Lec 3: Carbohydrates Flashcards
what are the fucntions of carbohydrates?
- provide a rapid and readily available supply og energyfor celular reactions e.g muscle l & liver glycogen
- Form part of important molecules in the cell e.g Sugar-phosphate backbones in DNA double helix
- Form markers on the cell surface which aid cell recognition e.g Blood group markers
what is monosacchride and disaccharide? what is the general formula
monosaccharides: any of the class of sugars (e.g. glucose) that cannot be hydrolysed to give a simpler sugar.
general formula: (CH2O)n
disaccharide: dimer= 2 monoscaccharides
what is a oligosaccharide
what is a polysaccharide
Oligosaccharide: is a saccharide polymer containing a small number (typically three to ten) of monosaccharides (simple sugars)
Polysaccharide: polymer of monosaccharide units linked together
which is the Fischer Projection and Haworth Projection of this glucose molecule
*Note*: Naming monosaccharides
*Monosaccharides contain an aldehyde or ketone functional group and hydroxyl groups
3 C- triose
4 C- tetrose
5 C- pentose
6 C- hexose
7 C- heptsoe
8 C- octose
9 C- nonose
10- decose
what is the name of the molecule?
*Note*: isomers of aldohexose
what is the chemical formula?
C6H12O6
what are n-deoxymonosaccharides?
these are monosaccharides where the hydroxyl group [OH] is replaced with [H]
what is a stereoisomers?
each of two or more compounds differing only in the spatial arrangement of their atoms
They have:
- they have the same chemical formula
- the same orders and types of bonds
but are non -overlapping mirror images of each other and thus have
- Different spatial arrangements
- Different biological functions
D-isomers and L-isomers
what is a chiral carbon centre
carbon with 4 different groups coming of it
what is meant by the oxidation/reduction of a carbon
oxidation is a process by which a carbon atom gains bonds to more electronegative elements, most commonly oxygen. Reduction is a process by which a carbon atom gains bonds to less electronegative elements, most commonly hydrogen.
*Note*: How to assign sugars as L or D
- If the OH on the bottom chiral centre points to the right = D
- If the OH on the bottom chiral centre points to the left = L
what is cyclization
in what conditions to monosaccharides cyclize?
this is where the hydroyl [OH] group on the second to last carbon reacts with carbonyl group [C=O]
Resulting product for an aldose = a hemiacetal
Resulting product for a ketose = a hemiketal
monosaccharides cyclize spontaneously under normal conditions
what is an anomeric carbon?
- an anomeric carbon is a stereocenter
- It depends on which direction the hydroxyl [OH] group attaches to the carbon
- so the anomeric carbon is either alpha or beta
(alpha= H above, beta= H below)
can happen for both hemiacetal and hemiketals
what 2 possible products arise from the cyclization of D-glucose?
the OH group can attack planar C=O gorup from either side
so you get:
α and β anomers of D-glucopyranose
how can you tell the difference between alpha and beta glucose?
in alpha glucose the OH is below the plane
in beta glucose the OH is above the plane
how is glucose generated?
from the production of starch
*Note* Generation of ATP from glucose
what is a furan-based ring structure?
Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring
e.g furanose= 5 membered cyclization product despite being a hexose (=6C)
*Note* Fructose structure
what is the primary function of disaccharides?
nutritional source of monosaccharides
what is maltose made up of? where does the glycosidic link form?
where is it usually present
made up of: a-1,4 alpha glucose and a-1,4 beta glucose
alpha - 1,4 glycosidic link
present in;
- germinating seeds/grains
- metabolism of maltose by yeast yields ethanol and CO2
what is maltose digested into and by what?
It is digested by maltase
into alpha-1,4 glucose and beta- 1,4 glucose
what does the metabolism of maltose yield?
it yields ethanol and CO2
what is lactose formed by?
made up of: beta glucose and galatose molecules
beta-1,4 glycosidic link
what is sucrose made up of? where does the glyocosidic link occur?
made up of: alpha glucose and fructose molecules
alpha-1,2 glycosidic link
what enzyme digests sucrose?
sucrase
what is the difference between oligosaccharides and polysaccharides?
oligosaccharides: small polymers, 3-20 monosaccharides
polysaccharides: long chains/branched
what is amylose?
long linear chains
of alpha-1,4-linked-D-glucose
residues that has a coiled structure
what is amylopectin
linear chains of α-1,4-linked D-glucose residues
joined through α-1,6-linked branch points
Has a brush-like structure
what enzymes digest starch? and which bonds do they break?
where are these enzymes found?
amylase and maltase: alpha-1,4 glycosidic lin
Isomaltase: alpha-1,6 glycosidic link
broken down to dextrins = oligosaccharides, maltotriose, maltose, isomaltose and glucose
amylase - saliva and gut
maltase and isomaltase - gut only
what is glycogen made up of?
- complex branched polysaccharide
- linear chains
- of alpha 1,4-linked D-gluose residues
joined through alpha-1,6-linked branch points
what is the difference between amylose, amylopectin and glycogen?
they are all made up of alpha 1,4-linked D-glucose residues
However:
amylose has a coiled structure
amylopectin has a brush-like structure due to the alpha 1,4-linked D-glucose residues joined through alpha-1,6-linked branch points
glycogen is similar to amylopectin but the branch points occur more frequently (every 8-12 residues vs 24-30 in amylopectin)
AND amylose and amylopectin make up starch which is only found in plants, glycogen is found in animals
where is starch found vs glycogen?
starch: amyloplasts (non pigmented plant cell organelles) and chloroplasts (from roots, tubers, seeds and fruits)
glycogen: in animals, liver and muscle cells
what are glycoproteins?
Proteins that contain oligosaccharide chains attached covalently to the protein structure
what are secreted glycoproteins made up of?
mucins and glucocalyx
what are mucins
prinicipal components of mucus by mucous membrsnes (lining of body cavitities open to the exterior) and as component of saliva
what are glycolipids and what are they associated with?
Lipids that contain oligosaccharide chains attached covalently to their lipid structure
Often associated with phospholipids on outer surface of the cell membrane
Function:
Recognition signals
Attachment factors
Membrane stabilisers
what are glycocalyx
Glycoprotein covering surrounding cell membranes of epithelial and other cell types as well as bacteria
what are sphingolipids?
they are subtype of lipids
they include:
- cermide (signalling molecule)
- sphingomyeline (membranes)
what are glycosphingolipids
Glycosphingolipids are a subtype of glycolipids containing the amino alcohol sphingosine
this includes:
Cerebrosides: found in muscles and nerves
Gangliosides: found in plasma membranes
what is a carbohydrate?
Formula = Cm(H2O)n
what is the function of glycosylated membrane proteins?
immune recognition
