How many codons (groups of three nucleotides) are possible from the “4 – letter” nucleotide alphabet? (U, A, C, G) 64

Question? How many amino acids are there that are coded for by these 64 codons/anticodons? 20

Question? How do 64 codons/anticodons code for 20 amino acids? Two or more codons can code for one amino acid.