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BCH EXAM 2 QUESTIONS WITH CORRECT ANSWERS
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BCH EXAM 2 QUESTIONS WITH CORRECT ANSWERS
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BCH EXAM 2 QUESTIONS WITHCORRECT ANSWERS
Properties of waxes - ANSWER- low melting points, stable solids, appear in both plants
and animals in nature
a wax coat protects the surface of many plant leaves from water loss and attack from
microorganisms
What defines a carbohydrate? - ANSWER- aldehydes & ketones with many OH groups,
or substances that form these when hydrolyzed
Where do carbohydrates come from? - ANSWER- primary products of photosynthesis-
extracts carbon from atmosphere and creates carbs out of that carbon
How are monosaccharides names - ANSWER- 1. Based off Aldose or Ketose
2. Based off # of Carbons
What is the simplest aldiose and the simplest ketone - ANSWER- aldose:
glyceraldehyde
Ketose: dihydroxylacetone
What is the structure of Glucose - ANSWER- aldohexose
What is the structure of Galactose - ANSWER- aldohexose
What is the structure of Mannose - ANSWER- aldohexose
What is the structure of Fructose - ANSWER- ketohexose
What is the structure of Sucrose - ANSWER- glucose a(1-2) fructose
What is the structure of Ribose - ANSWER- an aldopentose
Define the D & L stereochemistry of carbohydrates & how it is determined - ANSWER-
based off glyceraldehyde, CH2OH down in fisher projection
- look at side of -OH group
-OH on right: D- configuration
-OH on left L- configuration
*** OH of highest number Carbon
,What is an enantiomers - ANSWER- nonsuperimposable mirror images
D & L configurations
How many stereoisomers can a molecule have? - ANSWER- 2^n where n = # chiral
centers
What is a diastereomer? - ANSWER- don't differ at ALL chiral carbons, therefore not
mirror images
different physical and chemical properties
What is an epimer? Provide an example - ANSWER- 2 sugars that differ only in the
configuration around 1 carbon
galactose and mannose are epimers of glucose
alpha-D glucose has 3 epimers: B-D-glucose, a-D-mannose, and a-D-galactose
What are 2 most common, of the 4, D-aldopentoses
What are the 2 D-aldothreoses - ANSWER- D-aldopentoses:
1. D-ribose
2. D-xylose
What are the 2 D-aldothreoses:
1. D-erythrose
2. D-threose
What defines a disaccharide (upon a hydrolysis run)? - ANSWER- forms 2
monosaccharides when hydrolyzed
What defines a polysaccharide? - ANSWER- forms many monosaccharides when
hydrolyzed
What is a hemiacetal and a hemiketal? - ANSWER-
What kind of sugars can form rings? What are they called? - ANSWER- 5- 6-, and 7-
carbon sugars
Pyranose: 5 members
Furanose: 6 members
How are cyclic monosaccharides formed? What arises upon formation? - ANSWER- the
-OH group on a hexose will attack C-1 to form a ring
* the C-1 is the "ball" in the ball and stick models
,when the ring is formed, a new asymmetric carbon is introduced into the molecule
How does fructose form a 5 membered ring and a 6 membered ring? - ANSWER- 6
membered pyranose ring: run C2 keto group with the OH on C1
5 membered ring by reaction of C2 keto group with OH on C1
What do alpha and beta mean/why are they used? What are these structures called? -
ANSWER- alpha & beta decribe the orientation of the OH group on C1 in a cyclic sugar.
These classifications are used because a new stereocenter arises when the cyclic
structure is formed
the Alpha and Beta forms of a cyclic sugar are ANOMERS- they differ in
stereochemistry around the ring-forming carbon
since alpha and beta differ in one one chiral center, anomers can also be considered
epimers
For L sugars:
alpha: OH above the ring
Beta: OH below the ring
For D sugars:
alpha: OH below the ring
Beta: OH above the ring
What is a Haworth projection? - ANSWER- represent the cyclic sugars as having
essentially planar rings, with the OH at the anomeric C-1
anything on the LEFT of a fisher projection is ABOVE the ring in a haworth projection
what is the relationship between D-glucose and D-fructose - ANSWER- structural
isomers
How many epimers are there of D-glucose, alpha D-glucose? - ANSWER- 2, 3
Why do we use chair & boat conformations? What are the 2 rules for configuration?
Which is more stable? - ANSWER- C-C-C is 109 deg and C-O-C is 111 deg so durance
and furanose rings cant be planar
instead they take a puckered conformation which are best depicted in chair and boat
confirmations
Equatorial: coplanar with ring
Axial: parallel to axis down through ring
, 2 rules:
1. BULKY side chains are most stable in equatorial
2. Chair is slightly more stable than boat
explains why B-D-glucose is most widely occurring organic group in nature
What are the 6 sugar derivatives - ANSWER- sugar acid
sugar alcohol
deoxysugar
sugar ester
amino sugar
acetal, ketal, glycoside
What is a sugar acid? - ANSWER- - sugar that lacks aldehyde or ketone
--> monosaccharides w carbonyl on 1 or both ends
- carbonyl or hydroxyl is OXIDIZED to a carboxylic acid
- free anomeric C acts as reducing agent and
--> hence being called a REDUCING SUGAR
--> includes aldonic, olsonic, uronic, aldaric acids
What is a sugar alcohol? - ANSWER- mild reduction (NaBH4) of carbonyl group sugars
→ creates sugar alcohol
linear structure
Alditol
-itol : suffix of sugar acid
ex: sorbitol, mannitol, xylitol
What is a deoxysugar? - ANSWER- have 1 or more OH replaced by H
found in DNA and many polysaccharides & glycoproteins
ex: L-fucose, L- Rhamnose : 6-deoxysugars
What are sugar esters? - ANSWER- monosaccharide with added phosphate group
important in metabolic pathways as intermediates
ex: ATP, AMP, etc
What are amino sugars? - ANSWER- contain amino group instead of OH at C-2
found in oligosaccharide chains like CHITIN
muramic acid & neuraminic acid: bacterial cell walls
What are acetals, ketals, & glycosides? - ANSWER- hemiketals and hemiacetals react
with ALCOHOLS in acidic solution to form acetals and ketals via DEHYDRATION
pyranose and furanose react with alcohols in acidic solutions to from glycosides
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