1. Cells
Chapter 4

2. Cells Cells are the smallest unit of life.
Because they are so small, no one observed them until the microscope was invented. Robert Hooke was the first to describe a cell in 1665.

3. Cell Theory
Cell Theory – idea that all organisms are composed of cells.
All organisms composed of 1+ cells within which life processes occur.
Cells are the smallest living things.
Life evolved only once, 3.5 billion years ago.
Cells arise only by division of a previously existing cell.

4. Tiny Cells
Cells are usually very small because larger cells can’t function as efficiently.
Larger cells have a smaller surface area to volume ratio.

5. Cell Structure
Cells have a delicate cell (plasma) membrane surrounding them that controls permeability to water and dissolved substances.
Cholesterol
Cell identity
marker
Receptor protein
Protein channel
Phospholipid
Polar
hydrophilic
heads
Nonpolar
hydrophobic
tails
Polar areas
of protein
Phospholipids
Nonpolar areas
A semi-fluid matrix called cytoplasm fills the inside of the cell.

6. Plasma Membrane
Plasma membrane is made up of a variety of proteins in a lipid framework – the fluid mosaic model.
All cells have the same basic type of outer membrane.

7. Phospholipids The lipid layer is composed of phospholipids.
Polar phosphate group on one end.
Two nonpolar fatty acid chains on the other.

8. Phospholipid Bilayer
When lots of phospholipids are placed in water, they form a bilayer with fatty acid tails pointing in together – away from water.
Note that the layer is double – no fatty acid tails in contact with water.
Polar molecules can’t pass through nonpolar area without assistance.

10. Membrane Proteins
Proteins float in the lipid bilayer and provide channels that will allow certain molecules to pass through.

11. Cell Surface Proteins
Cell surface proteins project up from the membrane surface and may have carbohydrates or lipids attached to them.
Identify type of cell.
Binding sites for particular hormones or proteins.

12. Transmembrane Proteins
Transmembrane proteins span the entire lipid bilayer providing channels for polar ions and molecules.

13. Prokaryotic Cells Cytoplasm is not compartmentalized.
Prokaryotes include the two kingdoms of bacteria.
Bacteria are the simplest cellular organisms.
Ribosomes for protein construction are present. They are not organelles – no membrane.

14. Prokaryotic Cells Bacteria have a plasma membrane like all cells.
Cell wall (different than that found in plants or fungi)
Capsule encloses cell wall sometimes.

15. Prokaryotic Cells Bacteria have diverse array of shapes.
They can adhere in chains and masses, although the cells remain separate.

16. Eukaryotic Cells
Eukaryotes include all protists, fungi, plants, and animals.
Much larger than prokaryotic cells – complex internal compartmentalization.
Membrane bound organelles – specialized structures where particular cell processes occur.
Largest organelle is usually the nucleus.
Cells Alive!

19. Cytoskeleton
Cytoskeleton – a dense network of protein fibers which supports the shape of the cell and anchors organelles in place.

20. Cytoskeleton Three types of protein fibers make up the cytoskeleton.
Long, slender microfilaments made of actin.
Hollow tubes called microtubules made of tubulin.
Thick ropes called intermediate fibers.

21. Cytoskeleton
Cytoskeleton is important in determining the shape of an animal cell (no cell wall).
Filaments can form and dissolve quickly so the shape of an animal cell can change rapidly.

22. Nucleus
The nucleus is the control center of the cell and genetic library where hereditary information is stored.

23. Nucleus The nuclear envelope is actually 2 membranes.
Nuclear pores are depressions where the two membranes pinch together.
The pores contain many embedded proteins that permit proteins and RNA to pass into or out of the nucleus.

24. Nucleus
In bacteria and eukaryotes, all hereditary information is encoded in DNA.
In eukaryotes, the DNA is divided into several segments and is associated with protein, forming chromosomes.
The protein allows the condensing of the chromosomes during cell division.
Uncoiled, threadlike strands of DNA are called chromatin.

25. Nucleus The darkest region of the nucleus is called the nucleolus.
Ribosomal subunit assembly.
Subunits leave through nuclear pores – ribosomes are assembled in cytoplasm.

26. Ribosomes
Ribosomes read the RNA copy of a gene and uses the information to construct a protein.
Ribosomes are made up of several special forms of RNA – ribosomal RNA (rRNA) bound up with proteins.

