Unit 2

Protein Synthesis


Q. Demonstrate a knowledge of the basic steps of protein synthesis, identifying the roles of DNA,  mRNA, tRNA, and ribosomes in the processes of transcription and translation.
A. In transcription, DNA unwinds and a strand of RNA matches up its nucleotides with it. Then the DNA winds back up and a strand of mRNA leaves the nucleus and heads toward a ribosome. In translation, mRNA attaches to a ribosome. The ribosome reads the mRNA. Then tRNA matches its anti-codon to the mRNA's codon (group of three bases and code for specific amino acid). tRNA has a amino acid attached to it, and when it is matched with a codon, a peptide bond forms between the amino acids. The empty tRNA then leaves the ribosome and the amino acids bond to form a protein.

Q. Determine the sequences of amino acids coded for by a specific DNA sequence, given a table of mRNA codons.
A. AUG- Methionine, START , GUC- Valine, UAU- Tyrosine, UGA- STOP.

Q. Give examples of 2 environmental mutagens that can cause mutation in humans.
A. Ultraviolet light and gamma radiation.

Q. Use examples to explain how mutations in DNA affect protein synthesis and may lead to genetic disorders.
A. A mutation can cause amino acids to be changed. For example, one amino acid changed in a hemoglobin in the blood, glutamic acid being changed to valine, causes sickle shaped blood cells to develop. Other mutations are deletion and insertion mutations. In deletion a amino acid is deleted and in insertion a amino acid is added. Both result in the gene becoming unreadable.

Transport Across Cell Membrane


Q. Apply knowledge of organic molecules to explain the structure and function of the fluid mosaic membrane model.
A. The fluid mosaic membrane model is made up of several parts: a phospholipid bilayer which makes up most of the membrane and protects the intracellular fluids from the extracellular fluids, glycolipids are phospholipids attached to carbohydrate chains and act as self recognition markers for the cell, cholesterol is a lipid in the membrane that serves to make the bilayer more flexible and less fluid, receptor proteins that trigger a cellular response when it detects certain molecules, recognition proteins have an attached carbohydrate chain and act as identification tags, transport proteins control the movement of water soluble molecules through the membrane, channel proteins allow water-soluble molecules to pass through the membrane, and carrier proteins use ATP to move molecules across the membrane.

Q. Explain why the cell membrane is described as "selectively-permeable".
A. It will only allow certain molecules to pass through it.

Q. Compare and contrast the following: diffusion, facilitated transport, osmosis, active tranport.
A. Diffusion is movement of water solute molecules across the membrane from high to low concentrations. Facilitated transport is transport that uses channel proteins to move molecules from high to low concentrations. Osmosis the movement of water molecules across the membrane. Active transport is transport that uses energy (ATP) to move molecules from low to high concentrations.    

Q. Explain factors that affect the rate of diffusion across a cell membrane.
A. The size of the molecule (smaller molecules diffuse faster). Temperature (higher temperatures increase the rate of diffusion). The concentration gradient (greater difference in concentration makes molecules diffuse faster). The number of pores or carrier proteins in the cell membrane can also increase the rate of diffusion.

Q. Describe endocytosis, including phagocytosis and pinocytosis, and contrast it with exocytosis.
A. Endocytosis is the process of bringing particles into the cell that are too large for carrier proteins. The cell membrane folds in and then pinches off to form a vesicle in the cell that contains the particles. It then undergoes the process of  phagocytosis or pinocytosis. In phagocytosis, the particles in the vesicle are digested. In pinocytosis, nutrients are taken into the cell. The opposite of endocytosis is exocytosis. Exocytosis is the process of taking waste out of the cell by merging a vesicle filled with waste with the cell membrane, thus emptying its contents outside of the cell.

Q. Predict the effects of hypertonic, isotonic, and hypotonic environments on animal cells.
A. In a hypertonic environment, water would move out of the cell, causing it to shrink (crenation). In a isotonic environment, there is no change in the cell. In a hypotonic environment, water would move into the cell, causing it to expand or burst (lysis).

Q. Demonstrate an understanding of the relationships and significance of surface area to volume, with respect to cell size.
A. Small cells have a high surface area to volume ratio. This allows diffusion and osmosis to work faster.
Larger cells have a smaller surface area to volume ratio than small cells. This slows down diffusion and osmosis relative to its size.

Enzymes


Q. Demonstrate an  understanding of the following terms: metabolism, enzymes, substrate, coenzymes, activation energy.
A. Metabolism is all of the chemical processes in a cell. Enzymes are proteins that catalyze a chemical reaction. One enzyme catalyzes one reaction. A substrate attaches to an enzyme's active site and they combine to form a enzyme-substrate complex. Coenzymes work with the enzyme to complete the active site. Activation energy is the energy that is used to start a reaction.

Q. Identify the source gland for thyroxin  and relate the function of thyroxin to metabolism.
A. Thyroxin comes from the thyroid gland. Thyroxin promotes growth and increases metabolism.

Q. Explain the lock and key model of emzymatic action.
A. The enzyme and substrate fit together perfectly without having to change shape.

Q. Explain the role of vitamins in biochemical reactions.
A. Vitamins are used by enzymes to use energy during reactions.

Q. Differentiate between the roles of enzymes and coenzymes in biochemical reactions.
A. An enzyme catalyzes reactions ( speeds them up) and a coenzyme works with the enzyme by completing the active site so the reactions may occur.

Q. Apply knowledge of proteins to explain the effects on enzyme activity of pH, temperature, substrate concentration, enzyme concentration, competitive inhibitors, and heavy metals.
A. A very high or very low pH makes it very difficult, even impossible for an enzyme to function. So enzymes need a pH between 6 and 8 to work. Very high and very low temperatures also lower an enzymes effectiveness, a human's body temperature is about 37 degrees celsius which is the optimal temperature for our enzymes. High substrate concentrations will increase the reaction rates and low concentrations will lower the reaction rate. High enzyme concentrations will increase the reaction rate and low concentrations will lower the reaction rate. Competitive inhibitors completely prevent an enzyme from making any reactions while they are bound to the active site (can bind irreversibly). Heavy metals denature enzymes and bind irreversibly.