L10-11: Carbohydrates Flashcards
What is the most abundant main class of biomols?
Carbohydrates
What are the major roles carbohydrates play in biological processes?
-Storage and transport of energy
-cell-cell communication/adhesion
-Host-pathogen and host-symbiont interactions
-Structural components of animals, plants & fungi
-components of DNA and RNA
What is the main composition of carbs?
Contain C,H and O
2 or more hydroxyl groups
An aldehyde or ketone group
What are the 2 simplest carbs?
Glyceraldehyde and Dihydroxyacetone
What does it mean when sugars are chirally active?
They have 2 stereoisomers
What are the names when carbs contain aldehyde group or ketone group?
Aldehyde- Aldoses
Ketones- Ketoses
How do sugars with >4 carbons form rings?
Because the alcohol is part of the same molecule as the aldehyde/ketone
What are the names when aldehyde or ketone and alcohol form then when they form rings?
Aldehyde- Hemiacetal, ring- pyran
Ketone- Hemiketal, ring- furan
Why do the rings have a chair configuration?
Due to the tetrahedral geometry of carbon atoms
What are the 2 orientations on the carb rings?
Axial (up or down, opposite directions)
Equatorial (same plane as ring)
How do the alpha and beta forms arise from sugars?
The formation generates and additional asymmetric carbon at position 1 (NOT NEW) (for aldoses)
Where does the asymmetric carbon arise in ketoses?
C2
How many carbons do most sugars have?
5-6
What do L and D stand for?
Laevorotatory and Dextrorotatory
What happens when only asymmetric carbon 2,3 or 4 are in a different configuration to glucose?
Molecule is a different structure, they are epimers
What can sugars join to become?
Disaccharides
Oligosaccharides
Polysaccharides
(linked by glycosidic bonds)
What are the different configurations of the glycosidic bond?
Alpha or beta (from either 2 alpha or a alpha and a beta)
What are 3 disaccharides and what are they used as?
Maltose, lactose and sucrose used as an important energy source when hydrolysed
What are the main polysaccharide storage molecules?
Starch and glycogen
What are starch and glycogen polysaccharides of?
D-glucose
What type of glycosidic bonds to starch and glycogen have?
Alpha 1,4-glycosidic bonds
What makes a reducing sugar a reducing agent?
It has a free aldehyde or ketone group
What are most of the reducing sugars?
They are all monosaccharides and most disaccharides/oligo/poly
Why are alpha glycans good storage molecules?
The alpha1,4-linkage causes the polysaccharide to twist into a helical structure which makes it more compact
What does branching in starch and glycogen do?
Alpha1,6 branching makes it compact and has many non-reducing terminals so easy to digest
What are the structural properties of cellulose?
Plant polysaccharide
Long beta1,4-linked glucose chains (form highly crystalline microfibrils)
Very strong
Most abundant organic molecule on planet
How is biofuel formed?
Cellulose hydrolysed to glucose with enzymes then convert glucose to ethanol by microbial fermentation
What is the main component of bacterial cell walls?
Peptidoglycan
What are properties of the bacterial cell wall?
Without cell wall bacteria are osmotically sensitive and burst
Good target for antibiotics as not present in animal cells
Lysozyme targets bacterial cell wall
What are glycoconjugates?
When carbs are often covalently linked to molecules such as proteins or lipids
How is N-glycosylation useful?
As it plays a role in protein folding, stability and cell recognition
What are O-linked glycans?
Oxygen linked
What are characteristics of O-glycans?
Joined to hydroxyl of serine or threonine
Common is GlcNAc (N acetyl glucosamine)
Cytoplasmic
What are key components of mucus?
Mucins (O-glycoproteins)
What are proteins that are attached to mostly O-linked polysaccharides called?
Glycosaminoglycans
What are the functions of glycosaminoglycans?
Joint lubricants
Structural components of Extracellular Matrix
Mediate adhesion of cells the ECM
Bind factors that stimulate cell proliferation
What are characteristics or proteoglycans?
GAG component determines function
Made of disaccharide repeats of amino sugar & uronic acid
Heavily sulfated
Bind lots of water (hydrated gel withstand high compressive loads)
How are complex carbs synthesised?
Glycosyltransferases
How are blood groups different?
A- GTA puts GlcNAc on
B- GTB puts Gal on
O- GTs non-functional
AB- GTA and GTB
