1. Chapter 6
A Tour of the Cell

2. Overview: The Importance of Cells
All organisms are made of cells
Cell structure is correlated to cellular function
All cells are related by their descent from earlier cells
There is an opinion that cell is the simplest formation that can live (but others say it’s virus)

3. Concept 6.2: Eukaryotic cells have internal membranes that compartmentalize their functions
The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic
Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells
Protists, fungi, animals, and plants all consist of eukaryotic cells

4. Comparing Prokaryotic and Eukaryotic Cells
Basic features of all cells:
Plasma membrane
Cytosol
Chromosomes (carry genes)
Ribosomes (make proteins)

5. Prokaryotic cells have no nucleus
In a prokaryotic cell, DNA is in an unbound region called the nucleoid
Prokaryotic cells lack membrane-bound organelles

6. Eukaryotic cells have DNA in a nucleus that is bounded by a membranous nuclear envelope
Eukaryotic cells have membrane-bound organelles
Eukaryotic cells are generally much larger than prokaryotic cells

7. The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of the cell

8. A Panoramic View of the Eukaryotic Cell
A eukaryotic cell has internal membranes that partition the cell into organelles
Plant and animal cells have most of the same organelles

9. ENDOPLASMIC RETICULUM (ER
LE 6-9a
ENDOPLASMIC RETICULUM (ER
Nuclear envelope
Flagellum
Rough ER
Smooth ER
Nucleolus
NUCLEUS
Chromatin
Centrosome
Plasma membrane
CYTOSKELETON
Microfilaments
Intermediate filaments
Microtubules
Ribosomes:
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome
In animal cells but not plant cells: Lysosomes
Centrioles
Flagella (in some plant sperm)

10. LE 6-9b Nuclear envelope Rough endoplasmic NUCLEUS reticulum Nucleolus
Chromatin
Smooth
endoplasmic
reticulum
Centrosome
Ribosomes
(small brown dots)
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
CYTOSKELETON
Microtubules
Mitochondrion
Peroxisome
Plasma
membrane
Chloroplast
Cell wall
Plasmodesmata
Wall of adjacent cell
In plant cells but not animal cells: Chloroplasts
Central vacuole and tonoplast
Cell wall
Plasmodesmata

11. The nucleus contains most of the DNA in a eukaryotic cell
Concept 6.3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes
The nucleus contains most of the DNA in a eukaryotic cell
Ribosomes use the information from the DNA to make proteins

12. The Nucleus: Genetic Library of the Cell
The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle
The nuclear envelope encloses the nucleus, separating it from the cytoplasm

13. Ribosomes: Protein Factories in the Cell
Ribosomes are particles made of ribosomal RNA and protein
Ribosomes carry out protein synthesis in two locations:
In the cytosol (free ribosomes)
On the outside of the endoplasmic reticulum (ER) or the nuclear envelope (bound ribosomes)

15. Ribosomes ER Cytosol Endoplasmic reticulum (ER) Free ribosomes
Bound ribosomes
Large
subunit
0.5 µm
Small
subunit
TEM showing ER
and ribosomes
Diagram of
a ribosome

16. Components of the endomembrane system:
Concept 6.4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell
Components of the endomembrane system:
Nuclear envelope
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vacuoles
Plasma membrane
These components are either continuous or connected via transfer by vesicles

17. LE 6-12
Smooth ER
Nuclear
envelope
Rough ER
ER lumen
Cisternae
Ribosomes
Transitional ER
Transport vesicle
200 nm
Smooth ER
Rough ER

18. The Endoplasmic Reticulum: Biosynthetic Factory
The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells
The ER membrane is continuous with the nuclear envelope
There are two distinct regions of ER:
Smooth ER, which lacks ribosomes
Rough ER, with ribosomes studding its surface

19. Functions of Smooth ER The smooth ER Synthesizes lipids
Metabolizes carbohydrates
Stores calcium
Detoxifies poison

20. Functions of Rough ER The rough ER Has bound ribosomes
Produces proteins and membranes, which are distributed by transport vesicles
Is a membrane factory for the cell

22. The Golgi Apparatus: Shipping and Receiving Center
The Golgi apparatus consists of flattened membranous sacs called cisternae
Functions of the Golgi apparatus:
Modifies products of the ER
Manufactures certain macromolecules
Sorts and packages materials into transport vesicles

24. Lysosomes: Digestive Compartments
A lysosome is a membranous sac of hydrolytic enzymes
Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids
Lysosomes also use enzymes to recycle organelles and macromolecules, a process called autophagy

26. Vacuoles: Diverse Maintenance Compartments
Vesicles and vacuoles (larger versions of vacuoles) are membrane-bound sacs with varied functions
A plant cell or fungal cell may have one or several vacuoles

27. Food vacuoles are formed by phagocytosis
Central vacuoles, found in many mature plant cells, hold organic compounds and water

