1. CH 3 - Cells: The Living Units
Section 1: Overview of the Cellular Basis of Life (p. 62)

2. Cellular Diversity Cell Diversity of Cells
- Basic structural & functional unit of living organisms.
Diversity of Cells
- Over 200 different types of human cells
- Cells vary greatly in size, shape, & function

3. Generalized Cell All human cells have some common structures
Three basic human cell parts:
1) Plasma membrane
- Flexible outer boundary
2) Cytoplasm
- Intracellular fluid containing organelles
3) Nucleus
- Control center
Even though all cells have the same basic internal parts, it’s the number & combination of those parts that gives each cell it’s specific function.

4. CH 3 - Cells: The Living Units
Section 2: The Plasma Membrane – Structure (pp )

5. Plasma Membrane: Structure
- flexible, double membrane surrounding every cell
- sometimes referred to as a “cell membrane”
- composed of lipids & proteins
- plays critical role in cellular activity
- separates intracellular fluid from extracellular fluid

6. Plasma Membrane: Structure
Phospholipids
- 75% of membrane; lipid bi-layer
- Phosphate heads; hydrophilic
- Fatty acid tails; hydrophobic
Glycolipids
- 5% of membrane
- Act as markers for cell identification
Cholesterol
- 20% of membrane
- Maintains membrane stability & flexibility

7. Plasma Membrane: Structure
Membrane Proteins
- Responsible for the specialized membrane functions
Membrane protein functions:
- Transport of molecules in/out of cell
- Act as receptors for signals to/from the cell
- Provide ability to recognize & attach to adjacent cells

8. Plasma Membrane: Structure
Transport of molecules…

9. Plasma Membrane: Structure
Sending & receiving signals…

10. Plasma Membrane: Structure
Recognizing & attaching to other cells…

11. Plasma Membrane: Structure
Membrane Junctions
- Bind individual cells w/ other cells
- Allows cells to communicate w/ others to function correctly
Three main types of junctions:
1) Tight junctions
2) Desmosomes
3) Gap junctions

12. Plasma Membrane: Structure
Tight Junctions
- Prevent fluids/most molecules from moving between cells
- Cells fused together by proteins
- Found in places where you don’t want fluids to leak out of
tissues (e.g., digestive tract, blood vessels, etc.)

13. Plasma Membrane: Structure
Desmosomes
- Act as “rivets” or “spot-welds” that anchor cells together
- Prevent cells from separating
- Reduce chances of tearing when subjected to pulling forces
- Found in areas under mechanical stress (Skin, Heart, etc.)

14. Plasma Membrane: Structure
Gap Junctions
- “Communication” junction between cells
- Hollow cylinders; allow molecules to pass from cell to cell
- Found in areas that need to move ions & other substances
between cells (Cardiac cells, Smooth muscle)

15. CH 3 - Cells: The Living Units
Section 3: The Plasma Membrane – Transport (pp )

16. Plasma Membrane: Transport
Interstitial Fluid
- water-based fluid surrounding all cells in our body
- “Soup” of amino acids, sugars, fatty acids, vitamins,
hormones, neurotransmitters, & salts
Membrane Transport
- Plasma membranes are selectively permeable
- Some molecules easily pass through; others do not
- Substances pass to/from inside of cell & interstitial fluid
Animation: Membrane Permeability

17. Plasma Membrane: Transport
Types of Membrane Transport
Passive processes
- No cellular energy (ATP) is required
Active processes
- Cellular energy (ATP) is always required
- Require specialized carrier proteins

18. Plasma Membrane: Passive Transport
Types of passive processes:
Diffusion (aka “Simple Diffusion”)
- Movement of molecules from high to low concentration
- DOWN the concentration gradient
- Molecules inherently WANT to move apart
- Speed is influenced by temperature & particle size
(Higher temps = faster diffusion; Smaller particles = faster diffusion)
Examples = Oxygen, Carbon dioxide, Fat-soluble vitamins
Animation: Diffusion

