micro test 2

gene expression

uthe process of turning on a gene to produce RNA and protein

uAllows cells to conserve energy and space

uControl of gene expression is complex

Structural genes

genes that encode products that serve as structures or enzymes

Regulatory genes

genes that encode products that regulate gene expression

Prokaryotic organisms

are small, simple, single-celled organisms without a nucleus

Regulation of DNA transcription

allows them to stop transcription and translation together

Eukaryotic organisms

are larger, more complex, and contain membrane-bound organelles

Regulation of gene expression can occur

at all stages

Operon

collection of genes involved in a pathway that are transcribed together as a single mRNA in prokaryotic cells

Inducible

operons switched “on” by nutrient in question

Repressible

operons normally in the “on” position that are “turned off” when there is enough nutrient/amino acid available

Regulator gene

typically located outside the operon, codes for a DNA-binding protein that acts as a repressor to control whether the operon is active or not

Promoter

short sequence of DNA where RNA polymerase first attaches to begin transcription (start of the operon)

Activators

can bind and increase transcription

Operator

Operator

If a repressor is attached

transcription cannot occur

Inducers

small molecules that may be produced by the cell or within the cell’s environment

lac operon

encodes the genes necessary to acquire and process lactose from the local environment

Lactose presence is an

inducer of the lac operon and causes expression of genes

If lactose is present, allolactose (a metabolite) binds to

to the repressor and the repressor undergoes a change in shape

If lactose is absent, the repressor is

bound to the operator and prevents transcription of structural genes

Positive regulators

proteins that bind the promoter sequences to turn genes on and activate them

When glucose is low or unavailable

E. coli can utilize other sugars for fuel

cyclic AMP (cAMP)

a signaling molecule involved in glucose and energy metabolism) accumulates in the cell

catabolite activator protein (CAP),

which binds to the promoters of operons to control the processing of the alternate sugars

If both glucose and lactose are present

E. coli will preferentially break down the glucose

Ames test

is a method that allows for fast and inexpensive screening of the carcinogenic potential of new chemical compounds

Uses strain of Salmonella typhimurium that is a histidine auxotroph

auxotrophs

Used to detect nutritional mutants

Nucleotide excision repair (dark repair)

enzymes remove a portion containing the dimer and replace it with the correct nucleotides

Photoreactivation (light repair)

Photolyase enzyme recognizes the issue then removes the dimer and replaces it with the correct bases

DNA polymerase

Reads the new bases and ensures it is complementary to the corresponding base before adding another

Silent mutation

sequence base substitution still results in the same amino acid and polypeptide

Missense mutation

sequence base substitution results in a different amino acid

Nonsense mutation

sequence base substitution results in a stop codon and ends the protein earlier than it would normally

Point mutations

a change in a single DNA nucleotide

Frameshift mutations

occur when one or more nucleotides are added or deleted from DNA

Mutagens

\

environmental factors that can alter the base composition of DNA

Mutation

a permanent change in the sequence of bases in DNA

Mutant strain

recognizable changes in phenotype, nutritional characteristics, genetic control mechanisms, resistance to chemicals, temperature preference, etc.

Wild type

most observed phenotype in nature (the “normal” one)

Spontaneous mutations

arise as a result of abnormalities in normal biological processes

Induced mutations

may result from exposure to toxic chemicals or radiation

Transposons

jumping genes; molecules of DNA that include special inverted repeat sequences at their ends and a gene encoding an enzyme called transposase

Transduction

the use of viruses to move short pieces of chromosomal DNA from one bacterium to another

Generalized transduction

any piece of chromosomal DNA can be transferred into a host cell by accidental packaging of chromosomal DNA into a phage head during phage assembly

Specialized transduction

results from the imprecise excision of a lysogenic prophage from the bacterial chromosome such that it carries a piece of the bacterial chromosome from either side of the phage’s integration site into a new host cell

Transformation

the uptake of naked DNA from the environment

Competent cells

cells that actively bind to environmental DNA and transport it into their cytoplasm

