TranslationTranslationProteins are made by joining amino Proteins are made by joining amino

acids into long chains called acids into long chains called polypeptides (proteins).polypeptides (proteins).

Each polypeptide contains a Each polypeptide contains a combination of any or all of the 20 combination of any or all of the 20 different amino acids.different amino acids.

TranslationTranslationThe properties of proteins are The properties of proteins are

determined by the order in which determined by the order in which different amino acids are joined different amino acids are joined together to produce polypeptides.together to produce polypeptides.

The “language” of mRNA instructions The “language” of mRNA instructions is called the geneticis called the genetic code.code.

TranslationTranslation

RNA contains four different bases:RNA contains four different bases:Adenine = A Adenine = A Uracil = UUracil = UCytosine = CCytosine = CGuanine = GGuanine = G

TranslationTranslation These four letters carry These four letters carry

instructions for the 20 different instructions for the 20 different amino acids.amino acids.

This genetic code is read three This genetic code is read three letters at a time; so each “word” letters at a time; so each “word” of the coded message is three of the coded message is three bases long.bases long.

Each three-letter “word” in Each three-letter “word” in mRNA is known as a mRNA is known as a codon.codon.

A A codoncodon consist of three consist of three consecutive nucleotides that consecutive nucleotides that specify a single amino acid that specify a single amino acid that is to be added to the is to be added to the polypeptide.polypeptide.

TranslationTranslation

Example sequenceExample sequence::

mRNA: mRNA: UCGCACGGUUCGCACGGU

mRNA codemRNA code:: UCG-CAC-GGUUCG-CAC-GGU

Amino Acids:Amino Acids: Serine – Histidine - GlycineSerine – Histidine - Glycine

TranslationTranslation

Because there are four different bases, Because there are four different bases, there are 64 possible three-based there are 64 possible three-based codons:codons:

4 x 4 x 4 = 644 x 4 x 4 = 64

TranslationTranslation Some amino acids can Some amino acids can

be specified by more be specified by more than one codon.than one codon. Example: 6 different Example: 6 different

codons specify for the codons specify for the amino acid leucine.amino acid leucine.

There is also one codon, There is also one codon, AUG, which codes for AUG, which codes for the amino acid the amino acid MethionineMethionine. .

This is also the codon This is also the codon that serves as the “that serves as the “start start codoncodon” for protein ” for protein synthesissynthesis

TranslationTranslation

There are also three There are also three stop codonsstop codons that do that do not code for any not code for any amino acid.amino acid.

Stop codons act like Stop codons act like a period at the end a period at the end of a sentenceof a sentence

TranslationTranslation The sequence of nucleotide The sequence of nucleotide

bases in an mRNA molecule bases in an mRNA molecule serves as the instructions for the serves as the instructions for the order in which amino acids order in which amino acids should be joined together to should be joined together to produce a polypeptide.produce a polypeptide.

The structures that assemble the The structures that assemble the polypeptides from these polypeptides from these instructions are called instructions are called RibosomesRibosomes..

This process of decoding the This process of decoding the mRNA message into a mRNA message into a polypeptide chain (protein) is polypeptide chain (protein) is called called translationtranslation..

Translation takes place on Translation takes place on Ribosomes.Ribosomes.

Step-by-Step TranslationStep-by-Step Translation

Step 1:Step 1: Before translation Before translation

can occur, can occur, messenger RNA messenger RNA (mRNA) must first (mRNA) must first be transcribed be transcribed from DNA in the from DNA in the nucleus and nucleus and released into the released into the cytoplasm.cytoplasm.

Step-by-Step TranslationStep-by-Step Translation Step 2:Step 2: Translation begins when Translation begins when

the mRNA molecule in the the mRNA molecule in the cytoplasm attaches to a cytoplasm attaches to a ribosome (ribosome (InitiationInitiation). ).

As each codon of the As each codon of the mRNA molecule moves mRNA molecule moves through the ribosome, the through the ribosome, the proper amino acid is proper amino acid is brought into the ribosome brought into the ribosome and attached to the growing and attached to the growing polypeptide chain.polypeptide chain.

Step-by-Step TranslationStep-by-Step Translation

Step 2:Step 2:The ribosome does The ribosome does

not know which not know which amino acid to match amino acid to match to each codon. That to each codon. That is the job of the is the job of the transfer RNA transfer RNA (tRNA).(tRNA).

