Deck 2: The Chemical Basis of Life

Question 1

What kind of bond results from an unequal sharing of electrons?

A)ionic bond
B)polar covalent bond
C)H bond
D)nonpolar covalent bond

Answer 1

B

Question 2

Which polysaccharide bond cannot be broken by mammalian enzymes that normally digest polysaccharides?

A) $\alpha$ (1->4)glycosidic linkages
B) $\beta$ (1->4)glycosidic linkages
C) $\alpha$ (1->6)glycosidic linkages
D) $\beta$ (1->6)glycosidic linkages
E)phosphate ester linkages

Answer 2

$\beta$ (1->4)glycosidic linkages

Question 3

Which of the following is not a macromolecule formed by polymerization?

A)proteins
B)lipids
C)polynucleotides
D)polysaccharides
E)DNA

Answer 3

B

Question 4

Which of the following groups is capable of only hydrophilic interactions?

A)A
B)B
C)C
D)D
E)E

Question 5

Why is silicon not suitable for making covalent bonds stable and strong enough to form the basis of living organisms,even though it is just below carbon on the periodic table?

A)Silicon is too large for its nucleus to attract the valence electrons of neighboring atoms enough to hold molecules together sufficiently.
B)Silicon is too small for its nucleus to attract the valence electrons of neighboring atoms enough to hold molecules together sufficiently.
C)Silicon is too large for its nucleus to attract the protons of neighboring atoms enough to hold molecules together.
D)Silicon is too small for its nucleus to attract the protons of neighboring atoms enough to hold molecules together.

Question 6

The low-molecular-weight building blocks of polymers are called _______.

A)minipolymers
B)monoblocks
C)monomers
D)portions
E)octamers

Question 7

A release of hydrogen ions to a solution would most likely ____________.

A)raise pH
B)lower pH
C)buffer pH
D)change salinity
E)keep pH steady

Question 8

The most stable atoms and thus those that are typically nonreactive are the atoms that have _______.

A)equal numbers of electrons and protons
B)equal numbers of electrons and neutrons
C)full inner shells
D)full outer shells
E)all covalent bonds

Question 9

A molecule that is capable of releasing or donating a hydrogen ion is termed a(n)_______.

A)base
B)hydrion
C)acid
D)anachronism
E)pain

Question 10

Where are hydrophobic interactions most likely to occur?

A)on the surface of a water-soluble protein
B)the core of a water-soluble protein
C)in contact with water molecules
D)between two charged molecules
E)between two ions

Question 11

The most electronegative atoms typically present in biological molecules are ____ and ____.

A)O,C
B)O,P
C)O,N
D)C,N
E)C,Na

Question 12

In a living organism,where are ionic bonds most likely to be found?

A)in the cytoplasm
B)between DNA strands
C)deep in a protein's core where water is excluded
D)on the surface of a protein
E)on the surface of a lipid

Question 13

What bond is responsible for the branch points in glycogen and amylopectin?

A) $\alpha$ (1->4)glycosidic linkages
B) $\beta$ (1->4)glycosidic linkages
C) $\alpha$ (1->6)glycosidic linkages
D) $\beta$ (1->6)glycosidic linkages
E)3'-5' phosphodiester linkages

Question 14

Which of the groups below is capable of only hydrophobic interactions?

A)A
B)B
C)C
D)D
E)E

Question 15

What is the maximum number of 100 amino acid long polypeptides that could be made?

A)10020
B)2,000
C)20100
D)20101
E)20

Question 16

Under which circumstances would electrons be most likely to be shared equally?

A)when they are equidistant from nuclei
B)when they are equidistant from each other
C)when atoms of the same element are sharing them
D)when the atoms sharing them are different

Question 17

Which of the following tripeptides would be most likely to be soluble in an organic (hydrophobic)solvent like benzene?

