Chapter 2 - Cell Structure and Function PDF

# Organization of the Cell - Cell Membrane - thin, pliable, elastic structure - 7.5 to 10 nanometers thick - composed almost entirely of proteins and lipids - The approximate composition is: - 55% proteins, 25% phospholipids, 13% cholesterol, 4% other lipids, and carbohy...

# Organization of the Cell - Cell Membrane - thin, pliable, elastic structure - 7.5 to 10 nanometers thick - composed almost entirely of proteins and lipids - The approximate composition is: - 55% proteins, 25% phospholipids, 13% cholesterol, 4% other lipids, and carbohydrates - Cytoplasm: the jelly-like fluid portion of the cytoplasm in which the particles are dispersed is called. - contains mainly dissolved proteins, electrolytes, and glucose - **Organelles:** - neutral fat globules, glycogen granules, ribosomes, secretory vesicles, and 5 especially important organelles - endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and peroxisomes ## Membranous Structures of the Cell - cell membrane - nuclear membrane - membrane of the endoplasmic reticulum, - Membranes of the mitochondria, - lysosomes, - Golgi apparatus ## Cell Membrane - Bilayer of Phospholipids with Proteins ### Membrane Components: - **LIPIDS:** barrier to water and water-soluble substances - **PROTEINS:** - provide "specificity" to a membrane - defined by mode of association with the lipid bilayer - **integral:** channels, pores, carriers, enzymes, etc. - **peripheral:** enzymes, intracellular signal mediators - **CARBOHYDRATES:** - glycolipids (approx. 10%) - glycoproteins (majority of integral roteins) - proteoglycans - **Cholesterol:** - present in membranes in varying amounts - generally decreases membrane FLUIDITY and PERMEABILITY (except in plasma membrane) - increases membrane FLEXIBILITY and STABILITY ## Cell Organelles **Centrioles** - a pair of small cylindrical structures located near the nucleus of a cell. They are involved in the formation of microtubules, which are part of the cytoskeleton and involved in cell division. **Secretory Granules** - small, membrane-bound sacs that contain substances to be secreted from the cell. **Microtubules** - hollow, cylindrical structures that provide support for the cell and help in the movement of organelles. **Nuclear Membrane** - a membrane that encloses the nucleus of eukaryotic cells. It regulates the movement of substances between the nucleus and the cytoplasm. **Chromosomes and DNA** - Genetic material of the cell. **Golgi Apparatus** - a stack of flattened, membrane-bound sacs that modify, package, and transport proteins and lipids. **Cell Membrane** - thin, pliable, elastic structure that surrounds the cell. **Nucleolus** - a small, dense body within the nucleus of a cell. It is involved in the production of ribosomes **Glycogen** - a complex carbohydrate that is stored as an energy reserve in the liver and muscles. **Ribosomes** - small, granular organelles that are involved in the synthesis of proteins. **Lysosome** - membrane-bound organelles that contain enzymes that break down waste material and cellular debris. **Mitochondrion** - a complex organelle that is responsible for the production of energy in the form of ATP. **Granular Endoplasmic Reticulum** - a network of interconnected membrane-bound sacs and tubules that are studded with ribosomes. It is involved in the synthesis of proteins and lipids, as well as in the folding of proteins. **Smooth Endoplasmic Reticulum** - a network of interconnected membrane-bound sacs and tubules without ribosomes. It is involved in the synthesis of lipids and steroids, as well as in the detoxification of drugs and toxins. **Microfilaments** -thin, threadlike structures that contribute to cell shape, muscle contraction, and cell division. ## Structure - **Membranous Structures:** - cell membrane, - nuclear membrane, - membrane of the endoplasmic reticulum, - Membranes of the mitochondria, - lysosomes, - Golgi apparatus ## Cell Membrane - is a thin, pliable, elastic structure - only 7.5 to 10 nanometers thick - It is composed almost entirely of proteins and lipids. ## Cytoplasm - The jelly-like fluid portion of the cytoplasm in which the particles are dispersed is called. - contains mainly dissolved proteins, electrolytes, and glucose ### Endoplasmic Reticulum - Network of tubular and flat vesicular structures - Membrane is similar