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REVIEW-Cell Structure and Function
Chapter 3 REVIEW-Cell Structure and Function
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Cell Characteristics Plasma Membrane Cytoplasm Organelles
Outer cell boundary Cytoplasm Cytosol Cytoskeleton Cytoplasmic inclusions Organelles Specialized structures that perform specific functions
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Functions of the Cell Basic unit of life Protection and support
Movement Communication Cell metabolism and energy release Inheritance
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Plasma Membrane Intracellular versus extracellular Membrane potential
Glycolipids and glycoproteins Fluid-mosaic model
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Membrane Lipids Phospholipids form a lipid bilayer
Hydrophilic (water-loving) polar heads Hydrophobic (water-fearing) nonpolar heads Cholesterol: Determines fluid nature of membrane
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Membrane Proteins Integral or intrinsic Peripheral or extrinsic
Extend from one surface to the other Peripheral or extrinsic Attached to either the inner or outer surfaces of the lipid bilayer
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Marker Molecules Allow cells to identify one another or other molecules Glycoproteins Glycolipids Examples: Immune system Recognition of oocyte by sperm cell
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Channel Proteins Non-gated ion channels Ligand-gated ion channel
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
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Receptors Receptor molecules Linked to channel proteins
Exposed receptor sites Linked to channel proteins Acetylcholine Linked to G proteins Alter activity on inner surface of plasma membrane
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Enzymes and Carrier Proteins
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Movement through the Plasma Membrane
Diffusion Osmosis Filtration Mediated transport mechanisms Facilitated diffusion Active transport Secondary active transport
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Diffusion Movement of solutes from an area of higher concentration to an area of lower concentration in solution Concentration (or density) gradient Difference between two points Viscosity How easily a liquid flows
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Diffusion
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Osmosis Diffusion of water (solvent) across a selectively permeable membrane Important because large volume changes caused by water movement disrupts normal cell function Cell shrinkage or swelling Isotonic: cell neither shrinks nor swells Hypertonic: cell shrinks (crenation) Hypotonic: cell swells and bursts (lysis)
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Osmosis
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Osmosis
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Filtration Works like a sieve
Depends on pressure difference on either side of partition Small particles move through holes with liquid Larger particles cannot move beyond partition Moves from side of greater pressure to lower Example: In kidneys in urine formation BP moves fluid from blood through filtration membrane Water, ions, small molecules pass through partition; most proteins and blood cells remain in blood
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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
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Saturation of a Carrier Protein
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Mediated Transport Mechanisms
Facilitated diffusion Higher to lower concentration without metabolic energy Active transport Requires ATP Moves against gradient Secondary active transport Ions or molecules move in same (symport) or different direction (antiport)
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Secondary Active Transport
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Endocytosis Internalization of substances by formation of a vesicle
Types Phagocytosis Pinocytosis Receptor-mediated endocytosis
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Pinocytosis and Receptor-Mediated Endocytosis
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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
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Cytoplasm Cellular material outside nucleus but inside plasma membrane
Half cytosol, half organelles Cytosol: Fluid portion Cytoskeleton: Supports the cell Microtubules Microfilaments Intermediate filaments Cytoplasmic inclusions Melanin, hemoglobin, lipid droplets
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Organelles Small specialized structures for particular functions
Most have membranes that separate interior of organelles from cytoplasm Related to specific structure and function of the cell
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Centrioles In specialized zone of microtubule formation near nucleus: Centrosome Each unit consists of 9 triplet microtubules Before cell division, centrioles divide, move to ends of cell and become spindle fibers
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Cilia Short appendages projecting from cell surfaces
9 + 2 microtubule arrangement Capable of movement Moves materials over the cell surface
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Flagella Similar to cilia but longer Usually only one exists per cell
Moves the cell itself in wavelike fashion Example: Sperm cell
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Microvilli Extensions of plasma membrane Normally many on each cell
Increase the cell surface One tenth to one twentieth size of cilia Do not move
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Ribosomes Sites of protein synthesis
Composed of a large and small subunit, each consisting of rRNA Types Free Attached to endoplasmic reticulum
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Endoplasmic Reticulum
Types Rough Has attached ribosomes Proteins produced and modified for secretions Smooth Not attached ribosomes Manufacture lipids Cisternae: Interior spaces isolated from rest of cytoplasm
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Golgi Apparatus Modification, packaging, distribution of proteins and lipids for secretion or internal use Flattened membrane sacs stacked on each other
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Function of Golgi Apparatus
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Action of Lysosomes Membrane-bound vesicles that pinch off from Golgi
Hydrolytic enzymes for intracellular digestion, autophagia WBC’s have many lysosomes to digest bacteria Important in bone remodeling; digesting damaged cells
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Peroxisomes and Proteasomes
Membrane-bound vesicles smaller than lysosomes Contain enzymes to break down fatty acids and amino acids Hydrogen peroxide is a toxic by-product of breakdown; catalase breaks it down to water and oxygen Proteasomes Consist of large protein complexes Include several enzymes that break down and recycle proteins in cell
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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
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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 ribosomal units
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Chromosome Structure
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Overview of Cell Metabolism
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Overview of Protein Synthesis
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Protein Synthesis cont’d
Transcription Transcription DNA copied to make mRNA Translation Synthesis of a protein Requires mRNA, ribosomes, and tRNA Ribosomes align mRNA codons with tRNA anticodons
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Translation
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Cell Life Cycle Interphase Mitosis: Division of nucleus
3 Phases between cell divisions: G1, S, G2 Mitosis: Division of nucleus Prophase Metaphase Anaphase Telophase Cytokinesis: Division of cytoplasm Immediately follows mitosis
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Mitosis Interphase Prophase Metaphase
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Mitosis Anaphase Telophase Cytokinesis
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MEIOSIS Sex cells are formed by meiosis Nucleus undergoes 2 divisions (Meiosis I and Meiosis II) Resulting in 4 nuclei Each nuclei has half the number of chromosomes as parent cell Called haploid; 23 chromosomes in human sex cells Resulting daughter cells differentiate into gametes or sex cells Sperm cells in males; oocytes (egg cells) in females During fertilization, a sperm cell fuses with the oocyte This restores the normal number of 46 chromosomes in the human zygote
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MEIOSIS
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Meiosis
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Comparison of Mitosis and Meiosis
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Cellular Aspects of Aging
Aging involves lipids, proteins, and nucleic acids within the cell 35% or more factors are genetic Cellular clock: death of cell line after a certain number of cell divisions Death genes: turn on late in life DNA damage: results in cell degeneration and death Free radicals: direct damage (by atoms with unpaired electrons) to DNA in somatic cells Results in somatic mutations, cellular dysfunction, and cell death Mitochondrial damage: loss of energy to cell and cell death
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