Chapter 7:  A Tour of the Cell
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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.

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Chapter 7: A Tour of the Cell

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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 7.0 Fluorescent stain of cell


Figure 7 2 electron micrographs

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

Figure 7.3 Cell fractionation

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


Figure 7 4 a prokaryotic cell

Figure 7.4 A prokaryotic cell

Prokaryotes: Pro: before

Karyon: kernel (referring to nucleus)


Figure 7 4x2 e coli

Figure 7.4x2 E. coli


Figure 7 5 geometric relationships explain why most cells are microscopic

Figure 7.5 Geometric relationships explain why most cells are microscopic


Figure 7 6 the plasma membrane

Figure 7.6 The plasma membrane


Animal cell

Animal Cell


Chapter 7 a tour of the cell

  • Reference: Molecular Biology of the Cell CD

    • Media

      • Animation

        • 9.2 Liver Cell View 2


Chapter 7 a tour of the cell

  • Reference: Molecular Biology of the Cell CD

    • Media

      • Animation

        • 1.4 Plant Cells


Figure 7 8 overview of a plant cell

Typical Plant Cell

Figure 7.8 Overview of a plant cell


Figure 7 9 the nucleus and its envelope

Figure 7.9 The nucleus and its envelope 


Figure 7 x1 nuclei nucleus and actin within cells

Figure 7.x1 Nuclei Nucleus and Actin Within Cells


Figure 7 10 ribosomes

Figure 7.10 Ribosomes

Free and bound ribosomes have different functions


Figure 7 11 endoplasmic reticulum er

Figure 7.11 Endoplasmic reticulum (ER)


Chapter 7 a tour of the cell

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


Chapter 7 a tour of the cell

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

Figure 7.12 The Golgi apparatus

Molecular Biology of the Cell: Media-Video: 13.2 Secretory Pathway


Figure 7 13 lysosomes

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 7.14 The formation and functions of lysosomes (Layer 1)


Figure 7 14 the formation and functions of lysosomes layer 2

Figure 7.14 The formation and functions of lysosomes (Layer 2)


Figure 7 14 the formation and functions of lysosomes layer 3

Figure 7.14 The formation and functions of lysosomes (Layer 3)


Figure 7 15 the plant cell vacuole

Figure 7.15 The plant cell vacuole 


Figure 7 16 review relationships among organelles of the endomembrane system

Figure 7.16 Review: relationships among organelles of the endomembrane system 


Figure 7 17 the mitochondrion site of cellular respiration

Figure 7.17 The mitochondrion, site of cellular respiration


Chapter 7 a tour of the cell

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

Figure 7.18 The chloroplast, site of photosynthesis


Chapter 7 a tour of the cell

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

Figure 7.19 Peroxisomes


Chapter 7 a tour of the cell

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.


Chapter 7 a tour of the cell

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


Chapter 7 a tour of the cell

  • 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


Chapter 7 a tour of the cell

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


Chapter 7 a tour of the cell

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.


Chapter 7 a tour of the cell

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

Figure 7.24 Ultrastructure of a eukaryotic flagellum or cilium


Chapter 7 a tour of the cell

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.


Chapter 7 a tour of the cell

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


Chapter 7 a tour of the cell

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.


Chapter 7 a tour of the cell

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 cilium1

Figure 7.24 Ultrastructure of a eukaryotic flagellum or cilium


Figure 7 23 a comparison of the beating of flagella and cilia

Figure 7.23 A comparison of the beating of flagella and cilia


Figure 7 23x sea urchin sperm

Figure 7.23x Sea urchin sperm


Figure 7 25 how dynein walking moves cilia and flagella

Figure 7.25 How dynein “walking” moves cilia and flagella


Figure 7 20 the cytoskeleton

Figure 7.20 The cytoskeleton


Figure 7 21 motor molecules and the cytoskeleton

Figure 7.21 Motor molecules and the cytoskeleton


Table 7 2 the structure and function of the cytoskeleton

Table 7.2 The structure and function of the cytoskeleton


Figure 7 x2 actin

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

Figure 7.x2 Actin


Chapter 7 a tour of the cell

  • 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.


Figure 7 26 a structural role of microfilaments

Figure 7.26 A structural role of microfilaments


Figure 7 27 microfilaments and motility

Figure 7.27 Microfilaments and motility


Figure 7 28 plant cell walls

Figure 7.28 Plant cell walls


Chapter 7 a tour of the cell

Extracellular Matrix of Animal Cells

  • Characteristics of the ECM

    • Secreted by the cells

    • Made of collagen, a glycoprotein. Collagen is fibrous and makes up 50% of protein in humans.

    • Fibronectins connect cells to ECM

      • Integrins, proteins in the p. membrane, are attached to the cytoskeleton at one end and the fibronectins outside of the cell to anchor the cell and transmit changes within the cell to ECM and vice versa.


Figure 7 29 extracellular matrix ecm of an animal cell

Figure 7.29 Extracellular matrix (ECM) of an animal cell


Chapter 7 a tour of the cell

Intercellular Junctions

  • Types of Intercellular Junctions

    • Plasmodesmata

      • Channels between plant cells for water, solutes, hormones, to pass.

  • Tight junctions

    • In animal cells

    • Membranes of adjacent cells are fused

  • Desmosomes

    • Fasten cells together in sheets

  • Gap Junctions

    • Channels between cells: hormones, ions, sugars, amino acids, etc.


Figure 7 30 intercellular junctions in animal tissues

Figure 7.30 Intercellular junctions in animal tissues


Figure 7 22 centrosome containing a pair of centrioles

Figure 7.22 Centrosome containing a pair of centrioles


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