Cell OrganellesChapter 7, page 174 Modified from an original PPT of Beauchemin 2006
What is a cell? A cell is a collection of living matter enclosed by a barrier that separates the cell from its surroundings. The cell is the basic unit of all forms of life.
Remember the three parts to cell theory: All living organisms are composed of one or more cells. The cell is the basic unit of structure, function in all organisms. All cells come from preexisting, living cells. (An organism is a living thing.)
There are two main categories of cells: • Prokaryote (prokaryotic cells) • Have no membrane-bound nucleus • Nucleic acid is usually found in “loops” in the cytoplasm • Have no membrane bound organelles • Usually smaller than eukaryotes • Bacteria
Eukaryotes (eukaryotic cells) • Have a membrane-bound nucleus where DNA is located • Have membrane bound organelles • Larger • All organisms except bacteria are eukaryotes
Homework (To be handed in 2 days from now) • Review your handout on organelles • Check out the diagrams of organelles on pages 174 to 181 • Answer questions 1 to 4 on page 181 • Be able to label both a plant and an animal cell (use your handouts for practice)
Cell Organelles in Eukaryotes • Organelle means “little organ” • Cytoplasm is everything inside the cell membrane, except the nucleus
Cell Membrane • The boundary of the cell
Cell Membrane Surrounds the cytoplasm, acting as a barrier between the contents of the cell and its environment Protects the cell Allows certain material to pass through (selectively permeable)
Structure of the phospholipid molecule: • two hydrophobic fatty acid "tails" • a hydrophilic "head" consisting of a phosphate group.
Hydrophobic (nonpolar molecules) – Repelled by, not dissolved in or not combining with H2O. Hydrophilic (polar molecules) – Easily absorbing in H2O.
Cell Wall • Found in plant, fungi, some protists and bacteria cells • Rigid, protective barrier • Located outside of the cell membrane
Made of carbohydrates. In plants, made of cellulose (sugar/fiber), in fungi, chitin. Provides structural support and protection, sometimes preventing the cell from bursting from water entering the cell.
Nucleus • Control center of the cell • Contains DNA which contains the coded instructions for making proteins which are the molecules that do “everything”.
Nucleus continued • Surrounded by a double membrane called the nuclear membrane or nuclear envelope. • Nuclear envelope has thousands of pores which allow material to move into and out of the nucleus.
Usually one per cell (red blood cells do not have nuclei.) Usually the easiest organelle to see under a microscope
Chromatin in the Nucleus • The thread-like material in the nucleus is called chromatin which is DNA wrapped around protein. • Usually looks like this but as a cell prepares to divide, chromatin condenses to form chromosomes.
Nucleolus • Small dense region within the nucleus • The assembly of ribosomes begins here
Ribosome • Proteins are assembled by ribosomes, following instructions from DNA. • Ribosomes are found attached to rough endoplasmic reticulum or floating free in cytoplasm • Produced in a part of the nucleus called the nucleolus
Endoplasmic Reticulum (ER) • The internal membrane system of the cell • Connected to the nuclear membrane • Assembles lipid components of the cell membrane, proteins and other materials for export from the cell.
Rough Endoplasmic Reticulum • Studded with ribosomes • Proteins that are being synthesized for export from the cell and proteins that are to be used in the cell membrane are made on the these ribosomes.
Proteins synthesized on the ribosomes on the RER enter the RER where they may be chemically modified.
Smooth Endoplasmic Reticulum • No ribosomes • Synthesizes lipids • Contains many enzymes which have specialized jobs • Makes membrane lipids; carries proteins; detoxifies drugs
Golgi Apparatus • Looks like a stack of plates • Modifies, sorts, and packages proteins and other materials made in the ER for storage in the cell or secretion from the cell.
Golgi Apparatus (continued) • Vesicles which contain the materials modified by the Golgi Apparatus pinch off the ends.
Lysosomes • Clean-up crew (sometimes called cannibals) • Membrane-bound sacks filled with enzymes that break down lipids, carbohydrates and proteins from food into smaller molecules that the cell can use. Which organelles do lysosomes work with?
Lysosomes (continued) • Also break down organelles that have outlived their usefulness for disposal.
Vacuoles • Storage container for water, food, enzymes, wastes, pigments, etc. • Large central vacuole in plant cells • Many small vacuoles in animal cells What type of microscope may have been used to take this picture?
Mitochondria (singular = mitochondrion) • “Powerhouse of the cell” • Convert the chemical energy from food into energy that can be used by the cell. • Enclosed by two membranes---an outer one and another that is folded up inside the mitochondrion
Mitochondria (continued) Cellular respiration occurs here to release energy for the cell to use Has its own strand of DNA Our mitochondria are inherited from our mothers via the eggs cell.
Chloroplast • Found in plant cells • Contains the green pigment chlorophyll which captures the sun’s energy and converts it into chemical energy (glucose) in a process called photosynthesis.
Cytoskeleton • A network of protein filaments/tubes that helps the cell maintain its shape and which helps move materials around the cell.
Cytoskeleton (cont’d) Acts as skeleton and muscle Provides shape and structure
Microfilaments (1 type of cytskeleton) • Thread-like structures • Made of a protein called actin • Make a tough, flexible framework that supports the cell • May also help the cell move by assembling and disassembling
Microtubules (another type ofmicroskeleton) • Hollow structures made of proteins known as tubulins • Perform different functions in different cells: • Critical to maintaining shape of some cells
Form centrioles (animal cells only) • Build projections from cell’s surface such as flagella and cilia that enable some cells to “swim” • Some cells have them arranged so that they can be used to produce controlled movements of the cell.
Centrioles • Aid in cell division • Found in pairs in animal cells • Made of microtubules
Quick Review • Which organelle is the control center of the cell? Nucleus • Which organelle holds the cell together? Cell membrane • Which organelles are not found in animal cells? Cell wall, central vacuole, chloroplasts • Which organelle helps plant cells make food? Chloroplasts • What does E.R. stand for? Endoplasmic reticulum