Translation

Chapter 10: DNA, RNA and Protein Synthesis

The Genetic Code The Genetic Code is the term for the rules

that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid.

In the Genetic Code, three adjacent nucleotides (“letters”) in mRNA specify an amino acid (“word”) in a polypeptide.

Codon A sequence of three nucleotides that encode

for an amino acid or signifies a start or stop signal.

Examples:

UUU = phenylalanine

AUG = start

The Genetic Code

Examine the sequence of three bases: UAC

Codons There are 64 possible codons corresponding

to 20 amino acids Each amino acid has more than one possible

codon. There are Start and Stop signals built into the

code. The Start codon corresponds to the amino

acid methionine.

Flow of Information The sequence of nitrogenous bases in DNA

becomes complementary to the sequence of bases in the mRNA molecule during TRANSCRIPTION.

tRNA molecules bring amino acids to the ribosome and match up their complementary bases to the mRNA molecule during TRANSLATION.

Translation

The making of a protein by stringing together amino acids to make a polypeptide chain.

Information flows from DNA to mRNA and then tRNA brings the corresponding amino acid.

Peptide bonds are formed between adjacent amino acids and a polypeptide chain is formed.

Translation

- What is it?

The making of a protein- Where does it take place?

Prokaryotes = cytoplasm

Eukaryotes = cytoplasm- What is needed?

mRNA, 2 ribosomal subunits, tRNA and

amino acids

Steps of Translation

Initiation:The ribosomal subunits, the mRNA,

and the tRNA carrying methionine bind together.

Initiation

Elongation

The tRNA carrying the amino acid sequence specified by the next codon binds to the codon.

A peptide bond forms between adjacent amino acids

The ribosome moves the tRNA and mRNA.

Elongation

(Continued Elongation)

The first tRNA detaches and leaves its amino acid behind.

Elongation continues. The polypeptide chain continues to grow.

Elongation (continued)

Termination

The process ends when a stop codon is reached.

A stop codon is one for which there is no tRNA molecule that has a complementary anticodon.

Disassembly

The ribosome complex falls apart. The newly made polypeptide is released.

Summary- Information flows from DNARNAProteins- RNA serves as the intermediary between DNA and

proteins.- There are three types of RNA. mRNA, rRNA and

tRNA.- The Genetic Code represents 64 possible codons

corresponding to 20 different amino acids, start signal and stop signals.

- The process of TRANSLATION takes place within the cytoplasm on a ribosome.

- The process of TRANSLATION involves: initiation, elongation and termination.