Biology Questions

Explain what happens if even one amino acid is substituted for another in a polypeptide chain. Provide a specific example.

A change in gene sequence can lead to a different amino acid being added to a polypeptide chain instead of the normal one. This causes a change in protein structure and function. For example, in sickle cell anemia, the hemoglobin β chain has a single amino acid substitution—the amino acid glutamic acid in position six is substituted by valine. Because of this change, hemoglobin molecules form aggregates, and the disc-shaped red blood cells assume a crescent shape, which results in serious health problems.

Explain at least three functions that lipids serve in plants and/or animals.

Fat serves as a valuable way for animals to store energy. It can also provide insulation. Waxes can protect plant leaves and mammalian fur from getting wet. Phospholipids and steroids are important components of animal cell membranes, as well as plant, fungal, and bacterial membranes.

Why are fatty acids better than glycogen for storing large amounts of chemical energy?

Fats have a higher energy density than carbohydrates (averaging 9kcal/gram versus 4.3kcal/gram respectively). Thus, on a per gram basis, more energy can be stored in fats than can be stored in carbohydrates. Additionally, fats are packaged into spherical globules to minimize interactions with the water-based plasma membrane, while glycogen is a large branched carbohydrate that cannot be compacted for storage.

The monomers that make up proteins are called ________.

amino acids

The α helix and the β-pleated sheet are part of which protein structure?

secondary

Mad cow disease is an infectious disease where one misfolded protein causes all other copies of the protein to being misfolding. This is an example of a disease impacting ____ structure.

tertiary

Phospholipids are important components of ________.

the plasma membrane of cells

Saturated fats have all of the following characteristics except:

they are solid at room temperature . *they tend to dissolve in water easily .* they have single bonds within the carbon chain . they are usually obtained from animal sources

Cholesterol is an integral part of plasma membranes. Based on its structure, where is it found in the membrane?

within the tail bilayer

Part of cortisol's role in the body involves passing through the plasma membrane to initiate signaling inside a cell. Describe how the structures of cortisol and the plasma membrane allow this to occur.

Cortisol is a small, generally hydrophobic molecule, while the phospholipids that create plasma membranes have a hydrophilic head and hydrophobic tails. Since cortisol is hydrophobic, it can interact with the sequestered tails of the phospholipids in the center of the plasma membrane. This, along with its small size, allows cortisol to move through the plasma membrane to the inside of the cell.

Which categories of amino acid would you expect to find on the surface of a soluble protein, and which would you expect to find in the interior? What distribution of amino acids would you expect to find in a protein embedded in a lipid bilayer?

Polar and charged amino acid residues (the remainder after peptide bond formation) are more likely to be found on the surface of soluble proteins where they can interact with water, and nonpolar (e.g., amino acid side chains) are more likely to be found in the interior where they are sequestered from water. In membrane proteins, nonpolar and hydrophobic amino acid side chains associate with the hydrophobic tails of phospholipids, while polar and charged amino acid side chains interact with the polar head groups or with the aqueous solution. However, there are exceptions. Sometimes, positively and negatively charged amino acid side chains interact with one another in the interior of a protein, and polar or charged amino acid side chains that interact with a ligand can be found in the ligand binding pocket.

Aquaporins are proteins embedded in the plasma membrane that allow water molecules to move between the extracellular matrix and the intracellular space. Based on its function and location, describe the key features of the protein's shape and the chemical characteristics of its amino acids.

The protein must form a channel in the plasma membrane that allows water into the cell since water cannot cross the plasma membrane by itself. Since aquaporins are embedded in the plasma membrane and connect with both the intracellular and extracellular spaces, it must be amphipathic like the plasma membrane. The top and bottom of the protein must contain charged or polar amino acids (hydrophilic) to interact with the aqueous environments. The exterior transmembrane region must contain non-polar amino acids (hydrophobic) that can interact with the phospholipid tails. However, the inside of this channel must contain hydrophilic amino acids since they will interact with the traveling water molecules.

Describe the differences in the four protein structures.

The sequence and number of amino acids in a polypeptide chain is its primary structure. The local folding of the polypeptide in some regions is the secondary structure of the protein. The three-dimensional structure of a polypeptide is known as its tertiary structure, created in part by chemical interactions such as hydrogen bonds between polar side chains, van der Waals interactions, disulfide linkages, and hydrophobic interactions. Some proteins are formed from multiple polypeptides, also known as subunits, and the interaction of these subunits forms the quaternary structure.

Why have trans fats been banned from some restaurants? How are they created?

Trans fats are created artificially when hydrogen gas is bubbled through oils to solidify them. The double bonds of the cis conformation in the hydrocarbon chain may be converted to double bonds in the trans configuration. Some restaurants are banning trans fats because they cause higher levels of LDL, or "bad"cholesterol.