Bacterial Genetics, Metabolism, and Structure Flashcards
*the process of heredity and variation
*starting point from which all other cellular pathways,
functions, and structures originate
genetics
factor that contributes to the ability of a
microorganism to maintain viability, adapt, multiply, and
cause disease is determined by:
genetic composition
THREE major aspects of microbial genetic composition
- The structure and organization of genetic
material
• Replication and expression of genetic information
• The mechanisms by which genetic information is
altered and exchanged among bacteria
most common macromolecule that encodes genetic
information
DNA (Deoxyribonucleic Acid)
plays an essential role in several of the
genetic processes in prokaryotic and eukaryotic cells,
including the regulation and transfer of information
RNA (Ribonucleic acid)
DNA structure:
deoxyribose sugars connected by phosphodiester bonds (Covalent linking of bases)
composition of an intact DNA
5’ (prime) phosphate
and a 3’ (prime) hydroxyl terminus (nucleotide polymers)
direction of 2 DNA strands
antiparallel direction
arrangements of strands
complementary:
adenine (purine)=thymine (pyrimidine) (2 hydrogen bonds)
cytosine (pyrimidine)=guanine (purine) (3 hydrogen bonds)
- thymine is replaced by uracil in RNA sequence
- hydrophobic in nature
structural conformation of DNA
twisted ladder/double helix
The three major types of RNA
messenger RNA [mRNA], transfer RNA
[tRNA], and ribosomal RNA [rRNA]
PLAY KEY ROLE IN GENE EXPRESSION
important fact about RNA
it is NOT double stranded
A DNA sequence that encodes for a specific product
RNA or protein
gene
All the genes in an organism comprise the organism’s:
genome
size of a gene and an entire genome is usually
expressed in:
base pairs (bp) present
organization/arrangement of a genome into discrete elements
chromosome (usually arranged in a linear fashion)
since bacteria are prokaryotes, the chromosome…
the chromosome is not located in a membrane-bound organelle
arrangement of the bacterial chromosome
doublestranded, closed, circular macromolecule
– extensively folded and twisted (i.e., supercoiled) — in order to fit the confined space of the bacterial cell
aside from the chromosome, bacterial genes may also be found in what extrachromosomal elements
plasmids and transposable elements
— not stable and may be lost during replication
structure of plasmids
double-stranded, closed, circular,
autonomously replicating extrachroosomal genetic elements ranging in size from 1 to 2 kilobases up to 1 megabase or more
other notable characteristics of plasmids:
- do not code for cell viability
- may also become incorporated into the
chromosome
pieces of DNA that move from one genetic element to another, from plasmid to
chromosome or vice versa
transposable elements
other notable characteristics of transposable elements
- they are unable to replicate independently
* do not exist as separate entities in the bacterial cell
two types of transposable elements
1) simple transposon or insertion sequence (IS)
2) composite transposon
transposon that is limited to containing the genes that
encode information required for movement from one
site in the genome to another
simple transposon/ insertion sequence
transposon that is a cassette (grouping of genes) flanked by insertion sequences
composite transposon
this is imbedded in the insertion
sequence encodes for an accessory function, such as antimicrobial resistance
internal gene
four stages of replication:
- Unwinding or relaxation of the chromosome’s
supercoiled DNA – allows enzymes and cofactors to access DNA - Separation of the complementary strands of the
parental DNA so that each may serve as a template
(i.e., pattern) for synthesis of new DNA strands - Synthesis of the new (i.e., daughter) DNA strands
- Termination of replication, releasing two identical
chromosomes, one for each daughter cell
the origin of replication is recognized by:
several initiation proteins, followed by the separation of the complementary strands of parental DNA
site of active replication
replication fork (bidirectional forks)
notable on replication forks:
- each replication fork moves through the parent DNA molecule in opposite directions so that replication is a bidirectional process
- involves different cofactors and enzymes, with DNA polymerases playing a central role
termination of replication happens when:
when the replication forks meet
the processing of information encoded
in genetic elements (i.e., chromosomes, plasmids, and
transposons), which results in the production of biochemical molecules, including RNA molecules and proteins
gene expression
complex steps in gene expression (in order)
transcription and translation
beginning of transcription:
DNA -> mRNA (complementary to to gene’s DNA sequence)
— only one of the two DNA strands become the sense strand - encodes for functional gene product and template for mRNA synthesis
enzyme central to the transcription process
RNA polymerase
composition of RNA polymerase
sigma factor and 4 protein subunits
role of sigma factor in RNA polymerase
to identify the appropriate site
on the DNA template where transcription of mRNA is
initiated
other name for initiation site
promoter sequence
direction of transcription
5’ to 3’ direction
In bacteria, the mRNA molecules that result from the
transcription process are:
polycistronic — encode for several gene products
When a cluster of genes is under the
control of a single promoter sequence, the gene group
is referred to as:
operon
phase in gene expression that involves protein synthesis
translation — responsible for protein structure and function
genetic code consists of triplets of nucleotide
bases, referred to as:
codons
Ribosomes (compact nucleoproteins) components
rRNA and proteins
- – central to translation
- – assisting with coupling of all required components and controlling the translational process
three steps of translation
initiation
elongation
termination
association of ribosomal subunits, mRNA, formylmethionine tRNA ([f-met] carrying the initial amino acid of the protein to be synthesized), and various initiation factors
initiation
involves tRNAs mediating the sequential
addition of amino acids in a specific sequence that is
dictated by the codon sequence of the mRNA molecule
elongation
arrangement wherein multiple
ribosomes may be simultaneously associated with
one mRNA molecule
polysome
appearance of polysome
string of pearls
the final step in translation, occurs when
the ribosomal A site encounters a stop or nonsense
codon that does not specify an amino acid (stop codons)
termination
process wherein most proteins must undergo modification, such as folding or enzymatic trimming, so that protein function,transportation, or incorporation into various cellular structures can be accomplished
posttranslational modification
Genetic alterations and diversity in bacteria are accomplished by three basic mechanisms:
mutation
genetic recombination
exchange between bacteria (with or without recombination)
defined as an alteration in the original nucleotide sequence of a gene or genes within an organism’s
genome
mutation
— arise spontaneously
In this process, some segment
of DNA originating from one bacterial cell (i.e., donor)
enters a second bacterial cell (i.e., recipient) and is
exchanged with a DNA segment of the recipient’s
genome
homologous recombination
—occurs frequently
protein that plays a central role in genetic recombination
RecA protein
three mechanisms by which bacteria physically
exchange DNA
transformation
transduction
conjugation
involves recipient cell
uptake of naked (free) DNA released into the environment when another bacterial cell (i.e., donor) dies and undergoes lysis
transformation
— genomic DNA exists as fragments in the environment
second mechanism by
which DNA from two bacteria may come together in one cell, thus allowing for recombination
process is mediated through viruses capable of infecting bacteria (i.e., bacteriophages)
transduction
process occurs
between two living cells, involves cell-to-cell contact,
and requires mobilization of the donor bacterium’s chromosome
conjugation
considered the utilization of metabolic pathways involved in the acquisition of nutrients from the
environment, production of precursor metabolites, and
energy production
fueling
