Cells Structure and Function

Cells, the units of structure and function of living organisms, come in two main categories based on their structural complexity. Prokaryotic cells are small and simple; do not have a nucleus to store DNA, the genetic material; and lack membrane bound organelles. Eukaryotic cells are large and complex; DNA is stored in a nucleus, and there are many membrane bound organelles to conduct the functions of the cell.

All Organisms Are Composed of Cells Eukaryotic Cells Animals Plants Fungi Protists Prokaryotic Cells Bacteria Archea

Prokaryotic Organisms Bacteria and Archea are prokaryotic organisms. Unicellular and very simple, these prokaryotic organisms are vital to life on Earth due to their roles in ecosystems. Prokaryotic cells have ribosomes to make proteins and their DNA is in a nucleoid region. Pilli and flagella function for attachment and motility

In Eukaryotic Organisms Cells Have Organelles Unicellular Protists Multicellular: Animals, Plants, Fungi Eukaryotic cells are compartmentalized to increase metabolic efficiency. They contain many cellular organelles to conduct specific functions. Organelles have the surface area (room required to carry out work) and the materials required for specific functions of the cell.

All Eukaryotic Cells Have Similarities All eukaryotic cells have many membrane bound organelles in common. Plasma membrane – cell’s outer boundary Nucleus – site of DNA replication and transcription Endoplasmic Reticulum – involved in synthesis and transport Mitochondria – site of intracellular cellular respiration Gogi apparatus – involved in chemical modification and packaging Cytoskeleton – involved in structure and motility

Plasma Membrane The plasma membrane is found in all types of cells. It is the boundary (border), which defines the cell. It controls the entrance and exit of materials. It provides surface area for many of the cells enzymatic functions. Organelles have membranes, which are very similar to the plasma membrane.

Nucleus The nucleus houses DNA, the genetic material. The nucleus contains an organelle, the nucleolus, which deals with RNA. The nucleus has pores that selectively allow the entrance and/or exit of substances

Two Types of Endoplasmic Reticulum RER is the Rough Endoplasmic Reticulum, which has ribosomes. Within the RER proteins are modified into functional proteins and packed into transport vesicles. SER is the Smooth Endoplasmic Reticulum, which has no ribosomes. Within the SER lipids are synthesized. It also detoxifies substances. It stores Calcium ions for muscle contractions

Gogi Apparatus/Body/Complex Receives and modifies substances synthesized in the endoplasmic reticulum. Substances are packaged into vesicles to be used by the cell or transported out of the cell.

Lysosomes Lysosomes contain enzymes that fuse with food vacuoles for digestion. Within white blood cells of the immune system, enzyme filled lysosomes fuse with bacteria filled vacuoles and digest the bacterial cells. Lysosomes fuse with waste vacuoles or vesicles and recycle, salvageable materials for the cell.

Vacuoles Vacuoles are storage vesicles, which may contain, water, wastes, toxins, food, chemicals, and any other materials that the cells need to store. Vacuoles are essential to maintain homeostatic balance in cells Vacuoles increase the efficiency of the cells by providing a high degree of compartmentalization .

Endomembranes Together, the nuclear envelope; the endoplasmic reticulums, both smooth and rough, the Gogi Apparatus; vesicles; lysosomes; and vacuoles; compose the endomembrane system of the cell. All of these organelles are physically or strategically connected and function in tandem and synchrony.

Mitochondria Two main stages of cellular respiration, the Kreb’s Cycle and the Electron Transport Chain, occur in the mitochondria in order to transform energy from the food that organisms eat into chemical energy in the bonds of ATP.

Cytoskeleton Composed of fibrous proteins of various diameters, the cytoskeleton is responsible for support and movement of organelles and the cell.

Ribosomes Ribosomes are not membrane bound organelles. Rather they are composed of rRNA. Ribosomes are involved in the synthesis of proteins along with other types of RNA, mainly mRNA and tRNA. Ribosomes are found in both eukaryotic and prokaryotic cells.

Cells Are Models of Organization and Efficiency Cells illustrate the principle of emergent properties: the whole is greater than the individual part.