Chapter 2: Chemical Basis of Life

Question 1

Monosaccharides

Answer 1

The building blocks of carbohydrates

Question 2

What are the main functions of carbohydrates?

Answer 2

Storage of chemical energy

Building materials for biological construction

Question 3

Differentiate between a ketose and an aldose

Answer 3

Ketose: contains an internal carbonyl group

Aldose: contains an external carbonyl group

Question 4

What is a polysaccharide?

Answer 4

A polymer of monosaccharides linked by glycosidic bonds

Question 5

What are the main properties of lipids?

Answer 5

1. Ability to dissolve in organic solvents (chloroform, benzene)
2. Inability to dissolve in water

Question 6

Triacylglycerol

Answer 6

Glycerol linked to three fatty acids by ester linkages

Question 7

Amphipathic

Answer 7

Molecules containing both hydrophilic and hydrophobic regions

Question 8

What is the structure of fatty acids?

Answer 8

Hydrocarbon chains with one carboxyl group at the end

Question 9

Differentiate between saturated and unsaturated fatty acids

Answer 9

Saturated: no double bonds (stearic acid)
Unsaturated: presence of double bonds

Question 10

What conformation are the double bonds in naturally occurring fats usually in?

Answer 10

Cis conformation

Question 11

The more double bonds a fatty acid has…

Answer 11

The more liquid state it will be in due to less effective packing of the molecules

Question 12

Cholesterol

Answer 12

a steroid that is a component of animal cell membranes

Question 13

Differentiate between the primary, secondary, tertiary, and quaternary structure of proteins

Answer 13

Primary structure is the sequence of amino acids
Secondary structure is the conformation of certain portions of the protein
Tertiary structure is the 3D conformation of the entire protein
Quaternary structure is the conformation of a protein with multiple subunits

Question 14

Sickle cell anemia is a result of ___________.

Answer 14

a single change in the primary structure of the protein wherein a valine replaced a glutamic acid

Question 15

The degree to which changes in the amino acid sequence are tolerated depends on _______.

Answer 15

the degree to which the shape of the protein or the critical functional residues are disturbed

Question 16

The degree to which changes in the amino acid sequence are tolerated depends on _______.

Answer 16

the degree to which the shape of the protein or the critical functional residues are disturbed

Question 17

What is the stabilizing factor in alpha-helices?

Answer 17

The hydrogen bonds between between the atoms of a peptide bond and those situated above and below it

Question 18

What is the stabilizing factor in beta-sheets?

Answer 18

hydrogen bonds oriented perpendicular to the long axis and project across from one part of the chain to another

Question 19

Polypeptide chains exist in conformations that ________.

Answer 19

provide the maximum number of hydrogen bonds between neighboring amino acids

Question 20

What is the stabilizing factor for an entire protein?

Answer 20

array of non-covalent bonds between the diverse side chains

Question 21

Differentiate between fibrous and globular proteins

Answer 21

Fibrous: elongated, outside the cell

Globular: compact, within the cell

Question 22

What is the main function of molecular chaperones?

Answer 22

Guide misfolded or unfolded proteins to their proper three-dimensional conformations by preventing non-selective interactions with other molecules in close proximity

Question 23

What is the general mechanism of molecular chaperones?

Answer 23

Bind to hydrophobic amino acids that are usually exposed in the proteins nonnative conformation but buried in the native one

Question 24

Differentiate between the two families of molecular chaperones based on their mechanisms

Answer 24

1. Hsp70: bind to elongating proteins as they emerge from the large ribosomal subunit
2. Chaperonins: allow polypeptides to fold without interference from other macromolecules in the cell

Question 25

Describe the causative agent of Creutzfeld-Jakob disease

Answer 25

Prion - infectious agent composed solely of protein

Question 26

How can an inherited gene also be an infectious agent in the case of CJD?

Answer 26

Appearance of PrPSC in the body, whether it be sporadic or acquired from an external source, can start a chain reaction in the normal protein cells in the body causing them to fold into the abnormal form and aggregate to form the insoluble fibrils

Question 27

Compare and contrast the two gene products of PRNP

Answer 27

Normal gene product: prion protein cellular (PrPC)
Mutated gene product: prion protein scrapie (PrPSC)

Common: have an identical sequence of amino acids

Difference: PrPC is a monomeric molecule comprised of mostly alpha-helices that is susceptible to proteasomes

PrPSC molecules form insoluble fibrils that are resistant to enzymatic digestion

Question 28

What are the implications of CJD?

Answer 28

Loss of motor coordination and dementia

Question 29

Carleton Gajdusek

Answer 29

Discovered CJD in Papua New Guinea (named as “Kuru”)

Question 30

What are the forms of Transmissible Spongiform Encephalopathies? What do they have in common?

Answer 30

1. Mad Cow’s disease
2. Scrapie
3. Wasting disease
4. Creutzfeld-Jakob disease

All of them are characterized by microscopic holes in the brain tissue

Question 31

What is characteristic of a brain of a person with Alzheimers disease?

Answer 31

Presence of fibrillar deposits of amyloid

Question 32

Amyloid hypothesis for AD

Answer 32

AD is caused by the protein amyloid-beta-peptide

Question 33

TRUE or FALSE

the protein involved in AD is an infectious agent similar to that of CJD

Answer 33

False

Question 34

Explain the relationship between amyloid-beta-polypeptide, amyloid precursor protein, amyloid-beta-polypeptide 42, beta-secretase and gamma-secretase

Answer 34

AB polypeptide is part of the larger protein APP and is cleaved from such via the beta- and gamma-secretase

AB42 is a minor species of AB containing two mmore hydrophobic residues

Question 35

What is the nature of AB42?

Answer 35

Tendency to refold into a conformation of mostly beta-sheets and self-associates to form oligomers and aggregates that are deposited outside of the cell, known as amyloid plaque

Question 36

How is it that the soluble oligomers are more dangerous than the insoluble aggregates?

Answer 36

The soluble oligomers of AB42 are able to attack the synapses of the nerve cells thus effectively killing them

Question 37

What are factors that may result in overproduction of AB42?

Answer 37

1. Mutations in the APP gene
2. Mutations in the Prenesillin genes (PSEN1, PSEN2)
3. Duplications of the APP gene

Question 38

How do mutations in the Prenesillin genes (PSEN1, PSEN2) play a role in developing AD?

Answer 38

The Prenesillin genes encode for gamma-secretase. If they are not able to function properly then AB is not cleaved from APP thus resulting in accumulation in the brain

Question 39

Pursuit of new drugs for AD is motivated by _______.

Answer 39

1. Prevention of the formation of AB42 peptide
2. Removal of the AB42 peptide upon formation
3. Prevent interaction between AB molecules

Question 40

What is the function of Rubisco?

Answer 40

Catalyzes the reaction in which CO2 is covalently linked to organic molecules during photosynthesis

Question 41

What are the two proteins encoded by the GroE site? What are there functions?

Answer 41

GroEL and GroES proteins are chaperonins that work on conjunction with one another to allow proteins to fold into their proper conformations within a protected environment

Question 42

What is the structure of the GroEL protein?

Answer 42

Cylindrical assembly of two disks wherein each disk is composed of 7 subunits arranged symmetrically around the central axis