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

2. Structure and Function of Cells
OBJECTIVES
Define the cell doctrine
Relate cell structure to function
List and describe a cell’s internal structure/function of organelles
Describe plasma membrane
Discuss how to transport material across the membrane
Explain how cells use and transform matter and energy

3. 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

4. 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

5. A eukaryotic animal cell has a nucleus and numerous small
Figure 3.1
Plasma
membrane
Cell wall
Cytoplasm
Organelles
Nucleus
A eukaryotic animal cell has a
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. 5

6. Cell Structure Reflects Cell Function
Figure 3.2
A portion of several muscle cells
of the heart
Nerve cells of the central nervous
system – carry signals over distances
Cell Structure Reflects Cell Function
Figure 3.2 Human cells vary in shape.
Red blood cells
Cells lining a tubule of a kidney 6

7. Small cells have a higher surface to volume ratio
Figure 3.3
Small cells have a higher surface to volume ratio
High surface to volume ratio promotes efficiency in
Acquisition of nutrients
Disposal of wastes
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.
Cells Remain Small to Stay Efficient 7

8. Plasma Membrane A semi-permeable lipid bilayer
Phospholipids: has polar head and nonpolar tail
Cholesterol: increases membrane strength
Proteins: various function (e.g. transport, receptor)
Carbohydrates: recognition
Plasma membrabe is very important in cell homeostasis!!!
Hydrophilic
one layer of lipids
Hydrophobic
Hydrophilic
one layer of lipids

9. 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 9

10. Molecules Cross the Plasma Membrane in Several Ways
Passive transport—does not need energy
Diffusion
Osmosis
Active transport—must use energy
Transport in bulk
Involves membranous vesicles to move larger substances
Endocytosis
Exocytosis

11. Passive Transport: Principles of Diffusion and Osmosis
Passive transport: transports a substance without using energy
Diffusion: movement of molecules from:
High concentration  Low concentration
“Down” the gradient
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

12. https://www.youtube.com/watch?v=prfMUwjobo8 Diffusion through
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. 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. 12

13. 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 ATP as energy
Example: sodium-potassium pump
expels 3 Na+ ions
imports 2 K+ ions
uses ATP

14. 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

15. 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. 15

16. Tonicity Affects Cell Volume
Tonicity: comparison of the concentration of solutes in two different fluids or environments
Q: What happens to the cell in each case?

17. 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 17

18. 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

19. Endoplasmic Reticulum (ER)
Highly folded membranous network
Two types of endoplasmic reticulum (ER)
Rough ER
Has ribosomes on surface- Protein manufacturing
Smooth ER
No ribosomes on surface- Lipid synthesis, including the synthesis of some hormones
Rough ER
Smooth ER

20. Ribosomes- site of protein synthesis
Free: floating in cytoplasm
These ribosomes synthesize proteins for use in the cell
Bound: attached to endoplasmic reticulum
These ribosomes synthesize proteins that will be exported from the cell

21. Golgi Apparatus: Refines, Packages, and Ships
Protiens are modified & packaged into vesicles and shipped to other locations

22. Vesicles Peroxisomes Lysosomes
Contain enzymes that detoxify wastes produced by the cell
Lysosomes
Contain digestive enzymes

23. Mitochondria Provide Energy
“Power plant” of the cell
Surrounded by a double membrane
Site of cellular respiration
Utilizes O2
Generates ATP

24. Fat and Glycogen: Sources of Energy
Fat cells store
Triglycerides
Long-term energy storage
Muscle and liver cells store glycogen
Carbohydrate storage
Short-term energy storage in animals

25. Structures for support and movement
Cytoskeleton
Microtubules: tiny hollow tubes of protein
Microfilaments: thin solid fibers of protein
Microtubules and microfilaments form framework that supports the cell
Centrioles
Short rod-like structures near nucleus
Play important role in cell division

26. Structures for support and movement
Cilia
Short, many
Found on cells lining airways
Flagella
Long, single
Enable spermatozoa to swim
Cilia and flagella have similar internal structure

27. 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)

28. Glucose Provides the Cell with Energy
Metabolic activities of a living cell require a lot of energy
Energy in glucose is used to generate ATP
One glucose molecule may yield 36 ATP
In absence of glucose, fats, and protein can be catabolized to generate ATP

29. 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

30. Cellular respiration
Cellular respiration: major catabolic pathway that provides energy (C6H12O6 + 6O2  6H2O + 6CO2 + energy)
Glycolysis: glucose (C6H12O6) split into two pyruvates
Pyruvate converted to 2acetyl-Co A (+ CO2 released)
Citric acid (Krebs) cycle: acetyl-CoA broken into CO2
H ions and electrons from glucose used in electron transport system to provide energy to make ATP

31. 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 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. 31

32. 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

33. Some Questions Compare and contrast prokaryotic and eukaryotic cells
Why is the rough endoplasmic reticulum rough?
What are lysosomes? Give their function.
Which organelle converts the energy stored in food to ATP?
Which cell part is important for transporting material & maintaining homeostasis within the cell?
What cells/tissue are most likely to store glycogen?
What cells/tissue store triglycerides?
What term describes the combination of all catabolic and anabolic reactions?