to (and contiguous with) the plasma membrane - Space inside the tubules is called the endoplasmic matrix #### Rough or Granular ER - outer membrane surface covered with ribosomes - newly synthesized proteins are extruded into the ER matrix - proteins are "processed" inside the matrix - crosslinked - folded - glycosylated (N-linked) - cleaved #### Smooth ER - site of lipid synthesis - phospholipids - cholesterol - growing ER membrane, buds continuously forming transport vesicles, most of which migrate to the Golgi apparatus ### Golgi Apparatus - Membrane composition similar to that of the smooth ER and plasma membrane - Composed of 4 or more stacked layers of flat vesicular structures - Receives transport vesicles from smooth ER - Substances formed in the ER are "processed" - phosphorylated, glycosylated - Substances are concentrated, sorted and packaged for secretion. ### Exocytosis: - Secretory vesicles diffuse through the cytosol and fuse to the plasma membrane - Lysosomes fuse with internal endocytotic vesicles ### Secretion: - secretory vesicles containing proteins synthesized in the RER bud from the Golgi apparatus - fuse with plasma membrane to release contents. - constitutive secretion happens randomly - stimulated secretion requires trigger ### Lysosomes - vesicular organelle formed from budding Golgi - contain hydrolytic enzymes (acid hydrolases) - phosphatases - nucleases - proteases - lipid-degrading enzymes - lysozymes - digest bacteria ### Lysosomal Storage Diseases - Absence of one or more hydrolases. - not synthesized, inactive, or not properly sorted and packaged - Result: Lysosomes become engorged with undigested substrate - Examples: - Acid lipase A deficiency - I-cell disease (non-specific) - Tay-Sachs disease (HEX- ### Peroxisomes: - similar physically to lysosomes - two major differences: - formed by self-replication - they contain oxidases - Function: oxidize substances (e.g. alcohol) that may be otherwise poisonous. ### Secretory Granules - small, membrane-bound sacs that contain substances to be secreted from the cell. ### Mitochondria - Primary function: extraction of energy from nutrients - Outer membrane - Inner membrane - Crests - Matrix - Outer chamber - Oxidative phosphorylation enzymes ## The Cytoskeleton - **Intermediate Filaments:** - Comprised of cell-specific fibrillar monomers - (e.g. vimentin, neurofilament proteins, keratins, nuclear lamins) - **Microtubules:** - Heterodimers of alpha and beta tubulin - Make up spindle fibers, core of axoneme structure - **Thin Filaments:** - F-Actin - Make up "stress fibers" in non-muscle cells - **Thick Filaments:** - Myosin (types I and II) ## The Nuclear Membrane - The nuclear membrane is permeated by thousands of nuclear pores - 100 nm in diameter - functional diameter is 9 nm - (selectively) permeable to molecules of up to 44,000 MW - Nucleoplasm - Endoplasmic reticulum - Nucleolus - Nuclear envelope: outer and inner membranes - Chromatin material (DNA) - Cytoplasm ## The Nucleolus - Chromatin (condensed DNA) is found in the nucleoplasm. - one or more per nucleus - contains RNA and proteins - not membrane delimited - functions to form the granular subunits of ribosomes. ## Comparison of the Animal Cell with Precellular Forms of Life - 15 nm: Small virus - 150 nm: Large virus - 1 µm Bacterium - 350 mm: Rickettsia ## Receptor-mediated Endocytosis: - molecules attach to cell surface - receptors concentrated in clathrin-coated pits - receptor binding induces invagination - also ATP-dependent and involves recruitment of actin and myosin. ## Digestion of Substances in Pinocytotic or Phagocytic Vesicles - Lysosomes - Pinocytotic or phagocytic vesicle - Digestive vesicle - Residual body - Excretion ## Pinocytosis - begins when droplets of extracellular fluid containing dissolved solutes collect in a pit at the surface of the cell. - forming a vesicle that is drawn into the cytoplasm of the cell. - A lysosome, containing digestive enzymes, fuses with the vesicle. - Finally, the digestive enzymes break down the extracellular fluid, and the digested solutes are released into the cytoplasm. ## Phagocytosis: - begins when receptors on a phagocyte surface bind to large solid particles such as microbes, dead cells, and debris - binding action triggers the plasma membrane to extend finger-like projections, called pseudopods, around the bound