Bacterial Genetics Flashcards
How are genes collected in a bacteria
On a single chromosome (circular module of double helix DNA) and on plasmids. Bacterial chromosomes are smaller then human
DNA Characteristics
Bases: A,T,G and C. Double helixes antiparallel (1 read 5’-3’ and other 3’-5’). Progresses in wrappping from double stranded DNA, double helix and supercoiled DNA
Supercoiled DNA outline
Twisting DNA further after double helix (done in bacteria). Makes the DNA small enough to fit into a bacterial cell. Enzyme topoisomerase are needed to wind (positive supercoil) and unwind (negative supercoil) supercoiled DNA
DNA Gyrase Outline
Also known as topoisomerase 2. Negative supercoil enzyme, Inhibited by quinolones (antibiotics that kill bacteria)
How is DNA semi-conservative
During binary fission DNA replicates into 2 double stranded chromosomes. Each new chromosome has 1 strand of the old DNA helix
Helicase Function
Unwinds double stranded DNA to single stranded DNA during elongation
Leading strand
DNA Polymerase Omega builds a new strand of DNA by combining DNA bases in the 5’-3’ direction continuously
Lagging Strand Outline
DNA Polymerase Delta builds a new strand of DNA by using RNA primers to form discontinuos segments of DNA in the 5’ to 3’ direction. DNA ligase sticks these Okazaki Fragments together forming a full strand. Takes longer
Faults in DNA Replication
A possible change in a base sequence can lead to different gene expression, resulting in differnt protein producton and mutation. Counter balanced by DNA omega and delta has proof reading
Operons Outline
Group of genes. Rare in eukaryotes found mainly in prokaryotes. They are controlled by the same promoter/inhibitors
What types of prokaryotic cells can transcription occur in
Lial
Rifampicin Def
Antibiotic that prevents DNA transcription in bacteria
How many possible codons and amino acids exists
64 codons and 20 amino acids. Codons groups can be redundant
2 translation ribosomal sub units
30S and 50S. Complex breaks up to release proteain
Where does tRNA enter complex
Acceptor (A) site
Where does tRNA enter complex
Peptide (P) site
How do antibiotics stop translation
Antibiotics bind to mRNA
Where is gene expression mainly controlled
translation eg some bacteria begin to produce biofilm during extreme conditions, antibiotic ressistance and spore formation
Plasmids outline
Circular extra-chromosomal DNA. Replicates independently and moves between cells passing on genes not necessary for functioning but are advantagous mutations (eg antibiotic ressistance)
Nosocomial Def
Infections acquired in hospitals. Have a higher chance of being antibiotic resistance due to higher density and thus closer contact of bacteria for plasmid transfer. Harder to treat
Plasmid Use
Genetic engineering. Gene of interest is inserted into spliced plasmid and of uptake is successful bacteria will produce beneficial proteins eg insulin
Virulence Def
Production of toxins
3 Types of Mutation
Base deletion, base addition and base substitution
Silent Mutation Def
Change in base sequences where protein production isn’t impacted due to new codon coding for the same amino acid as the old 1 (codon redundancy) or specific amino acid change doesn’t impact protein function
Impacts of base insertion/deletion mutation on mRNA
How bases are read is shift (different group of 3 codons then there was originally). This may result in a reading of a stop codon before the end of the mRNA resulting in the end of that protein’s formation. This results in a non-functional (truncated protein)
4 ways of genetic exchange between bacteria
Transformation, Conjugation, Transduction and Transposition
Transformation Outline
Host cell takes up plasmid or DNA scraps. Most of the time DNA is degenerated (foreign material) but sometimes it is accepted and the genes are thus exptressed. Eg of natural streptococcus pnuemonia
Conjugation Outline
Bacteria cells transfer tra genes (in plasmid) to eachother when in contact through conjugate pilli. Plasmid denatures in new cell and single DNA strand has a complememtary strand synthesised (cells seperate only after DNA double helix is formed in recieving cell). This can be done between all bacteria (eg gram positive and gram negative can exchange plasmids with eachother)
Transduction Outline
Bacteriophage (virus) degrades DNA of host bacteria and inserts it’s own. New bacteriaphages are synthesised in cell and released in lysis. Pahge then infects difffernt cell intergrating it’s DNA with that cell’s chromosome
Transposition Outline
DNA sequences move from chromosome to plasmid in the same cell carried by transposases enzymes. can result in beneficial mutation (and passing it on) but can also disrupt genes
2 Types of microorganism testing
Susceptibility (see what antimicrobials effect growth of species, long time) or molecular (analyse sample for it’s DNA/RNA, faster)
Strain Typing
Identifying bacteria based on their genetic code. Used for diagnosis and treatment
Molecular Methods of Strain Typing
PCR, DNA probes (fluoresce after DNA binding (notes presence/absence)), Pulse Field Gel Electrophoresis (DNA finger printing) and whole genome sequencing (through computer algorithims)
PCR Outline
Identification and quantification of pathogens and their mutations. Target DNA is extracted from sample, thermal DNA denaturing, primer annnelaing (changing chemical properties) and extension of primers by DNA polymerase. This
REverse transcriptase PCR Outline
Used when target molecule is RNA
PCR Advantages
Fast, Sensitive and Easy
PCR Disadvantages
expensive and cross over of contamination
PCR for TB
Detection of TB in sputum. Difficult to grow. Specific genes for early diagnosis and treatment. TB is non-culturable disease thus can’t be grown in lab.
