Sugars and Polysaccharides Flashcards
How are carbohydrates produced
produce by photosynthesis in plants
- produces monosaccharides
what do carbohydrates consist of
- Composed of carbon hydrogen and oxygen in the ratio of 1:2:1
- The carbon atoms are hydrated which means it is carbon plus water
- during photosynthesis the carbon atom has had water added to it
why are the carbohydrates important
- Major source of energy in the diet
- Have many additional biological functions
- Complex
describe the structures of protein
- Well defined structure
- Coded by precise genes
- 20 amino acids - can put together in different combinations
- Peptide link apart from proline
- Tightly folded structures such as alpha helix and beta pleat
describe the structures of polysaccharides
- Poorly defined but some from helices such as amylose
- Synthesisied by enzymes without a template, lots of enzymes
- Lots of potential building blocks but many are homopolymers and rarely have greater than 3 to 4 different sugar molecules, if they have different sugar molecules then they are heteropolymers
- Have differnet links such as beta 1-4, alpha 1-6 this depends on which carbon atom we link togehter
- They have a range of structures, such as rods, coils or amorphous
- side lineages
- branched - enzymes have easy access for when energy is required
- takes up more space
compare protein and polysaccharides
Protein
- Well defined structure
- Coded by precise genes
- 20 amino acids - can put together in different combinations
- Peptide link apart from proline
- Tightly folded structures such as alpha helix and beta pleat
polysaccharide
- Poorly defined but some from helices such as amylose
- Synthesisied by enzymes without a template, lots of enzymes
- Lots of potential building blocks but many are homopolymers and rarely have greater than 3 to 4 different sugar molecules, if they have different sugar molecules then they are heteropolymers
- Have differnet links such as beta 1-4, alpha 1-6 this depends on which carbon atom we link togehter
- They have a range of structures, such as rods, coils or amorphous
- side linkages which are tough together
- branched - enzymes have easy access for when energy is required
- takes up more space
what are monosaccharides
sugars that are made out of individual sugars and cannot be hydrolysed any further
name some monosaccharides
- glucose
- fructose
- galactose
- mannose
what are disaccharides
2 monosaccharides that are linked together by a glycosidic bond
name some disaccharides
maltose
sucrose
lactose
what makes up disaccharides
- maltose
- sucrose
- lactose
- maltose - glucose and glucose
- sucrose - glucose and fructose
- lactose - galactose and glucose
what are oligosaccharides
contain 3-10 monosaccharides stuck together
name some ologiosacchardies
- Heparin - anticoagulant
- Fructo-oligosaccharides-
- Galacto-oligosaccharides
- Blood group antigens
whats a sugar called with more than 10 monosaccharides stuck together
polysaccharide
what is a polysaccharide
a sugar with more than 10 monosaccharides stuck together
describe fructo-oligosaccharides
not digested in the stomach and small intestine but are fermented in the colon therefore do not contribute to calories
- contain a linear chain of fructose units
- occur naturally in plants such as onion, garlic and banana
describe galacto-oligosaccharides
prebiotics therefore they feed the gut bacteria while not being digested in the upper gastrointestinal system
- consists of short chains of galactose molecules
- occur in human milk and help protect the gut from pathogenic bacteria
name some polysaccharides
- glycogen
- cellulose
- amylose - starch
- amylopectin - starch
what are the bonds that make up glycogen
alpha 1-4 bonds
what are the bonds that make up cellulose
beta 1-4 bonds
what are the two main family of monosaccharides
aldehyde and ketone
what are the functional groups for aldehyde
CHO
what is the functional group for ketone
C=O
how many carbon atoms do monosaccharides have
between 3-7 carbon atoms
what does an aldose contain
contains one aldehyde group
what does a ketone contain
contains one ketone group
what are entaniomers
pair of non superimposable isomers that are mirror images of each other
what is the most common isomer for
D form
- Have to be in a lab to make L glucose, therefore natural source if D glucose
what is the structure of the D isomer
D form the OH group is attached to the right of the carbon
what is the strucuture of L isomer
the L from OH group is attached to the left of the carbon
why does the L isomer have no calories
- cannot be digested, because it is not natural and we have not been exposed to it
- goes through the gut
- acts as a laxative as it draws water in as it still acts as a sugar
what is an asymmetric chiral carbon
this means the carbon as 4 covalent bonds to 4 different groups and cannot be superimposed on its mirror image
monosaccharides that contain…
one or more chiral carbon atoms have D and L forms
if there is more than one chiral carbon ..
