Ch.6- A Tour of the Cell

6.1- To study cells, biologists use microscopes and the tools of biochemistry.

6.2- Eukaryotic cells have internal membranes that compartmentalize their functions.

Microscopy
In light microscopes visible light is passed through the specimen then through glass lenses that bend the light so that the image of the specimen is magnified.
Magnification is the ratio of an object’s image size to its real size.
Resolution is a measure of the clarity of the image.
An electron microscope focuses a beam of electrons through the specimen.
The scanning electron microscope is used to study the surface of a specimen.
The transmission electron microscope is used to study the internal ultrastructure of cells.
Isolating Organelles by Cell Fractionation
We use cell fractionation to take cells apart and separate the organelles from each other.
We use centrifuges and ultracentrifuges to fractionate cells.

Comparing Prokaryotic and Eukaryotic Cells
Organelles are found in the cytosol.
Prokaryotic cells have a nucleoid and eukaryotic cells have a true nucleus.
Eukaryotic cells are larger than prokaryotic cells.
6.3- The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes.

6.4- The endomembrane system regulates protein traffic and performs metabolic functions in the cell.

The Nucleus: Genetic Library of the Cell
The nucleus contains most of the genes in a eukaryotic cell.
The nuclear envelope surrounds the nucleus; it’s lined by the nuclear lamina which supports the nuclear envelop.
In the nucleus the DNA is organized into units called chromosomes.
Each chromosome is made up of chromatin (protein and DNA).
The nucleolus directs protein synthesis by synthesizing messenger RNA.
Ribosomes carry out protein synthesis.
Free ribosomes are in the cytosol and bound ribosomes are attached to the outside of the endoplasmic reticulum or the nuclear envelop.

The membranes of the endomembrane system are related through direct physical continuity or by the transfer of membrane segments as vesicles.
The Endoplasmic Reticulum: Biosynthetic Factory
The ER consists of a network of membranes and sacs.
The smooth ER’s surface lacks ribosomes.
The smooth ER produces steroids, its enzymes help detoxify drugs and poisons, and it stores calcium ions.
The rough ER has ribosomes on its outer surface.

6.5- Mitochondria and chloroplasts change energy from one form to another.

The Golgi Apparatus: Shipping and Receiving Center
Products of the ER are modified and stored and sent to other destinations.
Products of the ER are modified in their transit from the cis region to the trans region.
Lysosomes: Digestive Compartments
A lysosome is a sac of hydrolytic enzymes that an animal cell uses to digest all kinds of macromolecules.
They break down ingested substances.
They recycle a cell’s organic material through a process called autophagy.
Vacuoles: Diverse Maintenance Compartments
Contractile vacuoles pump excess water out of the cell.
A plant cell’s central vacuole functions in digestion, storage, waste disposal, cell growth, and protection.
The tonoplast surrounds and protects the central vacuole.
Mitochondria are the sites of cellular respiration, and metabolic processes.
Chloroplasts are the sites of photosynthesis.
Mitochondria, chloroplasts, and peroxisome are not part of the endomembrane system.
Mitochondria: Chemical Energy Conversion
Mitochondria are enclosed by two membranes.

6.6- The cytoskeleton is a network of fibers that organizes structures and