Transcript Cells
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 “membranebound” • 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 (Ca2+) – 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