1. Genes and How They Work Chapter 15
Copyright © McGraw-Hill Companies Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

2. Cells Use RNA to Make Protein Genetic Code Transcription Translation
Outline
Cells Use RNA to Make Protein
Genetic Code
Transcription
Translation
Introns and Exons
Bacterial and Eukaryotic Gene Expression
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

3. Cells Use RNA to Make Protein
During polypeptide synthesis, ribosomal RNA (rRNA) is the site of polypeptide assembly.
Transfer RNA (tRNA) transport and position amino acids.
Messenger RNA (mRNA) direct which amino acids are assembled into polypeptides.
Central Dogma
DNA  RNA Protein
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

4. DNA sequence is transcribed into RNA sequence.
Gene Expression
Transcription
DNA sequence is transcribed into RNA sequence.
Initiated when RNA polymerase binds to promoter site.
Moves along DNA strand and adds corresponding complementary RNA nucleotide.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

5. Moves along three nucleotides at a time. Disengages at stop signal.
Gene Expression
Translation
Nucleotide sequence of mRNA transcript is translated into an amino acid sequence in the polypeptide.
rRNA molecule within ribosome recognizes and binds to start sequence on mRNA.
Moves along three nucleotides at a time.
Disengages at stop signal.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

6. Raven - Johnson - Biology: 6th Ed
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

7. Reading frame is composed of three nucleotide blocks (Triplet).
Genetic Code
The genetic code consists of a series of information blocks called codons.
Reading frame is composed of three nucleotide blocks (Triplet).
Each codes for one amino acid.
Genetic code is universal in almost all organisms.
Mitochondria
Chloroplasts
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

8. Non-transcribed strand is termed coding strand or sense strand.
Transcription
RNA Polymerase
Only one of two DNA strands (template or antisense strand) is transcribed.
Non-transcribed strand is termed coding strand or sense strand.
In both bacteria and eukaryotes, the polymerase adds ribonucleotides to the growing 3’ end of an RNA chain.
Synthesis proceeds in 5’3’ direction.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

9. Other eukaryotic factors bind, assembling a transcription complex.
Promoter
Transcription starts at RNA polymerase binding sites called promoters on DNA template strand.
Initiation
Other eukaryotic factors bind, assembling a transcription complex.
RNA polymerase begins to unwind DNA helix.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

10. Transcription Elongation
Transcription bubble moves down DNA at constant rate leaving growing RNA strands protruding from the bubble.
Termination
Stop sequences at the end of the gene cause phosphodiester bond formation to cease, transcription bubble to dissociate, and RNA polymerase to release DNA.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

11. Raven - Johnson - Biology: 6th Ed
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

12. Some tRNA molecules recognize more than one codon.
Translation
Begins when initial portion of mRNA molecule binds to rRNA in a ribosome.
tRNA molecule with complimentary anticodon, binds to exposed codon on mRNA.
Some tRNA molecules recognize more than one codon.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

13. Translation Activating Enzymes
tRNA molecules attach to specific amino acids through the action of activating enzymes (aminoactyl-tRNA syntheases).
Must correspond to specific anticodon sequences on a tRNA molecule as well as particular amino acids.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

14. Start signal coded by AUG codon.
Translation
Start and Stop Signals
Start signal coded by AUG codon.
Stop signal coded by one of three nonsense codons: UAA - UAG - UGA.
Initiation
Polypeptide synthesis begins with the formation of an initiation complex.
Initiation Factors
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

15. Formation of Initiation Complex
Copyright © McGraw-Hill Companies
Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

16. Translation Elongation
After initiation complex forms, large ribosome subunit binds, exposing mRNA codon adjacent to the initiating codon, positioning it for interaction with another amino acid-bearing tRNA molecule.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

17. Ribosome moves nucleotides along mRNA molecule.
Translation
Translocation
Ribosome moves nucleotides along mRNA molecule.
Copyright © McGraw-Hill Companies
Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

18. Translation Termination
Nonsense codons are recognized by release factors that release the newly made polypeptide from the ribosome.
Copyright © McGraw-Hill Companies
Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

19. Initially, a primary RNA transcript is produced for the entire gene.
Introns
DNA sequence specifying a protein is broken into segments (exons) scattered among longer noncoding segments (introns).
Initially, a primary RNA transcript is produced for the entire gene.
Small nuclear ribonucleicproteins (snRNPs) associate with proteins to form spliceosome.
Excise introns and joins exons to form mature RNA.
Alternative Splicing
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

20. Introns and Exons
Copyright © McGraw-Hill Companies Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

21. Remaining sequences are not translated.
RNA Splicing
During RNA processing, intron sequences are cut out of primary transcript before it is used in polypeptide synthesis.
Remaining sequences are not translated.
Remaining exon sequences are spliced together to form final processed mRNA.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

22. Differences Between Bacterial and Eukaryotic Gene Expression
Most eukaryotic genes possess introns.
Individual bacterial mRNA molecules often contain transcripts of several genes.
Eukaryotic mRNA molecules must be completely formed and must pass across the nuclear membrane before translation.
In bacteria, translation begins at AUG codon preceded by special nucleotide sequence.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

23. Differences Between Bacterial and Eukaryotic Gene Expression
Eukaryotic mRNA molecules have introns cut out and exons joined together before translation.
Eukaryotic ribosomes are larger than prokaryotic ribosomes.
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

24. Cells Use RNA to Make Protein Genetic Code Transcription Translation
Review
Cells Use RNA to Make Protein
Genetic Code
Transcription
Translation
Introns and Exons
Bacterial and Eukaryotic Gene Expression
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

25. Copyright © McGraw-Hill Companies Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies