Mr. Briner Unit 7.3 DNA Translation HL American School of Milan DP Biology Unit 7.3 DNA Translation HL

7.3.S2 The use of molecular visualization software to analyse the structure of eukaryotic ribosomes and a tRNA molecule.

Translation Structure of tRNA Many different types of tRNA in a cell All tRNA molecules have: A triplet of bases called the anticodon A loop of 7 nucleotides Two other loops A CCA base sequence at the 3’ terminal Forms a site for attaching an amino acid Sections that become double-stranded by base pairing

Translation

(c) Complementary base pairing sequence (a) Amino acid Specific to each tRNA (b) CCA base sequence Where amino acid is attached by the ‘Activating Enzyme’ (c) Complementary base pairing sequence Helical in shape

(f) Small open loop of RNA (d) 8 free bases Non-pairing giving one loop of RNA (e) 7 free bases Non-pairing giving second loop of RNA (f) Small open loop of RNA Variable in shape between different tRNA

(g) Anti-codon (3 bases) which binds to the mRNA codon Specific to the amino acids being carried Anti-codon is complementary to an mRNA codons

Translation Structure of tRNA Structure allows tRNA to attach to binding sites on ribosomes and to mRNA Variable features in each type of tRNA produce different properties Allowing for the correct binding of amino acids to specific tRNAs

7.3.a1 tRNA-activating enzymes illustrate enzyme–substrate specificity and the role of phosphorylation.

Translation Activation of tRNA Shape of each tRNA is different. Defined by the loop and helical sections Shape selects a specific enzyme tRNA activating enzyme Aminoacyl-tRNA synthetase Enzyme adds a specific amino acid to the CCA sequence (at 3' end of the tRNA)

Translation Activation of tRNA There are 20 different tRNA activating enzymes One for each of the 20 amino acids An example of a degenerate code Each of these enzymes attaches one particular amino acid To all of the tRNA molecules that have an anticodon corresponding to that amino acid

Translation Activation of tRNA tRNA Activating Enzyme uses energy ATP hydrolysis provides the energy for amino acid attachment to tRNA Stores energy that is also used later to link the amino acid to the growing polypeptide chain during translation

Translation

Translation Ribosome structure Proteins and Ribosomal RNA combine in the structure Protein (40% of mass) rRNA (60% of mass) Large sub-unit and a small sub-unit Large sub-unit has three binding sites for tRNA molecules ( A, P and E site) Small sub-unit has a binding site for mRNA

Translation Ribosome structure Ribosomes are enzymes Catalyze the translation of mRNA into a polypeptide Substrate is mRNA Can catalyze transcription of any mRNA

7.3.U2 Synthesis of the polypeptide involves a repeated cycle of events.

Translation Stages of translation There are three stages in translation: (Just like in transcription) Initiation: Ribosome, tRNA and mRNA come together to begin the translation

Translation Stages of translation There are three stages in translation: Elongation: tRNA molecules attach to the mRNA Based on the codon-anticodon recognition Amino acids are brought together and polymerized into the primary structure of the polypeptide

Translation Stages of translation There are three stages in translation: Termination: mRNA and the ribosomes detach Polypeptide is released and the tRNA return to be charged with more amino acid

Translation Direction of translation Translation happens in 5'  3' direction Ribosomes move along mRNA in this direction From the 5' free end to the 3' free end

Translation Peptide bonds between amino acids During translation amino acids are joined to form a polypeptide Sequence of amino acids is called the primary structure A peptide bond joins each amino acid together By condensation synthesis

Translation Peptide bonds between amino acids

Translation Peptide bonds between amino acids N-C-C-N-C-C backbone Polypeptides maintain this sequence no matter how long the chain R-groups project from the backbone As amino acids are added in translation, the polypeptide folds into specific shape Secondary and tertiary structure

Transcription and Translation Process of DNA Translation Initiation: 5’ end of mRNA binds to the small subunit of the ribosome Initial mRNA codon = AUG = start codon tRNA anticodon binds to mRNA codon by complementary base pairing tRNA with anticodon: UAC Methionine attached to tRNA 3’ terminal

Transcription and Translation Process of DNA Translation Initiation: Large ribosomal subunit binds Completes ribosomal structure Producing three ribosomal binds sites: A, P, & E A- (Amino acid) is where the new tRNA binds P- (Polypeptide) is where the amino acid on the tRNA adds to the polypeptide E- (Exit) is where the tRNA (without amino acid) is the released from the ribosome

Transcription and Translation Process of DNA Translation Initiation:

Translation Process of DNA Translation Start codon mRNA triplet codon AUG is universally the start codon Marks the beginning of the coding sequence of a gene Thus, tRNA with the anticodon UAC and carrying the amino acid methionine is always the first tRNA to enter the P-site during translation

Transcription and Translation

Transcription and Translation

7.3.U1 Initiation of translation involves assembly of the components that carry out the process.

