Cell Structure Nucleus, Organelles, and Cytoplasm • The nucleus is an internal compartment that houses the cell’s DNA • Organelles are other internal structures that carry out specific functions in the cell • Cytoplasm is everything inside the cell membrane but outside the nucleus Flagella and Cilia •Cilia are short, hair-like structures that protrude from cell surfaces •Flagella and cilia can propel cells or they can move substances across a cell’s surface •Cilia in lungs sweep mucus and debris away and in your ears they conduct sound vibrations Cytoskeleton • The cytoskeleton is a web of protein fibers • It holds the cell together and keeps cell membranes from collapsing • Anchored to cell membrane • It links one region to another • Anchors nucleus and organelles to fixed locations • 3 different kinds—microfilaments, microtubules, and intermediate filaments Microfilaments • Long and slender, made of actin • Network beneath cell’s surface that is anchored to the membrane proteins • Determines the shape of the cell Microtubules • Hollow tubes of tubulin • Within the cytoskeleton, microtubules act as the highway for transportation of information from the nucleus out • RNA/protein complexes are transported along the “tracks” of microtubules by motor proteins Cell Membrane • Cell membranes are made up of phospholipids, which are a phosphate group and two fatty acids • Phospholipids are made up of a polar “head” and two nonpolar “tails” • Phospholipids form a phospholipid bilayer Cell Membrane • Cell membranes have selective permeability • The lipid bilayer allows lipids and substances that dissolve in lipids to pass through • Membrane proteins are also part of the membrane—some are for transport Cell Membrane • There are several types of membrane proteins, including: – Marker proteins – Transport proteins – Enzymes – Receptor proteins • Proteins move, because phospholipids are constantly in motion Nucleus • Houses most of the DNA, which controls the cell’s functions • Surrounded by a double membrane, called the nuclear envelope or nuclear membrane • The nuclear envelope is made of two lipid bilayers • Why do you think that there are 2? Nucleus • Nuclear pores are small channels through the nuclear envelope • What are the pores for? • The nucleolus is an area of the nucleus where ribosomes are partially assembled • Eukaryotic DNA is tightly wound around proteins, and appears as a dark mass under magnification most of the time Ribosomes • Made up of dozens of proteins and RNA • Cells make proteins on ribosomes • Some are suspended in the cytosol. These are “free” ribosomes. “Free” ribosomes make proteins that remain in the cell. • Proteins that leave the cell are made on ribosomes on the surface of the endoplasmic reticulum Endoplasmic Reticulum • An extensive system of internal membranes that move proteins and other substances through the cell • The membrane of ER is a lipid bilayer with embedded proteins Rough Endoplasmic Reticulum • The Rough ER has ribosomes attached –It helps transport proteins made on the attached ribosomes –The proteins enter the ER and a small, membrane-bound sac, or vesicle, pinches off –Proteins made on ribosomes on the rough ER stay separate from proteins made on free ribosomes Smooth Endoplasmic Reticulum • The Smooth Endoplasmic Reticulum lacks ribosomes, so it appears smooth under an electron microscope • The smooth ER makes lipids and breaks down toxic substances Golgi Apparatus • A flattened, membranebound sac that serves as the packaging and distribution center of the cell • Enzymes in the Golgi Apparatus modify proteins from the ER Lysosomes • Lysosomes are small, spherical organelles that contain the cell’s digestive enzymes Mitochondria • Organelle that uses organic compounds to make ATP, the primary energy source of cells • Cells with high energy requirements, like muscle cells, may contain hundreds or thousands or mitochondria Mitochondria • The mitochondria has two membranes –The outer membrane is smooth –The inner membrane is greatly folded, so that it has a lot of surface area –The two membranes form two compartments Mitochondria • The mitochondria also contain DNA and ribosomes, because they make some of their own proteins • Most mitochondrial proteins are made in the cytosol Organelles Only Found in Plants • Plants have 3 unique organelles –Cell wall –Chloroplasts –Central vacuole Cell Wall • Plants’ cell membranes are surrounded by cell walls • Plant cell walls are made of proteins and carbohydrates, including cellulose • Helps support and protect the cells • Connects cells to one another Chloroplasts • Chloroplasts are organelles that use light to make carbohydrates from CO2 and H2O • Found in algae as well as plants • Surrounded by 2 membranes • Contain their own DNA Central Vacuole • • • • The central vacuole stores water It may contain ions, nutrients, and wastes It makes the cell rigid, when it is full Enables plants to stand upright Let’s Review • We use microscopes to look at cells that are too small to see with the naked eye • The Cell Theory • What is a cell? What do all cells share? • Prokaryotes vs. Eukaryotes • Nucleus, Organelles, and Cytoplasm, oh my! • What separates plants from other eukaryotes? The Cell contains Cytoplasm 1. Function as Ribosomes Function as 3. ER & Golgi apparatus Function as 4. 5. Function as Support/ structure 6. Function as Power Plants 2.