CELLS Structure

Cell Membrane Surrounds the cell to separate it from its external environment; it gives support and protection to the cell Composed of a double layer of phospholipids called the lipid bilayer; it also has proteins embedded in it The membrane acts as a selective barrier by controlling what substances enter and leave the cell

Cell Walls Found outside the cell membrane Function to give support and protection to the cell Found in plants, algae, fungi, and several prokaryotes

Cell Interior The cell has two major divisions: Cytoplasm Nucleus

Cytoplasm A semi-fluid substance in which all of the cell’s organelles are suspended Located between the nucleus and the cell membrane Contains the cytoskeleton, a network of microtubules that support the cell and give it shape

Nucleus The control center of the cell and where the cell’s DNA is located; is divided into 3 parts: Nuclear Membrane: Separates the nucleus from the cytoplasm and contains pores so that substances may enter or leave the nucleus Nucleolus: structure within the nucleus that is responsible for making rRNA Nucleoplasm: similar to the cytoplasm, it is a semifluid substance in which the DNA and nucleolus are suspended

Organelles Endoplasmic reticulum (ER): Extensive network of membranes There are 2 types: Rough ER: contains ribosomes that make proteins destined to leave the cell Smooth ER: makes lipids, steroids, and is involved in detoxification; important in cells that are responsible for ridding the body of toxic substances (i.e. liver)

Organelles (cont.) Ribosomes: Structures involved in protein synthesis Found attached to the RER or suspended in the cytoplasm Mitochondria: take the energy stored in food and transforms it into chemicals the cell can use Golgi apparatus: Series of flat membrane-bound sacs Packages proteins made from the RER and sends them in membrane-bound vesicles to their destination

Organelles (cont.) Lysosome: Membrane-bound organelles filled with enzymes These enzymes are used to break down lipids, carbohydrates, and proteins for use by the cell They also break down old organelles that no longer function

Organelles (cont.) Vacuole: Membrane-bound compartment that serves many functions (i.e. absorbs water, stores proteins, stores wastes, etc.) Plant cells have one large central vacuole Animal cells contain several small vacuoles

Organelles (cont.) Chloroplasts: plant cells have these organelles that absorb the energy from sunlight and transform it into chemical energy through the process of photosynthesis