Cell Biology: Anatomy of the Generalized Cell

Study Notes

The cell is the basic living unit of all organisms.
Humans are composed of trillions of cells.
Cells are extremely small, but complex structures.
Most cells are specialized to perform specific functions.
The human body is made up of many populations of these specialized cells.
Cells are primarily made up of four elements: carbon, oxygen, hydrogen, and nitrogen.
Cells also contain smaller amounts of other elements, such as iron, sodium, and potassium.

The nucleus is the control center of the cell and contains genetic material (DNA).
DNA contains instructions for building the entire body.
DNA is also necessary for cell reproduction.
A cell without a nucleus will die.
The shape of the nucleus typically conforms to the shape of the cell.
The nucleus has three distinct regions: the nuclear envelope, nucleoli, and chromatin.

The nuclear envelope is a double membrane barrier surrounding the nucleus.
The two membranes of the nuclear envelope fuse and create nuclear pores.
The nuclear envelope is selectively permeable, allowing freer passage of substances than other cellular membranes.
The nuclear membrane encloses a jellylike fluid called nucleoplasm, where nucleoli and chromatin are suspended.

Nucleoli are dark-staining, essentially round bodies in the nucleus.
They are the sites where ribosomes are assembled.
Ribosomes migrate into the cytoplasm and serve as the actual sites of protein synthesis.

Chromatin is a loose network of thread-like DNA combined with protein when a cell is not dividing.
When a cell divides, chromatin threads coil and condense to form chromosomes.
Chromosomes are dense, rod-like bodies.

The plasma membrane is a flexible, fragile, and transparent barrier that contains the cell contents.
It separates the cell contents from the surrounding environment.
The plasma membrane consists of two lipid layers arranged "tail to tail" with protein molecules floating within.
The lipid portion is primarily phospholipids, with a substantial amount of cholesterol.
The lipid bilayer forms the basic structure of the membrane.
The polar "heads" of the phospholipids face the watery environment inside and outside the cell, while the non-polar "tails" face each other in the interior of the membrane.

Cell: The basic living unit of all organisms.
Robert Hooke: Discovered cells while examining cork under a microscope in the late 1600s.
Human body: Composed of trillions of cells.
Cell size: An average-sized cell is about one-fifth the size of the smallest dot you can make with a pencil.
Cell specialization: While cells share basic characteristics, they also specialize to perform specific functions within the body.
Importance of cell study: Connects the study of chemistry and tissues.

Control center of the cell: Contains the genetic material (DNA) which carries instructions for building the body.
DNA differences: Human DNA is distinct from that of other organisms like frogs.
DNA function: Contains instructions for protein synthesis and is essential for cell reproduction.
Nucleus shape: Usually conforms to the shape of the cell.
Nucleus components:
- Nuclear envelope: A double membrane barrier surrounding the nucleus.
- Nucleoli: Dark-staining round bodies within the nucleus, responsible for ribosome assembly.
- Chromatin: A loose network of DNA and protein, which condenses to form chromosomes during cell division.
Chromosomes: Dense, rod-like bodies formed from condensed chromatin.

Outer cell boundary: It's a flexible, transparent barrier that separates the cell’s internal environment from the external environment.
Structure: Consists of two layers of lipids (fats) arranged "tail to tail" with embedded proteins.
Phospholipids: The majority of the lipid layer is composed of phospholipids.
Cholesterol: Found in substantial amounts within the membrane.
**Membrane "fabric": **The lipid bilayer acts as the basic structure of the membrane.
Membrane permeability: The plasma membrane is selectively permeable, controlling which substances can enter and leave the cell.