Unit 3.1 Bacterial Genetics

cellular functions of proteins

C, H, O, N, S, amino acids (20), enzymes, transporters, produces and kills bacteria, contraction, movement of microbial and cells, hormones, antibodies

pyrimidines

T, C, U, single ring nucleotide

purines

A, G, double ringed nucleotide

nucleotides

nitrogen containing base, pentose sugar, phosphate group,

adenine (A)

guanine (G)

cytosine (C)

thymine (T)

uracil (U)

antiparallel structure of DNA

paired DNA oriented in opposite directions

DNA replication in eukaryotic cells

supercoiling is relaxed by topoisomerase or gyrase, the dna strands are unwound by helicase and separated from each other, free nucleotides in the cytoplasm match up with the exposed bases of the exposed parent DNA. the nucleotides are then joined by dna polymerase (adds to 3’ end) then replication fork moves further . newly synthesized strand is semi conservative since new dss dna contained one parental strand

process of DNA replication in prokaryotic cells

bidirectionally around chromosomes, two replication forks that move in opposite directions away from origin of replication, since closed loop the replication fork eventually meet when replication is complete. the two loops are then speared by topoisomerase.

gene

determine all hereditary traits, control all the activities that take place within cells, sequence of nucleotide, code for functional products

translation

converting nucleic acids to proteins

transcription in prokaryotes

synthesis of a complementary strand of RNA from a DNA template, RNA poly. binds to promoter and dna unwinds at the beginning of a gene —> ran is synthesized by complementary base pairings of free nucleotides with he nucleotide bases on the template strand of DNA —> site of synthesis moves along dna, dna that has been transcribe rewinds —> transcription reaches terminator —> complete RNA strand RNA and RNA poly are released and DNA helix reforms

how is gene expression regulated by repression (repressive operons) (trp operon)

structural genes are transcribed until they are turned off. genes for the enzymes involved in the synthesis of tryptophan are regulated in this manner. genes are transcribed and translated leading to tryptophan synthesis, when present tryptophan acts as an corepressor and binds to the repressor protein so the protein can bind to the operator and stop further tryptophan production

how is gene expression regulated by induction

absence of lactose repressor binds to the operator site thus preventing transcription, in presence the repressor binds to a metabolite of lactose instead to the operator and lactose digested enzymes are transcribed

trp operons

lac operons

needed to metabolize lactose, inducible operon

central dogma chain of events

dna —> mrna —> protein —> function

mutations

base substitution and frameshift, permanent change in base sequence of DNA,

base substitution/ point mutation

a single DNA pair is altered, incorrect base of Mrna translated into protein incorrect amino acid

frameshift mutation

dna pairs are added or removed from the sequence causing a short in the sequencing reading, shift translational reading frame, trna during translation

Ames test

uses bacteria as a carcinogen (substance that cause cancer) indicator, based on observation that exposure of mutant bacteria to mutagenic substances may cause new mutations that reverse the effect (change in phenotype) of the original mutation (reversions), reversion of histamine auxotrophs

transformation

genes transferred from one bacterium to another as naked DNA in solution

conjugation

mechanism by which genetic material is transferred from one bacterium to another mediated by conjugative plasmid, differed from transformation because requires cell to cell contact & cells must be opposite mating type (donor cells must carry plasmid and recipient cells usually do not. used to map location of genes in bacterial chromosomes

transduction

mechanism of genetic transfer between bacteria, bacterial DNA is transferred from a donor cell to bacteriophage (a recipient cell inside a virus that infects bacteria)

factors that contribute to rapid evolution of microorganisms

mutation, horizontal gene transfer, generation time, population size

horizontal gene transfer

bacteria passing genes laterally to other microbes in the same generation

DNA ligase

makes covalent bonds to join DNA strands, Okazaki fragments, and new segments in excision repair

DNA polymerase

synthesize DNA, proofread and facilitate repair DNA, adds nucleotides to 3’ end only this makes two new strands of DNA grow in diff directions

helicase

unwinds dss DNA

Okazaki fragment

fragments of about 1000 nucleotides that make lagging strand

replication fork

unwound part of parental DNA and the point at which replication occurs

primase

an RNA polymerase that makes RNA primers from a DNA template

leading strand

synthesized continuously from 5’→3’

lagging strand

new DNA synthesized discontinuously in fragments (Okazaki fragments), joined later by ligase to make continuous strand

origin of replication

where dna replication starts

topoisomerase/ gyrase

relaxes supercoiling ahead of the replication fork, separates DNA circle at the end of DNA replication

DNA gyrase

relaxes supercoiling ahead of the replication fork

complementary strand of dna

because of specific base pairing one strand determines the sequence of this one, runs 5’ to 3’

peptide bond

bonds between amino acids, one water molecule is released when this is formed by dehydration synthesis

genome

genetic information in a cell

promotor

the site where the RNA polymerase binds to DNA, start of transcription

F+ cells

donors carrying f factors (fertility factor)