Transcription and Translation Process of DNA Translation Elongation: tRNA with anticodon complementary to 2nd mRNA codon binds to ribosomal A site Correct amino acid attached to tRNA 3’ end Enzymes in ribosome catalyze formation of peptide bond between methionine and 2nd amino acid

Transcription and Translation Process of DNA Translation Elongation: P site tRNA, now separated from methionine, move to E site Exits ribosome Ribosome moves one codon toward the 3’ end of mRNA Shifting previous A-site tRNA to P-site Opening A-site

Transcription and Translation Process of DNA Translation Elongation: tRNA with anticodon complementary to A- site mRNA codon binds to ribosomal A-site Correct amino acid attached to tRNA 3’ end Enzymes in ribosome catalyze peptide bond between 2nd and 3rd amino acids

Transcription and Translation Process of DNA Translation Elongation: P site tRNA, now separated from its amino acid, move to E site Exits ribosome Ribosome moves one codon toward the 3’ end of mRNA Shifting previous A-site tRNA to P-site Opening A-site Repeats process until stop codon reached

Transcription and Translation

Transcription and Translation

Transcription and Translation

Transcription and Translation

7.3.U3 Disassembly of the components follows termination of translation.

Translation Process of DNA Translation Stop codon There are three stop codons None of these have a corresponding tRNA When a ribosome encounters a stop codon, a release factor binds to the stop codon Which terminates translation and allows the separation of all of its components

Transcription and Translation Process of DNA Translation Termination: When ribosomal A-site reaches stop codon No tRNA has a complementary anticodon Release factor protein binds to ribosomal A-site stop codon Polypeptide and mRNA are released Protein further modified in endoplasmic reticulum or golgi, or secreted in a vesicle Large and small ribosomal subunits separate

Transcription and Translation

Transcription and Translation

Transcription and Translation ANIMATION

Transcription and Translation

7.3.U6 Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane.

Transcription and Translation Process of DNA Translation In eukaryotes: mRNA needs to leave nucleus to be translated by 80S ribosomes in the cytoplasm or on the RER In prokaryotes: mRNA can immediately be translated by free 70S ribosomes

7.3.S1 Identification of polysomes in electron micrographs of prokaryotes and eukaryotes.

Translation Process of DNA Translation Polysomes Several ribosomes translating the same mRNA into protein Each moving in the 5’ to 3’ direction Allows many proteins to be made from the same mRNA Speeds up protein production

Translation

Transcription and Translation ANIMATION

7.3.U4 Free ribosomes synthesize proteins for use primarily within the cell. 7.3.U5 Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes.

Translation Free vs. bound ribosomes Free ribosomes Bound ribosomes Synthesize proteins for use primarily within the cell itself Bound ribosomes Synthesize proteins primarily for secretion or for lysosomes

7.3.U7 The sequence and number of amino acids in the polypeptide is the primary structure.

7.3.U8 The secondary structure is the formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding.

7.3.U9 The tertiary structure is the further folding of the polypeptide stabilized by interactions between R groups.

7.3.U10 The quaternary structure exists in proteins with more than one polypeptide chain.

MAJOR SOURCES Thank you to my favorite sources of information when making these lectures! John Burrell (Bangkok, TH) www.click4biology.info Dave Ferguson (Kobe, JA) http://canada.canacad.ac.jp/High/49 Stephen Taylor (Bandung, IN) www.i-biology.net Andrew Allott – Biology for the IB Diploma C. J.Clegg – Biology for the IB Diploma Weem, Talbot, Mayrhofer – Biology for the International Baccalaureate Howard Hugh’s Medical Institute – www.hhmi.org/biointeractive Mr. Hoye’s TOK Website – http://mrhoyestokwebsite.com And all the contributors at www.YouTube.com