Structure and roles of carbohydrates Flashcards
What are the functions of carbohydrates
Fuel, structure, immune recognition and function, cell communication, blood groups, extracellular matrix
What are the 3 elements of carbohydrates
Carbon, oxygen and hydrogen
What is the generic formula for carbohydrates
CH2On
What is an oligosaccharide
3-10 sugar molecules
What is a polysaccharide
11+ sugar monomers
What is the simplest form of monosaccharides (rare)
C=3 e.g. glyceraldehyde
What are the two different types of carbonyl group
Aldehyde and ketone
What is the carbonyl carbon
Carbon 1 (in glucose)
In which projection is the carbonyl carbon easy to see
Fischer projection
Why is glucose a reducing sugar
In acyclic form glucose has a free aldehyde so can react with oxidising agents and in term reduce them
What are isomers
Compounds that have the same chemical formula but different structures
Give an example of isomers
Glucose, fructose and galactose are all C6H12O6
What are epimers
Isomers that differ in configuration around one carbon atom other the the carbonyl carbon (C1) e.g. glucose and galactose
What are enantiomers
Special type of structural isomer that are mirror images and non-superimposable
What are the two forms of enantiomers
D- and L- forms
Which enantiomer form are most sugars
D- form
Why can L-glucose not me metabolised
Our enzymes only interact with D-glucose (dextrose)
What are Anomers
The D (and L) form can exist as isomers when cyclized in dynamic equilibrium via non-cyclic form e.g. alpha D-glucose and beta D-glucose
How are the glycosidic bonds between carbon atoms named
In relation to the number of carbon atoms in both sugars that are joined
If a bond formed between c1 of one monomer and c4 of another in an alpha linkage what would this bond be called
Alpha 1,4- glycosidic linkage
How does branching occur
A saccharine molecule may be linked to other monomers at various sites via alpha 1-6 branch points
What is cellulose
A structural carbohydrate with poor nutritional value
What is chitin
A structural carbohydrate that forms cell wall in fungi, yeast and shells
What is Amylum
Starch
What is the structure of starch
Many D-glucose units linked in a long chain consisting of two molecules
What is the structure of starch
Many D-glucose units linked in a long chain consisting of two molecules
What are the two molecules in starch
Amylose and amylopectin
What is amylose
Linear chain of glucose with few branch points
What is amylopectin
1 branch every 25-30 units
Describe the structure of glycogen
Similar structure to amylopectin with a higher level of branching (1 every 10-14 units)
How is glycogen synthesised
On the core protein glycogenin
What are the key features of glycogen and starch
Storage inside cells (esp glucose), insoluble (no osmotic potential), quick glucose release for readily available energy
Describe the structure of cellulose
Linear molecules made up of beta D-glucose with beta 1-4 linkages and no branching (results in stacks/layers)
What is the collective name for the enzymes that digest poly and oligosaccharides
Glycoside hydrolyses/ glycosidases
What are endoglycosidases
Enzymes that randomly cut between sugar residues of start chain
Give an example endoglycosidase
Alpha amylase (salivary)
What bonds does alpha amylase hydrolyse
Alpha 1-4 bonds only
Why can we not digest cellulose
We do not have beta amylase
What is the function of pancreatic alpha amylase
Digest oligo and poly to tri/disaccharides
What is the function of disaccharidases in the small intestine
Hydrolysis of disaccharides into sugar monomers so they can be absorbed (membrane bound enzymes)
Give examples of disaccharidases
Maltose, sucrase, lactase and isomaltase
What is the function of isomaltase
Cleaves alpha 1-6 bonds that amylase could not
Where does most absorption of monosaccharides occur
Duodenum and upper jejunum
What is the function of the SGLT1 transporter protein
Cotransport of Na+ and and glucose and galactose into epithelial cell (energy dependent)
What is the function of GLUT5
transport of fructose into epithelial cell (energy independent)
What pumps all three monosaccharides into the hepatic portal vein
GLUT2
What is the function of cellulose once in the human body
Dietary fibre, provides bulk and contributes to gut health by feeding gut flora
What are examples of glycoproteins
Antibodies and mucins
What are examples of lipids modified by carbohydrates (glycolipids)
Sphingomyelin and galactocerebroside
How are glycoproteins produced
Oligosaccharides are attached to proteins during post translational modification (glycosylation)
What are the two ways sugars can be linked to proteins during glycosylation
Carbohydrate side chain joined to asparagine (N-linked) or joined to threonine or serine (O-linked)
