Carbohydrates 1 Flashcards
What are the properties of carbohydrates?
- Highly oxidizable
- Function to store potential energy
- Have structural and protective functions
- Contribute to cell-cell communication
In what form are carbohydrates stored?
- Starch in plants
- Glycogen in animals
Where do carbohydrates exhibit structural and protective functions?
- In plant cell walls
- Extra cellular matrices of animal cells
How are carbohydrates highly oxidizable?
-Sugar and starch molecules have high energy H atom- associated electrons
What is another name for a monosaccharide?
Hexose
What are the 3 important hexoses?
- Glucose (Glc)
- Galactose (Gal)
- Fructose (Fru)
How are disaccharides formed/
- From monomers that are linked by glycosidic bonds
- Covalent bonds formed when hydroxyl group one monosaccharide reacts with anomeric carbon of another
What is an anomeric carbon/
- Different anomers are mirror images of each other
- It is carbon #1 on the glucose residue
- It stabilises the structure of glucose
- It is the only residue that can be oxidised
What are the 3 important disaccharides?
- Maltose
- Lactose
- Sucrose
What is maltose?
- Break down product of starch
- Found in beer and baby foods
Why is maltose a reducing sugar?
Anomeric C-1 is available for oxidation
What is lactose?
-Main sugar in milk
How is lactose formed?
From a glycosidic bond between galactose and glucose
Why is lactose a reducing sugar?
Anomeric carbon the glucose is available fro oxidation
What is sucrose?
- Common sugar
- Only made y plants
- Sweetener in most processed foods
Why is sucrose not a reducing sugar?
It does not have a free anomeric C-1 so ther is no oxidation site
What are polysaccharides?
Polymers of medium to high molecular weight
How are polysaccharides distinguished from each other?
- Identity of their recurring monosaccharide units
- Length of their chain
- Types of bond linking monosaccharide units
- Amount of branching they exhibit
Homopolysaccharide
Single monomeric specie
Heteropolysaccharide
Have 2 or more monomer species
What 2 kind of glucose does starch contain?
- Amylose
- Amylopectin
Describe amylose.
- Can have thousands of glucose residues
- D-glucose residues in (a1-4) linkage
Describe amylopectin.
- Similar structure as amylose but branched.
- Glycosidic (a1-4) bonds join glucose in the chains but branches are (a1-6) and occur every 24-30 residues
Describe the structure of starch.
Has many non-reducing ends and very few reducing ends
How are amylose and amylopectin arranged in starch?
They are believed to form alpha helices
Describe the structure of glycogen.
- Polymer of glucose (a1-4) linked to sub units with (a1-6) branches every 8-12 residues
- This makes glycogen more extensively branched than starch
Where is glycogen found in the body?
90% is in:
- Liver (acts to replenish blood glucose when fasting)
- Skeletal muscle (catabolism produces ATP for contraction)
Why is glucose stored in polymers?
- Compactness
- Amylopectin and glycogen have many non-reducing ends
- The polymers form hydrated gels and are not really in solution
What does the many non-reducing ends of amylopectin and glycogen allow?
-Allows them to be synthesised and degraded to and from monomers respectively thus speeds up formation or degradation
What is meant by ‘The polymers form hydrated gels and are not really in solution’?
-They are osmotically inactive
-If free glucose were in the cells then [Glc]inside»_space; [Glc]outside
Either Glc would move out of the cell down the concentration gradient or the cell would use huge amounts of energy keeping it in the cell
What are glycoproteins?
Proteins that have carbohydrate covalently attached
Glycoproteins: What may the carbohydrates attached to the protein do?
- Increases the protein solubility
- Influence protein folding and conformation
- Protect it from degradation
- Act as a communication between cells
What is the carbohydrate content of glycoproteins
1-80% by mass
What is another name for glycosaminoglycans?
Mucopolysaccharides
Where do GAGs function?
In mucus and also synovial fluid
What are GAGs/
Un-branched polymers made from repeating units of hexuronic acid and an amino-sugar which alternate through the chains
What are proteoglycans?
- Macromolecules found on the surface of cells or in between cells in the ECM
- Carbohydrate»_space; Proteins
How are proteoglycans formed?
From GAGs covalently attaching to proteins
What do proteoglycans for part of?
Many connective tissues
What are glycoproteins?
-Very similar to glycoproteins but protein» carbohydrate
Where are glycoproteins usually found?
-On the outer plasma membrane and ECM but also in the blood and within cells in the secretory system
What are exampled of glycoproteins?
Some cytoplasmic and nuclear proteins
What are mucopolysaccharidoses?
Group of genetic disorders caused by the absence or malfunction of enzymes that are required for the breakdown of GAGs
How does mucopolysaccharidoses occur?
- Over time GAGS build up in connective tissue, blood and other somatic cells
- The build up damages cellular architecture and function
What can mucopolysaccharidoses cause?
?-Severe dementia
- Heart problems
- Build up of GAGs between endothelial cells causing damage
- Stunted bones
- Inflammed joints
What are examples of mucopolysaccharidoses
- Hurler Syndrome
- Scheie Syndrome
- Hunter Syndrome
- Sanfilippo Syndrome
What are the characteristics of Hurler Syndrome?
- Severe developmental delays
- Clouding and degradation of the cornea
- Areterial wall thickening
- Dementia
What is the dementia in Hurler syndrome caused by?
- Build up of CSF
- Enlarged vermicular spaces
What are the sever developmental delays seen in Hurler syndrome?
- Stop developing at around 4yo
- Death at around 10yo
What experimental therapies currently exist for Hurler syndrome?
- Gene therapy
- Enzyme replacement therapies
