1. Structure and Function of Cells3
Structure and Function of Cells 1

2. Cell Doctrine All living things are composed of cells
A single cell is the smallest unit that exhibits all of the characteristics of life
All cells come only from preexisting cells

3. Cells Are Classified According to Their Internal Organization
Prokaryotic Cells
Plasma membrane
No nucleus
Cytoplasm: fluid within membrane
No true organelles
Eukaryotic Cells
Plasma membrane
Nucleus: membrane bound information center
Cytoplasm: fluid within membrane
Organelles: membrane bound structures with specialized functions
All human cells are eukaryotic

4. A eukaryotic animal cell has a large nucleus and numerous small
Figure 3.1
Plasma
membrane
Cell wall
Cytoplasm
Organelles
Nucleus
A eukaryotic animal cell has a
large nucleus and numerous small
organelles. The cytoplasm is enclosed
by a flexible plasma membrane.
Prokaryotic cells such as this bacterium
have a rigid cell wall surrounding the
plasma membrane. The genetic material is not
surrounded by a membrane, and there are no
organelles in the cell. The elongated bacterium in
the center of the photo is about to divide in two, as
its genetic material is concentrated at both ends of
the cell.
Figure 3.1 Eukaryotes versus prokaryotes. 4

5. Cell Structure Reflects Cell Function
Though eukaryotic cells are remarkably similar, there are structural differences
Examples:
Muscle cells
Contain numerous organelles providing energy needed for muscle contraction
Nerve cells
Long and thin to carry impulses over distance
Small size is efficient

6. A portion of several muscle cells of the heart ( 1,500).
Figure 3.2
A portion of several muscle cells
of the heart ( 1,500).
Nerve cells of the central nervous
system ( 830).
Figure 3.2 Human cells vary in shape.
Cells lining a tubule of a kidney
( 250). 6

7. Cells Remain Small to Stay Efficient
Small cells have a higher surface to volume ratio
High surface to volume ratio promotes efficiency in
Acquisition of nutrients
Disposal of wastes

8. One large cell. Eight small cells. Cell with microvilli
Figure 3.3
One large
cell.
Eight small
cells.
Cell with
microvilli
on one surface.
Figure 3.3 Cell size and plasma membrane shape affect surface area and volume. 8

9. Visualizing Cells with Microscopes
Cells cannot be seen without magnification
Microscopes enable visualization and study of cells
Light microscope
Magnifies up to 1000
Transmission electron microscope
Magnifies up to 100,000
Scanning electron microscope
Provides 3-D view of cell surface

10. The light microscope (LM). The transmission electron microscope (TEM).
Figure 3.4
The light microscope (LM).
The transmission electron
microscope (TEM).
Figure 3.4 Visualizing cells with microscopes.
The scanning electron
microscope (SEM). 10

11. A Plasma Membrane Surrounds the Cell
Separates a cell from its environment
Selectively permeable
Permits movement of some substances into and out of the cell, but blocks others
Enables transfer of information between environment and cell

12. A Plasma Membrane Surrounds the Cell
Plasma membrane is a lipid bilayer
Phospholipids: polar head and nonpolar tail
Cholesterol: makes membrane a bit more rigid
Proteins: provide means of transport through membrane
Carbohydrates: recognition patterns for cells and organisms
Non-rigid
Fluid mosaic

13. Extracellular environment
Figure 3.5
Extracellular environment
Carbohydrate
groups
Receptor
protein
Channel
protein
(always open)
Gated channel
Protein
(closed
position)
Figure 3.5 The plasma membrane.
Lipid
bilayer
Glycoprotein
Phospholipid
Transport
protein
Cytoskeleton
filaments
Cytoplasm
Cholesterol 13

14. Molecules Cross the Plasma Membrane in Several Ways
Passive transport—cell does not need to expend energy for this
Diffusion
Osmosis
Active transport—cell must expend energy
Bulk transport
Involves membranous vesicles to move larger substances
Endocytosis
Exocytosis

