1. Unit 2
Cells

2. Cell Structure
Plasma membrane
Cytoplasm: cytosol + organelles
Nucleus

3. Cell Membrane Phospholipid bilayer Cholesterol
Proteins (integral and peripheral)
Attached carbohydrates (glycolipids and glycoproteins)

4. Membrane Function Barrier between inside and outside of cell
Controls entry of materials: transport
Receives chemical and mechanical signals
Transmits signals between intra- and extra- cellular spaces

5. Intercellular Junctions – Connect adjacent cell membranes
Tight junctions
Close space between cells
Located among cells that form linings
Prevent movement of substances between cells
Desmosomes
Form “spot welds” between cells
Located among outer skin cells
Structural reinforcement
Gap junctions
Tubular channels between cells
Located in cardiac muscle cells
Allow ions to pass from cell to cell for communication
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6. Cell Adhesion Molecules
Guide cellular movement
Selectin – allows white blood cells to “anchor”
Integrin – guides white blood cells through capillary walls
Important for growth of embryonic tissue
Important for growth of nerve cells
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7. Terminology: Body Fluid Pools
Intracellular (ICF)
Within cells: 2/3 of total
Extracellular (ECF):
Between cells = Interstitial
In blood vessels = Plasma
In lymphatic vessels = Lymph

8. Terminology: Solutions
Solvent: Liquid doing the dissolving
Usually water
Solute: Dissolved material (particles or gas)
Concentration:
Amount of solute in a given amount of solvent
Concentration gradient:
Difference in concentration between 2 areas of solution

9. Principle of Diffusion
Copyright 2010, John Wiley & Sons, Inc.

10. Passive Transport: Simple Diffusion
Requirements:
Concentration gradient
Pathways:
Across lipid bilayer
Lipid-soluble (O2, CO2, N2, fatty acids, steroids, fat-soluble vitamins), or if
Polar molecules (H2O, urea)
Pass through Ion Channels (which may be gated: gates open and close) if
Ions such as K+, Ca2+, Cl–

11. Copyright 2010, John Wiley & Sons, Inc.
Simple Diffusion
Copyright 2010, John Wiley & Sons, Inc.

12. Facilitated Diffusion
Requires a carrier in membrane but not ATP
Solute goes DOWN concentration gradient
Maximum transport speed depends on number of carriers
Ex: Insulin increases number of carriers for glucose in plasma membrane
Copyright 2010, John Wiley & Sons, Inc.

13. Facilitated Diffusion
Copyright 2010, John Wiley & Sons, Inc.

14. Facilitated Diffusion
Copyright 2010, John Wiley & Sons, Inc.

15. Osmosis Diffusion of water across selectively permeable membrane:
Permeable to solvent
Impermeable to solute
Types of solutions surrounding human RBCs
Isotonic: solution outside RBC has same concentration of solute as RBC: 0.9% NaCl
Hypotonic: solution outside of RBC has lower concentration: 0% NaCl  Hemolysis
Hypertonic: solution outside of RBC has higher concentration: 4% NaCl  Crenation

16. Copyright 2010, John Wiley & Sons, Inc.
Osmosis
Copyright 2010, John Wiley & Sons, Inc.

17. Copyright 2010, John Wiley & Sons, Inc.
Active Transport
Requires a carrier (called a pump)
Requires energy (ATP)
Can transport UP a concentration gradient
Critical for moving important ions
Major active transport in most cells is sodium-potassium (Na+/K+) pump
Copyright 2010, John Wiley & Sons, Inc.

18. Active Transport Example: Sodium-potassium pump 1 2 3 4 3 Na+ expelled
ADP P
2 K+
imported K+
gradient
Na+
Na+/K+ ATPase
Extracellular fluid
Cytosol
2K+
ATP 2 3 4
Active Transport
Example: Sodium-potassium pump
Copyright 2010, John Wiley & Sons, Inc.
Copyright 2009 John Wiley & Sons, Inc. 18 18

19. Transport in Vesicles Requires energy (ATP)
Involves small membrane sac
Endocytosis: Importing of materials into cell
Phagocytosis: Ingestion of Particles such as bacteria into white blood cells (WBCs)
Pinocytosis: Ingestion of Fluids
Exocytosis: Exporting materials

20. Copyright 2010, John Wiley & Sons, Inc.
Transcytosis
Endocytosis followed by Exocytosis
Transports a substance rapidly through a cell
EX: HIV crossing a cell layer
Copyright 2010, John Wiley & Sons, Inc.
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21. Cell Organelles: Cytoskeleton Flagella, cilia & centrioles
Endoplasmic reticulum
Golgi apparatus
Mitochondrion
Nucleus, nucleolus, nuclear envelope
Vesicles, e.g. lysosome

22. Cytoskeleton Maintains shape of cell Positions organelles
Changes cell shape
Includes: microfilments, intermediate filaments, microtubules

23. Centrosome Structure:
Two centrioles arranged perpendicular to each other
Function: moves chromosomes to ends of cell during cell division

24. Cilia and Flagella Specialized for motion
Flagellum: single tail like structure on sperm
Propels sperm forward in reproductive tract
Cilia: in groups
Found in respiratory system: move mucus