28. LE 6-15
Central vacuole
Cytosol
Tonoplast
Nucleus
Central
vacuole
Cell wall
Chloroplast
5 µm

29. Endomembrane system
Nucleus
Rough ER
Smooth ER
Nuclear envelope

30. LE
Nucleus
Rough ER
Smooth ER
Nuclear envelope
cis Golgi
Transport vesicle
trans Golgi

31. LE
Nucleus
Rough ER
Smooth ER
Nuclear envelope
cis Golgi
Transport vesicle
Plasma
membrane
trans Golgi

32. Concept 6.5: Mitochondria and chloroplasts change energy from one form to another
Mitochondria are the sites of cellular respiration
Chloroplasts, found only in plants and algae, are the sites of photosynthesis
Mitochondria and chloroplasts are not part of the endomembrane system
Peroxisomes are oxidative organelles

33. Mitochondrion Intermembrane space Outer membrane Free ribosomes in the
LE 6-17
Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
Mitochondrial
DNA
100 nm

34. Mitochondria: Chemical Energy Conversion
Mitochondria are in nearly all eukaryotic cells
They have a smooth outer membrane and an inner membrane folded into cristae
The inner membrane creates two compartments: intermembrane space and mitochondrial matrix
Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix
Cristae present a large surface area for enzymes that synthesize ATP

35. Chloroplasts: Capture of Light Energy
The chloroplast is a member of a family of organelles called plastids
Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis
Chloroplast structure includes:
Thylakoids, membranous sacs
Stroma, the internal fluid

36. LE 6-18 Chloroplast Ribosomes Stroma Chloroplast DNA Inner and outer
membranes
Granum
1 µm
Thylakoid

37. Concept 6.6: The cytoskeleton is a network of fibers that organizes structures and activities in the cell
The cytoskeleton is a network of fibers extending throughout the cytoplasm
It organizes the cell’s structures and activities, anchoring many organelles
It is composed of three types of molecular structures:
Microtubules
Microfilaments
Intermediate filaments

38. Roles of the Cytoskeleton: Support, Motility, and Regulation
The cytoskeleton helps to support the cell and maintain its shape
It interacts with motor proteins to produce motility
Recent evidence suggests that the cytoskeleton may help regulate biochemical activities

39. Components of the Cytoskeleton
Microtubules are the thickest of the three components of the cytoskeleton
Microfilaments, also called actin filaments, are the thinnest components
Intermediate filaments are fibers with diameters in a middle range

41. Microtubules

42. Cilia and Flagella
Microtubules control the beating of cilia and flagella, locomotor appendages of some cells

43. Vesicle ATP Receptor for motor protein Motor protein Microtubule
(ATP powered)
Microtubule
of cytoskeleton

45. Microfilaments

47. Intermediate filaments

48. Microfilaments (Actin Filaments)
Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actin subunits
The structural role of microfilaments is to bear tension, resisting pulling forces within the cell
They form a 3D network just inside the plasma membrane to help support the cell’s shape

49. Microfilaments that function in cellular motility contain the protein myosin in addition to actin
In muscle cells, thousands of actin filaments are arranged parallel to one another
Thicker filaments composed of myosin interdigitate with the thinner actin fibers

50. Muscle cell Actin filament Myosin filament Myosin arm
LE 6-27a
Muscle cell
Actin filament
Myosin filament
Myosin arm
Myosin motors in muscle cell contraction

51. These extracellular structures include: Cell walls of plants
Concept 6.7: Extracellular components and connections between cells help coordinate cellular activities
Most cells synthesize and secrete materials that are external to the plasma membrane
These extracellular structures include:
Cell walls of plants
The extracellular matrix (ECM) of animal cells
Intercellular junctions

52. The Extracellular Matrix (ECM) of Animal Cells
Animal cells are covered by an elaborate extracellular matrix (ECM)
The ECM is made up of glycoproteins and other macromolecules
Functions of the ECM:
Support
Adhesion
Movement
Regulation

53. Proteoglycan complex EXTRACELLULAR FLUID Collagen fiber Fibronectin
LE 6-29a
Proteoglycan
complex
EXTRACELLULAR FLUID
Collagen
fiber
Fibronectin
Plasma
membrane
CYTOPLASM
Integrin
Micro-
filaments

54. Collagens are, in most animals, the most abundant glycoproteins in the ECM.
Collagen is the most abundant protein in the human body, making up about 25% of the total protein content.
Collagens are present in the ECM as fibrillar proteins and give structural support to resident cells.

55. Fibronectins are proteins that connect cells with collagen fibers in the ECM, allowing cells to move through the ECM.
Fibronectins bind collagen and cell surface integrins, causing a reorganization of the cell's cytoskeleton and facilitating cell movement.

56. Intercellular Junctions
Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact
Intercellular junctions facilitate this contact

57. Animals: Tight Junctions, Desmosomes, and Gap Junctions
At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid
Desmosomes (anchoring junctions) fasten cells together into strong sheets
Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells