Cell Biology: Cell Structure and Function PDF

Cell is the basic unit of life, the smallest living part of the body In all tissues, cells themselves are the basic structural and functional units Types of Cell
 - Prokaryotic - Eukaryotic Eukaryotic cells
 Animal cells with distinct membrane-limited nuclei surrounded by cytoplasm contain...

Cell is the basic unit of life, the smallest living part of the body In all tissues, cells themselves are the basic structural and functional units Types of Cell
 - Prokaryotic - Eukaryotic Eukaryotic cells
 Animal cells with distinct membrane-limited nuclei surrounded by cytoplasm containing various organelles and the cytoskeleton - Prokaryotic cells
 Bacterial cells that typically have a cell wall around the plasmalemma and lack nuclei and membranous cytoplasmic structures - The human organism consists of hundreds of different cell types all derived from the zygote - The zygote is formed by the merger of a spermatozoon with an oocyte at fertilization - The first zygotic cellular divisions produce cells called blastomeres - Blastomeres give rise to all tissue types of the fetus - Embryonic stem cells
 Cells of the inner cell mass explanted to tissue culture - Most cells of the fetus undergo a specialization process called differentiation - Differentiation involves differential expression of sets of genes that mediate specific cytoplasmic activities - Muscle cell precursors elongate into fiber-like cells containing large arrays of actin and myosin - All animal cells contain actin filaments and myosin - Specialized cells
 Have greatly expanded their capacity for one or more functions during differentiation - Changes in cells' microenvironments can cause the same cell type to have variable features and activities - Cells that appear similar structurally often have different families of receptors for signaling molecules - The cell membrane functions as a selective barrier regulating the passage of materials into and out of the cell - The cell membrane facilitates the transport of specific molecules - One important role of the cell membrane is to keep constant the ion content of cytoplasm - Membranes carry out specific recognition and signaling functions - Certain plasma membrane proteins, the integrins, are linked to both the cytoskeleton and ECM components - Membranes range in thickness and are visible only in the electron microscope - Phospholipids
 Amphipathic molecules consisting of two nonpolar long-chain fatty acids linked to a charged polar head - Phospholipids are most stable when organized into a double layer (bilayer) - Some of the outer layer's lipids are known as glycolipids - Glycolipids include oligosaccharide chains that contribute to a delicate cell surface coating called the glycocalyx - Proteins are major constituents of membranes (\~50% by weight in the plasma membrane) - Integral proteins
 Incorporated directly within the lipid bilayer - Peripheral proteins
 Bound to one of the two membrane surfaces, particularly on the cytoplasmic side - Fluid mosaic model
 Membrane proteins are not bound rigidly in place and can move laterally - The plasma membrane is the site where materials are exchanged between the cell and its environment - Mechanisms for small molecules crossing the membrane - Diffusion - Channels - Carriers - Diffusion
 Transports small, nonpolar molecules directly through the lipid bilayer - Lipophilic molecules diffuse through membranes readily, water very slowly - Channels
 Multi-pass proteins forming transmembrane pores for selective passage of ions or small molecules - Cells open and close specific channels for Na+, K+, Ca2+ and other ions in response to various physiological stimuli - Water molecules usually cross the plasma membrane through channel proteins called aquaporins - Carriers
 Transmembrane proteins that bind small molecules and translocate them across the membrane - Passive Transportation
 1\. Diffusion 2\. Channels 3\. Carrier proteins operate passively - Passive transport allows movement of substances across membranes down a concentration gradient - Types of Passive Transportation - Simple Diffusion - Facilitated Diffusion - Osmosis - Osmosis is the diffusion of water across a selectively permeable membrane - Active Transport
 Membrane pumps utilize energy from ATP to move ions and solutes across membranes - Membrane pumps are often referred to as ATPases - Vesicular Transport
 1\. Endocytosis 2\. Exocytosis - Macromolecules enter cells by being enclosed within folds of plasma membrane in a process known as endocytosis - Types of Endocytosis
 - Phagocytosis - Pinocytosis - Receptor-mediated endocytosis - Phagocytosis
 The ingestion of particles such as bacteria or dead cell remnants - Macrophages and neutrophils are specialized for phagocytosis - When a bacterium binds to the surface of a neutrophil, it becomes surrounded by extensions of plasmalemma and cytoplasm - Fusion of the membranous folds encloses the bacterium in an intracellular vacuole called a phagosome - The phagosome merges with a lysosome for degradation of its contents - Pinocytosis
 Involves smaller invaginations of the cell membrane that entrap extracellular fluid and its dissolved contents - The resulting pinocytotic vesicles then pinch off inwardly from the cell surface - Pinocytotic vesicles either fuse with lysosomes or move to the opposite cell surface - Phagocytosis
 Process where a bacterium is engulfed by a cell - Phagocytosis
 1\. Bacterium binds to neutrophil 2\. Extensions of plasmalemma surround bacterium 3\. Fusion encloses bacterium in phagosome 4\. Phagosome merges with lysosome - Pinocytosis
 Involves smaller invaginations of the cell membrane that entrap extracellular fluid - Pinocytosis
 1\. Invagination of cell membrane 2\. Formation of pinocytotic vesicles 3\. Vesicles pinch off from cell surface 4\. Vesicles fuse with lysosomes or release contents - Receptor-mediated Endocytosis
 Involves receptors binding specific molecules (ligands) - Receptor-mediated Endocytosis
 1\. Receptors bind ligands 2\. Receptors aggregate in membrane region 3\. Membrane invaginates and pinches off 4\. Creates vesicle or endosome - Exocytosis
 Movement of large molecules from inside to outside the cell - Exocytosis
 1\. Vesicle containing molecules fuses with plasma membrane 2\. Release of contents into extracellular space - Membrane trafficking
 Process of membrane movement and recycling during endocytosis and exocytosis - Signal Reception & Transduction
 Cells communicate to regulate development, growth, and function - Gap junctions
 Allow exchange of ions and small molecules between adjacent cells - Types of signaling
 - Endocrine signaling - Paracrine signaling - Synaptic signaling - Autocrine signaling - Juxtacrine signaling - Synaptic signaling
 Neurotransmitters act on adjacent cells through synapses - Endocrine signaling
 Hormones are carried in the blood to target cells - Paracrine signaling
 Chemical ligand diffuses in extracellular fluid for local effect - Autocrine signaling
 Signals bind receptors on the same cells that produced them - Juxtacrine signaling
 Signaling molecules are cell membrane-bound proteins that bind surface receptors upon direct contact - Plasma Membrane
 Phospholipid bilayer forming a selectively permeable boundary - Cilia
 Short, numerous membrane extensions supported by microtubules - Flagellum
 Long, singular membrane extension supported by microtubules - Microvilli
 Thin membrane folds projecting from the free cell surface - Nucleus
 Large structure containing chromatin, nucleolus, and nucleoplasm - Nuclear Envelope
 Double membrane boundary between cytoplasm and nuclear contents - Nuclear pores
 Openings through the nuclear envelope - Nucleolus
 Large, prominent structure within the nucleus - Cytoplasm
 Contents of cells between the plasma membrane and nuclear envelope