Chapter 3: Cells - Lecture notes 3 PDF

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Chapter 3: Cells 3.1 Cells are the Basic Units of the Body ● Cells vary in size, but measured in units called micrometers ● Human egg cell= 140 micrometers in diameter ● Red blood cell= 7.5 micrometers in diameter ● Smooth muscle cells 20 to 500 micrometers long Cell is the basic unit of structure and function in the body ● Cells that have developed specialized characteristics are said to be differentiated ● Cells vary in size and shape; structure and function are inter-related 3.2 A Composite Cell ● There is no typical cell, but a composite cell shows the components found in most cells. Three major parts of a cell ● Nucleus- cellular structure enclosed by a double bilayer nuclear envelope and containing DNA; masses of interneuron cell bodies in the CNS and directs the cell’s function ● Cytoplasm- the contents of a cell including the gel-like cytosol and organelles, excluding the nucleus, enclosed by the cell membrane ● Cell membrane- selectively permeable outer boundary of a cell consisting of a phospholipid bilayer embedded w/ proteins -cell membrane (plasma membrane) contains the cytoplasm, which surrounds the nucleus Cell(plasma) membrane ● Outer boundary of the cell and maintains the integrity of the cell ● Extremely thin and only seen with electron microscope with its many outpouching and infoldings, greatly increase the surface area of the cell Selectively permeable- regulates entry and exit of substances Signal transduction- permits cell to receive and respond to messages ● Consists mainly of lipids and proteins, with some carbohydrates

Cell membrane framework is a phospholipid bilayer --water-soluble (hydrophilic) heads form surfaces

---water-insoluble (hydrophobic) tails form interior Bilayer is permeable to lipid-soluble substances, but impermeable to water-soluble substances (amino acids, sugars, proteins, nucleic acids, and various ions) middle portion---->fatty acids making them oily, molecule lipid soluble---> oxygen, carbon dioxide, and steroid pass through the phospholipid bilayer Cholesterol stabilizes membrane, helps keep it impermeable to water-soluble substances -- some lipids and proteins can move; “fluid mosaic” properties --- membrane proteins have many functions → pores, channels, receptors, enzymes cell contact and identification CAMS (Cell Adhesion Molecules)

Clinical Application 3.1 Faulty Ion Channels cause Disease ● Mutations in Na+ Channels can cause inability to feel pain or extreme pain conditions ● Mutations in K+ Channels can disrupt electrical activity of the heart and disturb heart rhythm, and/or impair hearing ● Abnormal Cl- channels are the cause of Cystic Fibrosis production of thick mucus causes difficulty breathing and clogged pancreas, salty sweat Cellular Adhesion Molecules (CAMS) ● Guide cells on the move ● Selectins coat white blood cells and anchor them by providing friction ● Integrins direct white blood cells through the capillary walls toward infection sites ● Guide embryonic cells to form placenta ● Establish connections between nerve cells Cytoplasm ● Cytoplasm consists of networks of membranes and organelles suspended in cytosol ● Cytoplasm= cytosol +organelles ● Cytosol= fluid portion of the cytoplasm ● Organelles= tiny solid structures w/ specific functions in the cell ● Cytoplasm contains the cytoskeleton, a supporting framework of protein rods and tubules Cytoplasmic Organelles Ribosomes ● Composed of protein and RNA

● Free in cytoplasm or on the Rough Endoplasmic Reticulum ● Provide structural support and enzyme activity to link amino acids in protein synthesis Endoplasmic Reticulum ● Membrane- bound sacs, canals, vesicles ● Tubular transports systems ● Rough ER contains ribosomes, conducts protein synthesis ● Smooth ER does not have ribosomes conduct lipid synthesis Vesicles ● Membranous sacs that store or transport substances ● Large vesicles that contain mainly water form when part of the cell membrane folds inward and pinches off, bringing material from outside the cell into the cytoplasm ● Smaller ones shuttle material from the Rough ER to the Golgi apparatus as part of secretion Vesicle trafficking- transport of substances into and out of cell by fleets of vesicles Golgi Apparatus (UPS) ● Stack of 5 to 8 flattened, membranous sacs called cisternae (resembles stacks of pancakes) ● Refines, packages, and delivers proteins made on the RER Cytoplasmic Organelles Milk secretion is an example of organelle interactions transport of substances by vesicles

