chapter 8 : Microbial Genetics ( textbook)

Genetics

the science of heredity

Genome

a cells chromosomes and plasmids

chromosomes

structures containing DNA that physically carry hereditary information, chromosomes contain the genes

Genes

segments of DNA that code for functional products

genetic code

the set of rules that determines how a nucleotide sequence is converted into the amino acid sequence of a protein

expressed

when the ultimate molecule for which a gene codes has been produced

central dogma

by Francis Crick in 1956, when her first propsed that the sequence of nucleotides in DNA determines the sequences of amino acids in a protein

Genotype

an organisms is it genetic makeup - all its DNA- the information that codes for all the particular characteristics of the organism

-represent potential properties, but not the properties themselves

Phenotype

refers to actual expressed properties

Short tandem repeats (STRs)

repeating sequences of two - to five base sequences, Used in DNA fingerprinting

genomics

the sequences between start and stop codons

Vertical gene transfer

the flow of genetic information from one generation to the next

DNA polymerases

an enzyme that joins nucleotides together to grow DNA

semiconservative replication

the process of replication that contains one original DNA strand and one new strand

Okazaki fragments

1000 nucleotides

DNA gyrase

relaxes supercoiling ahead of the replication fork

DNA ligase

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

DNA polymerases

synthesizes: DNA proofreads and facilitates repair

Endonucleases

cut DNA backbone in a strand of DNA : facilitates repair and insertions

Exonucleases

cut DNA from an exposed end of DNA: facilitate repair

helicases

unwinds double-stranded DNA

Methylases

adds methyl group to selected bases in newly made DNA

Photolyase

uses visible light energy to separate UV-induced pyramided dimers

Primases

AN RNA polymerase that make RNA primers form a DNA template

Ribozyme

RNA enzyme that removes introns and splices exons together

RNA Polymerase

copies RNA from a DNA template

snRNP

RNA-protein complex that removes introns an splices exons together

Topoisomerase or Gyrase

Relaxes supercooling ahead of the replication fork; separates DNA circles at the end of DNA replication

Transposase

Cuts DNA backbone, leaving single-stranded “sticky ends”

Eocyriboses’s is the

sugar in the nucleosides used to synthesize DNA

transcription

the synthesis of a complementary strand of RNA from a DNA template

Ribosomal RNA ( rRNA )

Forms a integral part of ribosomes, the cellular machinery for proteins synthesis

Messenger RNA ( mRNA)

carries the coded information form making specific proteins form DNA to ribosomes, where proteins are synthesized

Promoter

where transcription begins when RNA polymerase binds to the DNA a a site called the ____

Terminator

RNA synthesis continues until RNA polymerase reaches a site on the DNA called the ____

Translation

protein synthesis, includes decoding the “language “ of nucleic acids and converting it into the “language “ of proteins

codons

groups of three nucleotides, such a AUG,GGC or AAA

degeneracy

a situation where amino acids are signaled by several alternative codons

sense codons

code for amino acids

nonsense codons

(stop codons ) do not code for amino acids

transfer RNA ( tRNA)

recognize the specific codons and transport the required amino acids

anticodon

a sequence of three bases that is complementary to a codon

introns

the intervening regions of DNA that do not encode protein

exons

the regions of DNA expressed

small nuclear ribonucleoproteins (snRNPs)

remove the intros and splice the exons together. In some organisms, the introns act as ribozymes to catalyze their own removal

operon

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

operator

acts like traffic light , and is go and stop signal for transcriptions of the structural genes

operon

a set of operator and promoter sites and the structural genes that control define an _____

inducible operon

( lac operon)

Regulatory gene

(I gene ) encodes a repressor protein that switches inducible and repressible operons on or off

Repressible operons

the structural genes are transcribed until they are turned off. the genes for the enzymes involved in the synthesis of tryptophan are regulated in this manner

corepressor

binding to the repressor protein. the repressor protein can now bind to the operator, stopping further tryptophan synthesis

cyclic AMP (cAMP)

a substance derived from ATP that serves as a cellular alarm signal ( helps cells uses there glucose more efficiently )

catabolite repression

The inhibition of the metabolism of alternative carbon source by glucoses is termed ___

