1. Protein Synthesis

2. Flow of Genetic Information
Flow of genetic information from DNA to RNA to protein
The DNA genetic code (genotype) is expressed as proteins which provide the physical traits (phenotype) of an organism
GCTGCTAACGTCAGCTAGCTCGTAGC GCTAGCGCTTGCGTAGCTAAAGTCGAGCTCGCTTGCGTAGCTAAAGTCGAGCTGCTGCTAACGTCAGCTAGCTCGTAG AGCGCTTGCGTAGCTAAAGTCGAGCT AGCGCTTGCGTAGCTAAAGTCGAGCT GCTGCTAACGTCAGCTAGCTCGTAGC AGCGCTTGCGTAGCTAAAGTCGAGCT AGCGCTTGCGTAGCTAAAGTCGAGCT GCTGCTAACGTCAGCTAGCTCGTAGC AGCGCTTGCGTAGCTAAAGTCGAGCT AGCGCTTGCGTAGCTAAAGTCGAGCT GCTGCTAACGTCAGCTAGCTCGTAGC AGCGCTTGCGTAGCTAAAGTCGAGCT GCTGCTAACGTCAGCTAGCTCGTAGC AGCGCTTGCGTAGCTAAAGTCGAGC, cont.
RNA
Proteins

3. RNA Proteins Different DNA Sequence….
GCTGTAATTACGTAACTAGCTCGTAGCCTAGCGCTTGCGTAGCTAAAGTCGAGCTCGGCTGTAATTACGTAAGTCGAGCTGCTGCTAACGTCAGCTAGCTCGTAGGCTGTAATTACGTAAAGCGCTTGCGTAGCTAAAGTCGAGCTGCTGTAATTACGTAAAGCGCTTGCGTAGCTAAAGTCGAGCTGCTGCTAACGTCAGCTAGCTCGTAGCGCTGTAATTACGTAAAGCGCTTGCGTAGCTAAAGTCGAGCTGCTGTAATTACGTAAAGCGCTTGCGTAGCTAAAGTCGAGCTGCTGTAATTACGTAA GCTGCTAACGTCAGCTAGCTCGTAGCGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAA, cont.
RNA
Proteins

4. Protein Synthesis Transcription Translation
Process in which a molecule of DNA is copied into a complementary strand of RNA
Translation
Process in which the message in RNA is made into a protein

5. Forms of RNA 3 Main Types of RNA
mRNA (messenger RNA) – RNA that decodes DNA in nucleusbrings DNA message out of nucleus to the cytoplasm
Each 3 bases on mRNA is a “codon”
tRNA (transfer RNA) – RNA that has the “anticodon” for mRNA’s codon The anticodon matches with the codon from mRNA to determine which amino acid joins the protein chain
rRNA (ribosomal RNA) – make up the ribosomes—RNA that lines up tRNA molecules with mRNA molecules

7. Transcription produces genetic messages in the form of RNA
RNA nucleotide
RNA polymerase
Direction of transcription
Template strand of DNA
Newly made RNA
Figure 10.9A
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

8. Transcription Initiation:
RNA polymerase (enzyme) attaches to DNA at the promoter and “unzips” the two strands of DNA
Elongation:
RNA polymerase then “reads” the bases of DNA and builds a single strand of complementary RNA called messenger RNA (mRNA)
Termination:
When the enzyme reaches the terminator sequence, the RNA polymerase detaches from the RNA molecule and the gene

9. Transcription The code on DNA tells how mRNA is put together.
Example: DNAACCGTAACG
mRNAUGGCAUUGC
Each set of 3 bases is called a triplet or codon (in mRNA)
UGG CAU UGC

10. Eukaryotic RNA is processed before leaving the nucleus
Noncoding segments called introns are spliced out
Coding segments called exons are bonded together
A 5’cap and a ’ poly-A tail are added to the ends
DNA
RNA transcript with cap and tail
mRNA
Exon
Intron
Transcription Addition of cap and tail
Introns removed
Exons spliced together
Coding sequence
NUCLEUS
CYTOPLASM
Tail
Cap
Figure 10.10
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

12. Protein Synthesis Transcription Translation
Process in which RNA is used to make a protein

13. Transfer RNA molecules serve as interpreters during translation
Amino acid attachment site
In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide
The process is aided by tRNAs
Hydrogen bond
RNA polynucleotide chain
Anticodon
Figure 10.11A
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

14. Ribosomes build polypeptides
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

15. Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
The mRNA moves a codon at a time relative to the ribosome
A tRNA pairs with each codon, adding an amino acid to the growing polypeptide

16. Translation Initiation:
mRNA molecule binds to the small ribosomal subunit
Initiator tRNA binds to the start codon (AUG—Methionine) in the P-site of the ribosome
The large ribosomal subunit binds to the small one so that the initiator tRNA is in the P-site to create a functional ribosome

17. Translation Elongation:
Codon recognition: anticodon of incoming tRNA molecule, carrying its amino acid, pairs with the mRNA codon in the A-site of the ribosome
Peptide formation: polypeptide separates from the tRNA in the P site and attaches by a peptide bond to the amino acid carried by the tRNA in the A site
Translocation:
the tRNA in the P-site now leaves the ribosome, and the ribosome moves along the mRNA so that the tRNA in the A-site, carrying the growing polypeptide, is now in the P-site. Another tRNA is brought into the A-site

18. Translation Termination:
Elongation continues until a stop codon is reached—UAA, UAG, or UGA
The completed polypeptide is released, the ribosome splits into its subunits

20. An exercise in translating the genetic code
DNA
Start codon
Stop codon
RNA
Polypeptide

21. Mutations Mutagenesis—creation of mutations
Can result from Spontaneous Mutations
Errors in DNA replication or recombination
Mutagens—physical or chemical agents
High-energy radiation (X-rays, UV light)

22. Types of Mutations Mutations within a gene
Can be divided into two general categories.
Base substitution
Base deletion (or insertion)
Can result in changes in the amino acids in proteins.
Sickle-Cell
Disease

23. Substitution Mutations
Missense mutation: altered codon still codes for an amino acid, although maybe not the right one
Nonsense mutation: altered codon is a stop codon and translation is terminated prematurely
Leads to nonfunctional proteins

24. Insertions and Deletions
Frameshift mutation: addition or loss of one or more nucleotide pairs in a gene shifts the reading frame for translation and incorrect protein is made

25. Are all Mutations Bad? Although mutations are often harmful,
They are the source of the rich diversity of genes in the living world.
They contribute to the process of evolution by natural selection.