LS7A / Ch.5 Pre&Post Objectives

Define and term diffusion.

Diffusion is the random movement of molecules. Diffusion results in the movement of the molecule from an area of higher concentration to an area of lower concentration. (Net movement of molecules results only when there are concentration differences)

Describe the organization fo the eukaryotic cell.

Eukaryotic cells (i.e. animals plants, fungi, and protists) have a nucleus. The presence of a nucleus in eukaryotes allows for the processes of transcription and translation to be separated in time and space. This separations allows for more complex ways to regulate gene expression than are possible in prokaryotes. For the cell membranes, there are "sterols". Eukaryotes have a remarkable internal array of membranes, these membranes define compartments, called organelles, that divide the cell contents into smaller spaces specialized for different functions. (Membranes organize the insides of an eukaryotic cell)

Describe the function of the eukaryotic organelles: mitochondrion, chloroplast, nucleus, endoplasmic reticulum, Golgi apparatus, lysosome, and vacuole.

Mitochondria -- specialized organelles that harness energy for the cell from chemical compounds like sugars and convert it into ATP. Chloroplast -- (In plant cells only) Convert energy of the sunlight into chemical energy. Nucleus -- The compartment of the cell that houses the DNA in chromosomes, and it coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction (cell division). Endoplasmic Reticulum (E.R.) -- The organelle involved in the synthesis of proteins and lipids. Golgi Apparatus -- The organelle that modifies proteins and lipids produced by the E.R. and acts as a sorting station as they move to their final destinations. Lysosome -- A vesicle derived from the Golgi apparatus that contains enzymes that break down macromolecules such as proteins, nucleic acids, lipids, and complex carbohydrates. Vacuole -- (Only in plant cells) Organelles that contribute to the structural rigidity or plants by maintaining turgor pressure against cell walls.

Define the terms organelle, cytoplasm, and cytosol.

Organelle -- Any one of several compartments in eukaryotes that divide the cell contents into smaller spaces specialized for different functions. Cytoplasm -- The contents of the cell other than the nucleus. Cytosol -- The region of the cell inside the plasma membrane but outside the organelles; the jelly-like internal environment that surrounds the organelles.

Compare and contrast the different passive (simple diffusion, facilitated diffusion) and active (primary, secondary) transport mechanisms.

Passive Transport Mechanisms (simple diffusion, facilitated diffusions) -- Passive transport works by diffusion, which results in the movement of the molecule from an area of higher concentration to an area of lower concentration. Some molecules diffuse freely across the plasma membrane as a result of differences in concentrations between the inside and the outside of a cell. Facilitated diffusion is when some molecules that cannot move across the lipid bilayer directly can move passively toward a region of lower concentration through protein transporters. Active Transport Mechanisms (primary, secondary) -- When substances are moved against the concentration gradient, this "uphill" movement is called active transport and it requires energy. During active transport, cells move substances through transport proteins embedded in the cell membrane. Some of these proteins act as pumps, using energy directly to move a substance into or out of the cell. Active transport that uses energy directly in this manner is called primary active transport. Secondary active transport is active transport that uses the energy of an electrochemical gradient to drive the movement of molecules. The movement of the couples molecule is driven by the movement of protons and not by ATP directly, this form of transport is secondary active transport. Secondary active transport uses the potential energy of an electrochemical gradient to drive the movement of molecules.

Identify the structure of different lipids: triglycerides, fatty acids, phospholipids, and cholesterol.

Phospholipids, the major component of cell membranes, are made up of glycerol attached to a phosphate-containing head group and two fatty acid tails. They are amphipathic because they have both hydrophilic and hydrophobic domains. Cholesterol is amphipathic (has both hydrophilic and hydrophobic regions), they hydrophilic region is simply a hydroxyl group (-OH) and they hydrophobic regions consists of four interconnected carbon rings with an attached hydrocarbon chain. This structure allows cholesterol to insert into the lipid bilayer so that its head group interacts with the hydrophilic head group of phospholipids, while the ring structure participates in van der Waals interactions with the fatty acid chains. Cholesterol increases or decreases membrane fluidity depending on temperature. At temperatures typically found in a cell, cholesterol decreases membrane fluidity because the interaction of the rigid ring structure of cholesterol with the phospholipid fatty acid tails reduce the mobility of the phospholipids. However, at low temperatures, cholesterol increases membrane fluidity because it prevents phospholipids from packing tightly with other phospholipids. Fatty Acids- Triglycerides-

What is different about a plant cell compared to an animal cell?

Plant cells have chloroplasts in addition to organelles, they convert energy of sunlight into chemical energy. They also have a cell wall outside of the plasma membrane. Plants do not use mitochondria as their primary energy producer.

Describe the organization of a prokaryotic cell.

Prokaryotic cells (i.e. bacteria, archaeons) do not have nucleus. Since prokaryotic cells do not have a nucleus, there is no physical barrier separating the genetic material from the rest of the cell. Instead DNA is concentrated in a discrete region of the cell interior known as the nucleoid. Bacteria often contain additional small circular molecules of DNA known as plasmids that carry a few genes. Prokaryotes do not synthesize sterols, but some synthesize compounds called hopanoids. Prokaryotes are small, typically 1-2 micros in a diameter or smaller. The small prokaryotes have a relatively high ratio of surface area to volume. Most prokaryotes lack the extensive internal organization characteristic of eukaryotes.

Differentiate between saturated and unsaturated fatty acids.

Saturated fatty acids means that there are no double bonds, so they are straight and tightly packed. Unsaturated fatty acids means that there are double bonds, which introduces kinks in the fatty acid tails, reducing the tightness of packing and enhancing lipid mobility in the membrane.

Explain how the chemical properties of a phospholipid bilayer allow it to act as a semipermeable membrane.

The membrane's ability to act as a selective barrier is the result of the combination of lipids and embedded proteins of which it is composed. The hydrophobic interior of the lipid bilayer prevents ions as well as charged or polar molecules from diffusing freely across the plasma membrane. In this way, the phospholipid bilayer allows it to act as a semipermeable membrane.

Describe the structure of the plasma membrane and the different ways that proteins can be associated with the lipid bilayer.

The plasma membrane are made up of a phospholipid bilayer with a phosphate hydrophilic head and two hydrophobic fatty acid tails. Proteins can be associate with the membrane in two ways: Integral membrane proteins are permanently associated with cell membranes and cannot be separated from the membrane experimentally without destroying the membrane itself. Peripheral membrane proteins are temporarily associated with the lipid bilayer or with integral membrane proteins through weak noncovalent interactions. They are easily separated from the membrane by simple experimental procedures that leave the structure of the membrane intact.

Define and relate the terms tonicity, osmosis, hypertonic, hypotonic, and isotonic.

Tonicity -- The ability of an extracellular solution to make water move into or out of a cell by osmosis. Osmosis -- The net movement of a solvent, such as water, across a selectively permeable membrane toward the side of higher solute concentration. Hypertonic (solution) -- One with a higher solute concentration that that inside the cell. Hypotonic (solution) -- One with a lower solute concentration that that inside the cell. Isotonic -- The same solute concentration.