Frederick Griffith demonstrated the process of

transformation with his experiments involving 2 strains of Streptococcus pneumoniae

Plasmids often code for

genes involved in virulence

Antibiotic resistance on

R plasmids

Conjugation

the asexual transfer of DNA from one cell to another using direct contact through a pilus

F plasmid

contains genes encoding the ability to conjugate

F⁺ cells

donor cells; contain the F plasmid

F^- cells

recipient cells; those that lack an F plasmid

Horizontal gene transfer

introduction of genetic material from one organism to another organism through nonreproductive mechanisms

Plasmid

small, circular piece of DNA that can replicate independently of the bacterial chromosome

Vertical gene transfer

transmission of genetic information from generation to generation

Recombination

an event in which one bacterium donates DNA to another bacterium

Phase variation

process of turning a group of genes on or off and changing its phenotype in a heritable manner

Arginine (arg) is an amino acid needed by

bacterial cells and the arg operon contains genes needed to make (synthesize) it

If arginine is not present

the repressor is inactive and NOT bound to the operator allowing synthesis of arginine

If arginine is present

free arginine will act as a corepressor and attach to the repressor; this causes a change in shape and the repressor binds the operator

Heredity

transmission of traits from one generation to the next

Genome

sum total of genetic material in an organism

Chromosome:

distinct cellular structure composed of neatly packaged DNA

Genes

section of DNA on the chromosome that provides information specific to a particular cell function

Genotype

genetic makeup

Phenotype

displayed or actively expressed structures or functions

S strain bacterial growth on plates produced

smooth & shiny colonies

R strain bacterial growth on plates produced

colonies with a rough appearance

Transformation

process by which foreign DNA is taken up by a cell

Oswald Avery and his co-investigators determined that

DNA was responsible for Streptococcus producing a capsule (increasing its virulence as seen in Griffith’s experiment)

Alfred Hershey and Martha Chase established

DNA as the genetic material in the early 1950s

Erwin Chargaff

Analyzed the base content of DNA

Nucleotide content of DNA is not fixed across species

Rosalind Franklin & Colleagues

Studied DNA structure using X-rays

Colleague- Maurice Wilkins

Diffraction pattern of DNA shows a double helix

Watson and Crick-1950s

Determined how the nucleotides were arranged

Double helix structure

Strands are antiparalle

Backbone is held together by

phosphodiester bonds

DNA replication

the process of copying a DNA molecule

Semiconservative replication

each daughter DNA double helix contains an old strand from the parental DNA double helix and a new strand

Topoisomerase II

relaxes the supercoiled chromosome

DNA helicase

separates the strands by breaking hydrogen bonds between base pairs

replication fork

fork forms as the DNA opens (Y shape)

replication fork is coated with

single-stranded binding proteins that prevent the DNA from rewinding itself into a double helix

RNA primase

makes a primer to attach an RNA sequence to the DNA

DNA polymerase III will eventually

add nucleotides in the 5’ to 3’ direction

Leading strand

replicated continuously

Lagging strand

replicated in pieces called Okazaki fragments that are glued together with DNA ligase

Topoisomerase IV

separates the circular chromosomes from each other

DNA gyrase and topoisomerase IV

are specific to prokaryotes so they are a common target for quinolones (antimicrobial drugs)

Eukaryotes have larger

, more complex genomes

Eukaryotes have linear

chromosomes

In eukaryotes

DNA replication begins at numerous origins of replication

Ends of eukaryotic chromosomes are made up of

telomeres

Telomerase adds

telomeres in the correct number of repeats after the chromosome is replicated

Transcription

DNAàRNA; DNA serves as a template to produce a mRNA(messenger RNA) transcript

Translation

RNAàProtein; mRNA is read in nucleotide triplets which allows the correct amino acids to be connected to form a polypeptide

RNA

Mainly play a role in translation (protein synthesis)

Uracil

Transcription

takes a DNA sequence and creates an RNA message (mRNA

Template strand

DNA strand that is used for transcription

Messenger RNA (mRNA) is created whe

RNA nucleotides pair with DNA nucleotides on the template strand