4 A Tour of the Cell

Overview: The Fundamental Units of Life All living cells have 4 basic features: Cytoplasm (cytosol): gel-like substance inside cells Plasma membrane (PM): also called cell membrane Outermost surface of cell Surrounds cell from external environment Chromosome(s): contains genes/DNA; blueprint of life Ribosomes: site of protein synthesis © 2016 Pearson Education, Inc. 2

2 Major Kinds of Cells Prokaryotic Cells Eukaryotic Cells Only in Domains Archae and Bacteria (all bacteria) No nucleus: DNA in nucleoid region No membrane-bound organelles All have cell walls Eukaryotic Cells Domain Eukarya; Protista, Plantae, Fungi, Animalia Has a nucleus with nuclear membrane DNA in nucleus Contains membrane-bound organelles Plant and fungal eukaryotes: have a cell wall Animal eukaryotes: no cell walls © 2016 Pearson Education, Inc.

Concept 4.1: Biologists use microscopes and the tools of biochemistry to study cells In a light microscope (LM), visible light is passed through a specimen and then through glass lenses Lenses refract (bend) the light, so that the image is magnified LMs can magnify effectively to about 1,000 times the size of the actual specimen Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by light microscopy © 2016 Pearson Education, Inc. 4

10 m 1 m 0.1 m 1 cm 1 mm 100 mm 10 mm 1 mm 100 nm 10 nm 1 nm 0.1 nm Figure 4.2 10 m Human height 1 m Length of some nerve and muscle cells 0.1 m Chicken egg Unaided eye 1 cm Frog egg 1 mm Human egg 100 mm Most plant and animal cells LM 10 mm Nucleus Most bacteria 1 mm Mitochondrion EM Figure 4.2 The size range of cells 100 nm Smallest bacteria Super- resolution microscopy Viruses Ribosomes 10 nm Proteins Lipids 1 nm Small molecules 0.1 nm Atoms © 2016 Pearson Education, Inc.

Electron Microscopes: Used to study Subcellular Organelles 2 basic types of electron microscopes (EMs): Scanning electron microscopes (SEMs) :focus a beam of electrons onto the surface of a specimen, producing images that look three-dimensional Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen TEM is used mainly to study the internal structure of cells © 2016 Pearson Education, Inc. 6

Electron Microscopy (EM) Figure 4.3 Light Microscopy (LM) 50 mm Brightfield (unstained specimen) Brightfield (stained specimen) Phase-contrast Differential-interference contrast (Nomarski) 50 mm 10 mm Fluorescence Confocal (without technique) Confocal (with technique) Electron Microscopy (EM) Longitudinal section of cilium Cross section of cilium Figure 4.3 Exploring microscopy Cilia 2 mm Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) 2 mm © 2016 Pearson Education, Inc.

Plasma Membrane Found in all cells Bilayer of phospholipids Hydrophilic “heads” turn outward Hydrophobic “tails” face inward Proteins embedded in PL bilayer Surrounds cell; controls chemical traffic; selectively permeable © 2016 Pearson Education, Inc. 8

(a) TEM of a plasma membrane Figure 4.5 Outside of cell (a) TEM of a plasma membrane Inside of cell 0.1 mm Carbohydrate side chains Hydrophilic region Figure 4.5 The plasma membrane Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane © 2016 Pearson Education, Inc.

A thin section through the bacterium Corynebacterium Figure 4.4 Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0.5 mm Flagella Figure 4.4 A prokaryotic cell (a) A typical rod-shaped bacterium (b) A thin section through the bacterium Corynebacterium diphtheriae (colorized TEM) © 2016 Pearson Education, Inc.

Animation: Tour of an Animal Cell © 2016 Pearson Education, Inc.

Animation: Tour of a Plant Cell © 2016 Pearson Education, Inc.

ENDOPLASMIC RETICULUM (ER) Nuclear envelope Smooth ER NUCLEUS Figure 4.7-1 ENDOPLASMIC RETICULUM (ER) Nuclear envelope Smooth ER NUCLEUS Nucleolus Flagellum Rough ER Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes (small brown dots) Microvilli Figure 4.7-1 Exploring eukaryotic cells (part 1: animal cell cutaway) Golgi apparatus Peroxisome Lysosome Mitochondrion © 2016 Pearson Education, Inc.

Ribosomes (small brown dots) Figure 4.7-2 Nuclear envelope Rough endoplasmic reticulum Nucleolus Smooth endoplasmic reticulum Chromatin NUCLEUS Ribosomes (small brown dots) Golgi apparatus Central vacuole Microfilaments CYTO- SKELETON Microtubules Figure 4.7-2 Exploring eukaryotic cells (part 2: plant cell cutaway) Mitochondrion Peroxisome Plasma membrane Chloroplast Cell wall Plasmodesmata Wall of adjacent cell © 2016 Pearson Education, Inc.

