Flashcards in Biochemistry Deck (556)
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151
What are the 2 classifications of carbs?
Simple - monosaccharides
Complex - disaccharide, oligosaccharide(2+), polysaccharide (many)
152
Describe monosaccharides
Simple sugars: can't be converted into smaller molecules by acid hydrolysis
1 sugar, usually colourless, water-soluble, crystalline solids
Building blocks of di and polysaccharides
153
Describe the structure of monosaccharides
Generally have formula (CH2)n - deoxyribose is an exception
Simple monosaccharides C4-7 called tetroses, pentoses, hexoses, heptoses
Exceptions in animals N-acetyl sugars (8C), sialic acid (9,10,11C)
154
What are 2 classifications of monosaccharides?
Aldose and ketose
Aldose - -CHO (aldehyde group)
Ketose - C=O (ketone group)
e.g. aldopentose or ketopentose
155
Describe the structure of glucose in both straight chain and ring
C6H12O6
Is an aldose sugar i.e. has -CHO
Ring: C1 binds to C5 - C1-O-C5
O enables C atoms to bind to from ring
H from C5 OH binds to O on C1, C1 binds to O
156
Describe the structure of fructose
C6H12O6
Is a ketose i.e. has C=O on C2
Ring: C2 bonds to C5
H of C5 OH binds to O of C2, C2 binds to O on C5
157
What is stereochemistry?
Study of spatial 3D relations of atoms in molecules
158
What are Fischer projections?
Basic 2D drawing of 3D molecule
C1 is always at top
Projections drawn to left are ABOVE the ring
Projections to right are BELOW the ring
159
Explain D and L sugars
D and L sugars are optical isomers (mirror images of each other)
D and L refer to the absolute configuration of asymmetric C furthers away from aldehyde/ketone group OR if OH falls on either LHS/RHS
D-glucose is biologically active, OH of C5 falls on RHS
160
What is the structure of D-glucose?
OH of C2,4,5 to right
OH of C3 to left
L-glucose is opposite
161
What happens in solution of glucose in terms of structure?
Equilibrium favouring ring form established
Ring formation creates new chiral centres - C1 in aldoses, C2 in ketoses
This increases the number of possible isomeric forms
162
What are isomers of D-glucose called?
Anomers
163
Describe the 2 anomers of D-glucose
Alpha - (new) OH of C1 is TRANS to CH2OH on C5
Beta - OH of C2 is CIS to CH2OH on C5
164
What is mutarotation?
Interconversion between anomer stereoisomers
Different anomers have different optical rotations
165
What are monosaccharide derivatives?
Simple sugar molecules which contain functional groups as well as OH, either CHO/CO, vary from empirical formula
166
Describe deoxy derivatives
OH replaced by H
e.g. deoxyribose sugar - ribose with OH on C2 replaced by H
167
Describe sugar acid derivatives
OH group oxidised to COOH
168
Describe sugar alcohol derivatives
CO (aldehyde or ketone) reduced to primary/secondary OH
169
Describe phosphorylated sugars
P group attached
Alcoholic group esterified with phosphoric acid
170
What are amino sugars?
Sugar with primary amine group replacing OH
e.g. glucosamine precursor for GAGs (major component of joint cartilage) thus used to treat osteoarthritis
171
Explain the formation of disaccharides
Aldehyde/ketone group reacts with molecules own OH to form ring, then link to C bearing OH on another sugar molecule creating a disaccharide
172
How are monomers linked?
Glycosidic bonds formed when anomeric OH group condenses with alcohol of second monosaccharide
Catalysed by hydrolyse (dehydration) to form R-O-R link
173
Describe the structure of sucrose
Glucose and fructose monomers linked by alpha 1,2 linkage
174
What is glycogen?
Polysaccharide that is the principal storage form of glucose found as granules in cytosol
Liver cells have highest conc. but muscles have greater total amount
175
Describe the structure of glycogen
Highly branched (increases packing)
Linear chains of glucose connected by a-1,4 glycosidic linkages with branches attached through a-1,6 links every 10 residues
176
What 2 enzymes are required for glycogen degradation and why?
Glycogen phosphorylase to hydrolyse a-1,4 linkages but can only work on linear chains OR a-amylase (digestive)
Debranching enzyme to hydrolyse a-1,6 links to straighten out chain
177
Describe the degradation of glycogen
Glycogen phosphorylase breaks glycogen into glucose-1-P but is halted 4 residues from branching point
Glycogen debranching enzyme transfers trisaccharide to a-1,4 adjacent a-1,4 link leaving single glucose molecule at a-1,6
GDE hydrolyses remaining glucose molecule so glycogen phosphorylase can continue
178
Describe the structure of starch
(C6H10O5)n
2 polysaccharides monomers: amylose, amylopectin
Amylose: glucose monomers linked by a-1,4 links
Amylopectin: coiled structure, like glycogen but a-1,6 branch every 24-30 residues
179
What is the function of starch?
Digested by hydrolysis, catalysed by amylases, back to sugar monomers which can be broken down to glucose for energy
180
