1. Cell Structure Chapter 4
A Tour of the Cell
Cell Structure
Chapter 4

2. The Fundamental Units of Life
All organisms are made of one or more cells
The cell is the simplest collection of matter that can be alive
All cells are related by their descent from earlier cells
Though cells can differ substantially from one another, they share common features 2

3. Lenses refract (bend) the light, so that the image is magnified
Biologists use microscopes and the tools of biochemistry to study cells
Most cells are between 1 and 100 m in diameter, too small to be seen by the unaided eye-Scientists use Microscopes
In a light microscope (LM), visible light is passed through a specimen and then through glass lenses
LMs can magnify effectively to about 1,000 times the size of the actual specimen
Lenses refract (bend) the light, so that the image is magnified 3

4. Light Microscopy (LM)
50 m
10 m
Fluorescence
Confocal 4

5. Three important parameters of microscope
Magnification: the ratio of an object’s image size to its real size
Resolution: the measure of the clarity of the image, or the minimum distance between two distinguishable points
Contrast: visible differences in parts of the sample 5

6. 10 m Human height 1 m Length of some nerve and muscle cells
Unaided eye
Chicken egg
1 cm
Frog egg
1 mm
Human egg
100 m
Most plant and
animal cells LM
10 m
Nucleus
Most bacteria
Mitochondrion
1 m EM
Figure 4.2 The size range of cells and how we view them
Smallest bacteria
100 nm
Super-
resolution
microscopy
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
Small molecules
0.1 nm
Atoms 6

7. Electron Microscopes
Electron microscopes (EMs) are used to study subcellular structures 7

8. 2 types of Electron Microscopes
1. Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look three-dimensional

9. 2 Types of Electron Microscopes
2. Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen
TEM is used mainly to study the internal structure of cells

10. Electron Microscopy (EM)
Longitudinal section
of cilium
Cross section
of cilium
Cilia
Transmission electron
microscopy (TEM)
2 m
Scanning electron
microscopy (SEM) 10

11. History of the Microscope
Invention & development of the microscope enabled scientists to discover the cell
Simple Microscopes:
The microscope van Leeuwenhoek used is considered a simple light microscope because it contained one lens and used natural light to view objects
Light Microscopes:
The microscope Hooke used to look at thin slices of cork

12. Cell Discovery through Microscopes
Robert Hooke-the first to observe cells;built a microscope and looked at cork cells from the bark of a tree “coined the term cells” (1665)
Van Leeuwenhoek-observed the first living cells from pond water-protists. He called them (animalcules) & scraped tarter from his teeth
1838-Schleiden-botanist-all plants are made of cells
1839-Schwann-zoologists-all animals made of cells
10 yrs later-Virchow ( )-all cells come from cells—Cell Theory

13. Cell Theory
1. All living organisms are composed of one or more cells 2. Cells are the basic units of structure and function in an organism 3. Cells come only from the reproduction of existing cells

14. Comparing Prokaryotic and Eukaryotic Cells
The basic structural and functional unit of every organism is one of two types of cells:
Prokaryotic Cells: Organisms of the domains Bacteria and Archaea
Eukaryotic Cells: Protists, fungi, animals, and plants 14

15. Comparing Prokaryotic and Eukaryotic Cells
Basic features of all cells
Plasma membrane (phospholipids)
Semifluid substance called cytosol
Chromosomes (carry genes)
Ribosomes (make proteins) 15

16. Pili: (Fimbriae: attachment pili)
Nucleoid
Ribosomes
Plasma membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 m
Flagella
(a) A typical rod-shaped
bacterium
(b) A thin section through
the bacterium Bacillus
coagulans (TEM)
Figure 4.4 A prokaryotic cell 16

17. Prokaryotic cells are characterized by having:
No nucleus
DNA in an unbound region called the nucleoid
No membrane-bound organelles
Cytoplasm bound by the plasma membrane 17

19. Eukaryotic Cells Eukaryotic cells are characterized by having
DNA in a nucleus that is bounded by a membranous nuclear envelope
Membrane-bound organelles
Cytoplasm in the region between the plasma membrane and nucleus
Eukaryotic cells are generally much larger than prokaryotic cells 19

20. ENDOPLASMIC RETICULUM (ER) Nuclear envelope Smooth ER NUCLEUS
Nucleolus
Flagellum
Rough ER
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate
filaments
Ribosomes
Microtubules
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome 20

21. Rough endoplasmic Nuclear envelope reticulum Nucleolus
Smooth endoplasmic
reticulum
Chromatin
NUCLEUS
Ribosomes
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
CYTO-
SKELETON
Microtubules
Mitochondrion
Peroxisome
Plasma membrane
Chloroplast
Cell wall
Plasmodesmata
Wall of adjacent cell 21