The Nucleus: Information Central Found in all eukaryotes; largest organelles in animal eukaryotes Contains cell’s hereditary DNA DNA organized into linear “sticks” called chromosomes; Each chromosome is one long DNA molecule associated with histone proteins Segments are called genes Enclosed by nuclear envelope Also a PL bilayer that surrounds nucleus, separating it from cytoplasm Has pores to let molecules out of nucleus, especially mRNA Nucleolus: located within the nucleus the site of ribosomal RNA (rRNA) synthesis (which makes up ribosomes) © 2016 Pearson Education, Inc. 15

Nucleus 1 mm Nucleus Nucleolus Chromatin Nuclear envelope: Figure 4.8 Nucleus 1 mm Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Pore complex Surface of nuclear envelope (TEM) Ribosome Close-up of nuclear envelope Chromatin Figure 4.8 The nucleus and its envelope 0.25 mm 0.5 mm Pore complexes (TEM) Nuclear lamina (TEM) © 2016 Pearson Education, Inc.

Ribosomes: Protein Factories Found in all cells Complexes of rRNA and protein Made in nucleolus Ribosomes carry out protein synthesis in 2 locations: In the cytoplasm: called free ribosomes Make proteins for use in cytoplasm Attached to endoplasmic reticulum (RER); called bound ribosomes Make proteins for use in membrane or export © 2016 Pearson Education, Inc. 17

Computer model of a ribosome Figure 4.9 Free ribosomes in cytosol 0.25 mm Ribosomes ER Endoplasmic reticulum (ER) Ribosomes bound to ER Large subunit Small subunit TEM showing ER and ribosomes Diagram of a ribosome Computer model of a ribosome Figure 4.9 Ribosomes © 2016 Pearson Education, Inc.

Concept 4.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell Components of the endomembrane system: Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane These components are either continuous or connected through transfer by vesicles © 2016 Pearson Education, Inc. 19

Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi Figure 4.15 Nucleus Rough ER Smooth ER cis Golgi Figure 4.15 Review: relationships among organelles of the endomembrane system Plasma membrane trans Golgi © 2016 Pearson Education, Inc.

The Endoplasmic Reticulum: Biosynthetic Factory Found in all eukaryotes ER membrane is continuous with the nuclear envelope There are 2 regions of ER Smooth ER (SER): lacks ribosomes Makes lipids, PL, steroids Carbohydrate metabolism Detoxifies drugs and poisons Stores calcium for muscle contraction Rough ER (RER): surface is covered in ribosomes Makes proteins for membranes and export, same as bound ribosomes Distributes transport vesicles Membrane factory © 2016 Pearson Education, Inc. 21

Smooth ER Nuclear envelope Smooth ER Rough ER Rough ER ER lumen Figure 4.10 Smooth ER Nuclear envelope Smooth ER Rough ER Rough ER Figure 4.10 Endoplasmic reticulum (ER) ER lumen Cisternae Transitional ER Ribosomes Transport vesicle 0.2 mm © 2016 Pearson Education, Inc.

The Golgi Apparatus: Shipping and Receiving Center Found in all eukaryotes Consists of flattened membranous sacs called cisternae Functions of the Golgi apparatus Modifies products of the ER (takes proteins from RER and makes glycoproteins or lipids from SER and makes glycolipids) Sorts and packages materials into transport vesicles © 2016 Pearson Education, Inc. 23

Golgi apparatus cis face (“receiving” side of 0.1 mm Golgi apparatus) Figure 4.11 Golgi apparatus cis face (“receiving” side of Golgi apparatus) 0.1 mm Cisternae Figure 4.11 The Golgi apparatus trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus © 2016 Pearson Education, Inc.

Lysosomes: Digestive Compartments Found in animal eukaryotes only Membranous sac of hydrolytic (digestive) enzymes that can digest macromolecules Includes lipases, carbohydrases, proteases, nucleases Has acidic pH of 5 3 functions: Intracellular digestion; also called phagocytosis Human macrophage cells kill bacteria this way Recycle cell’s own organic material Programmed cell destruction © 2016 Pearson Education, Inc. 25

Digestion Food vacuole Figure 4.12 Nucleus 1 mm Lysosome Digestive enzymes Lysosome Figure 4.12 Lysosomes: phagocytosis Plasma membrane Digestion Food vacuole © 2016 Pearson Education, Inc.