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Transcript
Bell Ringer • Obtain a pencil and a blank sheet of loose-leaf paper. • Clear off your desk Exam • • • • 100 Points 60 minutes 50 MC 3 short answer Objective • Identify the internal and external structures of a prokaryotic cell and define the function of each. Chapter 3 Cell Structure and Function © 2012 Pearson Education Inc. Lecture prepared by Mindy Miller-Kittrell North Carolina State University Bacterial Cytoplasmic Membranes • Structure – Phospholipid bilayer – Composed of lipids and associated proteins – Integral and peripheral proteins – Head is hydrophilic, tail is hydrophobic – Fluid mosaic model – Proteins and lipids flow laterally within membrane © 2012 Pearson Education Inc. Figure 3.16 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer Head, which contains phosphate (hydrophilic) Phospholipid Tail (hydrophobic) Integral proteins Cytoplasm Integral protein Phospholipid bilayer Peripheral protein Integral protein Bacterial Cytoplasmic Membranes • Function – – – – – Energy storage Selectively permeable Naturally impermeable to most substances Proteins allow substances to cross membrane Maintain concentration and electrical gradient © 2012 Pearson Education Inc. Figure 3.17 Electrical potential of a cytoplasmic membrane Cell exterior (extracellular fluid) Cytoplasmic membrane Integral protein Protein DNA Protein Cell interior (cytoplasm) Bacterial Cytoplasmic Membranes • Function – Passive processes- No energy expanded! – Due to electrochemical gradient – 1) Diffusion – movement of chemical down concentration gradient – 2) Facilitated diffusion – protein channels that allow certain molecules through membrane – 3) Osmosis – movement of water through a selectively permeable membrane from low to high concentration © 2012 Pearson Education Inc. Figure 3.18 Passive processes of movement across a cytoplasmic membrane-overview Extracellular fluid Cytoplasm Diffusion through the phospholipid bilayer Facilitated diffusion through a nonspecific channel protein Facilitated diffusion Osmosis, through a permease specific for one chemical; binding of substrate causes shape change in the channel protein the diffusion of water through a specific channel protein or through the phospholipid bilayer Figure 3.19 Osmosis, the diffusion of water across a selectively permeable membrane-overview Solutes Semipermeable membrane allows movement of H2O, but not of solutes Figure 3.20 Effects of isotonic, hypertonic, and hypotonic solutions on cells-overview Cells without a wall (e.g., mycoplasmas, animal cells) H2O H2O H2O Cell wall Cells with a wall (e.g., plants, fungal and bacterial cells) Cell wall H2O H2O Cell membrane Isotonic solution H2O Cell membrane Hypertonic solution Hypotonic solution A bacterial cell, which has a cytoplasmic solute concentration equal to 0.85% NaCl, is placed into a tube containing a solution that has a NaCl concentration of 0.2%. Into what type of solution has the cell been placed? a. hypotonic b. isotonic c. pyrotonic d. hypertonic Bell Ringer • What is the purpose of heat-fixing when making a smear? Finish Simple Staining Lab • Turn in extra credit • I will collect worksheets in 15 minutes Objective • Identify the internal and external structures of prokaryotic and eukaryotic cells and define the function of each. – By doing this, students understand how antibiotics take advantage of difference between human cells and bacteria cells. • Quiz – 15 points – 16 Questions Figure 3.17 Electrical potential of a cytoplasmic membrane Cell exterior (extracellular fluid) Cytoplasmic membrane Integral protein Protein DNA Protein Cell interior (cytoplasm) Bacterial Cytoplasmic Membranes • Function – A) Active Transport– Require energy! – Move against electrochemical gradient – 1) Uniport – One substance transported – 2) Antiport – Two molecules transported in opposite directions – 3) Symports – Two molecules transported in same direction – 4) Coupled transport – one chemicals electrochemical gradient provides the energy to transport a second chemical © 2012 Pearson Education Inc. Figure 3.21 Mechanisms of active transport-overview Extracellular fluid Uniport Cytoplasmic membrane Symport Cytoplasm Uniport Antiport Coupled transport: uniport and symport Transport Review • https://www.youtube.com/watch?v=svAAiKsJa-Y Bacterial Cytoplasmic Membranes • Function – B) Group translocation – Require energy! – Substance chemically modified during transport – Membrane is then impermeable to altered molecule © 2012 Pearson Education Inc. Figure 3.22 Group translocation Glucose Extracellular fluid Cytoplasm Glucose 6-PO4 A cell may allow a large or charged chemical to move across the cytoplasmic membrane, down the chemical’s electrical and chemical gradients, in a process called a. active transport. b. facilitated diffusion. c. endocytosis. d. pinocytosis. Cytoplasm of Bacteria • Cytosol – Liquid portion of cytoplasm – Contain ions, organic molecules, and nucleoid in prokaryotes • Inclusions – May include reserve deposits of chemicals • Endospores –defensive strategy against unfavorable conditions – Bacillus and Clostridium species – Survive boiling water, alcohols, bleach, UV radiation © 2012 Pearson Education Inc. Figure 3.24 The formation of an endospore-overview Cell wall Cytoplasmic membrane DNA is replicated. DNA A cortex of calcium and dipicolinic acid is deposited between the membranes. Cortex Vegetative cell Spore coat forms around endospore. DNA aligns along the cell’s long axis. Cytoplasmic membrane invaginates to form forespore. Forespore Endospore matures: completion of spore coat and increase in resistance to heat and chemicals by unknown process. Endospore is released from original cell. Cytoplasmic membrane grows and engulfs forespore within a second membrane. Vegetative cell’s DNA disintegrates. First membrane Second membrane Spore coat Outer spore coat Endospore Outer spore coat Cytoplasm of Bacteria • Nonmembranous Organelles – Ribosomes – Sites of protein synthesis – 70S compared to 80S in eukaryotic cells – Cytoskeleton – Plays a role in forming the cell’s basic shape © 2012 Pearson Education Inc. Practice • Worksheet Antibiotics • Most antibacterial drugs disrupt or destroy prokaryotic cellular processes that are different from eukaryotic ones. – In what ways are bacterial cells different from human cells? – 1) Cell wall: peptidoglycan & LPS – 2) Ribosomes: Bacteria have a 70s structure, eukaryotic cells have a 80s structure – 3) Cellular appendages: Fimbriae and pili only found in bacteria Antibiotics • Inhibit cell wall synthesis – Stop NAG and NAM subunits from binding • Inhibit protein synthesis – Prevent protein synthesis at either 30s or 50s subunit • Inhibit Nucleic Acid Synthesis – Prevent transcription • Antimetabolite – Stop folic acid synthesis