CHAPTER 6: THE CELL
Introduction: Importance of Cells
 All organisms are made of cells
 Cell is smallest living unit
6.1: Tools to Examine Cells
 Microscopy
o Discovered in 1590; improved in 17th century
o Light Microscopes: LMs
 Parameters
 Magnification: ratio of image to real size
 Resolution: clarity of the image
 Limited in magnification & clarity; staining
 Cells discovered by Hooke in 1665
 Organelles can’t be seen with light microscope
o Electron Microscopes: EM
 Beam of electrons through specimen or on surface
 Look at cell ultrastructure
 SEM (scanning electron microscope): Detailed surface
study
 TEM (transmission electron microscope): internal
ultrastructure of cells
o Differences
 EM can look at organelles that can’t be resolved with LM
 EM preparation kills the cells and produces things that
don’t exist in cells
o Cytology: Study of Cells
 Cell Fractionation:
o Separate organelles
o Ultracentrifuge
o Figure 6.5
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6.2: Eukaryotic Cell Organelles
 Introduction
o Prokaryotes: Eubacteria and Archea
o Eukaryotes: Protists, Fungus, Plants, Animals
 Prokaryotic or Eukaryotic
o Common Features
 Cytosol (semifluid); Cytoplasm
 Chromosomes
 Ribosomes
 Plasma membrane: selective barrier
o Differences
 Nucleus
 Eukaryote: membrane bound nucleus
 Prokaryote: nucleoid
 Specialized Organelles
 Eukaryotic Cells are Bigger
 Cells remain small because smaller objects have
greater ration of surface area to volume can carry
out functions
 Need high ration if lots of exchange: intestinal cells
 Eukaryotic Cell
o Membranes (study figure 6.8 of plasma membrane)
 Surround organelles
 Metabolism (enzymes in membranes)
 Double layer of phospholipids and other lipids
 Embedded or attached to surface: Proteins
o STUDY 6.9 EUKARYOTIC CELLS
 Similarities and Differences
 Old Stuff
 New Stuff: flagellum, centrosome, cytoskeleton,
microvilli, peroxisome, plasmodesmata, tonoplast
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6.3: Genetic Instructions
 Genetic Control: Nucleus and Ribosomes
 Nucleus (Figure 6.10)
o Most of genes
o Nuclear envelope: double membrane
 Pores, continuous, pore complex proteins regulate in and
out traffic
 Nuclear lamina: nuclear side lining of filaments that
support the envelope
o Nuclear matrix: fibers throughout nucleus
o Chromosomes
 Chromatin: protein and DNA; diffuse until dividing
 Species have specific number of chromosomes (46)
o Nucleolus:
 rRNA is made
 proteins from cytoplasm are made into large and small
ribosomal units
o Figure 5.25
 Nucleus: DNA  mRNA
 mRNA  cytoplasm (through nuclear pores)
 ribosomes translate mRNA  primary polypeptide
 Ribosomes (Figure 6.11)
o rRNA and protein
o protein synthesis organelles (more proteins made --. More
ribosomes; pancreas)
o Not membrane bound
o Free ribosomes:
 In cytosol
 Most proteins stay in cell
o Bound ribosomes
 Attached to rough endoplasmic reticulum or nuclear
envelope
 Proteins that need to go into membranes (lysosomes,
secretion)
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6.4: Endomembrane System
 Introduction
o Tasks: make protein, transport proteins into membranes and
organelles or our of the cell, metabolize and move lipids, detox
poisons
o Direct contact membranes or vesicles
o Parts: nuclear envelope, ER, Golgi, lysosomes, vacuoles, plasma
membrane
 Endoplasmic Reticulum
o More than half the membrane
o Network of membranes of tubules and sacs (cisterna); Inside
is called the lumen or cisternal space
o Smooth ER
 Metabolic processes: make lipids (sex hormones),
metabolize carbohydrates, detoxification
 Enyzmes are important (make things, detox (liver))
 Detox: add –OH to make more soluble, stimulate more
smooth ER with use (increased tolerance)
 Stores Calcium ions (muscle cell)
o Rough ER
 Secretion (insulin); glycoproteins
 Keeps secretory proteins separate from proteins in the
cytosol
 Secretory proteins leave ER in vesicles
