Topic 7 Notes

DNA and Genetics Overview

  • Introduction to DNA

    • Humor: "I'VE BEEN A LOUSY SWIMMER RIGHT FROM THE START-- MY DNA ALMOST DROWNED IN ITS GENE POOL!" (Thaves, 1994)

  • Frustrations of DNA Molecules

    • Statement: "I HATE BEING A DNA MOLECULE. THERE'S SO MUCH TO REMEMBER!"

Genealogy and Genetics

  • Genealogy Service

    • Comic remark: "YES, BRILLIANCE RUNS IN YOUR FAMILY, BUT IN A ZIG-ZAG PATTERN." (Thaves, 1997)

  • Genetics Lab Insight

    • Observation about color blindness: "THAT LITTLE GENE FOR COLOR BLINDNESS IS ALL DECKED OUT IN PURPLE FOR ST. PATRICK'S DAY." (Thaves, 1988)

Central Dogma of Molecular Biology

  • Flow of Genetic Information

    • Central Dogma describes the process where:

    • DNA is transcribed into RNA

    • RNA is translated into polypeptides

    • Key Transitions:

    • Information in DNA (language) translated to polypeptides.

    • When DNA is transcribed, an RNA molecule is created.

    • RNA is then translated into a sequence of amino acids comprising a polypeptide.

  • Characterization of Nucleic Acids:

    • Digital Nature:

    • Both DNA and RNA are characterized as digital molecules.

Proteins and Their Functions

  • Roles of Proteins in Cells

    • Proteins execute the majority of cellular work and functionalities.

    • Proteins are polymers comprising amino acids linked through peptide bonds.

    • Distinction: Proteins are analog molecules, illustrated by the “lock and key hypothesis.”

Genetic Disorders Example

  • Complete Androgen Insensitivity Syndrome

    • Genetic disorder causing XY fetuses to be insensitive to androgen hormones.

    • Phenotype: Externally female despite male genotype.

    • Internal anatomy: Undersized vagina, absence of uterus, fallopian tubes, and ovaries, with testicles located in the abdomen or groin.

    • Diagnosis: Typically confirmed during puberty when menstruation does not commence.

    • Mechanism Overview:

    • Involves lipid-soluble testosterone binding to its receptor protein, forming a hormone-receptor complex that influences transcription.

    • Components:

      • N-terminal domain

      • DNA-binding domain

      • Ligand-binding domain of the Androgen Receptor.

Amino Acids Structure

  • Amino Acid Composition

    • Each amino acid consists of three groups:

    • Amino Group (NH₂)

    • Carboxyl Group (COOH)

    • R Group: Varies among different amino acids.

  • Common Structures of Amino Acids

    • Similar structural features distinguished by unique R groups.

Protein Structure

  • Levels of Protein Structure:

    • Primary Structure: Sequence of amino acids (peptide chain).

    • Secondary Structure: Formation of alpha helices and beta sheets due to hydrogen bonding.

    • Tertiary Structure: 3D conformation based on interactions between R groups.

    • Quaternary Structure: Multi-polypeptide arrangements forming a functional protein.

  • Folding Mechanisms:

    • Following linkage by ribosomes, proteins fold according to their sequences, determining function.

AI in Protein Folding Research

  • DeepMind's AlphaFold

    • AI program that predicts protein folding, solving a long-standing scientific problem.

    • Successfully predicted structures of around 200 million proteins.

    • Achievements include understanding the 3D shapes essential for biological functions.

  • Applications:

    • Example: Prediction of the spike protein of a common cold virus (Coronavirus OC43) and its interaction with antibodies and sugars.

Genetic Information Characteristics

  • Nucleic Acids as Genetic Material

    • Must contain complex information.

    • Must be compact and stable.

    • Must replicate accurately and allow for variability.

    • Retrieval of genetic information must be efficient.

DNA Packing and Stability

  • DNA Structure in Cell

    • Length: DNA in Escherichia coli can span approximately 1000 times the length of the cell.

    • Remarkable stability allows the extraction and analysis of ancient DNA, like that from Neanderthal remains.

Archaeological Genetics

  • Analysis of Ancient Remains

    • Example: Study of Neanderthal dental plaque revealing dietary habits.

    • Genetic traces inform on extinct ecosystems and the adaptability of different species to climate changes.

Genetic Sampling Techniques

  • Environmental DNA (eDNA)

    • DNA shed from organisms, including plants and animals, useful in environmental studies.

    • Applications: Assessing biodiversity through sampling of water, soil, or air for environmental shed DNA.

Nucleotide Structure

  • Components of Nucleotide:

    • Pentose sugar

    • Phosphate groups (one to three)

    • Nitrogenous base (one of four types)

  • Classes of Nucleic Acids:

    • RNA: Contains ribose.

    • DNA: Contains deoxyribose.

Base Pairing and Bonding Rules

  • Chargaff's Rules:

    • Formation rules based on molar proportions.

    • Pairing: Adenine (A) with Thymine (T) and Guanine (G) with Cytosine (C).

X-ray Crystallography in Genetics

  • Technique Overview:

    • Provides data on molecular structure through diffraction patterns.

    • Notable contributions from Rosalind Franklin and Maurice Wilkins, among others, leading to the understanding of DNA's helical structure.

Structural Characteristics of DNA

  • Double Helix Structure:

    • Backbones formed by phosphodiester bonds.

    • Antiparallel and complementary strands.

  • Phosphodiester Bonds:

    • Bonds join the 3’ carbon of one nucleotide to the 5’ carbon of another, forming the backbone of DNA.

Melting Temperature of DNA

  • Tm (Melting Temperature)

    • Defined as the temperature at which 50% of the DNA is single-stranded and 50% is double-stranded.

    • Can be estimated using the 2+4 rule (2°C for each A/T pair and 4°C for each G/C pair).

DNA Secondary Structures

  • Z-DNA

    • A left-handed helix that can appear in active genes.

  • Advantages of DNA's Double Structure:

    • Compact packing.

    • Enhanced stability protecting the nucleotide sequence.

Hairpin Formation in RNA

  • Hairpin Structures:

    • Occur in single strands of nucleotides where complementary sequences fold back on themselves.

    • Can contain a stem or a loop depending on the configuration of nucleotides.

Conclusion

  • Emphasizes the complexity and interconnectivity of genetics, molecular biology, and the implications of research in understanding biological systems.