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MCAT Biochem > Biochem #4 > Flashcards

Biochem #4 Flashcards

1
Q

carbohydrates containing 3 carbons

A

monosaccharides

trioses

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2
Q

carbohydrates containing 4 carbons

A

monosaccharides

tetroses

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3
Q

carbohydrates containing 5 carbons

A

monosaccharides

pentoses

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4
Q

carbohydrates containing 6 carbons

A

monosaccharides

hexose

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5
Q

monosaccharide carbohydrates containing aldehyde as the most oxidized group

A

aldoses

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6
Q

monosaccharide carbohydrates containing ketone as the most oxidized group

A

ketoses

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7
Q

D and L do not always means that they rotate optical light ____

A

in a certain direction

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8
Q

how to tell D vs. L

A

D has the OH on the highest numbered chiral center on the right ad L has it on the left.

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9
Q

stereoisomers

A

optical isomers: compounds that have the same chemical formula; these molecules differ from one another only in terms of the spatial arrangement of their component atoms.

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10
Q

absolute configuration

A

determined by the particular three-dimensional arrangement of the groups attached to the chiral carbon.

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11
Q

Fischer projection

A

two-dimensional drawing of stereoisomers.
o Be familiar with the following stereoisomers:
 Enantiomers: same sugars, different optical families (D and L-glucose)
 Diastereomers: two sugars that are in the same family (both are either ketoses or aldoses, and have the same number of carbons) that are not identical and are not mirror images
• Epimers: a special subtype of diastereomers that differ in configuration at exactly one chiral center (Ex: D-arabinose and D-ribose)

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12
Q

D- and L-glucose are

A

enantiomers

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13
Q

epimer

A

a special subtype of diastereomers that differ in configuration at exactly one chiral center (Ex: D-arabinose and D-ribose)

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14
Q

number of stereoisomers of a molecule with 4 chiral centers

A

16

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15
Q

hemiacetal

A

intramolecular reaction of aldose

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16
Q

hemiketal

A

intramolecular reaction of ketose

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17
Q

due to ring strain, the only cyclic molecules that are stable in solution are _______ and _____

A

 Due to ring strain, the only cyclic molecules that are stable in solution are six-membered pyranose rings or five-membered furanose rings

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18
Q

anomeric carbon

A

the name of the carbonyl carbon that becomes chiral in the process of ring formation. It is the one attacked by the hydroxyl group.

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19
Q

anomers

A

both formed from the intramolecular attack, one alpha and one beta.
• Ex: in glucose
o Alpha: -OH on C1 trans to CH2OH
o Beta: -OH on C1 cis to CH2OH

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20
Q

Hawthorn projection

A

useful method for describing the three-dimensional conformations of cyclic structures.
o FischerHawthorn: any group on the right in the Fischer projection will point down.
o Chair configuration is actually more accurate (with substituents in axial or equatorial positions to minimize steric hindrance)

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21
Q

downright, up lefting

A

for fischer to hawthorn

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22
Q

mutarotation

A

The spontaneous change in configuration about C-1, ring opening and closing.
o Occurs in water, happens more rapidly when catalyzed with an acid or bas

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23
Q

monosaccharides

A

contain alcohols and either aldehydes or ketones.

o These functional groups undergo normal functional group reactions.

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24
Q

lactone

A

when oxidation of the aldose occurs when it is in ring form.

