CHAPTER 4 A TOUR OF THE CELL

Most cells are between 1 & 100um in diameter (Fig. 4.2A p. 54) Sect. 4.2 Cell Size Most cells are between 1 & 100um in diameter (Fig. 4.2A p. 54) Plasma membrane (PM): selective barrier that consists of proteins & lipids (phospholipid bilayer)

Cell size is limited due to: -a single nucleus controlling the entire cell -enough surface area in relation to volume to obtain nutrients and dispose of wastes

Two Types of Cells Prokaryotic Sect. 4.3 Eukaryotic No membrane bound organelles, only nucleoid region Has ribosomes & DNA Cell wall, capsule & pili help attach, flagella Found in the Domains Bacteria & Archaea Eukaryotic Have cytoplasm – region between the nucleus and the cell membrane (consists of a semifluid medium called cytosol) Contain organelles – structures w/special functions Found in protists, plants, fungi, and animals

The Nucleus (genetic control center of a eukaryotic cell) Sect. 4.5 The Nucleus (genetic control center of a eukaryotic cell) Nuclear Envelope boundary around nucleus, separating it from the contents of the cytoplasm Double membrane – each with a phospholipid bilayer

Contents of the Nucleus - nearly all of the cell’s DNA is here (organized along w/proteins into chromosomes) - unless the cells are dividing, chromosomes are seen as a tangled up mess called chromatin - nucleolus functions in the synthesis of ribosomes

Sect. 4.4 Ribosomes Function assemble enzymes and the entire cell’s other proteins there are genetic instructions for this to occur not membrane bound

exist in 2 places w/in cytoplasm Location exist in 2 places w/in cytoplasm 1) free ribosomes - suspended in cytosol (make proteins for cell use) 2) bound ribosomes – attached to endoplasmic reticulum (make proteins for export outside cell)

ribosomes usually occur in clusters called polysomes

Endoplasmic Reticulum (ER) Sect. 4.6 Endomembrane System Endoplasmic Reticulum (ER) a network of interconnected compartments, continuous w/the outer membrane on the nuclear envelope p. 58 W/in the ER is a space known as the lumen

2 distinct regions of the ER (interconnected flattened sacs) Sect. 4.8 2 distinct regions of the ER (interconnected flattened sacs) Rough ER - has ribosomes on surface - makes proteins destined to be secreted - makes membranes

Smooth ER - lack ribosomes (p. 59), membrane is continuous w/rough ER Sect. 4.7 Smooth ER - lack ribosomes (p. 59), membrane is continuous w/rough ER - serves as a transition area for ER products - makes steroids and sex hormones - tolerance to drugs - calcium for muscles

after leaving the ER, most transport vesicles travel to this organelle Sect. 4.9 Golgi Complex (p. 60) after leaving the ER, most transport vesicles travel to this organelle manufactures, warehouses, and ships (products of the ER are modified, stored, and shipped to other locations in transport vesicles) - consists of flattened sacs stacked up like pancakes (not connected) - molecules move from sac to sac

membrane-bound bag of hydrolytic (digestive) enzymes Sect. 4.10 Lysosomes membrane-bound bag of hydrolytic (digestive) enzymes - cell uses these enzymes to digest macromolecules - these enzymes work best at pH 5

made by the rough ER, processed, and released by the Golgi function by using phagocytosis (engulfs particles) then digests them

also function in recycling cell’s own organic material (recycling centers for damaged organelles) ex: webbing between fingers in embryonic development

lysosomal storage diseases (missing one of the hydrolytic enzymes): Sect. 4.11 lysosomal storage diseases (missing one of the hydrolytic enzymes): Pompe’s disease (liver can’t break down polysaccharide glycogen) Tay-Sachs (overload of lipids on nervous system)

Microbodies bounded by a single membrane compartments specialized for specific metabolic pathways (each has a particular kind of enzymes)

2 kinds of microbodies: Peroxisomes - have enzymes which transfer H from various substrates to O (produce H2O2 as a byproduct) Glyoxysomes - contain enzymes to convert fats to sugar (in plants)

Vacuole a large membrane sac various functions: Sect. 4.12 Vacuole a large membrane sac various functions: food vacuole - formed by phagocytosis contractile vacuole - found in freshwater protists (pumps out excess water from the cell)

Central vacuole - found in mature plant cells - bounded by a tonoplast (membrane) - stores organic compounds

Energy Transducers (have their own DNA) Sect. 4.14 Energy Transducers (have their own DNA) Chloroplasts formed only in plants functions in photosynthesis chloroplast – contains a green pigment (chlorophyll) p. 63

chloroplast’s elaborative structure: -consists of flattened green sacs which are stacked up -sacs called thylakoids -stack of thylakoids called a granum (if more than one granum, it’s called grana) -stroma: thick fluid surrounding thylakoids

site for cellular respiration Sect. 4.15 Mitochondria (p. 63) site for cellular respiration found in plants and animals

these foldings divide inner region of mitochondria - intermembrane space – region between inner and outer membranes - has inner membrane that’s convoluted within foldings called cristae (this greatly increases surface area to enhance ATP production) - mitochondrial matrix – is enclosed by the inner membrane (most of the respiration takes place here)

Sect. 4.16 Cytoskeleton – supportive meshwork of fine fibers for structural support Microfilaments (thinnest type of fiber) solid rods of globular proteins called actin – linked in chains best known for role in muscle contraction

protein called myosin is imbedded in the actin molecule in plants, microfilaments are involved in cytoplasmic streaming (cytoplasm flows in a particular direction ex: moving chloroplasts)

Intermediate Filaments - ropelike - reinforces cell shape - anchors certain organelles (nucleus is caged by these to keep in place)

hollow rods of globular proteins called tubulins Microtubules p. 64 hollow rods of globular proteins called tubulins found in cytoplasm of all eukaryotic cells radiate out from cell centers give cell shape and reinforce it help w/animal cell division

also help other organelles navigate through cytoplasm w/in cell center are 2 centrioles – consist of 9 sets of triplet microtubules and must be 2 centrioles (a pair) in the center 9 sets p. 65 Fig. 4.17C

both have a core of microtubules and protrude from the cell Sect. 4.17 Cilia and Flagella Cilia – short fingerlike projections used for locomotion Flagellum – a whip-like tail both have a core of microtubules and protrude from the cell

wrapped in plasma membrane anchored to the cell by a basal body – similar to a centriole Ex: cilia on cells in wind pipe flagellum on sperm

Cell Wall Cell Surface plants only - thicker than PM Sect. 4.18 Cell Surface Cell Wall plants only - thicker than PM there is a thin, flexible primary cell wall (between the 2 cell walls is the middle lamella - like glue) (pectin)

cell wall strengthens as the cell matures some plants add a secondary cell wall between the PM and the primary cell wall plants use the plasmodesmata - channels in the cell wall - strands of cytoplasm connect one cell to another

no cell wall in animals Extracellular Matrix glycocalyx - fuzzy coat made of carbohydrates and helps cells stick together - strong surfaces

Intercellular Junctions provides a means by which many cells can be integrated into one functional organism cell to cell contact in animals provided by 3 junctions: 1. Tight junctions - binds cells together ex: digestive tract

2. Anchoring junctions - attach adjacent cells to each other to stretch ex: skin 3. Gap junctions - allow water and other small molecules to flow between neighboring cells (similar to plasmodesmata in plants)