21-09-21 - Introduction to Carbohydrates Flashcards
How are carbohydrates made?
What are they then used for?
- Carbohydrates are produced by photosynthesis in plants
- Glucose is synthesized in plants from CO2, H20 and energy from the sun
- Carbohydrates are oxidized in living cells to produce CO2, H20 and energy through respiration (1 glucose molecule produces 32 ATP)
What are the 3 types of carbohydrates?
What reactions are they made/split up in?
- Monosaccharide – The simplest carbohydrates
- Disaccharides - consist of 2 monosaccharides connected by glycosidic bonds
- Polysaccharides – contain many monosaccharides connected by glycosidic bonds
- These longer units are made through condensation reactions and broken up through hydrolysis reactions
How long are monosaccharides?
What chemical groups do they include?
What are the 2 types of monosaccharides?
What are the names given to molecules with different number of carbons?
- Monosaccharides typically contain 3-6 carbons
- They contain a carbonyl group (carbon to oxygen double bond) and several hydroxide groups
- The 2 types of monosaccharide are Aldoses and Ketoses.
- Aldoses contain an aldehyde group (carbonyl group at the end of chain)
- Ketoses contain a ketone group (carbonyl group in middle of chain)
- 3 carbons – triose
- 4 carbons – tetrose
- 5 carbons – pentose
- 6 carbons – hexose
What are chiral molecules?
What do molecules need to be chiral?
What are molecules that are mirror images of each other called?
How are chiral molecules distinguished from each other?
- Chiral molecules are non-superimposable mirror images of each other.
- To be chiral molecules, they must contain a chiral carbon, which is a carbon attached to 4 different groups
- Molecules that are mirror images of each other are called stereoisomers or enantiomers
- These enantiomers are distinguished by an L or D Infront of their name, L stands for laevorotatory and D is for dextrorotatory
- A Fischer projection can also be used to determine L or D isomers
- This is based on how each enantiomer rotates polarised light.
What is a Fischer projection used for?
In what way does it display molecules?
How can it be used to distinguish between L and D enantiomer carbohydrates?
- A Fischer projection is used to represent carbohydrates
- It places the most oxidised group at the top
- In a Fischer projection, the OH on the carbon furthest from the carbonyl group decides whether the molecule is the L or D enantiomer.
- If the OH is on the left, the isomer is L, if the OH is on the right, the isomer is D.
What stereoisomers of carbohydrates and amino acids are found in nature?
- Only D stereoisomers of carbohydrates are found in nature
- Only L stereoisomers of amino acids are found in nature
Where is D-glucose found?
What is its chemical formula?
What is it used for?
- Found in fruits and honey
- D-glucose is an aldohexose with formula C6 H12 06
- D-glucose is the monosaccharide found in polymers of starch, cellulose and glycogen
- Known as blood sugar in the body and is the most abundant sugar in the body.
What is the similarity/difference between D-glucose and D-galactose?
What does the body do with galactose?
- D-glucose and D-galactose are both monosaccharides with the same chemical formula.
- Both molecules also have 4 chiral centres
- They are epimers of each other, which are carbohydrates with the same chemical formula and more than 1 chiral centre, but each molecule differs in configuration at one of the chiral centres.
- In this case, the OH on carbon 4 of each molecule are on opposite sides
- Due to this difference in structure, galactose cant be broken down in the body, and must be converted to glucose first
What causes galactosemia?
What can galactosemia cause?
How is it detected and screened for?
How is it managed
- Galactosemia is a genetic disease involving the lack of enzymes required to convert galactose into glucose (GALT)
- This can result in the accumulation of galactose intermediates
- This has toxic effects on the liver, brain, kidneys and eyes and can be recognised from birth due to jaundice in the baby
- Screened from a heal prick blood test
- Managed by diet.
What are cyclic structures in monosaccharides?
How are they formed?
What are the different kinds of cyclic glucose?
What can they be referred to as?
- Cyclic forms are the prevalent form of monosaccharides with 5 or 6 carbon atoms
- Form when the hydroxyl group on C5 reacts with the aldehyde or ketone group.
- There are 2 versions of cyclic glucose. They are special forms of epimers called anomers which arise due to the formation of the cyclic structure
- α-D-glucose possesses an OH group that goes below the cyclic structure on Carbon 1
- β-D-glucose possesses an OH group that goes above the cyclic structure on Carbon 1
How do the 2 different types of cyclic glucose react in solution?