15. Passive Transport: Principles of Diffusion and Osmosis
Passive transport: transports a substance without having to expend energy
Passive transport relies on diffusion
Diffusion: movement of molecules from a region of high concentration to a region of low concentration
High concentration  Low concentration
“Down” the gradient

16. cm inches 5 2 4 3 1 2 1 10 minutes 1 hour 24 hours Figure 3.6
Figure 3.6 Diffusion. 1
10 minutes
1 hour
24 hours 16

17. Osmosis: Diffusion of Water
Osmosis: the diffusion of water across a selectively permeable membrane
Water moves from an area of low solute concentration to an area of high solute concentration
Osmotic pressure: fluid pressure required to exactly oppose osmosis

18. Diffusion of water (osmosis) Pressure-induced water movement
Figure 3.7
Osmotic
pressure
Glucose
Water
Selectively
permeable
membrane
Figure 3.7 Generation of osmotic pressure by osmosis.
Diffusion of water (osmosis)
Pressure-induced water movement 18

19. Passive Transport Moves with the Concentration Gradient
Diffusion directly through the lipid bilayer
Small uncharged nonpolar molecules
Example: O2, CO2, urea
Diffusion through protein channels in the bilayer
Some always open, others are “gated”
Example: H2O, ions
Facilitate transport (facilitated diffusion)
Membrane transport protein changes shape and transports molecule through the bilayer
Highly specific
Example: glucose

20. Facilitated transport.
Figure 3.8
Higher
concentration
Lower
concentration
Diffusion through
the lipid layer.
Lipid-soluble molecules
such as O2 and CO2
diffuse freely through
the plasma membrane.
Diffusion through
channels. Some polar
and charged molecules
diffuse through protein
channels that span the
membrane. Water is a
typical example.
Facilitated transport.
Certain molecules bind to
a protein, triggering a
change in protein shape
that transports the molecule
across the membrane.
Glucose typically enters
cells by this method.
Figure 3.8 The three forms of passive transport. 20

21. Active Transport Requires Energy
Active transport moves substances from an area of lower concentration to an area of higher concentration
Transported substance moves against the concentration gradient
Requires a membrane protein (transporter)
Requires ATP or other energy source
Example: sodium-potassium pump

22. In active transport using ATP, energy derived from the
Figure 3.9
ADP  PI
ATP
Figure 3.9 Active transport.
In active transport using ATP,
energy derived from the
breakdown of ATP is used to
change the shape of the
carrier protein.
Some carrier proteins use energy
derived from the downhill transport
of one molecule to transport another
molecule uphill. In this example, the
energy to transport the square molecules
comes from the facilitated transport of the
spearhead molecules. 22

23. Endocytosis and Exocytosis Move Materials in Bulk
Used to move larger molecules
Endocytosis: brings substances into the cell
As substance enters, it is surrounded by a membrane forming a membrane-bound vesicle
Exocytosis: expels substances from the cell
Substance is contained within a membranous vesicle, which then fuses with the membrane, releasing the substance to the external environment

24. Endocytosis. In endocytosis, material is surrounded
Figure 3.10
Extracellular environment
Plasma membrane
Cytoplasm
Vesicle
Endocytosis. In endocytosis, material is surrounded
by the cell membrane and brought into the cell.
Figure 3.10 Endocytosis and exocytosis.
Exocytosis. In exocytosis, a membranous vesicle fuses
with the plasma membrane, expelling its contents outside
the cell.
Photomicrograph showing
various stages of
endocytosis. 24

25. Information Can Be Transferred Across the Plasma Membrane
Receptor proteins span membrane—required for transmission of information to and from cell
Receptor sites (on receptor proteins)—interact specifically with signal molecules
A change is triggered within the cell as a result of binding of signal molecule to receptor site
Different cell types have different receptor proteins

26. Extracellular environment
Figure 3.11
Extracellular environment
Receptor
site
Figure 3.11 Receptor protein action.
Substrate
Product
Cytoplasm 26

