Cell Structure Chapter 4

Cell Theory Cells were discovered in 1665 by Robert Hooke. Early studies of cells were conducted by Mathias Schleiden (1838) - plant cells Theodor Schwann (1839) - animal cells Schleiden and Schwann proposed the Cell Theory.

Cell Theory Cell Theory 1. All organisms are composed of cells. 2. Cells are the smallest living things. 3. Cells arise only from pre-existing cells. All cells today represent a continuous line of descent from the first living cells.

Cell Theory Cell size is limited. As cell size increases, it takes longer for material to diffuse from the cell membrane to the interior of the cell. Surface area-to-volume ratio: as a cell increases in size, the volume increases 10x faster than the surface area

Cell Theory

Cell Theory Microscopes are required to visualize cells. Light microscopes can resolve structures that are 200nm apart. Electron microscopes can resolve structures that are 0.2nm apart.

Fig. 4.2

Cell Theory All cells have certain structures in common: 1. Genetic Material – in a nucleoid or nucleus 2. Cytoplasm – a semifluid matrix 3. Plasma Membrane – a phospholipid bilayer

Nonpolar Hydrocarbon Tail Phospholipids Chapter 3: Phospholipids are Amphiphilic molecules Polar Head Group Nonpolar Hydrocarbon Tail 101

Page 63

Two Cell Types Prokaryotic Cells Eukaryotic Cells Recall Three Domains (Ch. 1) Defined by cell type Eukarya Plantae Fungi Animlia Protista Bacteria Archaea Eukaryotic Prokaryotic 11

1. Prokaryotic Cells Prokaryotic Cells Origin: ‘pro’-before; ‘karyote’ - nut Lack a membrane-bound nucleus. genetic material is present in the nucleoid Two types of prokaryotes: Archaea Bacteria

1. Prokaryotic Cells Prokaryotic Cell Characteristics: Simplest organisms - simple internal organization Very small (1 to 10 microns across) Genetic material in the nucleoid No membrane-bound organelles Capsules Cytoplasm

1. Prokaryotic Cells Prokaryotic and Eukaryotic Characteristics: DNA, RNA Ribosomes Plasma membrane Cell walls (bacteria, archaea) Flagella Pilli

1. Prokaryotic Cell Structure

Prokaryotic Cell Structure Prokaryotic cell walls Surround and protect cell and maintain cell shape Composed of polysaccharides (sugar coated) Bacterial cell walls composed of peptidoglycan Archaean cell walls lack peptidoglycan.

Recall Ch. 3 Polysaccharides b. Function 1. Structural Molecules Cellulose - plant cell walls Chitin – Fungi cell walls Peptidoglycan - Bacterial cell walls 22

Prokaryotic Cell Structure Bacterial cell walls composed of peptidoglycan Two Types of Bacterial Cell Walls Gram Positive Gram Negative Gram Positive/Gram Negative type is determined by cell cell wall structure and the Gram Stain Reaction Gram Positive Bacteria Stain Purple Gram Negative Bacteria Stain Pink

Gram + vs. Gram - Gram + Bacteria stain Purple Gram – Bacteria stain Pink Courtesy: Dr. O’Steen

Prokaryotic Cell Structure Flagella (singular, flagellum) Whip-like proteins attached to cell wall used for locomotion Present in some prokaryotic cells one to several flagella on a single cell Rotary motion of flagellum propels the cell through fluid environment Flagella powered by protein motors uses energy of a proton gradient

Flagella Structure

2. Eukaryotic Cells Eukaryotic Cells Origin: ‘eu’ - true, good; ‘karyote’ - nut Possess a membrane-bound nucleus. genetic material is highly organized within double-layer nuclear envelope DNA never leaves the nuclear envelope Types of eukaryotes divided into 4 kingdoms: 1. Plantae 2. Fungi 3. Animalia 4. Protista

