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Chapter 2 The Cell: Basic Unit of Structure and Function
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Our friend, the cell all life is made of cells
Cells come from other cells
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Most cells are very small
We use microscopes to look at them Some cells are not small
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Plasma membrane Made of a bilayer of phospholipids
Table 2.3, 2.4 Plasma membrane Made of a bilayer of phospholipids Cholesterol molecules and proteins embedded in membrane Semi-permeable protective layer around cell
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Plasma membrane Each phospholipid has hydrophilic head, hydrophobic tail Hydrophilic head faces water Hydrophobic tail faces away from water two layers of tails face each other
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Plasma membrane extracellular fluid Fluid inside cell is part of cytoplasm, called intracellular fluid (ICF) Fluid outside cell is extracellular fluid (ECF) intracellular fluid
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Plasma membrane Lots of things inserted in plasma membrane
Fig. 2.4 Peripheral protein Extracellular fluid Plasma membrane Glycolipid Integral proteins Lots of things inserted in plasma membrane Cholesterol (lipid) strengthens and stabilizes membrane Glycocalyx (carbohydrate) Glycoprotein Protein Peripheral protein Filaments of cytoskeleton Cytoplasm Cholesterol
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Fig. 2.4 Peripheral protein Extracellular fluid Plasma membrane Glycolipid Integral proteins Glycolipid (lipid with carbohydrate attached) located only on outer layer of membrane important for cell-cell recognition, intracellular adhesion, communication between cells Glycocalyx (carbohydrate) Glycoprotein Protein Peripheral protein Filaments of cytoskeleton Cytoplasm Cholesterol
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Plasma membrane Integral proteins extend across plasma membrane
Fig. 2.4 Peripheral protein Extracellular fluid Plasma membrane Glycolipid Integral proteins Integral proteins extend across plasma membrane Some create pores, channels to let things into or out of cells Some are binding site for signaling molecules Glycocalyx (carbohydrate) Glycoprotein Protein Peripheral protein Filaments of cytoskeleton Cytoplasm Cholesterol
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Plasma membrane Peripheral proteins are not embedded in membrane
Fig. 2.4 Peripheral protein Extracellular fluid Plasma membrane Glycolipid Integral proteins Peripheral proteins are not embedded in membrane may float above membrane or be attached to something attached to membrane Some are receptors for signaling molecules Glycocalyx (carbohydrate) Glycoprotein Protein Peripheral protein Filaments of cytoskeleton Cytoplasm Cholesterol
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Fig. 2.4 Peripheral protein Extracellular fluid Plasma membrane Glycolipid Integral proteins Glycoproteins (proteins with carbohydrate attached to external surface) ~90% of all membrane molecules With glycolipids form glycocalyx on surface of cell protection and recognition Glycocalyx (carbohydrate) Glycoprotein Protein Peripheral protein Filaments of cytoskeleton Cytoplasm Cholesterol
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Table 2.2a-2 Cytosol Organelles Cytoplasm Inclusions
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Water cannot move easily across hydrophobic part of membrane
Copyright © McGraw-Hill Education. Permission required for reproduction or display. Water cannot move easily across hydrophobic part of membrane Proteins are too large to move across membrane without help hydrophilic hydrophobic Table 2.2a-1
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Passive transport Move particles across membrane without using energy
Diffusion particles moving down concentration gradient from area of high concentration to area of low concentration
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Passive transport Osmosis Facilitated diffusion
high glucose concentration Osmosis diffusion of water across a permeable membrane Facilitated diffusion requires use of transport proteins to move across plasma membrane does not use energy low glucose concentration
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Passive transport Bulk filtration
diffusion of solutes and solvents together across a membrane Ex. transport of water and nutrients from blood into extracellular fluid pushed by hydrostatic pressure (pressure of fluid against the wall of the blood vessel)
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Active transport Movement of a substance across a plasma membrane AGAINST a concentration gradient from area of low concentration to area of high concentration Uses energy from ATP, and usually a transport protein to move the substance Pumps use ATP or kinetic energy of another particle moving down its gradient
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Sodium-Potassium Pump
Phospholipid bilayer Sodium-Potassium Pump Extracellular fluid 1. ATP binds to transport protein Binding changes shape of protein, allowing sodium to bind ATP binding site ATP Na+ Transport protein Cytoplasm 1
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Sodium-Potassium Pump
