Micro 10 Mutations

Mutations

Errors in bacterial genes caused by mistakes in DNA replication

Increases genomic flexibility, helps rapid adaptation (diversifies genomes as bacteria reproduce asexually), and explains fast evolution of antibiotic resistance

Normal conditions they are often harmful but can be beneficial in stressful conditions

Rate controlled by environmental stress

Nucleotide sequence level

type of mutation common in bacterial DNA

Point or frameshift

Point mutations

Nucleotide sequence level mutation involving the change of one DNA nucleotide to another via transition or transversion

Transition

type of point mutation where nucleotide type stays constant.

Purine ↔ purine (A ↔ G) or Pyrimidine ↔ pyrimidine (C ↔ T)

Transversion

type of point mutation where nucleotide type changes.

Purine ↔ pyrimidine (e.g., A ↔ T)

Frameshift mutations

Nucleotide sequence level mutation involving the insertion or deletion of a nucleotide.

Shifts reading frame which completely alters amino acid sequence after mutation

Amino acid level

Type of mutation due to amino acid changes originating from nucleotide-level mutations (point or frameshift)

silent, missense, or nonsense

Silent mutation

Amino acid level mutation but no change in amino acid due to redundancy of codons

Often involves change in 3rd nucleotide

Missense mutation

Amino acid level mutation where nucleotide change/mutation causes different amino acid production

Nonsense mutation

amino acid level mutation where nucleotide change/mutation now is a stop codon, leading to premature termination of protein

Prototrophs

wild-type bacteria. Can grow in minimal media because it can synthesize all essential nutrients with the correct enzymes for biosynthesis

All genes functioning properly

Auxotrophs

Bacteria that cannot grow in minimal media because they lack ability to synthesize an essential amino acid due to a biosynthesis gene mutation

Must obtain missing nutrient from environment, so auxotrophs are naturally selected when the required amino acid is abundant in environment

Making nutrients costs energy (ATP/GTP), so it’s easier to absorb nutrients than synthesize them

Prototrophic bacteria

Where auxotrophs obtains nutrients

Diffusion of metabolites from ____ cells or production of nanotubes which extracts amino acids from neighboring ___ cytoplasm (ex. E. Coli)

Spontaneous and Induced

Two Causes of Mutations

Spontaneous mutations

When mutation occurs during DNA replication errors and rare due to proofreading mechanisms

Can provide advantages in certain conditions (e.g., antibiotics)

Induced mutations

When mutations are caused by chemicals or radiation that modify nucleotides and often lead to point mutations

Ames Test

test detecting mutagens or potential carcinogens by determining if a compound causes DNA mutations

Uses Salmonella bacteria that are histidine auxotrophs (mutation: can’t produce histidine)

Test checks if compound causes mutation restoring histidine production

• compares the number of restored bacteria (revertants) in an experimental culture (w/compound) to a control culture (w/out compound)

More revertants in experimental group → compound is mutagenic

The few revertants in control are due to rare spontaneous mutations

Mutation inheritance

Mutations become permanent in DNA if not corrected by proofreading

Mutations are passed during binary fission via vertical transmission from parent to daughter cells

Mutations will then spread throughout bacterial population