Nucleic Acids & Carbohydrates Flashcards
Building blocks of DNA?
The building blocks are purine (2 rings – adenine, guanine) and pyrimidine (1 ring – cytosine, uracil, thymine) bases and can form glycosidic bonds with carbohydrates
What is a nucleoside?
Link purine/pyrimidine bases to ribose/deoxyribose rings with glycosidic bonds
What is a nucleotide?
Formed by phosphorylating nucleosides at the ribose OH group
What energy sources do organisms use?
ATP, UTP, GTP and CTP, but all organisms use ATP.
Redox reactions?
NAD+, NADP+ and FAD are all derivatives of ADP.
NADH and FADH2 are used in oxidative metabolism
NADPH used in reductive biosynthesis
What is cyclic AMP/GMP used for?
Signal transduction.
Acts as a secondary messenger for some hormones.
Strongest base pairing?
GC > AT > AU
Structure of double helix?
Two complementary DNA strands arranged antiparallel to form a double helix
Deoxyribose rings are linked by phosphodiester links
external surface: hydrophilic (phosphate and deoxyribose)
internal surface: hydrophobic (base pairs)
How is DNA stabilised?
hydrophobic effect: drives polar groups away from water
Van der Waals attractions occur due to molecules being v close – electrons. Very weak electrical interaction between 2+ atoms/molecules close to each other
Purpose of major and minor grooves?
Provide access to edges of base pairs.
Proteins can have a complementary shape to edge of base pairs
What are ribozymes?
Some RNA molecules can fold into tertiary structures that create binding sites with catalytic activity.
Function without the involvement of proteins, but most function with accessory proteins.
Structural features of monosaccharides?
Carbonyl group (CH=0) determines whether the carbohydrate monosaccharide (C6H12O6) is an aldose or a ketose. On the end is an aldose, whereas in the middle is a ketose.
What is configurational isomerism?
Carbon atoms bonded to 4 groups (asymmetric carbon atoms) exist in 2 forms, which are non-superimposable mirror images – can’t be rotated to form the same structure. Enzymes won’t recognise as the same molecule. D-Glucose is more common than L-Glucose.
Many monosaccharides differ only in the spatial arrangement of atoms.
Changes are recognised by enzymes and other proteins and therefore can have major biological effects0
What is an enantiorner?
Stereoisomers which are mirror images of each other
What is a diastereoisomer?
Stereoisomers which are not mirror images of each other
Ring formation in carbohydrates?
Pentoses and hexoses form furanose (5 carbon atoms within the ring) and pyranose (6 carbon atoms within the ring).
What is steric hindrance?
Stopping of a chemical reaction which might be caused by a molecule’s structure.
What are solvation effects?
Interaction of a solute with the solvent, which leads to stabilisation of the solute species in the solution.
What are stereo-electronic factors?
Empahasise the relation between the electronic structure and the stereochemistry of a molecule.
Chemical modification of monosaccharides?
Esterification/phosphorylation
ADP can be phosphorylated to give ATP
RNA and DNA differ by the pentose sugar ring
Chemical reduction:
ribose -> deoxy-ribose
mannose -> mannitol
Oxidation:
glucose -> glucuronic acid
Amino sugars:
acetyl can be added to β-glucosamine to give acetyl-β-glucosamine
Glycosides:
formed by condensation reactions (basis for polymerisation). Allows the linkage of carbohydrates.
How do glycosidic bonds form between carbohydrates?
formation of kinetically stable oligo/polysaccharides – disaccharides (sucrose and lactose), trisaccharides (raffinose), polysaccharides (cellulose, glycogen, starch)
How do glycosidic bonds form between carbohydrates and amino acids?
Formation of O-linked and N-linked glycoproteins
Can modify proteins by adding carbohydrates
between carbohydrates and lipids
Formation of O-linked glycosides with sphingosine
How do glycosidic bonds form between carbohydrates and nitrogenous bases?
formation of N-linked glycosides with purines and pyrimidines
General functions of carbohydrates?
Storage of energy and reduced carbon.
Carbohydrates are central to metabolism and energy transduction. Most common product of CO2 fixation.
Storage of carbohydrate ensures continuation of cell function despite fluctuation in external inputs
Structural functions
Polysaccharides are major components in cell walls of plants/bacteria
Exoskeletons of invertebrates - chitin is stabilised by intermolecular H bonds
Connective tissue of vertebrates
Recognition functions
Modifying carbohydrates is easy to make a unique structure which is easily recognised.
Largest structural complexity
Blood groups - oligosaccharides attached to polypeptides during post translational processing direct proteins to specific intra/extracellular locations
