Carbohydrate structure and function Flashcards
Characteristics of carbohydrates?
Highly oxidizable
Function to store potential energy
Have structural and protective functions
Contribute to cell-cell communication
Describe how carbs are highly oxidizable?
Sugar and starch molecules have “high energy” H atom-associated electrons
Thus they are a major energy source
Carbohydrate catabolism is the major metabolic process for most organisms
Describe how carbs function to store potential energy?
Starch in plants
Glycogen in animals
Describe how carbs have structural and protective functions ?
In plant cell walls
Extra cellular matrices of animal cells
Describe how carbs contribute to cell-cell communication?
ABO blood groups
What are the 3 important monosaccharides in human biochemistry? (hexoses -6C sugar)
glucose
galactose
fructose
How are disaccharides formed?
Formed from monomers that are linked by glycosidic bonds
Covalent bond formed when hydroxyl group of one monosaccharide reacts with anomeric carbon of another monosaccharide
What’s an anomeric carbon?
Different anomers are mirror images of each other (left- and right-handed forms)
It is carbon #1 on the glucose residue
It stabilises the structure of glucose
Is the only residue that can be oxidised
What are the three important dissacharides in biochem?
Maltose
lactose
sucrose
Characteristics of maltose?
Don’t have much directly from the diet
It is a break-down product of starch
It is in beer (from the starch of the barley)
Found in many baby foods as a “natural” sweetener
Anomeric C-1 is available for oxidation, so maltose can be oxidised (termed a reducing sugar)
Characteristics of Lactose?
Main sugar in milk
It is formed from a glycosidic bond between galactose and glucose
Anomeric carbon on the glucose is available for oxidation so it is termed a reducing sugar
Characteristics of Sucrose?
Common (table) sugar
Only made by plants
Approx. 25% of dietary carbohydrate
Sweetener in most processed food
Does not have a free anomeric C-1 so there is no oxidation site, hence sucrose is termed a non-reducing sugar
Characteristics of amylose?
D-glucose residues in (α1→4) linkage (straight chained)
Can have thousands of glucose residues
What are homopolysaccharides and heteropolysaccharides?
Homopolysaccharides
Single monomeric species
Heteropolysaccharides
Have two or more monomer species
Characteristics of glycogen?
Animal cells use a similar strategy as plants to store glucose
Polymer of glucose (α1→4) linked sub-units with (α1→6) branches every 8 to 12 residues
This makes glycogen more extensively branched than starch
Characteristics of Starch?
Contains two types of glucose polymer:
Amylose (20-25% of starch)
and
Amylopectin (75-80% of starch)
Characteristics of amylopectin?
Similar structure as amylose but branched
Glycosidic (α1→4) bonds join glucose in the chains but branches are (α1→6) and occur every 24 – 30 residues
Where is glycogen stored?
90% is in:
Liver (acts to replenish blood glucose when fasting
Skeletal muscle (catabolism produces ATP for contraction
Glycogen structure?
highly branched
enzyme in middle
Why store glucose in polymers?
Compactness
Amylopectin and glycogen have many non-reducing ends
This allows them to be readily synthesised and degraded to and from monomers respectively
Thus speeds up the formation or degradation
The polymers form hydrated gels and are not really “in solution”
This means they are osmotically inactive
If free glucose were in the cells then [Glc]inside > > [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 carbohydrates covalently attached
Most extracellular eukaryotic proteins have associated carbohydrate molecules
Carbohydrate content varies between 1-80% by mass
What effect might carbohydrates attached to proteins have ?
Increases the proteins solubility
Influence protein folding and conformation
Protect it from degradation
Act as communication between cells
What are Glycosaminoglycans (GAGs) ?
A protein
In the ‘olden days’ they were called mucopolysaccharides
Hints at their function – in mucus and also synovial fluid around the joints
Un-branched polymers made from repeating units of hexuronic acid and an amino-sugar, which alternate through the chains
What are proteoglycans?
A protein
Carbohydrate > > protein
Formed from GAGs covalently attaching to proteins
They are macromolecules found on the surface of cells or in between cells in the extracellular matrix
Therefore form part of many connective tissues in the body
What are glycoproteins?
Protein > > carbohydrate
Very similar to proteoglycans
Usually found on the outer plasma membrane and extra cellular matrix, but also in the blood and within cells in the secretory system (Golgi complex, secretory granules)
Some cytoplasmic and nuclear proteins are also glycoproteins
What are Mucopolysaccharidoses?
Group of genetic disorders caused by the absence or malfunction of enzymes that are required for the breakdown of glycosaminoglycans
How do the genetic disorders caused by Mucopolysaccharidoses come about?
Over time the glycosoaminoglycans build up in connective tissue, blood and other cells of the body
This build up damages cellular architecture and function
What are the negative physical effects and syndromes of Mucopolysaccharidoses?
Can cause severe dementia, problems with the heart and any other endothelial structure as the glycosaminoglycans build up between the endothelial cells
Also, bones tend to be stunted and joints will be inflammed and become severely damaged
Hurler, Scheie, Hunter, Sanfilippo syndromes are all examples of mucopolysaccharidoses
Describe characteristics of Hurler syndrome?
Severe developmental defects:
Stop developing at around 4 years
Death at around 10 years old
Clouding and degradation of the cornea
Arterial wall thickening
Dementia caused by, amongst other things:
Build up of CSF (Cerebral sinal fluid)
Enlarged ventricular spaces
