Focus on the mechanisms underlying microbial genetics and the implications of mutations, gene transfer, and recombination.
HBB Gene Mutations:
Original sequence: GGACTCCTC
Example of a point mutation: HbSS
Change: GGACACCTC
Amino Acids: PRO -> VAL
Point mutations can lead to various disorders, including Cystic Fibrosis and Huntington's Disease.
Nonsense Mutation:
Removes the amino acid sequence and creates a stop codon.
Example: CAGCAGCAG (normal) vs. CAG repeats (mutated).
Missense Mutation:
Alters a single amino acid.
Example: A change from cysteine to tyrosine can alter neuronal function.
Mutation: Structural change in DNA base sequences. Can alter the resultant proteins.
Mutagen: Agents that induce mutations.
Wild Type: The typical form of organisms found in nature.
Spontaneous Mutations: Occur naturally without external influence.
Induced Mutations: Caused by environmental factors (mutagens).
Mutation Rate: Approximately 1 in 10^8 nucleotides in bacteria.
Reversion: A new mutation that reverses an old one.
Point Mutation/Base Substitution: Affects single bases, which can lead to:
Missense mutation: Amino acid change
Nonsense mutation: Stop codon generation
Silent mutation: No change in protein function
Insertion/Deletion: Changes reading frame leading to:
Frameshift mutation: Entire downstream sequence altered.
Alter Base Structures:
Example: Nitrous acid (A to G transitions).
Nucleoside Analogs: Compete with normal bases during replication.
Example: 2-Aminopurine replaces adenine but can pair with cytosine.
Intercalating Agents: Inserts itself between DNA base pairs, potentially causing mutations.
Example: Ethidium bromide.
Ionizing Radiation: Breaks DNA molecules (e.g., X-rays).
Nonionizing Radiation: Causes thymine dimers (e.g., UV light).
Result from adjacent thymines cross-linking due to UV radiation, altering DNA structure.
DNA Polymerase: Has proofreading capabilities to correct errors during DNA replication.
Repair Methods for Thymine Dimers:
Light Repair: Uses photolyases in the presence of light.
Nucleotide Excision Repair: Enzymatic removal of damaged sections.
A method for assessing the mutagenic potential of chemicals using Salmonella His-145 strains. Positive results indicate increased mutation rates.
Vertical Gene Transfer: From parent to offspring.
Horizontal Gene Transfer: Through mechanisms such as Transformation, Conjugation, and Transduction.
Griffith's Experiment: Demonstrated transformation using smooth (S) and rough (R) strains of Streptococcus pneumoniae.
Occurs through a sex pilus enabling transfer of gene material between bacteria (F+ to F- cells).
Mechanism of gene transfer involving bacteriophages that incorporate bacterial DNA.
Circular, self-replicating DNA molecules aside from chromosomal DNA that may carry beneficial genes, including antibiotic resistance.
Key causes include over-prescribing, incomplete courses, and agricultural use of antibiotics.
Operon: Regulatory unit comprising an operator, promoter, and genes whose expression it controls.
Example: Lac Operon
Regulates lactose metabolism based on glucose levels and lactose presence.
E. coli growth shows variances based on carbon source availability (glucose vs. lactose).
Key Areas Covered:
Replication, Transcription, Translation, Mutations, Genetic Recombination, Gene Regulation, Movement of Genetic Information (Transformation, Conjugation, Transduction).