Cell Theory Every organism is composed of one or more cells. Cells are the smallest units having the properties of life. Continuity of life arises from growth and division of single cells All cells come from pre-existing cells.

Cell Structures

Life is Cellular All cells share two characteristics: A barrier called a cell membrane that surrounds the cell. At some point in their lives cells contain DNA. DNA is a molecule that carries biological information.

Either one way or another… Cells fall into two groups, based on whether or not they have a nucleus. A nucleus is a membrane covered structure that holds DNA. This structure controls many of the cell’s activities.

Human Cheek Cells: the nucleus is the darker, spherical organelle near the center of each cell.

Either one way or another… Prokaryotes: do not have nuclei. Eukaryotes: have nuclei.

Prokaryotic Cells Prokaryotes have genetic material (DNA) that is not contained in a nucleus. Bacteria are prokaryotes.

Eukaryotic Cells Eukaryotes have a nucleus in which their genetic material is separated from the rest of the cell. Plants, animals, fungi, and protists are eukaryotes.

Eukaryotic Cell Structures Cell biologists divide the eukaryotic cell into two main parts: the nucleus and the cytoplasm. The cytoplasm is the part of the cell outside the nucleus.

In the Nucleus The nucleus contains most of a cell’s DNA. The DNA contains the coded instructions for making proteins and other important molecules.

In the Nucleus The nucleus is surrounded by a double membrane called a nuclear envelope. Most nuclei also have a small, dense region known as nucleolus (little nucleus) where ribosomes are made. Finally, inside the nucleus is a material known as chromatin. Chromatin is made of DNA bound to proteins.

In the Cytoplasm Cyto = cell Plasm = gel or liquid Eukaryotic cells have structures called organelles within the cytoplasm. Organelle = little organ ; any of a number of organized or specialized structures within a living cell.

Ribosomes Small particles of RNA and protein spread throughout the cytoplasm. Proteins are made by ribosomes. Proteins do everything…remember.

Endoplasmic Reticulum An internal membrane system. The ER is where lipids and proteins are assembled and distributed throughout the cell. The ER comes in two different varieties.

Smooth Endoplasmic Reticulum Does not have ribosomes. Helps make lipids. Rough Endoplasmic Reticulum Has ribosomes on it’s surface. Involved in a process called Protein Synthesis.

Golgi Apparatus/Complex/Body Appear as closely grouped membranes. Kind of looks like a WiFi symbol next to the cell membrane. The job of the Golgi is to change, sort and package proteins/materials from the ER for storage or export from the cell.

Lysosomes Small organelles filled with enzymes. Helps breakdown lipids, carbohydrates, and proteins into smaller molecules (monomers/subunits) that can be recycled by the cell.

Vacuoles Membrane bound structures that are used to store materials.

Chloroplasts These can be found in plants and protists. This organelle can capture the energy in sunlight and convert it into chemical energy (photosynthesis).

Mitochondria Most eukaryotic cells contain mitochondria. Mitochondria convert the chemical energy stored in food into compounds that are more convenient for the cell to use.

Cytoskeleton Structures that help support the cell. The cytoskeleton is a network of protein filaments that helps the cell maintain its shape. The cytoskeleton is also involved in movement.

Centrioles and the Centrosome The main function of the centrosome is to be a microtubule organizing center in animal cells.

Last but not least…Cell Membrane.