C. Bacteriology Module 2.3 Flashcards
[T or F] Bacterial reproduction is asexual.
True.
Bacteria reproduce asexually so progeny cells are identical to the parent cell.
[T or F] Bacteria reproduce asexually which prevents them from forming new genetic combinations.
False - Bacteria can still form new genetic combinations
(The bacterial genome may be subject to different forms of alterations that give rise to expression or appearance of characteristics not previously seen or observed in a species. )
Genetics came from the Latin word “genesis”, which means ______.
Birth/Generation
The science of inheritance or heredity.
Genetics
covers study ofthe composition of genes, how they carry information, how they are replicated and passed down through generations of cells or between organisms, and how the expression of their information within an organism affects the organism’s particularfeatures.
Genetics
A macromolecule composed of repeating units called nucleotides, hence a polynucleotide.
deoxyribonucleic acid (DNA)
[DNA] Each nucleotide consists of a ___________, ______________, and ____________.
pentose sugar (deoxyribose)
phosphate group
nitrogen-containing nucleobase
[DNA] What are the purine base nitrogen-containing nucleobase? What are the pyrimidine base nitrogen-containing nucleobase?
purine base: adenine (A), and guanine (G)
pyrimidine base: cytosine (C), and thymine (T).
The nucleotides are joined to one another in a chain by ___________ between the sugar of one nucleotide and the phosphate of the next, resulting in an ___________.
covalent bonds
alternating sugar-phosphate backbone
[T or F] According to base pairing rules, nitrogenous bonds bind the hydrogen bases of the two separate polynucleotide strands to make a double-stranded DNA. Thus, the sequence on one strand is complementary to that on the other.
False - hydrogen bonds bind nitrogenous bases
[T or F] Two strands of nucleotides are coiled around each other to form a double helix, a structure like a spiral ladder forming a double-stranded DNA that is helical.
True
Small sections of the DNA molecule that codes for production of proteins
Genes
Small sections of the DNA molecule that codes for production of proteins
Genes
the fundamental units of heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring.
Genes
The sum total of genes present in cell or organism
Genome
[T or F] Each genotype contains all of the information needed to build and maintain that organism.
False - Each genome […]
The genome size is expressed in _______.
Base pairs
For example, in humans, 3 billion base pairs (3 gbp) is are contained in all cells that have a nucleus.
The inheritable genetic makeup of an organism that codes for a particular trait.
Genotype
Refers to actual, expressed or observable trait and is governed by the genotype.
Phenotype
Among the bacteria, ___________, _________, _________, _________ are some of the environmental influences that may dictate whether the
genetic trait may be expressed or not.
temperature
pH
age
humidity
[T or F] Serratia marcescens form white colonies at 24 oC, and red colonies at 37 oC.
False - Serratia marcescens form red colonies at 24 oC, and white colonies at 37 oC.
Different types of DNA may be found in a bacterial cell. The genes are carried on: ___________, __________, ___________, or ___________.
bacterial chromosome
plasmid
phage
transposon.
Bacterial cell has ________ chromosome(s), which consists of a double-stranded DNA molecule arranged in a circular form.
Only one
[T or F] Most bacterial chromosomes are large, up to 1,000 um long, about 10 times the diameter of the cell.
False - 1,000 times the diameter of the cell
Bacterial chromosomes can range in size anywhere from about ____ kbp to ____ mbp, with 3,000 to 10,000 genes.
130 kbp to 14 mbp
Escherichia coli is about 4.6 mbp
Bacterial chromosome is found in the region of the
cytoplasm called ________.
nucleoid
All genes essential for bacterial growth are carried on ___________.
Chromosome
They are circular, double-stranded DNA.
Plasmids
They are small ranging from 1.5 to 400 kbp
[T or F] Plasmids are extra-chromosomal and can replicate autonomously in bacterial cells.
True
also known as bacteriophage, a bacterial virus
Phage
This are stable pieces of phage DNA
prophage
The process where stable pieces of phage DNA are inserted into bacterial chromosome.
lysogeny
a repressed virus — carried passively without replication and causing lysis of the infected bacterium
temperate phage
The ability of gene products to make bacteria more pathogenic.
lysogenic conversion
large, mobile genetic elements, with DNA sequences of several kbp , that can move themselves or a copy from one molecule of DNA to another, so are referred j to as “jumping genes”.
Transposons
referred j to as “jumping genes”.
Transposons
The process of transferring of transposons which can occur: plasmid to plasmid or plasmid to chromosome within bacterial cell.
transposition
genetic determinant in bacteria that can carry genes for specialized functions
plasmids and transposons
However, in contrast with plasmids, transposons do not contain genetic information for replication.
The unilateral transfer of genetic information from a donor cell to a recipient cell
Genetic exchange
Transferred genes can be stably incorporated into the recipient’s chromosome by ___________.
recombination
[T or F] Genetic exchange is not an essential step in the life cycle of bacteria.
True
(But, it is beneficial and may bring together combination of genes that enables the recombinant bacteria to carry out a valuable new function.)
the gene transfer from one bacterial cell to another involving direct cell-to-cell contact.
Conjugation
[Conjugation] F factor stands for ___________.
fertility plasmid
Conjugation is controlled by ____________ that carries the genes that code for sex pili formation which bring the two cells in physical contact.
F factor (fertility plasmid)
[T or F] Donor (male) cells have F factor, therefore form sex pili, meanwhile, Recipient (female) cells lack F factors and are called F- cells.
True
__________ have F factor in its “free state” (not incorporated into the bacterial chromosome); __________ have F factor that is “integrated” into the bacterial chromosome.
F+ cells; Hfr cells
The term Hfr denotes _______________, referring to the fact that Hfr cells donate copies of genes on the bacterial chromosome
high frequency of recombination
Two types of conjugal crosses:
a. F+ x F- conjugation
b. Hfr x F- conjugation
[Reading: not a question] Main difference between Hfr x F- conjugation to F+ x F- conjugation:
Note: Hfr x F- conjugation Transfer order: 1.first half of F factor 2.bacterial genes 3.integrated F factor
F+ x F- conjugation
transfer is quick so it is transferred in its entirety.
No genetic recombination and no transfer of bacterial genes.
Transfer in Hfr x F- conjugation takes approximately 90 mins and conjugative bridge is fine, so transfer is usually interrupted causing the entire genome of the donor cell not to be transferred completely which becomes a recombinant F-cell.
The uptake of free (or naked) extracellular DNA in the environment by a competent cell and subsequent integration into its chromosome by a competent
transformation
The recipient cell often acquires new characteristics as a result
[T or F] When a cell is destroyed, its genetic material is also destroyed.
False - Destruction of cell does not necessarily destroy its genetic material.
Competency is dependent on several factors. State the three:
• Stage of growth — logarithmic phase
• Alterations in the cell membrane that makes it permeable to the
DNA molecule
• Synthesis of receptor sites on the bacterial cell surface
Only a few bacterial species are capable of natural transformation since specific DNA sequences is required. Naturally competent transformable bacteria, of medical importance, are found in several genera and include:
Haemophilus influenzae
Neisseria gonorrhoeae
Neisseria meningitidis
Streptococcus pneumoniae
The procedure involves extraction of the DNA, and “treatment of cells with high salt” (e.g., CaCl2 ) and
“temperature shock” to render the cell membrane more permeable to DNA and make them readily take up DNA.
Artificial (or forced) transformation
transfer of DNA between bacteria by means of a phage (bacteriophage)
Transduction
Two major types of phage:
Virulent phage
Temperate phage
often have repressor genes to prevent phage replication; integrates their DNA into the bacterial chromosome where it stably stays as a prophage without lysing the host bacteria.— lysogeny
Temperate phage
infects bacterial cells, replicates, and and kills the
host bacteria, usually by lysing — lytic cycle.
Virulent phage
What are the two types of transduction?
