1. Chapter 3
Cells: The Living Units

2. Cell Theory
• The cell is the basic
structural and functional
unit of life
• Organisms depend on
individual and collective
activity of cells, dictated
by subcellular structures
• Continuity of life has a
cellular basis
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3. Structure of a Generalized Cell
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4. Plasma Membrane
• Separates intracellular fluids from extracellular fluids
• Plays a dynamic role in cellular activity
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5. Fluid Mosaic Model
• Double bilayer of lipids with imbedded, dispersed
proteins
• Bilayer consists of phospholipids, glycolipids,
cholesterol and proteins
• Phospholipid bilayer has hydrophobic (in the
middle) and hydrophilic (facing the outside)
portions
• Glycolipids are lipids with bound carbohydrates
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6. Fluid Mosaic Model of Plasma Membrane
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7. Functions of Membrane Integral Proteins
• Transport –
channels or
transporters
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8. Functions of Membrane Peripheral Proteins
• Attach to inner cytoplasm
• Part of glycocalyx outer
coating as:
• Receptors
• Enzymes
• Cell identification
markers
• Intercellular linkers
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9. Cell Environment Interactions
• Membrane receptors used for:
• Contact signaling – cell recognition
• Electrical signaling – voltage-regulated “ion gates”
in nerve and muscle tissue
• Chemical signaling – neurotransmitters and
hormones
• Cell linkers anchor cells, assist in movement of cells
past one another, send signals for repair and
immunity
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10. Membrane Potential
• Voltage across
a membrane
• Resting
membrane
potential
• Ranges from Figure 3.13
–20 to –200 mV
• Results from Na+ and K+ concentration gradients
across the membrane
• Differential permeability of the plasma membrane to
Na+ and K+
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11. Membrane Transport
• The cell membrane is selectively permeable to
substances in the interstitial (extracellular) fluid
• Passive transport processes require no energy
• Active transport processes require energy
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12. Diffusion
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13. Passive Membrane Transport: Diffusion
• Simple diffusion –
movement from higher to
lower concentration
• Nonpolar, lipid-soluble
substances diffuse
directly through the cell
lipid bilayer
• Most small polar
substances must go
through integral
protein channels
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14. Passive Membrane Transport: Facilitated
Diffusion
• Large polar
molecules
(sugars)
combine with
integral protein
transporters that
aid transport
across
membrane
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15. Passive Membrane Transport: Osmosis
• Diffusion of water across a semipermeable membrane
• Occurs when the concentration of water is different on
opposite sides of a selective, water permeable membrane
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16. Effect of Membrane Permeability on Osmosis
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17. Tonicity
• Isotonic – solution has
the same solute
concentration as that of
the cell
• Hypotonic – solution has
lesser solute
concentration than that
of the cell
• Hypertonic – solution
has greater solute
concentration than that
of the cell
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18. Passive Membrane Transport: Filtration
• The passage of water and solutes through a
membrane by pressure
• Pressure gradient pushes substances from a higher-
pressure area to a lower-pressure area
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19. Active Transport (Solute Pump)
• Solutes move against a concentration gradient (uphill)
• Uses ATP to help move solutes across the membrane
• Requires integral transport proteins
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20. Types of Active Transport
• Symport system – two substances are moved across
the membrane in the same direction
• Antiport system – two substances are moved across
the membrane in opposite directions
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21. Types of Active Transport
• Primary active transport – phosphate from ATP
causes conformational change of transport protein,
which then transports substance
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22. Types of Active Transport
• Secondary active transport – as Na+ goes across
membrane, other solutes (like glucose) “piggyback”
across with it
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23. Vesicular Transport
• Transport of large particles (macromolecules) across
plasma membranes
• Exocytosis – moves substance from the cell interior to
the extracellular space
• Endocytosis – enables macromolecules to enter the cell
• Phagocytosis – engulf solids and bring them into the
cell’s interior
• Pinocytosis – engulf liquids
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24. Vesicular Transport
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25. Cytoplasm
• Cytoplasm – material between plasma membrane and
the nucleus; contains:
• Cytosol – Colloid of water with dissolved protein,
salts, sugars and other solutes
• Inclusions – large chemical substances
• Cytoplasmic organelles – metabolic machinery of
the cell
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26. Cytoplasmic Organelles
• Specialized cellular compartments with specialized
functions – division of labor
• Most are membrane - bound
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27. Cytoskeleton
• The “skeleton”
of the cell
• Consists of
microfilaments,
intermediate
filaments and
microtubules
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28. Microfilaments
• Smallest strands like a beaded necklace
• Function to change cell shape, cell movement,
endocytosis, exocytosis and support microvilli
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29. Intermediate Filaments
• Tough, insoluble protein fibers constructed like rope
• Resist pulling forces in the cell
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30. Microtubules
• Hollow tubes made of a spherical protein
• Determine the overall shape of the cell and
distribution of organelles
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31. Centrioles
• Small barrel-shaped
organelles located
near the nucleus
• Pinwheel array of
microtubules
• Organize mitotic
spindle during
mitosis
• Form the bases of
cilia and flagella
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32. Cilia
• Hairlike, motile
cellular extensions on
exposed surfaces of
certain cells
• Move substances
across cell surface
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33. Flagella
• “Tail” of
sperm cells for
cell movement
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34. Ribosomes
• Granules containing
rRNA and protein
• Site of protein synthesis
• Free ribosomes
synthesize soluble
proteins
• Membrane-bound
