The Cell

1. 1Living matter of any plant or animal is called protoplasm
   

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2. 2A single unit of protoplasm is called a cell
   

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3. 3Plants, animals and humans consists of groups of interdependent cells
   

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4. 4These cells coordinate various functions
   

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5. 5Cells serving same general function are called a tissue (bone, cartilage, muscles, nervous tissue etc.)
   

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6. 6Pioneers

   1. ARobert Hook
      ~Cell
      Leeuwenhoek
      ~Microscopes
      Schwann and Schleiden
      ~Cell theory
   2. Bnone
7. 7Nucleus – contains nucleo- or karyoplasm, chromosomes
   

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8. 8Cytoplasm – site of metabolism and specialized functions and contains
   ~Organelles - metabolically active – carry on specific functions
   ~Membranous or membrane limited – with plasma membrane
   ~Nonmembranous organelles – without plasma membrane
   ~Cytoskeleton - fibrillar components (microtubules, microfilaments, intermediate filaments, cytoplasmic matrix
   

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9. 9Inclusions - metabolically inert, accumulate metabolic products (carbohydrates, proteins, lipids, crystals, pigments, secretory granules)
   

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10. 10Cytosol (cytoplasmic matrix) – fluid containing electrolytes (ions) and colloids
    

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11. 11Membranous Organelles -Plasma Membrane (PM)

    1. AVery thin, selectively permeable (more to lipids than to aqueous substances
       A lipid bilayer containing lipids, proteins and carbohydrates
       Is permeable to water and small uncharged molecules such as O2 and CO2
       Special transport systems such as active transport are available for charged particles such as Na+, K+, Cl-
       Two kinds of proteins in the PM
       ~Integral – embedded within lipid bilayer
       ~Peripheral – not embedded in lipid bilayer such as glycolipids, glycocalyx
       ~Lipid rafts in the membrane contain these proteins
       Integral proteins – important functions in cell metabolism, regulation and integration – six broad categories:
       ~Pumps – transport certain ions such as Na+ and metabolic precursors
       ~Channels – passage of small ions
       ~Receptors – for hormones, antibodies
       ~Linkers – anchor intracellular cytoskeleton
       ~Enzymes – variety of roles, Na+/K+ ATPase, ATP synthetase, digestive
       ~Structural – form junctions with neighboring cells
    2. Bnone
12. 12Membranous Organelles -Endosomes and Lysosomes

    1. ATwo populations of membrane bound endosomes early and late
       Endosomes could be stable or transient and are involved in endocytic pathways
       Early endosomes function is to sort and recycle proteins
       Late endosomes become lysosomes
       Lysosomes are rich in hydrolytic enzymes for intracellular digestion, most active in leukocytes and phagocytes
       Lysosomes have a unique membrane that is resistant to the hydrolytic digestion occurring in their lumen
       Lysosomes are implicated in lysosomal storage diseases such as Tay Sachs disease
    2. Bnone
13. 13Membranous Organelles -Rough-Surfaced Endoplasmic Reticulum (rER)

    1. AThe rER contains basophilic bodies called ribosomes bound to its cytosolic surface
       Typically composed of a network of flattened sacs (cisternae)
       The rER is continuous with the outer membrane of nuclear envelope which also bears ribosomes on its cytosolic surface
       The cells that secrete large amounts of proteins, such as liver, pancreas or salivary glands, have extensive rER
       Function is protein synthesis which after synthesis are transported to Golgi complex by vesicles
    2. Bnone
14. 14Membranous Organelles -Smooth-Surfaced Endoplasmic Reticulum (sER)

