Transcript The Cell
The Cell Chapter 3 Cell Diversity Cell Theory • All living things are composed of cells • Cells are the smallest unit to demonstrate the properties of life • Cells are only produced from existing cells Typical Animal Cell • Plasma membrane – Outer limiting barrier – Detect chemical signals and recognize self from non-self • Nucleus – Control center • Cytoplasm (cytosol) – Intracellular fluid including organelles (excluding) Plasma Membrane’s Role • Physical isolation – Separates intracellular from extracellular environment • Regulates exchange with environment – Selective permeability • Polarity (hydrophobic vs. hydrophilic) • Charge (charged vs. uncharged) • Size (large vs. small) – Ions & nutrient enter, wastes & secretions exit – Allows a concentration gradient to develop • Maintains homeostasis The Fluid Mosaic Model • Integral proteins – Channels, carriers, and signal transduction • Peripheral proteins – Enzymes, cell-cell recognition, and structure • Phospholipid bilayer (unsaturated) – Hydrophilic ends – Hydrophobic ends • Cholesterol Types of Transport Passive Active • Energy not required • Movement ‘down’ a concentration gradient • Specific types • Energy required • Movement against a concentration gradient – Diffusion • Simple • Facilitated – Osmosis – Filtration Clarifying Solutions • Liquid mix of 2+ substances – Aqueous solution when water is solvent • Solvent: dissolving agent • Solute: substance that is dissolved • Reviewing polarity – ‘Like dissolves like’ – Hydrophilic • Sugar or salt and water – Hydrophobic • Oil and water Simple Diffusion • Movement of MOLECULES ‘down’ their concentration gradient – Small, nonpolar molecules • E.g. O2 in and CO2 out in red blood cells – Each substance is independent • Continues until equilibrium = no NET movement Osmosis • Movement of WATER ‘down’ its concentration gradient – Water binds to solute in solution • More solute = less free water = less water available to move • Depends on TOTAL solute concentration – Selective permeability has a role too water molecules glucose molecules Tonicity • Ability of a solution to cause a cell to gain or lose water – Depends on [solutes] that can’t cross PM relative to those in the cell • Hypotonic solutions have a ___?__ [solute] than the cell – Water moves in – Cells lyse • Hypertonic solutions have a ___?__ [solute] than the cell – Water moves out • Cells crenate • Isotonic solutions have ___?__ [solute] as the cell – Water shows no NET movement Other Passive Transport Types Facilitated diffusion • Movement same as simple • Larger, water soluble substances – Glucose, water, & ions • Protein carriers or channels Filtration • Water and solutes move ‘down’ a pressure gradient – Water forced, solutes chosen by size • Bulk movement Active Transport • Movement of MOLECULES against their concentration gradient • ATP is energy source • Maintains disequilibrium Vesicular Transport • Exocytosis: removes from inside the cell – Golgi vesicles to PM • Endocytosis: brings into the cell – PM pinches in to form vesicles – 3 types • Phagocytosis • Pinocytosis • Receptor-mediated Plasma Membrane Specializations • Microvilli – Folds of PM to increase surface area • Membrane Junctions – Tight junctions • Integral proteins = impermeable • E.g. keep digestive enzymes out of blood – Desmosomes • Protein filaments = high tension protection • E.g. skin and heart muscle – Gap junctions • Integral proteins for communication • E.g. heart and smooth muscle Nucleus • Control center of the cell • Nuclear envelope – Double membrane continuous with rough ER – Maintains shape – Nuclear pores for transport; selectively permeable • Nucleoli – Build ribosome subunits • Chromatin – DNA and protein – Coils/condenses to become visible = chromosomes Organelles Within Cytosol Membranous Nonmembranous • Mitochondria • Cytoskeleton – Produces ATP • Endoplasmic reticulum (ER) – Rough – proteins to Golgi – Smooth – lipids & carb production; detoxification • Golgi apparatus – Modify and package secretory vesicles • Lysosomes – Digestive processes • Peroxisomes – Detoxification – Microtubules, microfilaments, & intermediate filaments • Centrioles – Formed by microtubules, 9 triplets – Microtubules originate in mitosis • Ribosomes – Small and large subunits – Free or attached = dynamic • Cilia – Move substances or organism • Flagella – 9 + 2 orientation The Cell Cycle (IPMATC) • Interphase about 90% – – – – Chromosomes not visible yet G1 phase S phase G2 phase • Mitotic (M phase) cell division – Mitosis is nuclear division • • • • Prophase Metaphase Anaphase Telophase – Cytokinesis is cytoplasmic division • Repeat as needed DNA Replication • Helicase – 2 templates formed • DNA polymerase – Complementary base pairing • Daughter strands – Leading strand – Lagging strand • DNA ligase • Semiconservative model – Chromatid sister chromatids Prophase Events • Sister chromatids condense • Nuclear envelope begins to disappear • Centrioles appear at opposite ends of cell • Mitotic spindles form Metaphase Events • Centrioles at opposite ends of cells • Sister chromatids line up with centromere on metaphase plate • Microtubules attached to each chromatid at the centromere Anaphase Events • Sister chromatids separate • Single chromosomes move toward opposite ends of the cell – Microtubule ‘tug of war’ • Cell elongates Telophase Events • Daughter nuclei form • Nuclear envelope reforms • Chromosomes begin to uncoil • Mitosis is complete Cytokinesis • Division of cytoplasm – Begins at the end of telophase (late anaphase too) • Cleavage furrow forms – Pinch plasma membrane in 2 • 2 identical daughter cells formed Meiosis • Similar to mitosis • Reduces genetic material of each daughter cell by half – Diploid (2n) adult produces haploid (n) gametes • n = # different chromosomes, paired = homologous • Autosomes (22) and sex chromosome (X or Y) • Event occurs in 2 cycles – Meiosis I • Most variation from mitosis – Meiosis II Protein Synthesis • DNA RNA protein – Genes instruct, but don’t build – Nucleotides and amino acids are different ‘languages’ – RNA connects them • Transcription: same language • Translation: different language Reviewing DNA and RNA DNA • Sugar is deoxyribose RNA • Sugar is ribose – Has –H • • • • • Bases are A,C, G, and T Double-stranded helix Only in nucleus Modified only by mutations 1 type – Has -OH • • • • Bases are A, C, G, and U Single-stranded Not confined to nucleus Lots of processing and modifications • 3 types (mRNA, tRNA, rRNA) Transcription • Only 1 template used • RNA polymerase – Complementary bases added • Steps – Promotion – Elongation – Termination • Pre-mRNA processing – Introns spliced out – Exons rejoined – mRNA Decoding Genes • 4 nucleotide bases to specify 20 amino acids • Based on codons – 43 = 64 (plenty) • Redundancy, but not ambiguity • Nearly universal across species Translation • Ribosome binds mRNA – In cytoplasm • tRNA with anticodon binds – Start codon to P site – 2nd tRNA to A site – Peptide bond joins AA’s • Ribosome translocates – P site with 1st & 2nd AA – New tRNA to A site • Stop codon terminates – Polypeptide folds = protein Summary of Protein Synthesis