Cell Theory The cell is the basic structural and functional unit of life Organismal activity depends on individual and collective activity of cells Biochemical activities of cells are dictated by subcellular structure Continuity of life has a cellular basis

Figure 3.2 Secretion being released from cell by exocytosis Peroxisome Ribosomes Rough endoplasmic reticulum Nucleus Nuclear envelope Chromatin Golgi apparatus Nucleolus Smooth endoplasmic reticulum Cytosol Lysosome Mitochondrion Centrioles Centrosome matrix Microtubule Microvilli Microfilament Intermediate filaments Plasma membrane

Plasma Membrane Separates intracellular fluids from extracellular fluids Plays a dynamic role in cellular activity Glycocalyx is a glycoprotein area abutting the cell that provides highly specific biological markers by which cells recognize one another

Fluid Mosaic Model Double bilayer of lipids with imbedded, dispersed proteins Bilayer consists of phospholipids, cholesterol, and glycolipids – Glycolipids are lipids with bound carbohydrate – Phospholipids have hydrophobic and hydrophilic bipoles PLAY Membrane Structure

Fluid Mosaic Model Figure 3.3

Functions of Membrane Proteins Transport Enzymatic activity Receptors for signal transduction Figure PLAY Receptor Proteins PLAY Enzymes PLAY Transport Protein

Functions of Membrane Proteins Intercellular adhesion Cell-cell recognition Attachment to cytoskeleton and extracellular matrix Figure PLAY Structural Proteins

Plasma Membrane Surfaces Differ in the kind and amount of lipids they contain Glycolipids are found only in the outer membrane surface 20% of all membrane lipid is cholesterol

Lipid Rafts Make up 20% of the outer membrane surface Composed of sphingolipids and cholesterol Are concentrating platforms for cell-signaling molecules

Membrane Junctions Tight junction – impermeable junction that encircles the cell Desmosome – anchoring junction scattered along the sides of cells Gap junction – a nexus that allows chemical substances to pass between cells

Membrane Junctions: Tight Junction Figure 3.5a

Membrane Junctions: Desmosome Figure 3.5b

Membrane Junctions: Gap Junction Figure 3.5c

Membrane Potential Voltage across a membrane Resting membrane potential – the point where K + potential is balanced by the membrane potential – Ranges from –20 to –200 mV – Results from Na + and K + concentration gradients across the membrane – Differential permeability of the plasma membrane to Na + and K + Steady state – potential maintained by active transport of ions

Generation and Maintenance of Membrane Potential PLAY InterActive Physiology ®: Nervous System I: The Membrane Potential Figure 3.15

Cell Adhesion Molecules (CAMs) Anchor cells to the extracellular matrix Assist in movement of cells past one another Rally protective white blood cells to injured or infected areas

Roles of Membrane Receptors Contact signaling – important in normal development and immunity Electrical signaling – voltage-regulated ion gates in nerve and muscle tissue Chemical signaling – neurotransmitters bind to chemically gated channel-linked receptors in nerve and muscle tissue G protein-linked receptors – ligands bind to a receptor which activates a G protein, causing the release of a second messenger, such as cyclic AMP

Operation of a G Protein An extracellular ligand (first messenger), binds to a specific plasma membrane protein The receptor activates a G protein that relays the message to an effector protein

Operation of a G Protein The effector is an enzyme that produces a second messenger inside the cell The second messenger activates a kinase The activated kinase can trigger a variety of cellular responses

Operation of a G Protein Figure 3.16 Extracellular fluid Cytoplasm Inactive second messenger Cascade of cellular responses (metabolic and structural changes) Effector (e.g., enzyme) Activated (phosphorylated) kinases First messenger (ligand) Active second messenger (e.g., cyclic AMP) Membrane receptor G protein

Operation of a G Protein Figure 3.16 Extracellular fluid Cytoplasm First messenger (ligand) Membrane receptor 1

Operation of a G Protein Figure 3.16 Extracellular fluid Cytoplasm First messenger (ligand) Membrane receptor G protein 1 2

Operation of a G Protein Figure 3.16 Extracellular fluid Cytoplasm Effector (e.g., enzyme) First messenger (ligand) Membrane receptor G protein 1 2 3

Operation of a G Protein Figure 3.16 Extracellular fluid Cytoplasm Inactive second messenger Effector (e.g., enzyme) First messenger (ligand) Active second messenger (e.g., cyclic AMP) Membrane receptor G protein

Operation of a G Protein Figure 3.16 Extracellular fluid Cytoplasm Inactive second messenger Effector (e.g., enzyme) Activated (phosphorylated) kinases First messenger (ligand) Active second messenger (e.g., cyclic AMP) Membrane receptor G protein