Mitochondria ● Elongated, fluid-filled sacs 2 to 5 micrometers long that house most of the biochemical reactions that extract energy from nutrient molecules (cellular respiration, which produces ATP) ● Contains a small amount of DNA that encodes information for making a few types

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of proteins and specialized RNA Two layers- outer membrane and inner membrane Cristae- inner membrane fold extensively inward, forming shelf like partitions that dramatically increase the surface area on which chemical reactions can occur From cristae arise small stalked particles that contain enzymes. ----these enzymes and others dissolved in the fluid called the matrix control many of the chemical reactions that release energy from glucose and other nutrients in a process called cellular respiration Adenosine triphosphate- organic molecule that transfers energy used in cellular processes; ATP called the “powerhouse of the cell”

Lysosome ● “Garbage disposals” of cell, where enzymes dismantle debris ● Process of a cell’s disposing of its own trash is called “autophagy” which means eating self ● Small membranous sacs contain powerful enzymes that digest proteins, carbohydrates, nucleic acids, bacteria, debris, worn out cell parts ● Digest bacteria that certain white blood cells engulf ● In liver cells, lysosomes break down cholesterol, toxins, and drugs ● Contain 43 types of enzymes ● Abnormality in just one type of lysosomal enzyme can be devastating to health Peroxisomes ● Membranous sac similar to lysosomes ● Abundant in cells of the liver and kidneys ● Contain enzymes, called peroxidase that digest lipids, alcohol, and hydrogen peroxide

Other Cellular Structures Centrosome: ● “Central body” consists of 2 centrioles ● In cytoplasm, near nucleus ● Centrioles are cylindrical, composed of microtubules

● Centrioles produce spindle fibers during cell division, which distribute chromosomes to form daughter cells ● Centrioles produce internal parts of cell membrane projections called cilia and flagella Cilia: ● Motile extension of cell membranes ● Internally, both cilia and flagella consist of 9 groups of 3 microtubules w/ 2 additional microtubules in the center, forming a distinct cylindrical pattern ● Form a “fringe” on surface of certain epithelial cells ● Shorter than flagella, but very abundant when present ● Beat back and forth in coordinated manner ● Propel mucus in respiratory tract, propel egg toward the uterus Flagella ● Another type of motile extension from cell membrane ● Similar in structure in cilia, but much longer ● Flagellum cause the entire cell to more tail of a sperm cell is the only flagellum in a human cell ● Each cell has only 1 flagellum Microfilaments, Microtubules and Intermediate Filaments ● Threadlike structures in cytoplasm ● Create the cytoskeleton that provides strength and the cell’s ability to resist force and maintain shape Microfilaments- tiny rods of actin, provide cellular movement, such as a muscle contraction

Microtubules ● Larger tubes of tubulin ● Rigidity maintains cell shape ● Make up cilia, flagella, and centrioles ● Help move organelles Intermediate filaments ● Composed of several proteins ● A cytoskeletal structure

● Support nuclear envelope ● Made of proteins called keratin are abundant in the actively dividing cells in the deepest part of the outer skin layer, the epidermis

Clinical Application 3.2 Disease at the Organelle Level MELAS: ● Mutant gene in DNA of mitochondria ● Person cannot extract maximum energy from nutrients Krabbe Disease: ● Caused by inability to produce one lysosomal enzyme ● Person cannot produce myelin for nerve cells, which leads to severe damage to the nervous system Adrenoleukodystrophy (ADL) ● Caused by lack of protein in membrane of peroxisomes ● Fatty acids buildup destroys myelin sheaths of nerve cells ● Nerve cells cannot transmit nerve impulses quickly

