S1-L3: Carbohydrates Flashcards
Define and describe “carbohydrates”
- Biological molecules containing C, H and O atoms
- empirical formula generally Cn(H2O)n
- fundamental cellular components vital for cellular function
- also termed “saccharides”
What is a “saccharide”?
-organic compound containing sugar(s)
Outline the function(s) of carbohydrates (refer to figure 1/2/3)
1-provide rapid & readily available energy supply for cellular reactions- E.G: muscle + liver glycogen
2-form part of important molecules in cell
–> such as sugar-phosphate backbone in DNA double helix
3-form markers on cell surface which aids cell recognition
–> like blood group markers
Briefly outline the following classifications of carbohydrates:
1-Monosaccharide
2-Disaccharide
3-Oligosaccharide
4-Polysaccharide
1- General formula (CH2O)n
2- dimer–> 2 monosaccharides
3- polymer of 3-20 monosaccharides
4- polymer of monosaccharide units linked together
Describe monosaccharides
- C atoms range 3-10
- simplest carbohydrate ends in “-ose”
- single sugar molecules providing instant energy
- contain aldehyde/ ketone F. Group AND hydroxyl groups
What are the names for the first 3-10 monosaccharides?
-3 c’s- triose/ 4 c’s- tetrose/ 5 c’s- pentose/ 6 c’s- hexose/ 7 c’s- heptose/ 8 c’s- octose/ 9 c’s- nonose/ 10 c’s- decose
What is the structure of aldehydes/ ketones and hydroxyl groups?
- Aldehyde: R(C=O)H
- ketone: R(C=O)R
- hydroxyl group: ROH
Describe the nomenclature of “Fischer projections”
-Count C atoms from top- top from aldehyde/ ketone group
Refer to the diagrams of Glucose and Fructose- Figure 5/6
- 6C sugar- aldohexose has aldehyde group
- 6C sugar- ketohexose has ketone group
Outline how the molecules in figure 7 differ and chemical formula for them
- Hydroxyl group position differs between different sugars
- distinct aldohexose sugars with same chemical formula
- -> C6H12O6
What are N-deoxymonosaccharides (refer to figure 8)?
- Can exists as “deoxy” forms
- -> hydroxyl (OH) replaced with H
Define and describe “stereoisomerism”
- Have same chemical formula/ orders AND bond types
- ->are non-overlapping mirror images of each other
- ->so have different spatial arrangements AND different biological functions
In what two forms can you find stereoisomers?
-D or L isomers
How are stereoisomers formed?
- require chiral C centre
- -> C chiral if has 4 different groups attached to it
- -> at least one chiral C needed for stereoisomerism
Outline how sugars are assigned as L or D isomers
- Use Fischer projections with most oxidised C at top
- If OH on bottom chiral centre points to right–> D
- If OH on bottom chiral centre points to left–> L
Which of the two isomers, L or D glucose, are more common and why?
- D as predominant energy source in cellular respiration
- L not as common as biologically inert in bodies
- -> can’t provide us with energy even though structure same as D-glucose
How may monosaccharides exist as cyclic structures and how do they form? (refer to figure 9)
- monosaccharides exist as open-chain OR ring (cyclic) structure joined by covalent bond
- process: OH group on second to last C atom reacts with carbonyl group
- monosaccharides cyclize under normal conditions
- ->only small amount of straight chain present
What would the cyclized product for Aldose and Ketose be?
- Aldose; Hemiacetal
- Ketose: Hemiketal
Describe the cyclization of D-glucose (refer to figure 10)
- OH group able to attack C=O group either side- so 2 possible hemiacetal products
- -> a and b anomers of D-glucosepyranose
- cyclic form of D-glucose is D-glucosepyranose
Outline glucose and its function(s) (figure 11)
- primary energy source of life
- 7 energy-rich C-H bonds
- bonds broken down during cellular respiration
- released energy stored as ATP for cell use
Describe the structure and function of fructose (figure 12)
- 7 rich C-H bonds
- forms furan-based ring structure despite being hexose (6C)
- furanose–> 5 membered cyclization product
- important energy source alongside glucose AND galactose
- found in fruits/honey/berries and lemon
Define and briefly explain the formation of “disaccharides”
- 2 monosaccharides linked together like sucrose/ maltose/ fructose
- formed by dehydration reaction synthesis- condensation reaction where H2O lost
- molecules joined at -OH groups by glycosidic bond
- biological catalyst (enzymes) aid reaction
- multiple configuration possible
What is the primary function of disaccharides?
-nutritional source of monosaccharides
What is maltose and it’s function? (figure 13)
- 2 glucose molecules joined at C 1 and 4 via an a-1, 4 glycosidc bond (via condensation reaction)
- primary function is as nutritional source of monosaccharide
Where can starch be found?