Operation of a G Protein Figure 3.16 Extracellular fluid Cytoplasm Inactive second messenger Cascade of cellular responses (metabolic and structural changes) Effector (e.g., enzyme) Activated (phosphorylated) kinases First messenger (ligand) Active second messenger (e.g., cyclic AMP) Membrane receptor G protein

Cytoplasm Cytoplasm – material between plasma membrane and the nucleus Cytosol – largely water with dissolved protein, salts, sugars, and other solutes

Cytoplasm Cytoplasmic organelles – metabolic machinery of the cell Inclusions – chemical substances such as glycosomes, glycogen granules, and pigment

Cytoplasmic Organelles Specialized cellular compartments Membranous – Mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus Nonmembranous – Cytoskeleton, centrioles, and ribosomes

Mitochondria Double membrane structure with shelf-like cristae Provide most of the cells ATP via aerobic cellular respiration Contain their own DNA and RNA

Mitochondria Figure 3.17a, b

Ribosomes Granules containing protein and rRNA Site of protein synthesis Free ribosomes synthesize soluble proteins Membrane-bound ribosomes synthesize proteins to be incorporated into membranes

Endoplasmic Reticulum (ER) Interconnected tubes and parallel membranes enclosing cisternae Continuous with the nuclear membrane Two varieties – rough ER and smooth ER

Endoplasmic Reticulum (ER) Figure 3.18a, c

Rough (ER) External surface studded with ribosomes Manufactures all secreted proteins Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes

Signal Mechanism of Protein Synthesis mRNA – ribosome complex is directed to rough ER by a signal-recognition particle (SRP) SRP is released and polypeptide grows into cisternae The protein is released into the cisternae and sugar groups are added

Signal Mechanism of Protein Synthesis The protein folds into a three-dimensional conformation The protein is enclosed in a transport vesicle and moves toward the Golgi apparatus

Signal Mechanism of Protein Synthesis Figure 3.19 Cytosol Ribosomes mRNA Coatomer- coated transport vesicle Transport vesicle budding off Released glycoprotein ER cisterna ER membrane Signal- recognition particle (SRP) Signal sequence Receptor site Sugar group Signal sequence removed Growing polypeptide

Signal Mechanism of Protein Synthesis Figure 3.19 Cytosol mRNA ER cisterna ER membrane Signal- recognition particle (SRP) Signal sequence Receptor site 1

Signal Mechanism of Protein Synthesis Figure 3.19 Cytosol mRNA ER cisterna ER membrane Signal- recognition particle (SRP) Signal sequence Receptor site Growing polypeptide 1 2

Signal Mechanism of Protein Synthesis Figure 3.19 Cytosol Ribosomes mRNA ER cisterna ER membrane Signal- recognition particle (SRP) Signal sequence Receptor site Signal sequence removed Growing polypeptide 1 2 3

Signal Mechanism of Protein Synthesis Figure 3.19 Cytosol Ribosomes mRNA Released glycoprotein ER cisterna ER membrane Signal- recognition particle (SRP) Signal sequence Receptor site Signal sequence removed Growing polypeptide

Signal Mechanism of Protein Synthesis Figure 3.19 Cytosol Ribosomes mRNA Transport vesicle budding off Released glycoprotein ER cisterna ER membrane Signal- recognition particle (SRP) Signal sequence Receptor site Sugar group Signal sequence removed Growing polypeptide

Signal Mechanism of Protein Synthesis Figure 3.19 Cytosol Ribosomes mRNA Coatomer- coated transport vesicle Transport vesicle budding off Released glycoprotein ER cisterna ER membrane Signal- recognition particle (SRP) Signal sequence Receptor site Sugar group Signal sequence removed Growing polypeptide

Smooth ER Tubules arranged in a looping network Catalyzes the following reactions in various organs of the body – In the liver – lipid and cholesterol metabolism, breakdown of glycogen and, along with the kidneys, detoxification of drugs – In the testes – synthesis of steroid-based hormones

Smooth ER Catalyzes the following reactions in various organs of the body (continued) – In the intestinal cells – absorption, synthesis, and transport of fats – In skeletal and cardiac muscle – storage and release of calcium

Golgi Apparatus Stacked and flattened membranous sacs Functions in modification, concentration, and packaging of proteins Transport vessels from the ER fuse with the cis face of the Golgi apparatus

Golgi Apparatus Proteins then pass through the Golgi apparatus to the trans face Secretory vesicles leave the trans face of the Golgi stack and move to designated parts of the cell

Golgi Apparatus Figure 3.20a

Role of the Golgi Apparatus Figure 3.21 Secretion by exocytosis Extracellular fluid Plasma membrane Vesicle incorporated into plasma membrane Coatomer coat Lysosomes containing acid hydrolase enzymes Phagosome Proteins in cisterna Membrane Vesicle Pathway 3 Pathway 2 Secretory vesicles Proteins Pathway 1 Golgi apparatus Cisterna Rough ER

