1. Lecture 1
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
MCAT Prep Exam
Cell Structure and
Function
1

2. Outline

Cellular Level of Organization




Prokaryotic Cells
Eukaryotic Cells






Cell theory
Cell size
Organelles
Nucleus and Ribosome
Endomembrane System
Other Vesicles and Vacuoles
Energy related organelles
Cytoskeleton

Centrioles, Cilia, and Flagella
2

3. Cell Theory
 Cell
was not discovered untill the development of
Microscope
 Detailed study of the cell began in the 1830s
 A unifying concept in biology
 States that:
All organisms are composed of cells
 All cells come only from preexisting cells
 Cells are the smallest structural and functional unit of
organisms
 Cells carry genetic information in the form of DNA

3

4. Sizes of Living Things
4

5. Cell Size
 Cells
range in size from one millimeter down to
one micrometer
 Cells need a large surface area of plasma
membrane to adequately exchange materials.
 The surface‑ area‑ to‑ volume ratio requires that
cells be small
5

6. Surface to Volume Ratio
6

7. Microscopy Today: Compound Light
Microscope
 Light
passed through specimen
 Focused
 Max
by glass lenses
magnification about 1000X
objects separated by 0.2 µm, 500X
better than human eye
 Resolves
 Resolution
is limited by the wavelength of light
(nanometer)
7

8. Compound Light Microscope
 Diaphragm
– controls
amount of light –
important for image
contrast
 Coarse
Adjustment Knob
– focuses the image
 Fine
Adjustment Knob –
finely focuses the image
8

9. Microscopy Today: Transmission
Electron Microscope
 Abbreviated
T.E.M.
 Uses
a beam of electrons to allow 100 fold higher
magnification

Because it uses beam of electrons, its resolution is at
the atomic level (picometer)
 Tissue
 Can
must be fixed and sectioned
living specimen be examined by T.E.M?
9

10. Transmission Electron Microscope
10

11. Microscopy Today: Immunofluorescence
Light Microscope
 Antibodies
developed against a specific protein
Fluorescent dye molecule attached to antibody
molecules
 Specimen exposed to fluorescent antibodies

 Ultra-violet
specimen
light (black light) passed through
Fluorescent dye glows in color where antigen is
located
 Emitted light is focused by glass lenses onto human
retina

 Allows
in cell
mapping distribution of a specific protein
11

12. Microscopy and Amoeba proteus
12

13. Cells Under the Microscope
 phase-contrast
light microscope - look at
unstained living animal cells.
 electron microscope - look at organelles
e.g. ribosomes.
 fluorescence microscope - look at a living
cell expressing green fluorescent protein or
to do confocal microscopy.

14. Autoradiography
 Radioactive
compounds decay or
transform into other compounds or
elements.
 An autoradiograph is an image on an xray film or nuclear emulsion produced by
the pattern of decay emissions (e.g., beta
particles or gamma rays) from a distribution
of a radioactive substance
 Autoradiography can also uses radioactive
molecule to study biochemical activity,
14

15. Cell Fractionation and Differential
Centrifugation
 Cell
fractionation is the breaking apart of
cellular components
 Differential
 Allows
separation of cell parts
 Separated
 Works
centrifugation:
out by size & density
like spin cycle of washer
 The
faster the machine spins, the smaller
the parts that are settled out
15

16. Cell Fractionation and Differential
Centrifugation
16

17. Eukaryotes Vs Prokaryotes
Eukaryotic Cells
Prokaryotic Cells
The cells of “complex” organisms,
including all plants, Protists, fungi and
animals
Contain a nucleus and membrane
bound organelles
“Simple” organisms, including
bacteria and cyanobacteria
(blue-green algae)
Lack a nucleus and other
membrane-encased organelles.
Can specialize for certain functions,
such as absorbing nutrients from food
or transmitting nerve impulses;
multicellular organs and organisms
Usually exist as single, virtually
identical cells
Cell Wall present in Plants and Fungi
only
Ribosome: 40s, 60S
Cell Wall
Ribosome: 30S, 50S
17

18. The Structure of Bacteria

Occur in three basic shapes:




Spherical coccus,
Rod-shaped bacillus,
Spiral spirillum (if rigid) or spirochete (if flexible).
Cell Envelope includes:


Plasma membrane - lipid bilayer with imbedded and peripheral
protein
Cell wall - maintains the shape of the cell
18

