This section covers the following topics

• Structures in prokaryotes
• General characteristics of eukaryotes
• Animal cells
• Plant cells
• The plasma membrane
• Movement of molecules through a membrane
• Structure and reproduction of viruses

Section Summary

Prokaryotes are relatively small, simple cells that lack organelles. Prokaryotes have a cell membrane and cell wall, internal cytoplasm, ribosomes, genetic material and an external capsule. Many prokaryotes can propel themselves with a structure called a flagellum.

Eukaryotic cells are larger, more complex and contain organelles. Plant and animal cells are both examples of eukaryotes. Important organelles include the nucleus, endoplasmic reticulum, Golgi, peroxisomes, centrioles and chloroplasts.

The plasma membrane encapsulates all cells and separates the cytoplasm from the outside world. Various proteins allow for transport across the membrane. Molecules can cross membranes through simple diffusion, facilitated diffusion, active transport, co-transport, or by opening receptor-gated channels and voltage-gated channels. The membrane itself can move substances into or out of a cell through endocytosis or exocytosis.

Viruses are very simple, consisting of a simple insertion vehicle for their genetic material. After infecting a cell, viruses will enter either the lytic or lysogenic cycle.

Types of Cells

Overview

There are two overarching groups of cells you need to be familiar with: prokaryotic cells and eukaryotic cells. Prokaryotic cells are relatively simple and small, whereas eukaryotes are much larger and more complex. All cells are contained by a plasma membrane, which holds the cell's interior fluid, or cytoplasm.

Prokaryotes

Prokaryotes are one of the most basic organisms in existence. Prokaryotes are generally single-celled organisms that have some means of propulsion. All prokaryotes lack internal membranes or organelles.

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