Chapter 13 Section 2

Chapter 13Section 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 oursuperhero, “There’s troublein paradise. They need mysecret plans for making protein. This is a job for ….da da ta da...DNA MAN!”

Quick as a flash, DNA MANraces toward the nuclearmembrane. But, alas, hefinds himself too large tosqueeze 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

DNA strand

“unzipping”

Step 2Free-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:

ATGCGAAAGTTCThen 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”.

EXAMPLEDNA Code: ATT - CCG - GATmRNA Code: UAA - GGC -

CUA

Step 3

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

Step 4At 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.