Chapter 2: Chemical Basis of Life Flashcards
Covalent Bonds Noncovalent Bonds Acids, Bases, and Buffers Nature of Biological Molecules Formation of Complex Macromolecular Structures
Monosaccharides
The building blocks of carbohydrates
What are the main functions of carbohydrates?
Storage of chemical energy
Building materials for biological construction
Differentiate between a ketose and an aldose
Ketose: contains an internal carbonyl group
Aldose: contains an external carbonyl group
What is a polysaccharide?
A polymer of monosaccharides linked by glycosidic bonds
What are the main properties of lipids?
- Ability to dissolve in organic solvents (chloroform, benzene)
- Inability to dissolve in water
Triacylglycerol
Glycerol linked to three fatty acids by ester linkages
Amphipathic
Molecules containing both hydrophilic and hydrophobic regions
What is the structure of fatty acids?
Hydrocarbon chains with one carboxyl group at the end
Differentiate between saturated and unsaturated fatty acids
Saturated: no double bonds (stearic acid)
Unsaturated: presence of double bonds
What conformation are the double bonds in naturally occurring fats usually in?
Cis conformation
The more double bonds a fatty acid has…
The more liquid state it will be in due to less effective packing of the molecules
Cholesterol
a steroid that is a component of animal cell membranes
Differentiate between the primary, secondary, tertiary, and quaternary structure of proteins
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
Sickle cell anemia is a result of ___________.
a single change in the primary structure of the protein wherein a valine replaced a glutamic acid
The degree to which changes in the amino acid sequence are tolerated depends on _______.
the degree to which the shape of the protein or the critical functional residues are disturbed
The degree to which changes in the amino acid sequence are tolerated depends on _______.
the degree to which the shape of the protein or the critical functional residues are disturbed
What is the stabilizing factor in alpha-helices?
The hydrogen bonds between between the atoms of a peptide bond and those situated above and below it
What is the stabilizing factor in beta-sheets?
hydrogen bonds oriented perpendicular to the long axis and project across from one part of the chain to another
Polypeptide chains exist in conformations that ________.
provide the maximum number of hydrogen bonds between neighboring amino acids
What is the stabilizing factor for an entire protein?
array of non-covalent bonds between the diverse side chains
Differentiate between fibrous and globular proteins
Fibrous: elongated, outside the cell
Globular: compact, within the cell
What is the main function of molecular chaperones?
Guide misfolded or unfolded proteins to their proper three-dimensional conformations by preventing non-selective interactions with other molecules in close proximity
What is the general mechanism of molecular chaperones?
Bind to hydrophobic amino acids that are usually exposed in the proteins nonnative conformation but buried in the native one
Differentiate between the two families of molecular chaperones based on their mechanisms
- Hsp70: bind to elongating proteins as they emerge from the large ribosomal subunit
- Chaperonins: allow polypeptides to fold without interference from other macromolecules in the cell
Describe the causative agent of Creutzfeld-Jakob disease
Prion - infectious agent composed solely of protein
How can an inherited gene also be an infectious agent in the case of CJD?
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
Compare and contrast the two gene products of PRNP
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
What are the implications of CJD?
Loss of motor coordination and dementia
Carleton Gajdusek
Discovered CJD in Papua New Guinea (named as “Kuru”)
What are the forms of Transmissible Spongiform Encephalopathies? What do they have in common?
- Mad Cow’s disease
- Scrapie
- Wasting disease
- Creutzfeld-Jakob disease
All of them are characterized by microscopic holes in the brain tissue
What is characteristic of a brain of a person with Alzheimers disease?
Presence of fibrillar deposits of amyloid
Amyloid hypothesis for AD
AD is caused by the protein amyloid-beta-peptide
TRUE or FALSE
the protein involved in AD is an infectious agent similar to that of CJD
False
Explain the relationship between amyloid-beta-polypeptide, amyloid precursor protein, amyloid-beta-polypeptide 42, beta-secretase and gamma-secretase
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
What is the nature of AB42?
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
How is it that the soluble oligomers are more dangerous than the insoluble aggregates?
The soluble oligomers of AB42 are able to attack the synapses of the nerve cells thus effectively killing them
What are factors that may result in overproduction of AB42?
- Mutations in the APP gene
- Mutations in the Prenesillin genes (PSEN1, PSEN2)
- Duplications of the APP gene
How do mutations in the Prenesillin genes (PSEN1, PSEN2) play a role in developing AD?
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
Pursuit of new drugs for AD is motivated by _______.
- Prevention of the formation of AB42 peptide
- Removal of the AB42 peptide upon formation
- Prevent interaction between AB molecules
What is the function of Rubisco?
Catalyzes the reaction in which CO2 is covalently linked to organic molecules during photosynthesis
What are the two proteins encoded by the GroE site? What are there functions?
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
What is the structure of the GroEL protein?
Cylindrical assembly of two disks wherein each disk is composed of 7 subunits arranged symmetrically around the central axis
