lecture recording Chapter 3

Principle of Complementarity

• Cells have organelles that allow them to perform specific functions tailored to their needs.

  • Example: Some cells have cilia, others do not; this is based on functional requirements.

• The principle can also be applied to groups of cells, affecting overall anatomy and physiology.

Cell Division and Propagation of Life

• Cells are the fundamental units necessary for life, which requires producing more cells.

  • Cells replicate through processes such as mitosis (for complex organisms) or cell fission (in bacteria).

• Sexual reproduction involves the fusion of gametes (sperm and egg), leading to the formation of a zygote that develops through mitosis.

Energy Requirements of Cells

• All cells require energy, primarily in the form of ATP (adenosine triphosphate).

  • Without adequate ATP, cells cannot sustain metabolic functions and will die.

DNA and Cellular Functions

• DNA is the genetic material that contains instructions necessary for cell function and reproduction.

  • All cells share DNA, but the expression and regulation can differ (e.g., red blood cells lose their nucleus).

Classifications of Cells

• The two main categories of cells are:

  • Prokaryotes: Simple cells, such as bacteria, that lack a nucleus.

  • Eukaryotes: Complex cells with a nucleus that houses DNA.

Special Cases of Cellular Structure

• Red blood cells are unique as they lose their nucleus to optimize oxygen transport, though they retain DNA.

• The cytoplasm consists of cytosol (fluid) plus organelles, aiding cell function.

• The cytoskeleton provides structure and integrity to the cell.

Organelles and Their Functions

• Endoplasmic Reticulum (ER): Has two forms:

  • Rough ER (with ribosomes) - synthesizes proteins.

  • Smooth ER - synthesizes lipids and detoxifies.

• Mitochondria: Powerhouse of the cell, generating ATP through cellular respiration.

• Lysosomes: Contain enzymes to degrade unwanted proteins.

• Peroxisomes: Store hydrogen peroxides, important in immune cells.

Plasma Membrane Structure and Function

• The plasma membrane separates internal cytosol from the external environment, regulating substance transport.

• The fluid mosaic model illustrates the plasma membrane as a flexible structure made of lipids with embedded proteins.

  • Phospholipids and cholesterol contribute to membrane stability and functionality.

Phospholipid Bilayer

• Composed of a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails.

• Forms a bilayer to protect internal structures of the cell from the aqueous environment.

Cholesterol's Role

• Stabilizes the fluidity of the plasma membrane, affecting its melting point and membrane integrity.

Glycoproteins and Glycolipids

• Glycoproteins and glycolipids on the extracellular surface attract water and form a protective glycohelix around the cell, vital for hydration and cell recognition.

• Unique sugar patterns help the immune system differentiate between self and non-self cellular components.

Transport Mechanisms Across the Plasma Membrane

• Membranes are selectively permeable, allowing some substances to pass freely while others require energy to cross.

  • Passive Transport: No energy used (e.g., diffusion, osmosis).

  • Active Transport: Requires energy to move substances against concentration gradients.

  • Vesicular Transport: Involves vesicles to move large molecules in and out of cells.

Passive Transport Types

• Simple Diffusion: Movement of small, lipid-soluble substances (e.g., oxygen, carbon dioxide) across the membrane.

  • Always moves from high to low concentration.

• Facilitated Diffusion: Requires integral proteins to help non-lipid soluble substances pass through the membrane.

  • Example: Ion channels and carrier proteins facilitate movement.

• Osmosis: Is the diffusion of water across a selectively permeable membrane, typically facilitated by aquaporins.

Factors Affecting Diffusion

• Magnitude of concentration gradient: Larger gradients increase the rate of diffusion.

• Temperature: Higher temperatures increase molecular movement, accelerating diffusion.

• Particle size: Smaller particles diffuse more rapidly.

• Distance: Greater distances decrease diffusion rates.

Conclusion

• Understanding cell structures, functions, and membrane transport mechanisms is essential for grasping the complex processes of life at the cellular level.