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Chapter 2

BIOL 1000 Chapter 2 - The Cell.docx

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Department
Biology
Course
BIOL 1000
Professor
Jennifer Steeves
Semester
Fall

Description
Chapter 2 – The Cell 2.1 – Basic Features of Cell Structure and Function • Cell Theory  All living organisms are composed of cells  Cells are the structural and functional units of life  Cells arise only form the division of pre-existing cells • Divided into 2 parts – Cytoplasm and Genetic Material (Nucleus) • Cytoplasm – Cytosol, cytoskeleton, and organelles; bound by the plasma membrane  Proteins are made  Most other molecules required for growth and reproduction are assembled  Energy absorbed from the surroundings is converted into energy usable by cell • Plasma Membrane – a lipid bilayer in which transport proteins are embedded 2.2 – Prokaryotic Cells • Surrounded by a plasma membrane and (in most groups) enclosed in a cell wall • Cell Wall – composed of sugars and amino acids (collectively called peptidoglycan)  Provide strength, rigidity, and protection  Destruction of the cell wall can result in lysis of the cell • Capsule – Layer of polysaccharides surrounding the cell wall  Protects from extreme temperatures, desiccation antibiotics, viruses, and antibodies • Genetic material is typically a single circular DNA molecule  Located in the nucleoid – not separate from the cytoplasm • Cytoplasm contains masses of ribosomes • Appear simple in structure when compared in Eukaryotic Cells • Organisms with Prokaryotic Cells:  Have the greatest metabolic diversity of all organisms  Vastly out number all other types of organisms  Live successfully in almost all regions of Earth’s surface 2.3 – Eukaryotic Cells • Have a True Nucleus and Cytoplasmic Organelles enclosed within a plasma membrane Cytoplasm • Contains a remarkable system of membranous organelles • Contains Ribosomes and The Endomembrane System  Nuclear Envelope, ER, Golgi Complex, Lysosomes, Vesicles, Plasma Membrane • Cytosol – cytoplasmic solution surrounding the organelles  Energy metabolism & molecular synthesis  Performs specialized functions in support and motility Plasma Membrane • Lipid Bilayer (usually phospholipid) - -philic heads & -phobic tails  Through evolution many membranes derived from the same membrane • Various functions through several types of embedded proteins  Transport substances in and out of the cell  Receptors; trigger internal responses  Recognize & adhere to molecules on the surfaces of other cells  Important markers in the immune system; marking as “self” Cell Wall • Lies outside the cell membrane • Supportive cell, extracellular structure Nucleus • Contains much more DNA than the prokaryotic nucleoid • Contains chromatin – combination of DNA and proteins (histone and non-histone)  Distinct regions; Euchromatin and Heterochromatin  Euchromatin – loosely packed regions; genes active in RNA transcription  Heterochromatin – densely packed masses; genes are inactive • Eukaryotic DNA Packing – Histones  DNA wraps around a nucleosome (two molecules each of histones H2A, H2B, H3, H4)  Linker DNA connects adjacent nucleosomes  Binding of Histone H1 causes nucleosomes to package into a coiled structure (solenoid or 30nm chromatin fibre)  Histone proteins help pack DNA into highly coiled/compact structure • Eukaryotic DNA – Nonhistone Proteins  Proteins associated with DNA that are NOT histones  Involved in gene expression and regulation  Gene accessibility (loosening or tightening histone association)  Mostly negatively charged or neutral and come in a variety of sizes  Play a role in the expression of certain genes Nuclear Envelope • Separates the nucleus from the cytoplasm • Consists of two membranes; separated by a narrow space • Network of protein filaments, lamins, lines and reinforces the inner surface of the nuclear envelope in animal cells – type of intermediate filaments Nuclear Pore Complex • Large, octagonally symmetrical, cylindrical structure • Formed of many types of proteins; nucleoporins • Largest protein complex in the cell • Large molecules, RNA and proteins, pass through nuclear pores • Small molecules usually pass through unassisted Nucleolus • Formed from a specialized segment of chromatin • Ribosomal RNA molecules are made and combined with ribosomal proteins to make ribosomes Ribosomes • Free Ribosomes – present in the cytosol • Bound ribosomes – attached to the cytosolic side of membrane of ER • Prokaryotic:  Bacterial – Smaller than eukaryotic; protein synthesis is similar  Archaeal – size similar to bacterial; different structure; protein synthesis is a combination of bacterial and eukaryotic processes • Eukaryotes can begin translation only after the mRNa is exported from the nucleus (after transcription) Endoplasmic Reticulum • There are two forms: Rough ER & Smooth ER • Rough ER – Makes proteins that become part of cell membranes or are released from the cell  Ribosome studded • Smooth ER – Synthesizes lipids&steroids and breaks down toxic substances Sarcoplasmic Reticulum • Present in Muscles +2 • Stores Ca – released upon nerve impulse to cause the muscle cell to contract Golgi Complex • Vesicles from the Rough ER fuse with the cis face of the Golgi • Chemically modifies proteins made in the Rough ER & Sorts finished proteins  Post-translational modification – E.g. molecular tags added  Secretory vesicles released from the trans face of the Golgi  Secreted from the cell, Embedded in the Plasma Membrane, or included in Lysosomes Lysosomes • Specialized vesicles that contain hydrolytic enzymes; Digest:  Complex molecules such as food molecules that enter the cell by endocytosis  Cellular organelles that are no longer functioning correctly  Engulfed Bacteria  Cell Debris • Enzymes work best at an acidic pH (approximately pH = 5) • E.g. – Amoeba: Takes in Food particle by phagocytosis  Food vacuole (vesicle) fuses with lysosome for food digestion • E.g. – Microphages: Type of white blood cell involved in immune response  Engulfs invaders (e.g. bacteria) and delivers them to lysosome to be destroyed Mitochondria • Carry out cellular respiration – conversion of fuel molecules into the energy of ATP • Cristae increase surface area; Matrix contains enzymes, DNA, and free ribosomes Cytoskeleton • Supportive & Motility structure made from three Elements: 1. Microtubules – 25nm thick  Largest cytoskeletal element – microscopic rigid hollow tubes
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