Cellular Basis of Life Quiz

The plasma membrane regulates the exchange of substances between the cell's interior and its external environment.

The three main components are phospholipids, membrane proteins, and cholesterol.

Phospholipids form a bilayer with their hydrophobic tails facing each other and their hydrophilic heads facing the watery solutions inside and outside the cell.

<p>Membrane proteins are involved in various functions, including transporting molecules and ions, facilitating communication between cells, and acting as receptors for signals.</p> Signup and view all the answers

<p>Cholesterol disrupts the close packing of phospholipid tails, preventing them from becoming too rigid. This makes the membrane more fluid and flexible.</p> Signup and view all the answers

<p>Prokaryotic cells lack a membrane-bound nucleus and organelles, while eukaryotic cells have a nucleus and other membrane-bound organelles.</p> Signup and view all the answers

<p>Cells are small to maintain a high surface area to volume ratio, which is essential for efficient exchange of materials with the environment.</p> Signup and view all the answers

<p>The three methods are active transport, facilitated transport, and passive transport.</p> Signup and view all the answers

<p>Ribosomes are responsible for protein synthesis.</p> Signup and view all the answers

<p>Rough ER is studded with ribosomes, while smooth ER lacks these organelles.</p> Signup and view all the answers

<p>The Golgi apparatus modifies, sorts, and packages proteins and lipids synthesized by the ER, preparing them for secretion or delivery to other cellular compartments.</p> Signup and view all the answers

<p>Lysosomes are responsible for the breakdown of macromolecules within the cell. They contain hydrolytic enzymes that break down substances such as proteins, carbohydrates, and lipids.</p> Signup and view all the answers

<p>Peroxisomes break down fatty acids through oxidation and also break down hydrogen peroxide, a by-product of this process, preventing its harmful effects.</p> Signup and view all the answers

<p>The ER is continuous with the nuclear envelope, meaning they are connected and share a common membrane.</p> Signup and view all the answers

<p>Protein synthesis involves the formation of polypeptide chains from amino acids. Ribosomes are responsible for reading the genetic code within mRNA and assembling the correct sequence of amino acids.</p> Signup and view all the answers

<p>Ribosomes can be found free in the cytoplasm or bound to the endoplasmic reticulum.</p> Signup and view all the answers

<p>Facilitated diffusion uses a protein carrier to move molecules across a membrane down their concentration gradient, requiring no energy. Active transport also uses a protein carrier but moves molecules against their concentration gradient, requiring energy such as ATP.</p> Signup and view all the answers

<p>The Na+, K+ ATPase pump actively transports sodium ions (Na+) out of the nerve cell and potassium ions (K+) into the cell. This process maintains the electrochemical gradient across the cell membrane, which is crucial for generating and transmitting nerve impulses. When a nerve impulse occurs, ion channels open briefly, allowing diffusion of ions. The pump then restores the electrochemical gradient, preparing the neuron for the next impulse.</p> Signup and view all the answers

<p>Exocytosis involves the fusion of a membrane-bound vesicle with the cell membrane, releasing its contents into the extracellular space. Molecules like hormones, digestive enzymes, mucus, and milk are commonly transported via exocytosis.</p> Signup and view all the answers

<p>Large molecules are too big to fit through protein channels or bind to carriers. Instead, they are transported by mechanisms like endocytosis and exocytosis, where vesicles encapsulate these larger molecules and move them across the membrane.</p> Signup and view all the answers

<p>Both channel-mediated and carrier-mediated diffusion are facilitated by protein carriers, moving molecules down their concentration gradients. Channel-mediated diffusion involves specialized protein channels that allow passage of small ions. Carrier-mediated diffusion uses carrier proteins that bind to specific molecules and undergo conformational changes to transport them. Both processes do not require energy.</p> Signup and view all the answers

<p>In facilitated diffusion, molecules move passively down their concentration gradient, from an area of high concentration to an area of low concentration. When the concentration gradient reverses, the net movement of molecules also reverses, flowing from the area of low concentration to the area of high concentration. However, this movement requires energy, making it active transport rather than facilitated diffusion.</p> Signup and view all the answers

<p>Endocytosis involves the inward invagination of the cell membrane, forming a vesicle that encloses extracellular material. Three main types of endocytosis are: phagocytosis (engulfing large particles or cells), pinocytosis (taking in fluids and dissolved substances), and receptor-mediated endocytosis (specific binding of molecules to receptors on the cell membrane, triggering vesicle formation).</p> Signup and view all the answers

<p>Active transport is crucial for maintaining the electrochemical gradient across cell membranes because it moves molecules against their concentration gradient, often concentrating essential molecules inside the cell or removing waste products. For instance, the Na+, K+ ATPase pump in nerve cells actively pumps sodium ions out and potassium ions in, maintaining the electrochemical gradient necessary for nerve impulse transmission. This process requires energy to counteract the natural tendency of the ions to move down their concentration gradients.</p> Signup and view all the answers

