I. INTRODUCTION: Cells as living machines A. Life is Cellular - All living things = cellular (made of cells).

* RECALL from first module: Cells are alive!

* Cells = analogous to bricks in a house. They are the "building blocks@ of the body.

** They are the basic structural & functional unit of the body. If your body has a job to get done, a cell has to do it.

Recall from the first module HIERARCHY OF LIFE: Life is made of atoms, which are arranged into molecules, which are combined into cells. Cells join to form tissues, which combine to form organs. All of your organs are made of cells.

* Cytology: the study of cells

- How many cells in the human body? Estimates of humans range 10-100 trillion. There are approximately 200 different types of diverse size & functions. - Cells make proteins. They contain "cellular machinery" to perform this task. The machinery follows instructions within the nucleus on the genetic material.

* Recall something else we discussed in the first module: METABOLISM

Cells take in nutrients and perform protein synthesis. In this respect, they are "protein machines", although they perform other processes, as well. During this process of metabolism, they make wastes which must be gotten rid of (excreted).

New Information:

1. Sometimes the proteins produced are for use inside the cell, sometimes they are used outside the cell (they must be exported).

*These exported proteins might be used for immunity, digestion, repair, or any number of necessary functions

2. The cell has intracellular machinery, called organelles, which make the proteins. They follow the info in the nucleus. The cell's genetic information guides this process. 3. So your body depends on the cell's genetic material for life's processes to be carried out. This material must be well protected, and it must be present in its complete form, or the cell can't make the proteins needed for its own survival.

B. Reproduction, Growth & Repair is Cellular, too

- Cells divide during the process of mitosis. This process is used by the body to grow & repair itself.

* When your body grows, the cells divide. Bigger = more cells. * This is true of the internal organs, too. An adult's liver has more cells than an adolescent's liver, not bigger cells. * if your body is damaged, this same process repairs the damage. Cells divide, and fill in damaged areas.

- Even the continuation of the body (reproduction) has a cellular basis.

Cells have chromosomes, which carry genetic information. Each cell has 2 sets of this material ... one from mom, one from dad.

Adults make special cells called gametes in their gonads (testes for the male, and ovary for the female). Gametes are the sex cell, with only 1 set of chromosomes. The process of producing them is called meiosis.

During reproduction, fertilization occurs as dad's gamete (the sperm) fuses with mom's gamete (the ovum, or egg) inside the woman's reproductive tract, forming a fertilized egg: the zygote.

* also recall from the introductory module: Cells are combined within the body to form TISSUES.

The fertilized egg now splits via mitosis, and again, and again, forming a mass of identical cells.. However, the human body is not a mass of identical cells. Instead, at some point the cells begin to differentiate from each other. They join together, forming the various tissues of the body. The body becomes an embryo, then a fetus, then a newborn, then a child, then an adult, when the body begins to make its own gametes. The cycle of life continues.

II. Basic Cell Anatomy A. Basic Regions - of an animal cell - Generalized cell: 3 major parts or regions:

Intracellular Matrix= inside cell, Extracellular Matrix = outside of cell. (by convention, down on the images) (by convention, up on the images)

III. Plasma Membrane A. Parts

1. Consists of a LIPID BILAYER (=@2 layers of fat@)

* Quick review of phospholipids from "Biochemistry" module:

- These molecules have a particular behavior in water, which is useful to the cell: In an open container: In a closed container (like your body)

- The phospholipids take on an even more complex form:

* HYDROSTATIC PRESSURE (the pressure of water pushing against its surroundings) is even all the way around, inside AND outside, giving the cell its basic round shape.

* This structure is very stable in water. If you disrupt it, the molecules have nowhere to go but right back where they were.

So, it is used by your cells for their boundary, as well as other structures, as a flexible barier.

- NOT a Apassive envelope@ - it is active; things are constantly moving across.

2. Embedded Molecules - Most of the PM's metabolic roles arise from 2 MAIN CHARATERISTICS (we will discuss in more detail later):

- In order to perform these 2 tasks, there are molecules embedded in the PM. Closer look:

PM is a fluid matrix -- A CHANGING MOSAIC PATTERN.

2 parallel sheets of phospholipid molecules with other molecules embedded

ANALOGY: liquid-y jello with several types of Afruit@ floating around in the jello:

a. Proteins -1/2 of the membrane by weight; 2 types:

1) INTEGRAL (Apart of@) - inserted w/in the bilayer. Some face the environment (inside or outside of cell) on one side.