27. Endoplasmic Reticulum – The Transportation System
Endoplasmic Reticulum - “Little net within the cytoplasm” - an extensive system of internal membranes.
Sometimes forms membrane enclosed sacs called vesicles.

28. Endoplasmic Reticulum
Carbohydrates and lipids are manufactured on the surface of the ER.
Manufacture of proteins intended for export occurs on ER that is studded with ribosomes and called rough ER.
ER with few ribosomes is called smooth ER.

29. Golgi Complex – The Delivery System
New molecules made on the ER surface are passed through the ER membrane and into flattened stacks of membranes called Golgi bodies.
Function – collection, packaging, and distribution of molecules manufactured in the cell.
Collectively Golgi bodies are called the Golgi complex.

31. Golgi Complex
Proteins & lipids manufactured on ER membranes are transported through the channels of the ER or as vesicles budded off of it and passed into Golgi bodies.
Inside Golgi bodies, carbohydrates may be attached.

32. Golgi Complex
Vesicles pinch off the Golgi and carry molecules to other parts of cell or to the plasma membrane so they can be released outside the cell.

33. Lysosomes – Recycling Centers
Lysosomes arise from the Golgi complex and contain a concentrated mix of powerful enzymes that break down macromolecules.
They act as recycling centers by digesting worn out cell components to make way for newly formed ones while recycling the proteins of the old components.

34. Lysosomes They also eliminate particles engulfed by the cell.
Enzymes that occur inside a lysosome digest cell parts that are engulfed – if not confined to the lysosome, they would digest the cell!

35. Organelles That Contain DNA
Eukaryotic cells contain some organelles derived from ancient bacteria assimilated by ancestral eukaryotes.
Mitochondria – occur in all but a few eukaryotes.
Chloroplasts – occur only in plants & some protists (algae).
Centrioles – relict organelles with no membrane that occur in all animals & most protists.

36. Mitochondria – Powerhouses of the Cell
Eukaryotic organisms extract energy from food through a complex series of chemical reactions called oxidative metabolism which takes place in mitochondria.

37. Mitochondria Mitochondria have two membranes Outer membrane is smooth
Inner membrane bent into numerous folds called cristae.
Cristae partition mitochondrion into two compartments, an inner matrix and an outer compartment – the intermembrane space.

38. Mitochondria
Mitochondria still have some of their original genes, contained in a circular, closed molecule of DNA (mtDNA).
This DNA loop contains genes that code for proteins essential to oxidative metabolism.

39. Chloroplasts – Energy Capturing Centers
All photosynthesis in plants and algae takes place within chloroplasts.
Likely derived from an ancient symbiotic bacteria.

40. Chloroplasts Two membranes, as in mitochondria.
Inner membranes are fused to form stacks of closed vesicles called thylakoids.
Light powered reactions of photosynthesis take place within thylakoids.
Stacks of thylakoids are called grana.
Interior fluid is called the stroma.

41. Chloroplasts
Like mitochondria, chloroplasts contain a circular DNA molecule containing genes that code for proteins essential to the process of photosynthesis.

42. Centrioles
Centrioles assemble microtubules from tubulin subunits in animals and most protists.

43. Centrioles Centrioles occur in pairs in the cytoplasm.
Often at right angles
Usually near nuclear envelope
Cilia and flagella are anchored by a type of centriole called a basal body.

44. Centrioles
Centrioles lack a membrane, but contain a circular DNA molecule involved in the production of structural proteins.
They resemble a type of bacteria.
May have originated as symbiotic bacteria.

45. Cell Movement
Cell motion is tied to movement of actin filaments, microtubules, or both.
Actin filaments form and dissolve quickly.

46. Cell Movement - Crawling
The arrangement of actin filaments in the cell cytoplasm allow a cell to crawl.
Motion essential to inflammation, clotting, wound healing, and the spread of cancer.
White blood cells move this way.
Produced in bone marrow, released in circulatory system, they crawl out of capillary into tissue to destroy pathogens.

47. Cell Movement
During animal cell reproduction, chromosomes move to opposite sides of a dividing cell because they are attached to shortening microtubules.
Cells pinch in two because the belt of actin filaments contracts.
Also essential for muscle contraction.

