UNIT SUMMARY

This was a big unit! It started with cell structure and genetic control and finished up with interactions between cells and the extracellular environment. Plasma membranes, cytoplasm, cell nucleus and gene expressions, protein synthesis and secretion, and DNA and cell division were all topics in part one of the unit. The second part of this unit consisted of extracellular environments, diffusion and osmosis, carrier-mediated transport, and cell signaling.


THREE MAJOR CONCEPTS OF CELL PHYSIOLOGY


CELL PHYSIOLOGY


The cell is the smallest functional unit on which all life is built. Knowledge of various cell parts and their functions is essential in order to identify the type of cell you are viewing as well as its function. The plasma membrane (cell membrane) encloses the nucleus and cytoplasm. The cytoplasm is
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comprised of organelles which are suspended in a fluid matrix called cytosol. Cytosol consists of water and dissolved substances such as proteins and nutrients.

The plasma membrane separates internal metabolic activities from the external environment and controls the movement of materials into and out of the cell. It is a double phospholipid membrane with the nonpolar hydrophobic tails pointing toward the inside of the membrane and the polar hydrophilic heads forming the inner and outer faces of the membrane. One of the many features of the phospholipid bilayer is that it is selectively permeable, meaning that only small, uncharged, polar molecules, such as H2O and CO2, and hydrophobic molecules-nonpolar molecules like O2 and lipid soluble molecules such as hydrocarbons- can freely cross the membrane.


Organelles are bodies within the cytoplasm that physically separate the various metabolic activities that occur within cells. They include the following parts:

The nucleus is enclosed by the nuclear envelope, which is a phospholipid bilayer similar to the plasma membrane. The nucleus contains DNA (deoxyribonucleic acid) and nucleoli. It also serves as the site for the separation of chromosomes during cell division.

The endoplasmic reticulum (ER) consists of stacks of flattened sacs involved in the production of various materials. They appear as a series of mazelike channels, often closely associated with the nucleus. When ribosomes are present, the rough ER attaches polysaccharide groups to polypeptides as they are assembled by the ribosomes. When ribosomes are not present, the smooth ER is responsible for various activities, including the synthesis of lipids and hormones, especially in cells that produce these substances for export from the cell.
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A Golgi apparatus is a group of flattened sacs arranged like a stack of bowls. They function to modify and package proteins and lipids into vesicles that bud from the ends of a Golgi apparatus. Vesicles often migrate to and merge with the plasma membrane, releasing their contents outside of the cell.

Lysosomes are vesicles from a Golgi apparatus that contain digestive enzymes. They break down food, cellular debris, and foreign invaders such as bacteria.

Mitochondria carry out aerobic respiration, a process in which energy (in the form of ATP) is obtained from carbohydrates.

Microtubules, intermediated filaments, and microfilaments are protein fibers that are involved in establishing the shape or movements of the cytoskeleton, which is the internal structure of the cell.

Flagella and cilia protrude from the cell membrane and make wavelike movements. They are classified by their lengths and by their number per cell. Flagella are long and few, and cilia are short and numerous. A single flagellum propels sperm, and the numerous cilia that line the respiratory tract sweep away debris.

This is a great step-by-step video explaining the physiology of a eucaryote cell.





PASSIVE VS. ACTIVE TRANSPORT


Passive transport is the movement of substances down a concentration gradient and does not require energy use.

Bulk flow is the movement of materials into a cell by endocytosis or phagocytosis and out of a cell by exocytosis.

Diffusion is the net movement of substances from an area of higher concentration to an area of lower concentration. If a concentration gradient exists, then the molecules will eventually become evenly distributed, causing a state of equilibrium.

Osmosis is the passage of solvent (water) from a more dilute to a more concentrated solution through a membrane that is more permeable to water that to the solute.

Dialysis is the diffusion of solutes across a selectively permeable membrane.

Facilitated diffusion is the diffusion of solutes through channel proteins in the plasma membrane. Water is able to pass freely through the plasma membrane without the help of specialized proteins.


Active transport is the movement of solutes against a gradient and requires the expenditure of energy (usually ATP). Active transport is achieved through one of the following two mechanisms:
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Transport proteins in the plasma membrane transfer solutes such as Na+, K+, Cl-, and H+, amino acids and monosaccharides.

Vesicles in the cytoplasm move large molecules or particles across the plasma membrane. Types of this kind of transport include:

Exocytosis is the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell .

Endocytosis is the capture of a substance outside the cell when the plasma membrane merges to engulf it. The substance then enters the cytoplasm enclosed in a vesicle. There are three types of endocytosis:
  • Pinocytosis is “cell drinking”. This occurs when the plasma membrane folds inward to form a channel allowing dissolved substances to enter the cell. When the channel is closed, the liquid is encircled within a pinocytic vesicle.
  • Phagocytosis is “cell eating”. This occurs when undissolved material enters the cell. The plasma membrane engulf the solid material forming a phagocytic vesicle.
  • Receptor-mediated endocytosis occurs when specific molecules in the fluid surrounding the cell bind to specialized receptors in the plasma membrane. The plasma membrane folds inward and a vesicle is formed.