Role of the Golgi Apparatus Figure 3.21 Secretion by exocytosis Extracellular fluid Proteins in cisterna Membrane Vesicle Secretory vesicles Proteins Pathway 1 Golgi apparatus Cisterna Rough ER

Role of the Golgi Apparatus Figure 3.21 Secretion by exocytosis Extracellular fluid Plasma membrane Vesicle incorporated into plasma membrane Coatomer coat Proteins in cisterna Membrane Vesicle Pathway 2 Golgi apparatus Cisterna Rough ER

Role of the Golgi Apparatus Figure 3.21 Extracellular fluid Plasma membrane Lysosomes containing acid hydrolase enzymes Phagosome Proteins in cisterna Membrane Vesicle Pathway 3 Secretory vesicles Golgi apparatus Cisterna Rough ER

Role of the Golgi Apparatus Figure 3.21 Secretion by exocytosis Extracellular fluid Plasma membrane Vesicle incorporated into plasma membrane Coatomer coat Lysosomes containing acid hydrolase enzymes Phagosome Proteins in cisterna Membrane Vesicle Pathway 3 Pathway 2 Secretory vesicles Proteins Pathway 1 Golgi apparatus Cisterna Rough ER

Lysosomes Spherical membranous bags containing digestive enzymes Digest ingested bacteria, viruses, and toxins Degrade nonfunctional organelles Breakdown glycogen and release thyroid hormone

Lysosomes Breakdown nonuseful tissue Breakdown bone to release Ca2 + Secretory lysosomes are found in white blood cells, immune cells, and melanocytes

Endomembrane System System of organelles that function to: – Produce, store, and export biological molecules – Degrade potentially harmful substances System includes: – Nuclear envelope, smooth and rough ER, lysosomes, vacuoles, transport vesicles, Golgi apparatus, and the plasma membrane PLAY Endomembrane System

Figure 3.23

Peroxisomes Membranous sacs containing oxidases and catalases Detoxify harmful or toxic substances Neutralize dangerous free radicals – Free radicals – highly reactive chemicals with unpaired electrons (i.e., O 2 – )

Cytoskeleton The skeleton of the cell Dynamic, elaborate series of rods running through the cytosol Consists of microtubules, microfilaments, and intermediate filaments

Cytoskeleton Figure 3.24a-b

Cytoskeleton Figure 3.24c

Microtubules Dynamic, hollow tubes made of the spherical protein tubulin Determine the overall shape of the cell and distribution of organelles

Microfilaments Dynamic strands of the protein actin Attached to the cytoplasmic side of the plasma membrane Braces and strengthens the cell surface Attach to CAMs and function in endocytosis and exocytosis

Intermediate Filaments Tough, insoluble protein fibers with high tensile strength Resist pulling forces on the cell and help form desmosomes

Motor Molecules Protein complexes that function in motility Powered by ATP Attach to receptors on organelles

Motor Molecules Figure 3.25a

Motor Molecules Figure 3.25b

Centrioles Small barrel-shaped organelles located in the centrosome near the nucleus Pinwheel array of nine triplets of microtubules Organize mitotic spindle during mitosis Form the bases of cilia and flagella

Centrioles Figure 3.26a, b

Cilia Whip-like, motile cellular extensions on exposed surfaces of certain cells Move substances in one direction across cell surfaces PLAY Cilia and Flagella

Cilia Figure 3.27a

Cilia Figure 3.27b

Cilia Figure 3.27c

Nucleus Contains nuclear envelope, nucleoli, chromatin, and distinct compartments rich in specific protein sets Gene-containing control center of the cell Contains the genetic library with blueprints for nearly all cellular proteins Dictates the kinds and amounts of proteins to be synthesized

Nucleus Figure 3.28a

Nuclear Envelope Selectively permeable double membrane barrier containing pores Encloses jellylike nucleoplasm, which contains essential solutes

Nuclear Envelope Outer membrane is continuous with the rough ER and is studded with ribosomes Inner membrane is lined with the nuclear lamina, which maintains the shape of the nucleus Pore complex regulates transport of large molecules into and out of the nucleus

Nucleoli Dark-staining spherical bodies within the nucleus Site of ribosome production

Chromatin Threadlike strands of DNA and histones Arranged in fundamental units called nucleosomes Form condensed, barlike bodies of chromosomes when the nucleus starts to divide Figure 3.29

Figure 3.30 Cell Cycle Interphase – Growth (G 1 ), synthesis (S), growth (G 2 ) Mitotic phase – Mitosis and cytokinesis

Interphase G 1 (gap 1) – metabolic activity and vigorous growth G 0 – cells that permanently cease dividing S (synthetic) – DNA replication G 2 (gap 2) – preparation for division PLAY Late Interphase