How much of each are present in solution?
- When placed in solution, the cyclic structures open and close and are dynamic
- α-D-glucose converts to β-D-glucose and vice versa
- At any time, only a small amount of open chain forms.
What are the different methods used to test sugars?
- Fehling’s reagent
- Spectrophotometer
- Glucose oxidase test
- Glycation of haemoglobin in red blood cells
How does testing for sugars using Fehling’s reagent work?
- All monosaccharides, whether an aldose or a ketose, are reducing sugars.
- Reducing sugars will reduce inorganic ions such as Cu2+ into Cu+
- Cu2+ is located in Fehling’s reagent, so glucose levels can be determined through Fehling’s reaction, where an open structure D-glucose becomes oxidised to D-gluconate while reducing Cu2+ to Cu+
- Cu2+ is blue and Cu+ is orange, so a colour change can display whether sugars are present and reducing Cu2+ into Cu+ or not.
How are spectrometers used to test for sugars?
- Spectrometers can be used to determine glucose concentration
- Spectrometers measure how much colour a liquid absorbs
- Beer-lambers law states the absorbance of a solution is directly proportional to the solutions concentration
- A control and known concentrations of glucose can be plotted on a graph and the curve formed can be used to find glucose concentration in unknown samples.
How are glucose oxidase tests used to test for sugars?
- More specific for glucose (used to measure blood glucose levels)
- Colour change is dependent on the reducing ability of the sugar
- Can tell us if glucose is present in someone urine at the current time, but not in the long term.
What is glycation?
How does glycation of haemoglobin in red blood cells test for sugars?
Why is this method good for long term?
- Glycation is the non-enzymatic addition of sugar.
- Glucose diffuses into red blood cells in a non-insulin dependent manner.
- Uncontrolled hyperglycaemia (excess of glucose in blood stream associated with diabetes) results in covalent linkage forming between glucose and the NH2 amino terminal of the haemoglobin β chain
- This modification is known as HBA1C.
- The greater the modification, the greater the concentration of glucose.
- The lifespan of a red blood cell is 120 days, which allows blood glucose concentration to be measured over 3 months, as opposed to that moment like other tests.
What is lactose?
Where is it found?
- Lactose is a disaccharide of β-D-galactose and α-D-glucose or β-D-glucose linked together by a β-1,4- glycosidic bond
- Lactose is found in milk and milk products.
What is lactose intolerance?
What does it cause?
What are the symptoms?
How can it be acquired?
- Lactose intolerance is the lack of lactase enzyme in the small intestine to break down galactose into glucose and galactose
- This results in lactose passing into the colon and being fermented by bacteria
- Causes stomach cramps, bloating, flatulence.
- Can be acquired genetically from birth
- Can be acquired through injury to small intestine
- With age, the genes for lactase expression can be turned off, causing lactose intolerance.
What is glycogen?
What is its structure?
What is it used for?
Where is it found?
- Glycogen is the most common homopolymer in animal cells
- It is a highly branched polysaccharide made of glucose units linked by α-1,4 (units) and α-1,6 (branches) glycosidic bonds
- Branches occur every 8-12 units of glucose
- Glycogen is the storage form of glucose
- Predominantly found in the liver and muscle.
What is Starch?
What are the 2 different types?
What are their structures?
Where is it found?
What is the enzyme that breaks down starch?
- Starch is the plant form of carbohydrate ingested by humans
- Amylose is an unbranched starch comprised of glucose units, with glycosidic bonds at α-1,4
- Amylopectin is a branched is the branched form of starch with α-1,4 (units) and α-1,6 (branches) glycosidic bonds. Branches occur after 30 units of glucose
- Amylose and amylopectin are hydrolysed in the pancreas to produce glucose
- Α-amylase is the enzyme that breaks down starch, which is secreted by the salivary glands (why we salivate when looking at food)
What is cellulose used for?
What is its structure like?
Where is it not found and why?
- Cellulose is for storage in plants
- Uses β-1,4 linkage, each glucose is inverted from its neighbour, the Carbon 6 alternates to above and below the ring
- Mammals don’t have cellulose because of lack of enzymes to digest it (cellulase)
How are sugars involved in nucleotides?
- Nucleotides consist of a nitrogen ring linked to a 5-carbon sugar (usually ribose or deoxyribose), which is linked to phosphate groups
