1. credit: modification of work by NIH
Chapter 15
General Biology I
BSC 2010
Genes and Proteins
credit: modification of work by NIH

2. credit: National Human Genome Research Institute
Genes
credit: National Human Genome Research Institute
Genes are tangible molecular entities composed of DNA and capable of replication, expression, and mutation.

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The Central Dogma
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4. The Central Dogma a sequence of DNA nucleotides
colinear
DNA
a sequence of DNA nucleotides
RNA polymerase does transcription.
RNA
a sequence of RNA nucleotides
Ribosomes and transfer RNA do translation.
polypeptide protein
a sequence of amino acids

5. The Genetic Code is Degenerate, Universal, and Unambiguous
Codons are
3-letter RNA sequences.
The reading frame is maintained as long as no nucleotides (letters) are inserted or removed.
credit: modification of work by NIH
credit: modification of work by NIH

6. Frameshift Mutations Disrupt the Reading Frame
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7. Polypeptides are Chains of Amino Acids
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8. Prokaryote Transcription
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Prokaryotes typically have a single chromosome where the genes are located.
They may also have plasmids (short circular pieces of DNA containing a few “bonus” genes).
Transcription occurs for individual genes.
Not all genes are “expressed” (transcribed) at all times.

9. Transcription Begins at the Promoter of a Gene
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The promoter is a region of the DNA having a specific sequence. It is “upstream” of the gene’s coding region. There are consensus sequences at -10 and -35.

10. Three Phases of Transcription
Initiation – RNA polymerase attaches to the promoter.
Elongation – RNA polymerase uses the DNA as a template to assemble a complementary sequence of RNA nucleotides.
Note: RNA that is eventually translated to make a polypeptide is called “messenger” RNA (mRNA).
Termination – RNA polymerase and the new RNA dissociate from the DNA.

11. Prokaryotic Transcription
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DNA Non-Template (coding) strand
DNA Template strand
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Termination, the end of transcription, is a mechanical phenomenon involving collision (Rho-dependent termination) or hairpin structures (Rho-independent termination).

12. Multiple Polymerases Can Transcribe a Single Gene
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13. Eukaryote Transcription is Similar to Prokaryote Transcription
Eukaryotes have multiple nuclear chromosomes where the genes are located.
They also have mitochondrial DNA.
Transcription occurs for individual genes.
Not all genes are “expressed” (transcribed) at all times.
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14. Eukaryotic RNA Polymerases
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15. Eukaryotic Genes Have Promoters
The TATA box at -30 has the sequence TATAAA. Regulation of transcription is complex, involving many transcription factors.
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16. Eukaryotic mRNAs Must Undergo Splicing and Processing
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Eukaryotic mRNA contains introns that must be spliced out. A 5’ cap and poly-A tail are also added.

17. mRNA Splicing
Splicing involves precise removal of introns. Spliceosomes recognize sequences at the 5’ and 3’ end of the intron.
Alternative splicing is possible.
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18. Translation Involves tRNAs (transfer RNAs)
tRNAs have amino acid attachment sites and anticodons.
They can translate the mRNA nucleotide language into the protein amino acid language, according to the genetic code.
Many copies of up to 60 types of tRNAs exist in the cytoplasm.
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19. Aminoacyl tRNA Synthetases are Enzymes
A tRNA becomes “charged” when an aminoacyl tRNA synthetase adds an amino acid to it.
They use ATP energy to charge the tRNA.
They are able to “read” the tRNA anticodon and select the corresponding amino acid (based on the genetic code).

20. Translation Happens at Ribosomes
Translation has initiation, elongation, and termination phases.
In E. coli, the Shine- Dalgarno sequence in the mRNA attaches to the ribosome.
Ribosome small and large subunits assemble together around the mRNA.
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21. Ribosome Structure
Parts of the ribosome are made of rRNA (ribosomal RNA).
Other parts are made of protein.
There are two subunits (large and small).
An important part is the enzymatic portion called peptidyl transferase.

22. Peptide Bonds Link the Amino Acids
Amino end of chain
Carboxyl end of chain
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Peptide bonds are covalent bonds, created by the peptidyl transferase of the ribosome. Protein synthesis involves making “polypeptide” chains.

23. Protein Folding, Modifications, and Targeting
Recall that polypeptide chains fold into secondary and tertiary shapes. They may also be involved in quaternary structures.
Modification examples include addition of functional groups (as in phosphorylation) and cleavage into smaller pieces.
In targeting, polypeptides are directed to specific cellular locations via a signal sequence at the end of the chain.

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