Structural carbohydrates Flashcards
What are the main functions of carbohydrates?
- main source of energy
- serve as strucutral components
Name 3 monsaccharides?
- Glucose
- fructose
- galactose
What are the 2 forms that enantiomers can be? For glucose enantiomers, what form occurs in nature?
D or L.
For glucose enantiomers, only the D enantiomer occurs in nature. L has to be synthesised in a lab
When glucose is in cyclic form, what is it called?
Glucosepyranose
Whats the position of the OH group in alpha and beta forms?
Alpha: The OH is down position
Beta: the OH is in the up position
Draw the most stable chain conformation of beta-D-galactopyranose
What are structural carbohydrates?
Polysaccharides (glycans) in which monosaccharide units are joined as in these disaccharides
What bond joins monosaccharides together?
glycosidic bonds
Name some strucutral carbohydrates in plants? (4 of them)
- cellulose
- Hemi-cellulose
- Pectin
- Agarose
Tell me about cellulose and about it’s linkages?
- most abundant polymer on the planet
- major structural components in plants
- organised into microfibrils
- important biofuel
- Linear polymer of D-glucose connected by beta1–> 4
What structural carbohydrate is this?
What type of sugar is Hemi-cellulose?
pentose sugar
Tell me about the structure of Hemi-cellulose ?
- Beta1–>4 polymer of D-xylopyranose
- sidegroups of various carbohydrates such as xylose, mannose, galactose, rhanmose and arabinose
- 500-3000 sugar units per polymer
- good as cross-linking (branched polymer)
Tell me about pectins structure and what its used for?
- family of a mixture of branched polysaccharides rich in alpha1-4
- linked D-galacturonic acid
- gelling agent in jams and marmalades
Tell me about the structure of Agarose? and where it can be found?
- D-galactose Beta1-4 with galactose
- ether bridge connecting C3 and C6 (some of these molecules also have a sulphate group)
- complex polysaccharide with lots of substitutions
- carbon 6 has an ether bond between the oxygen and CH2
Some plants such as red algae use agarose in their cell walls
What structural carbohydrate is this?
Name some structural carbohydrates found in animals?
- chitin
- Glycosaminoglycans
What is chitin the main component of?
the exoskeleton of nearly a million species of arthropod e.g. insects and crabs
What is chitin a polymer of and what bonds/linkages does it contains?
- Polymer of N-acetyl glucosamine (glucose with an acetylated amino group at C2)
- contains Beta 1–>4 linkages arranged in extended fibres in a similar way to cellulose
What strucutral carbohydrate is this?
Chitin
Why is the carbohydrate Glycosaminoglycans important?
its important as a matrix to hold together protein components of skin and connective tissue
What is proteoglycan? what is it made of/ its structure?
- it is a structure in cartilage
- made of protein and sugar units
Explanation of the structure in the image:
- dark blue are core proteins
- proteins stem off of the core proteins and then there are carbohydrate polymers coming off of those proteins on the stems
What are bacterial cell walls made of?
polysaccharides
What is the name of the polysaccharide-peptide complex that bacterial cells walls are made from?
peptidoglycan
What are the two classes that bacteria fall into?
Gram positive and gram negative
Tell me the properties of gram +ve bacteria
- cytoplasmic lipid membrane
- thick peptidoglycan layer
- retains the gram stain of dye-iodine complex which shows a blueish colour (helps to identify if gram +ve or -ve)
Tell me the properties of gram negative bacteria?
- cytoplasmic membrane
- thin peptidoglycan layer
- outer membrane containing lipopolysaccharides
- periplasmic space between cytoplasmic membrane and outer membrane
What is peptidoglycan composed of?
alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) linked tetrapeptides of (L-Ala)-(D-Glu)-(L-Lys)-(D-Ala)
Does this show a gram +ve or gram -ve bacteria?
gram +ve
Does this show a gram +ve or gram -ve bacteria?
gram -ve
What’s meant by the word glycan?
its another term for a polysaccharide
Whats glycosylation?
The attachment of oligosacchrides (sugars) to proteins
Proteins that are glycosylated mostly pass thorugh where?
the secretory pathway (ER and golgi)
Do cytoplasmic proteins tend to be glycosylated?
no
Whats are the two types of glycosylation? which one is most common? where does each occur?
1. N-linked
Occurs in the ER
modified in golgi
most common type
2. O-linked
occurs in golgi
What enzyme in golycosylation attaches the N-linked oligosaccharide in the ER?
oligosaccharyl transferase
What species lipid helps the precursor oligosaccharide in the ER membrane duirng glycosylation?
dolichol
in N-linked oligosaccharides, what is it linked to?
The -NH2 groups of an asparagine residue
What are the three major types of N-glycans?
- High-mannose oligosaccharide
- Hybrid oligosaccharide
- Complex oligosaccharide
What are O-linked oligosaccharides linked to?
either serine, threonine or hydroxyproline
what type of protein functions does glycosylation lead to?
- helps proteins fold in the ER
- help direct proteins to their final destination
- helps proteins function
What helps proteins fold in the ER?
- ER chaperones calnexin and calreticulin bind to oligosaccharide of partially folded proteins to stop aggragate and reain them in the ER
What helps to direct proteins to their final destination?
carbohydrate proteins called lectins help guide ER to golgi transport and protein sorting in the trans-golgi network
What types of protein functions does glycosylation help with?
- improve stability
- inprove solubility
- cell signalling