19. Plasma Membrane: Passive Transport
Types of passive processes:
Facilitated Diffusion
- Molecules move down concentration gradient
- Must have either carrier proteins or channel proteins
- Particles are either too large to pass through the bi-layer
or they are charged particles that are repelled
- Rate of diffusion is limited by number of carriers/channels

20. Plasma Membrane: Passive Transport
Types of passive processes:
Facilitated Diffusion
- Channels may be open all the time (“Leakage” channels)
- Channels may be controlled by chemical/electrical signals
(“Gated” channels)
Leakage channel
Gated channel

21. Plasma Membrane: Passive Transport
Types of passive processes:
Osmosis
- Diffusion of water thru selectively permeable membranes
- Water moves very freely through lipid bi-layers
- Water concentration determined by solute concentration
**In this case, b/c solutes cannot diffuse, water will instead. It moves from high water concentration (low solute concentration) to low water concentration (high solute concentration).

22. Plasma Membrane: Passive Transport
Importance of Osmosis
- When osmosis occurs, water enters or leaves cell
- Changes in cell volume disrupt cell function
Tonicity
- Ability of a solution to cause a cell to shrink or swell
Animation: Osmosis

23. Plasma Membrane: Tonicity
Isotonic solution
- Solution with same solute
concentration as the cytoplasm
- Cells in these solutions maintain
the same volume
- Our extracellular fluid is isotonic

24. Plasma Membrane: Tonicity
Hypertonic solution
- Solution with greater solute
concentration than cytoplasm
- Cells in these solutions lose
water & shrink (“crenate”)
- Dehydration leads to this

25. Plasma Membrane: Tonicity
Hypotonic solution
- Solution with lower solute
concentration than cytoplasm
- Cells in these solutions gain
water & can burst (“lyse”)

26. Plasma Membrane: Active Transport
Types of active processes:
Active transport
- Requires carrier proteins & ATP
- Moves molecules against concentration gradient
- Solutes “pumped” from low to high concentration
Example = Na+-K+ pump (found in all cells)

27. Plasma Membrane: Active Transport
Types of active processes:
Vesicular transport
- Requires ATP
- Cell uses vesicles (hollow capsules) to move large substances in/out
- Also called “bulk” transport

28. Plasma Membrane: Active Transport
Endocytosis:
bulk transport of substances INTO the cell
2 Types:
1) Phagocytosis
- Using pseudopods to engulf solids
- “Eating”
- Macrophages, white blood cells

29. Plasma Membrane: Active Transport
Endocytosis:
bulk transport of substances INTO the cell
2 Types:
2) Pinocytosis
- Membrane infolds, bringing in
extracellular fluid
- “Drinking”
- Nutrient absorption in small intest.

30. Plasma Membrane: Active Transport
Exocytosis:
bulk transport of substances OUT of the cell
Examples:
1) Hormone secretion
2) Neurotransmitter release
3) Mucus secretion

31. CH 3 - Cells: The Living Units
Section 4: The Cytoplasm, Organelles, & Nucleus (pp.81-95)

32. The Cytoplasm Cytoplasm
- located between the plasma membrane & nucleus
- site where most cellular activities are accomplished
Composed of:
1) Cytosol
- water w/ solutes (proteins, salts, sugars, etc.) in it
2) Organelles
- metabolic machinery of the cell
3) Inclusions
- glycogen, pigments, lipid droplets, crystals, vacuoles

33. Cytoplasmic Organelles
- “little organs”
- specialized components that perform specific jobs in cell
- work together to help cell carry out its specific function
1) Mitochondria
- Power plants of cell; provide cell with ATP
- Contain their own DNA & RNA
- Found in abundance in cells requiring huge quantities of
energy (kidney, liver, muscle, etc.)

