CHAPTER 3 A TOUR OF THE CELL

ALL ORGANISMS ARE MADE OF CELLS

THE CELL THEORY: 1. All living things are composed of cells. 2. Cells are the basic unit of structure and function in living things. 3. All cells come from pre-existing cells.

TYPES OF MICROSCOPES  Light Microscopes :  Use visible light  Used to examine living cells  Magnify about 1000 times  Not powerful enough to view internal cell structures

Light Microscope

TYPES OF MICROSCOPES:  Electron Microscopes:  Electron beams used for magnification  Specimens must be killed and placed in a vacuum to be viewed  Magnify up to a million times  SEM used to view cell surface  TEM used to view internal structures

Electron Microscope

Electron Micrograph Jumping spider foot

PROKARYOTIC CELLS  Most primitive cell type  Lack internal membrane-bound structures—organelles—that perform specific functions  First organisms to appear in fossil record  Include organisms from the Domains Archaea and Bacteria

Prokaryotic Cell

EUKARYOTIC CELLS  More advanced cell type  Cells contain membrane-bound structures called organelles—including a nucleus— that perform specific functions  Domain Eukarya  Includes the Kingdoms Plantae, Animalia, Protista, and Fungi

Eukaryotic Cells Human cells: Tissue

PROKARYOTIC vs. EUKARYOTIC

Prokaryotic Cell:

PLANT vs. ANIMAL CELLS  Both contain most organelles  Plant cells have 3 structures not seen in animal cells: 1. Cell wall: surrounds cell membrane 2. Chloroplast: photosynthesis occurs here 3. Central vacuole: large storage area

Animal Cell

Plant Cell

THE CELL BUILDS A DIVERSITY OF PRODUCTS

NUCLEUS  Directs the activities of the cell  Contains most of cell’s DNA  Chromatin: long fibers of DNA; - attached to proteins - organized when cell divides

NUCLEUS  Nuclear envelope: pair of membranes surrounding nucleus - has tiny holes or pores—substances made in the nucleus exit through these pores

NUCLEUS  Nucleolus: round structure made of fibers and granules inside nucleus - produces ribosomes—small organelles involved in protein synthesis - not surrounded by membranes

RIBOSOMES  Made of proteins and nucleic acids  Produce all the proteins for the cell  Float free in cytoplasm or are attached to membrane network within the cytoplasm

NUCLEUS

ENDOPLASMIC RETICULUM  Network of membranes within cytoplasm  Connected to the nucleus  One of the main manufacturing and transportation facilities of the cell  Two distinct regions: 1. Rough ER 2. Smooth ER

ROUGH ER  Has ribosomes attached  Ribosomes produce proteins and insert them into or through ER membrane  Some proteins produced are packaged in vesicles and exported  Cells that secrete many proteins are rich in rough ER

SMOOTH ER  No attached ribosomes  Produce lipid molecules  Cells of ovaries and testes that produce sex hormones (cholesterol derivatives) are rich in smooth ER

ENDOPLASMIC RETICULUM

GOLGI APPARATUS  Series of flattened sacs that receives chemical products in vesicles  Modifies, stores, and repackages cell products in vesicles  Routes repackaged vesicles with chemical products to their destinations

GOLGI APPARATUS Note vesicles forming and leaving Golgi apparatus

VACUOLES  Membrane-bound sacs that serve as storage areas  Many store undigested nutrients  Function varies from organism to organism

CONTRACTILE VACUOLES  Found in some unicellular freshwater organisms Fig 6-22a; p. 126  Pumps out excess water that diffuses into the cell

CENTRAL VACUOLE  Many plant cells  Contributes to growth by absorbing water and causing cells to expand  Contain pigments in flower cells that attract insects

Plant Cell

LYSOSOMES  Membrane-bound sacs containing digestive enzymes—several functions  Fuse with food vacuoles exposing nutrients to enzymes that digest them  Can digest harmful bacteria—in white blood cells, lysosomes release enzymes into vacuoles containing bacteria  Recycling centers for damaged organelles

LYSOSOMES

CHLOROPLASTS AND MITOCHONDRIA ENERGIZE CELLS

CHLOROPLASTS  Most living organisms run on energy provided by photosynthesis  Photosynthesis: process of converting light energy to chemical energy  Chloroplasts: organelle found in cells of plants and algae where photosynthesis occurs

Plant Cell

CHLOROPLAST STRUCTURE  Enclosed by two membranes  Inner membrane divides chloroplast into compartments  One compartment is fluid-filled—stroma  Other compartment contains membrane- bound disks—thylakoids—that trap light energy and convert it to chemical energy

CHLOROPLAST STRUCTURE

CELLULAR RESPIRATION  Cellular respiration: process organisms access energy needed for life activities  Releases energy from food (sugars and other organic molecules) and uses it to form another organic molecule—ATP  ATP (adenosine triphosphate): main energy molecule used by cells

MITOCHONDRIA  “Powerhouse of the cell”: site of cellular respiration—ATP production  Found in almost all eukaryotic cells—unlike chloroplasts which are found only in plants  Cells that are especially active, e.g. muscle cells have an abundance of mitochondria

STRUCTURE OF MITOCHONDRIA  Enclosed by two membranes  Inner membrane—cellular respiration occurs here—has many folds  Folds increase surface area of membrane, thereby increasing number of sites where cellular respiration can occur

MITOCHONDRIA Note highly folded inner membrane

AN INTERNAL SKELETON SUPPORTS THE CELL AND ENABLES MOVEMENT

CYTOSKELETON  Network of protein fibers extend throughout the cell  Structural pattern changes constantly  Made up of two types of fiber— microtubules and microfilaments

MICROTUBULES  Straight, hollow tubes of proteins  Give rigidity and shape to cell  Provide “tracks” along which other organelles can move

MICROFILAMENTS  Thinner, solid rods made of protein  Enable cell to move or change shape  Contribute to oozing movements of some cells—amoeba and white blood cells

MICROTUBULE STRUCTURE

FLAGELLA  Long, thin, whip-like structures projecting from cell  Wave in “S” shaped motion—enable some cells to move—e.g. sperm  Made up of microtubules

CILIA  Hair-like structures that project from cell  Shorter and more numerous than flagella  Also composed of microtubules  Have a back-and-forth motion—like oarss on a rowboat—that move a celll through its surroundings or move substances over the cell surface

THE CELL FUNCTIONS AS A COORDINATED UNIT  Each membrane-bound organelle performs its own unique function  However, no organelle works alone  The cooperation of organelles makes the cell a living unit that is greater than the sum of its parts