Transcription/Translation/Protein Secretion
Bio119
I. Transcription
A. Many bacterial genes are arranged in operons
1.
2. They are transcribed together
3. An operon of genes shares a:
4. This increases efficiency in gene expression and regulation
of a particular pathway.
B. During transcription, genes are copied into RNA
C. Most bacterial messenger RNAs (mRNA) encode for specific
proteins
1. RNA’s can also be catalytic, structural, regulatory, or
unknown.
D. Most bacterial mRNA’s:
E. Bacterial mRNAs are short-lived
F. Steps in RNA synthesis (13.9):
1. Initiation:
a) RNA polymerase binds to:
b)
c) RNA polymerase holoenzyme:
d) This is dependent on:
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2. Promoter clearance:
a)
3. Elongation:
a) Core RNA polymerase (4 subunits, no sigma factor)
takes over polymerization of nucleotides into RNA.
b) Only moves in one direction
4. Termination:
a) RNA polymerase terminates transcription in response
to specific DNA sequences:
G. The sigma 70 promoter (Fig. 13.10)
1. In E. coli sigma 70 recognizes the majority of promoters for
genes encoding essential functions
2. Sigma 70 dependent promoters are fairly conserved although
not identical.
3. The sigma 70 promoter has two features:
4.
5.
6.
7. The first base pair copied relative to the promoter is called:
8. Promoter strength:
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H. Bacteria are known to have a variety of genes encoding alternative
sigma factors that target certain promoters
1. Alternative sigma factors:
2. Conditions controlling alternative sigma factors:
3. Figure 13.10 list a variety of alternative sigma factors and
their promoters.
4. Some include stress response, motility, iron metabolism,
sporulation
II. Translation (Fig. 13.18)
A. Translation requires a variety of things such as:
1. mRNA with ribosome binding site
2. Ribosomes
3. tRNA’s (Fig. 13.17)
B. The Shine Dalgarno sequence (Fig. 13.19):
C. The protein message encoded in the mRNA is determined by the
types of codons.
D. There are 61 codons for 20 amino acids (Table 13.2)
1. Initiation codons:
2. Stop codons:
3. The reading frame:
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Transcription/Translation/Protein Secretion
III.
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E. Prokaryotes exhibit codon bias or preferences for certain codons.
1. Why?
2. This can cause problems if you want to translate an mRNA
from an archeaon in proteobacterium. Why?
Protein secretion
A. Why secret proteins?
B. What determines if a protein will be secreted?
C. Getting things to the periplasm (Fig. 11.10A):
1. Cotranslational:
2. Posttranslational:
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3. Proteins going through the Sec dependent pathway
a) Periplasmic binding proteins
b) Periplasmic proteins
c) Cell envelope binsynthetic enzymes
d) Outer membrane proteins (porins and lipoproteins)
e) ~500 translocase complexes per cell.
D. Getting mature proteins across the CM (Fig 11.10B).
1.
2. Secretion of:
3.
4.
5. The signal peptide is on one of the proteins in the complex:
6. Requires TatBC to recognize N-terminal signal and delivers
the complex to TatA channel.
7. Once translocated protein complex either stays on the
membrane or the signal peptide is cleaved freeing the protein to
enter the periplasm.
E. Getting lipoproteins to OM (Fig. 11.11)
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F. Getting proteins to OM (Fig. 11.12)
G. Other ways to get proteins and molecules to the outer membrane
and beyond (Fig. 11.13, 11.14):
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