1. CELLS: THE LIVING UNITS
Human Anatomy & Physiology
Chapter 3 (Pages )

2. Generalized Cell Cell – structural unit of all living things
All cells have some common structures and functions
Human cells have three basic parts:
Plasma membrane - flexible outer boundary
Cytoplasm - intracellular fluid containing organelles
Nucleus - control center

3. Types of Cells in the Human Body Erythrocytes Fibroblasts
Epithelial cells
Nerve cell
Fat cell
Sperm
Skeletal muscle
cell
Smooth
muscle cells
Macrophage
Figure 3.1

4. Cytoskeleton Nucleolus Nucleus Smooth endoplasmic Plasma membrane
Ribosomes
Rough
endoplasmic
reticulum
Nucleus
Golgi apparatus
Nucleolus
Smooth endoplasmic
Cytosol
Lysosome
Mitochondrion
Cytoskeleton
Plasma
membrane
Figure 3.2

5. Plasma Membrane Fluid mosaic model
Thin, double layer of lipid molecules with proteins plugged into it
Regulates what goes into and out of cell
Separates intracellular fluid (ICF) from extracellular fluid (ECF)
Interstitial fluid (IF) = ECF that surrounds cells

6. Extracellular fluid Cholesterol Polar head of phospholipid molecule
Glycolipid
Integral
proteins
*Red model*
Lipid bilayer
Peripheral
proteins
Nonpolar
tail of
phospholipid
molecule
Cytoplasm
Figure 3.3

7. Membrane Lipids 75% phospholipids (lipid bilayer) 5% glycolipids
Phosphate heads: polar and hydrophilic
Fatty acid tails: nonpolar and hydrophobic
(Fig. 2.16b)
5% glycolipids
20% cholesterol

8. Membrane Proteins Integral proteins Peripheral proteins
Firmly inserted into the membrane
Transport proteins
Channels – small water-soluble molecules
Carriers – bind large substances and move it through membrane
Enzymes – speeds up rate of reaction
Receptors - relay message to interior of cell
Peripheral proteins
Loosely attached to integral proteins
Enzymes, motor proteins, cell-to-cell links, provide support on intracellular surface

9. Transport A protein (left) that spans the membrane
may provide a hydrophilic channel across
the membrane that is selective for a
particular solute. Some transport proteins
(right) require ATP as an energy source
to actively pump substances across the
Membrane
>when might the latter happen?
Figure 3.4a

10. Receptors for signal transduction
Some hormones and other chemical
messengers require a membrane protein
That can carry their signal from the outside
of the cell to the inside
Receptor
Figure 3.4b

11. Membrane Transport Plasma membranes are selectively permeable
Some molecules easily pass through the membrane; others do not
-water v. glucose

12. Types of Membrane Transport
Passive processes
No cellular energy (ATP) required
Substance moves down its concentration gradient
Simple Diffusion, Facilitated Diffusion, Osmosis
Active processes
Energy (ATP) required
Occurs only in living cell membranes
Active Transport, Vesicular Transport

13. Passive Processes Simple Diffusion
Nonpolar lipid-soluble (hydrophobic) substances diffuse directly through the phospholipid bilayer O2
CO2
Fat-soluble vitamins
Figure 3.7a

14. Passive Processes 2) Facilitated Diffusion
molecules (e.g., glucose, amino acids, and ions) use
protein carriers in the membrane to ferry across
Channel proteins filled with water
Carrier-mediated facilitated diffusion
Channel-mediated facilitated diffusion
Figure 3.7

15. Passive Processes 3) Osmosis
Movement of solvent (water) across a selectively permeable membrane
Important because change in cell volume disrupts cell function
Water
molecules
Lipid
billayer
Aquaporin
Figure 3.7d

16. Summary of Passive Processes
Energy Source
Example
Simple diffusion
Concentration gradient
Movement of O2, CO2, fats through phospholipid bilayer
Facilitated diffusion
Movement of glucose and some ions into cells
Osmosis
Movement of H2O through phospholipid bilayer or Aquaporins
Also see Table 3.1 on page 72

17. Active Processes Active Transport (Primary)
Requires carrier proteins (solute pumps)
Uses ATP to move solutes against their concentration gradient
Energy from ATP causes shape change in transport protein so that bound solutes (ions) are “pumped” across the membrane
Example:
Sodium-potassium pump (Na+-K+ ATPase)