<p>Catalase breaks down hydrogen peroxide (H2O2) into water and oxygen.</p> Signup and view all the answers

<p>Mitochondria are double-membraned organelles responsible for cellular respiration. The inner membrane folds inwards to form cristae, which increase the surface area for electron transport and ATP synthesis.</p> Signup and view all the answers

<p>The cytoskeleton is composed of actin filaments, intermediate filaments, and microtubules. Actin filaments provide structural support, facilitate cell movement, and play a role in muscle contraction. Intermediate filaments provide structural support and help maintain cell shape. Microtubules function in intracellular transport, cell division, and the formation of cilia and flagella.</p> Signup and view all the answers

<p>During cytokinesis, actin filaments form a contractile ring around the middle of the dividing cell. This ring contracts, pinching the cell membrane inward and eventually separating the two daughter cells.</p> Signup and view all the answers

<p>Actin filaments are involved in cytoplasmic streaming, the movement of cytoplasm within cells. This movement helps distribute nutrients and organelles throughout the cell.</p> Signup and view all the answers

<p>Catalase does not directly break down purines. However, it removes hydrogen peroxide, a byproduct of purine breakdown. This helps prevent oxidative damage to cells.</p> Signup and view all the answers

<p>Mitochondria are the powerhouses of the cell, responsible for ATP production through cellular respiration. The inner membrane, with its folded cristae, provides a large surface area for the electron transport chain and oxidative phosphorylation, processes that drive ATP synthesis.</p> Signup and view all the answers

<p>A disrupted cytoskeleton can lead to problems with cell shape, movement, intracellular transport, and cell division. These issues arise because the cytoskeleton provides structural support, facilitates movement, and helps organize and transport components within the cell.</p> Signup and view all the answers

<p>Cholesterol helps regulate the fluidity of the cell membrane by maintaining its stability at varying temperatures.</p> Signup and view all the answers

<p>Diffusion is the movement of molecules from an area of higher concentration to one of lower concentration until equilibrium is reached.</p> Signup and view all the answers

<p>Osmosis specifically refers to the movement of water through a semipermeable membrane, while diffusion involves the movement of solutes.</p> Signup and view all the answers

<p>A hypotonic solution has lower osmolarity than the cell, a hypertonic solution has higher osmolarity, and an isotonic solution has equal osmolarity.</p> Signup and view all the answers

<p>Polar or ionic small solutes cross the membrane through specific protein carriers known as permeases.</p> Signup and view all the answers

<p>The cell membrane limits the transport of large molecules such as proteins and nucleic acids, which cannot easily pass through.</p> Signup and view all the answers

<p>Passive transport is important because it allows cells to move substances across the membrane without using energy.</p> Signup and view all the answers

<p>In a hypertonic solution, water will move out of the cell, causing it to shrink.</p> Signup and view all the answers

<p>Hydrolysis reactions break down complex macromolecules, such as carbohydrates, proteins, and fats, into their constituent monomers by adding water molecules, cleaving chemical bonds. For example, the hydrolysis of sucrose produces glucose and fructose, and the digestion of proteins results in amino acids.</p> Signup and view all the answers

<p>Oxidation involves the loss of electrons from a molecule, while reduction involves the gain of electrons. In cellular respiration, glucose is oxidized to carbon dioxide, losing electrons. These electrons are then used to reduce oxygen to water.</p> Signup and view all the answers

<p>Phosphorylation reactions involve the addition of a phosphate group to a molecule, often activating or deactivating it. This is a critical process in regulating metabolic pathways and controlling enzyme activity. The primary source of phosphate groups for phosphorylation is ATP (adenosine triphosphate).</p> Signup and view all the answers

<p>Catabolic reactions involve the breakdown of complex molecules into smaller ones, releasing energy in the process. One example is glycolysis, the breakdown of glucose into pyruvate. This process generates ATP, which is the primary energy currency of cells.</p> Signup and view all the answers

<p>A hydroxyl group makes a molecule more soluble in water due to its ability to form hydrogen bonds with water molecules. It also contributes to the molecule's polarity and reactivity.</p> Signup and view all the answers

<p>Carboxyl groups act as acidic functional groups due to the acidic nature of the hydrogen atom attached to the oxygen atom, which can be readily released as a proton (H+). They are hydrophilic because they can form hydrogen bonds with water molecules.</p> Signup and view all the answers

<p>Phosphate groups are crucial for energy storage in molecules like ATP. They are also key components of cell signaling pathways, like the phosphorylation of proteins to activate or deactivate them. For instance, the phosphorylation of certain proteins by kinases can trigger a cascade of events leading to cellular responses.</p> Signup and view all the answers

<p>Sulfhydryl groups play a crucial role in protein structure by forming disulfide bonds, which contribute to the stability and three-dimensional conformation of proteins. These bonds link two cysteine residues, bringing them closer, increasing the protein's stability and resistance to unfolding.</p> Signup and view all the answers