Lecture Notes on Prokaryote Gene Structure and Information Transfer (MCB2020F)

Prokaryote Gene Structure and
Information Transfer
RISE OF THE BACTERIA:................................................................................................................................. 2
FLOW OF GENETIC INFORMATION IN CELLS................................................................................................... 2
GENE STRUCTURE......................................................................................................................................... 2
GENE:....................................................................................................................................................................2
READING FRAME:.....................................................................................................................................................2
BACTERIAL GENE STRUCTURE:.....................................................................................................................................2
DNA.................................................................................................................................................................2
mRNA:.............................................................................................................................................................3
BACTERIAL OPERON:.................................................................................................................................................3
TRANSCRIPTION............................................................................................................................................ 3
PROKARYOTE TRANSCRIPTION INITIATION: (SIGMA FACTOR BINDS)....................................................................................4
PROKARYOTE TRANSCRIPTION ELONGATION:.................................................................................................................5
PROKARYOTE TRANSCRIPTION TERMINATION:................................................................................................................5
ANTIBIOTICS & CHEMICAL INHIBITORS THAT TARGET TRANSCRIPTION..........................................................5
GENETIC CODE.............................................................................................................................................. 6
CODON:..................................................................................................................................................................6
CODE DEGENERACY:..................................................................................................................................................6
NON-OVERLAPPING CODE:.........................................................................................................................................6
SENSE CODONS:.......................................................................................................................................................6
STOP CODONS:.........................................................................................................................................................6
TRANSLATION............................................................................................................................................... 6
PROTEIN SYNTHESIS:.................................................................................................................................................6
RIBOSOMES:............................................................................................................................................................6
AMINOACYL-TRNA:..................................................................................................................................................7
PROKARYOTIC TRANSLATION INITIATION:......................................................................................................................7
PROKARYOTIC TRANSLATION ELONGATION: (ENERGY DEPENDANT)....................................................................................7
PROKARYOTIC TRANSLATION TERMINATION:.................................................................................................................8
TRANSLATIONAL COUPLING IN POLYCISTRONIC MRNA..................................................................................8
ADVANTAGES:..........................................................................................................................................................8
PROKARYOTIC PROTEIN FOLDING & MODIFICATION.....................................................................................8
SUMMARY.................................................................................................................................................... 9




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, Prokaryote Gene Structure and
Information Transfer
Rise of the bacteria:
- There are 37-40 trillion human cells in a typical adult
- We have ±1.3 times more bacterial cells than human cells
- We are >65% bacterial and 35% human
o Human microbiome


Flow of genetic information in cells
- DNA replicated by DNA Polymerase
- DNA transcription by RNA polymerase
- DNA -> RNA -> Protein
- In viruses can go mRNA -> DNA



Gene structure

Gene:
- Basic unit of genetic information
- Polynucleotide sequence that codes for a functional product
- The linear sequence of nucleotides has a fixed start and end point
- A protein-coding gene results in a mRNA that can be ‘read’

Reading frame:
- mRNA read in discrete sets of 3 nucleotides termed a codon
- each codon codes for single amino acid
- organization of gene sequence results in reading frame that gives rise to a single
protein product
- certain viruses can have overlapping genes and therefore overlapping reading
frames which result in more than one protein product.
- Bacterial & viral coding info is continuous (no introns)

Bacterial Gene structure:

DNA
- DNA is double stranded and directional
- Coding strand (sense strand) = 5’ – 3’strand
- Template strand (antisense strand) = 3’ – 5’ strand
- DNA Has promoter and leader regions on left of coding region
- DNA Has trailer and terminator regions of right of coding region
- Promoter region:
o Located at start of gene

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