Dat Biology- The Cell

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The phospholipid membrane

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A selectively permeable layer that allows small, uncharged, polar molecules (like water and CO2) and hydrophobic molecules (like O2) across. Large polar molecules (glucose) and ions are impermeable.

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Channel proteins

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Provide passageway for hydrophilic (water soluble) substances like polar and charged molecules.

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Ion channels

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Allow the passage of ions across the membrane (ex: gated channels in nerve cells)

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Porins

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Proteins that allow the passage of certain ions and small polar molecules (ex: aquaporins in the plasma membrane of kidney cells) increases passage of water molecules.

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Carrier proteins

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Bind to molecules, which are then transferred across the membrane after the carrier changes shape. (ex: passage of glucose)

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Transport proteins

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Active transport (use ATP) to take materials across the membrane. (ex: Na+-K+ pump used to maintain ion levels on opposite sides of the plasma membrane)

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Recognition proteins

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Give each cell identification and distinction between self cells and foreign cells and virus cells. Called glycoproteins because they have short polysaccharide chains attached (this part extends through the membrane and onto the surface)

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Adhesion proteins

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Attach cells to neighboring cells or provide anchors for the internal filaments and tubules that give stability to the cell.

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Receptor proteins

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Provide specific binding sites for hormones or other trigger molecules. In response to the hormone or trigger molecule, a specific cell response is activated.

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Cholesterol

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These molecules are distributed throughout the phospholipid bilayer to provide some rigidity to the plasma membrane. *Found only in animal cells (called sterols in plant cells)

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Glycocalyx

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A carbohydrate coat that covers the outer face of the cell wall of some bacteria and the outer face of the plasma membrane of certain animal cells. Consists of various oligosaccharides that are attached to glycolipids and glycoproteins. Purpose changes depending on the cell- some adhesive capabilities, a barrier to infection, or markers for cell-cell recognition.

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Nucleus

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Bounded by a bilayer nuclear envelope. Contains DNA and nucleoli, or regions of ribosome synthesis. Also the site where chromosomes separate during cell division.

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Ribosome

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Manufactured in the nucleus and consist of RNA and protein. The two subunits move into the cytoplasm where they are assembled into a single unit. The purpose of the ribosome is to assist in the assembly of amino acids into proteins.

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Endoplasmic reticulum

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Consists of stacks of flattened sacs involved in the production of various materials.

When ribosomes are present on the surface, it is called rough ER. This ER creates glycoproteins by attaching polysaccharide groups to polypeptides as they are assembled by the ribosomes.

Smooth ER is responsible for synthesis of lipids and hormones and the breakdown of toxins, drugs, and toxic by-products from cellular respiration.

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Golgi apparatus

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Flattened sacs arranged like a stack of bowls. They modify and package proteins and lipids into vesicles (small, spherically shaped sacs that bud from the outside surface of the GA). Vesicles often migrate to and merge with the PM, releasing their contents by exocytosis.

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Lysosome

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Vesicles from a Golgi apparatus that contain digestive enzymes. They break down food, cellular debris, and foreign invaders like bacteria. A low pH is favorable to the activity of the enzymes and must be maintained inside the lysosome. *Not found in plant cells

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Peroxisomes

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Break down various substances, including hydrogen peroxide, fatty acids, and amino acids. Common in liver and kidney cells. Also found in plant cells where they modify the by-products of photorespiration,. Also, in germinating seeds peroxisomes (called glyoxysomes) help with growth.

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Mitochondria

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Carry out aerobic respiration, a process by which energy is obtained from carbohydrates.

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Chloroplasts

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Carry out photosynthesis

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Microtubules, intermediate filaments, and microfilaments

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Three proteins of decreasing diameter. All are involved in establishing the shape of the cytoskeleton (also involved in coordinating movement).

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Microtubules

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Made of tubulin and provide support and motility for cellular activities. They are found in the spindle apparatus, which guides the movement of chromosomes during cell division. They are also found in flagella and cilia.

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Intermediate filaments

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Provide support for maintaining the shape of the cell.

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Microfilaments

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Made of the protein actin and are involved in cell motility. They are found in muscle cells and in cells that move by changing shape such as phagocytes.

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Flagella and cilia

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structures that protrude from the cell membrane and make wavelike movements.

