Med microbiology exam 3

the study of inheritance, or heredity of living things

Genetics

the sum total of genetic material of an organism ( exists in the form of chromosomes)

Genome

a distinct cellular structure composed of a neatly packaged DNA molecule

chromosome

somatic cells

Reproductive cells that reproduce my mitosis

sperm cells and ovum cells

Reproductive cells that reproduce my meiosis

• DNA wound around histone proteins
• Located in the nucleus
• Diploid (in pairs) or haploid (single)
• More-or-less linear appearance

Eukaryotic chromosomes

• DNA condensed into a packet by means of histone-like proteins
. Mostly one chromosome with some exceptions

Bacterial chromosomes

Ø Structural genes that code for proteins
Ø Genes that code for RNA machinery used in protein production
Ø Regulatory genes that control gene expression

Three categories of genes

the sum of all gene types; an organism's distinctive genetic makeup

Genotype

the expression of the genotype creates traits (structures or functions)

Phenotype

discovered DNA in 1869

Meischer

discovered genes composed of DNA in 1944

Avery, MacLeod & McCarty

•Discovered the structure of DNA by reviewing the work of Rosalind Franklin (x-ray diffraction)
•A type of nucleic acid
•Two strands combined into a double helix in 1953

James Watson and Francis Crick

basic unit of DNA structure(Phosphate, Deoxyribose, Nitrogenous base)

Nucleotide

join with complementary bases using weak hydrogen bonds.

Purines and pyrimidines

thymine (T)

Adenine (A) always pairs. with

cytosine (C)

Guanine (G) always pairs with

one side of the helix runs in the opposite direction of the other

Antiparallel arrangement

Unzipping the DNA helix

Helicase (enzyme)

Helping to untangle the DNA supercoils

Gyrase (enzyme)

Synthesizing an RNA primer

Primase (enzyme)

Adding bases to the new DNA chain; proofreading the chain for mistakes

DNA polymerase III (enzyme)

Removing primer, closing gaps, repairing mismatches

DNA polymerase I (enzyme)

Final binding of nicks in DNA during synthesis and repair

Ligase (enzyme)

Supercoiling and untangling

Topoisomerase I and II (enzyme)

False

When DNA is replicated, two brand-new nucleotide strands are produced

master code of DNA that is first used to synthesize an RNA molecule

Transcription

transcribed RNA used to produce protein

Translation

•RNA viruses convert RNA to other RNA
•Retroviruses convert RNA to DNA

Exceptions of transcription and translation

RNA polymerase binds to promoter

transcription initiation

the RNA chain is extended

Transcription Elongation

RNA polymerase detaches from the DNA, after the transcript is made

Transcription Termination

. Contains uracil (U) instead of thymine.( AU no AT)
. Contains ribose rather than deoxyribose
• Can form secondary and tertiary levels of complexity, leading to specialized forms of RNA (tRNA and rRNA)

Difference of RNA and DNA

messenger RNA, transfer RNA, ribosomal RNA

Three RNA's involved in Translation

groups of three nucleotides that dictate which amino acid is added to the growing peptide chain

Codon

RNA that copies the coded message from DNA in the nucleus and carries the message into the cytoplasm

messenger RNA

type of RNA molecule that carries amino acids to ribosomes during translation.

Transfer RNA

type of RNA that combines with proteins to form ribosomes

ribosomal RNA

tRNA

RNA that has Hairpin loops

70S size

Ribosomes found in bacteria, mitochondria, and chloroplasts are

80S size

Eukaryotic ribosomes are

64

How many codons are there?

20

How many amino acids are there?

UAA, UAG, UGA

What are the stop codons?

AUG

What is the start codon?

a process where one bacterial cell donates DNA to another.

DNA recombination

any organism that contains genes that originated in another organism

Recombinant

Direct donor cell with pilus
Fertility plasmid in donor
Both donor and recipient are alive
Bridge forms between cells to transfer DNA

Conjugation (E. coli)

Indirect Free donor DNA (fragment)
Live; competent recipient cell

Transformation donor

Indirect donor is lysed bacterial cell; Defective bacteriophage is a carrier of donor DNA;
Live recipient cell of the same species as the donor

Transduction.

