A Tour of the Cell Chapter 4 Bozeman Tutorial: Tour of the Cell (14:16) Bozeman Tutorial: Cellular Organelles (9:37)

Overview of Cells Cell Theory – Several statements assembled in the 1800’s to explain cells: a. All living things are made of cells. b. Cells are alike in structure and function. c. Cells are the basic unit of life. d. New cells come from pre-existing cells Two reasons that cells are small: a. Efficiency: Smaller cells have increased surface area to volume. If the cell is too big, it’s difficult to move nutrients/wastes across the membrane and throughout the cell. b. Specialization: Having numerous small cells permits cells to have different functions.

Two Types of Cells 1. EUKARYOTIC – Kingdoms Animalia, Plantae, Fungi, Protista. Eukaryotes contain a membrane-bound nucleus and other structures, called organelles, that have specific functions. The organelles are found in a jelly-like medium called cytosol. Plant cells have three more organelles than the animal cells (cell wall, chloroplasts, and a large central vacuole). 2. PROKARYOTIC – Kingdoms Archaebacteria and Eubacteria. Prokaryotes are the simplest of all cells and were probably the first life forms, containing only cell wall, cell membrane, DNA, and ribosomes.

Nucleus Most prominent organelle in eukaryotic cells. Contains chromatin (DNA and histone proteins) and RNA. Has double-membrane envelope with pores for movement of materials.

Nucleolus Nucleoli (pl); found inside nucleus. Forms ribosomes.

Mitochondria Double-membrane bound; outer is smooth, inner is folded into cristae; matrix in center. Contain their own DNA and can copy themselves. Produce ATP energy through Krebs and ETC. (36 to 38 ATP per glucose in aerobic respiration).

Plastids Similar in structure to mitochondria; found in photosynthetic organisms; contain pigments. Thylakoids form stacks called grana, surrounded by stroma. Chloroplasts – green. Chromoplasts – colors vary. Leucoplasts – white.

Ribosomes Non-membrane bound; found also in prokaryotes; most numerous. Site of mRNA translation (polypeptide construction). 70S ribosomes found in prokaryotes and on endoplasmic reticulum. 80S free-floating in eukaryote cytoplasm.

Endoplasmic Reticulum (ER) Network of membranes often connected to Golgi body and cell membrane. Rough ER synthesizes, modifies, and transports proteins. Smooth ER… carbohydrates and lipids.

Golgi Complex (apparatus, body) Stacks of flattened membrane sacs. Packages and moves materials in vesicles. Cis face – vesicles join the Golgi (usually from ER). Trans face – vesicles bud off. Golgi produces lysosomes and forms cell wall.

Lysosomes Membrane bound vesicles containing digestive enzymes. Protease (proteins); Nuclease (nucleic acids); Lipase (lipids). Digest old organelles, food particles or bacteria, and cause cell death.

Peroxisomes (microbodies) Vesicles containing enzymes which can break down fats, alcohols, and poisons. Forms hydrogen peroxide which is then broken into water and oxygen by catalase.

Vacuoles Membrane sac formed by pinching of cell membrane. Storage for water, food, wastes, or pigments. Prominent in plants.

Cytoskeleton

Table 6-1b 10 µm Actin subunit 7 nm

Direction of organism’s movement Fig. 6-23 Direction of swimming (a) Motion of flagella 5 µm Direction of organism’s movement Power stroke Recovery stroke (b) Motion of cilia 15 µm

Intercellular Junctions Cells of a complex organisms are integrated into one functional organism. Cells interact through direct physical contact. Cell walls of plants have perforations called plasmodesmata through which the living contents of adjacent cells are connected. In animals there are three main types of junctions: tight junctions, desmosomes, and gap junctions.

Tight Junctions Membranes of neighboring cells are fused together forming a seal.

Desmosomes Cells are fastened together (spot weld) and reinforced with keratin filaments.

Gap Junctions Channels between cells provide for chemical communication.

Fig. 6-32 Tight junction Tight junctions prevent fluid from moving across a layer of cells 0.5 µm Tight junction Intermediate filaments Desmosome Desmosome Gap junctions 1 µm Extracellular matrix Space between cells Gap junction Plasma membranes of adjacent cells 0.1 µm