1. Cells!
Muse 2430 Lecture #2
5/8/13

2. Chapter 3 Cells vary in size possess distinctive shapes
measured in micrometers

3. An Introduction to Cells
Sex cells (germ cells)
Reproductive cells
Male sperm
Female oocyte (a cell that develops into an egg)
Somatic cells (soma = body)
All body cells except sex cells

4. Cell Membrane

5. The Plasma Membrane

6. Cell Membrane
The proteins are divided into two categories: integral and peripheral.
The integral proteins form the majority of membrane proteins. They penetrate and are embedded in the bilayer, bound to the non­polar tail regions.
The transmembrane proteins span the bilayer completely and may form channels (pores) for transport of substances across the membrane.
Integral proteins also may lie partly submerged in one side or the other. They have several functions.
Some integral proteins serve as cell surface enzymes.
Integral proteins bound to carbohydrates may form receptor sites for chemical messages from other cells, such as endo­crine glands.
Some also function as markers, or antigens, which identify cell types.
The peripheral proteins are loosely bound to the membrane surface and can be easily removed from it. Their functions are not as well known as those of integral proteins. They may be involved in structural support and changes in membrane shape during cell division or cell movement.

7. Structure of the Plasma Membrane

8. Intercellular Junctions
Tight junctions
close space between cells
located among cells that form linings
Desmosomes
form “spot welds” between cells
located among outer skin cells
Gap junctions
tubular channels between cells
located in cardiac muscle cells

9. The cytoplasm contains a complex network of structural components
Microfilaments
Structure
Microfilaments are solid thread-like cylinders made of protein and found in a variety of sites within the cell.
Function
Microfilaments are responsible for contractility of cells, which is a property of all cells but is especially well developed in muscle cells.
Contractility is responsible for cell locomotion and movements associated with phagocytosis, pinocytosis, and cell division.

10. Cell Adhesion Molecules
guide cells on the move
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

11. Structural Components
Microtubules
Structure
Microtubules are hollow tubes present everywhere in the cytoplasm in all cells.
They are composed of protein tubulin molecules.
Function
Microtubules contribute to the cytoskeleton, or supporting elements, of the cell.
They also are involved in cell division, cell movements, and the transport of materials from one area of the cell to another.

12. Cytoplasmic Organelles
Microfilaments and microtubules
thin rods and tubules
support cytoplasm
allows for movement of organelles
Inclusions
temporary nutrients and pigments

13. Movements Into and Out of the Cell
Passive (Physical) Processes
require no cellular energy
simple diffusion
facilitated diffusion
osmosis
filtration
Active (Physiological) Processes
require cellular energy
active transport
endocytosis
exocytosis
transcytosis

14. Simple Diffusion
movement of substances from regions of higher concentration to regions of lower concentration
oxygen, carbon dioxide and lipid-soluble substances

15. Osmosis
movement of water through a selectively permeable membrane from regions of higher concentration to regions of lower concentration
water moves toward a higher concentration of solutes

16. Osmosis
Osmotic Pressure – ability of osmosis to generate enough pressure to move a volume of water
Osmotic pressure increases as the concentration of nonpermeable solutes increases
hypertonic – higher osmotic pressure
hypotonic – lower osmotic pressure
isotonic – same osmotic pressure

17. Facilitated Diffusion
In facilitated diffusion, the carrier substance combines with the solute molecules to form a solute-carrier complex, which is soluble in the lipid-bilayer, and thus transports the solute across the membrane.
Once on the other side, the solute is released. The carrier breaks away from the complex, returns to the exterior of the membrane, and repeats the process.
The carriers exhibit specificity; i.e. they are highly selective in distinguishing between closely related molecules.
Facilitated diffusion can be inhibited by competitive and noncompetitive inhibitor molecules, which closely resemble the solute molecules.
The rate of passage of a solute through facilitated diffusion depends on:
its concentration difference on both sides of the membrane
the number of carrier molecules available
how rapidly the solute-carrier complex formation takes place.