27. The Sodium–Potassium Pump Helps Maintains Cell Volume
Sodium (Na+)–potassium (K+) pump expels unwanted ions (Na+), stockpiles needed ones (K+), and maintains cell volume
ATP is used to expel three Na+ for every two K+ brought into the cell
Increase in cell volume  more water in cytoplasm, accomplished by decreasing pumping and allowing more sodium inside cell
Decrease in cell volume  less water in cytoplasm, accomplished by increasing pumping and expelling more sodium ions

28. Figure 3.12a Extracellular fluid Cytoplasm
Sodium ions bind to
binding sites accessible
only from the cytoplasm. 2
Binding of three cytoplasmic
Na+ to the sodium-potassium
pump stimulates the
breakdown of ATP. 7
Na+
Most of the potassium
diffuses out of the cell,
but sodium diffuses in
only very slowly.
Na+
Na+
Na+
Na+ 3 K+
Na+
Energy released by
ATP causes the
protein to change its
shape, expelling the
sodium ions.
Na+ K+
Na+
ATP
ADP + Pi
Na+ K+
Cytoplasm
Na+
Na+ K+ K+ 6 K+
Figure 3.12a The cell membrane contains Na+-K+ pumps, and also channels that permit the rapid outward diffusion of K+ but only a slow inward diffusion of Na+.
Potassium is transported
into the cell, and the
sodium binding sites
become exposed again. 4
The loss of sodium
exposes two binding
sites for potassium. K+ K+ K+ 5
Potassium binding triggers
another change of shape.
The cell membrane contains Na+-K+ pumps, and also channels that permit the rapid outward diffusion of K+
but only a slow inward diffusion of Na+. 28

29. The rate of transport by the Na+-K+ pumps determines cell volume.
Figure 3.12b
Key:
Active transport of Na+
Sodium-potassium pump
Diffusion of K+
Diffusion of Na+
Diffusion of H2O
H2O
Na+
Na+
Na+
H2O
H2O
In the steady-state,
the rate of outward
sodium transport
equals the rate of
inward diffusion.
When the rate of
outward sodium
transport exceeds
inward diffusion,
water diffuses out
and the cell shrinks.
When the rate of
outward sodium
transport is less
than the rate of
inward diffusion,
water diffuses in
and the cell swells.
Figure 3.12b The rate of transport by the Na+-K+ pumps determines cell volume.
The rate of transport by the Na+-K+ pumps determines cell volume. 29

30. Isotonic Extracellular Fluid Also Maintains Cell Volume
Tonicity: relative concentration of solutes in two fluids
Isotonic
Extracellular and intracellular solute concentrations are equal
Cells maintain a normal volume in isotonic extracellular fluids
Regulatory mechanisms maintain extracellular fluid that is isotonic with intracellular fluid

31. Isotonic Extracellular Fluid Also Maintains Cell Volume
Variations in tonicity
Hypertonic
Extracellular solute concentration higher than intracellular solute concentration
Water will diffuse out of cell
Cell may shrink and die
Hypotonic
Extracellular solute concentration lower than intracellular solute concentration
Water will diffuse into cell
Cell may swell and burst

32. Water movement into and out of human red blood
Figure 3.13
Isotonic
Hypertonic
Hypotonic
9 grams of
salt in 1 liter
of solution
18 grams of
salt in 1 liter
of solution
Pure water
Water movement into and out of human red blood
cells placed in isotonic, hypertonic, and hypotonic
solutions. The amount of water movement is indicated
by the sizes of the arrows.
Figure 3.13 The effect of extracellular fluid tonicity on cell volume.
Scanning of electron micrographs of red blood
cells placed in similar solutions. 32

33. Nucleus Mitochondrion Lysosome Cytosol Peroxisome Centrioles
Figure 3.14
Cytosol
Semifluid gel material
inside the cell
Nucleus
Information
center for the cell.
Contains DNA
Peroxisome
Destroys cellular toxic waste
Centrioles
Microtubular structures
involved in cell division
Cytoskeleton
Structural framework
of the cell
Smooth endoplasmic
reticulum
Primary site of macro-
molecule synthesis
other than proteins
Rough endoplasmic
reticulum
Primary site of protein
synthesis by ribosomes
Golgi apparatus
Refines, packages, and
ships macromolecular
products
Figure 3.14 A typical animal cell.
Secretory vesicle
Membrane-bound
shipping container
Ribosomes
Site of protein synthesis
Mitochondrion
Produces energy
for the cell
Plasma membrane
Controls movement of materials
into and out of cell
Lysosome
Digests damaged organelles
and cellular debris 33

