Chapter 7: 7.1 Carbohydrates Flashcards
What are carbohydrates involved in?
- Postranslational modifications
- Cell recognition
What are carbohydrates also referred to as?
Sugars
Define:
Monosaccharides
The simplest carbohydrate
* Has the formula: (CH2O)n
How are carbohydrates named as?
Named based on the number of carbons they have
* E.x. triose, tetrose, pentose, hexose, heptose…
What are aldoses? What are ketoses?
- Aldoses: Carbohydrates have an aldehyde at C1
- Ketoses: Carbohydrates have a ketone at C2
- E.x. Ketohexose, aldotriose…
In Fischer Projections:
What do L and D represent?
L and D are in reference to the different enantiomers of the sugar structure (asymmetry)
In Fischer Projections:
What do enantiomers depend on?
Dependent on the chiral carbon furthest from the carbonyl group
In Fischer Projections:
What does it mean that enantiomers are optically active?
Rotate polarized light either to:
* The right (+, D)
* The left (-, L)
In Fischer Projections:
What determines the possible number of stereoisomers? State the formula
The number of chiral carbons (x)
* Possible number of stereoisomers = 2^x
Describe:
Carbohydrate Cyclization
The hydroxyl group nycleophilically attacks the aldehyde or the ketone (very reactive) forming the ring
In carbohydrate cyclization:
What types of rings are formed?
- Furan (5 membered ring)
- Pryan (6 membered ring)
What types of bonds can be formed in carbohydrate cyclization?
- Hemiacetal (from aldehyde)
- Hemiketal (from ketone)
In carbohydrate cyclization:
It result in — possible ——-
- Two
- Anomers
What are the two possible anomers resulting from carbohydrate cyclization?
- α (E.x. α-D-Glucose)
- β (E.x. β-D-Glucose)
In carbohydrate cyclization:
Which anomer is more stable?
β
Define:
Isomers
Same formula, different structures
What types of stereoisomers are there?
- Enantiomers
- Diastereoisomers
Define:
Enantiomers
Mirror images (not superimposable)
Define:
Diastereoisomers
Not mirror images (superimposable)
Define:
Anomers
Differs at a new asymmetric carbon in the ring conformation
True or False:
Anomers are a type of diastereoisomer
True
Define:
Reducing Sugars
Sugars able to act as a reducing agent due to a free aldehyde or free ketone group (all monosaccharides)
In reducing sugars:
What are aldehydes converted to?
Converted to carboxylic acids
In reducing sugars:
What are ketones converted to?
Tautomerized into aldehydes and then reduced to carboxylic acids
True or False:
Disaccharides are reducing sugars
Partially true. Disaccharides are reducing sugars as long as one of the units have an open chain with an aldehyde
Is maltose a reducing sugar? Is sucrose a reducing sugar?
- Maltose is reducing
- Sucrose is not reducing
What modifications are made to make complex carbohydrates?
- Phosphorylation
- Methylation
- Addition of N-containing groups
- Hydroxyl groups removed
Describe:
Naming of sugar complexes:
- Monosaccharide = 1
- Disaccharide = 2
- Oligosaccharide = 3-20
- Polysaccharides = 1000s
Describe:
Disaccharide formation
Condensation reaction forming a glycosidic bond
In disaccharide formation:
What type of glycosidic bonds are there?
- O-glycosidic bond
- N-glycosidic bond
In disaccharide formation:
List the linkage to proteins
- O-linkages (to Ser/Thr)
- N-linkages (to Asn)
Define:
Glycosyltransferase
The enzyme responsible for linking sugars via O-glycosidic bonds
How does glycosyltransferase work?
Uses UPD-glucose to attach sugars onto other sugars or proteins
Define:
UPD glucose
A high energy sugar nucleotide used by glycosyltransferase
—— are cleaved into ————— via ——-
- Sugars
- Monosaccharides
- Enzymes
True or False:
Monosaccharides are a source of fuel
True
What enzymes are used to cleave sugars into monosaccharides?
Lactase, maltase, sucrase
Explain:
Naming Disaccharides
- Identify N or O linkage
- Configuration of the first sugar plus the name ending in -yl
- The number identifiers of the carbons linked together
- Configuration of the second sugar plus the name ending in -ose
What are polysaccharides also referred to as?
Glycans
Describe:
Polysaccharides
Consist of 1000s of monosaccharides (linked either linearly or branched)
Polysaccharides play roles in…
- Energy storage
- Cell structure
- Cell recognition
Define:
Homopolymers
Polysaccharides made up of the same repeating monosaccharide
Define:
Heteropolymers
Polysaccharides made up of different monosaccharide repeats
Define:
Glycogen
A energy storage homopolymer with a multibranched structure
What is the repeating monosaccharide in glycogen?
Glucose
Describe structure of:
Glycogen
Consists of branched glucose units surrounding a glycogenin protein at its core
* Chain lengths of 8-12 of linearly linked glucose molecules (α(1-4) glycosidic bonds) with branches forming α(1-6) glycosidic bonds
What is starch comprised of?
- Amylose
- Amylopectin
Describe structure of:
Amylose
Linear linkages of glucose (α(1-4) glycosidic bonds)
Describe structure of:
Amylopectin
Linear linkages of glucose (α(1-4) glycosidic bonds) with α(1-6) glycosidic linkages occuring every 30 glucose units
Explain the function of:
α-amylase
Cleaves glycogen and starch at random locations yielding maltose and maltotriose
What secretes α-amylase?
Pancreas
Explain the function of:
β-amylase
Hydrolyzes glucose units in glycogen and starch systematically at non-reducing ends, producing maltose
True or False:
β-amylase is produced in the pancreas
False, β-amylase is not produced by mammals
Define:
Cellulose
Structural components in plants
Describe the structure of:
Cellulose
- Formed by β(1-4) glycosidic linkages
- Linear chains
- Formula: (C6H10O5)n
- More crystalline than starch
True or False:
Cellulose is digestible by humans
False, cellulose is not digestible by humans
List:
Common monosaccharides to know
- Glucose (Glucopyranose)
- Fructose (Fructofuranose)
- Galactose (Galactopyranose)
- Mannose (Mannopyranose)
- Ribose (Ribofuranose)
- Deoxyribose (Deoxyribofuranose)