A)N - phenylalanine - alanine - glycine - C
B)N - leucine - alanine - lysine - C
C)N - proline - phenylalanine - leucine - C
D)N - arginine - lysine - proline - C
E)N - glutamate - aspartate - glycine - C

Question 18

Why do sugars tend to be highly water soluble?

A)because they have only a few hydroxyl groups
B)because of their large numbers of hydroxyl groups
C)because of their large numbers of sulfhydryl groups
D)because of their large numbers of methyl groups
E)because of their small molecular weights

Question 19

What kind of noncovalent interaction is typified by interactions between two molecules that are so close together that they can experience weak attractive forces bonding them together?

A)H bonds
B)ionic bonds
C)hydrophobic interactions
D)polar covalent bonds
E)van der Waals forces

Question 20

Which interaction is most important in enhancing the solubility of macromolecules in water?

A)hydrophobic interactions
B)nonpolar covalent bonds
C)H bonds
D)van der Waals forces
E)Both hydrophobic interactions and nonpolar covalent bonds

Question 21

Which of the groups below is capable of only hydrophobic interactions? Explain your answer.Which is capable of only hydrophilic interactions? Explain your answer.

Question 22

Which amino acid is most likely to be found in the core of a protein?

A)methionine
B)asparagine
C)serine
D)threonine
E)glutamic acid

Question 23

You treat a partially purified preparation of protein with a reagent that breaks bonds between sulfur atoms.Which level(s)of protein structure are likely to be affected the most?

Question 24

You are a crew member on the starship Enterprise.Your responsibilities include investigation of biological life forms.You take out your tricorder after landing on the planet Yamihere and find a number of organisms,all of which contain DNA that follows the nitrogenous base pairing rules you are familiar with on Earth.For one species,the following relationships hold for the organism's DNA.
How many moles of guanine are present?
How many moles of thymine are present?
How many moles of uracil are present?
You isolate DNA from another organism living on the surface of Yamihere and find that it contains all the bases normally found in DNA,but does not obey the pairing rules.Can you explain these strange results?

Question 25

An enzyme is placed in a solution containing urea.Assuming that this protein contains no disulfide linkages,is it reasonable to suspect that it will be totally denatured by the treatment? How could you know that the enzyme has,in fact,been denatured? Why does the urea denature the tertiary structure of the enzyme?

Question 26

Not all proteins are able to renature.Some proteins when exposed to heat or some other denaturing treatment are irreversibly denatured.What is an example of such a protein?

Question 27

How do amino acids like hydroxylysine and thyroxine,which are not among the 20 amino acids that are inserted into proteins,get into proteins?

A)They are inserted directly.
B)They are the result of the alteration of R groups of the 20 amino acids after their incorporation into the polypeptide.
C)They are the result of the alteration of R groups of the 20 amino acids before their incorporation into the polypeptide.
D)There are more than the 20 amino acids that are said to be inserted into proteins.
E)Their atoms are altered by insertion into the polypeptide.

Question 28

The $\beta$ -pleated sheet is characterized by orientation of ______ the molecular axis.

A)H bonds parallel to
B)H bonds perpendicular to
C)ionic bonds parallel to
D)ionic bonds perpendicular to
E)peptide bonds perpendicular to

Question 29

What level of structure in DNA would be disrupted by a reagent that breaks apart hydrogen bonds?

Question 30

You are working with an enzyme altase that you denature in the presence of urea.If altase were denatured no further by the addition of mercaptoethanol,what would that suggest to you about the enzyme?

Question 31

Would all proteins be likely to require exposure to mercaptoethanol in order to accomplish full denaturation? If not,what trait would a protein that did not require mercaptoethanol possess?

Question 32

Mammals lack the enzyme that hydrolyzes cellulose.Yet many mammals are herbivores and they eat grass and other plant material for nutrition.How can this be,given that they cannot digest the food they are eating?

Question 33

Tertiary structure in DNA is also known as ________.

A)primary structure
B)supercoiling
C)double helix
D) $\alpha$ -helix

Question 34

DNA is isolated from two different species.Both DNA samples are found to be the same size.One of the DNA samples has a G+C/A+T ratio of 2.0 and the other 2.5.Which DNA sample has a higher G+C content? Which sample contains the smallest number of H bonds between strands? Which DNA sample would be easiest to denature?

Question 35

Which of the following tripeptides would be most likely to be soluble in an organic (hydrophobic)solvent like benzene: N - phenylalanine - alanine - glutamine - C,N - leucine - alanine - lysine - C,N - proline - phenylalanine - leucine - C,N - arginine - lysine - proline - C,N - glutamate - aspartate - glycine - C? Explain your answer.

Question 36

What is now thought to have been the genetic material in the first living organisms on Earth?

A)RNA
B)DNA
C)protein
D)polypeptides

Question 37

Which of the following is a nucleotide?

A)phosphate + ribose
B)adenine + deoxyribose
C)sugar + nitrogenous base
D)adenine + ribose + phosphate

Question 38

Proteins are often composed of two or more distinct modules that fold up independently of one another.They often represent parts of a protein that function in a semi-independent manner.These modules are called ______.

A)protein motifs
B)functionals
C)domains
D)dominoes

Question 39

What level of structure in proteins is held together by intermolecular R group interactions?

A)primary structure
B)secondary structure
C)tertiary structure
D)quaternary structure

Question 40

What type of protein secondary structure is characterized as being highly extensible because of its coiled structure?

A) $\beta$ -pleated sheet
B)double helix
C) $\alpha$ -helix
D)supercoiling

Question 41

What does the compound,2-phenylaminopyrimidine,inhibit? It was determined that 2-phenylaminopyrimidine would not have made a very effective drug.Why? What is the basis of Gleevec's effectiveness as a drug in the treatment of chronic myelogenous leukemia (CML)? Why do some patients taking Gleevec experience a recurrence of their cancer even though they initially went into remission?

Question 42

Given what you have learned about SOD,what do you hypothesize would happen to fruit flies that have been genetically engineered to produce large amounts of SOD? Why might houseflies that are kept caged and unable to fly live longer than those allowed to fly?

Question 43

Some proteins have multiple binding partners.In some cases,they have several different binding interfaces and they are thus capable of binding a number of different binding partners at the same time.On the other hand,other such proteins have a single binding interface,which is capable of binding several different partners,but only one at a time.They can play central roles in such processes as cell division and gene expression.What are such proteins called?

Question 44

You are studying a protein.It binds to elongating polypeptide chains as they emerge from an exit channel within the ribosome's large subunit.It appears to prevent partially formed or nascent polypeptides from binding to other proteins in the cytosol,which might cause them either to aggregate or misfold.What kind of proteins is this likely to be? Another protein you are studying picks up larger proteins from Hsp70 family proteins.It is a cylindrical protein complex that contains chambers in which newly synthesized polypeptides can fold without interference from other cellular macromolecules.What is this protein called?

Question 45

What are some possible explanations for the branched structure of glycogen?

Question 46

What is a randomized,double-blind,placebo-controlled study?

Question 47

What kinds of conditions can cause free radicals?

Question 48

What are some common antioxidants found in the body?

Question 49

If people are kept on diets containing about 25% fewer calories than would be required to maintain their initial body weight,what happens?

Question 50

You isolate superoxide dismutase from two cell culture lines.One of the lines (SOD1)has a level of SOD activity similar to that found in liver,the tissue from which the cell line was originally obtained.The other cell line (SOD10)has elevated SOD activity.The enzyme in SOD10 is extremely efficient at converting the superoxide free radical to hydrogen peroxide.In a routine check of other critical enzyme activities,catalase was found to have activity levels that were severely depressed in SOD10,while they appeared normal in SOD1.Observations of SOD10 reveal that this cell line cannot be maintained as easily as SOD1.SOD10 cells appear to die at an accelerated rate.What,if anything,can you conclude from these data?

