Cells as Basic Units of Life - Lecture Notes PDF

Cells LESSON OBJECTIVES Define cells, their organization, and their various forms. Describe crucial cellular functions such as membrane transport, cell division and cell cycle. Discuss the physical, emotional, and socioeconomic impact of cancer on patients and their families, as we...

Cells LESSON OBJECTIVES Define cells, their organization, and their various forms. Describe crucial cellular functions such as membrane transport, cell division and cell cycle. Discuss the physical, emotional, and socioeconomic impact of cancer on patients and their families, as well as the broader societal implications. Cell Theory Cells were discovered in 1665 by Robert Hooke. Early studies of cells were conducted by - Mathias Schleiden (1838) - Theodor Schwann (1839) Schleiden and Schwann proposed the 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. Prokaryotic vs Eukaryotic Cells Prokaryotes Prokaryotic cells lack a membrane-bound nucleus. -genetic material is present in the nucleoid Two types of prokaryotes: -archaea -bacteria Eukaryotes Eukaryotic cells -possess a membrane-bound nucleus -are more complex than prokaryotic cells -compartmentalize many cellular functions within organelles and the endomembrane system -possess a cytoskeleton for support and to maintain cellular structure Anatomy of the Cell  Cells are not all the same  All cells share general structures  Cells are organized into three main regions  Plasma membrane  Cytoplasm  Nucleus Plasma Membrane The fluid-mosaic model is the currently accepted concept describing plasma membrane structure. Plasma Membrane Specializations  Microvilli  Finger-like projections that increase surface area for absorption Plasma Membrane Specializations  Membrane junctions  Tight junctions (seals)  Desmosomes (strength)  Hemidesmosomes (base)  Gap junctions (communication) Cytoplasm  Material outside the nucleus and inside the plasma membrane  Cytosol  Fluid that suspends other elements  Organelles  Metabolic machinery of the cell  Inclusions  Non-functioning units Cytoplasmic Organelles Cytoplasmic Organelles  Ribosomes  composed of ribosomal RNA and proteins  Sites of protein synthesis  Found at two locations  Free in the cytoplasm  Attached to rough endoplasmic reticulum Cytoplasmic Organelles Endomembrane system -a series of membranes throughout the cytoplasm -divides cell into compartments where different cellular functions occur 1. endoplasmic reticulum 2. Golgi apparatus 3. vesicles (lysosomes) Cytoplasmic Organelles Rough endoplasmic reticulum (RER) -membranes that create a network of channels throughout the cytoplasm -attachment of ribosomes to the membrane gives a rough appearance -synthesis of proteins to be secreted, sent to lysosomes or plasma membrane Cytoplasmic Organelles Smooth endoplasmic reticulum (SER) -relatively few ribosomes attached -functions: -synthesis of membrane lipids and phospholipids -calcium storage -detoxification of foreign substances Cytoplasmic Organelles Cytoplasmic Organelles Golgi apparatus flattened stacks of interconnected membranes storage, modification, and packaging of polypeptide and protein products synthesis of cell wall components cis- “forming face” trans “maturing face” Cytoplasmic Organelles Cytoplasmic Organelles Lysosomes membrane bound vesicles containing digestive enzymes to break down macromolecules destroy cells or foreign matter that the cell has engulfed by phagocytosis Endomembrane System System for assembling, isolating, and secreting polypeptides and proteins for export in a eukaryotic cell, for lysosomes, or for incorporation into plasma membrane. Endomembrane System Cytoplasmic Organelles  Mitochondria  “Powerhouses” of the cell  self-replicating due to mtDNA  Carry out reactions where oxygen is used to break down food  contain oxidative metabolism enzymes for transferring the energy within macromolecules to ATP Cytoplasmic Organelles Cytoplasmic Organelles  Cytoskeleton  Network of protein structures that extend throughout the cytoplasm  Provides the cell with an internal framework  Locomotion and translocation of macromolecules and organelles within the cell  Cytoplasmic Organelles  Cytoskeleton  Three different types  Microfilaments  Actin-myosin (contraction)  Intermediate filaments  Fibrous (mechanical support)  Microtubules  Tubulin (architecture, organization, transport) Cytoplasmic Organelles  Centrosome  Centrioles  Rod-shaped bodies made of microtubules  Direct formation of Each centrosome contains a pair of mitotic spindle during centrioles and each centriole is composed of nine triplets of cell division microtubules arranged as a cylinder. The Nucleus  Control center of the cell  Contains genetic material (DNA)  Three regions  Nuclear membrane  Nucleolus  Chromatin Nuclear Membrane  Barrier of nucleus  Consists of a double phospholipid membrane  Contain nuclear pores that allow for exchange of material with the rest of the cell Nucleoli  Nucleus contains one or more nucleoli  Sites of ribosome production  Ribosomes then migrate to the cytoplasm through nuclear pores Chromatin  Composed of DNA and protein  Scattered throughout the nucleus  Chromatin condenses to form chromosomes when the cell divides Cellular Projections  Not found in all cells  Used for movement  Cilia moves materials across the cell surface  Flagellum propels the cell Cellular Physiology: Membrane Transport  Membrane Transport – movement of substance into and out of the cell  Transport is by two basic methods  Passive transport- No energy is required  Diffusion, Osmosis, Facilitated/Mediated Transport  Active transport- Energy is required  Endocytosis, Exocytosis Solutions and Transport  Solution – homogeneous mixture of two or more components  Solvent – dissolving medium  Solutes – components in smaller quantities within a solution  Intracellular fluid – nucleoplasm and cytosol  Interstitial fluid – fluid on the exterior of the cell Selective Permeability  The plasma membrane allows some materials to pass while excluding others  This permeability includes