absolute configuration of chiral carbon atom furthest away from the carbonyl group determines whether it is a D or a L enantiomer
what type of isomer can be digested
D
what type of isomer cannot be digested
L
monosaccadries with 5,6 atoms form…
a cyclic structure
describe how a cyclic structure forms
- Hydroxyl group of C5 reacts with the aldehyde or ketone group
- This produces a new asymmetric centre at C1 – the anomeric carbon, the 2 stero-isomers are called anomers of alpha and beta
why is beta cyclic more common
spread of OH makes it more stable
why is the cyclic form important EDIT THIS
- Different anomers of the same sugar are recognised by differnet enzymes
- Important for glycoside bond formation and hydrolysis
- Cyclic form is nonreaction, glucose 99.9% in cyclic conformation, least oxidzable and least reactive with protein, beta anomer of glucose is most stable as OH groups are distributed more evenly in the plane of the ring
describe the cyclic and monosaccharide structure exciting in equilibrium
- In solution equilibrium exists between straight chain and two cyclic forms
- Glucose equlibirum is 65:35 beta:alpha anomer
what is a property of the cyclic form
Cyclic form is locked and less amendable to modifications
why do you modify monosaccharides
- Modifications to monosaccharides give complexity
- Makes the monosaccharide more recognisable
- Often used in specific recognition determinants on cell surfaces
how are modifications made in the sugar
replacement of the OH group
removal of the OH group
what is sugar phosphate the starting point for
starting point in glycolysis to produce glucose phosphate
how are sulphated sugars produced
- Sulphated sugars form GAGs
- GAGs are found in the ECM
- Happens by the action of sulpho-transferase enzyme this catalyses the reaction in which the sulphur group on a donor molecule is transferred to the OH group on the sugar
name the sulphated sugars in GAGS which are found in the extracellular matrix
- Chondroitin sulphate
- Dermatan sulphate
- Heparan sulphate
what do sulphates do in GAGs
- Make the GAG highly negatively charged so that they attract and bind water and positive ions
- water attracted and held in place this allows resistive compressive forces to take place
- and act as a lubricant
how do you convert a monosaccharide to a polysaccharide
- Monosaccharides are joined by glycosodic bonds
- This is a covalent bond that is formed via a condensation reaction in which water is removed
- Leads to loss of water
- Dehydration reaction
what catalyses the formation of glycosidic bonds
- Glycosyl transferases (e.g. glycogen synthase) catalyse the formation of specific glycosidic bonds involved specific sugars and specific OH groups
what catalyses the hydrolysation of glycosidic bonds and name an example of one
- They are highly specific
- Can help us understand why we can’t metabolise certain food for example amylase hydrolysis specifically the Glc alpha 1-4 glyosidic bond in glycogen but is inactive for the Glc beta 1 – 4 glycosodic bond in cellulose
Diseases associated with glycogen not breaking down
- Red blood cells and the brain have an absolute requirement for blood glucose for energy metabolism.
- Together they consume 80% of the 200g of glucose consumed per day. There is only about 10g of glucose in the plasma and extracellular fluid volume, so blood glucose must be replenished constantly. Otherwise hypoglycaemia occurs and compromises brain function leading to confusion and disorientation and possible life-threatening coma at blood glucose below 2.5mmol/L. We absorb glucose from the intestines for only 2-3 hrs following a carbohydrate meal so we need a way to fill in the gaps between meals.
