© 2009 FIDM/The Fashion Institute of Design & Merchandising

FIDM eLearning Program Page 1 of 4

Chapter 4 – A Tour of the Cell

INTRODUCTION TO THE CELL 1. Microscopy

a. light microscope – magnifies cells up to 1000 times b. electron microscopes (EM) – uses beam of electrons instead of light; has

greater magnification (increase in size) and resolution (clarity) than light microscopes • scanning electron microscope (SEM) – study details of cell surfaces • transmission electron microscope TEM) – study details of internal cell

structures c. Most cells are microscopic – most too small to see with the unaided eye

• Cells range in size from the smallest bacteria (0.2μm) to chicken eggs (10cm wide) and human nerve and muscle cells (almost 1m long) (see figure 4.2A, p. 54)

• Cell size is determined by its requirement for enough surface area to obtain adequate nutrients and oxygen from the environment and to dispose of its wastes; smaller cells have more surface area relative to their volume than larger cells

2. Prokaryotic and Eukaryotic Cells a. ALL cells have basic features in common: plasma membrane (surrounds cell),

cytoplasm (fluid), DNA (hereditary material), and ribosomes (make proteins) b. Prokaryotic cells (bacteria and archaea) (see Figure 4.3B, p. 55)

• Small – 1 to 10μm long • no nucleus (not membrane-bounded) – nucleoid region contains DNA

c. Eukaryotic cells (protists, fungi, plants, animals) (see Fig. 4.4A/B, pp.56-7) • Larger, more complex cells • Has a true, membrane-bounded nucleus • Contain organelles, membrane-bounded structures within the cytoplasm that

facilitate a variety of chemical activities (cellular metabolism)

ORGANELLES OF THE ENDOMEMBRANE SYSTEM 1. Overview: Endomembrane System - a collection of membranous organelles that

are connected and work together to manufacture, store and transport cell products 2. Nucleus

a. Function: • Contains DNA and passes it on to daughter cells in cell division • Builds ribosomes in nucleolus • Copies DNA instructions into RNA to direct protein synthesis

FIDM eLearning Program Page 2 of 4

b. Structures: • Chromatin – long fibers (which coil into chromosomes) of nuclear DNA

attached to proteins • Nuclear envelope – porous membrane surrounding nucleus • Nucleolus – produces building blocks of ribosomes

3. Endoplasmic Reticulum (ER) “network within the cell” a. Smooth ER –smooth because it lacks attached ribosomes

• Synthesizes lipids • Helps process (detoxify) drugs and harmful substances in liver cell; however,

overexposure to harmful chemicals increases the amounts of smooth ER and its detoxifying enzymes which in turn increases the body’s tolerance to the drugs

• Stores calcium ions in muscle cells to aid in contraction b. Rough ER – appears “rough” due to attached ribosomes

• Produces more membrane and transport vesicles • Synthesizes, modifies, and packages proteins transported to other organelles

or secreted by cell (Ex: insulin) 4. Golgi Apparatus (named after Italian biologist, Camillo Golgi)

a. Looks like flattened stacks of pita bread; not interconnected like ER sacs; vary in number according to how active cell is in secreting proteins

b. Receives and modifies substances from ER, then ships them in transport vesicles to other organelles or to the cell surface for secretion

5. Lysosomes – “break-down body” a. Produced in animal cells by the rough ER and Golgi apparatus b. Sacs containing digestive (hydrolytic) enzymes that break down and recycle

organic molecules c. Abnormal lysosomes –hereditary disorders called lysosomal storage diseases,

where the lysosomes lack certain hydrolytic enzymes, can be fatal 6. Vacuoles

a. Membranous sacs, usually larger than vesicles b. Food vacuoles – function with lysosomes c. Large central vacuole – in plant cells, act as food vacuoles, absorb water to

enlarge cell, store chemicals or waste products, pigments to attract insects, or poisons to deter predators

d. Contractile vacuole – in protists, controls absorption of excess water

ENERGY-CONVERTING ORGANELLES 1. Chloroplasts – convert solar energy to chemical energy

a. Found in plant and some protist cells b. Photosynthetic organelles – can convert light energy into chemical energy which

is stored in sugar molecules of the cell c. Made of stroma, a thick fluid, and membranous tubules connecting stacked

disks, grana, containing the pigment chlorophyll, which traps the solar energy 2. Mitochondria – harvest chemical energy from food

a. Found in nearly all eukaryotic cells b. Carry out cellular respiration by converting the chemical energy of food such as

sugars to the chemical energy of a molecule called ATP, the main source of energy for cellular activities

FIDM eLearning Program Page 3 of 4

c. Made of intermembrane space, cristae (highly folded inner membrane embedded with enzymes that make ATP), mitochondrial matrix (fluid inside inner membrane where chemical reactions of cellular resp. occur)

THE CYTOSKELETON AND RELATED STRUCTURES 1. A meshwork of protein fibers, which provide structural support, are involved in

various types of cell movement, and help regulate cellular activities by transmitting signals from cell’s surface to its interior

2. Microfilaments – thinnest fibers; contain actin filaments (globular proteins) which enable cells to change shape and move

3. Intermediate filaments – varied and rope-like; reinforce the cell shape and anchor certain organelles

4. Microtubules – thickest, straight hollow tubes of globular proteins; give the cell rigidity and act as tracks for organelle movement

5. Cilia and Flagella – locomotor appendages, made of microtubules, in a “9+2” arrangement which allows for their bending ability and movement

CELL SURFACES AND JUNCTIONS 1. Plant cells

a. Cell walls – made of a matrix of cellulose fibers, which make cell wall rigid for protection and skeletal support (keeps plants upright on land)

b. Plasmodesmata – connecting channels between plant cells allows water, nutrients and chemical messengers to pass between cells

2. Animal cells a. Extracellular matrix – sticky layer of glycoproteins; helps hold cells together in

tissues, protects and supports cells, and helps regulate cell behavior b. Cell junctions – connect adjacent cells in tissues

• Tight junctions – binds cells tightly together to form a leak-proof sheet (lines digestive tract)

• Anchoring junctions – rivet cells together with cytoskeletal fibers forming strong sheets (skin and heart muscle)

• Gap junctions – channels similar to plasmodesmata; allow small molecules to flow between cells; facilitates chemical communication (ions flow to cells of heart muscle to coordinate their contraction)

FUNCTIONAL CATEGORIES OF ORGANELLES (see Table 4.19, p. 67) 1. Manufacturing

a. Nucleus b. Ribosomes c. Rough ER d. Smooth ER e. Golgi Apparatus

2. Breakdown a. Lysosomes (in animal cells and some protists) b. Peroxisomes c. Vacuoles

3. Energy Processing

FIDM eLearning Program Page 4 of 4

a. Chloroplasts (in plants and some protists) b. Mitochondria

4. Support, Movement, and Communication Between Cells a. Cytoskeleton (including cilia, flagella, and centrioles in animal cells) b. Cell walls (in plants, fungi, and some protists) c. Extracellular matrix (in animals) d. Cell junctions