34. The Nucleus Controls the Cell
Function:
Contains the genetic information of the cell
Controls all of the activities of the cell
Structural features:
Double-layered nuclear membrane
Nuclear pores
Chromosomes/chromatin
Nucleolus

35. A transmission electron micrograph
Figure 3.15
Nuclear
pores
Nucleolus
Nuclear
membrane
Nuclear
membrane
Figure 3.15 The nucleus.
A transmission electron micrograph
( 6,000) of the nucleus of an animal cell 35

36. Ribosomes Are Responsible for Protein Synthesis
Site of protein synthesis
Location
Free: floating in cytoplasm
These ribosomes synthesize proteins for immediate use in the cell
Bound: attached to outer surface of endoplasmic reticulum
These ribosomes synthesize proteins that will be transported to other organelles or exported from the cell

37. Endoplasmic Reticulum (ER) Is the Manufacturing Center
Highly folded membranous network
Two types of endoplasmic reticulum (ER)
Rough ER
Has ribosomes on surface
Protein manufacturing, particularly those that will be secreted from the cell
Smooth ER
No ribosomes on surface
Lipid synthesis, including the synthesis of some hormones
Packaging of proteins and lipids for delivery to Golgi apparatus

38. Nucleus Rough ER Vesicle Smooth ER Figure 3.16
Figure 3.16 The endoplasmic reticulum (ER). 38

39. Golgi Apparatus: Refines, Packages, and Ships
Refines synthesized products
Packaging and shipping center
Products are packaged into vesicles and shipped to other locations within the cell or to the cell membrane for export

40. Smooth ER Golgi apparatus Vesicle Lysosome Secretory vesicle Plasma
Figure 3.17
Smooth ER
Golgi
apparatus
Vesicle
Lysosome
Secretory
vesicle
Figure 3.17 The Golgi apparatus.
Plasma
membrane 40

41. Vesicles: Membrane-bound Storage and Shipping Containers
Four types
1. Secretory vesicles
2. Endocytic vesicles
3. Peroxisomes
Contain enzymes that detoxify wastes produced by the cell
4. Lysosomes
Contain digestive enzymes

42. Harmless waste Residual body
Figure 3.18
Harmless
waste
Alcohol
Peroxisome
Golgi
apparatus
Cell toxic
waste
Lysosome
Residual
body
Figure 3.18 Lysosomes and peroxisomes.
Bacterium
Plasma membrane 42

43. Mitochondria Provide Energy
“Power plant” of the cell
The number of mitochondria within a cell will vary with the cell’s energy requirement
Surrounded by a double membrane
Inner membrane is highly folded
Site of cellular respiration
Utilizes O2 and produces CO2
Generates ATP

44. The structure and overall function of a mitochondrion.
Figure 3.19 O2
ADP
Nutrients
from
foodstuffs Pi
Inner
membrane
Figure 3.19 Mitochondria.
Outer
membrane
ATP
CO2
The structure and overall
function of a mitochondrion.
A photomicrograph of a
mitochondrion. 44

45. Fat and Glycogen: Sources of Energy
Triglycerides
Long-term energy storage in animals
Glycogen
Carbohydrate storage
Short-term energy storage in animals
Stored in muscle cells and liver cells

46. The Cytoskeleton Supports the Cell
Microtubules: tiny hollow tubes of protein
Microfilaments: thin solid fibers of protein
Microtubules and microfilaments form framework that supports the cell
Cytoskeleton also supports and anchors other cellular structures

47. Glycoprotein Plasma membrane Microfilaments Microtubule Golgi
Figure 3.20
Glycoprotein
Plasma
membrane
Microfilaments
Figure 3.20 The cytoskeleton.
Microtubule
Golgi
apparatus
Mitochondrion 47