what happens when carbohydrate is stored and digested
- Blood glucose level rises
- Pancreases secretes insulin
- Insulin acts on hepatocytes and stimulates glycogen synthase
- Glucose molecules are added to chains of glycogen as long as both insulin and glucose remain high
- glycogenin is an enzyme that acts as a primer and starts the polymerisation for the first few glucose molecules then other enzymes take over
what makes up starch
amylose and amylopectin
describe amylose
- plant
- alpha glucose
- 1-4 bonds
- no side branches
- takes up less space
- less readily avliabale and useful
describer amylopectin
- plant
- alpha glucose
- 1-4 and 1-6
- side branches
- takes up more space
- more available and useful
what type of bonds do cellulose have
beta Glc 1-4 bonds
- made out of beta glucose
describe the sugar molecules that are present in blood groups A B AB O
- Group A – A oligosaccharide is present
- Group B – B oligosaccharide is present
- Group AB – A and B oligosaccharide is present
- Group O – only have precursor H oligosaccharide present
describe blood group antigens
- A,B,O blood groups have different oligosaccharides attached to glycoproteins and glycolipids on the surface
- ABO have the same precurosor H-oligosaccharide
- A and b have one extra monosaccharide unit added by specific glycosyltransferase
what must happen in blood transfusion
- Blood transfusion recipients must be compatible with the donor or agglutination occurs ( blood clotting)
what are lipo-polysaccharides
- Shared by large groups of pathogens
- Allow for detection by Toll-like receptors which are present on innate immune cells
- Conserved and essential structures attempt to modify result in death or loss of virulence of microorganism
- Detected by microbial pattern recognition receptors
- Distinct from self-antigens
what does activation of TLR4 by bacterial lPS lead to
Activation of TLR4 by bacterial LPS leads to inflammatory reaction through signalling cascade designed to clear the infection from the body
describe an example of a lip-polysaccharide activations
Activation of TLR4 by bacterial LPS leads to inflammatory reaction through signalling cascade designed to clear the infection from the body
name an oligosaccharide
Raffinose
what is glyceraldehyde
- simplest aldose
- contain a chiral carbon
- means that there are 4 different groups attached to the carbon
- therefore there are 2 isomers this that exist and they are called enantiomers
where is the oH on the alpha glucose
below the ring
where is the OH on the beta glucose
above the ring
what is glycosylation
this is a reaction in which a carbohydrate is attached to a functional group of another molecule
what is a glycosyl donor
a sugar molecule that is attached to a nucleotide that will react with a glycosyl acceptor
what is a glycosyl acceptor
a sugar with an unprotected hydroxyl group
Describe is heparin
- A polymer
- 3-30kDA in weight
- Glycosaminoglycan (GAG) FAMILY
- Related to heparan sulphate
- Highly negative charged and draws and holds water
- Heparan sulphate occurs as a proteoglycan where 2-3 heparan sulphate molecules are attached to a core protein
what is heparin used for
- Anticoagulant
Whats the importance of the ring structure
- above to add phosphates or sulphates
- monosaccharides have to be in open chain format
- cyclic forms can be added together for multimeric structures
- not possible to add functional groups to the cyclic ring
what are the ways that the OH groups are replaced
- Amine (NH2) = amino sugars
- Sulphate (SO4) = sulphated sugars
- Phosphate (PO4) = phosphorylated sugars
What are the ways that the OH group are removed
- Deoxy sugar
- - remove OH group to turn ribose to deoxyribose to make DNA
what will glycosylation enzymes differ to
- D or L form
- Alpha or beta anomer
- Location of OH groups
- More than 250 glycosyl transferases in humans
how do you convert a monosaccharide to a polysaccharide
- Glycosidic bonds are formed between sugars
- Donor sugar is first attached to a nucleotide to form a charged sugar, this is the substrate for the glycosyl transferase enzyme
- Sugar is then transferred to the growing chain of the polysaccharide and then the nucleotide can be reused, this is the sugar acceptor
describe the structure of glycogen
- This is a branched polysaccharide
- Monomer of glucose
- Backbone is Glc alpha 1-4
- Side chains Glc alpha 1-6
describe the function of glycogen
- Storage of carbohydrates
- Occurs in liver and muscle
- Converted to glucose as needed for energy demands by the action of glycogen phosphorylase
describe how heparin works
- Series of proteolytic enzymes in plasma that activates clotting (these are usually called factor X)
- Leads to activation of thrombin which cleaves fibrinogen forming fibrin which helps form a stable clot
- Heparin activates main inhibitor of thrombin and factor X(antithrombin III) by binding to the allosteric site therefore stopping the blood from forming a clot
describe the structure of heparin
- Heparin is approximately 40 monosaccharide units and activates antithrombin III that inhibits thrombin and factor X