22. In animal Cells but not plant cells:
In plant cells but not animal cells:
1. Lysosomes
2. Centrosomes with centrioles
3. Flagella (but present in some plant reproductive cells)
1. Chloroplast
2. Central Vacuole
Cell Wall
Plasmodesmata

23. 3 Features All Cells have in Common:
All cells have an outer boundary, inner substance, and a control region: 1. Plasma membrane: the delicate skin of lipids with embedded protein molecules 2. Nucleoid Region or Nucleus-the brain of the cell 3. Cytoplasm: region within the plasma membrane that is fluid based

24. 1. Plasma Membrane Cells outer boundary AKA Cell Membrane
Covers a cells surface and acts as a barrier between the inside and outside of the cell
All material enter and exit through here
Phospholipid bilayer with globular proteins embedded (proteins may be markers, transporters or receptors)

26. 2. Cytoplasm
A semi-fluid matrix (gel-like) that contains sugars, amino acids, and proteins; organelles are suspended within it
The Cytosol is the part of the cytoplasm that includes molecules and small particles like ribosomes, but do not include membrane-bound organelle.

27. 3. Nucleoid Region or Nucleus
Control center; a membrane bound organelle that contains a cell’s DNA
Center of the cell (usually); most prominent structure
Most eukaryotes have a single nucleus, but fungi and some other groups have many nuclei.

28. Organelles
Eukaryote cells have a variety of internal membranes that divide the cell into compartments called organelles or little organs
Well-defined, intracellular bodies that perform specific functions for the cell
They carry out cellular processes

29. Bacteria Cell Walls
Strong cell wall made of peptidoglycan, a carbohydrate matrix (polymer of sugars)
All bacteria is classified by into 2 types based on their cell wall:
1. Gram-positive bacteria
2. Gram-negative bacteria

30. Gram Staining Procedures
Gram-positive bacteria have a thick, single layered cell wall that stains violet
Gram-negative bacteria have a multi-layered cell layer and does not stain purple, but a pinkish red
The susceptibility of bacteria to antibiotics depends on the structure of the cell wall. Penicillin and vancomycin interfere with the ability of bacteria to cross-link the peptide units that hold the carbohydrate chain of the walls together. The matrix no longer prevents water from rushing in, swelling the cell and bursting.
See Notes

31. Bacterial Cell Wall Function
Protect the cell
Maintain the cell’s shape
Prevents excessive uptake of water
Some bacterial cell walls are covered with a polysaccharide-this helps the bacteria to stick to substances like teeth, skin, and food
Some bacteria secrete a jellylike capsule

32. Bacterial Flagella
Flagella are long threadlike structures that protrude from the surface of a cell
They are used for locomotion & feeding
Bacteria swim by rotating their flagella (rotary motor)
They are made of protein
Bacteria may have one flagellum or many flagella (depends on the species)

33. Interior Organization of a Bacterial Cell
Cytoplasm (no support structures)
A few ribosomes (but no other membrane bound organelles) make protein
Plasma (cell) membrane-controls what goes in and out of bacterium
Nucleoid: area within cytoplasm where DNA is located
Flagella: whip-like tail (with Rotary motor)
Pili: hairlike growths on the outside of the cell

35. Eukaryotic Cells More complex than prokaryotic cells
Many membrane organelles; functions important for cell division
Made of tiny organelles/little organs
-Nucleus Region - Cytoskeleton
-ER Region -Centriole
- Lysosome - Mitochondria
- Vacuole - Golgi Apparatus
Vacuoles- large membrane sacs that store proteins, pigments, wastes (plant cells)
Vesicles-small sacs that store and transport materials for plant and animals cells
Nucleus contains chromosomes which are made of DNA
Cytoskeletal structures
Plant cells have a cell wall made of cellulose

38. Cell Organelles and Features

39. Plasma membrane AKA: cell membrane; has several functions
Allows only certain molecules to enter or leave the cell
It separates internal metabolic reactions from external conditions & Allows the cell to excrete waste & interact with its environment
Made of phospholipids with embedded proteins

41. Nucleus “Control Center”
Nucleus controls most of the functions in eukaryote cells
Filled with a jellylike liquid called nucleoplasm holds the contents in place
The nucleus is surrounded by a double membrane called the nuclear envelope
Covering the surface of the nuclear envelope are tiny protein-lined holes called nuclear pores. They provide passageways for RNA and other materials to enter and leave the nucleus

