Chapter 7: A Tour of the Cell

Chapter 7: A Tour of the Cell • Objectives • The student is responsible for: • The definitions of all bold faced words in the chapter • Knowing the entire chapter especially: • Name, spelling and function of all organelles • Differences between prokaryotic and eukaryotic cells

Figure 7.0 Fluorescent stain of cell

Figure 7.2 Electron micrographs TEM or Transmission Electron Mic. SEM or Scanning Electron Mic. Image of trachea of a rabbit Image of trachea of a rabbit

Figure 7.3 Cell fractionation How a cell can be separated into its components (fractionation)

Figure 7.4 A prokaryotic cell Prokaryotes: Pro: before Karyon: kernel (referring to nucleus)

Figure 7.4x2 E. coli

Figure 7.5 Geometric relationships explain why most cells are microscopic

Figure 7.6 The plasma membrane

Animal Cell

Reference: Molecular Biology of the Cell CD • Media • Animation • 9.2 Liver Cell View 2

Reference: Molecular Biology of the Cell CD • Media • Animation • 1.4 Plant Cells

Typical Plant Cell Figure 7.8 Overview of a plant cell

Figure 7.9 The nucleus and its envelope

Figure 7.x1 Nuclei Nucleus and Actin Within Cells

Figure 7.10 Ribosomes Free and bound ribosomes have different functions

Figure 7.11 Endoplasmic reticulum (ER)

The ER manufactures membranes and performs many other biosynthetic functions • Functions of the Smooth ER • enzymes within the SER synthesize lipids, steroids, phospholipids • liver cells store lots of glucose in the form of glycogen. When glycogen is broken down it first becomes glucose phosphate which cannot pass through the cell membrane. An enzyme in the SER removes the phosphate group so glucose can leave the cell. • detoxifies drugs, alcohol. The SER adds a hydroxyl group to the metabolic by-products, making them water soluble. The more drugs /alcohol you ingest, the more SER and enzymes your cells make thus increasing tolerance. Also these same enzymes can provide tolerance to other drugs because of their general action of adding hydroxyl groups. • also helps in muscle contraction by controlling the flow of calcium ions required for contraction

The ER manufactures membranes and performs many other biosynthetic functions • Functions of the Rough ER • produces secretory proteins • insulin is made by the RER • the polypeptide (insulin) is modified inside the RER, new groups are added to it; it gets properly folded. • glycoproteins: a sugar/protein combo that is secreted. • these secretory proteins are carried from RER in vesicles • RER can become part of the membranes throughout the cell • Video: Molecular Biology of the Cell • Video: 12.2 ER Tubules

Figure 7.12 The Golgi apparatus Molecular Biology of the Cell: Media-Video: 13.2 Secretory Pathway

Figure 7.13 Lysosomes Molecular Biology of the Cell: Media – Video 13.5 Phagocytosis Contain enzymes to digest macromolecules Work at a pH = 5; obtain the hydrogen ions from the cytosol Compartmentalization: protection of the rest of the cell Autophagy: recycling of the cells components (organelles or material in cytosol) Lysosomes are involved in programmed cell death

Figure 7.14 The formation and functions of lysosomes (Layer 1)

Figure 7.15 The plant cell vacuole

Figure 7.16 Review: relationships among organelles of the endomembrane system

Figure 7.17 The mitochondrion, site of cellular respiration

Fundamental Characteristics of Mitochondria • Can increase in number depending on cellular conditions or demands • Contains its own DNA • Can reproduce separately from the nuclear DNA • Has TWO membranes, each a phospholipid bilayer • Enzymes are embedded in each of the membranes • Space between the outer and inner membrane is the intermembrane space. • Within the cristae (inner most membrane) is the matrix. • Enzymes in the matrix to help make ATP • Cellular respiration occurs here and the subsequent ATP production • Molecular Biology of Cell CD: Chapter – 14.5 Tomograph of Mit

Figure 7.18 The chloroplast, site of photosynthesis

Fundamental Characteristics of Chloroplasts • Can increase in number depending on cellular conditions or demands • Contains its own DNA • Can reproduce separately from the nuclear DNA • Has TWO membranes, each a phospholipid bilayer • Enzymes are embedded in each of the membranes • Space between the outer and inner membrane is the intermembrane space. • Stroma is the fluid within the chloroplast and contains enzymes • Thylakoids are flattened sacs, stacked into grana and contain chlorophyll • A chloroplast is a type of plastid. • Molecular Biology of Cell CD: Chapter – 14.5 Tomograph of Mit

Figure 7.19 Peroxisomes

Fundamental Characteristics of Peroxisomes • Bound by single membrane • Transfer hydrogen from different substrates to oxygen forming hydrogen peroxide which is actually toxic to the cell. • Catalase is present in the peroxisomes that breakdown the hydrogen peroxide. • When dormant seeds take in water, specialized peroxisomes, glyoxysomes, convert fatty acids to sugars since the seeds cannot photosynthesize and therefore cannot make their own sugars.

