Bio of the cell 2

Which of the following bases is not found in DNA a) adenince b) cytosine c) Thymine d) Uracil

d) Uracil

The three-dimensional structure of a protien is analyzed most definitively by a) electron microscopy b) light microscopy c) subcellular fraction d) X-ray crystallography

d) X-ray crystallography Subcellular fraction us an approach for separating organelles, membranes, and soluble molecules, either in individual molecules or in molecular complexes

Enzymes affect the transition state of a chemical reaciton by a) binding to the substrate(s) b) providing a surface on which the reactions converting substrate to product can occur more rapidly c) altering the conformation of the substrate(s) to approach that of the transition state d) all of the above

d) all of the above

Whereas small uncharged molecules can diffuse through the hydrophobic core ofa phospholipid bilayer, a larger polar substance such as glucose must enter cells by binding to a) a non-phospholipid such as cholesterol b) the carbohydrate portion of glycollipids c) peripheral membrane proeins located on the inner side of the membrane d) carrier proeins that facilitate the passage of specific molecules acorss membranes

d) carrier proteins that facillitate the passage of specific molecules across membranes

Enzymes act by a) lowering the overall change in the free energy of a reaction b) decreasing the distance that reactants must diffuse to find one another c) increasing the activation energy d) decreasing the activation energy

d) decreasing the activation energy Enzymes decrease the energy required to reach the transition state (the activation energy) thus speeding up a reaction

Transport across biological membranes is speeded by what class of biological molecules? a) carbohydrates b) lipids c) nucleic acids d) proteins

d) proteins

Coenzymes are chemically related to a) amino acids b) inorganic phosphate c) glucose d) viatmins

d) vitamins

The most abundant molecule in cells is a) aspartic acid b) DNA c) sucrose d) water

d) water Water is indeed the most abundant molecule in cells accounting for 70% of cellular mass, and considering its small size, an even higher fraction of the total molecules in cells

Which of the following is not true of coezymes? a) Chemically, they are branched amino acids b) They serve as carriers of several types of chemical groups c) They transfer specific chemical groups among a wide range of substrates d) They work together with enzymes to enhance chemical reactions without being irreversibly altered

a) Chemically, they are branched amino acids Coenzymes are regenerated in a cyclical manner

A disulfide bond is formed between ______ residues. a) cysteine b) glucine c) methionine d) tyrosine

a) cysteine

In the fluid mosaic model of biological membrane structure, thransmembrane proteins are a) embedded nearly randoml in the lipid bilayer b) almost completely surrounded by membrane lipid c) segregated into large protein clusters or rafts d) weakly held in place on the surface of the lipid bilayer

a) embedded nearly randomly in the lipid bilayer Typically, only small, alpha-helical portions of the rpotein are embedded in the membrane and individual proteins are distributed fairly randomly within the membrane bilayer

Cholesteral, a membrane lipid in animals, ahs a chemical structure similar to a) estradiol b) phosphatidylinositol c) thymine d) triacylglucerol

a) estradiol

Whihci is the major carbohydrate-storage molecule in plants? a) starch b) cellulose c)glycogen d) Deoxyribonucleic acid

a) starch

Molecules that are partly water-soluble and partly water-insoluble are a) hydrophillic b) amphipathic c) hydrophobic d) allosteric

b) amphipathic An example of an amphipathic molecule is a phospholipid, which has a long hudrocarbon chain (the water-insoluble part) attached to a polar head group (the water soluble part)

What is the effect of a Beta barrel on the permeability of a membrane a) it decreases permeability b) it increases permeability c) it has no effect d) beta barrels are never found in membranes

b) it increases permeability A beta barrel isa protein strucural feature that spans a membrane, creating a pore-like opening. The presence of this feature therefore increases the permeability of a membrane

Introducing a double bond into a fatty acid has the effect of putting a(n) ______ into the conformation of the molecule a) amino acid bulge b) kink c) reverse spiral d) reinforcing rod

b) kink

The lock-and-key and induced-fit models are two alternative models that can explain how enzymes and substrates interact. These two models can be distinguished from each other according to changes in the a) viscosity of the reaction solution as the substrate and enzymme bind b) shape as the substrate and enzyme bind c) reaction solution temperature as a result of the endothermic cooling that occurs during substrate binding d) reaction solution color as the substrate and enzyme bind

b) shape as the substrate and enxyme bind Typcally, no changes in color with enzyme-substrate binding. color changes may occur, however, during the overall enzyme-catalyzed reaction

How many amino acids are there? a) 5 b) 10 c) 20 d) 25

c) 20 There are 20 common amino acids

All of the followng are ways in which enzyme activity can be regulated except a) by binding to an allostericc site b) through feedback inhibition c) by modulation of intracellular sucrose concentrations d) through phosphorylation

c) by modulation of intracellular sucrose concentrations Typically, sucrose is not an intracellular metabolite; hence, this cannot regulate enzyme activity

Phospholipids consist of a 3-carbon core wto which fatty acids and phosphate group are linked. The most commmon 3- carbon core is a) dihydroxyacetone b) glyceraldehyde c) glycerol d) serine

c) glycerol

Lipids with unsaturated fatty acids a) decrease the fluidity of membranes b) increases the charge associated with the inner face of a membrane c) increase the fluidity of membranes d) are present only on the inner side of the plasma membrane

c) increase the fluidity of membranes

Which of the following classes of amino aids is buried within the folded structure of the protein? a) acidic b) basic c) nonpolar d) Polar

c) nonpolar Polar amino acids are hydrophillic and hence are on the surface of proteins, where theey can interact with water

Proteins must have more than on ___ to have a quaternary structure a) alpha helix b) beta sheet c) polypeptide chain d) transmembrane segment

c) polypeptide chain The quaternary structure of a protein is the association of multiple polypeptide chains with one another

The alpha helix is an example of which level of protein sructure? a) primary b) quaternary c) secondary d) tertiary

c) secondary Primary structure refers simply to the amino acid sequencce of a protein

About 50% of the mass of most biological membranes consists of lipids and about 50% consists of proteins. Therefore; a) the membranes contain few molecules of lipid than of protein b) the membranes contain equal numbers of lipid and protein molecules c) the membranes contain more molecules of lipid than of protein d) only a few membrane proteins are exposed at the cell surface

c) the membranes contain more molecules of lipid than of protein

Passive transport across a membrane refers to a) transport into the interior of a cell b) transport out of a cell c) transport in the energetically favorable direction d) simple diffustion acorss membranes, without the help of proteins such as channels or carriers

c) transport in the energetically favorable direction

Chymotrypsin, trypsin, elastase, and thrombin are all grouped together as members of the serine protease family because each a) has similar charge and shape properties in its substrate insertion pockets b) can form a heptahedral complex with its substrate c) uses the same catalytic mechanism involving the same key amino acids d) can be modified by the cell-wall biosynthetic degradative enzyme chitinase

c) uses the same catalytic mechanism involving the same key amino acids IF each had similar substrate binding properties, then each would cleave proteins at the same sequence. This is not the case. For example, chymotrypsin cleaves next to a hydrophobic amino acid and trypsin cleaves next to a basic amino acid. The insertion pocket of chymotrypsin is hydrophobic, while that of trypsin is negatively charged

Which of the following is not one of the four major classses of organic molecules in the cell? a) Carbohydrates b) lipids c) water d) proteins

c) water