Carbohydrates Flashcards
Classification of carbohydrates
Monosaccharides, oligosaccharides and polysaccharides.
Monosaccharide structure + examples
Simple sugar that consists of only one polyhydroxy aldehyde or polyhydroxyketone, many of them are sweet, water soluble.
Glucose, Galactose and Fructose
Oligosaccharides structure + examples
Polymers formed of 2-10 monosaccharides that can be separated by hydrolysis. Named disaccharides, trisaccharides etc depending on the number of monomers. Generally sweet taste and water soluble.
Sucrose, Lactose, maltose
Polysaccharides structure + examples
Large molecules formed by the assembly of monosaccharides arranged in linear or branched chains. In general insoluble in water, tasteless and amorphous.
Starch, cellulose, glycogen
Different types of monosaccharide sugar + examples
aldose- contains a carbonyl group on the end of the chain, glucose, galactose
ketose- contains a carbonyl group in the middle of the chain, fructose
Two forms of ring and how they are formed
Pyranose- between 1 aldehyde group and 5 hydroxyl group to create a hemiacetal. Reaction of an aldehyde and an alcohol. six membered ring. OH attacks the carbonyl
Furanose- reaction of an alcohol and a ketone- forms a hemiketal. Contains 4 carbons and one oxygen atom in ring and the other carbons on either side. five membered ring
Two shape considerations
Chair and boat- both planar conformations
Why does the chair shape form more often?
More stable due to the lack of steric interference between groups of the apical points. Boat contains orbitals that clash which are of higher energy.
Maltose glycosidic bond
alpha 1,4
Cellular glycosidic bond
beta 1,4
Lactose glycosidic bond
beta 1,4
Amylopectin glycosidic bond
alpha 1,4 and alpha 1,6
3 polysaccharides and structures
Starch- formed of alpha glucose, 1,4 glycosidic bonds form a coiling molecule with intramolecular hydrogen bonds.
Glycogen- formed of alpha glucose, 1,4 glycosidic bonds- similar to starch however more highly branched.
Cellulose- formed of beta glucose, beta 1,4 glycosidic bonds, form parallel chains with intermolecular hydrogen bonds forming strong microfibrils.
Structures of monosaccharides in cells
Always phosphorylated by ATP, often carbon 6. Always a ring structure, apart from trioses.
Lectin function
Carbohydrate binding protein. Have a role in recognition on the cellular and molecular level.
Main reaction of sugar molecules
Act as a reducing agent if they have a free carbonyl group
What must ketones first undergo?
Tautomerism
What form must the sugars be in?
Open chain, not a ring.
How does a blood test work?
Use glucometers to test blood sugar levels. Glucose is oxidised by glucose oxidase to hydrogen peroxide and D-gluconolactone.
Electronic meters use an electrode to take up the electrons that are released. Current measured is proportional to the concentration of glucose in the blood.
Colourimetric strips use peroxidase to change colour upon reaction with the hydrogen peroxide produced.
Glycoprotein definition
Compounds formed of conjugated proteins with prosthetic groups that are carbohydrates.
How do glycoproteins differ from proteoglycans?
Glycoproteins have shorter and more branched carbohydrate chains.
Proteoglycan structure
Proteins that are heavily glycosylated. Basic proteoglycan unit consists of a core protein with one or more covalently attached glycosaminoglycan chains. Point of attachment for the carbohydrate chains is serine residue.
Proteoglycan function
Mainly in the ECM, form large complexes to other proteoglycans such as hyaluronic acid and to fibrous components such as collagen.
Combination of proteoglycans and collagen form cartilage.
GAG chains contain negatively charged sulphates which attract water, therefore can be compressed at the joints and protect.
GAGs are very large, therefore provide large structural scaffold.
Proteoglycan structure in cartilage
Protein core aggrecan acts as linking protein attaching GAGs in intervals on the hyaluronic acid
Different types of glycosylation
N-linked and O-linked
Glycosylation definition
A process in which a carbohydrate is attached to a hydroxyl group of another molecule. Often with glycans being attached to proteins.
