Chapter 3 The Cell (part 1)

The Cell Theory Three Principles All organisms are composed of cells Cells are the smallest living units of life All cells arise from pre-existing cells (by cell division)

Cells Are Highly Structured Eukaryotic (“with nucleus”) cells are highly “compartmentalized” plasma membrane nucleus: information center cytoplasm: fluid within membrane organelles: structures with specialized functions Prokaryotes have no nucleus or true organelles

FIGURE 3.1 part 1 Eukaryotic cells, such as the generalized animal cell shown here, have internal membranebound organelles.

FIGURE 3.1 part 2 Eukaryotic cells, such as the generalized animal cell shown here, have internal membranebound organelles.

Prokaryotes have no nucleus or true organelles FIGURE 3.2 part 1 Prokaryotic cells, such as a bacterium, lack internal membrane-bound organelles.

FIGURE 3.2 part 2 Prokaryotic cells, such as a bacterium, lack internal membrane-bound organelles.

TABLE 3.1 REVIEW OF FEATURES OF EUKARYOTIC AND PROKARYOTIC CELLS

The Plasma Membrane Structure of the plasma membrane

FIGURE 3.5 The structure of the plasma membrane of a cell according to the fluid mosaic model.

Structural Features of the Plasma Membrane Lipid bilayer Phospholipids: polar head and nonpolar tail Cholesterol: makes membrane a bit more rigid Proteins: provide means of transportation through membrane Carbohydrates: provide recognition for cells and organisms

TABLE 3.2 REVIEW OF PLASMA MEMBRANE FUNCTIONS

Movement Across the Plasma Membrane Diffusion Movement from area of high concentration to low Passive transport: no energy required

FIGURE 3.7 Diffusion is the random movement of a substance from a region of higher concentration to a region of lower concentration.

Facilitated Diffusion Diffusion that uses transport (carrier) proteins in membrane to assist moving molecules across the membrane both: Down the concentration gradient Without expending energy

FIGURE 3.8 Facilitated diffusion is the movement of a substance from a region of higher concentration to a region of lower concentration with the aid of a membrane protein that acts as a channel or a carrier protein.

Active Transport Active transport uses proteins and energy to move substances from an area of lower concentration to an area of higher concentration

Active Transport Proteins Use Energy FIGURE 3.10 Active transport is the movement of molecules across the plasma membrane from an area of lower concentration to one of higher concentration with help from a carrier protein and energy, usually in the form of ATP.

Osmosis Osmosis: net diffusion of water across a semi-permeable membrane

FIGURE 3.9 Osmosis is diffusion of water across a selectively permeable membrane. The drawings show what happens when a membranous bag through which water but not sugar can move is placed in solutions that are (a) hypertonic, (b) isotonic, or (c) hypotonic to the solution inside the bag. The width of the arrows corresponds to the amount of water moving into and out of the bag. The photographs show what happens to red blood cells when placed in the three kinds of solutions. Red blood cells are normally shaped like flattened disks, as in part b.

Osmosis and Tonicity

Endocytosis (Phagocytosis) Moves Materials in Bulk Endocytosis moves material into cell Example: WBC engulfs bacteria

FIGURE 3.11a Endocytosis—phagocytosis or pinocytosis—occurs when a localized region of the plasma membrane surrounds a bacterium, large molecule, or fluid containing dissolved substances and then pinches off to form a vesicle that moves into the cell.

Exocytosis Moves Materials in Bulk Exocytosis moves material out of the cell Example: secretion of hormones

FIGURE 3.12 Cells package large molecules in membrane-bound vesicles, which then leave by exocytosis.

TABLE 3.3 REVIEW OF MECHANISMS OF TRANSPORT ACROSS THE PLASMA MEMBRANE

FIGURE 3.13a The nucleus contains almost all the genetic information of a cell.

FIGURE 3.13b The nucleus contains almost all the genetic information of a cell.

Structure and Function of the Nucleus Functions: Contains the genetic information of the cell Controls the function & the operations of the cell Structural features: Double-layered nuclear membrane Nuclear pores Chromosomes/chromatin Nucleolus (synthesizes ribosomes)

Our Cells Are Highly Structured Chromosomes contained in the nucleus are made of DNA

FIGURE 3.14a Chromosomes are composed of DNA and associated proteins.

FIGURE 3.14b Chromosomes are composed of DNA and associated proteins.

Endoplasmic Reticulum (ER)

FIGURE 3.15 The endoplasmic reticulum (ER), shown in this electron micrograph, is continuous with the plasma and nuclear membranes and consists of two regions: rough ER and smooth ER.

Endoplasmic Reticulum (ER) and Ribosomes Ribosomes: used in synthesis of proteins Free and membrane bound Endoplasmic Reticulum (ER): packages the proteins Smooth ER: no ribosomes, lipid synthesis & detoxifies alcohol and drugs Rough ER: has ribosomes, protein synthesis