Carbohydrates & Nucleic Acids Flashcards
(19 cards)
Empirical formula of carbohydrates
CH2On
Where is at least 3
What are monosaccharides?
- taste sweet
- trioses are the smallest and simplest
Basic nomenclature of carbohydrates
- Monosaccharides are one monomeric unit
- Oligosaccharides (e.g. found in milk) are 2-20 monosaccharides
- Polysaccharides are more than 20 monosaccharides
- Glycoconjugates are linked to proteins or lipids
Examples of monosaccharides
Two families based on the position of the most oxidised carbon
- Aldoses = have an aldehyde group at the end of the chain
- Ketoses = have a ketone group in the middle of the chain
Stereochemistry of monosaccharides
- enatiomers
- Fischer projection = L (points left) and D (points right)
What if there is more than one asymmetric carbon atom?
Naming (D or L) is determined by the chiral carbon furthest away from the aldehyde/ketone group
D isomers are more common in nature for sugars
Pentoses and hexoses
Monosaccharides can form a cyclic Hemiacetal between the C1 aldehyde group and one of the hydroxyl groups
Hemiacetal form
Generates 2 different isomeric forms (anomers) at the C1 carbon = anomeric Carbon atom
- ß-D = the OH points up
- alpha-D = the OH points down
Nomenclature of pentoses and hexoses
- sugars that have a 6-membered ring (5C+O) are called pyranoses
- those with 5-membered rings are called furanoses
- pentoses more commonly form furanoses
- hexoses more commonly form pyranoses
- but some monosaccharides can form both ring sizes
What are disaccharides?
- Monosaccharides linked by a glycosidic bond
- The anomeric carbon reacts with an OH group on the second monosaccharide (Hemiacetal to acetal)
Types of polysaccharides
- Homoglycans = contain only one type of monosaccharide and can be linear or branched
- Heteroglycans = contain residues of more than one type of monosaccharide
Lengths and compositions of a polysaccharide may vary
Glucose storage in polysaccharides
- D-glucose is stored intracellularly in polymeric form —> plants = starch and animals/fungi = glycogen
- Starch is a mixture of amylose and amylopectin
- Amylose is D-glucose linked by alpah1-4 glycosidic bonds
Amylopectin
- Chains will spiral but have branches due to the alpha1-4 glycosidic bonds
- Branches every 24-30 glucose units
- This increases compactness
- And increases the number of chain ends
- Resulting in faster formation and degradation
Glycogen
Very similar to amylopectin but usually larger (more glucose units) and more branches (every 8-12 residues)
Results in more compact structure and fast metabolism
Cellulose structure
- component of plant cell wall
- most abundant biopolymer on earth
- ß1-4 linkages = relatively straight and unbranched chains
- adjacent chains linked via hydrogen bonds
- forms fibrils which associate into a high strength insoluble polymer
Carbohydrates linked to proteins
- many are components of cell membranes
- proteins secreted from cells
- O-glycosidic linkage = by the OH group (Ser & Thr)
- N-glycosidic linkage = by the CONH2 group (Asn)
- proteins can be glycosylated to a level that the majority of the mass is carbohydrate
- several monosaccharide units can attach to proteins
What are nucleic acids?
Polynucleotides = composed of nucleotide monomers
Nucleotide monomers are composes of
- A 5 carbon sugar (ribose/deoxyribose)
- a nitrogenous base
- phosphate groups
Structure of a DNA dinucleotide
- Deoxynucleotide triphosphate (dNTPs) are joined by a phosphodiester linkage
- Inorganic pyrophosphate is a leaving group on formation of linkage
Structure of DNA
- 2 polynucleotides associated to form a double helix
- Planar aromatic nitrogenous bases joined by hydrogen bonds to give a ‘ladder’ of base pairs
- Phosphodiester backbone
- Genetic information is carried by the sequence of base pairs