18. Active Processes 2. Vesicular Transport
Transport of large particles, macromolecules, and fluids across plasma membranes inside membranous sacs called vesicles
Types:
Exocytosis - transport out of cell
Endocytosis - transport into cell
Phagocytosis
Pinocytosis
Receptor-Mediated Endocytosis

19. Exocytosis
Substance enclosed in a membranous vesicle which fuses with the plasma membrane and ruptures, releasing the substance to the exterior
Examples:
Hormone secretion
Neurotransmitter release
Mucus secretion
Ejection of wastes

20. The Process of Exocytosis
Extracellular
fluid
Plasma membrane
Fusion pore formed
Secretory
vesicle
The membrane-
bound vesicle
migrates to the
plasma membrane. 1
Vesicle
The vesicle
and plasma
membrane fuse
and a pore
opens up 3
Molecule to
be secreted
Cytoplasm
Proteins
at the vesicle
surface bind with
plasma membrane
proteins 2
Vesicle
contents are
released to the
cell exterior 4
Fused
proteins
Figure 3.14a

21. Endocytosis
Phagocytosis - pseudopods engulf solids and bring them into cell’s interior
Engulf bacteria, cell debris, inanimate particles – asbestos fibers, glass
Macrophages and some white blood cells
Figure 3.13a

22. Endocytosis
Pinocytosis (fluid-phase endocytosis) - plasma membrane infolds, bringing extracellular fluid and solutes into interior of the cell
Nutrient absorption in the small intestine, solute absorption in kidney
Vesicle
Figure 3.13b

23. Endocytosis
Receptor-Mediated Endocytosis – extracellular substances bind to specific receptor proteins, enabling the cell to ingest and concentrate specific substances in vesicles
Vesicle
Receptor recycled
to plasma membrane
Figure 3.13c

24. Summary of Active Processes
Energy Source
Example
Primary active transport
ATP
Pumping of ions across membranes
Phagocytosis
White blood cell phagocytosis
Pinocytosis
Absorption by intestinal cells
Receptor-mediated endocytosis
Hormone and cholesterol uptake
Exocytosis
Secretion of hormones and neurotransmitters
Also see Table 3.2 on page 77

25. Cytoplasm Located between plasma membrane and nucleus Cytosol
Water with solutes (protein, salts, sugars, etc.)
Cytoplasmic organelles
Metabolic machinery of cell

26. Mitochondria Double-membrane structure w/ shelflike cristae
Site of cellular respiration
Provide most of cell’s
ATP via aerobic
cellular respiration
Contain their own
DNA and RNA
Enzymes
Matrix
Cristae
Mitochondrial
DNA
Ribosome
Outer
mitochondrial
membrane
Inner

27. Ribosomes Granules containing protein and rRNA
Site of protein synthesis
Free ribosomes synthesize soluble proteins
Membrane-bound ribosomes (on rough ER) synthesize proteins to be incorporated into membranes or exported from the cell

28. Endoplasmic Reticulum (ER)
Interconnected tubes and parallel membranes
Continuous with nuclear membrane
Two types:
Rough ER
Smooth ER

29. Nuclear
envelope
Ribosomes
Rough ER
Smooth ER
Figure 3.18a

30. Rough ER External surface studded with ribosomes
Manufactures all secreted proteins
Synthesizes membrane integral proteins and phospholipids
Proteins then go to Golgi Apparatus
Abundant in liver cells, secretory cells

31. Smooth ER Tubules arranged in a looping network
Enzyme (integral protein) functions:
In the liver—lipid and cholesterol metabolism, breakdown of glycogen, and, along with kidneys, detoxification of drugs, pesticides, and carcinogens
Synthesis of steroid-based hormones
In intestinal cells—absorption, synthesis, and transport of fats
In skeletal and cardiac muscle—storage and release of calcium

32. Golgi Apparatus Stacked and flattened membranous sacs
Modifies, concentrates, and packages proteins and lipids
Transport vessels from ER fuse with Golgi apparatus
Proteins then pass through Golgi apparatus to shipping side
Secretory vesicles leave Golgi stack and move to designated parts of cell

