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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.

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Presentation on theme: "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."— Presentation transcript:

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


6 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

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

8 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

9 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

10 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

11 Bacteria on the Tip of a Pin  Bacteria are the smallest and simplest cells

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

13 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

14 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

15 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 Fluid mosaic model A cell membrane can be considered a two- dimensional fluid of mixed composition

16 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

17 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

18 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


20 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

21 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

22 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

23 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

24 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

25 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

26 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

27 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

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

29 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

30 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

31 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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