19. The Structure of Bacteria
19

20. The Structure of Bacteria
20

21. The Structure of Bacteria Cytoplasm &
Appendages

Cytoplasm

Semifluid solution





Bounded by plasma membrane
Contains water, inorganic and organic molecules, and enzymes.
Nucleoid is a region that contains the single, circular DNA
molecule.
Plasmids are small accessory (extrachromosomal) rings of DNA
Appendages



Flagella – Provide motility
Fimbriae – small, bristle-like fibers that sprout from the cell
surface
Sex pili – rigid tubular structures used to pass DNA from cell to
cell
21

22. Eukaryotic Cells

Domain Eukarya includes:


Fungi

Plants


Protists
Animals
Cells contain:

Membrane-bound nucleus that houses DNA

Specialized organelles

Plasma membrane

Much larger than prokaryotic cells

Some cells (e.g., plant cells) have a cell wall
22

23. Hypothesized Origin of Eukaryotic Cells
23

24. Eukaryotic Cells: Organelles
 Eukaryotic

cells are compartmentalized
They contain small structures called organelles
Perform specific functions
 Isolates reactions from others

 Two

classes of organelles:
Endomembrane system:

Organelles that communicate with one another



Via membrane channels
Via small vesicles
Energy related organelles
Mitochondria & chloroplasts
 Basically independent & self-sufficient

24

25. Plasma Membrane
25

26. Animal Cell Anatomy
26

27. Plant Cell Anatomy
27

28. Cytosole
 Cytosol,
contains many long, fine filaments
of protein that are responsible for cell
shape and structure and thereby form the
cell’s cytoskeleton
28

29. Nucleus
 Command
center of cell, usually near center
 Separated from cytoplasm by nuclear envelope
Consists of double layer of membrane
 Nuclear pores permit exchange between nucleoplasm
& cytoplasm

 Contains
chromatin in semifluid nucleoplasm
Chromatin contains DNA of genes, and proteins
(Histones)
 Condenses to form chromosomes


Chromosomes are formed during cell division
 Nucleolus

is a dense structure in the nucleus
Synthesize ribosome RNA (rRNA)
29

30. Anatomy of the Nucleus
30

31. Ribosomes
 Are
the site of protein synthesis in the cell
 Composed
of rRNA and protein

Consists of a large subunit and a small subunit

Subunits made in nucleolus
 May
be located:

On the endoplasmic reticulum (thereby making it
“rough”), or

Free in the cytoplasm
31

32. Nucleus, Ribosomes, & ER
32

33. Endomembrane System
 Series
of intracellular membranes that
compartmentalize the cell
 Restrict
enzymatic reactions to specific
compartments within cell
 Consists
of:

Nuclear envelope

Membranes of endoplasmic reticulum

Golgi apparatus

Vesicles

Several types

Transport materials between organelles of system
33

34. Endomembrane System:
The Endoplasmic Reticulum


A system of membrane channels and saccules (flattened vesicles)
continuous with the outer membrane of the nuclear envelope
Rough ER


Studded with ribosomes on cytoplasmic side
Protein anabolism


Synthesizes proteins
Modifies and processes proteins



Adds sugar to protein
Results in glycoproteins
Smooth ER




No ribosomes
Synthesis of lipids
Site of various synthetic processes, detoxification, and storage
Forms transport vesicles
34

35. Endoplasmic Reticulum
35

36. Endomembrane System:
The Golgi Apparatus
 Golgi
Apparatus
 Consists
of flattened, curved saccules
 Resembles
 Modifies
stack of hollow pancakes
proteins and lipids
 Receives
vesicles from ER on cis (or inner face)
 Modifies
them and repackages them in vesicles
 Release
the vesicles from trans (or outer face)

Within cell

Export from cell (secretion, exocytosis)
36

37. Golgi Apparatus
37

38. Endomembrane System: Lysosomes
 Membrane-bound
vesicles (not in plants)

Produced by the Golgi apparatus

Contain powerful digestive enzymes and are highly
acidic

Digestion of large molecules

Recycling of cellular debris and resources

Autolysis may occur in injured or dying cell to cause
apoptosis (programmed cell death, like tadpole losing tail)
38

39. Lysosomes
39

40. Endomembrane System: Summary
 Proteins
produced in rough ER and lipids from
smooth ER are carried in vesicles to the Golgi
apparatus.
 The Golgi apparatus modifies these products and
then sorts and packages them into vesicles that
go to various cell destinations.
 Secretory vesicles carry products to the
membrane where exocytosis produces
secretions.
 Lysosomes fuse with incoming vesicles and
digest macromolecules.
40

