Chapter 4 Cell Structure (Sections 4.8 - 4.13)

4.8 The Endomembrane System The endomembrane system includes rough and smooth endoplasmic reticulum (ER), vesicles, and Golgi bodies This system makes and modifies lipids and proteins; it also recycles and disposes of molecules and particles endomembrane system Series of interacting organelles (endoplasmic reticulum, Golgi bodies, vesicles) between nucleus and plasma membrane; produces lipids, proteins

The Endomembrane System

Endoplasmic Reticulum endoplasmic reticulum (ER) Organelle that is a continuous system of sacs and tubes An extension of the nuclear envelope Site where many new polypeptide chains are modified Rough ER is studded with ribosomes that make polypeptides that enter the ER as they are assembled Smooth ER has no ribosomes: Enzymes assemble lipids that form cell membranes, and break down substances

A Variety of Vesicles Small, membrane-enclosed, saclike vesicles form in a variety of types, either on their own or by budding Many vesicles transport substances from one organelle to another, including endocytic vesicles and exocytic vesicles Other vesicles include peroxisomes, lysosomes, and vacuoles (including central vacuoles)

Key Terms vesicle Small, membrane-enclosed, saclike organelle; different kinds store, transport, or degrade their contents lysosome Enzyme-filled vesicle that functions in intracellular digestion peroxisome Enzyme-filled vesicle that breaks down amino acids, fatty acids, and toxic substances

Key Terms vacuole A fluid-filled organelle that isolates or disposes of waste, debris, or toxic materials central vacuole Fluid-filled vesicle in many plant cells

Golgi Bodies Enzymes in a Golgi body finish proteins and lipids that are delivered by vesicles from the ER Golgi body Modifies polypeptides and lipids; attaches phosphate groups or oligosaccharides, and cuts certain polypeptides Sorts and packages the finished products into vesicles that carry them to lysosomes or to the plasma membrane

Functions of the Endomembrane System polypeptide RNA Rough ER Some of the RNA in the cytoplasm is translated into polypeptide chains by ribosomes attached to the rough ER. The chains enter the rough ER, where they are modified into final form. 1 Vesicles Vesicles that bud from the rough ER carry some of the new proteins to Golgi bodies. Other proteins migrate through the interior of the rough ER, and end up in the smooth ER. 3 Figure 4.16 Endomembrane system, where many proteins are modified and lipids are built. These molecules are sorted and shipped to cellular destinations or to the plasma membrane for export. nucleus ribosome attached to ER vesicle budding from ER Fig. 4.16.1,3, p. 62

Functions of the Endomembrane System (cont.) Smooth ER Some proteins from the rough ER are packaged into new vesicles and shipped to Golgi bodies. Others become enzymes of the smooth ER. These enzymes assemble lipids and inactivate toxins. 2 Golgi body Proteins arriving in vesicles from the ER are modified into final form and sorted. New vesicles carry them to the plasma membrane or to lysosomes. 4 Plasma membrane A vesicle’s membrane fuses with the plasma membrane, so the contents of the vesicle are released to the exterior of the cell. 5 Figure 4.16 Endomembrane system, where many proteins are modified and lipids are built. These molecules are sorted and shipped to cellular destinations or to the plasma membrane for export. protein in smooth ER Fig. 4.16.2,4,5, p. 62

4.9 Mitochondria and Plastids Mitochondria make ATP by breaking down organic compounds in the oxygen-requiring pathway of aerobic respiration Chloroplasts are plastids that produce sugars by photosynthesis

Function of Mitochondria mitochondrion Double-membraned organelle that produces ATP by aerobic respiration in eukaryotes

Mitochondrion outer membrane outer compartment inner compartment Figure 4.17 The mitochondrion. This organelle specializes in producing large quantities of ATP. inner membrane Fig. 4.17a, p. 64

Mitochondrion Figure 4.17 The mitochondrion. This organelle specializes in producing large quantities of ATP. Fig. 4.17b, p. 64

Energy powerhouse; produces many ATP by aerobic respiration Mitochondrion Energy powerhouse; produces many ATP by aerobic respiration Figure 4.17 The mitochondrion. This organelle specializes in producing large quantities of ATP. Fig. 4.17c, p. 64

