A Tour of the Cell AP Biology: Chapter 6

What are Cells? Cells are the basic unit of ALL LIFE –The single cell is a microcosm of life: Interactions among all the other cellular components Structure and Function are connected Interaction with other cells outside the environment

The plasma membrane (5) bounds the cell and encloses the nucleus and cytoplasm. The cytoplasm consists of specialized bodies called organelles. They are suspended in a fluid matrix called cytosol (cytoplasm). Plasma Membrane

The plasma membrane separates internal metabolic events from the outside environment. The membrane is made of a double phospholipid bilayer. The membrane has polar hydrophilic heads and nonpolar hydrophobic tails.

Cell Fractionation Cell Fractionation enables researchers to isolate organelles. That is, cells are taken apart, separating the major organelles so that their function can be studied.

Overview of all Cells Prokaryotic –No Nucleus –--No internal membrane structures ––Include bacteria and archaea Eukaryotic –Nucleus Present ––Include protists, plants, fungi, and animals

Cell Size Cell size is typically microns There is a LARGE surface area per volume ratio in order for a cell to grow successfully. WHY? Compartmental Organization increases the possibility of division of labor

Nucleus or Nucleoid The nucleus (4) is bound by the nuclear envelope (1), a phospholipid bilayer similar to the plasma membrane. Eukaryotic Cells: membrane bound nucleus Prokaryotic Cells: nucleoid mass of “naked DNA” Nucleus contains DNA, the DNA is spread out within the nucleus as a threadlike matrix called Chromatin (3) When the cell begins to divide, the chromatin condenses into rod-shaped bodies called Chromosomes.

Nucleus/Histones/Nucleoli Before dividing, the chromosomes are made up of 2 long DNA molecules and various histones. Histones are proteins that organize the lengthy DNA, coiling it into bundles called nucleosomes. Nucleoli (2) are also found in the nucleus, they are concentrations of RNA in the process of manufacturing ribosomes

Endoplasmic Reticulum Endoplasmic Reticulum (ER)(**) consists of stacks of flattened sacs involved in the production of various materials. When ribosomes are present around the ER, it is considered rough ER.(**) When ribosomes are present, the ER will make glycoproteins. (a protein with a carbohydrate component)

ER If there are no ribosomes present, the ER is considered smooth ER (6). Smooth ER synthesizes lipids and hormones. Smooth ER produces substances that help the cell export materials out of the cell. Smooth ER helps break down toxins, drugs and toxic products from cellular reactions.

Golgi (7) Golgi apparatus is also a group of flattened sacs, they are located away from the nucleus. Golgi modify and package proteins and lipids into vesicles that will bud out from the surface of the Golgi. Vesicles will migrate to and merge with the membrane and release their contents outside of the cell.

Lysosome (8) Lysosomes are vesicles from a Golgi that contain digestive enzymes. They break down food, cellular debris, and foreign invaders. Lysosomes are not found in plant cells.

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Peroxisomes Peroxisomes break down substances with in cells and tissues. For example, cellular respiration produces H 2 O 2, which is toxic to cells, peroxisomes assist in breaking the H 2 O 2 into H 2 O. (Enzyme present?) Common in liver and kidney cells where they break down toxic substances.

Mitochondria (9) Mitochondria carry out aerobic respiration, a process in which energy (ATP) is obtained from carbohydrates.

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Chloroplasts (15) Chloroplasts carry out photosynthesis, the plant process of incorporating energy from sunlight into carbohydrates (CH 2 0)

Ribosomes (6) Ribosomes are made of 2 subunits. The two subunits are labeled 60S and 40S and are made of proteins and RNA molecules. Ribosomes move across the nuclear envelope and into the cytoplasm to be assembled into a single ribosome. In the cytoplasm, ribosomes assist in the assembly of amino acids into proteins.

Microtubules (11) Microtubules, intermediate filaments, and microfilaments are 3 proteins fibers of decreasing diameter. (microtubules are largest, microfilaments are smallest) All are involved in establishing the shape of the cytoplasm AND coordinating movements of the cytoplasm.

Microtubules/Cytoskeleton Microtubules are made of the protein TUBULIN and provide support and motility for cellular activities. Cells are active, not “STILL”. (largest of all 3 protein fibers) The are found in the spindle apparatus in cell division and in flagella and cilia. These are best known for providing MOTILITY to the cell.

Intermediate filaments/Cytoskeleton Intermediate filaments provide support for maintaining the shape of the cell.

Microfilaments/Cytoskeleton Made of the protein actin, and are also involved in cell motility. They are found in muscle cells, and in cells that change shape (phagocytes, WBC).

Flagella/Cilia (14) Structures that protrude from a cell membrane and make wavelike movements. Flagella are long and few –A single flagella propels sperm Cilia are short and many –Numerous cilia line the respiratory tract to sweep away debris Both are arranged in a “9+2” array. –9 pairs (doublets) of microtubules arranged in a circle surrounding a pair of microtubules

Centrioles (13) & basal bodies Centrioles and basal bodies act as microtubule organizing centers Centrioles make up the spindle apparatus in cell division…they organize microtubular movement Basal Bodies are at the base of flagella and cilia, they organize development of the flagella and cilia. They have a 9-triplet configuration.

Cell Walls (16) Cells walls are found in plants, fungi, protists, and bacteria. They develop outside the cell membrane and provide support for the cell. In plants, the cell wall consists of cellulose (found in Plant Kingdom). Cell walls can also be made of chitin (found in Fungi Kingdom).

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Vacuoles (17) and Vesicles Fluid-filled membrane bound bodies. There are many different types of vacuoles/vesicles. –Transport vesicles, move materials between organelles and/or the membrane –Food vacuoles, temporarily store nutrients –Storage vacuoles, in plants store starch, pigments, toxic substances –Central vacuoles, large bodies in plant cells that store nutrients. They exert pressure (turgor) on the cells, making them rigid. –Contractile vacuoles, collect and pump excess water out of the cell.

Cell Junctions Serve to anchor cells to another or to provide a passageway for cellular exchange.

Intercellular Junctions Tight Junctions: the membranes of neighboring cells are fused, forming belts around the cells. Prevents leakage (i.e. intestinal epithelium) Desmosomes: fasten cells together into strong sheets. Gap Junctions: provide cytoplasmic channels between adjacent cells. Salts, sugars, amino acids and other small molecules can pass from cell to cell. Common in animal embryos, allows for chemical communication Page 121

Cell Junctions Narrow channels between PLANT cells. A narrow tube of ER, called desmotubule, surrounded by a cytoplasm and plasma membrane, passes through the channel.