3-1 Structure and Function of the Cell Chapter 3

3-2 How we learn about cells. Brightfield Microscopy –visible light passes through the specimen and then through glass lenses. (magnification up to 1000x) Magnification is the ratio of an object’s image to its real size. Resolving power is a measure of image clarity. –It is the minimum distance two points can be separated and still viewed as two separate points. –Resolution is limited by the shortest wavelength of the source, in this case light. –Resolution of a light microscope is about 0.2um.

3-3 The minimum resolution of a light microscope is about 2 microns, the size of a small bacterium Light microscopes can magnify effectively to about 1,000 times the size of the actual specimen. –At higher magnifications, the image blurs. Fig. 7.1

3-4 While a light microscope can resolve individual cells, it cannot resolve much of the internal anatomy, especially the organelles. To resolve smaller structures we use an electron microscope (EM), which focuses a beam of electrons through the specimen or onto its surface. –Electron microscopes with shorter wavelengths than visible light have finer resolution. –The resolution of a modern EM is about 2 nm.

3-5 Transmission electron microscopes (TEM) are used mainly to study the internal ultrastructure of cells. –A TEM aims an electron beam through a thin section of the specimen. –The image is focused and magnified by electromagnets. –To enhance contrast, the thin sections are stained with atoms of heavy metals. Fig. 7.2a

3-6 Scanning electron microscopes (SEM) are useful for studying surface structures. –The sample surface is covered with a thin film of gold. –The beam excites electrons on the surface. –These secondary electrons are collected and focused on a screen. The SEM has great depth of field, resulting in an image that seems three-dimensional. Fig. 7.2b

3-7 Cell Characteristics Plasma Membrane –Outer cell boundary Cytoplasm –Cytosol –Cytoskeleton –Cytoplasmic inclusions Organelles –Specialized structures that perform specific functions

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3-9 Plasma Membrane Intracellular versus extracellular Membrane potential Glycolipids and glycoproteins Fluid-mosaic model

3-10 Membrane Lipids Phospholipids form a lipid bilayer –Hydrophilic (water-loving) polar heads –Hydrophobic (water-fearing) nonpolar heads Cholesterol: Determines fluid nature of membrane

3-11 Membrane Proteins Integral or intrinsic –Extend from one surface to the other Peripheral or extrinsic –Attached to either the inner or outer surfaces of the lipid bilayer

3-12 Plasma membrane

Marker Molecules Allow cells to identify on another or other molecules Glycoproteins –Also Glycolipids Examples: –Immune system –Recognition of oocyte by sperm cell Membrane Proteins

3-14 Integrins: Proteins in the plasma membrane attach to extracellular molecules. 2. Attachment Sites

Channel Proteins Nongated ion channels –Always open Ligand gated ion channel –Open in response to small molecules that bind to proteins or glycoproteins Voltage-gated ion channel –Open when there is a change in charge across the plasma membrane

Receptors Receptor molecules –Exposed receptor site Linked to channel proteins –Acetylcholine Linked to G proteins –Alter activity on inner surface of plasma membrane

Enzymes and Carrier Proteins

3-18 Nucleus DNA dispersed throughout Consists of : –Nuclear envelope: Separates nucleus from cytoplasm and regulates movement of materials in and out –Chromatin: Condenses to form chromosomes during cell division –Nucleolus: Assembly site of large and small ribosomal units

3-19 Nucleus

3-20 Cytoplasm Cellular material outside nucleus but inside plasma membrane Cytosol: Fluid portion Cytoskeleton: Supports the cell –Microtubules –Microfilaments –Intermediate filaments Cytoplasmic inclusions

3-21 The Endomembrane System If you stick your finger in the hole of a doughnut is it inside or outside the doughnut? Nuclear Envelope Endoplasmic Reticulum Golgi Apparatus Secretory Vesicle

3-22 Organelles Small specialized structures for particular functions Most have membranes that separates interior of organelles from cytoplasm Related to specific structure and function of the cell

3-23 Ribosomes Sites of protein synthesis Composed of a large and small subunit Types –Free –Polyribosomes –Attached to endoplasmic reticulum

3-24 Endoplasmic Reticulum Types –Rough Attached ribosomes Proteins produced and modified –Smooth Not attached ribosomes Manufacture lipids Cisternae: Interior spaces isolated from rest of cytoplasm

