Week 9 Flashcards
Gene
Functional unit of genetic information
Genetic elements
large molecules and/or chromosomes
genome
genetic information in a cell
informational macromolecules
nucleic acids and proteins
genomics
sequencing and molecular characterization of genomes
genotype
genetic makeup containing potential properties
phenotype
actual expressed properties
nucleotides
nucleic acid monomers
dna and rna are polynucleotides
three components; pentose sugar, nitrogenous base, phosphate
nucleoside
has pentose sugar and nitrogenase base, no phosphate
Phoephodiester bonds
connect ‘3 carbon of one sugar 5’ carbon of the adjacent sugar
Primary structure
sequence of nucleotides that encode genetic information
Properties of double helix
double stranded, held together by hydrogen bonding between bases
two strands complementary base sequences AT GC
Strands anti parallel 5-3 3-5 forming double helix
major and minor grooves
Positive supercoiling
Double helix is overwound
wound in same direction as the right handed double helix
DNA helicase mediated
Negative supercoiling
double helix is underwound
wound in opposite direction of the right handed double helix
dna gyrase mediated
predominant form in nature
Topoisomerases
insert and remove supercoils
negative supercoiling
twisted in opposite sense relative to right handed double helix, most cells
DNA gyrase
introduces supercoils into dna via double strand breaks
positive supercoiling
helps prevent dna melting at high temps, ex. some archaea
Central dogma
genetic information flow can be divided into three stages, dna to rna to protein
messenger rna
carry info to ribosomes
transfer rna
convert mrna information to amino acid sequence
ribosomal rna
catalytic and structural ribosome components
replication
dna is duplicated by dna polymerase
transcription
information from dna is transferred to rna by rna polymerase
translation
information in mrna is used to build polypeptides on ribosome
eukaryotes info flow
each gene transcribes indivi into single mrna
replication and transcri occurs in nucleus
rnas must be exported outside nucleus for translation
prokaryotes into flow
multiple genes may be transcribed in one mrna
coupled transcription and translation occur producing proteins at maximal rate
chromosome
main genetic element in prokaryotes
most bacteria and archaea have single circular chromosome carrying all/most genes
euk: 2+ linear chromosomes
Plasmids
small circular or linear dna molecules
replicate sep from chromosome
generally beneficial
not extracellular
expendable
virulence factor
Ability to attach or produce toxins (some bacteria have them encoded by plasmids)
bacteriocins
proteins that inhibit or kill closely related species or different strains of same species (can be plasmid encoded)
Rhizobia
require plasmid encoded functions to fix nitrogen
4 types of plasmids
- Resistance plasmids
- Virulence plasmids
- metabolic plasmids
- conjugative plasmids
Direction of DNA replication?
Always 5 to 3
DNA polymerases
catalyze polymerization of deoxynucleotides
can only add nucleotides to preexisting and require primer (short stretch of rna)
DNA helicase
unwinds double helix
Replisome
large replication complex of multiple proteins
Primosome
helicase and primase sub complex within replisome
mutations
change in dna sequence, proofreading to ensure high fidelity
Wild type strain
a reference strain or a strain isolated from nature
mutant
a strain (cell or virus) differing from parental (wild) strain
mutation
stable inheritable changes in dna base sequencing
single base changes more common, point mutations
larger mutations are less common, insertion, deletion, inversion, duplication, translocation
can be spontaneous or induced
frame shift mutation
deletions or insertions of one to two base pairs
dramatic changes to dna
reading frame is shifted causing downstream codons to be read incorrectly
Reversion
point mutations are typically reversible
occurs when alteration in DNA reverses effects of prior mutation
same site revertant
mutation is at the same site as original mutation
second site revertant
mutation is at a different site in the dna (suppressor mutation)
chemical mutagens (3)
base analogs, mistakes occur when incorporated and propagated
dna modifying agents, higher freq than base analogs, faulty base pairing
intercalating agents, distort dna to induce single base insert or delete
auxotroph
any mutant microorganism with a nutritional requirement that is absent in the parent (wild type)
Ames test
looks for inc in mutation of bacteria in presence of suspected mutagen
mutagens lead to a reversion of mutants back to wild type phenotype
wide variety of chemicals have been screened for toxicity and carcinogenicity
Transformation
taking up naked dna from the surrounding environment
conjugation
pilus mediated transfer between neighbouring cells
transduction
viral transfer of genes
