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Translation

Translation. mRNA exits the nucleus through the nuclear pores In the cytoplasm, it joins with the other key players to assemble a polypeptide. The other parts of the machinery are: t-RNAs and ribosomes.

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Translation

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  1. Translation • mRNA exits the nucleus through the nuclear pores • In the cytoplasm, it joins with the other key players to assemble a polypeptide. • The other parts of the machinery are: t-RNAs and ribosomes

  2. T-RNA: small, 80n, single strand with secondary structure (folding). Anticodon at end of loop. function = picks up aa & transports it to ribosome

  3. Ribosomes: composed of rRNA and proteins

  4. Sequence of 4 Steps in Translation... • ACTIVATION : Add an amino acid to tRNA • Requires enzyme and ATP Creates an aa-tRNA

  5. 2. INITIATION: assemble players -ribosome, -mRNA, -aa-tRNA -Small ribosomal sub units binds to mRNA. -Initiator tRNA binds to P site -Large ribosomal unit binds to complex

  6. 3. ELONGATION: adding new aa’s - peptidyltransferase

  7. 4. TERMINATION: stopping the process

  8. Components of translation

  9. Another view of translation

  10. PUTTING IT ALL TOGETHER!

  11. REGULATION OF GENE EXPRESSION • The control in the DNA transcription process is very tight. • Cells are able to "turn on" or "turn off" genes when their products are not required in cell metabolism or control. • Regulation of gene expression is now only being to be fully understood and is a major area of research today.

  12. GENE REGULATION IN PROKARYOTES • Genes for a particular metabolic pathway are usually in clusters, under the control of one promoter and one operator. • This cluster of genes, with its regulatory sites is called an operon

  13. The lac operon • E. coli can use lactose as a source of energy • To use lactose, it must split the lactose into glucose and galactose. This means producing enzymes. • Only produces enzymes when lactose is present in the environment. WHY?

  14. Three genes are involved: 1. LacZ: codes for B-galactosidase: degrades lactose 2. LacY: codes for B-galactosidase permease: causes lactose to enter the cell 3. LacA: codes for a transacetylase: function unknown!

  15. The lacl gene codes for the lacl protein • This protein is always produced. • When lactose is NOT present in the environment, the lacl protein binds to the operator site. • This blocks RNA polymerase from attaching to the promoter site. Transcription is turned OFF

  16. operator - binds repressor protein

  17. When lactose is PRESENT in the environment, The lactose binds to the lacl protein, and changes its shape • The lacl protein “falls” off the operator site and RNA polymerase can now attach to the promoter site and transcription of the lac genes proceeds. • Lactose is an inducer molecule. Its presence activates transcription of the genes that degrade it.

  18. Often, both glucose and lactose are present in the environment. • E. coli uses glucose first, since the enzymes for its use are always present. • There is a mechanism to slow down the use of lactose even if it is present. • When all glucose is used, then transcription of lac genes will speed up.

  19. CATABOLIC REPRESSION • glucose prevents the action of the LAC operonthrough another regulator-likeprotein, the cAMP receptor protein (CRP) • CRP binds to DNA at the CRP gene • CRP is aka as CAP ( Catabolite Activator protein) • This involves the use of cAMP as an intermediate messenger

  20. CRP gene

  21. CRP (aka CAP) is an allosteric protein, regulated by cAMP     • when glucose is high - lots of ATP & little cAMP • CRP-alone conformation doesn't bind to CRP DNA region - favors slow transcription of lac genes • when glucose is low - all the ATP is hydrolyzed favoring high cAMP amounts • cAMP-CRP conformation can bind to CRP DNA region -favors rapid transcription of lac genes

  22. The TRP operon • This cluster of genes is responsible for the enzymes that synthesize Tryptophan, an essential amino acid. • They are always turned on EXCEPT when tryptophan is present in the environment. • The operon consist of five genes, an operator, a promoter and the trp repressor protein.

  23. Tryptophan is needed to inactivate the trp operon—it is a corepressor. • This type of regulation is by repression because the effector molecule interacts with the repressor protein so that it can bind to the operator

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