Nucleic Acids & Carbohydrates

Question 1

Building blocks of DNA?

Answer 1

The building blocks are purine (2 rings – adenine, guanine) and pyrimidine (1 ring – cytosine, uracil, thymine) bases and can form glycosidic bonds with carbohydrates

Question 2

What is a nucleoside?

Answer 2

Link purine/pyrimidine bases to ribose/deoxyribose rings with glycosidic bonds

Question 3

What is a nucleotide?

Answer 3

Formed by phosphorylating nucleosides at the ribose OH group

Question 4

What energy sources do organisms use?

Answer 4

ATP, UTP, GTP and CTP, but all organisms use ATP.

Question 5

Redox reactions?

Answer 5

NAD+, NADP+ and FAD are all derivatives of ADP.
NADH and FADH2 are used in oxidative metabolism
NADPH used in reductive biosynthesis

Question 6

What is cyclic AMP/GMP used for?

Answer 6

Signal transduction.

Acts as a secondary messenger for some hormones.

Question 7

Strongest base pairing?

Answer 7

GC > AT > AU

Question 8

Structure of double helix?

Answer 8

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)

Question 9

How is DNA stabilised?

Answer 9

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

Question 10

Purpose of major and minor grooves?

Answer 10

Provide access to edges of base pairs.

Proteins can have a complementary shape to edge of base pairs

Question 11

What are ribozymes?

Answer 11

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.

Question 12

Structural features of monosaccharides?

Answer 12

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.

Question 13

What is configurational isomerism?

Answer 13

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

Question 14

What is an enantiorner?

Answer 14

Stereoisomers which are mirror images of each other

Question 15

What is a diastereoisomer?

Answer 15

Stereoisomers which are not mirror images of each other

Question 16

Ring formation in carbohydrates?

Answer 16

Pentoses and hexoses form furanose (5 carbon atoms within the ring) and pyranose (6 carbon atoms within the ring).

Question 17

What is steric hindrance?

Answer 17

Stopping of a chemical reaction which might be caused by a molecule’s structure.

Question 18

What are solvation effects?

Answer 18

Interaction of a solute with the solvent, which leads to stabilisation of the solute species in the solution.

Question 19

What are stereo-electronic factors?

Answer 19

Empahasise the relation between the electronic structure and the stereochemistry of a molecule.

Question 20

Chemical modification of monosaccharides?

Answer 20

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.

Question 21

How do glycosidic bonds form between carbohydrates?

Answer 21

formation of kinetically stable oligo/polysaccharides – disaccharides (sucrose and lactose), trisaccharides (raffinose), polysaccharides (cellulose, glycogen, starch)

Question 22

How do glycosidic bonds form between carbohydrates and amino acids?

Answer 22

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

Question 23

How do glycosidic bonds form between carbohydrates and nitrogenous bases?

Answer 23

formation of N-linked glycosides with purines and pyrimidines

Question 24

General functions of carbohydrates?

Answer 24

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