Cell Structure and Function: Key Concepts for Anatomy & Physiology

Cell Structure and Function

Key Terms in Cytology

Cytology is the study of cells, which are the fundamental units of life. Understanding basic terminology is essential for exploring cell structure and function.

• Cell: The smallest structural and functional unit of an organism, typically microscopic and consisting of cytoplasm and a nucleus enclosed in a membrane.

• Cytology: The branch of biology concerned with the structure and function of plant and animal cells.

• Selectively Permeable: Refers to the property of cell membranes that allows certain molecules or ions to pass through it by means of active or passive transport.

Animal vs. Plant Cell Design

Animal and plant cells share many structural features but also have distinct differences that reflect their unique functions.

• Similarities: Both have a plasma membrane, cytoplasm, nucleus, and various organelles.

• Differences:

  1. Plant cells have a cell wall and chloroplasts; animal cells do not.

  2. Plant cells contain a large central vacuole; animal cells have smaller vacuoles.

  3. Animal cells have centrioles (within the centrosome matrix); plant cells typically do not.

Plasma Membrane and Its Molecular Components

The plasma membrane is a selectively permeable barrier that surrounds the cell, controlling the movement of substances in and out.

• Phospholipid Bilayer: Provides structural integrity and forms the basic framework.

• Proteins: Serve as channels, carriers, receptors, and enzymes.

• Cholesterol: Stabilizes membrane fluidity.

• Carbohydrates: Attached to proteins and lipids, involved in cell recognition.

Nucleus and Its Components

The nucleus is the control center of the cell, housing genetic material and coordinating cellular activities.

• Nuclear Envelope: Double membrane that encloses the nucleus and regulates passage of materials.

• Chromatin: DNA and associated proteins; condenses to form chromosomes during cell division.

• Nucleolus: Site of ribosome synthesis within the nucleus.

Major Cytoplasmic Organelles and Their Functions

Organelles are specialized structures within the cytoplasm that perform distinct cellular functions.

• Rough Endoplasmic Reticulum (RER): Studded with ribosomes; synthesizes and transports proteins.

• Smooth Endoplasmic Reticulum (SER): Lacks ribosomes; involved in lipid synthesis and detoxification.

• Ribosomes: Sites of protein synthesis; found free in cytoplasm or attached to RER.

• Mitochondria: Powerhouse of the cell; site of ATP production via cellular respiration.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Secretory Granules/Vesicles: Store and transport substances to be released from the cell.

• Lysosomes: Contain digestive enzymes for breaking down waste and cellular debris.

• Centrioles (within Centrosome Matrix): Involved in organizing microtubules during cell division.

• Cytoskeletal Elements:

  • Microtubules: Provide structural support and facilitate intracellular transport.

  • Microfilaments: Involved in cell movement and shape maintenance.

Surface Specializations: Cilia, Flagella, and Microvilli

Cells may possess specialized surface structures that aid in movement or increase surface area.

• Cilia: Short, hair-like projections that move substances across the cell surface (e.g., respiratory tract).

• Flagella: Long, whip-like structures used for cell movement (e.g., sperm cells).

• Microvilli: Finger-like extensions that increase surface area for absorption (e.g., intestinal lining).

Plant Cell Organelles and Structures

Plant cells contain unique organelles and structures that support their functions.

• Chloroplast: Site of photosynthesis; contains chlorophyll.

• Cell Wall: Rigid outer layer that provides structural support and protection.

• Central Vacuole: Large, fluid-filled sac that maintains cell turgor and stores nutrients and waste products.

Prokaryotes vs. Eukaryotes

Cells are classified as prokaryotic or eukaryotic based on their structural features.

• Prokaryotes: Lack a true nucleus and membrane-bound organelles; genetic material is in a nucleoid region (e.g., bacteria).

• Eukaryotes: Have a true nucleus and membrane-bound organelles; include animal, plant, fungal, and protist cells.

Summary Table: Animal vs. Plant Cell Features

Feature	Animal Cell	Plant Cell
Cell Wall	No	Yes
Chloroplasts	No	Yes
Central Vacuole	Small or absent	Large
Centrioles	Present	Absent

Example: ATP Production in Mitochondria

The mitochondria generate ATP through cellular respiration, summarized by the equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Additional info: Some details, such as the specific functions of organelles and the summary table, were expanded for academic completeness.