Bacterial Genetics Flashcards
Discovered DNA
FREDERICK MIESCHER (1869)
Discovered that DNA contained phosphates, five-carbon sugars (cyclic pentose), and nitrogen containing bases.
PHOEBUS A.T LEVINE (1920S)
Discovered the helical structure by x-ray crystallography
ROSALIND FRANKLIN
Described the three-dimensional structure of the DNA molecule.
JAMES WATSON AND FRANCIS CRICK
● Process of heredity and variation
● Ability to maintain viability, adapt, multiply, and cause disease is determined by the organism’s genetic composition
GENETICS
3 MAJOR ASPECTS OF MICROBIAL GENETICS
- Structure and organization of genetic material
- Replication and expression of genetic information
- Mechanisms by which genetic information is altered and exchanged among bacteria
● double helical chain of nucleotides
● helix is a double strand twisted together, referred to as a “spiral staircase”
● information contained in DNA is determined primarily by the base sequence—Genetic Code
● involved in the production of RNA
DNA molecule
● Is a complex combination of the following:
A. A phosphate group (PO4)
B. A cyclic five-carbon pentose sugar (deoxyribose)
C. A nitrogen-containing base, or the “steps,” either a purine or a pyrimidine
Nucleotide
single-stranded and short, not double-stranded and long, and contains the sugar ribose, not deoxyribose
RNA molecule
Three major types of RNA:
A. messenger RNA (mRNA)
B. transfer RNA (tRNA)
C. ribosomal RNA (rRNA)
a DNA sequence that encodes for a specific product (RNA or protein)
Gene
all the genes in an organism
Genome
organized genome into discrete elements
CHROMOSOMES
● contain a single, unpaired (i.e., haploid) chromosome
● contains the genes essential for viability and exists as a double-stranded, closed, circular macromolecule
BACTERIAL CHROMOSOME
EXTRACHROMOSOMAL ELEMENTS
Plasmids
Transposable Elements
double-stranded, closed, circular, autonomously replicating extrachroosomal genetic elements
Plasmid
Genes encode for:
● products that mediate plasmid replication and transfer between bacterial cells
● products that provide a specialized function, such as determinants of antimicrobial resistance or a unique metabolic process
● Do not usually encode for products essential for viability.
● pieces of DNA that move from one genetic element to another
● unable to replicate independently
● do not exist as separate entities in the bacterial cell
Transposable Elements
2 types if Transposable Elements
Simple Transposon or Insertion Sequence (IS)
Composite Transposon
contain the genes that encode information required for movement from one site in the genome to another
Simple Transposon or Insertion Sequence (IS)
cassette (grouping of genes) flanked by insertion sequences
Composite Transposon
● complex process mediated by various enzymes, such as DNA polymerase and cofactors
1. Unwinding of the chromosome’s supercoiled DNA
2. Separation of the complementary strands of the parental DNA
3. Synthesis of the new DNA strands
4. Termination of replication, releasing two identical chromosomes, one for each daughter cell
Process generally takes approximately 20 to 40 minutes in rapidly growing bacteria such as E. coli
Replication
● processing of information encoded in genetic elements (i.e., chromosomes, plasmids, and transposons)
● results in the production of biochemical molecules, including RNA molecules and proteins
EXPRESSION OF GENETIC INFORMATION
○ Synthesis of single-stranded RNA using one strand of the DNA as a template
○ DNA base sequence of the gene is converted into an mRNA molecule
TRANSCRIPTION
● involves protein synthesis
● mRNA molecules is translated into specific
amino acid sequences that are responsible for protein structure and function
TRANSLATION
GENETIC EXCHANGE AND DIVERSITY
Three basic mechanisms:
Mutation
Genetic recombination
Genetic exchange
● alteration in the original nucleotide sequence of a gene or genes within an organism’s genome
● change in the organism’s genotype
● induced by chemical or physical factors (mutagens) or by biologic factors
Maturation
● segment of DNA originating from one bacterial cell (donor) enters a second bacterial cell (recipient) and is exchanged with a DNA segment of the recipient’s genome
● pieces of DNA are usually have extensive similarities in nucleotide sequences
● involves a number of binding proteins
GENETIC RECOMBINATION
Three mechanisms of genetic exchange
TRANSFORMATION
Transduction
Conjunction
● Cells that can take up naked DNA
● Example: Streptococcus pneumoniae, Neisseria
gonorrhoeae, H. influenzae
Competent
Type of transduction where bacterial DNA may be randomly incorporated with viral DNA
GENERALIZED TRANSDUCTION
Type of transduction that is incorporated along with adjacent viral DNA
SPECIALIZED TRANSDUCTION
● transfer of genetic material from a donor bacterial strain to a recipient strain
● Occurs between two living cells, involves cell-to-cell contact, and requires mobilization of the donor bacterium’s chromosome
● Plasmids and transposons—transferred by conjugation
Conjugation