    1. AMembranous elements of sER are typically tubular
       Form an interconnecting system of pipelines curving through the cytoplasm
       sER is extensively developed in cells of skeletal muscle, kidney tubules, and steroid producing endocrine cells
       When homogenized, the sER fragments into smooth-surfaced vesicles (called microsomes) and rER into rough-surfaced vesicles.
       The sER is involved in:
       ~Synthesis of lipids including oils, phospholipids and steroids.
       ~Detoxication and bioactivation of a variety of organic compounds - microsomal enzymes
       ~Carbohydrate (glycogen) metabolism - Release of glucose-6-phosphate in liver cells
       ~Membrane formation and recycling
       ~As sarcoplasmic reticulum it sequesters and releases Ca++ in muscles fibers
    2. Bnone
15. 15Membranous Organelles -Golgi Apparatus or Complex (GC)

    1. AA network of tubules with double membranes
       Site of concentration, modification, packaging and shipping of synthesized products
       Consists of cisternae
       Cis-face toward ER and trans-face toward PM
       Transport accomplished by membrane vesicles
    2. Bnone
16. 16Membranous Organelles -Mitochondria

    1. APower houses of cells, slender, rod like, double membranes
       Inner membrane extensively folded forming cristae
       Greater number in active cells generating ATP
       Three principle reaction cycles:
       ~Krebs cycle and β-oxidation of fatty acids in mitochondrial matrix and
       Electron transport chain in mitochondrial membranes
       Are self duplicating, have their own DNA and ribosomes and hence called semiautonomous
    2. Bnone
17. 17Membranous Organelles -Peroxisomes (Microbodies)

    1. APeroxisomes are single membrane bounded organelles containing oxidative enzymes including urate oxidase, D-amino acid oxidase and catalase
       Virtually all oxidative enzymes produce hydrogen peroxide (H2O2) as a by-product which is a toxic substance
       H2O2 is later degraded by catalases thus protecting the cells
       A disorder involving non-functional peroxisomes results in Zellweger syndrome which leads to early death.
    2. Bnone
18. 18Nonmembranous Organelles (Cytoskeleton) Microtubules

    1. AMicrotubules are hollow tubules, walls made of protofilaments (a polymer of tubulin)
       Function – maintenance of cell shape
       Originate or grow from a microtubule-organizing center (MTOC)
       Movement of intracellular organelles in generated by molecular motor proteins associated with microtubules
       Two families of these proteins identified
       ~Dyneins – cytoplasmic dyneins move organelles from cell periphery to MTOC
       ~Kinesins move organelles from the MTOC toward the cell periphery
    2. Bnone
19. 19Nonmembranous Organelles (Cytoskeleton) Microfilaments

    1. AMicrofilaments (MF) include:
       ~Actin and myosin
       ~Ankyrin and Spectrin in red blood cells
       ~Dytsrophin in muscle cells
       ~Specialized in muscle cells – responsible for contractility of protoplasm
    2. Bnone
20. 20Nonmembranous Organelles (Cytoskeleton) -Intermediate Filaments

    1. AThe diameter of intermediate filaments is in between that of microtubules and microfilaments
       Four major classes
       ~Keratins (cytokeratins) – skin, hair
       ~Vimentins – mesoderm derived cells
       ~Neurofilaments – neurons
       ~Lamins – nuclear envelope
    2. Bnone
21. 21Inclusions

    1. AGlycogen – major sites are liver and muscles
       ~β or single and α or cluster particles
    2. BLipids – spherical droplets of neutral lipids
       ~Histological preparations – lipids are removed – appear as clear vesicles
       ~Glutaraldehyde and osmium tetroxide preserve dark globules
       ~Adipose tissue are specialized for fat storage
       Crystalline inclusions – are found in certain cells such as Sertoli cells and interstitial cells of Leydig
       Pigments
       ~Lipofuscin – brown-gold pigment – in cells of long life – cardiac, skeletal muscle and brain cells (neurons)
       ~Hemosiderin – by-product of hemoglobin degradation – brown pigments in spleen and phagocytes – iron-storage pigment
       ~Melanin – responsible for skin and hair color, bound to a protein melanosomes – a product of tyrosine
    3. Cnone
22. 22Cytoplasmic Matrix