Any transfer of DNA that results in organisms acquiring new genes that did not come from parent organisms

Horizontal Gene

•Small, circular pieces of DNA
•Contain their own origin of replication
•Replicate independently
•Not necessary for survival
•Can carry useful traits

Plasmids

Must integrate into the bacterial chromosome in order to be replicated

Chromosomal fragments:

Donor plasmid that allows the synthesis of a pilus in bacterial conjugation. The presence of the factor is indicated by F+, and the lack of the factor is indicated by F-.

Fertility "F" factor (conjugation)

the plasmid becomes integrated into the F+ donor chromosome

when replicated, begins to transfer to the recipient cell

some chromosomal genes get transferred to the recipient

plasmid genes may or may not be transferred

High-frequency recombination (Hfr) donors

an opening is created between two adjacent cells, replicated DNA passes across from one cell to another

Gram-positive conjugation

is a conservative process in which the donor bacterium retains ("conserves") a copy of the genetic material being transferred.

Conjugation

Bear genes for resisting antibiotics or other drugs
Commonly shared among bacteria through conjugation
Can confer multiple resistance to antibiotics
R factors can also carry genetic codes for resistance to heavy metals, or synthesizing virulence factors

Resistance (R) plasmids or factors

•Nonspecific acceptance by a bacterial cell of small fragments of DNA from the environment
•Facilitated by DNA-binding proteins on the cell wall.

Transformation

cells that are capable of accepting genetic material

Competent

similar process to transformation carried out in eukaryotic cells to form genetically engineered yeasts, plants, and mice

Transfection

•Bacteriophage serves as a carrier from a donor cell to a recipient cell
•Random fragments of disintegrating host DNA are taken up by the bacteriophage
•Virtually any gene from the bacterium can be transmitted

Generalized transduction

•Highly specific part of the host genome is regularly incorporated into the virus
•Explained by the prior existence of a temperate prophage inserted in a fixed site on the bacterial chromosome
•When activated, prophage DNA separates from the bacterial chromosome, carrying a small segment of host genes with it
•During the lytic cycle, these specific viral-host gene combinations are incorporated into the viral particles and carried to another bacterial cell

Specialized transduction

D. Transduction

Which of the following mechanisms of horizontal transfer involves the transfer of bacterial DNA through a bacteriophage?
A. Transposition
B. Conjugation
C. Transformation
D. Transduction
E. None of the choices is correct.

Genetic change is the driving force of evolution (Any change to the nucleotide sequence in the genome is a mutation)

Mutations

a microorganism that exhibits a natural, nonmutated characteristic

Wild type

•Morphology
•Nutritional characteristics
•Genetic control mechanisms
•Resistance to chemicals
•Temperature preference
Any type of enzymatic function

Mutant strain shows variance in one or more of the following

a random change in the DNA arising from errors in replication

Spontaneous mutation

results from exposure to known mutagens, physical or chemical agents that disrupt DNA:
•Radiation: UV light, X rays
•Chemicals: nitrous acid

Induced mutation

addition, deletion, or substitution of single bases

Point mutation

•Any change in the code that leads to the placement of a different amino acid
•Can create a faulty, nonfunctional protein
•Can produce a protein that functions differently
•Can cause no significant alteration

Missense mutation

changes a normal mutation into a stop codon.

Nonsense mutation

alters a base, but does not change the amino acid, and has no effect

Silent mutation

when a gene that has undergone a mutation reverses back to its original base composition

Back-mutation

•One or more bases are inserted or deleted
•Changes the reading frame of the mRNA
•nearly always results in a nonfunctional protein

Frameshift mutation

-Requires visible light and a light-sensitive enzyme, DNA photolyase
-Successful only for a small number of UV mutations
-Cells cannot repair severe, widespread damage and will die

UV damage repair

•Enzymes break the bonds between the bases and the sugar-phosphate strand at the site of the error
•A different enzyme removes the defective bases, one at a time
•The remaining gap is filled in by DNA polymerase I and ligase

