Protein Synthesis: THE BIG PICTURE

We continually say that DNA is our “genetic code” or “instruction manual” for

life. If that’s true, then how does DNA determine our hair color, body type, or eye

color?

Well, all of those things—hair, eyes, muscle—are made of proteins. So, the

instructions contained in DNA are used to make different kinds of proteins!

But, there is a problem…

• Where is the genetic code, or instructions for making proteins found?

• DNA (in the nucleus)

• Where are proteins made & assembled?• Ribosome (in the cytoplasm)

• Can DNA leave the nucleus?• NO! Its too valuable

• How do the instructions get from the nucleus to the ribosome?

• RNA

The Scoop On RNA:

• Examine the following pictures…how is RNA different from DNA?

One nucleotide of RNA

RNA vs. DNA

Name:

Structure:

Building Block:

Base Pairing Rules:

Ribonucleic Acid

Single-Stranded

Nucleotide sugar (ribose), phosphate, nitrogen base

Cytosine with Guanine, Adenine with Uracil

NO T’S IN RNA!!!

3 Types of RNA:

• mRNA Messenger: Carries DNA’s information to the ribosome.

• tRNA Transfer: Changes the language of the information, from RNA to amino acids.

• rRNA Ribosomal: Makes up ribosomes.

Each type of RNA is composed of nucleotide chains. They are just different

in structure.

Protein Synthesis: An Overview

1. Transcription• Process by which genetic

information is copied from DNA to mRNA, occurs in the nucleus

2. Translation• Process of assembling

proteins, occurs at the ribosome. Order of nucleotides in mRNA converted into an order of amino acids.

Transcription

• Purpose: To get instructions from DNA inside the nucleus out to the ribosomes in the cytoplasm.

• What Happens? – In the nucleus, a portion of

DNA (gene) unwinds and unzips, revealing it’s code.

– DNA is transcribed into mRNA according to base pairing rules.

– Ex: G becomes C, C becomes G A becomes U, T becomes A

Transcription

Practice, Practice, Practice!

• DNA: • AGGCTATAC• mRNA:• UCCGAUAUG• CODONS?• UCC, GAU, AUG

Codon = Each combination of 3

mRNA nucleotides

Practice: If this is the sequence of DNA, what mRNA strand would be transcribed?

G-A-T-T-C-C-G-A-G

C-U-A-A-G-G-C-U-C

Once the mRNA is made in the nucleus, where does it go?

• To RIBOSOMES in the cytoplasm to be TRANSLATED!

Translation• Purpose:

To translate mRNA into a protein. Like switching languages (nucleotides to amino acids)

• What Happens? – mRNA attaches to a ribosome. The

ribosome moves along the mRNA, “reading” codons.

– Each codon is paired with the opposite tRNA anticodon according to base pairing.

– Each tRNA anticodon carries an amino acid. The chain of amino acids attaches with peptide bonds and becomes a protein!

Codon

Anti -Codon

Amino

Acid

How does the right amino acid get there?

Practice Makes Perfect!• DNA:• CGTGCCCAAATT

• mRNA:• GCACGGGUUUAA• Codons? GCA, CGG, GUU, UAA

• tRNA:• CGUGCCCAAAUU• Anti-Codons? CGU, GCC, CAA, AUU

• Amino Acids:• Ala, Arg, Val, STOP