42. Nucleus “Control Center”
The nucleolus is the site where DNA concentrated by processing ribosomes
DNA in the form of thread-like materials is called chromatin. Before the cell divides, chromatin changes to chromosomes

44. Close-up of nuclear envelope Chromatin Nucleus Nucleolus Chromatin
Inner membrane
Outer membrane
Nuclear pore
Rough ER
Pore
complex
Figure 4.8a The nucleus and its envelope (part 1: detail of art)
Ribosome
Close-up
of nuclear
envelope
Chromatin 44

45. Mitochondria
Transfer energy from organic molecules to adenosine triphosphate (ATP)
High active cells (muscle cells) have hundreds of mitochondria
Low active cells (fat storage cells) have few mitochondria
Mitochondria have their own DNA-contains genes that make proteins needed for cellular respiration
Mitochondria can divide-but also involves nuclear enzymes

46. Parts of the Mitochondria
Double membrane:
1. Outer Membrane: separates the mitochondrion from the cytosol
2. Inner Membrane: has many folds called cristae
Cristae contain proteins that carry out energy-harvesting chemical reactions
The matrix (fluid) is inside the inner membrane
This is were cellular respiration occurs-glucose is metabolized into ATP (energy molecules)

49. Ribosomes “Protein Makers”
Where amino acids are assembled to make proteins
Has 2 subunits: a large and a small
Subunits are made of ribosomal RNA (rRNA) and protein
The subunits are made in the nucleolus then move through the nuclear pores to the cytoplasm
The subunits assemble when mRNA is present (mRNA carries the DNA code)
Ribosomes on the ER make protein to be exported
Ribosomes in the cytoplasm make proteins to used within the cell

51. Endoplasmic Reticulum “Highway”
A system of membranous tubes and sacs called cisternae (sis-TUHR-nee)
Functions as an intracellular highway or path that molecules move from one part of the cell to another
It is a Network of internal membranes made of a lipid bilayer embedded with proteins

52. 2 Types of ER
1. Rough ER: interconnected flattened sacs covered with proteins; the ER transports the newly made protein Ex: Ribosomes on the rough ER make digestive enzymes that accumulate inside the ER. Distributes Vesicles: little sacs that pinch off from the ends & store them until they are released from the cell

53. 2 Types of ER
2. Smooth ER: lacks ribosomes; contain very little smooth ER
contain enzymes involved in making carbs and lipids
Ex: 1. In ovaries & testes: makes steroid hormones estrogen and testosterone
2. In skeletal & heart muscle: releases calcium
3. Abundant in liver, kidney cells to help detoxify drugs & poisons ( long-term use causes more smooth ER)

54. Functions of Smooth ER The smooth ER Synthesizes lipids
Metabolizes carbohydrates
Detoxifies drugs and poisons
Stores calcium ions 54

55. Smooth ER Rough ER Nuclear envelope ER lumen Cisternae Ribosomes
Transitional ER
Transport vesicle 55

57. Liver Cell

58. 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 58

59. Golgi Apparatus
The sacs nearest the nucleus receive vesicles from the ER containing newly made proteins or lipids
Vesicles travel from 1 part of the Golgi body to the next transporting substances as they go
Proteins get “address labels” that direct them to other parts of the cell
Protists may have 1, animal cells 20 or more, plant cells have several hundred
Very abundant in glandular cells that manufacture and secrete substances
They collect, package, and distribute molecules made in one place but used in another place (proteins & lipids from ER-converts them to glycolipids & glycoproteins)

60. cis face (“receiving” side of Golgi apparatus) Cisternae trans face
Figure 4.11a The Golgi apparatus (part 1: detail of art)
trans face
(“shipping”
side of Golgi
apparatus) 60

61. Made at a ribosome
Released into the rough ER
Transport vesicle buds of the ER & carries the protein to the Golgi Apparatus
The Golgi packages the protein with sugar
A secretory vesicle buds off the Golgi and carries the protein to the cell membrane for export

63. Lysosomes “suicide sacs”
Digestive vesicles
Arise from the Golgi
Contain enzymes that can digest carbs, proteins, lipids and nucleic acids
Break down worn out organelles and recycle molecules
In White Blood cells they phagocytize bacteria
Can merge with food vesicles and digest food

65. Other Vesicles Enzyme-bearing, membrane-enclosed vesicles
Found in the cells of plants, animals, fungi, and protists
2 types:
1. glyoxysome: specialized peroxisomes; found in seeds of some plant cells; contain enzymes that convert fats to carbs.
2. peroxisomes: contain catalase enzymes, which convert hydrogen peroxide into water and oxygen; Similar to lysosomes