Excision repair

permanent and heritable

Mutations are.................... and will be passed on to the offspring of organisms

B. Frameshift mutation

Which of the following types of mutations will have the most devastating effect on a cell?
A. Point mutation
B. Frameshift mutation
C. Missense mutation
D. Nonsense mutation
E.Silent mutation

Mutations are permanent and heritable and will be passed on to the offspring of organisms:
•Most spontaneous mutations are not beneficial
•A small number create variant strains that more readily adapt, survive, and reproduce
As long as the environment is stable, mutants only comprise a small percentage of the population:
•When the environment changes, some mutants will be equipped to survive in the new environment
•Acquired drug resistance is a clear model for this type of selection and adaptation

Positive and Negative Effects of Mutations

1940s

The introduction of modern drugs to control infections was a medical revolution in the

Administer a drug to an infected person that destroys the infective agent without harming the host's cells

Goal of antimicrobial chemotherapy

- Be easy to administer and able to reach the infectious agent anywhere in the body
- Be toxic to the infectious agent and non-toxic to the host
- Remain active in the body as long as needed and be safely and easily broken down and excreted

A drug must be able to

•Toxic to the microbe but nontoxic to host cells
•Microbicidal rather than micro bistatic
•Relatively soluble; functions even when highly diluted in body fluids
•Remains potent long enough to act and is not broken down or excreted prematurely
•Does not lead to the development of antimicrobial resistance
•Complements or assists the activities of the host's defenses
•Remains active in tissues and body fluids
•Readily delivered to the site of infection
•Does not disrupt the host's health by causing allergies or predisposing the host to other infections

Characteristics of the Ideal Antimicrobial Drug

Use of a drug to prevent infection of a person at risk

Prophylaxis

The use of drugs to control infection

Antimicrobial Chemotherapy

All-inclusive term for any antimicrobial drug, regardless of its origin

Antimicrobials

Substances produced by the natural metabolic processes of some microorganisms that can inhibit or destroy other microorganisms; generally, the term is used for drugs targeting bacteria and not other types of microbes

Antibiotics

Drugs that are chemically modified in the laboratory after being isolated from natural sources

Semisynthetic Drugs

Drugs produced entirely by chemical reactions

Synthetic Drugs

Antimicrobials effective against a limited array of microbial types—for example, a drug effective mainly against gram-positive bacteria

Narrow-Spectrum (Limited Spectrum)

Antimicrobials effective against a wide variety of microbial types—for example, a drug effective against both gram-positive and gram-negative bacteria.

Broad-Spectrum (Extended Spectrum)

•Produced to inhibit the growth of competing microbes in their habitat

Antibiotics are originally metabolic products of bacteria and fungi:

•Bacteria in the genera Streptomyces and Bacillus
•Molds in the genera Penicillium and Cephalosporium

Greatest numbers of antibiotics derived from

- The identity of the microorganism causing the infection
- The degree of the microorganism's susceptibility (also called sensitivity) to various drugs
- The overall medical condition of the patient

What three factors must be considered before actual antimicrobial therapy can begin?

•Should occur before antimicrobial drugs are given and before their numbers are reduced
•Direct examination of body fluids, sputum, or stool samples is a rapid method for the detection
•Doctors often begin "empiric therapy" on the basis of immediate findings and informed guesses
Epidemiological statistics may be required

Identification of infectious agents should ideally begin as soon as possible

•Staphylococcus species
•Neisseria gonorrhoeae
•Enterococcus faecalis
•Aerobic, gram-negative intestinal bacilli

Testing for drug susceptibility is necessary for which organisms?

•Surface of an agar plate is spread with test bacterium (for example)
•Small discs containing a prepared amount of antibiotic are placed on the plate
•Zone of inhibition surrounding the discs is measured and compared with a standard for each drug

Kirby-Bauer technique

provide data for drug selection

Antibiograms

More sensitive and quantitative than the Kirby-Bauer test
Antimicrobial is diluted serially in tubes of broth
Each tube is inoculated with a small uniform sample of pure culture, incubated, and examined

Tube Dilution Test