48. Cilia and Flagella Are Specialized for Movement
Short, many
Found on cells lining airways
Flagella
Long, single
Enable spermatozoa to swim
Cilia and flagella have similar internal structure
Centrioles
Short rod-like microtubular structures near nucleus
Play important role in cell division

49. Figure 3.21
Microtubule
pair
Figure 3.21 Flagella. 49

50. Cells Use and Transform Matter and Energy
Metabolism: sum of all chemical reactions in an organism
Two types of metabolic pathways:
Anabolism:
Assembly of larger molecules from smaller ones
Requires energy (ATP input)
Catabolism:
Larger molecules are broken down
Releases energy (ATP output)

51. Glucose Provides the Cell with Energy
Energy in glucose is used to generate ATP
One glucose molecule may yield 36 ATP
In absence of glucose, other carbohydrates, fats, and protein can be catabolized to generate ATP
ATP is a more readily used “pocket change” form of energy.
Glucose and other fuel molecules must be “cashed in” for ATP
ATP can then be used to do cellular work

52. (carbon dioxide + water)
Figure 3.23
C6 H12 O6 + (6) O2
(glucose + oxygen)
(6) CO2 + (6) H2O
(carbon dioxide + water)
(36) ADP + (36) Pi 36
ATP
Figure 3.23 Glucose provides energy for the cell.
Anabolism
Transport
Muscle contraction 52

53. Glucose Provides the Cell with Energy
Cellular respiration: the breakdown of glucose in the presence of oxygen to yield ATP
Four stages of cellular respiration
Glycolysis
Preparatory step
Citric acid cycle
Electron transport system

54. Citric acid cycle Electron transport system Prepatory step Glycolysis
Figure 3.24
Energy
Energy
Energy
Energy
Citric
acid
cycle
Electron
transport
system
Prepatory
step
Glycolysis
Figure 3.24 Cellular respiration: An overview.
ATP
ATP
ATP 54

55. Glycolysis: Glucose Is Split Into Two Pyruvate Molecules
Occurs in the cytoplasm
Series of 10 reactions that split glucose into two molecules of pyruvic acid (pyruvate)
Requires investment of two ATP, four ATP are produced
Net ATP yield: two
High-energy electrons and hydrogen ions (H) are removed and picked up by a coenzyme NAD, forming NADH
Later in the cell respiration process, the NADH will be used to generate additional ATP

56. 2 Glyceraldehyde-3-phosphate (PGAL)
Figure 3.25
Glycolysis
1 Glucose
(6-carbon)
ATP
Energy
investment
steps
ADP
ATP
ADP
2 Glyceraldehyde-3-phosphate (PGAL)
(3-carbon)
2 NAD+
Figure 3.25 Glycolysis.
2 NADH + 2 H+
2 ADP
2 ATP
Energy-yielding
steps
2 ADP
2 ATP
2 Pyruvate
(3-carbon) 56

57. The Preparatory Step: Pyruvate Is Converted to Acetyl CoA
Pyruvate (from glycolysis) enters mitochondria
Pyruvate converted to acetyl group and CO2
High-energy electrons and hydrogen ions are removed and picked up by a coenzyme NAD, forming NADH
Acetyl group is joined to coenzyme A to form acetyl CoA
Acetyl CoA will enter citric acid cycle

58. Preparatory step Pyruvate (3-carbon) CO2 NAD NADH  H Acetyl group
Figure 3.26
Preparatory step
Pyruvate
(3-carbon)
CO2
NAD
NADH  H
Figure 3.26 The preparatory step.
Acetyl group
(2-carbon)
Coenzyme A
Acetyl CoA 58

59. The Citric Acid Cycle (Krebs Cycle) Harvests Energy
Occurs in mitochondria
Cyclic series of eight reactions which break down the acetyl CoA
Molecule (oxaloacetate) that accepts acetyl CoA is regenerated at the end of one full turn of the cycle
High-energy electrons are extracted to form NADH and FADH2
Produces two ATP and four CO2 per glucose molecule

