Overview
This lecture introduces the foundational concepts of cell biology for the MCAT, focusing on cell theory, the structure and function of eukaryotic cells, and tissue formation.
Cell Theory and History
- Cell theory defines cells as the basic units of life and outlines four key principles.
- Early discoveries by Hooke, Leeuwenhoek, and Virchow shifted the understanding of living organisms to being composed of cells.
- The four tenets: (1) all living things are made of cells, (2) the cell is the basic unit of life, (3) all cells arise from preexisting cells, and (4) genetic information is stored and transmitted as DNA.
Eukaryotic vs. Prokaryotic Cells
- Eukaryotic cells have a true nucleus and membrane-bound organelles; found in animals, plants, fungi, and protists.
- Prokaryotic cells lack a nucleus and have simpler organization; genetic material floats in the cytoplasm.
- Eukaryotes may be unicellular or multicellular, while prokaryotes are always unicellular.
Eukaryotic Cell Structure and Function
- Key organelles include: nucleus (stores DNA), mitochondria (ATP production), lysosomes (waste breakdown), endoplasmic reticulum (protein and lipid synthesis), Golgi apparatus (modifies and ships proteins/lipids), and peroxisomes (oxidative reactions).
- The cytosol is the fluid that supports these organelles.
- Organelles are enclosed by phospholipid bilayers that control substance movement.
The Nucleus in Detail
- The nucleus is surrounded by a double membrane (nuclear envelope) with nuclear pores for selective exchange.
- DNA is wrapped around histones to form chromatin, which condenses into chromosomes during cell division.
- The nucleolus inside the nucleus produces ribosomal RNA and assembles ribosomal subunits.
- The nucleoplasm supports nuclear structures and molecular movement.
Mitochondria
- Mitochondria have a double membrane; the inner membrane forms cristae for ATP synthesis.
- The mitochondrial matrix contains enzymes, DNA, and ribosomes and supports independent replication (binary fission).
- Mitochondrial DNA is maternally inherited, supporting the endosymbiotic theory of cell evolution.
Endoplasmic Reticulum and Golgi Apparatus
- Rough ER (with ribosomes) synthesizes proteins; smooth ER synthesizes lipids and detoxifies substances.
- The Golgi apparatus modifies, sorts, and packages proteins/lipids for final destinations.
The Cytoskeleton
- Made up of microfilaments (actin; shape and movement), microtubules (tubulin; transport and cell division), and intermediate filaments (structural support).
- Microfilaments drive cell movement and division; microtubules enable transport, cilia/flagella movement, and chromosome segregation; intermediate filaments provide mechanical strength.
Tissue Formation
- Eukaryotic cells can organize into four tissue types: epithelial, connective, muscle, and nervous (focus here on epithelial and connective).
- Epithelial tissue covers surfaces and lines cavities; classified by layers (simple, stratified, pseudostratified) and shape (cuboidal, columnar, squamous).
- Connective tissue forms the stroma, provides support, and produces the extracellular matrix (collagen, elastin).
Key Terms & Definitions
- Cell Theory — Fundamental principles outlining what defines a cell.
- Eukaryotic Cell — Cell with nucleus and organelles enclosed in membranes.
- Prokaryotic Cell — Cell lacking a nucleus and membrane-bound organelles.
- Organelle — Specialized cell structure performing specific functions.
- Nucleus — Organelle containing genetic material; control center.
- Mitochondria — Organelle producing ATP; site of cellular respiration.
- Endoplasmic Reticulum (ER) — Network for protein/lipid synthesis; rough (with ribosomes), smooth (without).
- Golgi Apparatus — Organelle for modifying, sorting, and shipping proteins/lipids.
- Cytoskeleton — Structural protein network (microfilaments, microtubules, intermediate filaments).
- Extracellular Matrix — Network of proteins/fibers providing tissue support.
Action Items / Next Steps
- Review and memorize key organelle functions and cell theory principles.
- Study the structural differences between eukaryotic and prokaryotic cells.
- Complete any assigned readings for chapter 1 before proceeding to the next lecture.