Week 5: Genetic Variation & Microbial Genetics Flashcards
nucleotides are made up of
5-carbon sugar, phosphate group, and nitrogenous base
phosphate group always attaches to
number 5
base is always attached to
number 1
when nucleotides join together a bond forms between
the phosphate group and carbon 3 adjacent nucleotide
nucleotides are read from
the 5’ end to the 3’ end
anti parallel
one strand in the DNA molecule runs 5’-3’, the other 3’-5’
chromosomes are made up of
DNA and specific DNA binding proteins that package the DNA neatly in the cell
DNA replication begins at the
origin
what enzyme binds at the origin and replication is initiated in
either direction along the circular chromosome
DNA polymerase
how does DNA polymerase move
moves in one direction only. Adds nucleotides in a 5’-3’ direction, so it
adds nucleotides continuously to one daughter strand and in short segments on the
other that are fused together later in the process
replication proceeds in
both directions from the origin using two replication forks
gene expression involves two important processes
transcription and translation
transcription is the process by which
a gene’s DNA is converted into a complementary RNA molecule
transcription is an enzyme-mediated process led by the enzyme
RNA polymerase
RNA polymerase attaches to a specific site on the DNA template
the promoter
RNA polymerase synthesizes a complementary strand of
mRNA as it moves along the DNA template
how does eukaryotic transcription differ from prokaryotes
RNA polymerase does not bind to the promotor directly, instead transcription factors bind the promotor and RNA polymerase recognizes these proteins
introns
noncoding sequences of DNA within a gene
exons
coding sequences of DNA within a gene
introns are
removed from the mRNA molecule by
RNA splicing
second step in gene expression is
translation; the mRNA is converted into a
specific amino acid sequence that forms a
specific protein
Codons on the mRNA specify
which amino acid is added to a growing protein
start codon
AUG
stop codons
UAA, UAG, UGA
first amino acid in protein synthesis
mathionine
bacteria reproduce
asexually
transformation (horizontal gene trasnfer)
Bacteria take up DNA from the environment; environmental DNA is usually a result of dead
bacteria releasing DNA in to the environment
transduction
Bacteriophages (viruses that infect bacteria) transferring DNA from one bacterium to another
conjugation
A donor bacterium transfers short DNA segments (usually plasmids) to another bacterium via
a sex pilus;
transposons
‘jumping genes’ that can relocate to other parts of the genome, increasing genetic diversity
reasons for mutation
- Spontaneous mutations
- Chemical mutagens and intercalating agents
- Free radicals
- Radiation
neutra mutation
phenotype/ protein is
unchanged
missense mutation
A different amino acid is substituted due to the mutation
• The phenotype is changed; can be positive or negative, or have little effect
nonsense mutation
Translation terminates early due to a mutation that results in a stop codon where an amino
acid would have normally been
• Usually very harmful to the protein
frameshift mutation
When a base is added or deleted mistakenly shifting the entire ‘reading frame’ of the mRNA
• Usually very harmful to the protein
