BIOLOGY 205: Exam 1 Questions and 100% Correct Answers
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Course
BIO 205
Institution
BIO 205
Enzymes Catalyze covalent bond breakage or formation Example: Kinase-adds a phosphate group to a protein molecule
Structural Proteins Provide mechanical support to cells and tissues Example: actin-forms filaments that underlie and support the plasma membrane
Transport Proteins Carry small molecul...
BIOLOGY 205: Exam 1 Questions and 100% Correct Answers Enzymes ✅Catalyze covalent bond breakage or formation Example: Kinase -adds a phosphate group to a protein molecule Structural Proteins ✅Provide mechanical support to cells and tissues Example: actin -forms filaments that underlie and support the plasma membrane Transport Proteins ✅Carry small molecules or ions Example: Glucose -carriers shuttle glucose into and out of cells Motor Proteins ✅Generate movement in cells and tissues Example: Myosin -in skeletal muscle cells provides the motive force for humans to move Storage Proteins ✅Stores amino acids or ions Example: casein -in milk is a source of amino acids for baby mammals Signal Proteins ✅Carry extracellular signals from cell to cell Example: Epidermal growth factor -stimulates the growth and division of epithelial cells Receptor Proteins ✅Detects signals and transmit them to the cell's response machinery Example: Rhodopsin -in the retina detects light Gene Regulatory Proteins ✅Bind to DNA to switch genes on and off Example: The lactose repressor in bacteria -silences the genes for the enzymes that degrade the sugar lactose Special -Purpose Proteins ✅Highly variable Example: monellin -a protein found in an African plant, has an intensely sweet taste Shape determines function ✅Protein is made from long chain of amino acids, held together by covalent polypeptide bonds. In each type of protein, amino acids are present in an unique order called the amino acid sequence, which is exactly the same from one molecule of that protein to the next Proteins fold into a conformation of lowest energy ✅Each type of protein has a 3D shape which is determined by the order of the amino acids in its polypeptide's chain, the final folded structure is known as the conformation, is determined by energetic considerations. A protein generally folds into the shape in which its free energy is minimized. Alpha Helix and Beta Sheets ✅These two folding patterns are very common as they result from hydrogen bonds between N -H and C=O groups in the polypeptide backbone. Helix: abundance of helices in proteins, it is generated by placing many similar subunits next to one another, each in the same strictly repeated relationship to the one before. An alpha helix: When a single polypeptide chain turns around itself to form a structurally rigid cylinder. Beta sheet: A beta sheet is made when hydrogen bonds form between segments of a polypeptide chain that lie side by side. Protein level of organization ✅1. Primary Structure: amino acid sequence 2. secondary structure: alpha helices and beta sheets that form within certain segments of the polypeptide chain 3. Tertiary: The 3D conformation formed by an entire polypeptide chain 4. Quaternary: If the protein molecule is formed as a complex of more than one polypeptide chain The Backbone Model ✅The backbone model is a way of showing a protein's 3D structure, which shows the overall organization of the polypeptide chain and provides a straightforward way to compare the structures of related proteins The Ribbon Model ✅The ribbon model shows the polypeptide backbone in a way that emphasizes its various folds The Wire Model ✅The wire model includes the positions of the amino acid side chains, it is useful for predicting which amino acids might be involved in the protein's activity Space -Filling Model ✅The space -filling model provides a contour map of the protein surface, which reveals which amino acids are exposed on the surface and shows how the protein might look to a small molecule such as water or to another macro -molecule in the cell Breaking Cells and Tissues ✅-The first step in purification is to disrupt tissues and cells in a controlled fashion. -Using gentle mechanical procedures (homogenization) the plasma membrane of cells can be ruptured so that the cells contents are released: 1. ultrasound: break cells with high -frequency 2. Use a mild detergent to make holes in the plasma membrane 3. Force cells through a small hole using high pressure 4. Shear cells between a close -fitting rotating plunger and the thick walls of a glass vessel -The resulting thick soup (homogenate) contains large and small molecules from the cytosol, such as enzymes, ribosomes, and metabolites, as well as all of the membrane -
enclosed organelles The Centrifuge ✅Centrifugation: Is the most widely used procedure to separate a homogenate into different parts or fractions. The homogenate is placed in test tubes and rotated at high speed. Supernatant: smaller and less dense components Pellet: Larger and more dense components Differential Centrifugation ✅Repeated centrifugation at progressively higher speeds will fractionate cell homogenates into their components. Remember: Centrifugation separates cell components based on size and density. The larger and denser components experience the greatest centrifugal force and move most rapidly. They sediment to form a pellet at the bottom of the tube, while smaller, less dense components remain in suspension above, a portion called the supernatant. Velocity Sedimentation ✅Subcellular components sediment at different rates according to their size after being carefully layered over a dilute salt solution and then centrifuged through it. when sedimented through such a dilute sucrose gradient, different cell components separate into distinct bands that can be collected individually Equilibrium Sedimentation ✅The ultra -centrifuge can also be used to separate cell components on the basis of their buoyant density, independently of their size or shape. At equilibrium, components have migrated to a region in the gradient that matches their own density. The final ba nds can be collected from the base of the tube, as shown above for velocity sedimentation. Protein Separation ✅Proteins are very diverse. They differ in size, shape, charge, hydrophobicity, and their affinity for other molecules. All of these properties can be exploited to separate them from one another so that they can be studied individually. Column Chromatography ✅Proteins are often fractionated by column chromatography. A mixture of proteins in solution is applied to the top of a cylindrical column filled with a permeable solid matrix immersed in solvent. A large amount of solvent is then pumped through the column. Because different proteins are retarded to different extents by their interaction with the matrix, they can be collected separately as they flow out from the bottom. According the the choice of matrix, proteins can be separated according to their charge, hydrophobicity, size, or ability to bind to particular chemical groups. Ion-Exchange Chromatography ✅Ion-exchange columns are packed with small beads carrying either positive or negative charges that retard proteins of the opposite charge. The association between a protein and the matrix depends on the pH and ionic strength of the solution passing down th e column. These can be varied in a controlled way to achieve an effective separation.
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