2. Eukaryotic Cells Eukaryotic Cell Characteristics: More complex organisms highly organized structure (compartmentalization) known as endomembrane system Typically larger than prokaryote (10-100 microns) Genetic material in the membrane-bound nucleus Many membrane-bound organelles Cytoplasm Cytoskeleton

2. Eukaryotic Cells Eukaryotic and Prokaryotic Characteristics: DNA, RNA Ribosomes Plasma membrane Cytoplasm Cell walls (plantae, fungi, protista, not present in animal cells) Flagella

Eukaryotic Cells

Eukaryotic Cells

Eukaryotic Cells Nucleus Largest most definitive organelle in the cytoplasm Surrounded by a nuclear envelope composed of 2 phospholipid bilayers Stores the genetic material of the cell as long separate chains of DNA known as chromosomes Cell DNA is organized with proteins to form chromatin

Eukaryotic Cells Nucleus Cell DNA is organized with proteins to form chromatin Chromosomes are tightly packed (condensed) with proteins inside the nucleus into nucleosomes DNA is wound around histone proteins to resembles beads on a string

Fig. 4.9

Eukaryotic Cells Nucleolus (plural, nucleoli) Dark staining zone within the nucleus Composed of RNA Synthesis of ribosomal RNA (rRNA) occurs here rRNA is involved in the translation of DNA into protein

Eukaryotic Cells Nuclear Envelope Composed of an inner and outer phospholipid bilayer the outer layer is continuous with the membrane of the endoplasmic reticulum - an organelle for protein synthesis Nuclear pores provide passage for proteins and rRNA into and out of the nucleus DNA never leaves the nucleus

Eukaryotic Cells

Eukaryotic Cells Ribosomes Present in prokaryotic and eukaryotic cells Composed of ribosomal RNA and proteins Found in the cytoplasm and attached to internal membranes of the endoplasmic reticulum Important protein function in protein synthesis in the cell Translate the DNA code into RNA

Eukaryotic Cells Ribosomes Composed of 2 subunits of ribosomal RNA (rRNA) and protein The two subunits associate to form complete Ribosomes Other types of RNA assist with protein synthesis: mRNA tRNA

Fig. 4.10

Endomembrane System Endomembrane system A series of membranes throughout the eukaryotic cytoplasm Divides cell into compartments where different cellular functions occur: 1. Endoplasmic Reticulum 2. Golgi Apparatus 3. Lysosomes

Endomembrane System 1. Endoplasmic Reticulum (ER) Membranes that create a network of channels throughout the cytoplasm Membrane continuous with the outer membrane of the nuclear envelope Location for protein synthesis Two Sections of the ER Rough Endoplasmic Reticulum Smooth Endoplasmic Reticulum

Endomembrane System 1. Rough Endoplasmic Reticulum (RER) System of cytoplasmic membranes that create a network of channels throughout the cytoplasm Ribosomes are attached to the outside of the RER membrane giving it a rough appearance under the microscope Synthesis of proteins to be secreted out of the cell, or packaged and sent to lysosomes or plasma membrane Proteins are synthesized into the RER channels (cisternal space)

Endomembrane System 2. Smooth Endoplasmic Reticulum (SER) Relatively few associated ribosomes Functions: - Synthesis of membrane lipids - Calcium storage - Detoxification of foreign substances

Endomembrane System

Endomembrane System Golgi Apparatus Flattened stacks of interconnected membranes folds (cisternae) known individually as Golgi bodies Located peripheral to the nucleus and ER Function in packaging and distribution of materials to different parts of the cell Synthesis of cell wall components

Fig. 4.12

Cis face of Golgi faces and receives products from the ER Trans face of Golgi releases secretory vesicles

Endomembrane System Lysosomes Membrane bound vesicles containing digestive enzymes to break down macromolecules Packaged and secreted by Golgi apparatus Function to destroy cells or foreign matter that the cell has engulfed by phagocytosis

Endomembrane System Microbodies Membrane bound vesicles that do not originate from the endomembrane system Contain enzymes: Glyoxysomes in plants contain enzymes for converting fats to carbohydrates Peroxisomes contain oxidative enzymes such as H2O2 and catalase