Origins of Mitochondria Theory of endosymbiosis: Mitochondria evolved from aerobic bacteria that took up permanent residence inside a host cell Resemble bacteria in size, form, and biochemistry Have their own DNA, which is similar to bacterial DNA Divide independently of the cell, and have their own ribosomes

Chloroplasts and Other Plastids An organelle that functions in photosynthesis or storage, e.g. chloroplast, amyloplast chloroplast Organelle of photosynthesis in the cells of plants and many protists

Chloroplast Structure Two outer membranes enclose a semifluid interior (stroma) that contains enzymes and chloroplast DNA In the stroma, a highly folded stack of membrane (grana/granum ) forms a single, continuous compartment Photosynthesis takes place at the thylakoid membrane, which incorporates pigments such as chlorophylls, which are green

Photosynthesis Chlorophylls and other molecules in the thylakoid membrane use the energy in sunlight to synthesize ATP ATP is used to build carbohydrates (sugars) from carbon dioxide and water

Specializes in photosynthesis Chloroplasts Figure 4.18 The chloroplast, a defining character of photosynthetic eukaryotic cells. Bottom, transmission electron micrograph of a chloroplast from a tobacco leaf (Nicotiana tabacum). The lighter patches are nucleoids where the chloroplast’s own DNA is stored. Chloroplast Specializes in photosynthesis Fig. 4.18a, p. 65

Specializes in photosynthesis Chloroplast Specializes in photosynthesis Plant Cell Mitochondrion Figure 4.18 The chloroplast, a defining character of photosynthetic eukaryotic cells. Bottom, transmission electron micrograph of a chloroplast from a tobacco leaf (Nicotiana tabacum). The lighter patches are nucleoids where the chloroplast’s own DNA is stored. Fig. 4.18b, p. 65

Chloroplast Structure

(inner membrane system folded into flattened disks) two outer membranes stroma thylakoids (inner membrane system folded into flattened disks) Figure 4.18 The chloroplast, a defining character of photosynthetic eukaryotic cells. Bottom, transmission electron micrograph of a chloroplast from a tobacco leaf (Nicotiana tabacum). The lighter patches are nucleoids where the chloroplast’s own DNA is stored. Fig. 4.18c, p. 65

Other Plastids Chromoplasts are plastids that make and store pigments other than chlorophylls Red, orange, and yellow pigments color many flowers, leaves, fruits, and roots

4.12 Summary: Plant Cells

Summary: Animal Cells

Modifies proteins made by ribosomes attached to it Nucleus Keeps DNA separated from cytoplasm; makes ribosome subunits; controls access to DNA nuclear envelope nucleolus DNA in nucleoplasm Cytoskeleton Structurally supports, imparts shape to cell; moves cell and its components microtubules Ribosomes (attached to rough ER and free in cytoplasm) Sites of protein synthesis microfilaments Intermediate filaments Rough ER Modifies proteins made by ribosomes attached to it Mitochondrion Energy powerhouse; produces many ATP by aerobic respiration Smooth ER Makes lipids, breaks down carbohydrates and fats, inactivates toxins Centrioles Special centers that produce and organize microtubules Golgi Body Finishes, sorts, ships lipids, enzymes, and proteins Figure 4.26 Organelles and structures typical of A plant cells and B animal cells. Plasma Membrane Selectively controls the kinds and amounts of substances moving into and out of cell; helps maintain cytoplasmic volume, composition Lysosome Digests, recycles materials B Typical animal cell components. Fig. 4.26b, p. 70

Summary: Cell Components

Key Concepts Eukaryotic Cells Cells of protists, plants, fungi, and animals are eukaryotic They have a nucleus and other membrane-enclosed compartments Cells differ in internal parts and surface specializations

4.13 The Nature of Life Life is a property that emerges from cellular components, but a collection of those components in the right amounts and proportions is not necessarily alive Characteristics of life: A set of properties unique to living things Collectively, these properties characterize living things as different from nonliving things

Characteristics of Living Things They make and use organic molecules of life They consist of one or more cells They engage in self-sustaining biological processes such as metabolism and homeostasis They change over their lifetime by growing, maturing, and aging They use DNA as hereditary material They have the collective capacity to change over successive generations by adapting to environmental pressures