ribosomes synthesize
proteins to be
incorporated into
membranes
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35. Endoplasmic Reticulum (ER)
• Interconnected tubes and parallel membranes enclosing
cisterna
• Two varieties – rough ER and smooth ER
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36. Rough Endoplasmic Reticulum
• External surface studded with ribosomes
• Manufactures and transports protein containing
compounds for internal use, integral proteins of
plasma membranes and ultimately secretion
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37. Smooth Endoplasmic Reticulum
• Function to synthesis and internal transport of lipid
containing compounds
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38. Golgi Complex
• Stacked and flattened
membranous sacs
• Functions in packaging
compounds from the ER to
make:
• Secretory vesicles for
export from the cell,
plasma membrane
components or lysosomes
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39. Role of the Golgi Complex
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40. Lysosomes
• Spherical sacs containing
digestive enzymes:
• Digest ingested bacteria,
viruses or toxins
• Breakdown useless
tissue
• Degrade nonfunctional
organelles
• Cell suicide
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41. Peroxisomes
• Sacs that contain detoxifying enzymes to
detoxify harmful substances, including free
radicals – highly reactive chemicals that can
damage cells
• Ex: liver & kidney
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42. Proteasomes
• Contain proteases, enzymes that cut or degrade faulty
cellular proteins into small peptides
• 4 stacked rings around a central core
• Too small to see under a light microscope
• In both the cytosol & nucleus
• Malfunction can result in Alzheimer’s & Parkinson’s
diseases
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43. Mitochondria
• Double membrane
structure with
inner membrane
shelves called
cristae and matrix
between
• Function to
provide the cell’s
ATP via aerobic
cellular respiration
• Contain their own
DNA and RNA
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44. Nucleus
• Gene-containing control center of the cell contains
the genetic library with blueprints for nearly all
cellular proteins; dictates the kinds and amounts of
proteins to be synthesized
• Contains nuclear envelope, nucleolus and chromatin
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45. Nucleus
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46. Nuclear Envelope
• Selectively permeable double membrane barrier
containing pores
• Pore complex regulates transport of large molecules
into and out of the nucleus
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47. Nucleolus
• Dark-staining spherical body within the nucleus
• Site of ribosome production
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48. Chromatin
• Threadlike strands of
DNA
• Condense and form
barlike bodies called
chromosomes when the
nucleus starts to divide
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49. Protein Synthesis
• DNA serves as master
blueprint for protein
synthesis
• Genes are segments of
DNA carrying
instructions for a
polypeptide chain
• Triplets of nucleotide
bases form the genetic
library; each triplet
specifies coding for an
amino acid
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50. Transcription
• Occurs in the nucleus
• Transfer of information from the DNA strand to the
mRNA as mRNA is synthesized
• Each DNA triplet codes for a corresponding 3-base
sequence of RNA, called a codon
• Each codon corresponds to a DNA triplet
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51. Transcription
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52. Genetic Code
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53. Translation
• Involves all three types of RNA – mRNA, rRNA,
and tRNA
• Occurs in the cytoplasm at the ribosomes; mRNA
leaves the nucleus and goes to the ribosomes
• rRNA (part of ribosomes) is the anchoring site where
mRNA is read and tRNA brings in the various amino
acid to build a polypeptide
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54. Translation
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55. Roles of the Three Types of RNA
• Messenger RNA (mRNA) carries the genetic
information from DNA in the nucleus to the
ribosomes in the cytoplasm
• Ribosomal RNA (rRNA) is a structural component of
ribosomes and site of protein synthesis
• Transfer RNAs (tRNAs) bound to amino acids base
pair their anticodons with the codons of mRNA at the
ribosome to begin the process of protein synthesis
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56. Information Transfer from DNA to RNA
to Make Proteins
• DNA triplets are transcribed into mRNA codons
• Codons base pair with tRNA anticodons at the
ribosomes
• Amino acids are peptide bonded at the ribosomes to
form polypeptide chains
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57. Information Transfer from DNA to RNA
to Make Proteins
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58. Cell Life Cycle
• Interphase
• Growth (G1), synthesis
(S), growth (G2)
• Cell division is essential
for body growth and
tissue repair
• Mitosis (nuclear
division)
• Cytokinesis (cytoplasm
division)
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59. Interphase Parts
• G1 – normal metabolic activity and growth
• If cell gets signal to divide, then
• S (synthesis) – DNA (chromosomes) and centrioles replicate
• G2 – enzyme preparation for division
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60. DNA Replication
• The DNA double helix
unwinds into two
complementary nucleotide
chains; hydrogen bonds
between nucleotides break
• Freed nucleotide strands
serve as templates for
replication
• Complementary nucleotide
strands form: A-T; G-C
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61. Mitosis Phases
• Prophase
• Metaphase
• Anaphase
• Telophase
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62. Prophase
• Chromatin condenses into chromosomes
• Nuclear envelope and nucleolus disappear
• Centriole pairs separate and the mitotic spindle forms
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63. Metaphase
• Chromosomes cluster at the middle of the cell with
their centromeres aligned at the exact center, or
equator, of the cell
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64. Anaphase
• Sister chromatids split
• Chromosomes are pulled toward poles
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65. Telophase and Cytokinesis
• Chromosomes nearly reach poles
• New sets of chromosomes unwind into chromatin
• New nuclear membrane and nucleolus reappear
• Cytokinesis occurs at the same time
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66. Cytokinesis
• Cleavage furrow formed in late anaphase by a
contractile ring
• Cytoplasm is pinched in two as mitosis ends
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67. Aging Theories
• Mitosis ceases
• Telemeres (tips of chromosomes) lost each mitosis
• Glucose bridges to proteins
• Free radical damage
• Autoimmunity
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