MITOSIS VS. MEIOSIS


Mitosis is a process of cell division in which the two daughter cells receive the same number of chromosomes as the parent cell. The daughter cells are identical to one another and to the original parent cell. In a typical animal cell, mitosis can be divided into four stages:
  • Prophase: The chromatin condenses into chromosomes. Each chromosome duplicates and consists of two chromatids. At the end of this phase, the nuclear envelope breaks down into vesicles.
  • Metaphase: The chromosomes align and are held in place by microtubules.
  • Anaphase: The centromeres divide. Chromatids separate and move toward the corresponding poles.
  • Telophase: Daughter chromosomes arrive at the poles and the microtubules disappear. The condensed chromatin expands and the nuclear envelope reappears. The cytoplasm divides and the cell membrane pinches inward eventually producing two daughter cells.

Meiosis is the type of cell division in which germ cells (eggs & sperm) are produced. Meiosis involves a reduction in the amount of genetic material. It comprises two successive nuclear divisions with only one round of DNA replication. There four stages for each nuclear division.
  • Interphase: Before meiosis begins, genetic material is duplicated.
  • First division of meiosis:
  • Prophase I: Duplicated chromatin condenses.
  • Metaphase I: Homologous chromosomes align at the equatorial plate.
  • Anaphase I: Homologous pairs separate with chromatids remaining together.
  • Telophase I: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.

  • Second division of meiosis:
  • Prophase II: DNA does not replicate.
  • Metaphase II: Chromosomes align at the equatorial plate.
  • Anaphase II: Centromeres divide and chromatids migrate separately to each pole.
  • Telophase II: Cell division is complete. Four daughter cells are obtained. One parent cell produces four daughter cells. Daughter cells have half the number of chromosomes in the original parent cell and are genetically different.

Meiosis differs from mitosis mainly because there are two divisions in meiosis, resulting in cells with a haploid number of chromosomes. The following website gives a great side by side explanation and demonstration of the similarities and differences between mitosis and meiosis.
__http://www.pbs.org/wgbh/nova/miracle/divi_flash.html__



CAREER APPLICATION

Knowledge of cell physiology is essential for anyone thinking of going into a career in health care. Since cells are the basis of all life, it is important to know how they work and their effect on the body. When we can begin to understand cell physiology, we can then understand other aspects of human physiology. To be a nurse, you must be able to understand how the human body functions. I believe that starts with understanding cell physiology.



CASE STUDY



Agony & Ecstasy

The patient in this case study is a college student who, after taking the drug Ecstacy, begins to feel ill and is taken to the hospital for treatment.

The answers to the case study questions are as follows….

CQ#1: What do the test results suggest is causing Brittany’s illness?
A. High blood pressure or rapid heart rate
B. Hypoglycemia (too little blood sugar water)
C. Hyperthermia (too hot)
D. Hypothermia (too cold)
E. Excess water (too much water)
F. Dehydration (too little water)

The correct answer is……… E. Excess water (too much water).

CQ#2: Assume movement of a molecule is limited. It can move to the opposite side of a container or stay where it is. If movement is random, what is the probability (0-100%) that the molecule will move to the opposite side?

The correct answer is………100% Because diffusion is the random movement that eliminates concentration differences, the molecule will move to the area of lower concentration. This movement will continue until the concentration difference no longer exists.

CQ#3: Assume there are 10 molecules on one side of a container. How many would you expect to move to the opposite side?
A. 10 C. 0
B. 5 D. It is impossible to predict

The correct answer is………B. 5

CQ#4: Which statement best describes how these molecules will behave over time due to random movement?
A. Red molecules will move from side A to B.
B. Blue molecules will move from side B to A.
C. All of the molecules will move so that red and blue will become equal on both sides.
D. More molecules will move from side A to B than from side B to A.

The correct answer is ………C. All of the molecules will move so that red and blue will become equal on both sides.

CQ#5: Which of the following molecules could move through a phospholipid membrane with the least difficulty?
A. H2O
B. Glucose
C. Na
D. O2
E. An amino acid

The correct answer is ………D. O2

CQ#6: What do you expect to happen over time in Brittany’s cells?
A. Water will move from inside to outside ONLY.
B. Water will move from outside to inside ONLY.
C. Water will move in both directions, but more water will move inside.
D. Water will move in both directions, but more water will move outside.
E. Water will not move.

The correct answer is………D. Water will move in both directions, but more water will move outside.



RESOURCES

Images
1: www.terrebonneonline.com/b2eukpro.htm
2: __www.health-choices-for-life.com__
3: __www.thescienceupdate.blogspot.com__
All information came from Human Physiology; Stuart Ira Fox; 12th Edition and Burton’s Microbiology For The Health Sciences; Paul G. Engelkirk and Janet Duben-Engelkirk; 9th Edition.