Carbohydrates Flashcards Preview

PHYS3522 Bionanophysics 1 > Carbohydrates > Flashcards

Flashcards in Carbohydrates Deck (15)
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1
Q

Carbohydrates

Functions

A
  • structural, e.g.
  • -glycosaminoglycans in cartilage
  • -chitin in exoskeletons
  • -cellulose in cell walls
  • coenzymes in biological processes e.g. immune system, fertilisation, prevention of blood clotting
  • energy storage and metabolism: glycogen/glucose
2
Q

Carbohydrates

Structure

A

-biomolecules made of carbon, hydrogen and oxygen
-usually with a hydrogen to oxygen atom ratio of 2:1:
Cm(H2O)n
-carbohydrates have a cyclic form and an acyclic form, there is constant turn over between these forms in aqueous solution

3
Q

How do monosaccarides form complex polysaccacrides?

A
  • variation in spatial orientation of OHs and side groups
  • chemical modification of side groups can add complexity
  • side groups can sit almost anywhere on the ring
  • type of linkage/branching
  • combination of monosaccarides
4
Q

Enantiomers

Definition

A
  • swapping the orientation of all OH or other side groups creates enantiomers (mirror image molecules) e.g. D-glucose and L-glucose
  • only D-glucose is created naturally in biological systems, but L-glucose is possible to chemically construct
5
Q

Epimers

Definition

A
  • swapping position of OH or side groups on only one carbon
  • if it is the first carbon group that swaps, the two molecules are called anomers
  • if it is any other carbon group that swaps, the two molecules are distinct monosaccharides
6
Q

Ring Puckering

A
  • the 6-membred ring is not flat, it can adopt different conformations
  • conformers can interconvert with each other but this may be a slow process
7
Q

Glycosidic Linkage

A
  • the linkage type effects interactions between monosaccharides and their rigidity
  • α(1-4) bonds are more flexible than β(1-4)
8
Q

Do polysaccharides have a secondary structure?

A

many polysaccharides have no defined secondary structure e.g. hyaluronan

  • but some have defined secondary structures and higher order structure e.g. amylose and cellulose
  • amylose has α(1-4) bonds and a helical secondary structure stabilised by hydrogen bonds
  • cellulose has β(1-4) bonds and a sheet secondary structure stabilised by hydrogen bonds
9
Q

Hydrogels

A
  • heterogeneous polysaccharides can for hydrogels

- e.g. pectin can form a hydrogel structure stabilised by ion bridges of carboxyl groups with Ca2+ ions

10
Q

Cumulus Matrix

A
  • an example of an ultrasoft hydrogels, what the oocyte moves through
11
Q

Stretching Polysaccharide Chains

Small Forces

A
  • at small forces, polysaccharides are entropically elastic chains
  • follow the worm-like chain model
  • pyranose ring and glycosidic linkage lead to rigidity in bending
12
Q

Stretching Polysaccharide Chains

Large Forces

A
  • at higher forces, conformational transitions of pyranose ring add enthalpic elasticity
  • mechanical forces could modulate protein binding to polysaccharides
13
Q

Carbohydrates in Cell Recognition

A
  • cells present specific patterns of carbohydrates on surface (attached to proteins and lipids)
  • these are important for cell-cell recognition and hijacked pathogens
  • these surface carbohydrates can form catch bonds with cognate proteins:
  • -holding firm at high shear flow to avoid washing away
  • -holding weak at low shear flow to enable surface migration
14
Q

Polysaccharides vs. Proteins

Force-Extension Curve

A
  • polysaccharides are stiffer than polypeptides
  • when considering the WLC model, Lp is greater for polysaccharides than for polypeptides so the force is smaller for a given extension
  • polysaccharides also feature enthalpic elasticity in addition to entropic elasticity
15
Q

α(1-4) bonds vs. β(1-4) bonds

Force-Extension Curve

A
  • polysaccharides with β(1-4) bonds (e.g. cellulose, hyaluronin) are stiffer and have a sharp narrow peak
  • polysaccharidse with α(1-4) bonds (e.g. amylose, heparin) are more flexible, have a wider peak with a hump, wavy lines