 Membrane factory for cell (makes own phospholipids)
 Golgi Apparatus: (6.13)
o Shipping and receiving
o After ER, transport vesicles go to Golgi where products are
modified, stored and sent
o Flattened membranous sacs (cisternae)
o Two faces
 Cis face: near ER, receives
 Trans face: away from ER, sends
 Modification between the two points
o Makes some polysaccharides
o Cisternal Maturation Model (move cis  trans) 6.13
o Sorts and tags products before sending; molecular tags,
docking sits
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 Lysosomes: 6.14
o Membrane bound sac of hydrolytic enzymes; digestion
o Acidic environment
o Made by rough ER  Golgi
o Phagocytosis: amoeba, macrophages
o Autophagy
o Tay-Sachs lysosomes cant digest lipids
 Vacuoles: 6.15
o Plants and fungus have many
o Similar to lysosomes; also: food vacuoles, contractile vacuoles
o Plants have central vacuole
 (from smaller vacuoles)
 surrounded by tonoplast (selective; different solution
inside  cell sap)
 hold reserves, ions, pigments, poisonous compounds for
defense, cell growth by absorbing water,
 REVIEW ENDOMEMBRANE SYSTEM: 6.16
6.5 Energy
 INTRO
o Transformation of energy: mitochondria and chloroplasts
 Mitochondria: cell respiration; ATP from organic
molecules
 Chloroplasts (plants and algae): photosynthesis
o Membranes but not part of endomembrane system
 2 membranes
 proteins made by free ribosomes not by ER
 have DNA (make proteins on own ribosomes)
o Peroxisome: oxidative organelle that imports proteins from
cytosol
 Mitochondria: converts chemical energy
o Almost all eukaryotic cells
o Varies in number, move, change shape, divide
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o 2 membranes (phospholipid bilayers with proteins)
 inner membrane is folded into cristae
 internal compartments
 intermembrane space
 mitochondrial matrix
o enzymes
o mitochondrial DNA
o ribosomes
 respiration proteins and enzymes
 Folding  large surface area
 Chloroplast: Capture Light Energy
o Plastids (amyloplasts store starch, chromoplasts have
pigments, cholorplasts have chlorophyll for photosynthesis)
o Two membranes
 Intermembrane space
 Thylakoic sacs  granum stacks
 Stroma is fluid outside the thylakoid: DNA, ribosomes,
enzymes
o Change Shape, mobile
 Peroxisomes: Oxidation
o Metabolic compartment with membrane
o Enzymes that transfer hydrogen  oxygen and make
hydrogen peroxide as a byproduct
 Break fatty acids into smaller molecules to use for
cellular respiration
 Liver: detoxifies
o Peroxide is toxic but it will convert it to water
o Glyoxysomes: specialized peroxisomes that are found in fat
storing tissues of plants seeds that initiate converting fatty
acids  sugars; energy for plant, and carbon
o Not from endomembrane
 Get proteins from cytosol
 Lipids made in ER and peroxisome
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6.6 Cytoskeleton:
 Introduction
o fibers in the cytoplasm
o organizes structures and activities of the cell
o Three types
 Microtubules
 Microfilaments
 Intermediate filaments
 Roles of Cytoskeleton
o Support and shape for cell (important in animal cells)
 Anchorage for organelles
 Can dismantle and reassemble: dynamic
o Motility (movement)
 Interaction of cytoskeleton with motor proteins
 Plasma membrane: move fibers outside cell
 Move cilia and flagella
 Microfilaments can cause muscle contraction
 Vesicles travel along cytoskeleton monorails
 ER vesicles travel to Golgi along tracks of cytoskeleton
 Forms food vacuoles for phagocytosis
 Circulate materials by cytoplasmic streaming in plant
cells
o Regulate biochemical activities in the cell: Transmit force from
outside to inside the cell
 Components of Cytoskeleton (Table 6.1)
o Microtubules: thickest
 Hollow rods in all eukaryotic cytoplasms
 Made from protein called tubulin (can be assembled and
disassembled)
 Shape and support cell and make tracks; separate
