Chapter 3: Cellular Form and Function Concepts of cellular structure Cell surface Membrane transport Cytoplasm Application to T.E.

Development of the Cell Theory Hooke in 1663, observed cork (plant): named the cell Schwann in 1800’s states: all animals are made of cells Pasteur’s work with bacteria ~ 1860 disproved idea of spontaneous generation (living things arise from nonliving matter) Modern cell theory emerged by 1900 Even today get yogurt put it on a slide you will see life.

Principles of Modern Cell Theory All organisms composed of cells and cell products. A cell is the simplest structural and functional unit of life. There are no smaller subdivisions of a cell or organism that, in themselves, are alive. An organism’s structure and all of its functions are ultimately due to the activities of its cells. Cells come only from preexisting cells, not from nonliving matter. All life, therefore, traces its ancestry to the same original cells. Because of this common ancestry, the cells of all species have many fundamental similarities in their chemical composition and metabolic mechanisms. Structure & function. Cells from cells: if you know where you came from you can predict where you’re going. Can we tie this in with evolution? I think we just did

Cell Shapes thin, flat, angular contours round to oval irregular angular shapes, with more than 4 sides disc shaped

Cell Shapes 2 squarish thick middle with tapered ends taller than wide So what? Form fits function that’s what IF you take a stem cell and force it into a shape, it improves the chance that the stem cell will differentiate (specialize) into a particular kind of cell Make a sphere: fat cell Stretch and flatten them they tend to become bone cells Human red blood cells (primarily carriers of oxygen to tissues) are among the smallest in the body. Why is it advantageous that they are so small? Surface area is in inverse proportion to cell size. The tiny size of erythrocytes allows for more rapid diffusion of oxygen in an out of the cell. p 95, Fig. 3.2 taller than wide long, slender Stellate star-shaped

Cell Size Human cell size Limitations on cell size most range from 10 - 15 µm in diameter egg cells (very large)100 µm diameter, visible to naked eye nerve cell over 1 meter long, muscle cell up to 30 cm long, (too slender to be seen) Limitations on cell size as cell enlarges, volume increases faster than surface area so the need for increased nutrients and waste removal exceeds ability of membrane surface to exchange On the board a 2 mm circle represents the size of the smallest bacteria, a 10 cm circle represents a small eukaryotic cell, a Meter wide circle represents a large eukaryotic cell. What size do you predict stem cells to be? Why? Smaller because they have yet to specialize. Why not have huge cells? Dinosaurs were bigger did they have bigger cells? Do elephants, infedelephants? Have bigger cells? no

Cell Surface Area and Volume Surface area squares it self, Volume cubes itself which will increase faster? Volum Lots of the things in this book will take place at the cell’s surface. Can we overcome this? What about the 30 cm long nerve cells? How are they pulling it off? Cells can overcome the surface area problem by growing in only one dimesion. Like very long nerve cells. Human red blood cells (primarily carriers of oxygen to tissues) are among the smallest in the body. Why is it advantageous that they are so small? Surface area is in inverse proportion to cell size. The tiny size of erythrocytes allows for more rapid diffusion of oxygen in an out of the cell.

Parts of a Typical Cell Note: cell membrane, nucleus, organelles, cytoskeleton and cytosol (intracellular fluid or ICF)

Plasma Membrane Defines cell boundaries Controls interactions with other cells Controls passage of materials in and out of cell Appears as pair of dark parallel lines around cell (viewed with the electron microscope) intracellular face - side faces cytoplasm extracellular face - side faces outwards Current theory of molecular structure an oily film of phospholipids with diverse proteins embedded in it Plastic bag demo?

Plasma Membrane Red polar heads on phospholipids are hydrophillic, tails oily, hydrophobic. If you put a bunch of phospholipids in a cup of water they naturally form these bi layres.

