Anatomy 32. Chapter 2 Cells: The Living Units. I. Introduction to the cell - The cell is the smallest living unit. All living organisms are composed of cells
Cells: The Living Units
a. Robert Hooke first observed a cell when microscopes were invented in the 1600’s. Matthias Schleidena nd Theodor Schawn declared that all living things are made up of cells. Rudolf Virchow concluded that cells arise from other living cells.
b. All of these observations contributed to the Cell Theory=
all living things are made up of cells,
the smallest unit of life is the cell,
cells arise from other living cells by cell
c. Organelles are discrete specialized structures that assist in cell function and structure. In this chapter you will learn about the function of cell organelles and how they assist the cell to perform its overall function.
a. Structure- A phospholipid bilayer with proteins and cholesterol molecules used to stabilized the membrane.
2. Carbohydrates (sugars) may be attached to proteins and form glycoproteins, or attach to lipids and form glycolipids. Carbohydrates are found on the outer surface of the membrane and serve as receptors or markers.
3. Integral proteins cross through the membrane and may be used as transport channels. Peripheral proteins adhere to the underside of the membrane and stabilize it.
1. The side of the membrane that faces externally presents receptors and markers unique to each kind of cell.
2. The membrane controls what molecules cros it based on size, polarity, solubility, and receptor signals.
3. The membrane expels objects out of the cell by exocytosis or surrounds them and brings them in by endocytosis through either phagocytosis or pinocytosis.
a. Cytosol- a jelly-like substance that fills the cell and suspends the organelles
1. Mitochondria- A double membrane bound organelle responsible for producing energy for the cell in the form of ATP (The Power House)
1. Smooth ER- no ribosomes on surface, processes fats, toxins, hormones
2. Rough ER- has surface ribosomes, site of protein synthesis
Collaboration between organelles. Some proteins remain in the cell and some are excytosed.
Lysosomes- vesicles containing lytic or digestive enzymes that break down cell debri and foreign substances in the cell, like bacteria
Ribosome- protein units that specialize in protein production, may be free floating or attach to Rough ER. (Assembly workers)
a. Nuclear Envelope -a double membrane layer with pores that allow transport into and out of the nucleus.
b. Chromatin- DNA strands loosely wrapped around histone protein. Under the microscope it make the nucleus look cloudy. DNA is readable and accessible in this form and thus most of the time the cell contains chromatin
c. Chromosomes- DNA strands super coiled to form dense discrete structures. These are seen during cell division and resemble an X. Humans have 46 chromosomes. Chromatin condenses to form chromosomes.
d. Nucleoli – Region within the nucleus where ribosome production takes place
a. Interphase- The majority of the time the cell is interphase. At this time it grows, performs its normal cell function, and prepares for cell division. A cell in interphase seen under the microscope shows a distinct cloudy nucleus filled with chromatin.
1. G1 (growth 1)- after a cell is created it enters this stage and performs its specialized function
2. S (synthesis)- DNA is copied so there are two sets of chromosomes
3. G2 (growth 2)- cell continues to grow and prepare for cell division
1. Mitosis- the division of the cell’s nucleus describe in four stages that may take about 2 hours to complete.
1. Prophase- the nuclear envelope breaks down, DNA condenses from chromatin to chromosomes, mitotic spindle forms
2. Metaphase- mitotic spindle lines the chromosomes at the equatorial plate
3. Anaphase- chromosome strands (sister chromatids) are pulled apart to opposite poles of the cell
4. Telophase- the cell forms a cleavage furrow, nuclear envelopes begins to form and chromosomes return to chromatin
2. Cytokinesis- the division of the entire cell into two cells.
a. Cells that connect body parts or line organs
b. Cells that move organs and body parts
c. Cells that store nutrients
Cells that fight disease
Cells that gather information and control body functions
f. Cells for reproduction
All humans originated from a single cell. This cell is formed when the egg and sperm unite, it’s called the zygote. All other cells are produced from this cell, thus every cell in our body contains the exact same DNA. As the embryo develops the cells become specialized, a process known as cell differentiation. Their structural differences reflect their functional difference. A group of specialized cells forms a type of tissue and each tissue type will have a different function.
a. Youth – before birth the fetus develops all the organs and systems necessary for a functional body. After birth the infant continues to mature and cells divide for growth. By adulthood cell division reduces to only occur during repair of tissues
b. Aging- there are several theories that try to explain the cause of aging. The end result is the same: cell greatly decrease division rate and dead cells are replaced at a slower rate, tissue mass is lost, and weakening occurs.
Mitochondrial Theory- the mitochondria produces free radicals as a result of cellular respiration/ high metabolism. Those that eat less or have a slow metabolism live longer because less radicals are produced
Genetic Theory- our genes have a pre-determined life span for cells indicating that it is a normal part of human development
Telomeres- sections of DNA that do not contain genes but influence the amount of times a cell divides. As the cells divide the number of telomeres decreases. An enzyme called telomerase, which adds telomeres, is found in excess in cancer cells and may increase cell division.