Cell Nucleus Contains genetic material and controls cell activities Nuclear envelope ● Porous double- layered membrane ● Separates nucleoplasm from cytoplasm ● Nuclear pores allow passage of certain substances Nucleolus ● Dense body of RNA and protein ● Site of ribosome protection Chromatin ● Consists of cell’s chromosomes, each containing DNA wound around proteins ● Stores information for protein synthesis

3.3 Movement into and out of the cell

Physical (Passive) Processes: Do Not require ATP ● Diffusion ● Osmosis ● Facilitated diffusion ● Filtration Physiological (Active) Processes: Require ATP ● Active transport ● Endocytosis ● Exocytosis ● Transcytosis

Diffusion ● Movement of atoms, molecules, or ions, from a region of higher concentration to regions of lower concentration (down a concentration gradient) ● Occurs due to constant motion of atoms, molecules, ions ● Only substances that the cell membrane is permeable to: oxygen, carbon dioxide, and other lipid soluble substances ex: dissolving sugar cubes ● Membrane is permeable to both water and the solute ● Equilibrium is reached when the concentrations of water and the solute are equal in both compartments Diffusional equilibrium- concentration of a given substance becomes uniform throughout a solution ● Diffusional equilibrium does not normally occur in organism instead, organisms tend to reach a physiological steady state, where concentrations of diffusing substances are unequal but stable Facilitated Diffusion ● Diffusion across the cell membrane through ion channels or transporters ● Water- soluble substances (Na+, K+, Cl-, glucose, and amino acids) ● Passive process; no ATP required *****can move molecules only down a concentration gradient and is specific for a particular solute (a glucose carrier can only carry glucose) ● Process moves substances such as ions, sugars, and amino acids from regions of higher concentration to regions of lower concentration

Osmosis

It is the movement of water across a selectively permeable membrane from region of higher water concentration to lower water concentration ● Water moves into region containing higher impermeant solute concentration ● Passive process; no ATP required. ● Osmotic pressure= ability of osmosis to generate enough pressure to lift a volume of water ● Osmotic pressure increases as the concentration of impermeant solutes increases Isotonic Solution- same osmotic pressure cells in an isotonic solution have no net gain or loss of water Hypertonic Solution- higher osmotic pressure in a hypertonic solution lose water Hypotonic Solution- lower osmotic pressure in a hypotonic solution gain water

Filtration It is a process that forces molecules through the membranes by exerting pressure ● Commonly used to separate solids from water, or small particles from large ones ● Ex: When blood plasma leaves the capillaries, water, and small solutes are filtered, but large plasma proteins are not Passive process; no ATP required Edema- swelling of soft tissues as a result of excess fluid accumulation

Active Transport- movement of substances across a membrane from a region of lower concentration to a region of higher concentration (against the concentration gradient) ● Use carrier molecules in cell membrane ● Active process, requires ATP energy Ex: sugars, amino acids, Ca 2+, H+, Na+/K+ pump Endocytosis- movement of a substance into the cell inside the vesicle ● Substances too large to enter by other methods can enter cell this way ● 3 types of endocytosis Pinocytosis- membrane engulfs droplets of liquid

Phagocytosis- membrane engulfs solid particles ● Important line of defense against infection Receptor- mediated endocytosis- membrane engulfs specific substances which have bound to receptor proteins on the membrane ----> cholesterol molecules Low-denisty lipoproteins (LDL)- cholesterol molecules synthesized to liver cells are packaged into large spherical particles; has a coating that contains a binding protein (apolipoprotein-B) Exocytosis ● Release of substances/ particles from cell ● Vesicles containing particles fuses w/ cell membrane and releases contents Ex: release of neurotransmitters from nerve cells Transcytosis ● Involves receptor- mediated endocytosis followed by exocytosis ● Quickly transports substances from one end of the cell to the other ● Moves substances across barriers formed by tightly connected cells Ex: Transport of HIV across the linning of the anus or vagina

