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Cells Karen Malt, MSN, RN Cells (part 1) • Robert Hooke (1635-1703)- a scientist who first applied the word “cell” to describe the basic unit of life after viewing small spaces created by cell walls using a very primitive microscope. • Cells- the smallest unit of all living things. Cells (part 1) •Cells differ in size and shape. • Human cells are microscopic in size and vary in shape (threadlike, flat, irregular, brick-shaped) and size. • Ovum – (female sex cell) is about 150 micrometers • Red Blood Cell (RBC) – 7.5 micrometers Cells (part 1) • Cell Composition – • Cytoplasm- a living substance that exists only in cells. • Plasma Membrane- thin membrane which surrounds the cell. This membrane separates the contents of the cell from the saltwater solution called “Interstitial Fluid” (tissue fluid), which bathes every cell inside the body. Cells (part 1) •Parts of the Cell (main parts) • Plasma Membrane –outer boundary • Cytoplasm- living material in the cell (except the nucleus) • Nucleus- large structure that contains the genetic code Cells (part 1) • Plasma Membrane –forms the outer boundary of the cell, very delicate, thin structure 3/10,000,000 of an inch thick. • The Plasma Membrane is made up of two layers of fat molecules; • Phospholipids – form a framework • Cholesterol – provides stabilization to prevent breakage Cells (part 1) • Plasma Membrane – although fragile, is strong enough to keep the cell intact. • Allows certain substances in and bars certain substances from entering the cell. • The Plasma Membrane has “receptors” on it which allows for certain chemicals to bind to these receptors therefore a change in the cell function will follow. • The Plasma Membrane also identifies a cell as being part of a particular individual (Tissue Typing). This is done before transplanting tissue from one person into another. Cells (part 1) • Cytoplasm- Internal living material of cells. This substance fills the space between the plasma membrane and the nucleus. • Organelles- (little organs) numerous small structures that make up much of the cytoplasm and function for the cell, like organs in the body. • Cytoskeleton- “cell skeleton” or the cell’s internal supporting moving framework. Cells • Organelles: • • • • • • • Ribosomes Endoplasmic Reticulum Golgi Apparatus Mitochondria Lysosomes Centrosome Cell Extensions (part 1) Cells (part 1) • Ribosomes- very small particles found throughout the cell. Each ribosome is made up of two tiny subunits constructed mostly of a specific type of RNA called “ribosomal RNA” or (rRNA). • Function: make enzymes and other protein compounds. Also known as “protein factories.” Cells (part 1) • Endoplasmic Reticulum –tubular passage ways that carry proteins and other substances through the cytoplasm of the cell from one area to another. • Two Types of ER • Rough- A rough surface on the ER is due to all of the ribosomes attached to its surface. The rough ER receives, folds, and transports newly made proteins. • Smooth- ER has no ribosomes attached to it and the smooth ER makes a new membrane for the cell. Cells (part 1) • Golgi Apparatus- tiny, flattened sacs stacked on one another near the nucleus, which makes carbohydrate compounds, combines them with protein molecules and then packages the product in a globule. Cells (part 1) • Mitochondria- energy converting chemical reactions occur within this organelle. These supply most of the “power” for the cellular work. This organelle has been nicknamed the cells “power plants.” •NOTE: the mitochondria has its own DNA. Cells (part 1) •Lysosomes – nicknamed “digestive bags” because lysosomes contain enzymes that promote hydrolysis. They break apart or digest large nutrient molecules. They can also digest microbes that are invading the cell. • NOTE: lysosomes were once thought to be responsible for “cell death” or apoptosis, which makes space for new cells, but a different mechanism is now known to cause this. Cells (part 1) • Centrosome – is a region of cytoplasm near the nucleus, which is responsible for organizing and moving the structures within the cell. • Centrioles- paired organelles found within the centrosome. These structures form a “spindle” which moves chromosomes during cell division. Cell •Cell Extensions• Microvilli • Cilia • Flagella (part 1) Cell (part 1) • Microvilli- “fingerlike” projections off of the cell membrane of some cells. Increase its ability to absorb substances. • Cilia- “hair-like” extensions that allow for movement. Example; propel mucus over the surface of cells in the respiratory/reproductive tract. • Flagella- A single projection extending from a cell. Whips around like a propeller. Example: sperm cell Cell (part 1) • Nucleus – central structure of a cell. • Appears like a small sphere in the center portion of the cell. The nucleus contains most of the cells genetic code, which controls every organelle in the cell. It also controls cellular reproduction. • Nuclear Envelope- has tiny openings called “nuclear pores” that permit large molecules to move in and out of the nucleus. Within the nuclear envelope is “nucleoplasm.” Within the nucleoplasm are: • Nucleolus- Critical in protein formation • Chromatin Granules- substance in the nucleus of cells made up of DNA Cells (part 1) •Chromosomes – During cellular division, DNA molecules become coiled tightly forming chromosomes. Each cell of the body has 46 different DNA molecules.