movement into and out of the cell Passive Transport Processes  Diffusion  Particles tend to distribute themselves evenly within a solution  Movement is from high concentration to low concentration, or down a concentration gradient Passive Transport Processes  Types of diffusion  Simple diffusion- unassisted process  lipid-soluble materials  gases  alcohol  urea Passive Transport Processes  Osmosis – simple diffusion of water  Highly polar water easily crosses the plasma membrane Passive Transport Processes  Water and solutes are forced through a membrane by fluid, or hydrostatic pressure  A pressure gradient must exist  Solute-containing fluid is pushed from a high pressure area to a lower pressure area Diffusion through the Plasma Membrane Diffusion Through Channels Water and dissolved ions, since they are charged, cannot diffuse through the phospholipid component of the plasma membrane. Signalling mechanisms in NS and muscles Instead, they pass through specialized pores or channels created by transmembrane proteins. Aquaporin- water channel Absorption of water in DS and kidneys Diffusion through the Plasma Membrane Gated Channels-signal to open or close them 1. Chemically-gated ion channels 2. Voltage-gated ion channels *channels allow a particular protein to pass across the c.m. Figure 3.9 Diffusion through the Plasma Membrane Carrier-mediated transport Nutrients such as sugars and materials for growth such as amino acids must enter a cell, and wastes of metabolism must leave. Transporters/ carriers -special transmembrane proteins; combines with the substance *facilitated diffusion Diffusion through the Plasma Membrane Facilitated transport movement only in a downhill direction (in the direction of a concentration gradient) requires no metabolic energy to drive the transport system Diffusion through the Plasma Membrane Active Transport Processes  Transport substances that are unable to pass by diffusion  They may be too large  They may not be able to dissolve in the fat core of the membrane  They may have to move against a concentration gradient  Two common forms of active transport  Solute pumping  Bulk transport Active Transport Processes  Solute pumping  Amino acids, some sugars and ions are transported by solute pumps  Na-K ion pump  ATP energizes protein carriers, and in most cases, moves substances against concentration gradients Active Transport Processes Figure 3.10 Active Transport Processes  Bulk transport  Exocytosis  Moves materials out of the cell  Material is carried in a membranous vesicle  Vesicle migrates to plasma membrane  Vesicle combines with plasma membrane  Material is emptied to the outside Active Transport Processes  Active Transport Processes  Bulk transport  Endocytosis  Extracellular substances are engulfed by being enclosed in a membranous vesicle  Types of endocytosis  Phagocytosis – cell eating  Pinocytosis – cell drinking Active Transport Processes animation Cell Life Cycle Structure of Chromosome Genetic Terminologies Slide 3.36b Structure of Chromosome  Cell Life Cycle  Events of Cell Cycle  Interphase (G1,S,G2)  Cell grows  Cell carries on metabolic processes  No cell division occurs  Cell division (Mitosis)  Cell replicates itself  Function is to produce more cells for growth and repair processes  Cytokinesis  Division of the cytoplasm  Begins when mitosis is near completion  Results in the formation of two daughter cells Cell Life Cycle Mitosis One part of the cell cycle Growth, cell replacement, tissue repair Unique to eukaryotes Happens in somatic cells only Nuclear & cellular division that maintains chromosome # Diploid (2n) Stages of Mitosis  Prophase  First part of cell division  Centromeres migrate to the poles where the centrioles are  Nuclear membrane disintegrates Stages of Mitosis  Metaphase  Spindle from centromeres are attached to chromosomes that are aligned in the center of the cell Stages of Mitosis  Anaphase  Daughter chromosomes are pulled toward the poles  The cell begins to elongate Stages of Mitosis  Telophase  Daughter nuclei begin forming  A cleavage furrow (for cell division) begins to form  Followed by cytokinesis (splitting of the cytoplasm) Meiosis Occurs only in sex (gamete) cells 1st step in formation of gametes Gametes fuse with opposite sex gametes to form new individual Humans are diploid (2n) with 46 chromosomes (23 + 23 homologous chromosomes) Meiosis halves chromosome number so daughter cells (gametes) are haploid (n) with 23 chromosomes Meiosis Have only 1 set of chromosomes = haploid (n) Each gamete has 1 allele for each gene In humans = eggs or sperm Meiosis During meiosis, one cell goes through 2 divisions to end with formation of 4 cells, all with haploid (n) nuclei. Meiosis Meiosis: Interphase Same as in mitosis: Cell grows & duplicates cytoplasmic components DNA is replicated Meiosis I  Meiosis I: Synapsis & Crossing over When chromosomes condense during prophase, homologous chromosomes stick very closely together & form a tetrad. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Meiosis I: Independent Assortment Metaphase alignment Random alignment Duplicated chromosomes randomly tether to spindle poles i.e. no set rules for where maternal & paternal chromosomes should be positioned Meiosis I: Independent Assortment Which half of homologous chromosome pair ends up at which pole is totally random 223 (8,388,608) possible combos of maternal & paternal chromosomes! Meiosis II Meiosis: Things to remember 1. DNA replication: a. Occurs only during interphase before Meiosis I 2. Meiosis I a. Prophase: crossing-over b. Metaphase: line up in 2 rows c. Anaphase: separation of homologous chromosomes d. Interkinesis: short period of rest prior to meiosis II 3. Meiosis II a. Similar to mitosis but no interphase precedes it b. Division results in haploid cells c. Female gametes: completion of meiosis takes place only when cell is fertilized.  Meiosis: Things to remember Source of Genetic Variability a. Random fertilization b. Crossing over in prophase I c. Independent Assortment in metaphase I Mitosis vs Meiosis