Cells as the Basic Unit of Life
The Cell Theory
Major Contributors:
Galileo = first observations made with a microscope
Robert Hooke = first to observe small compartments in dead plant tissue, coined the term "cell"
Antony van Leeuwenhoek = first to observe living, mobile cells and bacteria
Robert Brown = first to observe the nucleus
Rudolf Virchow = every new cell comes from a pre-existing cell
Schleiden and Schwann = plants and animals are composed of cells and cell products
Tenements of the Cell Theory:
1) All organisms are composed of one or more cells.
2) The cell is the smallest unit having the properties of life.
3) The continuity of life arises directly from the growth and division of single cells.
Cell size and cell function: Surface area to volume ratio!
- The larger the ratio, the better off the cell!
- Impact of surface area to metabolism
What is the largest cell in the human body? The smallest?
Cell Structures and Their Functions
All cells are placed in one of 2 classes:
Prokaryotic = lack a nucleus (bacteria)
Eukaryotic = have a nucleus (protists, fungi, plants,
and animals)
PROKARYOTIC CELLS
· very, very small
· very simple structure
Parts:
A) Plasma (cell) membrane = encloses cytoplasm of cell
B) Nucleoid Region = where DNA is at (not a nucleus)
C) Ribosomes = assembles proteins with info from DNA
D) Bacterial Cell Wall = a rigid outer layer that surrounds
the cell membrane, protects the cell, maintains shape
E) Capsule = a sticky outer layer over cell wall
F) Pili and Fimbriae = numerous short projections that
help with adherence
G) Prokaryotic Flagella = longer projections that help with
motility
H) Plasmids = extra-chromosomal pieces of DNA
EUKARYOTIC CELLS
· have a nucleus
· very, very large
· complex internal organization
· compartmentalized
· membrane bound organelles
Organelle = "small organ", membrane enclosed structures found inside the cell, each for a specialized function. All chemical activities of the cell occur within organelles.
Benefits of Organelles:
1) Separate environments for chemical reactions
2) Increased membrane surface area
Eukaryotic Cells Broken Up into 3 Regions:
1. Cell Membrane
2. Cytoplasm (cytosol and organelles)
3. Nucleus
Organelles:
1. Nucleus *
2. Endoplasmic Reticulum (ER, smooth and rough)
3. Golgi Apparatus (or Body)
4. Vesicles (lysosomes and peroxisomes)
5. Mitochondria
6. Chloroplasts (only in plants)
7. Storage Vacuole (mainly in plants)
8. Centriolus (only in animal cells)
Other Structures:
1. Ribosomes
2. Cell Wall (in plants)*
3. Cell Membrane
4. Cytoskeleton
a. Microtubules
b. Microfilaments
c. Intermediate Filaments
5. Flagella and Cilia (mainly in animals)
6. Nucleolus
The Nucleus
· Cell's genetic control center
· Double membrane
· Nucleoplasm
· Nuclear envelope
· Nuclear pores
· Chromatin = DNA + associated proteins
· Nucleolus = internal structure of nucleus, site of ribosome assembly
· Chromatin vs. Chromosome
The Cytomembrane System
· Function: internal transport, importing and exporting of cell
· 3 parts:
1. ER
2. Golgi Apparatus
3. Vesicles
Endoplasmic Reticulum
· Single, continuous membrane
· Pipes, tubes and tunnels in cell
· Continuous with nuclear envelope
· Superhighway of the cell
· 2 kinds: Rough ER + Smooth ER
Rough ER
- Flattened connected sacs
-