Chapter 7: A View of the Cell

Objectives Relate advances in microscope technology to discoveries about cells and cell structure. Compare the operation of a compound light microscope with that of an electron microscope Identify the main ideas of the cell theory

The History of the Cell Theory Cells- the basic units of living organisms Compound light microscope uses a series of lenses to magnify objects in steps ▫Magnify by up to 1500 times ▫Beam of light to magnify an object

The Cell Theory Van Leeuwenhoek was the first to describe living cells seen through a simple microscope Studied with a simple microscope The research on cells was halted for 200 years until the compound light microscope was created Robert Hooke studied cork, dead cells of oak bark Called them cells because it reminded him of the small rooms monks lived in at a monastery

Cell Theory 3 Main ideas 1.All organisms are composed of one or more cells 1.Some organisms just have one, plants and animals multicelluler 2.The cell is the basic unit of structure and organization of organisms 3.All cells come from preexisting cells 1.The cell divides to form identical cells

Electron Microscopes Uses a beam of electrons instead of light to magnify structures up to times their actual size ▫See structures inside the cell ▫Electrons can collide with air particles and scatter, specimens must be examined in a vacuum 2 basic types 1.Scanning electron microscope (SEM)- learn 3- D shape 2.Transmission electron microscope (TEM)- study structure contained in a cell

Two Basic Cell Types Organelles- small, specialized structures inside the cell that help the cells function Each organelle has a specific function in the cell 2 broad types of cells ▫Contain membrane bound organelles ▫Do not contain membrane bound organelles

Prokaryotic Cells Don’t contain any membrane-bound organelles Prokaryotes- unicellular organisms, bacteria, do not have membrane bound organelles

Eukaryotic Cells Cells that contain membrane bound organelles Eukaryotes- most of the multicellular organisms we know are made up of eukaryotic cells ▫Some eukaryotes are unicellular ▫Amoebas, some algae, and yeast

Nucleus Eukaryotic cells contain a prominent structure Responsible for cell division Nucleus- the central membrane bound organelle that manages or controls cellular functions

Objectives Describe how a cell’s plasma membrane functions Relate the function of the plasma membrane to the fluid mosaic model

Maintaining a Balance All living things cells must maintain a balance regardless of inter and external conditions Plasma membrane- flexible boundary between the cell and its environment ▫Allows a steady supply of nutrients to come into the cell Maintaining the balance of an environment is called what? ▫Homeostasis

Selective Permeability A process in which a membrane allows some molecules to pass through while keeping others out ▫Some molecules freely enter and leave through the cell membrane ▫Others must be allowed into the cell only at certain times, amounts, and channels

Structure of the Plasma Membrane Phospholipids have a glycerol backbone, two fatty acid chains, and a phosphate group Membrane is composed of a phospholipid bilayer ▫Two layers of phospholipids back-to-back

The Phospholipid Bilayer Phosphate group is critical in the formation and function of the plasma membrane Two fatty acid tails are nonpolar The head, containing the phosphate, is polar Polar heads allow the cell membrane to interact with its water environment because water is polar The tails avoid water, form the interior of the membrane

Water soluble molecules do not easily move through the membrane because they are stopped by water-insoluble layer in the middle The phospholipid bilayer is a fluid mosaic model because the phospholipids move within the membrane just as water molecules move with the currents in a lake Proteins also move ▫Create “mosaic” or pattern on the surface

Cholesterol is also in the membrane ▫helps prevent fatty acid tails from sticking together ▫Necessary for diet

Proteins help transport molecules through the membrane that can’t normally pass ▫Such as water-soluble substances Transport membranes- move needed substances or waste materials through the plasma membrane Other proteins and carbohydrates identify molecules

Objectives Identify the structures and function of the parts of a typical eukaryotic cell. * Not all cells look like the cells we will be looking at, but these cells are a model for how the majority of the cells are organized Explain the advantages of highly folded membranes in cells. Compare and contrast the structures of plant and animals cells.