3.4 The Cell Cycle- series of changes a cell undergoes from the time it forms until the time it divides Stages ● Interphase ● Mitosis ● Cytokinesis Interphase ● A very active period in cell cycle cell grows ● Cell maintains normal functions ● Cell replicates genetic material (DNA) to prepare mitosis (nuclear division) ● Cell synthesizes organelles, membranes, and biochemicals to prepare for cytokinesis (division of cytoplasm) Phases: ● S (synthesis) phase DNA is replicated G1 and G2 (growth or gap) phases

structures other than DNA are replicated and cell grows Mitotic Cell Division ● Produces two daughter cells from an original somatic cell ● Mitosis: division of the nucleus ● Cytokinesis: Division of the cytoplasm Phases of mitosis: ● Prophase: chromatin condenses to form chromosomes, nuclear envelope and nuceleolus disperse ● Metaphase: chromosomes attach to spindle fibers, and align midway between centrioles ● Anaphase: chromosomes separate and move in opposite directions, toward centrioles ● Telophase: chromosomes return to chromatin structure, nuclear envelope forms, nucleoli become visible

Cytoplasmic Division ● Cytokinesis= cytoplasmic division ● Begins during anaphase ● Continues through telophase ● Contractile ring of actin filaments pinches cytoplasm in half ● Newly formed cells will have identical DNA, may have slightly different size and number of organelles

3.5 Control of Cell Division ● Frequency of cell division is strictly regulated, and varies by cell type ● Skin cells, intestinal cells, and blood-forming cells divide often and continually ● Neurons divide a specific number of times, then cease ● Chromosomes tips (telomeres) that shorten w/ each mitosis provide a mitotic clock ● Fluctuating levels of certain proteins in cell control cycle ● Cells divide to provide a more favorable surface area to volume relationship ● Hormones and growth factors are external controls for cell division ● Contact inhibition: healthy cells stop dividing when they become crowded ● Tumors can result from a loss of control over the frequency of mitosis

Tumors ● 2 types of tumors ● Benign- remains in local area ● Malignant- invasive, cancerous, can spread or metastasize ● 2 major types of genes cause cancer. Oncogenes: abnormal forms of genes that control cell cycle, but are overexpressed Tumor Suppressor Genes ● Normally limit mitosis, but if inactivated/removed, cannot regulate mitosis ● Cancer cells called “immortal” since they do not stop dividing after 40 to 60 divisions 3.6 Stem, amd Progenitor Cells Differentiation: process of specialization of cells

Stem Cell: ● Can divide to form new stem cells (self-renewal) ● Can also divide to form a stem cell and progenitor cell ● Can differentiate as any of many cell types Progenitor cell ● Partially specialized stem cell, daughter of stem cell Ex: formation of blood, cells in red bone marrow ● Can divide to become any of a restricted number of cells (committed cell) Totipotent: daughter cells that can specialize to become any cell type Ex: Fertilized egg, cells of early embryo Pluripotent: daughter cells that can become a limited number of cell types Ex: Stem cells of later development, progenitor cells Differentiation of Cells Differentiation: maturation and specialization of cells A fertilized egg was the ability to produce any type of human cell, while partially differentiation cells can only produce some types or single type of cell From Science to Technology: Stem Cells to Study and Treat Disease

● Stem and progenitor cells are required for growth and healing ● Regenerative medicine: Field of study that uses body’s ability to generate new cells to treat disease and injuries; includes stem cell technology Sources of stem cell research, treating disease/injuries ● Donor stem cells, such as umbilical cord cells ● Stem cells from patient- either from natural site, such as bone marrow, or reprogrammed differentiated cells growth in cell culture

3.7 Cell Death Aptosis ● Programmed cell death ● Normal part of development ● A continuous, stepwise process ● Removes webbing between fetal fingers and toes ● Protective, peels away damaged skin cells after sunburn Necrosis ● Cell death from damage ● Not a normal process...