33. Golgi Apparatus & Proteins
containing
vesicles pinch
off rough ER
and migrate to
fuse with
membranes of
Golgi
apparatus 1
Rough ER ER
membrane
Phagosome
Plasma
mem-
brane
Proteins in
cisterna
Pathway C:
Lysosome containing
acid hydrolase
enzymes
Proteins are
modified within
the Golgi
compartments 2
Vesicle becomes
lysosome
Proteins are
then packaged
within different
vesicle types,
depending on
their ultimate
destination 3
Secretory
vesicle
Golgi
apparatus
Pathway B:
Vesicle membrane
to be incorporated
into plasma
membrane
Pathway A:
Vesicle contents
destined for exocytosis
Secretion by
exocytosis
Extracellular fluid
Figure 3.20

34. Lysosomes Spherical membranous sacs containing digestive enzymes
Digest ingested bacteria, viruses, and toxins
Degrade nonfunctional organelles
Break down and release glycogen
Break down bone to release Ca2+
Destroy cells in injured or nonuseful tissue (autolysis)

35. Cytoskeleton Elaborate series of rods throughout cytosol Microtubules
hollow tubes
determine overall shape of cell and distribution of organelles
Microfilaments
actin strands attached to plasma membrane
involved in cell motility, change in shape, endocytosis and exocytosis
Intermediate filaments
tough, insoluble ropelike protein fibers
resist pulling forces on the cell

36. Cellular Extensions Cilia and flagella
Whiplike, motile extensions on surfaces of certain cells
Cilia move substances across cell surfaces
Longer flagella propel whole cells

37. Cellular Extensions Microvilli
Fingerlike extensions of plasma membrane
Increase surface area for absorption
Core of actin filaments for stiffening
Microvillus
Actin filaments

38. Nucleus Largest organelle Control center of the cell
Most cells are uninucleate
Skeletal muscle cells, bone destruction cells, and some liver cells are multinucleate
Mature red blood cells are anucleate

39. Chromatin (condensed)
Nuclear pores
Nuclear envelope
Nucleus
Chromatin (condensed)
Nucleolus
Rough ER
Figure 3.29a

40. Nuclear Envelope Double-membrane barrier containing pores
Outer layer is continuous with rough ER and bears ribosomes
Inner lining maintains shape of nucleus
Pore complex regulates transport of large molecules into and out of nucleus

41. Nucleoli Chromatin Dark-staining spherical bodies within nucleus
Involved in rRNA synthesis and ribosome subunit assembly
Chromatin
Threadlike strands of DNA (30%), histone proteins (60%), and RNA (10%)
Condense into barlike bodies called chromosomes when the cell starts to divide

42. Cell Cycle Period from cell formation to cell division Interphase
4 subphases:
G1 (gap 1) - vigorous growth and metabolism
G0 - gap phase in cells that permanently cease dividing
S (synthetic) - DNA replication
G2 (gap 2) - preparation for division

43. S Growth and DNA synthesis
G1 checkpoint
(restriction point) S
Growth and DNA
synthesis G2
Growth and final
preparations for
division G1
Growth M
G2 checkpoint
Figure 3.31

44. Cell Division Mitotic (M) phase of the cell cycle
Essential for body growth and tissue repair
Does not occur in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle
Includes two distinct events:
Mitosis - four stages of nuclear division:
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis—division of cytoplasm

45. Control of Cell Division
“Go” signals:
Critical volume of cell when area of membrane is inadequate for exchange
Chemicals (e.g., growth factors, hormones, cyclins, and cyclin-dependent kinases (Cdks)
“Stop” signals:
Contact inhibition
Growth-inhibiting factors produced by repressor genes

46. Theories of Cell Aging
Wear and tear theory: Little chemical insults and free radicals have cumulative effects
Immune system disorders: Autoimmune responses and progressive weakening of the immune response
Genetic theory: Cessation of mitosis and cell aging are programmed into genes

47. Developmental Aspects of Cells
All cells of the body contain the same DNA but are not identical
Chemical signals in the embryo channel cells into specific developmental pathways by turning some genes off
Development of specific and distinctive features in cells is called cell differentiation
Elimination of excess, injured, or aged cells occurs through programmed rapid cell death (apoptosis) followed by phagocytosis