Gene ActionGene Action

Protein SynthesisProtein Synthesis

Overview of Protein Synthesis … Overview of Protein Synthesis … the short versionthe short version

DNA contained in genes provides DNA contained in genes provides instructions for making proteininstructions for making protein

Information from a specific section of DNA Information from a specific section of DNA is first transcribed to produce a specific is first transcribed to produce a specific molecule of RNAmolecule of RNA

RNA attaches to a ribosome where the RNA attaches to a ribosome where the information is translated into a information is translated into a corresponding sequence of amino acidscorresponding sequence of amino acids

Protein Synthesis VocabProtein Synthesis Vocab

Nucleotide – building block of nucleic acid: Nucleotide – building block of nucleic acid: sugar, phosphate, basesugar, phosphate, base

Protein Synthesis VocabProtein Synthesis Vocab

Base Triplet – a sequence of three Base Triplet – a sequence of three successive DNA nucleotidessuccessive DNA nucleotides

Codon – a sequence of three successive Codon – a sequence of three successive mRNA nucleotides that correspond with a mRNA nucleotides that correspond with a base tripletbase triplet

TRANSCRIPTIONTRANSCRIPTION

DNA base triplets DNA base triplets mRNA codons mRNA codons

Just copying a message in the Just copying a message in the same languagesame language! ! – Nucleotide Nucleotide nucleotide nucleotide

Occurs in the NucleusOccurs in the Nucleus

Catalyzed by the enzyme RNA polymeraseCatalyzed by the enzyme RNA polymerase– Promoter – a special sequence of DNA nucleotides Promoter – a special sequence of DNA nucleotides

near the beginning of a gene that tell the RNA near the beginning of a gene that tell the RNA polymerase where to begin readingpolymerase where to begin reading

TRANSCRIPTIONTRANSCRIPTION

Nucleotides pair complementarily:Nucleotides pair complementarily:DNADNA RNARNA

CC - - GG

G -G - CC

A -A - UU

T -T - AA

TRANSCRIPTIONTRANSCRIPTION

Terminator – a specific sequence of Terminator – a specific sequence of DNA nucleotides that signals the end DNA nucleotides that signals the end of the gene.of the gene.

RNA polymerase detaches from the RNA polymerase detaches from the RNA molecule and the DNA strand.RNA molecule and the DNA strand.

The RNA leaves the nucleus through a The RNA leaves the nucleus through a nuclear porenuclear pore

TranslationTranslation

The process in which mRNA associates The process in which mRNA associates with ribosomes and directs the synthesis with ribosomes and directs the synthesis of proteins by converting the sequence on of proteins by converting the sequence on nucleotides in RNA to a sequence of nucleotides in RNA to a sequence of amino acids…HUH?amino acids…HUH?

Changing Languages Now…Changing Languages Now…– Nucleotide Nucleotide Amino Acids Amino Acids

TranslationTranslation

http://staff.jccc.net/PDECELL/proteinsynthhttp://staff.jccc.net/PDECELL/proteinsynthesis/translation/steps.htmlesis/translation/steps.html

TranslationTranslation

1. An mRNA molecule binds to the small 1. An mRNA molecule binds to the small ribosomal subunit and a special tRNA ribosomal subunit and a special tRNA molecules (the initiator) binds to the start molecules (the initiator) binds to the start codon (AUG), where translation beginscodon (AUG), where translation begins

TranslationTranslation

2. The large ribosomal subunit attaches to 2. The large ribosomal subunit attaches to the small subunit, creating a functional the small subunit, creating a functional ribosomeribosome– The initiator tRNA binds to the start codonThe initiator tRNA binds to the start codon– One end of the tRNA carries a specific amino One end of the tRNA carries a specific amino

acid, the other consists of a triplet of bases acid, the other consists of a triplet of bases called an anticodon.called an anticodon.

– The anticodon pairs with the complementatry The anticodon pairs with the complementatry codon on mRNAcodon on mRNA

TranslationTranslation

3. The anticodon of another tRNA with its 3. The anticodon of another tRNA with its amino acid attaches to the next section of amino acid attaches to the next section of mRNAmRNA

4. A peptide bond is formed between the 4. A peptide bond is formed between the amino acids carried by the 2 tRNA’samino acids carried by the 2 tRNA’s

TranslationTranslation

5. After the peptide bond forms, the tRNA 5. After the peptide bond forms, the tRNA detaches from the ribosome and the detaches from the ribosome and the ribosome shifts the mRNA strand by 1 ribosome shifts the mRNA strand by 1 codon. A new tRNA with amino acid binds codon. A new tRNA with amino acid binds to the exposed codon.to the exposed codon.

Steps 3-5 repeat as the polypeptide Steps 3-5 repeat as the polypeptide lengthenslengthens

Protein synthesis ends when the ribosome Protein synthesis ends when the ribosome reaches a stop codon.reaches a stop codon.– The new protein detaches, the tRNA detaches The new protein detaches, the tRNA detaches

and the ribosome splits into its sub unitsand the ribosome splits into its sub units

How fast can this possibly happen?How fast can this possibly happen?

In the body translation occurs at a rate of In the body translation occurs at a rate of about 15 amino acids per second!about 15 amino acids per second!

Before 1 ribosome finishes moving down Before 1 ribosome finishes moving down the mRNA another can attach to that same the mRNA another can attach to that same strand allowing large amounts of protein to strand allowing large amounts of protein to be built. be built.

tRNAtRNA