chromosomes during cell division
 Centrosomes and centrioles
 Microtubules grown from centrosome
(microtubule organizing center) near nucleus
 Animal centrosomes contain centrioles
o 9 sets of triplet microtubules in a ring
o before division centrioles replicate
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 Cilia and Flagella
 Flagulla: Locomotor appendages from cells; longer;
undulating motion
 Cilia line windpipe to sweep out debris; sweep egg
to uterus; shorter and more of them; alternating
power
 Common ultrastructure (6.24)
o Core of microtubules sheathed in extension
of plasma membrane
o 9 doublets of microtubules are in a ring;
center of ring are 2 microtubules: 9 + 2
pattern in eukaryotes
o Cross linking proteins connect the tubules to
each other and the center
o Anchored in cell by basal body (centriole)
o Dyenin
 large motor protein extending from
one microtubule doublet to the next;
 binding from changes in protein and
ATP for energy
 dynein walking 6.25
 Compression resisting
o Microfilaments: actin filaments; thinnest
 Molecules of actin (globular protein)
 Twisted double chain of actin
 Filaments or networks (proteins on side allow for
branching)
 Tension (pulling forces)  support cell shape
 Bundles in microvilli
 Cell motility, contraction of muscle cells
 Thousands of actin with myosin
 Myosin walks along actin
 Cleavage furrow, pseudopodia (amoeba; white blood
cells)
 Cytoplasmic streaming: flow of cytoplasm in cell
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o Intermediate filaments: middle diameter
 Bearing tension
 Keratin proteins; diverse group
 More permanent fixtures; after dead like skin cells
 Reinforce shape of cell and fix organelles (nucleus)
6.7 Extracellular Components and Cell Connections
 Cell Wall
o Extracellular structure in plant cells (some prokaryotes,
protists and fungi too!)
o Protects cell, maintains shape, prevents too much water
uptake, holds up plant
o Thicker and varies in composition
 Microfibrils made from cellulose; polysaccharides and
other proteins
 Matrix design
 Thin primary cell wall with lamella inside (sticky pectin)
 harder cell wall or secondary cell wall (wood)
 Extracellular Matrix of Animal Cells
o Animal Cells lack walls but have ECM
o Made of secreted glycoproteins (collagen fibers outside of cell)
made from proteoglycans
o Some cells are attached to ECM by fibronectin and other ECM
proteins
o Fibronectin and ECM proteins bind to cell surface protein
receptors called integrins
o Integrins in plasma membrane span the membrane and bind to
proteins on the cytoplasmic side that are attached to
microfilaments of cytoskeleton; transmit changes between
ECM and cytoplasm; integrate changes inside and outside of
cell
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o ECM
 Regulate cell behavior (integrins)
 Can influence activity of genes in nucleus; mechanical
and chemical signaling
 Mechanical signaling: fibronectin, integrin,
microfilaments
 Changes in cytoskeleton signal chemical signaling
pathways inside the cell  change in proteins
being made by the cell  change in cell function
 Intercellular Junctions
o Plants: Plasmodesmata
 Connects inside of plant cell chemical environment
 Continuum: things pass between cells
o Animals: (6.32)
 Tight Junctions: membranes tightly pressed together
 Desmosomes: anchoring junctions; rivets fasten cells
together into sheets
 Gap Junctions: cytoplasmic channels from1 cell to
adjacent cell
WRAP UP
 Structure relates to function!
 Cellular integration (macrophage example)
o Macrophage crawls along and reaches out with pseudopodia
using actin filaments and cytoskeleton
o Engulfs bacteria and lysosomes destroy bacteria made by
endomembrane system; enzymes and proteins are made on
ribosomes and programmed from DNA in nucleus
o Need energy from mitochondria
 CELL IS LIVING UNIT GREATER THAN SUM OF ITS PARTS
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