If it goes all the way across the membrane it is a "transmembrane protein"

2) PERIPHERAL - @to the side@ - not embedded at all. *many on extracellular side = are enzymes. *man on the intracellular side attach membrane to CYTOSKELETON = Acell=s skeleton@ (see later discussion during "organelle" section of module).

b. Carbohydrates

- I’m including other molecules with a sugar attached *prefix or suffix 'glyco' = sugar * lipid = fat * glycolipid = fats with sugars attached. * proteoglycans - mostly protein, with a carbohydrate attached. * glycoproteins - mostly carbohydrate, with a protein attached. - Face EXTERNALLY (outside) of cell. Help form GLYCOCALYX = "sugar coating"

- uses of glycocalyx:

(i) Immune system: as identification, like flags on a ship. Immune cells use them to ID "self" from "non-self" cells.

** Hundreds of these molecules on each plasma membrane of each cell. Different pattern for everyone, except identical twins. Rejection of transplanted organs caused by this.

** Autoimmune disorder: immune system wrongly identifies body's cells as foreign, and attacks!

(ii) Anchor cell

(iii) Lubricate & protect cell (iv) Other uses: too numerous to name all of them!

c. Cholesterol - Recall from your biochemistry module: Cholesterol is a steroid = a lipid-based molecule, and lipids are soluble in other lipids. - Cholesterol floats inside the fluid-y matrix, act to stabilize inside the membrane.

** Phospholipid molecules are attracted to the cholesterol molecule, so they don't disperse as easily.

3. Special Features of the PM a. Extensions - Outward finger-like folds that allow the cell to do several things. - Here, we will look at 3 examples: (i) Microvilli

- Micro = Alittle@, villus = hair, villi = Ahairs@. - Finger-like extensions of the PM - Purpose = increase surface area, usually found on cells whose function= absorption.

The relationship between surface area and volume is important!

* This is why so many of your organs have folds, ridges, etc.

(ii) Cilia. Extensions which are used to move substances past the cell's surface (NOT to increase SA!) - ALSO finger-like extensions, but longer. - Can do "powered movement" - wave under their own power.

(iii) Flagellum (flagella = plural)

- long single cilium used for moving cell through space

- only found on the male's sperm cell

b. Junctions

- Many cells are attached to other cells to form a structure. * Recall: your body's cells join to form tissues, then organs.

- Some important types of junctions (attachments) between cells:

(i) Tight junctions: cells whose membranes join together forming a virtually impermeable barrier to fluid. Proteins "weave" to form a "zipper-like" connection. (ii) Desmosomes: Localized spot-like protein connections randomly arranged on the lateral sides of plasma membranes. They help prevent "shearing" of cells; the cells won't move away from each other. They are strong ... they are connected to the internal skeleton of each cell. There are big spaced between them, so substances can move more easily between cells. (iii) Gap Junctions: allow stuff (ions, etc.) to pass from 1 cell to another.

*connections = hollow protein Atubes@ (transmembraneous proteins) that pass from 1 cell to another. *allow ions, sugars, etc. to pass between cells.

c. Signal Molecules - communication & regulation

- embedded molecules in the plasma membrane that allow other cells and molecules outside of the cell to affect what happens inside the cell.

* Often involve proteins, although some may also include other molecules, such as carbos.

* Usually work via a molecule produced by one cell attaching to a protein embedded in the membrane of another cell. This "docking" causes something to occur in the TARGET CELL

.This docking begins some metabolic process within the cell. Examples include production of ATP, begin protein synthesis, begin mitosis, etc. Literally thousands of processes controlled this way.

* Recall some terms:

Ligand - In biology, a ligand (Latin ligare = to bind) is a substance that is able to bind to and form a complex with another molecule. ** It is anything that can attach to something!

Receptor - A molecule that can be attached to!

Active site - The specific site on the receptor where the ligand attaches. Any change to this can interfere with the system!

* Come in many forms. They do a lot of things. Mainly, help coordinate the activities of neighboring cells.

Most of what you learn in A&P or biology is studying these molecules!!

* Here, I will give 2 common examples that demonstrate how many work. But keep in mind that there are thousands of examples! Here are two:

(i) Antigens

- We saw this already in the "Glycocalyx" section of this module.

- Glycoproteins in the membrane act as a signal to the immune system that this cell is part of "self". If the immune system detects "non-self" glycoproteins, they attack!

- These particular protein-based molecules are called ANTIGENS.

(ii). Secondary Messenger Systems

- Series of proteins embedded in the membrane that act as an important means of info transfer for both the endocrine and nervous systems!

- There are several. One common type acts as a good example:

"G-Protein Linked" Secondary Messenger Systems:

In PM, there is a special protein called "G" (belongs to the G-protein linked system)

If a ligand attached to "G", a series of events occur (ignore details for now).

These events results in the formation of a Secondary Messenger being formed called Cyclic AMP (cAMP for short).

Now that cAMP is inside the cell, it will begin activating other molecules within the cell.

Important term: Kinase. An enzyme that activates other molecules by phosphorylizing them! (phosphorylation = adding a phosphate)

(cAMP is a kinase)

Now the cell has activated enzymes inside, and begins metabolism.