18. Filtration smaller molecules are forced through porous membranes
hydrostatic pressure important in the body
molecules leaving blood capillaries

19. Active Transport
carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration
sugars, amino acids, sodium ions, potassium ions, etc.

20. Transport in Vesicles
Vesicle - a small spherical sac formed by budding off from a membrane
Endocytosis - materials move into a cell in a vesicle formed from the plasma membrane
three types: receptor-mediated endocytosis
phagocytosis
bulk-phase endocytosis (pinocytosis)
Exocytosis - vesicles fuse with the plasma membrane, releasing their contents into the extracellular fluid
Transcytosis - a combination of endocytosis and exocytosis

21. Phagocytosis

22. Endocytosis

23. Transcytosis endocytosis followed by exocytosis
transports a substance rapidly through a cell
HIV crossing a cell layer

24. Exocytosis reverse of endocytosis
substances in a vesicle fuse with cell membrane
contents released outside the cell
release of neurotransmitters from nerve cells

26. Nucleus
Structure
The nuclear envelope consists of a double membrane separated by the perinuclear space.
The inner membrane is smooth. The outer membrane often contains ribosomes and is continuous with the surrounding ER.
The inner and outer membranes fuse at irregular intervals around the nucleus to form nuclear pores, which allow for exchange of materials between the nucleus and the cytoplasm.
Chromatin appears as irregular clumps or granules material dispersed throughout the nucleus.
Chromatin is composed of coiled strands of DNA bound to basic proteins called histones, varying amounts of RNA, and other nonhistone proteins and enzyme systems.
In a dividing cell, the chromatin is condensed and coiled into discrete units, the chromosomes. Human cells contain 23 pairs of chromosomes.
The nucleoplasm is the matrix that surrounds the chromatin. It is composed of proteins, metabolites, and ions.
The nucleolus is a spherical structure composed of RNA and protein. The size of the nucleolus and the number present vary in different cell types. It is missing in cells that do not synthesize protein, such as spermatozoa. It is the site of ribosome production

27. Ribosomes Structure Function
Ribosomes are small granules composed of ribosomal RNA and almost 80 different proteins.
They occur as individual granules or in clusters called polyribosomes.
They may be free in the cytoplasm (free ribosomes) or attached to the membranes of the endoplasmic reticulum.
Function
Ribosomes are the site of protein synthesis.
Free ribosomes are involved in the synthesis of proteins for the cell’s own use; for example, in the renewal of enzymes and membranes.
Attached ribosomes are the site of synthesis of proteins that are secretory products to be released from the cell.

28. Golgi Apparatus Function
The Golgi apparatus is the site of accumulation, concentration, packaging, and chemical modification of the secretory products synthesized on the rough ER.
The transport vesicles pinch off from the ER and carry the secretions to the Golgi apparatus, where the secretions fuse with its cisternae.
The large condensing vacuoles concentrate the secretion and package them to become secretory granules.
Secretory granules, which are large, densely packed, membrane-bounded structures, unload their contents via exocytosis upon nervous or hormonal stimulation.
The Golgi apparatus also chemically modifies the molecules synthesized in the ER for incorporation into the plasma membrane. It adds fatty acid residues to certain proteins to convert them to lipoproteins, and it synthesizes and attaches carbohydrate side chains to proteins to form glvcoproteins.
The Golgi apparatus processes proteins that function intracellularly, such as the lysosome enzymes.

29. Golgi Complex

31. The cell cycle and mitosis
The cell cycle, in cells that are capable of dividing, refers to the events in a cell’s life span in the period between the time it was formed by cell division to the beginning of the next cell division.
The greatest portion of the cycle (about 90%) is devoted to growth and synthesis, called interphase, with a smaller portion devoted to nuclear and cell division, or mitosis.

32. The Cell Cycle

33. Stem and Progenitor Cells

34. Mitosis = cell copying

35. The End