3. The Cell The Fundamental Unit of Life PDF

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1. The Cell a. Every living organism is composed of one or more cells b. Nothing smaller than a cell is capable of performing all the activities required for life c. Some living creatures are unicellular (composed of just one cell) i. Ex. microscopic bacteria d. Other living creatures are composed of trillions of cells i. Ex. humans or other mammals e. All cells can be classified into two general kinds i. Prokaryotic Cells 1. Smaller than a eukaryotic cell 2. Simple 3. No membrane enclosed organelles 4. First appeared about 3.5 billion years ago 5. Not contained w/in any cellular structure 6. Unicellular 7. Bacteria and Archaea 8. Structure a. Plasmids i. Small rings of DNA that duplicate independently and can be exchanged among cells b. Cytoplasm i. Interior of the cell c. Capsule i. A sticky outer coat that surrounds the cell wall 1. Provides protection and helps cell stick to surfaces d. Cell Wall i. Rigid outer layer that protects cell and provides shape e. Plasma Membrane i. A thin layer that regulates the passage of substances between the cell and the surroundings f. Flagellum i. Long cellular appendage that aids in movement g. Nucleoid i. Nucleus like region where DNA is coiled ii. NOT surrounded by membrane h. Ribosomes i. Small structures that build proteins using instruction encoded in DNA i. Pilus i. Plural-Pili ii. Short projections that can attach to surfaces or other prokaryotes ii. Eukaryotic Cells

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Typically, 10-100x larger than prokaryotic cell More structurally complex Has plasma membrane enclosed organelles Evolved from prokaryotes about 1.8 billion years ago Housed in membrane enclosed nucleus Unicellular or multicellular Plants, animals, fungi and protists (basically all nonprokaryotic life) 8. Many organelles are surrounded by their own cell membranes along with the plasma membrane 9. Structure (Idealized Animal Cell) a. Lysosome i. Membrane enclosed bubble of digestive enzymes that can break down and recycle foreign or worn out cellular substances ii. Unique to animal cells b. Ribosomes i. Sites of protein manufacturing ii. May be free-floating or attached to rough endoplasmic reticulum c. Golgi Apparatus i. An organelle that receives, refines and ships many cellular products d. Vesicle i. Membrane enclosed sac that stores or transports materials in the cytoplasm e. Plasma Membrane i. Outer boundary of the cell ii. Regulates movement of substances into and out of the cell f. Cytoskeleton i. Network of fibers that maintains the cell’s shape, provides support and aids movement g. Cytoplasm i. Fluid filled region of the cell between the nucleus and the plasma membrane h. Flagellum i. Long appendage that propels the cell i. Mitochondrion i. Plural Mitochondria ii. Site where the cell harvests energy from food molecules j. Endoplasmic Reticulum (ER) i. A manufacturing site for a wide variety of cellular products k. Nuclear Envelope

i. A double layer of membrane that regulates traffic between the nucleus and the cytoplasm l. Nucleus i. Location of most of the cell’s DNA 10. Structure (Idealized Plant Cell) a. Chloroplast i. Organelle containing structures that convert light energy into food energy during the process of photosynthesis ii. Unique to plant cells b. Mitochondrion c. Nuclear envelope d. Nucleus e. Ribosomes f. Cytoskeleton g. Golgi Apparatus h. Vesicle i. Endoplasmic Reticulum (ER) j. Cytoplasm k. Plasma Membrane l. Cell Wall i. Rigid, protective layer made of cellulose that helps maintain cell shape ii. Only in plant cells m. Central Vacuole i. Storage sac that can hold a variety of substances, like nutrients or water iii. Membranes 1. To ensure survival, cells must maintain a relatively constant internal environment regardless of external environment changes a. This is accomplished through the use of a Plasma Membrane i. A thin, flexible oily sheet that forms the boundary between each living cell and its surroundings ii. Has a pretty simple structure iii. Can perform many functions iv. Most importantly, regulates passage of materials in and out of the cell v. Structure 1. Composed mostly of phospholipids and proteins a. (other membranes w/in cell are also composed this way) 2. Phospholipids a. A special kind of lipid in biological membranes