particle, forming a vesicle, known as a phagosome. - The phagosome then fuses with a lysosome, which contains digestive enzymes. - The digestive enzymes break down the engulfed particles into smaller molecules, and any remaining undigested material is contained in a vesicle known as a residual body. ## Receptor-mediated Endocytosis: - binds to a specific receptor on the cell's plasma membrane, forming a ligand-receptor complex. - Each receptor is associated with a protein, known as a clathrin, on the membrane's cytoplasmic side. - The regions of the plasma membrane in which these receptors and their associated clathrin molecules collect are called clathrin-coated pits. - The clathrin-coated pit sinks into the cell, forming a vesicle that contains the ligand-receptor complexes. - The uncoated vesicle fuses with an endosome, and the ligands and receptors separate, collecting at opposite ends of the endosome. - Next, the endosome fuses with a lysosome containing digestive enzymes. ## Receptor-mediated endocytosis ### Lysosomes: - DIGEST PINOCYTOTIC AND PHAGOCYTIC FOREIGN SUBSTANCES INSIDE THE CELL - **Lysosomes:** Regression of Tissues and Autolysis of Damaged Cells. - If the damage is severe, the entire cell is digested, a process called autolysis. - The lysosomes also contain bactericidal agents that can kill phagocytized bacteria before they cause further damage. - These agents include the following: - **lysozyme,** which dissolves the bacterial cell wall; - **lysoferrin,** which binds iron and other substances before they can promote bacterial growth; and - **acid at pH 5.0,** which activates the hydrolases and inactivates bacterial metabolic systems. ## ATP Production - **Step 1.** - Carbohydrates are converted into glucose - Proteins are converted into amino acids - Fats are converted into fatty acids - **Step 2.** - Glucose, AA, and FA are processed into Acetyl CoA - **Step 3.** - Acetyl CoA reacts with O2 to produce ATP. - A maximum of 38 molecules of ATP are formed per molecule of glucose degraded. ## The Use of ATP for Cellular Function - under "standard" conditions ΔGo is only -7.3 kcal/mole - ATP concentration is ~10x that of ADP, the ΔG is -12 kcal/mole - Membrane transport - Synthesis of chemical compounds - Mechanical work ## Amoeboid Locomotion - continual endocytosis at the "tail" and exocytosis at the leading edge of the pseudopodium. - attachment of the pseudopodium is facilitated by receptor proteins carried by vesicles. - forward movement results through interaction of actin and myosin (ATP-dependent). ### Cell movement is influenced by - chemical substances... - Low concentration (negative) - Chemotaxis - High concentration (positive) ## Cilia and Ciliary Movements - Occurs only on the inside surfaces of the human airway and fallopian tubes - Each cilium is comprised of: - 11 microtubules - 9 double tubules - 2 single tubules - axoneme - Each cilium is an outgrowth of the basal body and is covered by an outcropping of the plasma membrane. - Ciliary movement is ATP-dependent. ## Amoeboid Locomotion: ## Mechanism of Ciliary Movement - Fourth, during forward movement on a cilia, the edge of the cilium slides those on the back edge - Fifth, multiple protein arms attach to the double tubule (adenosine triphosphate) - These structures are encircled by nine double fibers and a cellular membrane, a unique combination that enables motility. - Cilia and Flagella assist in fluid movement and in the locomotion of single cells. - In particular, single-celled organisms, such as paramecium and bacteria, move with the help of Cilia and Flagella, respectively. ## Non-motile Primary Cilia - Found on nearly every type of cell... (except RBC) - Primary cilia are non-motile and generally occur only as a single cilium on each cell. - Physiological functions of primary cilia are not fully understood. - current evidence indicates they function as cellular "sensory antennae," which coordinate: - cellular signaling pathways involved in chemical and mechanical sensation; - signal transduction, and - cell growth. - Prominent in retinal photoreceptors & renal epithelial cells (as mechanoreceptors) - **Motile Cili** - Solitary motile cilia (SMC) - Multiple motile cilia (MMC) - **Non-motile Cili** - Primary cilia - Pair of microtubules - Microtubule singlets - Radial spoke - Dynein arm - **Transversal View** ### "GOOD EVENING"