Breakdown of ATP releases energy 2. ATP separates into ADP and a phosphate group, releasing energy Transport protein uses energy to change shape Shape change releases sodium outside cell; binding sites for potassium open K+ Na+ ADP P Extracellular fluid Cytoplasm Transport protein changes shape (requires energy from ATP breakdown) 2
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Sodium-Potassium Pump
Cytoplasm Sodium-Potassium Pump Extracellular fluid 3. Potassium from ECF binds to transport protein; phosphate group from ATP releases K+ Na+ P 3
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Fig. 2.5 Sodium-Potassium Pump
Cytoplasm Extracellular fluid 4. Potassium is released into cytoplasm; transport protein resumes its original shape K+ Transport protein resumes original shape 4
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1. Vesicle nears plasma membrane
Fig. 2.6, Exocytosis 1. Vesicle nears plasma membrane Extracellular fluid Secretory proteins Secretory vesicle Plasma membrane Cytoplasm Vesicle membrane
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2. Vesicle membrane fuses with plasma membrane
Fig. 2.6, Exocytosis Cytoplasm 2. Vesicle membrane fuses with plasma membrane Membrane proteins Extracellular fluid
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3. Exocytosis as plasma membrane opens externally
Fig. 2.6, Exocytosis 3. Exocytosis as plasma membrane opens externally
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4. Release of vesicle components into the
Secretory proteins Fig. 2.6, Exocytosis 4. Release of vesicle components into the extracellular fluid and integration of vesicle membrane components into the plasma membrane
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Fig. 2.7, Forms of Endocytosis
Phagocytosis: cell engulfs or captures a large particle from extracellular space by forming membrane extensions called pseudopodia Membrane sac enters cell, called vacuole if large Pseudopodia Cytoplasm (a) Phagocytosis Extracellular fluid Particle Plasma membrane Vacuole
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Fig. 2.7, Forms of Endocytosis
Plasma membrane Vesicle (b) Pinocytosis Pinocytosis: cellular drinking cell brings in small droplet of ECF into internal vesicle moves against concentration gradient
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Fig. 2.7, Forms of Endocytosis
Receptors Plasma membrane Cytoplasmic vesicle (c) Receptor-mediated endocytosis Receptor-mediated endocytosis: movement of specific molecules into cell by formation of vesicles Molecule binds to receptors on surface of cell Receptor proteins signal for formation of vesicle
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Other parts of the cell Cytosol (AKA intracellular fluid) Inclusions
very viscous mostly water with dissolved ions, nutrients, proteins, carbohydrates, lipids, etc. solutes provide nutrition to cell, make building blocks of membranes, proteins Inclusions temporarily stored chemicals not bound by membranes include pigments, protein crystals, nutrient stores ex. melanin and glycogen
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Other parts of the cell Organelles bound by membrane
each has specific function
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Membrane-bound organelles
Each bound by plasma membrane like the cell itself Each carries out specific function membrane is basically the same, may have different protein-lipid composition
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Smooth endoplasmic reticulum
Table 2.2a-4 Smooth endoplasmic reticulum Synthesizes, transports, and stores lipids more smooth ER in cells that make steroids (forms of lipids) Metabolizes carbohydrates Detoxifies drugs, alcohol, and poisons lots of smooth ER in liver Continuous with rough ER
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Makes proteins for inclusion in plasma membrane
Table 2.2a-5 Makes proteins for inclusion in plasma membrane Makes proteins that will be used in lysosomes Makes proteins that will be secreted out of cell Transports and stores proteins proteins packaged into transport vesicles Rough endoplasmic reticulum
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Golgi composed of cisternae, stacks of membranes
Table 2.2a-6 Golgi apparatus AKA Golgi complex Modifies, packages, and sorts proteins for secretion or transport within cell Golgi composed of cisternae, stacks of membranes
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Golgi Apparatus One side of Golgi stack receives vesicles from ER
Transport vesicle from rough ER Transport vesicle from rough ER Golgi Apparatus “Receiving” side of the Golgi apparatus One side of Golgi stack receives vesicles from ER 1 2 3 Figure The Golgi apparatus (part 1: detail) Plasma membrane Plasma membrane
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Golgi Apparatus One side of Golgi stack receives vesicles from ER
Transport vesicle from rough ER Transport vesicle from rough ER Golgi Apparatus “Receiving” side of the Golgi apparatus One side of Golgi stack receives vesicles from ER Proteins modified by enzymes (folded, signaling molecules attached) 1 2 3 Figure The Golgi apparatus (part 1: detail) Plasma membrane Plasma membrane
