Unit_9 Cell Differentiation, Mutations, and DNA Technologies

Overview of Biological Growth and Cell Differentiation

• Initial Growth Stage

  • Every multi-cellular organism begins life as a single fertilized somatic cell.

  • This initial cell undergoes a continuous process of mitosis to generate more cells, eventually forming a ball of stem cells.

• Stem Cells

  • Defined as cells with no assigned role or specific function.

  • These cells possess the potential to develop into any type of cell within the organism's body.

• The Process of Differentiation

  • In humans, cell differentiation begins at approximately $9$ weeks of gestation.

  • Prior to this point, human cells remain as unspecialized stem cells.

  • Cell Differentiation (Definition): A process where specific genes are expressed to produce proteins, leading to the creation of more specific cell types.

  • Cell Specialization (Definition): The process of a cell becoming its final, restricted cell type by turning certain genes on or off.

• Regulation of Differentiation and Specialization

  • This regulation is controlled by genes being active ("on") or inactive ("off"), which determines gene expression.

  • Constants in Cellular Biology: All cells in an organism have the same number of chromosomes (e.g., $46$ in humans) and the same DNA sequence.

• Factors Affecting Gene Expression

  • External Factors: Temperature, pH levels, salinity, chemicals/toxins, radiation, diet, and light.

  • Internal Factors: Hormones.

Genetic Mutations: Mechanisms and Impacts

• Definition of Mutation

  • A mutation is a change in the sequence of nitrogenous base pairs within a DNA strand.

• Effects and Causes of Mutations

  • Effect can be harmful, helpful, or neutral relative to the organism.

  • Causes include errors during DNA replication, chemical exposure, and radiation.

  • Mutations are the primary source of genetic variation and genetic diversity within a population.

• Molecular Consequences

  • An error (mutation) can lead to an incorrect codon sequence.

  • An incorrect sequence can code for an incorrect protein, which subsequently changes the genetic expression of the organism.

• Primary Types of Mutations

  • Substitution.

  • Insertion.

  • Deletion.

Point Mutations: Substitution

• Mechanism of Substitution

  • Also known as a point mutation because it involves a change in a single base.

  • In substitution, one nitrogenous base replaces another.

• Categorization of Substitution Mutations

  • Silent Mutation: A substitution that replaces one base with another but still translates to the same amino acid, resulting in no change to the organism.

  • Missense Mutation: A substitution that results in a different amino acid being coded, thereby altering the function of the produced protein.

  • Nonsense Mutation: A substitution that produces a "stop" codon prematurely, which significantly alters or halts protein function.

• Identification Tip

  • Since codons are transcribed in sets of three, if the mutation results in even sets of three nitrogen bases, it is likely a substitution.

Frameshift Mutations: Insertion and Deletion

• Insertion Mutation

  • Occurs when an extra nitrogen base is added to the DNA sequence.

  • This addition shifts the "reading frame" of all subsequent bases, which typically results in many incorrect codons following the site of insertion.

  • Identification Tip: If there is an extra base at the end of a sequence of sets of three, it is an insertion.

• Deletion Mutation

  • Occurs when a nitrogen base is removed or taken away from the sequence.

  • Like insertions, deletions shift the reading frame, causing systematic errors in every codon after the deletion point.

  • Identification Tip: If a base is missing from the end of what should be sets of three, it is a deletion.

• Comparison Example: Original vs. Mutated (Deletion Path)

  • Original DNA: GGC AAA TAT CGG

  • Transcribed mRNA: CCG UUU AUA GCC

  • Translated Amino Acids: Proline (Pro) ---- Phenylalanine (Phe) ---- Isoleucine (Iso) ---- Alanine (Ala)

  • Mutated DNA (Deletion of one base): GGC AAT ATC GG

  • Transcribed mRNA: CCG UUA UAG CC

  • Translated Amino Acids: Proline (Pro) --- Leucine (Leu) --- STOP -- (Protein is truncated and non-functional).

Real-World Mutation Analogies and Associated Diseases

• Normal Sequence (Control)

  • Analogy: THE BIG FAT CAT ATE THE WET RAT.