25. Ribosomes Made within the nucleus (in nucleolus)
Sites of protein synthesis (on E.R. or freely within cytoplasm)
Consist of ribosomal RNA (rRNA) + proteins

26. Endoplasmic Reticulum (E.R.)
Structure: network of folded membranes
Functions: synthesis, intracellular transport
Types of E.R.
Rough E.R.: studded with ribosomes (sites of protein synthesis)
Smooth E.R. lacks ribosomes. Functions:
lipid synthesis
release of glucose in liver cells into bloodstream
drug detoxification (especially in liver cells)
storage and release of Ca2+ in muscle cells (where smooth E.R. is known as sarcoplasmic reticulum or SR)

27. Golgi Complex Structure: Functions:
Flattened membranes (cisterns) with bulging edges (like stacks of pita bread)
Functions:
Modify proteins  glycoproteins and lipoproteins that:
Become parts of plasma membranes
Are stored in lysosomes, or
Are exported by exocytosis

28. Small Bodies Lysosomes: contain digestive enzymes
Help in final processes of digestion within cells
Carry out autophagy (destruction of worn out parts of cell) and death of old cells (autolysis)
Tay-Sachs: hereditary disorder; one missing lysosomal enzyme leads to nerve destruction
Peroxisomes: detoxify; abundant in liver
Proteasomes: digest unneeded or faulty proteins
Faulty proteins accumulate in brain cells in persons with Parkinson or Alzheimer disease.

29. Mitochondria Structure: Function:
Sausage-shaped with many folded membranes (cristae) and liquid matrix containing enzymes
Have some DNA, ribosomes (can make proteins)
Function:
Nutrient energy is released and trapped in ATP; so known as “power houses of cell”
Chemical reactions require oxygen
Abundant in muscle, liver, and kidney cells
These cells require much ATP

30. Nucleus
Round or oval structure surrounded by nuclear envelope with nuclear pores
Contains nucleolus: makes ribosomes that pass into cytoplasm through nuclear pores
Store genetic material (DNA) in genes arranged in 46 chromosomes (the human genome containing 30,000 genes!)
DNA contains information for directing protein synthesis:

31. Protein Synthesis 2 steps: Nuclear = transcription
Cytoplasmic = translation

32. Transcription In nucleus
RNA polymerase (enzyme) transcribes DNA into RNA; complementary base pairs
C-G, G-C, T-A, A-U
Types of RNA formed:
1. Messenger RNA (mRNA)
2. Ribosomal RNA
3. Transfer RNA (tRNA)

33. Anatomy of a ChromosomeX
Telomere
Telomere
Centromere
Telomere
Telomere
Chromatid
Chromatid
Chromosome

34. Somatic Cell Division In all body cells except gametes Interphase
Period of growth and development of cell
Preparation for reproduction: DNA synthesis
Mitotic Phase = division of nucleus
karyokinesis
4 phases
Cytokinesis = division of cytoplasm
Apoptosis – orderly programmed cell “death”

35. Prophase Chromatin condenses into chromatids connected at centromeres
Centrosomes form the mitotic spindle (composed of microtubules)
Some chemotherapy drugs fight cancer cells by inhibiting formation of the mitotic spindle
Nuclear envelope and nucleolus break down

36. Metaphase
Centromeres are aligned at the center (“equator”) of the metaphase plate

37. Anaphase
Centromeres split, separating “sister chromatids” (chromosomes)
Chromosomes are pulled to opposite ends
Cytokinesis (division of cytoplasm) begins by the formation of a cleavage furrow

38. Telophase Chromosomes revert to threadlike chromatin
Nuclear envelope and nucleolus reappear
Mitotic spindle breaks up
Cytokinesis is completed

39. Cellular Diversity
Because structure determines function, cells differ in structure related to their functions.
Nerve cells may reach several feet in length to carry nerve impulses from spinal cord to toe
Microvilli increase surface area of intestinal cells to maximize absorptive ability
Most cells are microscopic; the diameter of the largest human cell (an oocyte) can barely be seen with the unaided eye.

40. Aging A number of factors contribute to aging:
Decreased rate of mitosis; nerve cells and skeletal muscle cells cannot be replaced
Telomeres (DNA at tips of chromosomes)
Telomeres shorten with aging
Progeria (rapid aging): profound telomere shortening
Free radicals damage. (See Focus on Wellness: action of antioxidants to reduce effects of free radicals.)

41. Abnormal Cell Division (cancer)
Neoplasm -tumor
Oncology – study of tumors – Oncologist
Carcinogen – cancer causing agent

42. Tumors benign – usually remains localized
Two types of tumors
benign – usually remains localized
malignant – invasive and can metastasize through the bloodstream or lymph system; cancerous
Genes that cause cancer
oncogenes – activate other genes that increase cell division
tumor suppressor gene – normally regulate mitosis; if inactivated they will not regulate mitosis
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43. Stem and Progenitor Cells
Stem cell
can divide by mitosis to form two new stem cells
can divide to form a stem cell and a progenitor cell
totipotent – can give rise to any cell type
Differentiation – process of specializing cell types due to gene activation
Progenitor cell
committed cell (i.e. epithelial, connective, muscle, nervous)
pluripotent – can give rise to a restricted number of cell types
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44. What are Stem Cells?