34. Cytoplasmic Organelles
Ribosomes
- Sites of protein synthesis
- Cells are protein factories; all proteins made by the cell are built here
- May be floating freely in cytoplasm or attached to endoplasmic reticulum
Ribosomes

35. Cytoplasmic Organelles
Endoplasmic Reticulum (ER)
- Interconnected network of passageways through cell
Two Types:
a) Rough ER
- surface is studded w/ ribosomes
- make all proteins that are to be secreted by cell
- build proteins that will be incorporated into lipid bi-layer
- particularly abundant in secretory cells & liver cells

36. Cytoplasmic Organelles
Endoplasmic Reticulum (ER)
- Interconnected network of passageways through cell
Two Types:
b) Smooth ER
- surface is smooth
- involved in lipid/cholesterol/glycogen breakdown
- deals w/ detoxification of drugs & carcinogens
- builds steroid-based hormones
- abundant in liver, kidney, & intestinal cells

37. Cytoplasmic Organelles
Golgi Apparatus
- modifies, concentrates, & packages proteins
- proteins pass from ER into Golgi apparatus
- proteins placed in vesicles & transported throughout cell
Animation: Endomembrane System

38. Cytoplasmic Organelles
Lysosomes
- membranous bags containing digestive enzymes
- break down ingested bacteria, viruses, & toxins
- degrade nonfunctional organelles
- break down bone to release calcium
- destroy cells in injured tissue

39. Cytoplasmic Organelles
Peroxisomes
- membranous sacs containing oxidases/catalases
- function to detoxify alcohol
- most importantly, they neutralize free radicals (chemicals that scramble biological molecules)

40. Cytoplasmic Organelles
Cytoskeleton
- elaborate series of “rods” running throughout the cytosol
- provides a framework that supports all cellular structures
2 Main Types:
a) Microfilaments
- involved in cell motility, change in cell shape, &
endocytosis/exocytosis

41. Cytoplasmic Organelles
Cytoskeleton
- elaborate series of “rods” running throughout the cytosol
- provides a framework that supports all cellular structures
2 Main Types:
b) Microtubules
- hollow tubes that can change in shape, size, & location
- determine overall cell shape & placement of organelles

42. Cytoplasmic Organelles
Cilia
- small, hair-like extensions on the surface of cells
- move in a wavelike motion propelling substances across the surfaces of cells (cells lining the respiratory system)
Flagella
- long, tail-like extensions that rotate & propel the entire cell through a solution (sperm)

43. Cytoplasmic Organelles
12) Microvilli
- fingerlike extensions of plasma membrane
- increase surface area for absorption
- very extensive in the lining of the small intestine

44. Cytoplasmic Organelles
Nucleus
- genetic library w/ blueprints for all cellular proteins
- responds to various signals & determines type & amount of proteins to be made
- most cells have 1 nucleus
- red blood cells have no nucleus
- skeletal muscle cells have multiple nuclei

45. Cytoplasmic Organelles
14) Nuclear Envelope
- double membrane surrounding nucleus; porous
- pores regulate transport of molecules into/out of nucleus
15) Nucleoli
- spherical bodies in nucleus
- produce new ribosomes that are sent out thru pores in nuclear envelope into the cytoplasm

46. CH 3 - Cells: The Living Units
Section 5: Cell Growth & Reproduction (pp )

47. Cell Growth
Cell Cycle
- series of changes cells go through from formation to reproduction
- includes interphase & cell division/mitosis

48. Cell Growth Interphase Subphases:
- period from cell formation to beginning of cell division
- cell is essentially doing all routine activities & growing
Subphases:
1) G1 phase (Gap 1) – cell is metabolically active, building proteins, & growing vigorously
2) S phase (synthetic) – DNA replication
3) G2 phase (Gap 2) – enzymes & other proteins needed for division are made
G0 phase – only seen in cells that never divide; continue to function normally until death

49. Cell Growth Cell Division
- period of time where the cell splits into 2 smaller cells
- essential for body growth & tissue repair
- very short amount of time compared to interphase
Two distinct events:
1) Mitosis
- nuclear division
- prophase, metaphase, anaphase, telophase
2) Cytokinesis
- division of the cytoplasm