    1. AThe cytoplasmic matrix (ground substance or cytosol) is:
       ~A concentrated aqueous gel
       ~Contains molecules of different size and shape (electrolytes, metabolites, RNA, and proteins)
       ~The largest single component in most cells
       ~The site of protein synthesis, breakdown of nutrients, etc.
       ~A complex 3 D network of microtrabecular strands and cross-linkers.
    2. Bnone
23. 23The Nucleus

    1. ALargest organelle, centrally located, elliptical or spherical
       Stains dark purple or blue with H & E
       Irregular clumps in nucleoplasm called chromatin – contains genetic material DNA and RNA
       The Nuclear Envelope
       ~A double membrane with pores made of proteins
       ~Peritubular cisternae continuous with ER space
       ~Pores communicate between nucleus and cytoplasm
       ~Envelope breaks during cell division and forms again after division
       The Chromatin - Consists of ribonucleoproteins and histones
       ~Condensed – heterochromatin – stainable
       ~Dispersed – euchromatin – not stainable
       ~In dividing cells chromosomes become visible and are basophilic
       ~Human somatic cells have 46 chromosomes (diploid or 2n)
       ~Germ cells have 23 chromosomes (haploid or n)
       ~Abnormal cells exhibit polyploidy
       The Nucleolus - Is retractile, eccentric and basophilic
       ~Forms nucleolus organizing region (NOR) and consists of various kinds of RNA
    2. Bnone
24. 24Cell Division – Mitosis

    1. AProphase
       ~Condensation of chromosomes, disappearance of nucleolus and nuclear envelope, formation of spindle, chromosomes with sister chromatids migrate toward center of spindle
       Metaphase
       ~Centromeres align in center of spindle (equatorial plate), each chromatid attached to different poles, centromere duplicated
       Anaphase
       ~Chromosomes migrate toward poles – sister chromatids separate, cytokinesis begins
       Telophase
       ~Condensation of chromosomes, nucleolus and nuclear membrane reappear
    2. Bnone
25. 25Cell Division -Meiosis

    1. AA form of nuclear division of fundamental importance among sexually reproducing organisms
       Occurs in eukaryotes with diploid (2n) chromosomes
       Chromosomes of each diploid cell are called homologous chromosomes
       Humans have 46 or 23 pairs of chromosomes
       46 chromosomes of a zygote contain 23 from sperm and 23 from ova
       Zygote multiplies for several generations to become an adult organism
       Sperm and ova are called haploid cells because they have only one member of the homologous pair of chromosomes
       Prophase I
       ~Leptotene – chromosomes condense, sister chromatids visible
       ~Zygotene – homologous chromosomes aligned together – synapsis and tetrad formation
       ~Pachytene – chromatids continue to condense
       ~Diplotene – separation of paired homologous chromosomes
       ~Diakinesis – condensation complete, Prophase I ends
       Metaphase I
       ~Spindle develops, chromosomes align at equatorial plate
       Anaphase I
       ~Homologous chromosomes (not sister chromatids) separate
       Telophase I
       ~First meiotic division is completed with complete separation of homologous chromosomes
       Interphase
       ~A short recess between telophase and prophase II
       Meiotic Division II
       ~Events similar to mitosis, include all four phases prophase,
       metaphase, anaphase, and telophase II
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26. 26The Cell Locomotion and Death

    1. ACell Locomotion
       ~Ameboid movement of leukocytes; in cells in close contact; villi and microvilli are involved
       ~Cell movement may be random or directional; directional movement is called chemotaxis
       Cell Death
       ~Necrosis – mechanical injury, toxins or anoxia
       ~Apoptosis – active and programmed cell death – environment, developmental history or genome
       ~Normal cell life span is from a few days to 80 years or more
    2. Bnone

Descripción

Test sobre The Cell, creado por Ruben De Santiago el 22/08/2021.

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Ruben De Santiago

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