Cell Structure and Function Chapter 4 Cell Structure and Function

4.1 What Features Are Shared By All Cells? Cells are the smallest unit of life. Cells are enclosed by a plasma membrane. Cells use DNA as a hereditary blueprint. Cells contain cytoplasm, which is all the material inside the plasma membrane and outside the DNA-containing region. Cells obtain energy and nutrients from their environment.

4.1 What Features Are Shared By All Cells?

4.1 What Features Are Shared By All Cells? Diameter Relative sizes 100 m tallest trees 10 m adult human 1 m visible with unaided human eye 10 cm chicken egg 1 cm 1 mm frog embryo 100 m light microscope visible with most eukaryotic cells 10 m mitochondrion 1 m most bacteria visible with conventional electron microscope 100 nm virus 10 nm Units of measurement: special electron visible with microscopes proteins 1 meter (m) = 39.37 inches diameter of DNA double helix 1 centimeter (cm) = 1/100 m 1 nm 1 millimeter (mm) = 1/1,000 m 1 micrometer (mm) = 1/1,000,000 m atoms 1 nanometer (nm) = 1/1,000,000,000 m 0.1 nm Fig. 4-1

4.1 What Features Are Shared By All Cells? Cell function limits cell size. Diffusion of molecules across cell membranes limits the diameter of cells. As cells get bigger, their nutrient and waste elimination needs grow faster than the membrane area to accommodate them.

4.1 What Features Are Shared By All Cells? The volume of cytoplasm grows faster than the plasma membrane area. Fig. 4-2

4.2 How Do Prokaryotic And Eukaryotic Cells Differ? There are two kinds of cells. Prokaryotic cells Are found only in two groups of single-celled organisms—the bacteria and archaea Eukaryotic cells Are structurally more complex cells Possess a membrane-enclosed nucleus Probably arose from prokaryotic cells

4.2 How Do Prokaryotic And Eukaryotic Cells Differ? PLAY Animation—Cell Structure

4.3 What Are The Main Features Of Eukaryotic Cells? Eukaryotic cells differ from prokaryotic cells because the former possess a number of membrane-enclosed organelles that perform specific cell functions. Nucleus: contains DNA Mitochondria: produce energy Endoplasmic reticulum: synthesizes membrane components and lipids Golgi apparatus: molecule sorting center Lysosomes: digest cellular membranes or defective organelles Microtubules: make up the cytoskeleton

4.3 What Are The Main Features Of Eukaryotic Cells? A generalized animal cell nuclear pore chromatin (DNA) nucleus nucleolus nuclear envelope flagellum centriole intermediate filaments cytoplasm plasma membrane rough endoplasmic reticulum ribosome lysosome Golgi apparatus microtubules vesicle free ribosome smooth endoplasmic reticulum vesicle mitochondrion Fig. 4-3

Suggested Media Enhancement: Tour of an Animal Cell To access this animation go to folder C_Animations_and_Video_Files and open the BioFlix folder.

4.3 What Are The Main Features Of Eukaryotic Cells? A generalized plant cell microtubules (part of cytoskeleton) mitochondrion chloroplast central vacuole Golgi apparatus plasmodesma smooth endoplasmic reticulum vesicle rough endoplasmic reticulum cell wall plasma membrane nucleolus nuclear pore chromatin nuclear envelope intermediate filaments nucleus ribosomes free ribosome Fig. 4-4

Suggested Media Enhancement: Tour of a Plant Cell To access this animation go to folder C_Animations_and_Video_Files and open the BioFlix folder.

4.4 What Role Does The Nucleus Play? The nucleus is the largest organelle in the cell. It is bounded by a nuclear envelope. It contains granular-looking chromatin. It contains the nucleolus.

4.4 What Role Does The Nucleus Play? nuclear envelope nucleolus nuclear pores nucleus nuclear pores chromatin (a) Structure of the nucleus (b) Yeast cell Fig. 4-5

4.4 What Role Does The Nucleus Play? The nuclear envelope is a double membrane. The membrane is perforated with channels called nuclear pores. Some smaller materials can move through the pores, while others, such as DNA, are excluded.

4.4 What Role Does The Nucleus Play? The nucleus contains chromosomes. DNA and protein are closely associated in the nucleus in chromatin. Chromatin can become condensed into chromosomes. chromatin chromosome Fig. 4-6

4.4 What Role Does The Nucleus Play? Ribosomes are composed of RNA and proteins, and serve as a “workbench” for the manufacture of proteins.

4.4 What Role Does The Nucleus Play? Ribosome components are made at the nucleolus. A darkly staining region in the nucleus is called a nucleolus. The nucleolus contains DNA, RNA, proteins, and ribosomes in various stages of construction. This is the site where components of ribosomes are constructed. Ribosome components leave the nucleus and are assembled in the cytoplasm.

4.5 What Roles Do Membranes Play In Eukaryotic Cells? The plasma membrane isolates the cell, and alternately, helps it interact with its environment. The phospholipid bilayer contains globular proteins that regulate the transport of molecules into and out of the cell. Plant cells also have a rigid structure outside the plasma membrane, called a cell wall, which forms a protective coating.