50. Mitosis Stages of Mitosis (Quick overview) Prophase
- chromosomes become visible
- nuclear envelope breaks down
- spindle fibers begin to form

51. Mitosis Stages of Mitosis Metaphase
- chromosomes line up at the cell’s equator
- spindle fibers attach to the chromosomes

52. Mitosis Stages of Mitosis Anaphase
- spindle fibers pull chromosomes to opposite poles of cell
- poles of cell itself begin to be pushed apart
- cell starts to elongate

53. Mitosis Stages of Mitosis Telophase
- begins when chromosome movement stops
- nuclear membrane forms around each set of DNA
- spindle fibers disappear
- cytokinesis can now be completed

54. Control of Cell Division
WHY cells divide…
- Cells function most efficiently at a very specific size
- when they become too large, surface area of the plasma membrane isn’t large enough to match the cell’s volume
- large cells have difficulty taking in nutrients & getting rid of wastes fast enough to maintain life
- when cells grow above the optimum size, they divide

55. Control of Cell Division
HOW cells divide…
- various factors involved in control of cell division
“Go” signals
- chemicals that respond to large cell size
- growth factors, growth hormones, cyclins
“Stop” signals
- p53 gene creates proteins that inhibit cell division (more than half of all cancers have defective p53 genes)
- contact inhibition; cell grows until it touches another cell

56. Protein Synthesis Remember… Gene - cells are protein factories
- DNA holds the information for building proteins
Gene
- segment of DNA that codes for an individual protein
- can be broken down into triplet groups (3 bases each)
- each triplet (“codon”) specifies an individual amino acid

57. Central Dogma of Genetics
Protein Synthesis
Central Dogma of Genetics
*The ultimate goal of the cell is to turn DNA into protein. In order to do that, the cell must use an intermediate step involving RNA.
Transcription
DNA → RNA → protein
Translation

58. Protein Synthesis Three main types of RNA: Messenger RNA (mRNA)
- carries the re-written instructions for building proteins from the nucleus to the ribosome
- disposable copy of the blueprint
Ribosomal RNA (rRNA)
- structural component of the ribosome
- helps to physically combine amino acids into a protein

59. Protein Synthesis Three main types of RNA: Transfer RNA (tRNA)
- carries amino acids from the cytoplasm to the ribosome
- ribosome takes amino acid; releases tRNA back into cytoplasm to pick up new amino acid

60. Protein Synthesis Steps of protein synthesis: Transcription
- process of converting (“rewriting”) DNA blueprint into
mRNA so that it can be “read” by ribosomes.
Translation
- process of converting (“translating”) mRNA into an amino
acid sequence (a.k.a. “protein”)

61. Protein Synthesis - Transcription

62. Protein Synthesis - Translation

63. Protein Synthesis Genetic Code:
- each mRNA codon specifies individual amino acids
- there are 64 letter combinations for codons & 20 different amino acids
- some amino acids have more than one codon

64. Protein Synthesis So here’s how it works…
- All proteins start with the mRNA codon “AUG”
- All proteins end with 1 of 3 mRNA codons (“UAA”, “UAG”, “UGA”)

65. Protein Synthesis
Role of Rough ER…

66. Developmental Aspects of Cells
Body cells contain the same DNA; but aren’t all identical
Cell differentiation
- Chemical signals in the embryonic stage of development channel cells down certain pathways by turning off certain genes
- Gives each cell a specific function/role within the body

67. Theories of Cell Aging Why do we get old??? Wear & Tear Theory
- various theories exist explaining why our cells age & die
Wear & Tear Theory
- over time, chemical “attacks” & free radicals have a cumulative effect, wearing the cell out
Immune System Disorders
- Autoimmune responses & progressive weakening of immune response damages cells

68. Not-so-young Katie Holmes
Theories of Cell Aging
Why do we get old???
- various theories exist explaining why our cells age & die
The Genetic Theory
- Termination of mitosis & cell aging are programmed into genes
- Number of times a cell can divide may be pre-determined
Young Katie Holmes
Not-so-young Katie Holmes