2.2 Cell Organelles

Nucleus

Contains most of the genetic material of a cell in the form of chromatin. RNA transcription and processing occur within the nucleus. The nucleus is encased in a plasma membrane with nuclear pores that tightly restrict movement of molecules in and out and to the endoplasmic reticulum.

Mitochondria

Membrane-bound organelles where cellular respiration and the synthesis of ATP from ADP occurs. Mitochondria have a double membrane, the outer one is smooth, while the inner one is rough. Mitochondria have their own circular DNA, are able to reproduce within cells.

Chloroplast

Membrane-bound organelles that contain chlorophyll and make energy through photosynthesis. Like mitochondria, they also have their own DNA.

Endoplasmic reticulum

Folded, membrane-bound organelles that are transport hubs from the nucleus to the Golgi apparatus. There are both rough and smooth ER. The rough ER is covered with ribosomes and is the site where membrane-bound proteins and proteins that are packaged in vesicles are made. The smooth ER does not have ribosomes on it, hence the smoother appearance, and is the site where many things are synthesized including lipids, fats, and steroids.

Golgi Apparatus

Made of stacks of membrane sacks. This is the site where most protein modification takes place and where proteins are packaged and targeted for export from the cell.

Ribosomes

Translation of RNA into protein. Made of ribosomal RNA (rRNA) and some associated proteins and can be free in the cell, making proteins in the cytoplasm, or can be found on the rough endoplasmic reticulum where they synthesize proteins that end up on or in cell membranes. Ribosomes are found in every form of life on Earth, providing evidence for a common ancestor.

Lysosomes & Peroxisomes

Vesicles in the cell where cell waste is destroyed and recycled. Lysosomes contain hydrolytic enzymes that destroy proteins, cell waste, and damaged organelles. Peroxisomes are where lipids are destroyed.

Cytoskeleton

Give structure to the cell, keep organelles in place, help cells move, and provide the framework that proteins move along in a cell.

Centrosome

Organizes the mitotic spindle during cell division. A cell has a single centrosome unless it is in the cell cycle.

Vesicles

Membrane sacs that transport molecules in a cell.