Cells The cell is the structural and functional unit of life Human adults are made up of ~100 trillion cells Each cell has an outer boundary called the plasma (cell) membrane which isolates the fluid within the cell from the fluid that surrounds the cell Some cells function individually, while most cells work together with similar cells forming tissues Within each cell is a collection of subcellular components called organelles which accomplish a specific task for the cell –membranous –nonmembranous (inclusions)

Cell Diversity

Cellular Membranes The outer boundary of the cell as well as the boundary of many of the internal organelles is made of a cellular membrane Composed primarily of phospholipids that are arranged in a bilayer (2 layers) with proteins, carbohydrates and cholesterol molecules are integrated within

Phospholipid Models

Cellular Membrane Anatomy

Cell (Plasma) Membrane At the surface of a cell, the plasma membrane separates the intracellular fluid (ICF or cytosol) from the extracellular fluid (ECF) of a cell Provides a means to communicate with other cells Provides a gateway for exchange between the ECF and ICF –the arrangement of phospholipids in a bilayer makes most of the thickness of the membrane NON-POLAR and thus creates an extremely effective barrier against the movement of polar substances into or out of the cell –membrane proteins determine what gets or stays in/out of a cell which allows the composition of the ICF to be optimal for cellular functions control the movement of substances into/out of the cell

Cell Membrane Proteins Integral or transmembrane proteins –completely pass through the bilayer extracellular portion is exposed to the ECF –composed of polar amino acids intracellular portion is exposed to the ICF –composed of polar amino acids “connect” the ICF and ECF –composed of nonpolar amino acids –different classes of integral proteins are based on function Peripheral membrane protein –associated only with the intracellular surface of the cell membrane (located in the ICF) –capable of detaching and moving into the cytosol to interact with other molecules within the cell

Integral Membrane Protein Structure

Integral Membrane Protein Functions

Membrane Carbohydrates The small polysaccharides that are part of the plasma membrane are always immersed in the ECF –covalently bound to an integral membrane protein or a phospholipid head 2 varieties –Glycolipids polysaccharides are covalently bound to the polar head of a phospholipid –Glycoproteins polysaccharides are covalently bound the extracellular portion of an integral membrane protein

Ribosomes Site of protein synthesis in a cell Move around the cell between 2 locations –floating in the ICF, ribosomes are “free” synthesize proteins that remain within the cell –temporarily attached to the membrane of the endoplasmic reticulum, ribosomes are “membrane- bound” synthesize: –integral membrane proteins –secreted proteins which are exported out of the cell into the ECF to go elsewhere in the body once the ribosome finishes making the protein, it detaches from the ER becoming “free” again

Nucleus Largest organelle of a cell –only intracellular organelle visible with a compound light microscope (plasma membrane is also visible) Consists of 3 parts: –nuclear envelope –chromatin –nucleolus Some cells are anuclear (no nuclei) and some are multinucleated

Nuclear Structure

ER Interconnected maze of membranous tubes and sacs Smooth ER –Storage site of intracellular calcium (Ca 2+ ) –Location of enzymes which: synthesize lipids –steroids –phospholipids hydrolyze drugs and toxins Rough ER –ribosomes on the outer surface of the ER synthesize proteins that are then moved to the Golgi complex for modification

Endoplasmic Reticulum (ER)

Golgi Complex Layers of flattened membranous sacs Modifies proteins synthesized at the rough ER –addition of carbohydrates to make glycoproteins –the removal of some amino acids makes these proteins biologically active

Golgi Complex

Mitochondria Double membrane organelle which functions to synthesize most of the ATP for the cell –Outer membrane faces the cytoplasm –Inner membrane contains many folds called cristae increases surface area to maximize ATP synthesis –Intermembrane space is the fluid filled area between the 2 membranes –the matrix is the fluid filled area in the center of the mitochondria

Mitochondria

Lysosomes Spherical membranous bags containing hydrolytic (digestive) enzymes –hydrolyze bacteria and viruses that infect a cell –hydrolyze old, worn out organelles allows cells to “recycle” the macromolecules that make up organelles

Lysosomes