Flagella are long with fewer numbers per cell. They move in a snakelike motion.

Cilia are shorter, with many per cell and they move with back-and-forth movement.

Structurally, both flagella and cilia consist of microtubules in a "9+2" array- nine pairs surrounding a central pair.

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Centrioles and basal bodies

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Act as microtubule organizing centers. A pair of centrioles (enclosed in a centrosome, found outside the nucleus) gives rise to the microtubules that make up the spindle apparatus used in cell division.

Basal bodies are at the base of each flagellum and cilium and appear to organize their development. *Plant cells lack centrioles and only "lower" plants (mosses and ferns) have flagella and basal bodies.

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Vacuoles and vesicles

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Fluid-filled, membrane-bound bodies. Transport vesicles move material between organelles or between organelles and the PM.

Food vacuole (store food, bind with lysosomes), storage vacuoles (store starch, pigment, and toxic substances), central vacuoles (large, occupy most of the interior of plant cells, store water and maintain turgor or rigidity in the cell), contractile vacuoles (found in single celled organisms, pump water out)

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Cell wall

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Found only in plants, fungi, protists, and bacteria. They develop outside the plasma membrane and provide support for the cell walls of fungi.

Usually consist of cellulose (plants) or chitin (fungi)

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Extracellular matrix

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Found in animals, in the area between adjacent cells (outside the PM and the glycocalyx). This area is filled with fibrous structural proteins, adhesion proteins, and polysaccharides secreted by the cells.

Provides mechanical support and helps bind adjacent cells together.*Where collagen is found

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Anchoring junctions

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Protein attachments between adjacent animal cells. Ex: desmosome, consists of proteins that bind cells together, providing mechanical stability. Associated with protein filaments that extend into the interior of the cell.

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Tight junctions

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Tightly stitched seams between animal cells. The junction completely encircles each cell, producing a seal that prevents the passage of materials between the cells.

Characteristic of the lining of the digestive tract where materials must pass through ells (not intracellular spaces).

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Gap junction

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A type of communicating junction found in animal cells. Narrow tunnels between cells that consist of connexins. These are proteins that prevent the cytoplasm form mixing but allow the passage of small ions.

Allow communication between cells through the exchange of materials or through transmission of electrical impulses.

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Plasmodesmata

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A type of communicating junction. Narrow channels found in plant cells, a tube of ER (called a desmotubule) surrounded by cytoplasm and the PM passes through the channel. Material exchange through a plasmodesmata occurs through the cytoplasm surrounding the desmotubule.

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Distinguishing plant cells from animal cells

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1. the presence of cell walls, chloroplasts, and central vacuoles in plant cells and their absence in animal cells.

2. The presence of lysosomes, centrioles, and cholesterol in animal cells and their absence in plants.

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Prokaryotic characteristics

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Do not have a nucleus, DNA is a single naked DNA molecule (no proteins), smaller ribosomes, cell walls of bacteria (when present) are made of peptidoglycans and the cell walls of archaebacteria contain various polysaccharides but not peptidoclycan, cellulose, or chitin, and flagella are not constructed of microtubules.

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Simple diffusion

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the net movement of substances from an area of higher concentration to an area of lower concentration.

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Osmosis

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The diffusion of water molecules across a selectively permeable membrane. Causes an increase in turgor.

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Dialysis

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The diffusion of solutes across a selectively permeable membrane.

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Plasmolysis

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The movement of water out of a cell that results in the collapse of the cell

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Facilitated diffusion

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The diffusion of solutes or water through channel proteins in the plasma membrane.

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Countercurrent exchange

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Describes the diffusion of substances between two regions in which substances are moving by bulk flow in opposite directions. (ex: flow of water vs. flow of blood in the gills of a fish)

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Active transport

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The movement of solutes against their gradient. Requires energy use. Usually transfer small ions (Na, K, Cl, H), amino acids, and monosaccharides across the membrane.

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Vesticular transport

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Uses vesicles or other bodies in the cytoplasm to move macromolecules or large particles across the PM.

Exocytosis- vesicle fuses with PM and releases contents outside of cell
Endocytosis- Plasma membrane merges to engulf substance outside of cell. Three kinds: phagocytosis (undissolved material is engulfed), pinocytosis (dissolved material is engulfed), and receptor mediated (a form of pinocytosis, when specific molecules are bound)