Membrane Lipids Lipids constitute Phospholipid bilayer 90 to 99% of the plasma membrane Phospholipid bilayer 75% of the lipids hydrophilic heads (phosphate) on each side hydrophobic tails in the center motion of these molecules creates membrane fluidity, an important quality that allows for self repair Why are fat-soluble toxins more rapidly taken in through diffusion than water-soluble poisons? Fat-soluble materials can more easily pass through the cell membrane since it consists of 90-99% lipids. p. 99, Fig. 3.6b A number of the nerve gases enters the body through the skin quite easily since they are lipid-soluble: nerve gasses stop the enzyme acetycholinesterase which allows muscle contraction: antidotes include atropine which is derived from deadly nightshade (belladonna) Its fluid, like Willy Wonka

Membrane Protein Functions Receptors, Second messenger systems, Enzymes, Channel proteins, Carriers, Motor molecules Cell-identity markers, Cell-adhesion molecules Receptors& 2nd messenger systems: receive hormones: If cells communicate with chemical signals that cannot enter target cells membrane receptors bind these messengers (hormones, neurotransmitters) each receptor is usually specific for one messenger Activation of receptor may produce a second messenger inside of the cell Receptors and Second-messenger Systems: So your DNA screws up; your amino acid sequence screws up; your proteins screw up and you join the make a wish foundation Channel proteins: Nerve signal conduction I.D. Markers matter to immune system These are the cell’s eyes & ears. What would happen if the plasma membrane were made primarily of a hydrophilic substance such as carbohydrate? In such a case, the plasma membrane would dissolve in the water that surrounds it, and the cell would rupture. The necessity of a hydrophobic plasma membrane to containment of the cytoplasm is an example of the unity of form (hydrophobic lipids) and function (retention of the aqueous cell contents).

Glycocalyx On surface of animal cells Functions (see Table 3.2) carbohydrate portions of membrane glycoproteins and glycolipids unique in everyone but identical twins Functions (see Table 3.2) enables immune system to recognize normal cells from transplanted tissue, diseased cells and invading organisms cushions and protects cell membrane cell adhesion, fertilization, embryonic development  Trypanosoma, hides from the immune system by mimicking the glycocalyx So this is what we have to fool to implant a scaffold, Some blood parasites hide from the immune system by mimicking the glycocalyx: Pictures: Trypanosoma,

Cilia Hairlike processes 7-10m long Functions single, nonmotile cilum found on nearly every cell 50 to 200 on one cell in respiratory and uterine tube move mucus Functions sensory in inner ear, retina and nasal cavity motile cilia beat in waves, sequential power strokes followed by recovery strokes Tar & Hydrogen Cyanide come from tobacco smoke, Tar makes mucus in your lungs, but HCN kills the cilia so smokers cough to get the mucus out. How would the movement of mucus in the respiratory tract be affected if cilia were equally stiff on both their power and recovery strokes? Each recovery stroke would simply push the mucus back to where it was at the start of the power stroke. The mucus would merely be jostled back and forth rather than being moved progressively along the surface of the mucosa.

Cystic Fibrosis Chloride pumps fail to create adequate saline layer Sticky mucus plugs pancreatic ducts and respiratory tract Inadequate absorption of nutrients and oxygen Lung infections Life expectancy of 30 years 65 roses, genetic, fatal won’t live much into 30s What diseases and abnormal conditions might a person be more prone to having if an outside chemical immobilized the cilia? Everyone would be more likely to have respiratory infections more often. Women might be infertile (or have ectopic pregnancies—see chapter 28) since the cilia are needed to move the egg cells through the uterine tube.