60. Citric acid cycle Figure 3.27 Acetyl CoA CoA Acetyl group (2-carbon)
NADH
Oxaloacetate
(4-carbon)
NAD
Citric acid cycle
NAD
CO2
NADH
Figure 3.27 The citric acid cycle.
Fumarate
(4-carbon)
-ketoglutarate
(5-carbon)
CO2
NAD
FADH2
Succinate
(4-carbon)
NADH
ADP
FAD
ATP 60

61. The Electron Transport System Produces ATP
Located in inner mitochondrial membrane
Takes electrons from NADH and FADH2
Movement of electrons from one electron carrier to the next releases energy that is harvested to generate ATP
Final electron acceptor is O2, which forms water upon receiving electrons and hydrogen ions
ATP is generated by ATP synthase enzyme
Process also known as oxidative phosphorylation

62. Electron transport system ATP Synthase
Figure 3.28 H
Outer membrane H H H H H H H H H H H H H H
Inner membrane
of mitochondrion H e e e
Figure 3.28 The electron transport system and oxidative phosphorylation.
FADH2
FAD
NADH
NAD
1/2O2  2H  2e
H2O
ADP  Pi
ATP H
Electron transport system
ATP Synthase 62

63. Summary of Energy Production from Glucose
Over 20 enzyme-catalyzed reactions
Approximately 36 ATP (net) produced from each molecule of glucose
Oxygen (O2) consumed, carbon dioxide (CO2) produced
Cellular respiration: cellular process that uses O2 and produces CO2 in the process of making ATP

64. Mitochondrion Electron transport chain and oxidative phosphorylation
Figure 3.29a
2 NADH
2 ATP
to shuttle
electrons
from NADH
in cytosol to
NADH within
mitochondrion
Mitochondrion
2 NADH
6 NADH
2 FADH2
Electron
transport chain
and oxidative
phosphorylation
Glycolysis 2
Acetyl
CoA
Citric
acid
cycle 2
Pyruvate
Preparatory
step
Glucose
2 ATP
 4 ATP
 2 ATP
 about 34 ATP
to initiate
glycolysis
by substrate-level
phosphorylation
by substrate-level
phosphorylation
by oxidative
phosphorylation
Figure 3.29a Most of the ATP generated during cellular respiration is synthesized in the electron transport system.
About
36 ATP
Most of the ATP generated during cellular respiration is synthesized in the electron
transport system. 64

65. Fats and Proteins Are Additional Energy Sources
Glycogen (storage form of glucose)
Can be rapidly catabolized to glucose which then participates in cellular respiration
1% of total energy reserves
Fats: 78% of total energy reserves
Triglycerides have twice the energy of carbohydrates
Proteins: 21% of total energy reserves
Have the same amount of energy as carbohydrates

66. Acetyl CoA Preparatory step
Figure 3.30
Fats
Glycogen
Protein
Glucose
Amino acids
Carbon
backbone
NH3
Urea (waste)
Fatty acids
Glycerol
Pyruvate
Citric
acid
cycle
Acetyl
CoA
Electron
transport
system
Preparatory
step
Figure 3.30 Metabolic pathways for fats, glycogen, and proteins as sources of cellular energy.
(2)
many
ATP
ATP 66

67. Anaerobic Pathways Make Energy Available without Oxygen
Cellular respiration cannot continue in the absence of O2
Glycolysis will continue, pyruvate will build up
Pyruvate will be converted to lactic acid
Lactic acid buildup in muscles will cause a burning sensation
Two ATP produced per molecule of glucose
When O2 is available, lactic acid will be metabolized aerobically

68. Glucose Mitochondrion (Glycolysis) (2) ATP Lactic acid Pyruvate
Figure 3.31
Glucose
(Glycolysis)
(2) ATP
Lactic acid
buildup
Pyruvate
Mitochondrial
metabolism
blocked without
oxygen
Mitochondrion
Figure 3.31 Anaerobic metabolism. 68