- can generate from starch (polysaccharide) breakdown
- found in germinating seeds AND grain AND metabolism of maltose by yeast yields ethanol + CO2
How may starch be broken down?
-enzyme maltase digests maltose down in to individual monosaccharides
What is lactose? (figure 14)
- glucose + galactose molecules joined at C 1 + C 4
- B-1, 4 glycosidic bond (C1 OH group above glucose ring)
How is lactose produced?`
-produced by lactating mammals as energy source for young
Which enzyme is needed to digest lactose and what products are produced?
- digested to glucose + galactose
- enzyme lactase needed
Outline the structure of sucrose (figure 15)
-Glucose + fructose molecules joined at C 1 + C 2 via an a-1, 2 glycosidic link
Where is sucrose found?
- abundant in plant/ sap especially sugar cane AND sugar beet
- plentiful in western diet (sugar)
What is digested products of sucrose and the enzyme needed for this process?
- digested to glucose + fructose
- enzyme sucrase needed for this process
What is a hydrolysis reaction?
-cleavage of chemical bonds by water addition
Describe the breaking down of disaccharides
- gylcosidic links in disaccharide broken in to constituent monosaccharides during digestion
- ->reaction requires H2O + specific enzyme in gut
- monosaccharides more easily absorbed through gut lining
Outline reactions for digestion of:
1-maltose
2-lactose
3-sucrose
1- Maltose–> Glucose + glucose (maltase)
2- Lactose–> Glucose + Galactose (lactase)
3- Sucrose–> Glucose + Fructose (sucrase)
Which two polysaccharide components does starch consist of?
-Amylose and amylopectin
Outline the structure of:
1-amylose
2-amylopectin
refer to figure 16 and 17 respectively
1- long linear chains of a-1, 4-linked D-glucose residue
–> has coiled structure
2- linear chains of a-1, 4-linked D-glucose residue joined via a-1, 6 linked branch points
–> has brush-type of structure
What is the function of starch and where is it found?
- Main dietary source of carbohydrate
- main storage polymer in plants
- found in amyloplasts + chloroplasts of plant cells from roots/ tubers/ seeds & fruits
Describe “amyoplasts” and their function
- non-pigmented plant cell organelles
- responsible for synthesis AND storage of starch granules via polymerisation of glucose
Breakdown of Starch after eating:
What is the role of amylase/maltase?
-brekdown a-1, 4 glycosidic links
Outline the role of isomaltase
-breaks down a-1, 6 glycosidic links
What is the process of starch digestion to glucose?
- Amylase (in saliva + gut) digests/ maltase + isomaltase (gut only)
- -> to dextrins (oligosaccharides/ maltoriose/ maltose/ isomaltose)
- -> then ultimately glucose
What is glycogen? (refer to figure 18)
-complex branched polysaccharide of linear chains of a-l, 4-linked D-glucose residue joined through a-1, 6-linked branch point
Describe the structure of glycogen
- structure similar to amylopectin BUT branch points occur more frequently
- ->every 8-12 residues VS 24-30 in amylopectin
What is use glycogen?
- main storage polymer of animals–> found in liver AND muscle cells
- readily hydrolysed to glucose when energy needed
Outline the effect of fasting/ starving on an individual in terms on glucose/ starch
- blood generally contains 5-6mM glucose any given time
- ->starving/fasting individual attempts to maintain level outlined above at expense of glycogen stores in liver/ muscle cells
Define glycoproteins and their importance
- proteins which contain oligosaccharide chains attached covalently to protein structure
- glycosylated membrane proteins play important role in immune recognition
- secreted glycoproteins make up mucins AND glycocalyx
Briefly explain what Mucins are
- Principal components of mucus by mucous membranes (lining of body cavities open to exterior) AND as saliva components
- Glycocalyx Glycoprotein covering surrounding cell membranes
Describe the glycocalyx
-Glycocalyx glycoprotein covering surrounding cell membranes of epithelial/ bacteria and other cell types
What are glycolipids?
-Lipids which contain oligosaccharide chains covalently attached to their lipid structure
Where are glycolipids generally found and how does this relate to their function?
- often associated with phospholipids on outer surface of cell membrane
- ->in such cases usually function as recognition signals/ attachment factors/ membrane stabilisers
Define a “sphingolipid”
- subtype of lipid which include
- -> ceramide (signalling molecule)
- sphingomyelin (membranes)
What are “glycosphingolipids”?
- Cerebrosides–> found in muscles and nerves
- Gangliosides–> found in plasma membranes
Summary of lecture
- Carbohydrates contain C/ H/ O atoms
- -> formula Cn(H2O)n
- monosaccharides have chiral C which determines stereochemistry–> D VS L
- monosaccharides join together to form di-, olgi- and polysaccharides
- polysaccharides have key functional roles–> starch glycogen
- glycoproteins AND glycolipids have important structural roles–> glycocalyx/ glycosphingolipids
