Microbial genetics Flashcards
What is a genome?
all genetic information in cell
What is a chromosome?
molecule of DNA + proteins
How are prokaryotic chromosomes organized?
1 circular= genome
How are eukaryotic chromosomes organized?
multiple pairs=genome
What is a gene?
a segment of DNA encoding a functional product (ie protein)
What is a genotype?
just genes of an organism
What are plasmids?
exist in prokaryotes
small circular dsDNA
Extrachromosomal (not part of genome)
not essential but often advantageous
How are plasmids advantageous?
antibiotic resistance
toxins
How can DNA be described?
complementary (A:T and C:G)
antiparallel (opposite directions)
What must happen before a cell divides?
DNA replication
What is semiconservative DNA replication?
each strand of original molecule serves as template
new DNA contains one conserved “parental” and one new strand
What does helicase do in DNA replication?
unzips the DNA
What does topoisomerase do in DNA replication?
relaxes
What is the function of primase in DNA replication?
RNA primer
What does DNA polymerase do in DNA replication?
Reads 3’ to 5’
Synthesizes 5’ to 3’
What does ligase do in DNA replication?
glues lagging fragments
What happens in prokaryotic DNA replication?
Circular DNA
1 replication bubble
2 forks at each origin (bidirectional forks)
What happens in eukaryotic DNA replication?
many origins and bubbles
linear DNA
bidirectional forks (2 forks at each origin)
What is a phenotype?
physical features/functional traits of an organism
include structures, morphology, metabolism
How does transcription stop and start?
start: promoter
stop: terminator
What happens in transcription?
RNA polymerase reads DNA
synthesizes complementary mRNA
What happens in translation?
ribosomes read mRNA three nucleotides at a time (codon)
start codon is AUG and stop codons
Transfer RNA (tRNA) is an anticodon plus an amino acid
What is a genetic code rule?
1 start codon- Met
64- other amino acids (19)
3-stop codons- no amino acids
Why does more than one codon code for the same amino acid?
protects from mutations
How does gene expression happen in prokaryotes?
coupled
translation can begin before transcription complete
How does gene expression happen in eukaryotes?
transcription completed in the nucleus before translation in cytoplasm
What is point mutation?
one nucleotide is changed
What is substitution?
one nucleotide replaced by another
What is frameshift?
insertion/deletion of nucleotide
What is silent mutation?
one result of substitution
only affects genotype
protein not affected
What is missense mutation?
one result of substitution
amino acid changed
may or may not have an effect on function
sickle cell disease- altered hemoglobin shape
What is nonsense mutation?
one result of substitution
premature stop codon
often nonfunctional protein
What do drastic missense and nonsense mutations do?
ribosome reading frame shifted (reads in 3’s remember)
non functional protein
What do base analog chemical mutations do?
look like normal bases initially but base pair incorrectly once incorporated
induce point mutations
used in research and as drugs
example is 5-bromouracil
What do intercalating agents do in chemical mutations?
slip in between adjoining nucleotides
bulge in backbone- polymerase makes mistakes (insertion/deletion of nucleotides
frameshifts for ribosomes
example is benzopyrene in smoke
What does ionizing radiation do?
X-rays and gamma rays
energize electrons in atoms- some electrons escape
free electrons strike other atoms- ions reaction with DNA- point mutations
What does non-ionizing radiation do?
UV Light
induces thymine dimers- covalent bonds between adjacent T’s
distorts backbone
improper replication- frameshift mutation
What is vertical gene transfer?
passing of genes down from parent to offspring
What is horizontal gene transfer?
genes passed down laterally in same generation (same recombination of transferred genes)
Prokaryotes (donor and recipient (recombinant cells)
What is transformation?
recipient takes up DNA fragments in environment from dead cell
antibiotic resistance has spread this way
What happens in conjugation?
fertility plasmid allows bacteria to form special pilus (allows plasmid transfer to recipient)
How does antibiotic resistance spread?
conjugation, transformation, transduction
What happens in transduction?
new assembling phage accidentally package piece bacterial chromosome (transferred to new cell when phage infects it
dead end for phage but could be good for bacteria (antibiotic resistance)