3-25 Golgi Apparatus Modification, packaging, distribution of proteins and lipids for secretion or internal use Flattened membrane sacs stacked on each other

3-26 Function of Golgi Apparatus

3-27 Action of Lysosomes

3-28 Peroxisomes and Proteasomes Peroxisomes –Smaller than lysosomes –Contain enzymes to break down fatty and amino acids –Hydrogen peroxide is a by-product of breakdown Proteasomes –Consist of large protein complexes –Include several enzymes that break down and recycle proteins in cell

3-29 Mitochondria Provide energy for cell Major site of ATP synthesis Membranes –Cristae: Infoldings of inner membrane –Matrix: Substance located in space formed by inner membrane

3-30 Centrioles In specialized zone near nucleus: Centrosome Each unit consists of microtubules Before cell division, centrioles divide, move to ends of cell and become spindle fibers

3-31 Cilia Appendages projecting from cell surfaces Capable of movement Moves materials over the cell surface

3-32 Flagella Similar to cilia but longer Usually only one exists per cell Move the cell itself in wavelike fashion Example: Sperm cell

3-33 Microvilli Extension of plasma membrane Increase the cell surface Normally many on each cell One tenth to one twentieth size of cilia Do not move

3-34 Movement through the Plasma Membrane Diffusion Osmosis Filtration Mediated transport mechanisms –Facilitated diffusion –Active transport –Secondary active transport

3-35 Diffusion Movement of solutes from an area of higher concentration to lower concentration in solution –Concentration or density gradient Difference between two points –Viscosity How easily a liquid flows –Temperature –Size of the diffusing molecule

3-36 Diffusion

3-37 Osmosis Diffusion of water (solvent) across a selectively permeable membrane Important because large volume changes caused by water movement disrupt normal cell function Cell shrinkage or swelling –Isotonic: cell neither shrinks nor swells –Hypertonic: cell shrinks (crenation) –Hypotonic: cell swells (lysis)

3-38 Osmosis

3-39 Osmosis

3-40 Filtration Works like a sieve Depends on pressure difference on either side of partition Moves from side of greater pressure to lower –Example: In kidneys in urine formation

3-41 Mediated Transport Mechanisms Involve carrier proteins Characteristics –Specificity To a single type of molecule –Competition –Saturation Rate of transport limited to number of available carrier proteins

3-42 Saturation of a Carrier Protein

3-43 Mediated Transport Mechanisms Facilitated diffusion –Higher to lower concentration without metabolic energy Active transport –Requires ATP Secondary active transport –Ions or molecules move in same (symport) or different direction (antiport)

3-44 Secondary Active Transport

3-45 Endocytosis Internalization of substances by formation of a vesicle Types –Phagocytosis –Pinocytosis –Receptor-mediated endocytosis

3-46 Pinocytosis and Receptor-Mediated Endocytosis

3-47 Exocytosis Accumulated vesicle secretions expelled from cell Examples –Secretion of digestive enzymes by pancreas –Secretion of mucus by salivary glands –Secretion of milk by mammary glands

3-48 Overview of Cell Metabolism

3-49 Chromosome Structure

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3-53 Overview of Protein Synthesis

3-54 Overview of Protein Synthesis Transcription –Copies DNA to form mRNA –tRNA carries amino acids to ribosome Translation –Synthesis of a protein at ribosome

3-55 Translation

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3-68 Cell Life Cycle Interphase –Phase between cell divisions Mitosis –Prophase –Metaphase –Anaphase –Telophase Cytokinesis –Division of cell cytoplasm

3' 5' 3' 5' Helicase unwinds DNA RNA primer made by RNA polymerase Newly synthesized DNA DNA polymerase adds complimentary base pairs to 3’ end. Leading strand (Continuous replication) Lagging strand: (Okazaki fragments ) 1. Unwinding - Helicase 2. Complimentary base pairing - RNA polymerase makes RNA primer - DNA polymerase adds nucleotides to 3' end 3. Joining -DNA polymerase removes RNA sequences. -Ligase joins DNA fragments 5' 3'

3-70 Mitosis

3-71 Mitosis

3-72 Meiosis

3-73 Comparison of Mitosis and Meiosis

3-74 Cellular Aspects of Aging Cellular clock Death genes DNA damage Free radicals Mitochondrial damage