Week 8 - chronic diseases Flashcards
What are carbohydrates? (LO1)
- The most abundant organic molecule.
- Energy souce (glucose –> ATP).
- Energy storage (glycogen).
- Structural component.
- Immune function.
- Intracellular communication.
Describe the general classification and structure of carbohydrates. (LO1)
- Carbo = carbon.
- Hydrate = water.
- General formula is (CH₂O)n
- Monosaccharide = 1 sugar unit.
- Disaccharide = 2 sugar units.
- Oligosaccharide = 3-10 sugar units.
- Polysaccharides = 11- >100 sugar units.
Describe the classification of carbohydrates by the number of carbon atoms. (LO1)
- Triose = 3 carbons, e.g. glyceraldehyde.
- Tetrose = 4 carbons, e.g. erythrose.
- Pentose = 5 carbons, e.g. ribose.
- Hexose = 6 carbons, e.g. glucose.
- Heptose = 7 carbons, e.g. sedoheptulose.
- Nonose = 9 carbons, e.g. neuraminic acid.
Describe the classification of carbohydrates by functional group. (LO1)
The most common functional groups are aldehydes (O=C-H) or ketones (C=O).
- Monosaccharides + aldehyde function = aldoses (suffix -ose).
- Monosaccharides + ketone function = ketoses (suffix -ulose).
- Hexose + aldehyde function = ALDOHEXOSE.
- Hexose + ketone function = KETOHEXOSE.
N.B. ketohexose is also known as fructose (it should be called fructulose but some idiot decided to make things confusing).
Describe the classification of carbohydrates by structure. (LO1)
- Compounds that have the same chemical formula, but different structures are called isomers.
- Carbohydrate isomers which only differ around one specific carbon atom are called epimers.
What are enantiomers? (LO1)
- Pairs of structures that are mirror images of each other.
- Even if you rotate one mirror image, the molecules still do not superimpose on each other.
What is meant by L and D designations? (LO1)
- These designations are based on the configuration of a single asymmetric carbon atom in glyceraldehyde.
- Sugars with >1 chiral centre.
- D and L refer to the farthest asymmetric carbon atom from the carbonyl group.
- Most naturally occurring sugars are D isomers.
Describe the cyclisation of monosaccharides. (LO1)
> 99% of monosaccharides with >5 carbon atoms form a ring structure.
- To form this, the aldehyde/ketone group reacts with the hydroxyl group of the same monosaccharide.
- 5 carbon atoms + 1 oxygen atom = PYRANOSE RING.
- 4 carbon atoms + 1 oxygen atom = FURANOSE RING.
How does cyclisation of monosaccharides change them? (LO1)
- Creates a new stereogenic centre (also known as chiral centre).
- The chiral centre becomes asymmetric.
- In D-glucose, the newly generated hydroxyl group can be above or below the midplane of the cyclised molecule. Thus, the open chain monosaccharide yields two cyclic isomers: α-anomer and β-anomer.
- In glucose, the full names of these molecules are α-D-glycopyranose and β-D-glucopyranose.
- Both anomers of the sugar are in equilibrium in solution and can spontaneously interconvert.
- This process is called mutarotation and can take hours.
- In glucose, the ratio is 64:36 of β:α.
What is the chiral centre? (LO1)
The carbon atom bearing the carbonyl.
Give three examples of monosaccharides and their sources. (LO1)
- Glucose.
- Primary energy source: preferred energy source for the brain, required energy source for cells with few/no mitochondria, essential in exercising muscles.
- Source: diet, degradation of glycogen, gluconeogenesis. - Fructose.
- Sweeter than glucose.
- Source: fruits, vegetables, honey. - Galactose.
- Less sweet than glucose.
- Source: dairy products.
Give three examples of disaccharides. How are they made? (LO1)
- Sucrose = glucose + fructose.
- Maltose = glucose + glucose.
- Lactose = glucose + galactose.
Describe the disaccharide bond between glucose and fructose in sucrose. (LO1)
- Glycosidic bonds.
- These bonds are named according to the numbers of the connected carbon atoms and the position of the anomeric hydroxyl groups involved in the bond.
- E.g. if the hydroxyl group is in α-configuration, then it’s an α-bond.
- In sucrose: α-(1–>2)-β-glycosidic bond.
- This means that the hydroxyl group of carbon atom 1 in α-configuration has reacted with the hydroxyl group of carbon atom 2 in β-configuration.
- This reaction leads to the elimination of one water molecule.
- Scientific name of sucrose: α-D-glucopyranosyl-(1–>2)-β-D-fructofuranoside.
Describe the bond between the two glucose molecules in maltose. (LO1)
- α-(1–>4)-glycosidic bond.
- The hydroxyl group on carbon atom 1 on one glucose molecule in α-configuration reacts with the hydroxyl group on carbon atom 4 of another glucose molecule to form a bond between them by the elemination of one water molecule.
- Scientific name of maltose: α-D-glucopyranosyl-(1–>4)-β-D-fructofuranoside.
Describe the bond between glucose and galactose in lactose. (LO1)
- β-(1–>4)-glycosidic bond.
- The hydroxyl group on carbon atom 1 of galactose in β-configuration reacts with the hydroxyl group on carbon atom 4 of glucose to form the bond between them by the elimination of one water molecule.
Give three examples of polysaccharides and their functions. (LO1)
- Cellulose - structural.
- Starch - storage (plants).
- Glycogen - storage (animals).
What is cellulose? (LO1)
- Polysaccharide consisting of a linear chain of 100,000s of β-glucose units.
- Glucose molecules linked together by β-(1–>4)-glycosidic bonds.
- Cellulose is an important component of dietary fibre which acts as a hydrophilic bulking agent for the faeces.
- Major component of plant cell walls.
What is starch? (LO1)
- Polysaccharide consisting of 100,00s of glucose units.
- Glucose molecules linked together by α-(1–>4)-glycosidic bonds.
- Found in all plant seeds and tubers.
- Amylose and amylopectin are the 2 forms of starch.
What is amylose? (LO1)
- Unbranched polymer.
- A form of starch.
- Linear polysaccharide just like cellulose.
- Glucose molecules linked together by only α-(1–>4)-glycosidic bonds.
What is amylopectin? (LO1)
- Branched polymer (every 20-30 carbon residues).
- A form of starch.
- Most glucose molecules linked by α-(1–>4)-glycosidic bonds.
- Every 20-30 residues, the glucose molecules are also linked by α-(1–>6)-glycosidic bonds which form the branches.
What is glycogen? (LO1)
- Branched polysaccharide consisting of 100,000s of glucose molecules.
- More extensively branched and compact than amylopectin.
- Similar structure to amylopectin with mainly α-(1–>4)-glycosidic bonds.
- Every 8-10 residues, the glucose molecules are also linked by α-(1–>6)-glycosidic bonds.
Describe the the three areas where carbohydrates are digested and the enzymes involved. (LO1)
- Salivary glands - alpha amylase.
- Small intestine - pancreatic α-amylase.
- Upper jejunum - dextrinase, glucoamylase (gamma amylase), isomaltase, maltase, sucrase, lactase.
How do the salivary glands aid the digestion of carbohydrates? (LO1)
- Occurs in the mouth during chewing.
- Saliva contains α-amylase which hydrolyses α-(1–>4) bonds.
- E.g. starch –> maltose + dextrin.
- Dextrin is a mixture of glucose polymers linked by α-(1–>4)-glycosidic bonds and α-(1–>6)-glycosidic bonds.
How does the small intestine aid the digestion of carbohydrates? (LO1)
- Pancreatic alpha amylase creates more maltose and dextrin.