Fundamental Characteristics of the Cytoskeleton • The cytoskeleton is a system of filaments of proteins that: • Helps cells to organize their internal space • Interact mechanically with their environment • Allow the cell to change shape and move • Allow the cell to move its internal components on tracks • All of these functions depend on three main types of filaments • Intermediate Filaments: provide mechanical strength and resistance to shear stress • Microtubules: determine the position of organelles and direct intracellular transport • Actin Filaments: determine cell shape and whole-cell locomotion

All three of these cytoskeletal filaments depend upon accessory proteins • These accessory proteins control the assembly of the cytoskeletal filaments in their particular locations. • A most notable accessory protein is a motor protein(s) that move organelles along the filaments or move the filaments themselves. • Examples: mitotic spindle or spindle that a pulls the chromosomes apart; cilia and flagella; tracks for vesicles to move down in the axon of the nerve cell; contractile ring during cytokinesis. • Molecular Biology of the Cell • Chapter – 16.5 Organelle Movement on MTs • Chapter – 18.4 Mitotic Spindle • Media – 16.7 Kinesin: How the motor protein moves the organelles • Media – 16.3 Microtubule Dynamics in vivo

Intermediate Filaments • Main function is to enable cells to withstand mechanical stress that occurs when cells are stretched. • “intermediate” because size is between the thin actin filaments and thicker myosin filaments of smooth muscle. • Toughest of most durable • Surround nucleus and extend to periphery as well as reside in nucleus • In cytoplasm, they anchor the cell membrane at cell-cell junctions • In nucleus, they underlie and strengthen the nuclear envelope

Intermediate Filaments (cont’d) • Present in the axons of nerve cells where the long extension needs strengthening • Present in skin cells and muscle cells which constantly stretch • Connect to each other from one cell to another at desmosomes, junctions fastening cells together. • Epidermolysis bullosa simplex: gene mutation causes skin cells to rupture under gentle pressure and skin blisters • Intermediates filaments must breakdown and reform during cell division when the nuclear envelope (membrane) disappears and reforms.

Microtubules • Stiff, hollow tubes of a protein, tubulin. • Tubulin can be disassembled and reassembled • Tracks of tubulin extend from the centrosome. Organelles, vesicles move along these tracks which therefore controls the position of the membrane-bound organelles in a cell and guiding intracellular transport. • MTs form the mitotic spindle or spindle that segregates the chromosomes during cell division. • MTs also form the cilia and flagella in a “9 + 2” arrangement. • Free tubulin subunits exist in the cytosol. • Colchicine is a drug that binds to free tubulin and prevents its polymerization into MTs, thus no spindle assembly. • Taxol binds to MTs and prevents them from disassembling so they can grow but cannot shrink. It also stops cell division.

Figure 7.24 Ultrastructure of a eukaryotic flagellum or cilium

Microtubules (cont’d) • The centrosome is the major microtubule-organizing center in animal cells • MTs demonstrate “dynamic instability.” This is growing and shrinking of MTs on their own. • MTs organize the interior of the cell. Growing MTs can be stabilized and “fixed” to maintain organization with a cell. • The axons of nerve cells have vesicles of neurotransmitters flowing down them along MTs. [10 cm / day; others, a week or longer] • Again, this movement is associated with motor proteins.

Motor Proteins Drive Intracellular Transport Molecular Biology of the Cell Media – 16.7 – Kinesin: How Kinesin Works in Detail • Bind to actin and MTs and use ATP hydrolysis to move along the actin or MT filament. The other end of the motor protein is attached to a cellular component and thus transports it and its cargo. • Kinesin Family of Motor Proteins: move towards the end of the MT • Kinesins attach to outside of ER membrane pull the ER membrane outward along microtubules. • Colchicine causes the ER to alter location because the MTs are disassembled. The ER collapses to the center, towards the nucleus. • Dynein Family of Motor Proteins: move inward, towards the centrosome

Motor Proteins Drive Intracellular Transport (cont’d) • Dynein Family of Motor Proteins: move inward, towards the centrosome • Dynein pulls the Golgi apparatus toward the cell center • Cilia and Flagella Contain MTs Moved by Dynein • Cilia and flagella propel water over the surface of the cell • A cilium’s microtubules grow from a basal body in the cytoplasm. • A cilium is made of a core of stable (not dynamic instability) microtubules • Cilia can propel, they can move mucus in your respiratory tract, they can move eggs through your oviducts or capture food if you were a protozoan. • Cilia move in a whiplike motion whereas flagellum generate waves along their length.

Motor Proteins Drive Intracellular Transport (cont’d) • Microtubules are arranged as doublet microtubules, nine of them. • These nine surround a pair of single MTs • Dynein generates the bending motion of the core. One end, its tail, is attached to one MT, while the head end interacts with an adjacent MT to produce a sliding motion that causes the cilium to bend.

Figure 7.24 Ultrastructure of a eukaryotic flagellum or cilium

Figure 7.23 A comparison of the beating of flagella and cilia

Figure 7.23x Sea urchin sperm

Figure 7.25 How dynein “walking” moves cilia and flagella

Figure 7.20 The cytoskeleton

Figure 7.21 Motor molecules and the cytoskeleton

Table 7.2 The structure and function of the cytoskeleton

Actin Filaments are responsible for many cellular movements such as crawling, phagocytosis or division. Figure 7.x2 Actin

Actin filaments are thinner, more flexible and shorter than MTs. • Actin filaments can polymerize and depolymerize such as in cell crawling • Actin is found throughout the cytoplasm. Just underneath the plasma membrane is actin that supports the outer cell surface and gives it mechanical strength. • Many cells move by crawl’n: amoeba, neutrophils migrating from the blood into infected tissues, Linkin Park in your skin, growing tip of an axon. • Integrins are transmembrane proteins in the p. membrane that adhere to a surface on which the cell is crawling. • Myosin Motor Proteins work with actin for muscle contraction • First found in skeletal muscle cells • Myosin head moves actin filaments together to shorten muscle cells. • Actin and Myosin also work in the contractile ring that pinches a dividing cell in two by contracting and pulling inward on the p. membrane.

Chapter 7: A Tour of the Cell