Step-by-Step TranslationStep-by-Step Translation

Step 2:Step 2:Each tRNA has an Each tRNA has an

amino acid amino acid attached to one end attached to one end of the molecule and of the molecule and a region of three a region of three unpaired bases on unpaired bases on the otherthe other

Step-by-Step TranslationStep-by-Step Translation

Step 2:Step 2:The three bases on The three bases on

the tRNA molecule, the tRNA molecule, called the called the anticodonanticodon, , are complimentary to are complimentary to one of the mRNA one of the mRNA codons.codons.

Step-by-Step TranslationStep-by-Step Translation Step 3:Step 3: Like an assembly line worker Like an assembly line worker

who attaches one part to who attaches one part to another, the ribosome forms a another, the ribosome forms a peptide bond between the peptide bond between the first and second amino acids first and second amino acids ((ElongationElongation).).

At the same time, the ribosome At the same time, the ribosome breaks the bond that held the breaks the bond that held the first tRNA molecule to its amino first tRNA molecule to its amino acid and releases the tRNA acid and releases the tRNA molecule.molecule.

The ribosome then moves to the The ribosome then moves to the third codon, where a tRNA third codon, where a tRNA molecule brings it the amino molecule brings it the amino acid specified by the third acid specified by the third codon.codon.

Step-by-Step TranslationStep-by-Step Translation

Step 4:Step 4: The polypeptide chain The polypeptide chain

continues to grow until the continues to grow until the ribosome reaches a stop ribosome reaches a stop codon on the mRNA codon on the mRNA molecule.molecule.

When the ribosome reaches When the ribosome reaches a stop codon, it releases the a stop codon, it releases the newly formed polypeptide newly formed polypeptide and the mRNA molecule, and the mRNA molecule, completing the process of completing the process of translation (translation (TerminationTermination).).

The Roles of RNA and DNAThe Roles of RNA and DNA

You can compare the different roles You can compare the different roles played by DNA and RNA molecules in played by DNA and RNA molecules in directing protein synthesis to the two directing protein synthesis to the two types of plans used by builders.types of plans used by builders.

The Roles of RNA and DNAThe Roles of RNA and DNA

A master plan has all the A master plan has all the information needed to information needed to construct a building.construct a building.

But builders never bring But builders never bring the valuable master plans the valuable master plans to the building site, where it to the building site, where it might be damaged or lost.might be damaged or lost.

Instead they make an Instead they make an invaluable copy of the invaluable copy of the master plans called master plans called blueprints.blueprints.

The Roles of RNA and DNAThe Roles of RNA and DNA

The master plans stay safely The master plans stay safely stored in the office, and the stored in the office, and the blueprints are taken to the job blueprints are taken to the job site.site.

Similarly, the cell uses the Similarly, the cell uses the vital DNA “master plan” to vital DNA “master plan” to prepare RNA “blueprints”.prepare RNA “blueprints”.

The DNA molecule remains The DNA molecule remains safely in the nucleus, while safely in the nucleus, while the RNA molecules go to the the RNA molecules go to the protein-building sites in the protein-building sites in the cytoplasm – the ribosomes.cytoplasm – the ribosomes.

Genes and ProteinsGenes and Proteins Gregor Mendel might have been Gregor Mendel might have been

surprised to learn that most surprised to learn that most genes contain nothing more than genes contain nothing more than instructions for assembling instructions for assembling proteins.proteins.

He might of asked what proteins He might of asked what proteins could possibly have to do with could possibly have to do with the color of flowers, the shape of the color of flowers, the shape of the leaves, a human blood type, the leaves, a human blood type, or the sex of a newborn baby.or the sex of a newborn baby.

The answer is that proteins have The answer is that proteins have everything to do with these everything to do with these things.things.

Genes and ProteinsGenes and Proteins

Remember that many Remember that many proteins are enzymes, proteins are enzymes, which catalyze and which catalyze and regulate chemical regulate chemical reactions.reactions.

A gene that codes for A gene that codes for an enzyme to produce an enzyme to produce pigment can control pigment can control the color of a flower.the color of a flower.

Genes and ProteinsGenes and Proteins

Another enzyme-Another enzyme-specifying gene specifying gene helps produce a helps produce a red blood cell red blood cell surface antigen.surface antigen.

This molecule This molecule determines your determines your blood type.blood type.

Genes and ProteinsGenes and Proteins

Genes for certain Genes for certain proteins can regulate proteins can regulate the rate and pattern of the rate and pattern of growth throughout an growth throughout an organism, controlling organism, controlling its size and shape.its size and shape.

In short, proteins are In short, proteins are the keys to almost the keys to almost everything that living everything that living cells do.cells do.