Two types of eukaryotes ▫Animal ▫Plant Schleiden was the scientist who discovered that all plants are made up of cells Schwann was the scientist who concluded that all animals are composed of cells

Cellular Boundaries Plasma membrane is a fluid mosaic model that describes a flexible boundary of a cell Plant cells, fungi, bacteria, and some protists have an additional boundary Cell wall- a fairly rigid structure located outside the plasma membrane that provides additional support and protection

Cell Wall Function- forms an inflexible barrier that protects the cell and gives support Cell wall is composed of cellulose Forms a thick tough mesh of fibers Very porous and allows molecules to enter Does not select which molecules can enter into the cell

The Nucleus and Cell Control Nucleus Function- gives direction to make proteins Every part of the cell depends on proteins to function The nucleus contains the blueprint to form proteins Controls the activity of the organelles “Control center”

Chromatin- strands of genetic material, DNA Master set of directions When the cell divides, the chromatin condenses to form chromosomes Nucleolus- organelle inside the nucleus Function- makes ribosomes Ribosomes- Function- the sites where the cell produces proteins according to the directions of DNA ▫Not bound by a membrane ▫Made of RNA and protein

Cytoplasm- clear gelatinous fluid inside a cell Function- suspends the cell’s organelles Ribosomes and translated RNA are transported to the cytoplasm through the nuclear envelope Nucelar envelope Function- separates the nucleus from the cytoplasm ▫Double membrane made up of two phospholipid bilayers containing small nuclear pores for substances to pass through ▫Ribosomes and translated RNA pass into the cytoplasm through these pores in the nuclear envelope

Assembly, Transport, and Storage Endoplasmic reticulum (ER)- Function - site of cellular chemical reactions Takes up tremendous space Folds and pleats fit into compact units ▫Increases surface area Ribosomes are attached to the surface called rough endoplasmic reticulum ▫Where they carry out the function of protein synthesis ▫Proteins go to other organelles Also found floating in the cytoplasm

Area of the ER that are not studded with ribosomes are known as smooth ER Function: Produce and store lipids

Golgi apparatus After proteins are made, they are transferred to the Golgi apparatus Function- sorts proteins into packages and packs them into membrane-bound structures to be sent to the appropriate destination Vesicles- the membrane –bound structures Like mail being sorted at the post office

Vacuoles- membrane bound compartment Function- temporary storage of materials ▫Stores food, enzymes, and other materials ▫Some store waste Animals cells usually don’t contain vacuoles, if they do the vacuoles are much smaller

Lysosomes Lysosomes- organelles that contain digestive enzymes Function- digest excess or worn out organelles, food particles, and viruses or bacteria ▫“Garbage disposal” Lysosomes can fuse with vacuoles and dispense their enzymes into the vacuole, digesting its contents 1Ihttps:// 1I

Energy in a cell Protein production, modifications, transportation, and digest all require energy Chloroplasts and mitochondria provide energy

Chloroplasts Function: cell organelles that capture light energy and convert it to chemical energy Only found in plant cells Located in green plants and some protists Has a double membrane Thylakoid trap energy from sunlight Stacked in grana, resemble stacked coins The fluid that surrounds them is called stroma

Chloroplast belongs to a group of plant organelles called plastids, used for storage Some store starches or lipids Other contain pigments, molecules that give off color Named according to their pigment or color they contain Chloroplasts contain green pigment chlorophyll Chlorophyll trap light energy and give leave and stem their green color

Mitochondria Mitochondria- membrane-bound organelles in plant and animal cells Function- transform energy for the cell “Power house” Energy is stored in the bonds of other molecules that cell organelles can access easily and quickly when energy is needed Folded inner membrane Occur in varying numbers depending on the function of the cell

Cytoskeleton Function- support structure for the cell within the cytoplasm Forms a framework for the cell Constantly changing Microtubules- thin, hollow cylinders made of protein Microfilaments- smaller, solid protein fibers

Centrioles- occur in pairs and made up of microtubules Important in cell division

Cilia and Flagella Cilia- short, numerous projections that look like hairs Flagella- longer projections that move with a whip-like motion Usually one or two flagella Unicellular organisms, cilia and flagella are the major means of locomotion

Cell PartProkaryotic CellEukaryotic Cell Plasma MembranePresent Cell wallPresentPresent in plants RibosomePresent ChloroplastAbsent CytoskeletonAbsentPresent Endoplasmic reticulumAbsentPresent Golgi apparatusAbsentPresent LysosomeAbsentPresent in some MitochondriaAbsentPresent NucleusAbsentPresent VacuoleAbsentPresent