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Study Guide: The Molecular Basis of Inheritance, Gene Expression, and Biotechnology

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Chapter 16 – The Molecular Basis of Inheritance

Components and Structure of DNA

DNA is the hereditary material in all living organisms. Its structure and replication are fundamental to genetics and cell biology.

  • Components of DNA:

    • Phosphate group

    • Deoxyribose sugar

    • Nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C)

  • DNA "Backbone": Composed of alternating sugar and phosphate groups.

  • Base Pairing: Bases pair via hydrogen bonds (A with T, G with C) forming the rungs of the double helix.

Base Pairing and Chargaff’s Rules

  • Chargaff’s Rule: In any DNA sample, the amount of A = T and G = C.

  • Example Calculation: If A = 20%, then T = 20%, G = 30%, C = 30%.

DNA Packaging: Histones and Nucleosomes

  • Histones: Proteins that DNA wraps around to form nucleosomes, aiding in DNA compaction.

  • Nucleosomes: "Beads on a string" structure; further coiling forms chromatin.

DNA Replication

DNA replication is the process by which DNA makes a copy of itself during cell division.

  • Semiconservative Replication: Each new DNA molecule consists of one old strand and one new strand.

  • Enzymes Involved:

    • Helicase: Unwinds the DNA double helix.

    • Primase: Synthesizes RNA primers.

    • DNA Polymerase: Adds nucleotides to the growing DNA strand.

    • Ligase: Joins Okazaki fragments on the lagging strand.

  • Okazaki Fragments: Short DNA fragments synthesized on the lagging strand.

DNA vs. RNA

Feature

DNA

RNA

Sugar

Deoxyribose

Ribose

Bases

A, T, G, C

A, U, G, C

Strands

Double-stranded

Single-stranded

Function

Stores genetic info

Makes proteins (mRNA, tRNA, rRNA)

Base Pairing and Hydrogen Bonds

  • A–T base pairs have 2 hydrogen bonds.

  • G–C base pairs have 3 hydrogen bonds.

Chapter 17 – Gene Expression: From Gene to Protein

Mutations

  • Mutation: Any change in DNA sequence.

  • Point Mutation: Change in one nucleotide pair.

  • Types of Mutations:

    • Silent: No change in amino acid sequence.

    • Missense: Changes one amino acid to another.

    • Nonsense: Changes a codon to a stop codon, terminating translation early.

Transcription and Translation

  • Transcription: Synthesis of mRNA from DNA by RNA polymerase.

  • Translation: Process of building proteins from mRNA at the ribosome.

  • RNA Polymerase: Enzyme responsible for transcription.

  • tRNA: Transfers amino acids to the ribosome during translation.

Genetic Code

  • Codon: Three-nucleotide sequence on mRNA that codes for an amino acid.

  • Redundancy: Multiple codons can code for the same amino acid.

  • Universality: The genetic code is nearly universal among organisms.

RNA Processing

  • 5’ cap added

  • Poly-A tail added

  • RNA splicing (removal of introns, exons joined)

Alternative Splicing

  • Allows one gene to code for multiple proteins by combining exons in different ways.

Chapter 18 – Regulation of Gene Expression

Feedback Regulation

  • End product of a pathway regulates its own production (negative or positive feedback).

Operons

  • Operon: Segment of DNA that acts as an on/off switch for transcription.

  • Lac Operon: Inducible; turns ON when lactose is present.

  • Trp Operon: Repressible; turns OFF when tryptophan is present.

Gene Regulation in Eukaryotes

  • Heterochromatin: Densely packed, inactive chromatin.

  • Euchromatin: Loosely packed, active chromatin.

  • Transcription Factors: General (all genes) vs. specific (certain genes).

Post-Transcriptional Regulation

  • mRNA degradation, blocking translation, or triggering degradation.

  • Small RNAs (siRNA, miRNA) can silence gene expression.

Developmental Genes

  • Homeotic Genes: Control body structure development.

  • Myod: Master regulatory gene for muscle cell differentiation.

Chapter 20 – DNA Tools and Biotechnology

Restriction Enzymes

  • Enzymes that cut DNA at specific sequences (restriction sites).

  • Produce "sticky ends" or "blunt ends".

Transgenic and Recombinant Organisms

  • Transgenic Organism: Contains DNA from another species (e.g., GMO crops).

  • Recombinant DNA: DNA combined from two or more sources.

Plasmids

  • Circular DNA molecules used as vectors to carry foreign genes.

Polymerase Chain Reaction (PCR)

  • Technique to amplify (copy) specific DNA sequences rapidly.

  1. Denaturation (DNA separates)

  2. Annealing (primers bind)

  3. Extension (DNA polymerase builds new DNA)

  • Taq Polymerase: Heat-resistant enzyme used in PCR.

Applications of PCR

  • Cloning, forensics, diagnostics, research.

RT-PCR and qRT-PCR

  • RT-PCR: Converts mRNA to DNA, then amplifies it.

  • qRT-PCR: Quantitative; measures the amount of mRNA in real time.

Genetic Variation and Genomics

  • SNPs (Single-Nucleotide Polymorphisms): Single base-pair variations among individuals.

  • Short Tandem Repeats (STRs): Short, repeated DNA sequences used in DNA fingerprinting.

Stem Cells

  • Totipotent: Can become any cell type (e.g., zygote).

  • Pluripotent: Can become almost any cell type (e.g., embryonic stem cells).

  • Induced Pluripotent Stem Cells (iPSCs): Adult cells reprogrammed to pluripotency.

Genetically Modified Organisms (GMOs)

  • Organisms engineered to contain modified or foreign DNA.

  • Examples: Pest-resistant corn, fast-growing salmon, golden rice.

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