carbonyl group on the anomeric carbon

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25
describe reagents used to detect the presence of reducing sugars
 Tollens’ reagent: reduced to form a silvery mirror when aldehydes are present.  Benedict’s reagent: red precipitate when aldehyde group of an aldose is readily oxidized.  Ketose sugars can tautomerize to form aldehydes and then be reduced, giving positive tests. • Tautomerization: the rearrangement of bonds in a compound, usually by moving a hydrogen and forming a double bond. • This specific case, ketone group picks up a hydrogen and the double bond moves onto adjacent carbons, forming an enol (a compound with a double bond to an alcohol group)
26
Tautomerization
the rearrangement of bonds in a compound, usually by moving a hydrogen and forming a double bond.
27
deoxy sugar
contains a hydrogen that replaces a hydroxyl group on the sugar (carbohydrate found in DNA)
28
esterification of carbohydrates
replace all of the OH with the ester being reacted | @0C and pyridine
29
acetal formation of hemiacetal reacting with oxygen
only replace the anomeric OH with the alcohol being added.
30
glycosidic bond
involves anomeric carbons. Glycosidic bonds are the covalent chemical bonds that link ring-shaped sugar molecules to other molecules. They form by a condensation reaction between an alcohol or amine of one molecule and the anomeric carbon of the sugar and, therefore, may be O-linked or N-linked
31
glycoside formation
when a hemiacetal reacts with an alcohol to form an acetal.
32
dissacharides
formed when glycosidic bonds are formed between hydroxyl groups on two monosaccharides. o Linkage is named based on which carbons are involved. o Important disaccharides include sucrose, lactose, and maltose.
33
polysaccharides
long chains of monosaccharides linked together by glycosidic bonds
34
what do cellulose, starch, and glycogen have in common?
glycogen (all composed of D-glucose). Differ in configuration about the anomeric carbon and the position of glycosidic bonds.
35
cellulose
* Homo, made up of Beta-D-glucose molecules linked by B-1,4 glycosidic bonds * Humans cannot digest cellulose, we lack cellulase, good source of fiber.
36
starch
more digestible, broken down by enzymes and used as an energy source. • Linked alpha-D-glucose monomers. • Plants store starch as amylose, a linear glucose polymer linked via alpha-1,4 glycosidic bonds. • Amylopectin: starts off like amylose but then has branches caused by alpha 1,6 glycosidic bonds. • Beta and alpha amylase: cut at different points in the chain to break it down. o Beta: cleaves amylose at the nonreducing end of the polymer. o Alpha: cleaves randomly
37
glycogen
carbohydrate storage unit in animals. • Similar to amylopectin but it has more 1,6 glycosidic linkages. • The branching optimizes it, better storage. • Glycogen phosphorylase: functions by cleaving glucose from the nonreducing end of a glycogen branch and phosphorylating it, producing glucose 1-phosphate.
38
what is the name of a 6 carbon sugar with a ketone group as its most oxidized group? what is the name of a 5 carbon sugar with an aldehyde group as its most oxidized group?
ketohexose aldopentose
39
the aldehyde carbon can participate in____ linkages
glycosidic
40
how to name D vs. L carbohydrates
depends on the location of the hydroxyl on the highest number chiral center carbon - if OH is on the right, "D" - if OH is on the left, "L"
41
enantiomers
nonidentical, nonsuperimposable mirror images of each other. EVERY chiral center is different.
42
how to calculate the number of stereoisomers?
2^n where n is the number of chiral centers
43
how is the optical rotation of a sugar determined? From D and L confiugurations?
No, it is determined experimentally and is not compliant with the D and L configurations
44
Do all D isomers have R configuration?
No
45
+ optical rotation
postive rotation
46
- optical rotation
negative rotation
47
in a fischer diagram, horizontal lines are ____, going ___ the page
wedges, out of
48
in a fischer diagram, vertical lines are ____, going ___ the page
dashes, into
49
the same sugars, in different optical families, are _____
enantiomers
50
two sugars that are in the same family (both ketoses or aldoses and have the same number of Carbons), are _____
diastereomers
51
a special subtype of diastereomers that differ in configuration at exactly one chiral center are called ____
epimers
52
what is the enantiomer of D-gluocse?
L-gluocse
53
how many carbons are in the more stable rings of carbohydrates?
5 (furanose) or 6 (pyranose)
54
compare the alpha anomer and the beta anomer of gluocse?
alpha: the OH group on C-1 is axial and down beta: the OH group on C-1 is equitorial and up
55
any group on the _____ in a fischer projection will point down in a hawthorn projection
right
56
during hemiacetal or hemiketal formation, the carbonyl carbon becomes ______
chiral
57
compare chair and haworth drawings
chair is the diamond thing while haworth is the flat ring
58
what is the name of an oxidized aldose?
aldonic acid
59
any monosaccharide with a hemiacetal ring is considered a ____
reducing sugar because it can be oxidized.
60
what two methods are used to detect the presence of reducing sugars?
Tollens' reagent and Benedict's reagent
61
what is the actual Tollens' reagent?
[Ag(NH3)2]+
62
what does Tollens' reagent do when there are aldehydes present?
it is reduced to form a silvery mirror
63
what does Benedict's reagent do when there are aldehydes present?
the aldehyde group of an aldose is oxidized which is indicated with a red precipitate (Cu2O)
64
what is benedict's reagant?
contains cupric Cu+2 ions.
65
do ketose sugars provide positive benedict's and tollens' tests?
yes, thanks to tautomerization under basic conditions
66
enol
double bond and an alcohol group
67
what is a phosphate ester?
refer to ATP addition to glucose: H2C-O-PO3
68
hemiacetals react with alcohols to form ____
acetals
69
what are the names of acetals formed from hemiacetals reacting with alcohols
glycosides
70
what is the leaving group when hemiacetals react with alcohols
water
71
compare esterification and glycoside formation
esterification: hemiacetal + carboxylic acid (or derivative) and forms an ester (carbonyl with O) glycoside: hemiacetal + alcohol and forms alkoxy group
72
for metabolic purposes, does it make more sense for carbohydrates to be oxidized or reduced?
oxidized so that electron carriers can be reduced, these electron carriers can go on to facilitate processes such as oxidative phosphorylation
73
describe sucrose
glucose-alpha-1,2-fructose
74
describe lactose
galactose-beta-1,4-glucose
75
describe maltose
glucose-alpha-1,4-glucose
76
homopolysaccharide
a polymer made up of entirely one monosaccahride
77
heteropolysaccharide
a polymer made up of more than one type of monosaccharide
78
what can be used to detect starch?
iodine
79
what enzyme is responsible for breaking down glycogen?
glycogen phosphorylase
80
what are the two forms of starch we need to know and which is more soluble?
amylopectin and amylose amylopectin is more branched and therefore more soluble: decreases intermolecular interactions and increases contact with environment.
81
does glycogen or amylopectin have more branching?
glycogen
82
glycogen branching consists of ____ linkages
alpha 1,6
83
enantiomers have ______ optical activities
equal but opposite
84
compare the chemical and physical properties of diastereomers
they are slightly different
85
racemization
moving a solution toward an equal concentration of both enantiomers
86
how do you form an acetal?
react a hemiacetal with alcohol
87
beta amylase vs. alpha amylase
beta amylase cleavage results in maltose | alpha amylase cleavage results in maltose, polysaccharide chains and glucose (cause it cuts everywhere along the chain)
88
compare cellulose and amylose linkages
cellulose used Beta 1,4 linkages | amylose uses alpha 1,4 linkages
89
hemiacetal and hemiketal are monosaccharides in ring form but when alcohol is added they become _____ which is no longer a monosaccharide
acetal or ketal

MCAT Biochem (12 decks)

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