4.5 What Roles Do Membranes Play In Eukaryotic Cells? The endoplasmic reticulum (ER) forms channels within the cytoplasm. There are two kinds of ER membranes: Rough endoplasmic reticulum: is studded with ribosomes Smooth endoplasmic reticulum: has no ribosomes

4.5 What Roles Do Membranes Play In Eukaryotic Cells? The endoplasmic reticulum ribosomes smooth ER smooth ER rough ER rough ER vesicles (a) Endoplasmic reticulum may be rough or smooth (b) Smooth and rough ER Fig. 4-7

4.5 What Roles Do Membranes Play In Eukaryotic Cells? The rough ER is the site where proteins are made. The smooth ER makes phospholipids and cholesterol. Together, the rough and smooth ER are the sites of new membrane synthesis for the cell.

4.5 What Roles Do Membranes Play In Eukaryotic Cells? The Golgi apparatus sorts, chemically alters, and packages important molecules. This organelle looks like a stack of flattened sacs. Its membranes are derived from the ER. Vesicles containing preformed molecules from the ER are transferred to the Golgi for further processing.

4.5 What Roles Do Membranes Play In Eukaryotic Cells? The Golgi apparatus Protein-carrying vesicles from the ER merge with the Golgi apparatus Golgi apparatus Vesicles carrying modified proteins leave the Golgi apparatus Fig. 4-8

4.5 What Roles Do Membranes Play In Eukaryotic Cells? Once the molecular work of the Golgi has been done, new vesicles bud off and travel elsewhere in the cytoplasm, where they fuse with membranes of other organelles, such as the plasma membrane. A major role of the Golgi is to add sugar molecules to proteins formed in the ER and to pass them on to other places in the cell.

4.5 What Roles Do Membranes Play In Eukaryotic Cells? We can follow the travels of a secreted protein. An antibody protein is synthesized on ribosomes of the rough ER. Formed antibody is packaged into vesicles that travel to the Golgi, where carbohydrates are attached to protein to make an antibody.

4.5 What Roles Do Membranes Play In Eukaryotic Cells? We can follow the travels of a secreted protein (continued). The vesicle containing antibody leaves the Golgi and goes to the plasma membrane, where it fuses with it. The antibody inside the vesicle is released to the outside of the cell (to the blood), where it helps defend the body against infection.

4.5 What Roles Do Membranes Play In Eukaryotic Cells? Animation—Membrane Traffic

4.5 What Roles Do Membranes Play In Eukaryotic Cells? Lysosomes are vesicles that serve as the cell’s digestive system. They are formed as buds from the Golgi. Lysosomes contain digestive enzymes that they receive from Golgi during their production. In the cytoplasm, they digest defective organelles or pieces of membrane into component parts that can be recycled.

4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Vacuoles regulate water and store substances. They are fluid-filled sacs surrounded by a single membrane. Many plant cells have a large central vacuole. Vacuoles hold water and help maintain the proper water balance of the cell. Vacuoles can also serve as dump sites for hazardous waste that can’t be excreted. They can also store sugars and amino acids, which can be used for energy.

4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Mitochondria extract energy from food molecules. Mitochondria provide the energy needed for all cellular processes. Energy is obtained from sugar molecules in mitochondria and is stored in ATP molecules. Once formed, ATP can be used anywhere in the cell where energy is needed. Mitochondria have a complex set of outer and inner membranes, and both sets are used in the process of energy production.

4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Chloroplasts capture solar energy. Only plant cells contain chloroplasts. Chloroplasts capture energy from sunlight and store it in sugar molecules. They are the site of photosynthesis, the process upon which all life depends. Like mitochondria, chloroplasts contain both outer and inner membranes.

4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? The cytoskeleton provides shape, support, and movement. All organelles in the cell do not float about the cytoplasm, but instead, are attached to a network of protein fibers called the cytoskeleton.

4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Several type of protein fibers make up the cytoskeleton. Microfilaments: thin fibers Intermediate filaments: medium-sized fibers Microtubules: thick fibers

4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? The cytoskeleton plasma membrane microfilaments microtubules (red) mitochondrion intermediate filaments ribosomes endoplasmic reticulum nucleus microtubule vesicle microfilaments (blue) (a) Components of the cytoskeleton (b) Cell with stained cytoskeleton Fig. 4-9

4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Cilia and flagella move the cell or move fluid past the cell. Cilia and flagella are slender, movable extensions of the plasma membrane. They contain microtubules that extend along their length. They may be used to move small animals or particle-containing fluids past a surface.

4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Cilia and flagella move the cell or move fluid past the cell (continued). Differences between cilia and flagella lie in their length, number, and the direction of force generated. Cilia are shorter and more numerous than flagella.

4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Cilia provide force parallel to the plasma membrane, which can be described as a “rowing” motion. propulsion of fluid power stroke return stroke plasma membrane cilia lining the trachea (a) Cilium Fig. 4-10a

4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Flagella provide a force perpendicular to plasma membrane, like the engine on a motorboat. direction of locomotion propulsion of fluid continuous propulsion flagellum of human sperm (b) Flagellum Fig. 4-10b

4.7 What Are The Features Of Prokaryotic Cells? Prokaryotic cells are much smaller than eukaryotic cells, are more abundant, and are very reproductively successful. The are very small and have a simple internal structure. They are surrounded by a stiff cell wall, which provides shape and protection. Some move with a whiplike flagellum.

4.7 What Are The Features Of Prokaryotic Cells? A single, circular strand of DNA is attached to the plasma membrane and is concentrated in an area called the nucleoid, which lacks a membrane. There are no membrane-enclosed organelles. The cytoplasm contains ribosomes used for protein synthesis.

4.7 What Are The Features Of Prokaryotic Cells? A generalized prokaryotic cell chromosome (nucleoid region) ribosomes food granule prokaryotic flagellum cell wall plasma membrane cytoplasm Fig. 4-11