Cell Structure, Microorganisms, and Membrane Transport: Study Notes for Anatomy & Physiology

Prokaryotic vs Eukaryotic Cells

Comparison of Cell Types

Cells are classified as either prokaryotic or eukaryotic based on their structure and complexity. This distinction is fundamental in biology and underpins many physiological processes.

• Prokaryotic Cells: Small, simple, lack membrane-bound organelles, single-celled (e.g., bacteria).

• Eukaryotic Cells: Larger, more complex, contain a nucleus and membrane-bound organelles, can be single-celled or multicellular (e.g., plants, animals, fungi, protists).

Prokaryotic	Eukaryotic
Small	Large
Bacteria - single celled	Plants, Fungi (multicellular), some protists (single celled)
Divide by Asexual Binary Fission	Meiosis
No membrane-bound organelles	Distinct nucleus and membrane-bound organelles
More basic	More complex

Infectious Organisms

Bacteria

Bacteria are single-celled prokaryotic organisms that play vital roles in ecosystems and human health.

• Source of all food chains; extremely numerous.

• 1 gram of dental plaque contains more bacteria than the number of humans on Earth.

• Most are beneficial; some are extremophiles.

• Some form spores to survive harsh conditions (drought, freezing, heat, low oxygen, radiation).

Cell Structure and Shape

• No membrane-bound organelles (no nucleus), but have ribosomes.

• Cell wall made of peptidoglycan.

• Shapes:

  • Cocci: Spherical (single, pairs, chains, clusters)

  • Bacilli: Rod-shaped

  • Spirilla/Spirchetes: Spiral-shaped (e.g., syphilis)

Grouping and Staining

• Gram Positive: Thick peptidoglycan wall, stains purple.

• Gram Negative: Thin wall, outer membrane, stains red/pink.

Bacterial Reproduction

• Reproduce by binary fission: DNA is copied, cell divides.

• Can divide rapidly (as fast as every 20 minutes under ideal conditions).

Good vs. Bad Bacteria

• Many bacteria are beneficial (e.g., gut flora, skin bacteria).

• Some are pathogenic, causing disease by:

  • Invading cells (e.g., chlamydia, salmonella).

  • Changing the environment to suit their needs.

  • Producing toxins.

Antibiotics and Resistance

• Antibiotics (e.g., penicillin) inhibit cell wall synthesis.

• Antibiotic resistance is a growing problem (e.g., MRSA, C. difficile, gonorrhea).

Viruses

Viruses are non-cellular infectious agents that require host cells to replicate.

• Very specific in host range; most infect bacteria (bacteriophages).

• Pathogenic viruses can evade immune defenses.

Structure

• Composed of a few strands of nucleic acid (DNA or RNA) and a protein coat (capsid).

• Some have an envelope derived from host cell membrane.

Method of Infection

• Obligate parasites: must invade host cells to reproduce.

• Use glycoproteins to bind to specific receptors on host cells.

Life Cycles

• Lytic Cycle: Virus replicates rapidly, destroys host cell (e.g., flu).

• Lysogenic Cycle: Viral DNA integrates into host genome, remains dormant (e.g., herpes).

Control and Vaccines

• Few antiviral drugs; vaccines are primary prevention (e.g., smallpox, cowpox).

Prions

Prions are infectious proteins that cause neurodegenerative diseases.

• Misfolded proteins that induce misfolding in normal proteins.

• Cause diseases such as:

  • Bovine spongiform encephalopathy (BSE, "mad cow disease")

  • Scrapie (sheep)

  • Chronic wasting disease (deer)

  • Kuru, Creutzfeldt-Jakob disease (humans)

• Long incubation periods; progressive neurological decline.

Fungi

Fungi are eukaryotic organisms, mostly multicellular (except yeast), that can be parasitic and cause disease, especially in immunocompromised individuals.

• Kingdom Fungi; many are decomposers or pathogens.

• Can cause extensive crop damage.

Cell Structure and Function

Plasma Membrane

The plasma membrane surrounds the cell, providing a barrier and regulating entry and exit of substances.

• Structure: Phospholipid bilayer with embedded proteins and cholesterol.

• Hydrophilic (polar) heads face outward; hydrophobic (nonpolar) tails face inward.

• 20%+ of membrane lipids are cholesterol, which stabilizes the membrane.

• Proteins serve as gateways (channels), receptors, and anchors.

• Glycocalyx: Carbohydrate-rich area on the cell surface for recognition and docking.

Membrane Transport

Cells use various mechanisms to move substances across the plasma membrane.

• Passive Transport: No energy required.

  • Diffusion: Movement from high to low concentration (e.g., O2, CO2).

  • Osmosis: Movement of water across a semi-permeable membrane to equalize solute concentration.

  • Facilitated Diffusion: Uses protein channels to move larger or polar molecules down their concentration gradient.

  • Filtration: Water and solutes forced through a membrane by pressure (e.g., in kidneys).

• Active Transport: Requires energy (ATP).

  • Moves substances against their concentration gradient (e.g., ions, amino acids).

  • Allows cells to concentrate substances inside or outside the cell.

• Vesicular Transport: For large particles or volumes.

  • Endocytosis: Cell engulfs material, forming a vesicle.

  • Exocytosis: Vesicle fuses with membrane to expel contents.

  • Phagocytosis: Engulfing of solids (e.g., white blood cells ingesting bacteria).

Blood in Different Solutions

• Hypertonic: Solution is saltier than the cell; cell shrinks.

• Isotonic: Solution has same salt concentration as cell; no net water movement.

• Hypotonic: Solution is less salty; cell swells and may burst.

Nucleus

Structure and Function

The nucleus is the control center of the cell, storing genetic material and coordinating activities like growth and protein synthesis.

• Contains chromatin (DNA and proteins), organized into chromosomes during cell division.

• Enclosed by a double membrane (nuclear envelope) with pores for molecular exchange.

Protein Synthesis

• DNA contains genes (segments coding for proteins).

• To make a protein:

  1. DNA is unzipped and transcribed into messenger RNA (mRNA).

  2. mRNA exits the nucleus via nuclear pores.

  3. mRNA is translated by ribosomes in the cytoplasm to assemble proteins.

Additional info:

• Cellular respiration equation: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Energy (ATP)}$

• Cell division (mitosis) produces two identical daughter cells; phases include prophase, metaphase, anaphase, and telophase.