Fig. 4.15

Endomembrane System Vacuoles ‘Blank spaces’ Membrane-bound structures with a variety of functions depending on the cell type There are different types of vacuoles: - Central Vacuole in plant cells - Contractile Vacuole of some protists - Storage Vacuoles

Fig. 4.16

Mitochondria Mitochondria ‘Power house of the cell” Present in all types of eukaryotic cells Contain oxidative metabolism enzymes for the chemical reactions of cellular respiration the transferring of energy within macromolecules to ATP

Mitochondria Structure Surrounded by 2 membranes: Smooth outer membrane Folded inner membrane with layers (cristae) intermembrane space is located between the two membranes matrix within the inner membrane Similar in structure and function to chloroplasts of photosynthesis Contain their own DNA (Mitochondrial DNA) Produce some essential proteins Mitochondria undergo their own division

Mitochondria

Chloroplasts Organelles present in cells of plants and some other eukaryotes (Kingdom Protista) Contain chlorophyll for photosynthesis Surrounded by 2 membranes Inner membrane forms sacs known as thylakoids Stacks of thylakoids are known as Grana Mitochondria, chloroplasts and similar DNA containing organelles known collectively as plastids

Chloroplasts

Mitochondria & Chloroplasts Endosymbiosis Proposal that eukaryotic organelles evolved through a symbiotic relationship One prokaryotic cell engulfed a second prokaryotic cell and a symbiotic relationship developed Mitochondria and chloroplasts are thought to have evolved this way

Mitochondria & Chloroplasts Evidence supports this endosymbiosis theory: Mitochondria and chloroplasts: have 2 membranes possess DNA and ribosomes are about the size of a prokaryotic cell divide by process of simple fission similar to bacteria

Mitochondria & Chloroplasts

Cytoskeleton Cytoskeleton Network of protein fibers found in all eukaryotic cells Supports the shape of the cell Keeps organelles in fixed locations Helps move materials within the cell

Cytoskeleton Three Fiber Types of Cytoskeleton: Actin Filaments – responsible for cellular contractions, crawling, “pinching” Composed of actin protein subunits Microtubules – provide organization to the cell and move materials within the cell Composed of tubulin protein subunits Intermediate Filaments – provide structural stability Composed of vimentin protein subunits

Cytoskeleton

Fig. 4.20a

Cytoskeleton Centrosomes Organelles that organize microtubule function within the cell Cell division Composed of two perpendicular centrioles bundles of microtubules organized in 9 triplets

Fig. 4.21

Cell Movement Cell movement takes different forms: Crawling is accomplished via actin filaments and the protein myosin Molecular motor proteins such as kinesin and dyein use ATP energy to move organelles in the cytoplasm along microtubule tracks Flagella undulate to move a cell Cilia can be arranged in rows on the surface of a eukaryotic cell to propel a cell forward

Fig. 4.22

Cell Movement The cilia and flagella of eukaryotic cells have a similar structure: 9-2 structure: 9 pairs of microtubules surrounded by a 2 central microtubules dynein protein motors slide the microtubules across each other causing them to undulate Flagella attached to cell body at basal body Cilia are usually more numerous than flagella on a cell

Cell Movement

Fig. 4.24b

Fig. 4.24a

Extracellular Structures Cell Walls: plants fungi some protists Extracellular Matrix surrounding animal cells

Extracellular Structures Cell Walls Present surrounding the cells of plants, fungi, and some protists Composed of carbohydrates Type of carbohydrate present in the cell wall vary depending on the cell type: plant and protist cell walls composed of cellulose fungal cell walls composed of chitin

Fig. 4.25

Extracellular Structures Extracellular matrix (ECM) Surrounds animal cells animal cells lack cell walls Composed of glycoproteins and fibrous proteins such as collagen and elastin provide a protective layer over the cell Connected to plasma membrane via fibronectins Connected to the cytoplasm via integrin proteins present in the plasma membrane

Extracellular Structures