41. Endomembrane System: A Visual Summary
41

42. Peroxisomes
 Similar
to lysosomes

Membrane-bounded vesicles

Enclose enzymes that rid the cell of toxic peroxides

Participate in the metabolism of fatty acids and many
other metabolites
42

43. Peroxisomes
43

44. Vacuoles
 Membranous
sacs that are larger than vesicles
Store materials that occur in excess
 Others very specialized (contractile vacuole)

 Plants
cells typically have a central vacuole
Up to 90% volume of some cells
 Functions in:

Storage of water, nutrients, pigments, and waste products
 Development of turgor pressure
 Some functions performed by lysosomes in other eukaryotes

44

45. Vacuoles
45

46. Energy-Related Organelles:
Chloroplast Structure
 Bounded
 Inner
by double membrane
membrane infolded

Forms disc-like thylakoids, which are stacked to form
grana

Suspended in semi-fluid stroma
 Chlorophyll

Green photosynthetic pigment

Chlorophyll capture solar energy
46

47. Energy-Related Organelles: Chloroplasts

Serve as the site of photosynthesis

Captures light energy to drive cellular machinery

Photosynthesis

Synthesizes carbohydrates from CO2 & H2O

Makes own food using CO2 as only carbon source

Inorganic molecules (Energy-poor compounds) are converted to organic
molecules (energy-rich compounds)

Only plants, algae, and certain bacteria are capable of conducting
photosynthesis
47

48. Chloroplast Structure
48

49. Energy-Related Organelles: Mitochondria

Smaller than chloroplast

Contain ribosomes and their own DNA

Surrounded by a double membrane

Inner membrane surrounds the matrix and is convoluted (folds) to form
cristae.

Matrix – Inner semifluid containing respiratory enzymes

Break down carbohydrates

Involved in cellular respiration

Produce most of ATP utilized by the cell

Contain their own DNA and ribosome i.e. they are semiautonomous

Inherited from Oocyte
49

50. Mitochondrial Structure
50

51. Mitochondrial Origin Hypothesis
51

52. The Cytoskeleton
 Maintains
 Assists
 Aids
cell shape
in movement of cell and organelles
movement of materials in and out of cells
 Three
types of macromolecular fibers

Microfilament

Intermediate Filaments

Microtubules
 Assemble
and disassemble as needed
52

53. The Cytoskeleton: Actin Filaments
 Microfilament are rods of actin
 Extremely thin filaments like twisted
pearl
necklace
 Support for microvilli in intestinal cells
 Intracellular traffic control
For moving stuff around within cell
 Cytoplasmic streaming

 Function in pseudopods of amoeboid cells
 Important component in muscle contraction
53

54. The Cytoskeleton: Actin Filament Operation
54

55. The Cytoskeleton: Intermediate Filaments
 Intermediate
microtubules
 Rope-like
in size between actin filaments and
assembly of fibrous polypeptides
 Functions:

Support nuclear envelope

Cell-cell junctions, like those holding skin cells tightly
together
55

56. The Cytoskeleton: Microtubules
 Hollow
cylinders made of two globular proteins called
α and β tubulin
 Spontaneous pairing of α and β tubulin molecules
form structures called dimers
 Dimers then arrange themselves into tubular spirals
of 13 dimers around
 Assembly:


Under control of Microtubule Organizing Center (MTOC)
Most important MTOC is centrosome
 Function:



Provide framework for movement of organelle within cell
Direct separation of chromosomes during cell division (e.g.
Centrioles are composed of microtubules)
Provide locomotion and movement (e.g. flagella and cilia)
56

57. The Cytoskeleton: Microtubule Operation
57

58. The Cytoskeleton
58

59. Microtubular Arrays: Centrioles
 Short,
 One
hollow cylinders
pair per animal cell

Located in centrosome of animal cells

Oriented at right angles to each other

Separate during mitosis to determine plane of division
59

60. Cytoskeleton: Centrioles
60

61. Microtubular Arrays: Cilia and Flagella
 Hair-like
projections from cell surface that aid in
cell movement
 In eukaryotes, cilia are much shorter than flagella
Cilia move in coordinated waves like oars
 Flagella move like a propeller or cork screw

61

62. Structure of a Flagellum
62

63. Comparison of Prokaryotic and
Eukaryotic Cells
63

64. Lecture 1
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
MCAT Exam Prep
Membrane Structure
and Function
64

65. Outline
 Membrane

Models
Fluid-Mosaic
 Plasma
Membrane Structure and Function

Phospholipids

Proteins
 Plasma
Membrane Permeability

Diffusion

Osmosis

Transport Via Carrier Proteins
 Cell
Surface Modifications
65

66. Structure and Function:
The Phospholipid Bilayer
 The
plasma membrane is common to all cells
 Separates:

Internal living cytoplasmic from

External environment of cell
 Phospholipid
bilayer:

External surface lined with hydrophilic polar heads

Cytoplasmic surface lined with hydrophilic polar heads

Nonpolar, hydrophobic, fatty-acid tails sandwiched in
between
66

67. Unit Membrane
67

68. Membrane Models
 Fluid-Mosaic
Model
 Three components:
 Basic
membrane referred to as phospholipid
bilayer
 Protein molecules
 Float
around like icebergs on a sea
 Membrane proteins may be peripheral or integral


Peripheral proteins are found on the inner membrane
surface
Integral proteins are partially or wholly embedded
(transmembrane) in the membrane
 Some
have carbohydrate chains attached
 Cholesterol
68

69. The Fluid Mosaic Model
69

70. Transmembrane Proteins
70

71. Functions of Membrane Proteins

Channel Proteins:



Carrier Proteins:




Provides unique chemical ID for cells
Help body recognize foreign substances
Receptor Proteins:



Combine with substance to be transported
Assist passage of molecules through membrane
Cell Recognition Proteins:


Tubular
Allow passage of molecules through membrane
Binds with messenger molecule
Causes cell to respond to message
Enzymatic Proteins:

Carry out metabolic reactions directly
71

72. Membrane Protein Diversity
72

73. Science Focus: Cell Signaling
73

74. Types of Transport: Active vs. Passive
 Plasma
membrane is differentially (selectively)
permeable

Allows some material to pass

Inhibits passage of other materials
 Passive
Transport:

No ATP requirement

Molecules follow concentration gradient
 Active
Transport

Requires carrier protein

Requires energy in form of ATP
74

75. Passage of Molecules Across the
Membrane
75

76. Types of Membrane Transport: Overview
76

77. Types of Transport: Diffusion
A
solution consists of:
A solvent (liquid), and
 A solute (dissolved solid)

 Diffusion
Net movement of solute molecules down a
concentration gradient
 Molecules move both ways along gradient
 Molecules move from high to low
 Equilibrium:

When NET change stops
 Solute concentration uniform – no gradient

77

78. Gas Exchange in Lungs: Diffusion
Across Lung
78

79. Types of Transport: Osmosis
 Osmosis:
Special case of diffusion
 Focuses on solvent (water) movement rather than
solute
 Diffusion of water across a differentially (selectively)
permeable membrane

Solute concentration on one side high, but water
concentration low
 Solute concentration on other side low, but water
concentration high

Water diffuses both ways across membrane but
solute can’t
 Net movement of water is toward low water (high
solute) concentration

 Osmotic
pressure is the pressure that develops
due to osmosis
79

80. Types of Transport: Carrier Proteins
 Facilitated
Transport
 Small
molecules
 Can’t
get through membrane lipids
 Combine
 Follow
 Active
with carrier proteins
concentration gradient
Transport
 Small
molecules
 Move
against concentration gradient
 Combining
 Requires
with carrier proteins
energy
80

81. Types of Transport: Carrier Proteins
 Facilitated
Transport
 Small
molecules
 Can’t
get through membrane lipids
 Combine
 Follow
 Active
with carrier proteins
concentration gradient
Transport
 Small
molecules
 Move
against concentration gradient
 Combining
 Requires
with carrier proteins
energy
81

82. Types of Transport:
Membrane-Assisted Transport
 Macromolecules
transported into or out of
the cell inside vesicles
 Exocytosis
– Vesicles fuse with plasma
membrane and secrete contents
 Endocytosis
– Cells engulf substances into
pouch which becomes a vesicle
 Phagocytosis
 Pinocytosis
vesicle
– Large, solid material into vesicle
– Liquid or small, solid particles go into
 Receptor-Mediated
using a coated pit
– Specific form of pinocytosis
82

83. Cell Surface Modifications: Junctions
 Cell
Surfaces in Animals
 Junctions
Between Cells
 Adhesion

Intercellular filaments between cells
 Tight

Junctions
Form impermeable barriers
 Gap

Junctions
Junctions
Plasma membrane channels are joined (allows
communication)
83

84. Cell Surface Modifications
 Extracellular
Matrix

External meshwork of polysaccharides and proteins

Found in close association with the cell that produced
them
 Plant

Cell Walls
Plants have freely permeable cell wall, with cellulose
as the main component

Plasmodesmata penetrate cell wall

Each contains a strand of cytoplasm

Allow passage of material between cells
84