Biol Units 13-19 Review

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).