• Missense (Substitution)

  • Analogy: THE BIZ FAT CAT ATE THE WET RAT.

  • Disease Example: Achondroplasia (improper development of cartilage on bone ends, resulting in a form of dwarfism).

• Nonsense (Substitution)

  • Analogy: THE BIG RAT.

  • Disease Example: Muscular Dystrophy (progressive weakening of muscles).

• Deletion (Frameshift)

  • Analogy: THB IGF ATC ATA TET HEW ETR AT.

  • Disease Example: Cystic Fibrosis (abnormally thick mucus in lungs, intestines, and pancreas).

• Insertion (Frameshift)

  • Analogy: THE BIG ZFA TCA TAT ETH EWE TRA.

  • Disease Example: Crohn's Disease (chronic intestinal inflammation leading to various gastrointestinal symptoms).

• Duplication

  • Analogy: THE BIG FAT FAT CAT ATE THE WET RAT.

  • Disease Example: Charcot-Marie-Tooth disease (type 1A) (damage to peripheral nerves leading to hand/leg muscle weakness).

• Expanding Mutation (Tandem Repeats)

  • Analogy:

    • Generation 1: THE BIG FAT CAT ATE THE WET RAT.

    • Generation 2: THE BIG FAT CAT CAT CAT ATE THE WET RAT.

    • Generation 3: THE BIG FAT CAT CAT CAT CAT CAT CAT ATE THE WET RAT.

  • Disease Example: Huntington's Disease (brain cells waste away, causing motor and mental deterioration).

• Other Conditions Resulting from Mutations

  • Albinism.

  • Epidermodysplasia verruciformis (EV) (Tree Man Syndrome).

  • Syndactyly (fused digits).

Chromosomal Mutations

• Nature of Chromosomal Mutations

  • Unlike gene mutations which affect few nitrogen bases, chromosomal mutations affect a major part of a chromosome.

  • These mutations often occur in gamete cells during reproduction/replication.

• Four Types of Chromosomal Mutations

  • 1. Duplication: An extra chromosome or segment is present.

  • 2. Deletion: A chromosome or segment is missing.

  • 3. Inversion: A chromosome segment shifts location or is reversed.

  • 4. Translocation: A piece of one chromosome breaks off and joins another non-homologous chromosome.

• Disorder Example: Down Syndrome

  • Results from an Insertion Mutation (characterized by an extra chromosome).

Mutation Practice and Translation Examples

• Example 1 Analysis

  • Original DNA: AAA GCA TTT AGC / mRNA: UUU CGU AAA UCG / Amino Acids: Phe Arg Lys Ser.

  • Mutated DNA: AAA CAT TTA GC.

  • Identification: This is a Deletion mutation because a base has been removed, causing a frameshift that changes the subsequent amino acids.

• Example 2 Analysis

  • Original DNA: TAC GGC TAT CCC / mRNA: AUG CCG AUA GGG / Amino Acids: Met Pro Iso Gly.

  • Mutated DNA: TAC GGC TAG CCC.

  • Identification: This is a Substitution mutation (specifically resulting in a stop codon UAG if translated). Because a stop codon appears early, the protein function will be severely affected.

DNA and Molecular Technologies

• Core Functions

  • Used to analyze DNA, RNA, or proteins.

  • Comparisons of segments via DNA fingerprinting.

  • Detecting genetic disorders and viruses.

• Key Molecular Techniques

  • Polymerase Chain Reaction (PCR): Used to amplify (make more copies of) small pieces of DNA for extensive analysis.

  • Gel Electrophoresis: A method using an electrical charge to separate DNA fragments by size for comparison.

  • Gene Therapy: Clinical approach to treating disease by editing or replacing genes.

  • Genetic Engineering: Producing Recombinant DNA by combining genetic information from different sources (e.g., producing human insulin via bacteria or yeast).

  • CRISPR: A precise technology used to locate and edit specific genes within a genome.

  • Genetically Modified Organisms (GMOs): Altering or editing an organism's DNA for desired traits.