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Transport vesicle from rough ER Transport vesicle from rough ER Golgi Apparatus “Receiving” side of the Golgi apparatus Receiving side (AKA cis- face) receives vesicles from ER Proteins modified by enzymes (folded, signaling molecules attached) Vesicles emerge from shipping side (AKA trans- face); sent to organelles or plasma membrane for secretion 1 New vesicle forming New vesicle forming 2 Transport vesicle from the Golgi apparatus 3 Figure The Golgi apparatus (part 1: detail) “Shipping” side of the Golgi apparatus Plasma membrane Plasma membrane
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Golgi Apparatus Transport vesicle Vacuole Vacuole Shipping region Secretory vesicles Shipping region Receiving region Vacuole Transport vesicle TEM 17,770x Transport vesicle (a) Cisternae Lumen of cisterna filled with secretory product Vesicles form at the edges of cisternae, fuse with next cisternae
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Lysosomes Sac of digestive enzymes enclosed in a membrane
Organelle fragment Lysosomes Vesicle containing two damaged organelles Sac of digestive enzymes enclosed in a membrane formed by Golgi apparatus Contain enzymes that break down proteins, polysaccharides, fats, nucleic acids “digestion” within cell TEM Figure Two functions of lysosomes (part 3: TEM) Organelle fragment
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Lysosomes Lysosomes in immune cells (white blood cells) fuse with vacuole containing engulfed bacteria or virus Cell recycles molecules from engulfed particles Figure Two functions of lysosomes (part 1: digesting food)
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Lysosomes Lysosomes can break down old or damaged organelles within cell process called autophagy Cell can recycle parts to make new organelles Autolysis destroys whole cell when lysosomes break Lysosome Digestion Vesicle containing damaged organelle (b) A lysosome breaking down the molecules of damaged organelles Figure Two functions of lysosomes (part 2: breaking down damaged organelles)
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Lysosomes In embryo, digest webbing between developing fingers
if process doesn’t work correctly, digits are fused by skin fusion called syndactyly Programmed cell death is apoptosis body getting rid of old, unnecessary, or damaged cells
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Lysosomes If lysosomes don’t work correctly, causes disease
Tay-Sachs disease: nerve cells accumulate excess lipids causes deafness, lack of muscle tone fatal
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Detoxifies some harmful materials by oxidizing
Table 2.2b-2 Peroxisome Detoxifies some harmful materials by oxidizing Converts hydrogen peroxide from metabolism into water Smaller than lysosomes Formed by rough ER Most abundant in liver
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Mitochondria sing. mitochondrium
Table 2.2b-3 Mitochondria sing. mitochondrium Synthesizes ATP through cellular respiration “Powerhouse” of the cell Surrounded by double membrane Inner membrane folded into cristae, increased surface area for ATP production Inner membrane cristae together called matrix Outer membrane Inner membrane Cristae Matrix Space between membranes
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Outer membrane Inner membrane Space between membranes
TEM Inner membrane Cristae Figure 4.18 The mitochondrion: site of cellular respiration Matrix Space between membranes
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Mitochondria are Special
Outer membrane Inner Cristae Matrix Space between membranes TEM More mitochondria in cells that use lots of energy Have their own DNA single, circular chromosome, like prokaryotic chromosome have their own ribosomes evidence that eukaryotes came from symbiotic prokaryotes Figure The mitochondrion: site of cellular respiration (part 1: TEM)
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Mitochondria are Mom’s Gift
Mitochondria come from egg, not sperm Human evolution can be traced through mitochondrial DNA
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Non-membrane-bound organelles
Other parts of the cell that do not have a plasma membrane
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Ribosomes synthesize proteins
Table 2.2b-4 Free ribosomes Fixed ribosomes Ribosomes synthesize proteins Free ribosomes make proteins for use in cell Fixed ribosomes attached to endoplasmic reticulum make proteins for secretion, plasma membrane, or in lysosomes
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Fig. 2.13 Free ribosome Small subunit + Rough endoplasmic reticulum
with fixed ribosomes Large subunit = TEM 12,510x Functional ribosome
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Cytoskeleton is network of protein fibers
Microfilament Intermediate filament Microtubule Cytoskeleton Cytoskeleton is network of protein fibers give structural support to cell enable movement within cell Assist with cell division and mitosis Intermediate filaments and microfilaments are narrow and solid Microtubules are hollow
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Centrosome organizes microtubules during mitosis (cell duplication)
Table 2.2b-6 Centriole Centrosome Centrosome organizes microtubules during mitosis (cell duplication) Centrioles (2) sit within centrosome, perpendicular to each other move chromosomes during cell division