67. Cytoskeleton Made of protein fibers that assemble and disassemble
Support the shape of the cell
Anchor organelles to fixed locations
Functions based on 3 structural elements
1. Microtubules
2. Microfilaments
3. Intermediate Filaments

69. 3 Types of Cytoskeleton
Microtubules: Hollow tubes made of a protein called tubulin which consist of 2 slightly different subunits
Function:
1. holds organelles in place
2. maintain a cells shape
3. acts as tracks that guide organelles and molecules as they move within the cell

70. 3 Types of Cytoskeleton
Microfilaments (Actin Filaments): long threads of protein actin that are linked end to end & wrapped around each other like two strands of a rope
Function:
1. Contribute to cell movement (crawling, or swim)

71. 3 Types of Cytoskeleton
Intermediate Filaments: are rods that anchor the nucleus and other organelles to their places in the cell
They maintain internal shape of the nucleus
Found in : hair-follicles (produce large quantities which makes up most of the hair shaft)

72. Cell Movement Cell Crawling:
Essential to inflammation, clotting, wound healing, and spread of cancer
Gel-sol state: some regions of cell (perimeter)are rigid (gel); some (interior)are fluid (sol)
To crawl, the cell creates a weak area in the gel perimeter and forces the sol through the weak area forming pseudopods (false feet)-cytoplasm oozes in that direction

73. Cell Movement Cell Swimming: Flagella: Long, whip-like tail (sperm)
In Eukaryotes: flagella (different from prokaryotes

74. Cell Movement Cell Swimming: Cilia: Short, hair-like projections
Organized in rows
Move mucus in
respiratory passage,
Move egg in
fallopian tube

76. Centrioles Barrel- shaped organelles in animals & protists
Occur in pairs: usually at right angles to one another and situated in the cytoplasm near the nuclear envelope
Usually near the nucleus
The region around them is called the centrisome
Some centrioles have DNA which makes structural protein
Centrioles help to organize microtubules and are found in areas called microtubule-organizing centers Replicate and move to opposite ends of the cell during mitosis (cell division)

79. Plant Cells
Have 3 additional structures that are important to plant function
1. Cell Walls
2. Large Central Vacuoles
3. Plastids
Large central vacuole: stores water, ions, and sugars

82. Plants lifestyle Differ from Animals
Plants make their own carbon-containing molecules directly from carbon taken from the environment
Plant cells take carbon dioxide gas from the air and process it as photosynthesis (convert carbon dioxide & water into sugars

83. Cell Wall A ridged layer that lies outside the cell’s plasma membrane
Contain a carbohydrate called cellulose
Pores in the cell wall allow water, ions, and some molecules to enter and exit the cell

84. Cell Walls: made of cellulose; protect and support plant cell
Primary cell wall-laid down while cell is growing
Middle lamella-sticky substance that glues cells together
Secondary walls: are deposited inside the primary walls in some plants

85. Central Vacuole
Is a large, fluid filled organelle that stores water, enzymes, metabolic waste, and other materials
Forms as smaller vacuoles fuse together
Make up 90% of the plant cell’s volume & can push all other organelles into a thin layer against the plasma membrane

87. Other Vacuoles Other vacuoles store toxic materials
Ex: Acacia Trees store poisons that provide a defense against plant-eating animals
Ex: Tobacco plant cells store the toxic nicotine in a storage vacuole
Other vacuoles store plant pigments like the pigment found in rose petals

88. Plastids
Surrounded by a double membrane & have their own DNA (like mitochondria)
Several types of plastids
1. Chloroplasts
2. Chromoplasts
3. Leucoplasts:

90. 1. Chloroplasts “Photo synthesizers”
Carry out photosynthesis; manufacture own food
Contain photosynthetic pigment chlorophyll that gives most plants their green color
Double membrane
Have their own DNA

91. Bodies of Chloroplast
Each chloroplast contains a system of flattened membranous sacs called thylakoids; contain the green pigment chlorophyll (absorbs light & captures light energy for the cell)
The stroma is an area inside of the chloroplast where reactions occur and starches (sugars) are created; fluid matrix
One thylakoid stack is called a granum
Outer & inner membranes: lie close to each other

94. 2. Chromoplasts
Are plastids that contain colorful pigments that may or may not take part in photosynthesis
Ex: carrot root cells contain chromoplasts filled with orange pigment carotene
Chromoplasts in flower petal cells contain red, purple, yellow or white pigments

95. Other Plastids
Leucoplasts: starch (white) storage sites in root cells and other plant cells
A leucoplast that stores starch is sometimes called an amyloplast

96. Comparing Cells Plant Cell have a Cell Wall
Plant Cells contain a large central vacuole
Plant cells contain a variety of plastids