BIOCHEM: Nucleotides, carbs & lipids

Question 1

How can we prove that a pathway works?

Answer 1

• Look at the pathway, an important/unique step from that pathway must be inhibited to see if the effects are changed.

Question 2

nucleoside

Answer 2

is a pentose (five-carbon) sugar linked to a nitrogenous base on the 1′ carbon by a covalent glycosidic bond.

Question 3

nucleotide

Answer 3

consists of a nucleoside attached to one or more phosphate groups by a phosphoester bond.

Question 4

If a pentose has a hydroxyl group at the 2′ carbon, it is __________

Answer 4

ribose

Question 5

If the pentose has a hydrogen at the 2′ carbon it is a ________

Answer 5

deoxyribose

Question 6

What are hydrogen bond acceptors?

Answer 6

Hydrogen bond acceptors are electronegative atoms (nitrogen or oxygen) that have at least one lone pair of electrons

Question 7

what are hydrogen bond donors

Answer 7

are hydrogen atoms bound to electronegative atoms.

Question 8

For each nucleotide of thw watson & crick model, how many donors & acceptors does each pair have?

Answer 8

Question 9

Melting Temperature T_m of DNA & whats the proportion to that of IMF?

Answer 9

• the temperature at which 50% of the double helices in solution have been seperted into single strands
• it is determined by the strength of intermolecular forces holding the strands together (an inc IMF(hydrogen bonding)=inc Tm bc more energy is required to disrupt them)
• DNA molecules with high GC content have higher melting temperatures than those with low GC content.

Question 10

Enantiomers

Answer 10

• compounds with the same chemical formula but DIFFER AT EVERY STEREOCENTER
• Example: L-glucose & D-glucose on fishcer projections

Question 11

Carbs:

what determines the absolute configuration (D or L)?

Answer 11

the chiral carbon furthest from the carbonyl group determines the absolute configuration L or D of the sugar

Question 12

Carbs:

Stereoisomers (aka optical isomers):

Answer 12

two or more compounds with identical molecular formulas and arrangements of atoms that only differ in the spatial arrangement of their atoms; they have non-superimposable mirror images.

Question 13

Carbs:

Enantiomers

Answer 13

• the same sugars in different optical families (such as D-glucose and L-glucose).
• differ at every chiral carbons
• no internal planes of symmetry

Question 14

The number of possible stereoisomers of a compound can be calculated by:

Answer 14

2ⁿ

n=the number of chiral carbons present

Question 15

Carbs:

Fischer projections, how to determine L or D?

Answer 15

Question 16

Carbs:

Diastereomers

Answer 16

• are two sugars that are in the same family (that are stereoisomers), but are not identical and are not mirror images of each other.

Question 17

Carbs:

Epimers

Answer 17

• are a special subtype of diastereomers that differ in configuration at exactly one chiral center.
• D-ribose and D-arabinose are epimers (at carbon number 2)

Question 18

Anomers can exist only in:

Answer 18

• in cyclized sugars (furanose or pyranose) and _differ at the anomeric carbon_
• Anomeric carbon: A carbon derived from the carbonyl carbon (the ketone or aldehyde functional group) of the open-chain form of the carbohydrate molecule
  
  • α form: OH on the bottom
  • β form: OH on the top

Question 19

mutarotation

Answer 19

• The opening and closing of sugars repeats continuously in an ongoing interconversion between anomeric forms and is referred to as mutarotation
• Cyclic compounds undergo mutarotation, in which they shift from one anomeric form to another with the straight-chain structure