48. Flagella
Flagella are long, threadlike organelles protruding from the cell surface.
Each flagellum is anchored at a basal body and consists of 9 microtubule pairs surrounding 2 central microtubules (9+2 arrangement).
9+2 arrangement is fundamental feature of eukaryotes.
Examples: human sperm cell, many single celled organisms - used for locomotion.

50. Cilia
When flagella are very numerous and organized in dense rows they are called cilia.
Cilia have the same structure as flagella, but are usually short.
Examples: lining of human trachea to move dust and mucus out of the respiratory tract to the throat, protists such as the Paramecium.

51. Plant Cell Specializations
Vacuoles – a central storage compartment for water, sugars, ions, & pigments.
Also functions to increase surface area to volume ratio.

52. Plant Cell Specializations
Cell walls provide protection & support.
In plants, cell walls made of cellulose.
In fungi, cell walls made of chitin.
Both different from the composition of bacterial cell walls.

53. Transport Across Cell Membranes
Food particles, water, and other materials must pass into a cell, waste must be eliminated.
Water can diffuse through a membrane.
Food particles can be engulfed by membrane folding around them.
Proteins in the membrane act as doors allowing only certain molecules through.

54. Diffusion Molecules move randomly.
Random motion tends to create uniform mixtures.
Net movement of molecules toward the area where they are scarce – down the concentration gradient.
Diffusion allows O2, CO2, & nonpolar liquids to cross plasma membrane.

55. Diffusion
Diffusion – net movement of molecules from region of higher concentration to region of lower concentration.

56. Osmosis
Water molecules are small enough to pass through the plasma membrane.
Diffusion of water across the plasma membrane toward the side with more polar molecules is called osmosis.

57. Solutions Solutes are molecules dissolved in a solution.
Osmotic concentration – concentration of all molecules dissolved in a solution.
Hyperosmotic – solution with higher concentration.
Hypoosmotic – solution with lower concentration.
Isoosmotic – solutions with equal concentration.

58. Osmosis
Movement of water into a cell creates pressure – osmotic pressure.
Can cause cell to swell and burst.
Cell walls protect cells from bursting.

59. Endocytosis
Endocytosis - cells can extend their plasma membranes around food particles or liquid engulfing them in vesicles.
Phagocytosis – food
Pinocytosis – drink

60. Exocytosis
Exocytosis – the process of ridding a cell of material by discharging it from vesicles at the cell surface.

61. Selective Permeability
Endocytosis is energetically expensive.
It also is not picky – whatever is there gets engulfed.
Proteins in plasma membrane can allow only certain molecules through – selective permeability.

62. Selective Diffusion
Some channels act like open doors – if a molecule fits, it can pass through in either direction.
The concentrations tend to equalize through the process of diffusion.
Selective diffusion.

63. Facilitated Diffusion
Facilitated diffusion - most diffusion channels use a special carrier protein.
These proteins bind only to certain molecules, binding them on one side of the membrane, releasing them on the other.
This process requires no energy.

64. Facilitated Diffusion
Net movement is from region of higher concentration to lower concentration.
Just like simple diffusion, but facilitated by carrier proteins.
Facilitated Diffusion

65. Active Transport
Some channels through the plasma membrane are like closed doors – they require energy to pass through.
Active transport channels only work in one direction.
Movement of molecules from a region of lower concentration to a region of higher concentration.

66. Active Transport Two types of active transport channels.
Sodium-Potassium pump
Proton pump

67. Sodium-Potassium Pump
Sodium ions (Na+) pumped out of cell. (300/second)
Potassium ions (K+) pumped into cell.
Energy to run pump derived from ATP.
Important in nerve signal conduction.

68. Proton Pump
Proton pump – a complex channel that expends energy to pump protons (H+) across the membrane.
The pump is the key to cell metabolism – the way cells convert photosynthetic energy or chemical energy from food to ATP.
This activity is called chemiosmosis.

69. How Cells Get Information
Some cells can sense light or pressure changes.
Most use chemical or electrical signals.
Use cell surface proteins embedded in plasma membrane.
Cell’s only contact with outside world.

70. Sensing Chemical Information
Cells sense chemical information using cell surface proteins called receptor proteins.
Bind to particular molecules – no channel.
Pass information about concentration of certain molecules which may indicate the presence of another cell.

71. Sensing Voltage
Voltage sensitive channels for sodium or other ions that are usually closed.
Open in response to voltage change.
Voltage sensitive “door” contains charged amino acids.
Important in muscle & nerve tissue.