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

MITOCHONDRIANote 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