Biology Theme 1 Module 1 Quiz

Cells in Our Body

• Humans originate from a single fertilized egg, which undergoes mitotic divisions to develop into approximately 10 trillion cells.
• These cells include diverse types such as muscle, skin, kidney, and neurons, all categorized as eukaryotic due to their nucleus containing genetic material.
• Key cell classifications:
  • Eukaryotic cells: Plant, animal, fungi
  • Prokaryotic cells: Bacterial cells
• Human body harbors ten times more bacterial cells than eukaryotic cells, contributing to 2-3% of body mass (e.g., a 150-pound person may carry 3-4.5 pounds of bacteria).
• Most bacteria are beneficial, performing essential functions within physiological systems; some can be harmful if they enter the body.

Microbiome

• Defined as populations of microorganisms, invisible to the naked eye but observable under a microscope.
• Composed of prokaryotic bacteria and small eukaryotic organisms that inhabit all parts of the body, including the skin and digestive system.
• Approximately 10,000 distinct microbial species exist on and in a healthy human body.
• Notable bacteria include:
  • Streptococcus Aureus: Can induce skin and respiratory infections.
  • Streptococcus Salivarius: Harmless in oral cavity; contributes to dental plaque formation and colonizes newborns' gastrointestinal tract.
  • Staphylococcus haemolyticus: Common on skin.
  • Bacteroides thetaiotaomicron: Important intestinal bacteria breaking down plant material.

Phospholipids: Building Blocks of Membranes

• All cells are encased in membranes rich in phospholipids.
• Definition of a cell includes macromolecules:
  • Nucleic acids: Hereditary information; DNA is processed into RNA for protein synthesis.
  • Proteins: Structural and functional elements including enzymes.
  • Polysaccharides: Structural roles and energy sources (e.g., plant cell walls).
  • Phospholipids: Key components of cell membranes, creating barriers.
• Cell membranes maintain distinct internal environments, crucial for toxin control and nutrient absorption.

Structure and Function of Cell Membranes

• Membranes consist of lipid macromolecules with hydrophobic cores and hydrophilic properties, forming lipid bilayers.
• Phospholipids are amphipathic, possessing hydrophobic tails and hydrophilic head groups, allowing bilayer formation.
• Membrane thickness ranges from 5-10 nm, thin enough that 100 layers equal the thickness of paper.
• Phospholipid properties:
  • Tails consist of saturated (single bonds) or unsaturated (double bonds) hydrocarbons, affecting fluidity and permeability.

Membrane Fluidity Factors

• Fatty Acid Tail Length: Longer chains pack tightly, reducing membrane fluidity.
• Saturation: Double bonds create bends in tails, increasing fluidity by spacing out phospholipids.
• Temperature: Higher temperatures enhance fluidity; cold-adapted organisms have more unsaturated phospholipids to maintain fluidity under lower temperatures.
• Cholesterol: Integral in membranes, making up 50% of lipid molecules; moderates membrane fluidity by restricting phospholipid movement.

Cellular Energy and Metabolism

• ATP serves as the molecular fuel for cellular activities, generated primarily through cellular respiration from glucose.
• Glycolysis occurs in the cytosol, producing 2 ATP and 2 NADH, followed by pyruvate processing leading to the Krebs cycle in mitochondria.

Protein Synthesis and Folding

• Translation of mRNA to polypeptide involves amino acids linking through peptide bonds, forming polypeptides characterized by R groups that define properties.
• Proteins reaching functional shapes rely on interactions of R groups, leading to established three-dimensional structures.
• Ribosome location influences protein destination:
  • Free ribosomes produce cytosolic proteins or those targeting organelles.
  • Special sequences within proteins guide them to specific organelles.

Test your understanding of the composition and structure of membranes in biological cells. This quiz covers the fundamental aspects of cell division and the differences among various eukaryotic cells in the human body. Challenge yourself with questions on cell types, functions, and the importance of membranes.