A Tour of the Cell
Dutch republic started making microscopes
Anthony Van Leeuwenhoele (1673) is known for the best microscope for his time.
Made people such as the Dutch royalty interested in “looking at things”
Robert Hooke coined the word “cell” as the tiniest living system
Called it a cell because it looked like a cell in a bee hive.
Types of Microscopes
Stero-scanning microscopes used to look at surface of specimen.
Light microscopes and Electron microscopes are used to look inside specimen
Light microscopes has resolution limit of about 0.2 microns
Magnification limit of about 1000 times
In 1950 electron microscope was introduced
Allowed to view protons, viruses etc.
Take cells apart to study their components
Done by use of centrifuge with spins the specimen.
The spinning causes certain elements of the cell to fall to bottom depending
on density of organelle and speed of centrifuge
A cell is the simplest collection of matter, which has all components of life.
1. Lowest Hierarchical level which is alive
2. Cell is the basic unit of life
3. Cells preform all functions necessary to live and reproduce
Occurs in virtually every kind of organism
Some wreck havoc others cause no disease or outwards sign of their presence
Often highly specific to host
Can only reproduce when they enter a host cell
Cant reproduce by themselves
There are two types of cells: Prokaryotes and Eukaryotes.
Derives from words Pro=before and Karyote=nucleus
An example of a prokaryotic cell is bacteria, cyanobacteria, mycoplasmas etc.
No nucleus (genetic information is located in nucleioud)
Plasma membrane, ribosomes, nucleoid, cytoplasm, cell wall, pilli, flagella,
mesosomes, photosynthetic membrane.
Early form of life Eukaryotic cells:
Derived from the words Eu=true and karyote=nucleus
Found in 4 kingdoms:
Surrounded with nuclear membrane
Plasma membrane, cytoplasm. Nucleus, ribosomes, organelles,
Most genes in nucleus
Some in mitochondria and chloroplast
Average size about 5 microns in diameter
Separated from the cytoplasm by a double membrane
Separated by 20-40nm
Where the double membranes are fuses, a pore allows large macromolecules and
particles to pass through
The nuclear side of the envelope is lined by the nuclear lamina, a network of
intermediate filaments that maintain the shape of the nucleus
Within the nucleus, DNA and associated proteins are organized into fibrous
Appears as diffuse mass
When the cell prepares to divide, the chromatin fibers coil up to be seen as separate
Each eukaryotic species has a characteristic number of chromosomes
In the nucleus is a region of density stained fibers and granules adjoining chromatic,
In the nucleolus, ribosomal RNA is synthesized and assembled with proteins
from the cytoplasm to form ribosomal subunits.
The nucleus directs protein synthesis by synthesizing messengers RNA.
Material between the plasma membrane and the nuclear envelop.
Has a variable viscosity
Main chemical constituents are water (approx. 80%) nucleic acids, proteins, lipids,
carbohydrates, pigments, etc. Ribosomes Build:
Ribosomes contain rRNA and proteins.
Ribosomes are composed of two subunits that combine to carry out protein
Cell types that synthesize large quantities of proteins (e.g. the pancreas) have large
numbers of ribosomes and prominent nuclei.
Free ribosomes, are suspended in the cytosol and synthesize proteins that function
within the cytosol.
Bound ribosomes, are attached to the outside of the endoplasmic reticulum.
Ribosomes can shift between roles.
Many of the internal membranes in a eukaryotic cell are part of the endomembrane
These membranes are either in direct contact or connected via transfer of vesicles,
sacs of membrane.
The endomembrane system includes:
Nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes,
vacuoles, and the plasma membrane.
There are two regions of ER that differ in structure and functions:
1. Smooth ER looks smooth because is lacks ribosomes
2. Rough ER look rough because ribosomes are attached to the outside
including the outside of the nuclear envelope.
Smooth ER is rich in enzymes and plays a role in a variety of metabolic processes
Synthesize lips, including oils, phospholipids and steroids
Smooth ER also catalyzes a key step in the mobilization of glucose from stored
glycogen in the liver.
Other enzymes in the smooth ER of the liver help detoxify drugs and poisons
These include alcohol and barbiturates
Frequent exposure leads to proliferation of smooth ER, increasing tolerance
to the target and other drugs
Muscle cells are rich in enzymes that pump calcium ions from the cytosol to the
cisternae. Rough ER:
Rough ER is especially abundant in those cells that secrete proteins
As a polypeptide is synthesized by the ribosome, it is threaded into the
cisternal space through a pore formed by a protein in the ER membrane.
Secretory proteins are packaged in transport vesicles that carry them to their next
Rough ER is also a membrane factory.
Membrane bound proteins are synthesized directly into the membrane
Enzymes in the Rough ER also synthesize phospholipids from precursors in
As the ER membrane expands, parts can be transferred as transport vesicles
to other components of the endomembrane system.
Transports vesicle from the ER for modification of their contents
It is the center of manufacturing, sorting and shipping