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Post-Translational Modifications (PTMs)
Changes to proteins after translation affecting function.
Phosphorylation
addition of phosphate groups altering protein activity
Methylation
addition of methyl groups influenceing gene expression
Acetylation
additon of acetyl groups regulating protein stability
Glycosylation
Addition of carbohydrates aiding in protein folding
Proteolytic cleavage
cutting proteins in to functional segments
Ubiquitination
Tagging proteins for degradation by proteasomes.
Translation Elongation
Process of peptide bond formation by ribosomes.
Translation Termination
Release of polypeptide at stop codons.
Genetic Code
Codons of three nucleotides corresponding to amino acids.
Codons
Triplet nucleotide sequences coding for amino acids.
Synonymous Codons
Multiple codons coding for the same amino acid.
Isoaccepting tRNAs
tRNAs that accept the same amino acid
Third-base Wobble
Flexibility in base pairing at codon position.
tRNA Charging
Process of attaching amino acids to tRNA.
Aminoacyl-tRNA Synthetases
Enzymes that charge tRNAs with amino acids.
Nirenberg and Khorana
Researchers who deciphered the genetic code
Universal Genetic Code
Code nearly identical across all organisms.
Signal Hypothesis
Proteins have sequences directing them to locations.
Eukaryotic Chromosomes
Linear DNA wrapped around histones forming nucleosomes.
Prokaryotic Chromosomes
Single, circular DNA organized in loops.
Histones
Proteins that package DNA into nucleosomes.
Nucleosomes
DNA-histone complexes, fundamental units of chromatin.
Chromatin Compaction
Process of DNA folding into higher-order structures.
Euchromatin
Less condensed, active form of chromatin.
Heterochromatin
Condensed, inactive form of chromatin.
Nondisjunction
Failure of chromosomes to separate during division.
Chromosome Territories
Distinct nuclear regions occupied by chromosomes.
Karyotype
Ordered display of chromosomes for analysis.
Chromosome Banding
Cytogenetic technique producing identifiable patterns.
Gene Dosage
Imbalance of gene products due to aneuploidy.
Chromosome Breakage
Breaks in DNA causing mutations or deletions.
Frameshift Mutations
Insertions or deletions shifting the reading frame.
Base Pair Substitution
Replacement of one base pair causing mutations.
Cis-acting elements
DNA sequences (e.g., promoters, operators) that regulate genes on the same DNA molecule.
Trans-acting factors
DNA-binding proteins that regulate genes on different DNA molecules.
Negative control
Repressor proteins inhibit transcription by binding to regulatory sequences.
Positive control
Activator proteins enhance transcription by binding to regulatory DNA.
Lac operon
A set of genes in E. coli regulating lactose metabolism, including lacZ, lacY, and lacA.
Inducible operon
An operon activated by an inducer (lactose) to enable gene transcription.
Lac repressor
A protein that binds to the operator to prevent transcription unless inactivated by lactose.
Induction
The process where lactose binds to the repressor, preventing it from blocking transcription.
CAP-cAMP complex
Enhances lac operon transcription when glucose is low.
Mutations
Changes in the DNA sequence, which can be spontaneous or induced by mutagens.
Spontaneous mutations
Mutations occurring naturally due to replication errors or chemical changes in DNA.
Chemical mutagens
Substances like alkylating agents and deaminating agents that cause mutations.
Ames test
A method to detect mutagenic properties of chemicals using bacteria.
DNA repair mechanisms
Systems like proofreading, excision repair, and mismatch repair that fix mutations to maintain genome integrity.
Regulatory mutations
Mutations that affect gene expression without altering the protein's amino acid sequence.
Promoter mutations
Mutations in promoter regions that reduce or prevent transcription initiation.
Splicing mutations
Mutations affecting the splicing of mRNA, often leading to diseases like spinal muscular atrophy.
Repressor proteins
Proteins that inhibit gene expression by binding to operators.
Activator proteins
Proteins that enhance transcription by binding to regulatory sequences.
Super-repressor
A mutated lac repressor that binds the operator even in the presence of lactose, preventing operon activation.
Intercalating agents
Compounds that insert into DNA, causing replication errors.
DNA repeat mutations
Mutations caused by instability in genomic regions with repetitive sequences, leading to diseases like CNG repeat expansion.
Key Indicators
Increased revertants (his- to his+) suggest mutagenic potential.
Mutation Types
Compares base substitutions and frameshifts.
Control Strains
Establish baseline to interpret results.
Use of Ames Test
Identifies potential carcinogens, but further tests needed to confirm carcinogenicity.
Types of Damage
Includes UV-induced thymine dimers, ionizing radiation, and alkylation.
Repair Systems
Direct repair, base excision repair, and nucleotide excision repair (NER).
Role of DNA Damage Repair
Critical for preventing mutations and diseases like cancer.
Direct Repair
Reverses DNA damage without removing nucleotides.
Key Enzymes in Direct Repair
DNA polymerase (proofreading) and O6-methylguanine methyltransferase (alkylation repair).
Importance of Direct Repair
First line of defense against DNA damage.
Nucleotide Excision Repair (NER)
Repairs bulky adducts and UV damage.
Key Enzymes in NER
UVR-A, UVR-B, UVR-C, and UVR-D in E. coli.
Clinical Relevance of NER
Prevents mutations linked to skin cancer.
Eukaryotic Gene Regulation
Regulates gene expression via complex mechanisms, including transcription and translation compartmentalization.
Gene Expression
Some genes are always on, while others are inducible.
Transcription
Involves RNA polymerase II and numerous transcription factors.
Transcriptional Regulation
RNA polymerase II synthesizes mRNA, regulated by transcription factors (e.g., TBP, TFIID).
Post-transcriptional Modifications
Capping, polyadenylation, and splicing.
Significance of Transcriptional Regulation
Provides precise control of gene expression.
Chromatin Structure and Function
Nucleosomes composed of histones (H2A, H2B, H3, H4) wrap DNA.
Gene Expression in Chromatin
Euchromatin (active genes) vs. heterochromatin (inactive genes).
Regulation of Chromatin
Chromatin compaction controls gene access for transcription.
Transcription Factors
Regulate gene expression by binding to specific DNA sequences.
Types of Transcription Factors
Monomers, homodimers, or heterodimers, classified by DNA-binding domains.
Enhancers
DNA sequences that enhance gene expression.
Transcription Activation
Transcription factors recruit RNA polymerase II and chromatin-modifying enzymes.
Transcription Repression
Repressors inhibit activators and recruit enzymes to condense chromatin, silencing genes.
Insulators
DNA sequences that block enhancers from activating adjacent genes.
GAL Gene Regulation.
In yeast, GAL4 (activator) and GAL80 (repressor) control galactose metabolism
Steroid Hormone Receptors
Hormones bind to receptors, activating gene expression by binding to hormone response elements (HREs).