b. Each molecule has a phosphate groups as its head and two fatty acids for tails i. Heads are hydrophilic ii. Tails are hydrophobic c. Because of its head and tail, these molecules will spontaneously organize themselves into a two layered membrane i. Tails orient toward interior of membrane and form an oily barrier ii. Heads face the water environment on the inside and outside of the membrane d. Organized into two layers (Phospholipid Bilayer) i. Along w/ most of the proteins in the bilayer, the actual bilayer drifts in the plane of the membrane, causing it to flex and undulate e. In animal molecules i. Molecules of cholesterol w/in bilayer provide additional flexibility ii. Fluid Mosaic- fluid because molecules can move freely past one another/ mosaicbecause of diversity of proteins that float like icebergs in the phospholipid sea b. Extracellular Fluid i. Liquid environment outside the cell ii. Plasma membrane regulates passage of materials between this fluid and the cell’s inside c. Cytoplasm i. Interior of the cell, consisting primarily of a watery liquid called Cytosol, various organelles and dissolved molecules d. Membrane Proteins i. Most membranes had embedded proteins 1. Some help regulate passage of materials in and out of the cell

2. Others aid in communication between neighboring cells, facilitate chemical reactions or help anchor the cell or its components ii. Some proteins are fixed in place while others float w/in the phospholipid bilayer iii. Some proteins extending from the plasma membrane have carbohydrate chains that serve as markers that other cells can recognize iv. Transport 1. Passive Transport a. Occurs when a substance moves across a membrane from an area where its concentration is higher to an area where its concentration is lower i. Said to occur along a concentration gradient b. Substances that move via passive transport flow freely w/ no requirement for energy expenditure by the cell i. Ex. O2 w/in human lungs 1. Gas diffuses from air into the blood while CO2 diffuses from the blood into the lungs c. Diffusion i. The movement of molecules from an area of higher concentration to an area of lower concentration 1. Ex. perfume molecules moving out of a bottle and into a room d. Osmosis i. The diffusion of water ii. Water always flows from an area of higher water concentration to an area of lower water concentration 1. EX. placing meat in salt will cure it (draw out the water) iii. Water can sometimes flow through a membrane itself iv. Other times it requires a protein channel to pass through the membrane e. Facilitated Diffusion i. Some substances cannot cross a membrane alone 1. Possibly because they are too long ii. Such substances are then transported through specific proteins embedded in the membrane 1. Proteins act as selective channels, each allowing specific molecules to cross membrane iii. Always move down the concentration gradient 2. Active Transport

a. Involves moving a substance against its concentration gradient from where it is less concentrated to where it is more so b. Requires an expenditure of energy on the cell’s part c. Usually driven by a protein that sits w/in the membrane d. Endocytosis i. Means of accomplishing the transport of large substances ii. Substances to be ingested (food or foreign substances to be destroyed) are packaged into vesicles (bubbles surrounded by membranes) that bud inward from the plasma membrane 1. The vesicle then travels through cytoplasm to its destination e. Exocytosis i. An export of large quantities of material from the cell ii. Vesicles containing material to be exported fuse w/ plasma membrane, dumping the contents into the environment around the cell 1. Ex. cells in tear glands use exocytosis to export salty tears v. The Nucleus 1. The most prominent membrane-enclosed organelle 2. Houses most of the cell’s DNA packaged as chromosomes a. Structures consisting of one DNA molecule and associated protein molecules b. Control cell’s activities by directing protein production 3. Structure a. Nuclear Envelope i. A double phospholipid membrane that regulates the passage of material in and out of the nucleus ii. Aka nuclear membrane iii. Each of the two layers has a structure similar to the cell’s outer plasma membrane 1. Has a phospholipid bilayer and associated proteins b. Nuclear Pore i. An opening through which materials may pass into and out of the nucleus ii. Protein lined c. Nucleolus i. Site where ribosomal RNA is made d. Chromosomes i. Storage site for most of the cell’s genetic information