Generalized transduction (mediated by virulent phages) Specialized transduction (mediated by temperate phages)
Occasionally, bacterial DNA are
packaged in a phage capsid by mistake —
these are called ______________.
transducing particles
Generalized transduction process:
- Attachment and infection
- Replication of the phage DNA
- Assembly and package
- Lysis of the host bacterium
summary: virulent phage DNA is injected into the bacterium where it replicated, packaged with bacterial phage, and then released. The released transducing particle infects other bacterium by injecting DNA and not viral nucleic acid since it cannot kill its host bacterium.
Specialized transduction process:
- Attachment and infection
- Lysogeny and lysogenic conversion
- Replication (entire bacterium)
- Continuous cell division showing no evidence of viral infection.
- Spontaneous induction
- Reactivation of phage DNA, assembly and package.
- Lysis of the host bacterium
The temperate phage is injected into the bacterium and instead of replicating, it integrates into the bacterium’s chromosome, leading the bacteriumto acquire new features. The bacterium is then replicated with the host chromosome, resulting in daughter cells that can produce temperate phages but lack evidence. The prophage DNA gradually cutsitself out of the bacterial chromosome,then replicates, while the progeny temperate phages accumulate within a capsid and detach from the bacterial chromosome with abacterial DNA, allowing them to become specialized transducing particles. The host bacterium is then lyzed, allowing infectious phages to escape.
Summary: The temperate phage is injected into the bacterium and instead of replicating, it integrates into the bacterium’s chromosome, leading the bacteriumto acquire new features. The bacterium is then replicated with the host chromosome, resulting in daughter cells that can produce temperate phages but lack evidence. The prophage DNA gradually cutsitself out of the bacterial chromosome,then replicates, while the progeny temperate phages accumulate within a capsid and detach from the bacterial chromosome with abacterial DNA, allowing them to become specialized transducing particles. The host bacterium is then lyzed, allowing infectious phages to escape.
Phage-coded pathogenic factors:
- O antigen of Salmonella
- Botulinum toxin of Clostridium botulinum (causing botulism)
- Erythrogenic toxins of Streptococcus pyogenes (causing scarlet fever)
- Diphtheria toxin of Corynebacterium diphtheriae
a permanent alteration in the base sequence of the gene (DNA) resulting in phenotypic change
Mutation
3 Mechanisms of mutation:
- Insertion
- Deletion
- Substitution
takes place when a nitrogenous base (nucleobase) is “added” to the nucleotide sequence.
Insertion.
the “removal” of a nucleobase from the nucleotide chain.
Deletion
arise when there is mispairing between complementary bases. It occurs when one or more nucleobases in a
nucleotide sequence is replaced with another base.
Substitution
[T or F] Mutations can be spontaneous, or induced by a mutagen in the environment.
True
a random, undirected alteration of the DNA base sequence that arise as a consequence of mistakes in DNA replication.
Spontaneous mutation
[T or F] Spontaneous mutation is natural.
True
caused by exposure to external influences or agents that result in the DNA to breakdown.
Induced mutation
agents that induce mutations are collectively referred to as
mutagens
external influences that causes induced mutation
chemicals radiation viruses diet lifestyle.
converts the nucleobase adenine (A) to a form that no longer pairs with thymine (T) but cytosine (C). Thus, when DNA containing such modified adenines replicates, one daughter DNA molecule will have a base-pair sequence different from that of the parent DNA.
Nitrous acid (HNO2)
ionize atoms and molecules with the formation of highly reactive ions and free radicals. Some of these ions can combine with bases in DNA, resulting in errors in DNA replication and repair that produce mutations.
X rays and gamma rays
a non-ionizing component of ordinary sunlight. Its most important effect on DNA is the formation of harmful covalent bonds between certain bases. Adjacent thymines in a DNA strand can cross-link to form thymine dimers. Such dimers, unless repaired, may cause serious damage or death to the cell because it cannot properly transcribe or replicate such DNA.
Ultraviolet (UV) light
The transfer of either a chromosomal DNA or plasmid through a sex pilus is called
Conjugation
Genetic recombination requires a competent cell
Transformation
results from a permanent change in the base sequence of a gene through natural or artificial means
mutation