Cilium At Cell Surface

Flagella Long whiplike structure that has an axoneme identical to that of a cilium Only functional flagellum in humans is the tail of the sperm

The Cytoplasm Organelles Cytoskeleton Inclusions surrounded by membrane nucleus, mitochondria, lysosome, perioxisome, endoplasmic reticulum, and golgi not surrounded by membrane ribosome, centrosome, centriole, basal bodies Cytoskeleton collection of microfilaments and microtubules Inclusions stored products Can you think of a reason for an organ to consist of many small cells rather than fewer larger ones? For one thing, this ensures that damage to one cell, or even to many, destroys a smaller portion of the organ and is less compromising to organ function. For another, it ensures a large pool of cells that can specialize for different functions within that organ. Another reason is that the plasma membrane and especially the cytoskeleton are unable to physically support cells of excessive size. A large cell, like an extremely full water balloon, will rupture more easily. Bring in two water balloons

Nucleus Largest organelle (5 m in diameter) Nuclear envelope some cells anuclear or multinucleate Nuclear envelope two unit membranes held together at nuclear pores Nucleoplasm chromatin is thread-like matter containing DNA and protein nucleoli is dark masses where ribosomes are produced

TEM Micrograph of The Nucleus

Endoplasmic Reticulum Rough ER extensive sheets of parallel unit membranes with cisternae between them and covered with ribosomes, continuous with nuclear envelope function in protein synthesis and production of cell membranes Smooth ER lack ribosomes, cisternae more tubular and branch more extensively, continuous with rough ER function in lipid synthesis, detoxification, calcium storage

Smooth and Rough Regions of ER

Endoplasmic Reticulum Rough ER and protein synthesis. Smooth ER and lipid synthesis

Ribosomes Small dark granules of protein and RNA free in cytosol or on surface of rough ER Interpret the genetic code and synthesize polypeptides

Golgi Complex Synthesizes CHO’s, processes proteins from RER and packages them into golgi vesicles Golgi vesicles irregular sacs near golgi complex that bud off cisternae some become lysosomes, some fuse with plasma membrane and some become secretory vesicles Secretory vesicles store a cell product for later release

TEM of the Golgi Complex

Lysosomes Package of enzymes in a single unit membrane, variable in shape Functions intracellular digestion - hydrolyze proteins, nucleic acids, complex carbohydrates, phospholipids and other substrates autophagy - the digestion of worn out organelles and mitochondrion autolysis - programmed cell death glucose mobilization - lysosomes in liver cells break down glycogen

Lysosomes and Peroxisomes

Peroxisomes Appear similar to lysosomes but not produced by golgi complex In all cells but abundant in liver and kidney Function neutralize free radicals produce H2O2 in process of alcohol detoxification and killing bacteria break down excess H2O2 with the enzyme catalase break down fatty acids into acetyl groups

Mitochondrion Double unit membrane Inner membrane contains folds called cristae ATP synthesized by enzymes on cristae from energy extracted from organic compounds Space between cristae called the matrix contains ribosomes and small, circular DNA (mitochondrial DNA) Reproduce independently of cell and live for 10 days mDNA mutates quicker than nuclear DNA, which allows researchers to track human evolution with it. In 1992 the Vietanmese government turned over bone fragments of Americans who had died in the war. Using mDNA in four years scientists had ID’d 37 missing persons.

Centrioles Short cylindrical assembly of microtubules, arranged in nine groups of three microtubules each Two centrioles, perpendicular to each other, lie near the nucleus in an area called the centrosome these play a role in cell division

Cytoskeleton Collection of filaments and tubules that provide internal support and movement of cell Composed of microfilaments, and microtubules microfilaments made of protein actin, form network on cytoplasmic side of plasma membrane called the membrane skeleton supports phospholipids of p.m., supports microvilli and produces cell movement, and with myosin causes muscle contraction microtubules

Microtubules Cylinder of 13 parallel strands called protofilaments (a long chain of globular protein called tubulin) Hold organelles in place and maintain cell shape Form tracks to guide organelles and molecules to specific destinations in a cell Form axonemes of cilia and flagella, centrioles, basal bodies and mitotic spindle Not all are permanent structures and can be disassembled and reassembled where needed

Cytoskeleton Diagram

Recognition of Cell Structures