ii. Human body has 46 chromosomes in the nucleus iii. Chromatin 1. w/in nucleus, DNA molecules are wrapped around proteins to form these fibers 2. Long chromatin fibers twist and folds to form a chromosome 3. When a cell is not dividing, much of the chromatin Is very loose a. Coils tightly during cell division vi. Protein Production 1. Begins in the nucleus a. Process of transcription results in production of a molecule of RNA from DNA b. RNA molecule then carries the instructions for making a protein from the nucleus to the cytoplasm where translation at the ribosomes occurs i. During translation, info contained in the RNA is used to produce proteins 2. Endoplasmic Reticulum a. Network of membrane enclosed passageways and sacs that touches the outside of the nuclear envelope and extends deep into the cytoplasm b. Smooth ER membrane i. Contains enzymes that produce lipids 1. Ex. steroid hormones c. Rough ER membrane i. Studded w/ ribosomes attached to its surface 1. Produce many different kinds of proteins 3. Ribosomes a. Sites where proteins are made b. Some ribosomes are bound to membrane of rough ER while others float freely in cytoplasm 4. Golgi Apparatus a. A series of sacs where proteins are modified, stored and distributed b. One side of the Golgi receives vesicles containing new proteins i. As the protein travels, it is modified by enzymes and emerges as refined product ii. Modified protein travels in vesicles that may be transported w/in the cell or exported outside of it 5. Vesicles a. Small bubbles made of membrane b. Used to transport material through the cell c. Lysosomes

i. Type of vesicle that contain digestive enzymes that can dissolve large food molecules, old cellular components or invasive organisms such as bacteria ii. Not involved w/ protein production vii. Chloroplasts and Mitochondria 1. All cells require a continuous supply of energy to power life’s processes 2. Both organelles contain membranes that fold inward, forming fluid-filled spaces 3. Chloroplasts a. Exclusive to plant cells and some algae b. Are the organelles of photosynthesis i. The energy of sunlight is captured and used to create molecules of sugar ii. Sugar is then used to power cellular activities or are stored in plant tissues, such as stems and leaves iii. During photosynthesis, chloroplasts required a steady supply of water and carbon dioxide for building sugars iv. Oxygen and heat are released as waste produces c. Sugars produced by photosynthesis provide the energy that powers most ecosystems on Earth d. Surrounded by double membrane 4. Mitochondria (singular: mitochondrion) a. Provide energy to nearly all eukaryotic cells b. In both plant and animal cells c. W/in mitochondria i. Series of enzymes perform a sequence of chemical reactions called Cellular Respiration 1. Uses oxygen to harvest chemical energy from sugar molecules (namely glucose) 2. Some harvested energy is stored as chemical energy in ATP molecules a. Can be used to power many other cellular processes i. i.e. growth 3. Carbon dioxide, water and heat are released as waste products d. Also contains a small amount of DNA (mtDNA or mitochondrial DNA) i. Thought to be evidence that mitochondria evolved from free-living bacteria ii. Often used in genetic studies viii. Cellular Organelles 1. Eukaryotic cells contain a wide variety of organelles that perform many functions important to life

2. Vacuoles a. Intracellular sacs that come in a variety of sizes b. Perform diverse functions i. Some store food ii. Others pump water out of a cell c. Many plant cells have large central vacuoles that can store nutrients, pigments, toxins and water 3. Flagella (singular: flagellum) a. Long extension that can propel the cell by whipping back and forth, like the tail of a sperm 4. Cilia (singular: cilium) a. Move in a coordinated back and forth motion b. Usually short and numerous c. Ex. ciliated cells in the windpipe help keep airway dust free 5. Cell Walls a. contained in the cells of plants, fungi and some protists but not in animal cells b. surrounds the plasma membrane c. Walls of plant cells are made from fibers of a carbohydrate called cellulose i. Cell walls of other types of cells are made from other molecules d. Provides protection, helps maintain the cell’s shape, and provides the stiffness that allows thin leaves to stand upright 6. Cytoskeleton a. A network of protein fibers that provides mechanical support, anchorage and reinforcement b. Reason animal cells are able to maintain their shape c. Provides a series of tracks along which vesicles move d. Form extensive network but can be quickly dismantled and reassembled, providing flexibility to cell’s shape 7. Extracellular Matrix a. Produced by animal cells b. Helps hold cell together c. Lies just outside the plasma membrane d. Consists primarily of an interwoven network of collagen protein i. Connects to proteins that span the plasma membrane allowing signals to be transmitted into the cell...