8.5 Translation Wed., 10/26Wed., 10/26Write Questions & ANSWERS! Write Questions & ANSWERS!

1.1. REPLICATE this DNA:REPLICATE this DNA:

A G G T C A T G CA G G T C A T G C

2. TRANSCRIBE this DNA:2. TRANSCRIBE this DNA:

A G G T C A T G CA G G T C A T G C

3. Does DNA stay in the nucleus?3. Does DNA stay in the nucleus?

4. Does RNA stay in the nucleus?4. Does RNA stay in the nucleus?

8.5 Translation

8.5 TranslationSo what did you learn So what did you learn yesterday???yesterday???

replication

transcription

translation

8.5 Translation

8.5 Key Concept:8.5 Key Concept:

• TranslationTranslation converts an mRNA converts an mRNA message into a polypeptide, or protein.message into a polypeptide, or protein.

8.5 TranslationProtein “Protein “SynthesisSynthesis””

• What does this MEAN?????What does this MEAN?????

• MakingMaking proteins! proteins!

8.5 Translation

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•Let’s do this!!!Let’s do this!!!

8.5 Translation

Amino acids are coded by mRNA base sequences.Amino acids are coded by mRNA base sequences. • Translation converts mRNA messages Translation converts mRNA messages

into polypeptides.into polypeptides.• A A codoncodon is a sequence of three is a sequence of three

nucleotides that codes for an amino acid.nucleotides that codes for an amino acid.codon formethionine (Met)

codon forleucine (Leu)

8.5 Translation

• The genetic code matches The genetic code matches EACHEACH codon to its amino acid or codon to its amino acid or function.function.– three three stop stop codonscodons

– one start one start codon, codon, codes for codes for methionimethioninene

The genetic code matches each RNA codon with its amino acid or function.

What amino acid is coded by GGA?........UGG……ACU?

8.5 Translation

A 3-nucleotide A 3-nucleotide sequence; sequence; CODES for an CODES for an amino acid!amino acid!Signals start of Signals start of

translation; codes translation; codes for methioninefor methionine

Signals STOP of Signals STOP of translationtranslation

Set of 3 Set of 3 nucleotides, nucleotides, read in orderread in order

8.5 Translation

• A A changechange in the order in which in the order in which codons are codons are readread changeschanges the the resulting protein.resulting protein.

• Regardless of the organism, codons Regardless of the organism, codons code for the code for the samesame aminoamino acidacid!!!!!!!!

8.5 Translation

• RibosomesRibosomes consist of two subunits. consist of two subunits.– The large subunit has three binding sites for The large subunit has three binding sites for

tRNA.tRNA.– The small subunit binds to mRNA.The small subunit binds to mRNA.

What is the function of mRNA?What is the function of mRNA?

•Site for translationSite for translation

•rRNA & proteinsrRNA & proteins

•Catalyzes bonds Catalyzes bonds between amino acidsbetween amino acids

8.5 TranslationAmino acids are linked to become a Amino acids are linked to become a proteinprotein. . • An An anticodonanticodon is a set of 3 nucleotides that is complementary to is a set of 3 nucleotides that is complementary to

an mRNA codon.an mRNA codon.

• An anticodon is carried by a An anticodon is carried by a tRNAtRNA..

•Carries amino acids Carries amino acids from cytoplasm to from cytoplasm to ribosomeribosome

•1 end: anticodon1 end: anticodon

•1 end: amino acid1 end: amino acid

8.5 Translation

Set of 3 Set of 3 nucleotides, read nucleotides, read in orderin order A 3-nucleotide A 3-nucleotide

sequence; sequence; CODES for an CODES for an amino acid!amino acid!Signals start of Signals start of

translation; codes translation; codes for methioninefor methionine

Signals STOP of Signals STOP of translationtranslation

3 nucleotides 3 nucleotides on on tRNAtRNA, bind , bind to to complementarcomplementary y mRNAmRNA

Site for translationSite for translation

rRNA & proteinsrRNA & proteins

Catalyzes bonds Catalyzes bonds between amino between amino acidsacids

Carries amino acids Carries amino acids from cytoplasm to from cytoplasm to ribosomeribosome

1 end: anticodon1 end: anticodon

1 end: amino acid1 end: amino acid

Codons “code” Codons “code” for same amino for same amino acids in almost acids in almost ALLALL organismsorganisms!!

8.5 Translation

Ribosome assembles @ Ribosome assembles @ start codonstart codon

Complementary tRNA Complementary tRNA anticodon pairs up to anticodon pairs up to mRNA codon in the mRNA codon in the ribosomeribosome

8.5 Translation

• For translation to beginFor translation to begin, tRNA binds to , tRNA binds to a start codon and signals the ribosome a start codon and signals the ribosome to assemble.to assemble.– A A complementary tRNA moleculecomplementary tRNA molecule binds binds

to the exposed codon, bringing its to the exposed codon, bringing its amino acid close to the first amino acid.amino acid close to the first amino acid.

What is the function of mRNA?

8.5 Translation

tRNAs keep bringing tRNAs keep bringing amino acids to ribosome, amino acids to ribosome, which moves down mRNAwhich moves down mRNA

Ribosome forms peptide Ribosome forms peptide bonds b/w amino acids & bonds b/w amino acids & breaks bond w/its tRNAbreaks bond w/its tRNA

8.5 Translation

– The ribosome helps form a polypeptide The ribosome helps form a polypeptide bond between the amino acids.bond between the amino acids.

– The ribosome pulls the mRNA strand the The ribosome pulls the mRNA strand the length of one codon.length of one codon.

8.5 Translation

Keeeeeeeeeeps going til Keeeeeeeeeeps going til the ribosome reaches the the ribosome reaches the STOP codon!STOP codon!

8.5 Translation

– The now The now empty tRNAempty tRNA molecule molecule exitsexits the the ribosome.ribosome.– A A complementary tRNAcomplementary tRNA molecule binds to molecule binds to the next exposed codonthe next exposed codon..

– Once the stop codon is reached, the ribosome Once the stop codon is reached, the ribosome releases the protein and disassemblesreleases the protein and disassembles..

What is the function of ribosomes?

8.5 Translation