The Cell

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Cells are structural & functional units of all living organisms

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They are the building blocks of the human body

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An adult human body contains about 75 trillion cells

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Each cell type in the body performs specific functions

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All cells perform the general functions necessary to sustain life

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Obtain nutrients and other materials essential for survival from its surrounding fluids

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Dispose of the wastes they produce

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Shape and Integrity

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Cell Division

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Most cells in the human body are between 1 micrometer and 100 micrometers in diameter

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Individual cells are usually observed by LIGHT microscopy

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subcellular structures are studied by ELECTRON microscopy

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plasma cell membrane

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Forms outer, limiting barrier separating the internal contents of the cell from external materials

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cytoplasm

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is a general term for all cellular contents located between the plasma membrane and the nucleus

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The nucleus is the cell's control center

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It controls protein synthesis and directs the functional and structural characteristics of the cell

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Facilitated Diffusion

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Requires the participation of specific transport proteins that help specific substances or molecules move across the plasma membrane

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Bulk filtration

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involves the diffusion of both solvents and solutes together across the selectively permeable membrane

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Active Transport

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Movement of a substance across a plasma membrane against a concentration gradient

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Materials must be moved from an area of low concentration to an area of high concentration.

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Requires cellular energy in the form of ATP (adenosine triphosphate) and sometimes a transport protein as well

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ATP is continually synthesized by mitochondria ion pumps

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Active transport processes that move ions across the membrane are called ION PUMPS

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ion pumps allow a cell to maintain its internal concentrations of small molecules or ions

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Bulk Transport

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The means by which large molecules are secreted from the cell is called EXOCYTOSIS

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exocytosis is a process whereby the cell acquires materials from the extracellular fluid (3 forms)

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PHAGOCYTOSIS occurs when membrane extensions, termed pseudopodia, engulf a particle and internalize it into a vaculoe

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PINOCYTOSIS is the incorporation of droplets of extracellular fluid into the cell in small vesicles

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RECEPTOR-MEDICATED ENDOCYTOSIS is when receptors with specific molecules bound to them aggregate within the membrane, and then an invagination forms around them to create a cytoplasmic vesicle

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Passive Transport

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Movement of substances along a concentration gradient

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ATP is not required

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Organelles

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are complex, organized structures with unique, characteristic shapes

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Each type performs a different function for the cell

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Collectively, the specialized functions of all organelles are essential for normal cellular structure and activities

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Mitochondria

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organelles with a double membrane

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produce large amounts of ATP

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are called the powerhouse of the cell

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Ribosomes

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very small, dense granules that are responsible for protein production (synthesis)

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Each has a small and large subunit

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the small subunit is about one half the size of the large subunit

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The Cytoskeleton

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Filamentous proteins form the cytoskeleton, which helps give the cell its shape and coordinates cellular movements

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Microfilaments
Intermediate filaments
microtubles

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Membranous Organelles

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Some organelles are surrounded by a membrane

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called Membrane-bound organelles, or membranous organelles

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i.e. Cilia and Flagella

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Appendages extending from the surface of some cells

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Cilia usually occur in large numbers

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work together to move materials or fluids along the surface of a cell

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Flagella are longer than cilia, and usually occur as single appendages

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The nucleus:

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central core, control center, of cellular activities.

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Usually the largest structure and appears as a single spherical or oval structure

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enclosed by a double membrane called the nuclear envelope

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Nuclear envelope controls the entry and exit of materials between the nucleus and the cytoplasm

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Nucleolus:

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the cell nucleus may contain one or more usually spherical, darkstaining bodies called nucleoli

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They are responsible for making the small and the larger subunits or ribosomes

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Chromatin and DNA:

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DNA is the genetic material housed within the nucleus of the cell

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DNA is a polymer of nucleotides (sugar, phosphate, nitrogen base) in the shape of a double helix

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Strands of DNA and histone proteins associate within the nucleus to form chromatin

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Chromosome:

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the most organized level of genetic material

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each chromosome contains a single, long molecule of DNA and associated proteins

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become visible only when the cell is dividing

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The cell cycle: life cycle of a cell

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New cells must be made continuously in order for an organism to grow and replace its damaged cells

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Mitosis and Meiosis:

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There are two types of cell division

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Mitosis is the cell division process that takes place in somatic cells

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Sex cells undergo a cell division process called MEIOSIS

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interphase
prophase
metaphase puffy
anaphase middle
telophase apart
cytokinesis two

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Tumor:

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normal tissue development exhibits a balance between cell division and cell death

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if this balance is upset and cells multiply faster than they die, abnormal growth results in a new cell mass that is called a NEOPLASM or TUMOR

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Cancer:

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Benign neoplasms usually grow slowly and are confined within a connective tissue capsule

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Cells within these tumors dedifferentiate--they revert to a less specialized state, and cause an increase in their own vascular supply to support their growth

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these tumors are usually not lethal, but they have the potential to be life-threatening

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if they compress brain tissue, nerves, blood vessels, or airways

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Cancer is general term used to describe a group of diseases characterized by various types of malignant neoplasms unencapsulated

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contain cells that dedifferentiate

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increase their vascular supply

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grow rapidly and spread easily to other organs by way of the blood or lymph metosis

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cancer cells lose control of their cell cycle

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they divide too frequently and grow out of control

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cancer cells lose contact inhibition they overgrow one another and lack the ability to stop growing and dividing when they crowd other cells

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Exhibit dedifferentiation and revert to an earlier, less specialized developmental state

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Produce chemicals that cause local blood vessel formation resulting in increased blood vessels in the developing tumor (angiogenesis)

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have the ability to squeeze into any space invasiveness permitting them to leave their place of origin and travel elsewhere in the body

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Acquire the ability to metastasize aka spread to other organs in the body

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