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Cell Structure

Cell Structure. Chapter 3. Examples of Cells. 3.2 What, Exactly, Is a Cell?. Cells are the fundamental units of all life All cells start life with a plasma membrane, cytoplasm, and a region of DNA which, in eukaryotic cells only, is enclosed by a nucleus. Cell Structure.

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Cell Structure

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  1. Cell Structure Chapter 3

  2. Examples of Cells

  3. 3.2 What, Exactly, Is a Cell? Cells are the fundamental units of all life • All cells start life with a plasma membrane, cytoplasm, and a region of DNA which, in eukaryotic cells only, is enclosed by a nucleus

  4. Cell Structure • A plasma membrane surrounds the cell and controls which substances move in and out • Plasma membrane • A cell’s outermost membrane • Lipid bilayer • Structural foundation of cell membranes; mainly phospholipids arranged tail-to-tail in a bilayer

  5. Cytoplasm • An important part of homeostasis is maintaining the composition of cytoplasm, which differs from fluid outside the cell • Cytoplasm • Semifluid substance enclosed by a cell’s plasma membrane

  6. Organelles • Cell metabolism occurs in cytoplasm and internal compartments, including organelles • Organelle • Structure that carries out a specialized metabolic function inside a cell

  7. Prokaryotes and Eukaryotes • Cells are classed as eukaryotes or prokaryotes based on how DNA is housed in the cell • Nucleus • Organelle with two membranes that holds a eukaryotic cell’s DNA • Nucleoid • Region of cytoplasm where DNA is concentrated in a prokaryotic cell

  8. The Cell Theory • Cell theory is the fundamental theory of biology • Cell theory • All organisms consist of one or more cells • The cell is the smallest unit of life • Each new cell arises from another cell • A cell passes hereditary information to its offspring

  9. 3.3 Measuring Cells • Most cells are visible only with the help of microscopes • Different types of microscopes use light or electrons to reveal different details of cells

  10. Bacteria on the Tip of a Pin • Bacteria are the smallest and simplest cells

  11. “Animalcules and Beasties” • No one knew cells existed until microscopes were invented • 1600s: van Leeuwenhoek’s microscope

  12. Hooke, Schleiden, and Schwann • 1600s: Robert Hooke improved the microscope and coined the term “cell” • 1839: Matthias Schleiden and Theodore Schwann realized cells were alive and proposed the cell theory

  13. 3.4 The Structure of Cell Membranes • The plasma membrane is basically a lipid bilayer balloon filled with fluid • The nonpolar tails of both layers are sandwiched between the polar heads

  14. The Fluid Mosaic Model • A cell membrane is a mosaic of proteins and lipids (mainly phospholipids) that functions as a selectively permeable barrier that separates an internal environment from an external one • Fluid mosaic model • A cell membrane can be considered a two-dimensional fluid of mixed composition

  15. Membrane Proteins • Proteins associated with a membrane carry out most membrane functions • Transport proteins passively or actively assist specific ions or molecules across a membrane • Enzymes speed chemical processes • Adhesion proteins help cells stick together • Recognition proteins tag cells as “self” • Receptor proteins bind to a particular substance outside the cell

  16. 3.5 Introducing Prokaryotic Cells • Domains Bacteria and Archaea make up the prokaryotes • Prokaryotes are single-celled organisms with no nucleus, but many have a cell wall and one or more flagella or pili

  17. 3.6 A Peek Inside a Eukaryotic Cell • All eukaryotic cells start life with a nucleus, ribosomes, organelles of the endomembrane system (including endoplasmic reticulum, vesicles, Golgi bodies), mitochondria, and other organelles

  18. The Nucleus • Pores, receptors, and transport proteins in the nuclear envelope control the movement of molecules into and out of the nucleus • Nuclear envelope • A double membrane that constitutes the outer boundary of the nucleus

  19. The Endomembrane System • The endomembrane system includes rough and smooth endoplasmic reticulum, vesicles, and Golgi bodies • Endomembrane system • Series of interacting organelles between the nucleus and plasma membrane • Makes and modifies lipids and proteins • Recycles molecules and particles such as worn-out cell parts, and inactivates toxins

  20. The Endomembrane System • Endoplasmic reticulum (ER) • A continuous system of sacs and tubes that is an extension of the nuclear envelope • Rough ER is studded with ribosomes (for protein production) • Smooth ER has no ribosomes

  21. The Endomembrane System • Vesicle • Small, membrane-enclosed, saclike organelle • Stores, transports, or degrades its contents • Peroxisome • Enzyme-filled vesicle that breaks down amino acids, fatty acids, and toxic substances • Lysosome • Vesicle with enzymes for intracellular digestion

  22. The Endomembrane System • Golgi body • Organelle that modifies polypeptides and lipids • Sorts and packages the finished products into transport vesicles • Vacuole • A fluid-filled organelle that isolates or disposes of wastes, debris, or toxic materials

  23. Mitochondria and Chloroplasts • Mitochondria and chloroplasts have their own DNA – they resemble bacteria and may have evolved by endosymbiosis • Mitochondrion • Double-membraned organelle that produces ATP • Chloroplast • Organelle of photosynthesis

  24. The Cytoskeleton • Cytoskeleton • Dynamic network of protein filaments that support, organize, and move eukaryotic cells and their internal structures • The cytoskeleton interacts with accessory proteins, such as motor proteins

  25. Cilia and False Feet • Cilia • Short, hairlike structures that project from the plasma membrane of some eukaryotic cells • Coordinated beating stirs fluid, propels motile cells • Moved by organized arrays of microtubules • Example: clears particles from airways

  26. Flagella • Eukaryotic flagella are whiplike structures that propel cells such as sperm through fluid • Different internal structure and motion than prokaryotic flagella

  27. False Feet • Pseudopod (false foot) • Extendable lobe of membrane-enclosed cytoplasm for movement or to engulf prey • Moved by motor proteins attached to microfilaments that drag the plasma membrane • Example: amoebas

  28. 3.7 Cell Surface Specializations • Cell junctions • Connect a cell structurally and functionally to another cell or to extracellular matrix (ECM) • Extracellular matrix (ECM) • Complex mixture of substances secreted by cells • Supports cells and tissues • Functions in cell signaling

  29. Types of Animal Cell Junctions • Tight junction • An array of fibrous proteins that joins epithelial cells and prevents fluids from leaking between them • Adhering junction • Anchors cells to each other or to extracellular matrix • Gap junction • Forms a channel across plasma membranes of adjoining animal cells

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