Understanding Biological Molecules and Processes: A Comprehensive Guide

Posted on May 5, 2024 in Biology

Amino Acids and Proteins

Amino Acid Structure

Amino acids are the building blocks of proteins. They have a central carbon atom (alpha carbon) bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group). The R group determines the unique properties of each amino acid.

Peptide Bonds and Protein Structure

Peptide bonds link amino acids together to form peptides and proteins. Proteins have four levels of structure:

  • Primary structure: The linear sequence of amino acids.
  • Secondary structure: Regular folding patterns, such as alpha helices and beta sheets, stabilized by hydrogen bonds.
  • Tertiary structure: The overall 3D shape of a protein, stabilized by various interactions, including ionic bonds, hydrogen bonds, disulfide bridges, and hydrophobic interactions.
  • Quaternary structure: The arrangement of multiple protein subunits.

Protein Functions

Proteins have diverse functions in living organisms, including:

  • Enzymatic: Enzymes catalyze biochemical reactions.
  • Hormonal: Some hormones, like insulin and growth hormone, are proteins.
  • Defensive: Antibodies are proteins that protect against pathogens.
  • Transport: Hemoglobin transports oxygen in the blood.
  • Structural: Collagen and keratin provide structural support.
  • Homeostatic: Proteins help maintain internal balance, such as pH.
  • Contractile: Actin and myosin enable muscle contraction.
  • Storage: Albumin in eggs and casein in milk are storage proteins.

DNA Structure and Cell Division

DNA Organization

DNA is organized into hierarchical structures:

  • DNA duplex: Two complementary strands of DNA held together by hydrogen bonds.
  • Nucleosomes: DNA wrapped around histone proteins.
  • Chromatin fiber: A chain of nucleosomes.
  • Chromosomal domains: Loops of chromatin fiber.
  • Metaphase chromosome: Highly condensed chromatin visible during cell division.

Cell Division and Centrioles

During cell division, centrioles play a crucial role in chromosome segregation. They migrate to opposite poles of the cell and form spindle fibers that attach to chromosomes, ensuring their equal distribution to daughter cells.

Energy Metabolism

Autotrophs and Heterotrophs

Autotrophs, like plants, use CO2 as a carbon source and synthesize organic molecules using light energy. Heterotrophs obtain carbon from organic molecules produced by other organisms.

ATP: The Energy Currency

Adenosine triphosphate (ATP) is the primary energy currency of cells. Energy is stored in the high-energy bonds between phosphate groups and released when ATP is hydrolyzed.

Oxidative Phosphorylation

Oxidative phosphorylation is the process by which ATP is synthesized using energy from the electron transport chain in mitochondria. Electrons from NADH and FADH2 are transferred to oxygen, and the energy released is used to pump protons across the inner mitochondrial membrane, creating a proton gradient. The flow of protons back across the membrane drives ATP synthesis.

Photophosphorylation

Photophosphorylation is the process of ATP synthesis during photosynthesis. Light energy excites electrons in chlorophyll, and the energy is used to generate ATP from ADP and inorganic phosphate.

Bacteria and Viruses

Bacterial Colonization and Virulence

Bacteria can colonize a host organism and cause disease. Virulence refers to the ability of a microbe to cause disease.

Bacterial Antigens

Bacteria have various antigens, including toxins and other molecules that trigger an immune response.

Immunity

Innate and Acquired Immunity

Innate immunity is present from birth and provides general protection against pathogens. Acquired immunity develops over time through exposure to specific pathogens. It can be acquired naturally (through infection or maternal antibodies) or artificially (through vaccination).