N-linked glycosylation explained
Sugars attached to the protein on the nitrogen on asparagine.
1. Processing steps include removal of some of the original sugar molecule during trimming.
- addition of new sugars at the non reducing end of the glycan
- Lipid linked precursor formed first in the cytoplasm and then undergoes second phase in the lumen of the ER.
- Core structure occurs in the lumen during translation.
N-linked trimming in more detail
- exoglycosidases cleave sugars from non reducing end
- series of mannosidases remove mannose linked alpha 1,2
- high mannose olligosaccharides (glycans containing 5-9 mannose sugars)
- complex glycans are built on a core containing 3 mannose residues and GlnNAc residues.
Two main forms of o-linked proteins
proteoglycans and mucins
How do glycans attach?
attach to serine/threonine or tyrosine OH group
Dolichol phosphate function
Function as a membrane anchor for the formation of an oligosaccharide with glucose, mannose and N-acetylglucosamine.
Oligosaccharide is transferred from the dolichol phosphate to asparagine on polypeptide chains
4 examples of proteoglycans
Hyaluronic acid, chondroitin, derma tan and keratin sulphate
Hyaluronic acid structure + function
Glycosaminoglycan is a disaccharide formed of G-glucuronic acid linked to N-acetylglucosamine. Each unit is bound to the next to form a polysaccharide.
forms a highly viscous solution with lubricating properties- associated with many connective tissues
Chondroitin sulfate structure and function
N-acetyl-D-glucosamine and glucuronic acid.
Important component in cartilage and bone- provides resistance from compression
Dermatan sulphate structure and function
L- iduronic acid and N-acetyl-D-glucosamine
Found in skin and connective tissue of various organs.Role in coagulation, cardiovascular disease and wound repair.
Keratan sulfate structure and function
No uronic acid- formed of galactose and acetylated glucosamine, esterified by sulphate
Found in cornea and cartilage.- act as a dynamic buffer in corneal hydration and shock absorber in cartilage
Glycogen structure + function
Energy store in animals, fungi and bacteria. Glucose linked together linearly by 1,4 glycosidic bonds. Branches are linked o changes by 1,6 bonds. Each glycogen granule has its core glycogenin protein
Starch structure + function
energy store in plants.
Formed of two components: amylose which is unbranched and amylopectin which is branched. Branches are longer and less frequent compared to glycogen.
Cellulose structure and function
Structural component in plant cell walls, withstand pressure
Parallel chains formed of beta glucose with string hydrogen bond intermolecular forces between chains, forming microfibrils.
Function of glycoproteins
marker proteins e.g glycoprotein of the ovule the zone pellucida contains oligosaccharides recognised by sperm, allowing the interaction of gametes prior to fertilisation. .
Binds to toxins, preventing them from invading cells
Explain blood groups
The surface of red blood cells and other cells contain glycoproteins and glycolipids. The antigenic determinant of these molecules lies in the carbohydrate moiety.
Antigenic glycans built up on the ends of polylactosamine chains by the action of a fucosyltransferase which generates H antigens.
Individials with an O group only have H antigens.
Blood type A individuals contain polylactosamines with an extra N-acylglucosamine residue added to the terminal galactose.
B type, Galactose resided is added
What is the Bombay phenotype?
Individuals lack genes for fucosyl transferase, therefore cannot form terminal disaccharide fucose-galactose present in H antigens, therefore have no antigens on their red blood cells.
Role of carbohydrates in synthesis of lipids
Synthesised from acetyl CoA which is formed from the breakdown of carbohydrates.
Role of carbohydrates in synthesis of proteins
Amino acids components obtained from glucose during glycolysis
Role of carbohydrates in synthesis of nucleotides
Phosphorylated ribose-5-phosphate derived from glucose-6-phosphate which is obtained from glucose during glycolysis in the cytoplasm