Riboswitch

a part of an mRNA molecule, that binds to a substrate to change the mRNA structure. Depending on the type of change, translation can be initiated r stopped. Both eukaryotes and prokaryotes use riboswitches to control expression of some genes

microRNAs (miRNAs)

single -stranded RNA molecules of approximately 22 nucleotides, inhibited protein productions in eukaryotic cells. in human, miRNAs produced during development allow different cells to produce different proteins ( allows different organ, to create different cells 0

natural selections

the survival of new genotypes

mutation

a permanent change in the base sequence of DNA

Base substitution

In which a single base at one point in the DNA sequence is replaced with a different base

Nonsense mutation

a base substitution resulting in a nonsense codon

frameshift mutations

in which one or a few nucleotides apairs are delered or inserted in the DNA

spontaneous mutations

occur in the absence of any mutations-causing agents

mutagens

agents in the environment, such as certain chemicals and radiation, that directory or indirectly bring about mutation are ____

nucleoside analog

a type of chemical mutagen, these molecules are structurally similar to normal nitrogenous bases, but they have slightly altered base-paring

Photolyases

Light repair enzyme, use a viable light energy to separate the dimer back to the original two thymine

Nucleotide excision repair

not restricted to UV- induced damages, it can repair mutations from other causes as well. enzymes cut out the incorrect base and fill in the gap with newly synthesizes DNA that is complementary to the correct strand

methylases

these enzymes add a methyl group to selected bases soon after a DNA strand is made. A repair endonuclease then cuts the nonmethylated strand

Mutations rate

the probability that a gene will mutate when a cell divides

Positive (direct) selection

Involoves the detection of mutant cells by rejecting of the unmutated parent cells

Negative (indirect ) selection

selects a cell that perform a certain functions, using the technique of replica plating

repilica plating

growing colony of bacteria in bulk and comparing weather they are function properly or not

Auxotroph

any mutant microorganism having a nutritional requirement that is absent in the parent is known as a ____

carcinogens

substances that causes cancer in animals, including humans

Ames test

uses bacteria as carcinogen indicators

Genetic recombination

refers to the exchange of genes between two DNA molecules to form new combinations of genes on a chromosomes

Crossing over

some of the genes carried by the chromosome are shuffled. The DNA has recombined, so that the chromosomes now carries a portions of the donor’s DNA

Vertical gene transfer

occurs when genes are passed from an organism to its offspring. Plants and animals transmit their genes by vertical transmission

Horizontal gene transfer

bacteria can pass their genes not only to their offspring, but also laterally, to other microbes of the same generation

donor cell

gives a potion of its total DNA to a recipient cell

mobile genetic elements

plasmids and transposons

Plasmids

self-replicating, gene-containing, circular pieces of DNA about 1-5% the size of bacterial chromosomes. they are mainly found in bacteria but are in some eukaryotic microorganisms.

Conjugative plasmid

(f-factor) carries gens for sex pili and for the transfer of the plasmid to another cell ( although plasmid are usually dispensable, under certain conditions gene carried by plasmids can by crucial to the survival and growth of the cell )

Dissimilation plasmids

code for enzymes that trigger the catabolism of certain unusual sugars and hydrocarbons ( allows for some bacteria to use unusual substance of sources of power because of there catabolic enzymes )

Bacteriocins

toxic proteins that kill other bacteria

Resistance factors

( R factors ) plasmids that have significant medical importance, these bacteria acquired resistance through the spread of genes from one organism to another

transposon

small segment of DNA that can move from one region of DNA molecule to another

resistance transfer factor (RTF)

includes genes for plasmid replication and conjugation

r-determinate

resistance genes, it codes for the production of enzymes the inactivate certain drugs or toxic substances

insertion sequences (IS)

the simplest transposes, contains only a gene that codes for an enzyme and recognition sites

transformation

genes are tranferred from one bacterium to another