F- cells

transfer plasmid recipients

operon

group of genes that are transcribed together and controlled by one promoter

Hfr cell

high frequency of recombination, in some cells carry F factors the factor integrates into the chromosome converting the F+ cells

β-galactosidase

involved in transport of lactose into the cell, encoded by lacZ

permease

aka transport proteins, mem bound in facilitated diffusion to transport specific proteins across membrane, lac one helps transport lactose into the cell and the lacY gene encodes for it

transacetylase

metabolizes certain disaccharides other than lactose

plasmid

genetic elements hat exist outside of chromosomes, occurs in prokaryotes and eukaryotes.

mutagen

agents in environment, chemicals or radiation, that directly or indirectly bring about mutations

R plasmid

resistance factors, have significant medical imporance, resistant to a lot of antibiotic, acquired resistance through spread of genes from one organism to another, plasmids that mediated this transfer is called this.

bacteriophage

recipient cell inside a virus that infects bacteria

sex pilus

one or two per cell, involved in motility and dna transfer from one cell to another. this in the F+ cell connects to the receptors on the surface of another bacterium of its own species or a different species. they make physical contact and DNA from F+ cell is transferred to the other cell

F plasmid

conjugative plasmid, carries genes for sex pili and for transfer of the plasmid to another cell

Frederick Griffith

working with two strands of streptococcus pneumonia, on virulent with capsule prevents phagocytosis, bacteria grows and cause pneumonia. the other avirulent lacks capsule and doesn’t cause disease. studied wheather injections heat killed bacteria of encapsulated strain could be use to vaccinate mice against pneumonia. injections of living encapsulated killed mice injections of non incapsulated or dead encapsulated didn’t kill mice. but live non capsuled mixed with dead encapsulated killed many mice,

inducer

molecule that triggers expression of a gene

repressor

molecule that inhibits expression in two or more genes

polyribosome

many ribosomes in a single bacterial gene

DNA

double helix, most viruses are double stranded helix but some have single stranded (parvoviruses), deoxyribose sugar, A, T, G, C, contains genes (determine all hereditary traits)

RNA

single stranded in cells and most viruses but double stranded in some viruses (reoviruses), ribose sugar, C, G, A, U, protein synthesis

genotype

an organisms genetic makeup, all its dna, codes for particular characteristics of organism and represents potential properties.

phenotype

actual expressed properties or characteristics in an organism

chromosome

structures containing DNA that physically carry hereditary information, contains genes, typically single circular in bacteria

haploid

one set of chromosomes (n)

diploid

two sets of chromosomes (2n)

messenger rna

carries the coded information for making specific proteins from DNA to ribosomes where proteins are synthesized, acts as an intermediate between the permanent storage form of DNA and he process that uses the info in translation, codons. ribosomes move 5’—>3’

ribosomal rna

forms integral part of ribosomes, cellular machinery for protein synthesis

transfer RNA

reorganize the specific codons and transport the required amino acids.

auxotroph

any mutant microorganism having a nutritional requirement that is absent in the parent, ex:may lack enzymes needed o synthesize a particular amino acid and will therefore require amino acid as a growth factor in nutrient medium

prototroph

organism capable of synthesizing all its metabolites or has the same nutritional requirements as its parent or original strain

spontaneous mutation

mutations that occur spontaneously because of occasional mistakes during dna replication

induced mutaton

purposefully exposure to a carcinogens (most common UV) and genotoxins

codon

groups of three nucleotides, mRNA determines the sequence of amino acids that will be in the protein synthesized.

anticodon

in trna, sequence of 3 bases complementary to a codon so the trna can base pair with its associated codon

minus strand of DNA

3’—>5’antisense used for transcription

plus strand of DNA

5’ —> 3’, sense strand, mrna

constitutive enzyme

their products are constantly at a fixed rate

inducible enzyme

enzyme whose activity is increased as a response to a molecule

origin of transfer

specific sequencethat initiates transfer of genetic material from donor bacterium to recipient

central dogma

the sequence of nucleotides in DNA determines the sequence of amino acids in a protein, how dna is transcribed to messenger RNA to turn into protein that carry out function.

RNA polymerase

copies RNA from a DNA template

transcription in eukaryotes

takes place in nucleus, mrna must be completely synthesized and move through nuclear mem to cytoplasm before translation begins, exons (region of dna. expressed) and introns (intervening regions of DNA that do not encode protein) RNA poly synthesize mole called ran transcript that contains copies of introns and snRNPs remove introns and act as ribozymes to catalyze their own removal

methods of genetic transfer between bacteria

transformation, conjugation, transduction