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Lots of tiny hairs attached to the cell membrane
Table 2.2b-7 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Cilia Lots of tiny hairs attached to the cell membrane Move fluid, mucus, and materials over cell surface Inside of trachea and bronchi in lungs Inside fallopian tubes in females
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Table 2.2b-8 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Flagellum Single, long extension of membrane filled with microtubules (sometimes 2-8 in other organisms) In humans, propel sperm Frequently used by single-celled organisms for propulsion
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Multiple folds and extensions in membrane
Table 2.2b-9 Microvilli Multiple folds and extensions in membrane Increase surface area to increase absorption and/or secretion Found in lining of intestine
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Largest structure in most cells Houses DNA
Table 2.2a-3 Nucleus Nuclear pores Nucleolus Nuclear envelope Chromatin Largest structure in most cells Houses DNA Makes mRNA, instructions for making proteins Nucleolus assembles rRNA and ribosomes
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The Nucleus Has a double-membrane called nuclear envelope
pore The Nucleus Chromatin fiber Has a double-membrane called nuclear envelope Pores control movement into and out of nuclear envelope TEM TEM Surface of nuclear envelope Nuclear pores
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DNA storage DNA strands are very, very long Stored coiled up
total DNA in each cell is 1.8 m (~5 ft) long if stretched out Stored coiled up DNA binds with protein fibers called chromatin each chromatin fiber is one chromosome DNA molecule Proteins Chromatin fiber Chromosome
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The Nucleolus Sits within nucleus Makes parts of ribosomes
sent into cell to make proteins
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How to Make a Protein 1. Translate DNA into RNA in the nucleus 1
Synthesis of mRNA in the nucleus 1 1. Translate DNA into RNA in the nucleus Strand of RNA called messenger RNA or mRNA mRNA Nucleus Cytoplasm Figure 4.10-s1 DNA → RNA → protein (step 1)
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How to Make a Protein 1. Translate DNA into RNA in the nucleus
Synthesis of mRNA in the nucleus 1. Translate DNA into RNA in the nucleus Strand of RNA called messenger RNA or mRNA 2. Transport mRNA out of nucleus into cytoplasm mRNA Nucleus Cytoplasm 2 mRNA Figure 4.10-s2 DNA → RNA → protein (step 2) Movement of mRNA into cytoplasm via nuclear pore
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How to Make a Protein 1. Translate DNA into RNA in the nucleus
Synthesis of mRNA in the nucleus 1. Translate DNA into RNA in the nucleus Strand of RNA called messenger RNA or mRNA 2. Transport mRNA out of nucleus into cytoplasm 3. Ribosome reads mRNA instructions; binds amino acids together into strand of protein mRNA Nucleus Cytoplasm 2 mRNA Movement of mRNA into cytoplasm via nuclear pore Ribosome Figure 4.10-s3 DNA → RNA → protein (step 3) 3 Synthesis of protein in the cytoplasm Protein
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Fig The Cell Cycle Anaphase G2 phase (Growth) G1 phase (Growth) Metaphase Mitosis Telophase Prophase Interphase S phase (DNA replication and growth) Mitotic (M) phase Cytokinesis
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Fig. 2.20 Interphase and Mitosis -- Interphase
Nucleus with chromatin Nucleolus Two pairs of centrioles Chromatin Nuclear envelope Plasma membrane Synthesis of cellular components needed for cell division, including synthesis of DNA.
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Fig. 2.20 Interphase and Mitosis -- Prophase
Nucleus with dispersed chromosomes Chromosome (two sister chromatids joined at centromere) Sister chromatids Centromere Developing spindle Chromosomes appear due to coiling of chromatin. Nucleolus breaks down. Spindle fibers begin to form from centrioles. Centrioles move toward opposing cell poles. Nuclear envelope breaks down at the end of this stage.
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Fig. 2.20 Interphase and Mitosis - Metaphase
Equatorial plate Chromosomes aligned on equatorial plate Spindle fibers Spindle fibers Spindle fibers attach to the centromeres of the chromosomes extending from the centrioles. Chromosomes are aligned at the equatorial plate of the cell by spindle fibers.
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Fig. 2.20 Interphase and Mitosis -- Anaphase
Sister chromatids being pulled apart Sister chromatids being pulled apart Spindle fibers Centromeres that held chromatid pairs together separate; each sister chromatid is now a chromosome with its own centromere. Sister chromatids are separated and moved toward opposite ends of the cell. Cytokinesis begins.
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Fig. 2.20 Interphase and Mitosis -- Telophase
Re-forming nuclear envelope Cleavage furrow of cytokinesis Cytokinesis occurring Nucleolus Chromosomes uncoil to form chromatin. A nucleolus reforms within each nucleus. Spindle fibers break up and disappear. New nuclear envelope forms around each set of chromosomes. Cytokinesis continues as cleavage furrow deepens. Cleavage furrow
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