Question 51

Many so-called temperature-sensitive mutations have been discovered in a wide variety of organisms.These are proteins that are non-functional at higher temperatures,while,at lower temperatures (often just a few degrees lower),they function normally.For example,the coloration patterns in Siamese Cats arise from a temperature-sensitive mutation.An enzyme required for the synthesis of dark pigment is unable to function in areas close to the body where normal physiological temperatures prevail.However,at the tips of the ears,paws,the tip of the tail and other extremities where the temperature is slightly lower,the enzyme works correctly and dark pigment is produced.What is happening at the molecular level that explains this?

Question 52

If mice are maintained on very strict diets with reduced caloric intake,what happens to their life span as compared to littermates fed diets with normal caloric content? What is a possible explanation for the effect of this diet on these animals?

Question 53

Why are free radicals capable of altering molecules,such as proteins,nucleic acids and lipids?

Question 54

Why might an organism that had functional SOD but mutant catalase and/or glutathione peroxidase be at a disadvantage?

Question 55

What is some specific evidence that demonstrates the importance of superoxide dismutase in getting rid of superoxide free radicals?

Question 56

Red wine supposedly has health-related benefits.What antioxidant chemical is reputed to be responsible for these benefits? Where is this chemical normally found that explains its ending up in red wine? How is this chemical thought to exert its antioxidant effects?

Question 57

Why is hydrogen peroxide often used as a disinfectant and bleaching agent? How do cells generally rid themselves of hydrogen peroxide?

Question 58

What enzyme is responsible for the destruction of a type of free radical formed when molecular oxygen picks up an extra electron?

Question 59

Scientists have sequenced proteins by using specific proteases to "clip" a purified protein preparation between two specific amino acids,thus forming a number of moderately sized fragments;they have used acid hydrolysis to produce smaller fragments.Each fragment can then be sequenced by breaking the moderate fragments into dipeptides that are easily sequenced.The fragments below are obtained after the initial enzymatic cleavages.Can you deduce the sequence of the original polypeptide? (HINT: the original cleavages at specific locations differ depending on which proteolytic enzyme was used to create each fragment;this causes an overlap in the fragments' sequences. )The final polypeptide should have 18 amino acid residues.

Question 60

It is thought that most human diseases leave telltale patterns among the thousands of proteins present in the blood or other bodily fluids.It was hoped that analysis of the proteins present in the blood would help in the diagnosis of human disease;however,thus far,searches for these proteins in blood or bodily fluids have been largely unsuccessful and their use in diagnostics largely unreliable.What are these telltale patterns of proteins called?

Question 61

How was it proved that CJD could be passed to another organism?

Question 62

What appears to be the effect of reduced calorie intake on rhesus monkeys?

Question 63

What human disease was found to be similar to kuru in the brain abnormalities it caused? What disease in sheep contributes its name to the abnormal prion molecule,PrPSC? What have been the causes of outbreaks of acquired CJD?

Question 64

Since replication is a property characteristic of nucleic acids,how might a prion,which lacks nucleic acids,"replicate" itself?

Question 65

What is spongiform encephalopathy?

Question 66

When it was discovered that CJD could be acquired in addition to being inherited,why was it at first assumed that the infectious agent was a virus?

Question 67

What evidence suggests that lower blood levels of insulin may be important in promoting longevity?

Question 68

How was it proved that the brains of patients suffering from CJD,an inherited disease,contain an infectious agent?

Question 69

An infectious agent is discovered that causes a particular disease.It has a relatively low molecular weight.Treatment with phenol or proteolytic enzymes,treatments that destroy proteins,render the infectious agent harmless,while treatment with nucleases and ultraviolet radiation,treatments that damage polynucleotides,has no effect.What is your interpretation of the above data and why?