carbohydrates (p) Flashcards
Carbohydrates contain only the elements
carbon, hydrogen and oxygen
Monosaccharides all have the formula …..Name 3 common properties.
(CH2O)n, where n is between 3 and 7. Soluble in waterSweet tastingAble to form crystals
The most common & important monosaccharide is It’s formula is
glucose, which is a six-carbon sugar. C6H12O6
There are many monosaccharides, with the same chemical formula (C6H12O6), but different structural formulae. Give 2 examples.
These include fructose and galactose.
Disaccharides are formed when two monosaccharides are joined together by
a glycosidic bond e.g.two glucose molecules joining together to form the disaccharide maltose.
Disaccharides are formed when two monosaccharides are joined together by ……………….. reaction involves the formation of what
a molecule of water (H2O).This kind of reaction, where water is formed, is called a condensation reaction
Why is it is called a 1-4 glycosidic bond.
Because this bond is between carbon 1 of one molecule and carbon 4 of the other molecule
When bonds are broken by the addition of water (e.g. in digestion), is called a
hydrolysis reaction
polymerisation reactions are ___________ reactions whilstbreakdown reactions are ___________ reactions
condensationhydrolysis
what are the three common disaccharides:
maltose sucrose lactose
what is maltose
(or malt sugar) is glucose & glucose. It is formed on digestion of starch by amylase, because this enzyme breaks starch down into two-glucose units. Brewing beer starts with malt, which is a maltose solution made from germinated barley.
what is sucrose
(or cane sugar) is glucose & fructose. It is common in plants because it is less reactive than glucose, and it is their main transport sugar. It’s the common table sugar that you put in tea.
what is lactose
(or milk sugar) is galactose & glucose. It is found only in mammalian milk, and is the main source of energy for infant mammals
Polysaccharides are long ________ of many _________ joined together by ____________
chains monosacharidesglycosidic bonds
There are three important polysaccharides
STARCHGLYCOGENCELLULOSE
Describe starch - 5 facts
is the plant storage polysaccharideinsoluble forms starch granules inside many plant cellsbeing insoluble means starch does not change the water potential of cells, so does not cause the cells to take up water by osmosis (more on osmosis later). Stored in chlorplasts and in starch grains.Starch can be broken down to glucose molecules that can be respired to release energy for ATP.
Starch is not a pure substance but is a mixture of (2)
amylose and amylopectin
Amylose is simply _________, so is a straight chain.
poly-(1-4) glucose In fact the chain is floppy, and it tends to coil up into a helix.
Amylopectin is poly(1-4) glucose with about 4% ___________
(1-6) branches.This gives it a more open molecular structure than amylose. Because it has more ends, it can be broken more quickly than amylose by amylase enzymes.
Both amylose and amylopectin are broken down by the enzyme __________ into __________, though at different rates.
amylasemaltose
Describe glycogen (5)
It is made by animals as their storage polysaccharide is found mainly in muscle and liver. *Because it is so highly branched, it can be mobilised (broken down to glucose for energy) very quickly. *Glycogen is similar in structure to amylopectin. *It is poly (1-4) glucose with 9% (1-6) branches.
Describe cellulose (5)
Cellulose is only found in plantswhere it is the main component of cell walls. *It is poly (1-4) glucose, but with a different isomer of glucose. *Cellulose contains beta-glucose, in which the hydroxyl group on carbon 1 sticks up. *This means that in a chain alternate glucose molecules are inverted.
Can the beta-glycosidic bond of cellulose be broken down by amylase?
No. It requires a specific cellulase enzyme. The only organisms that possess a cellulase enzyme are bacteria, so herbivorous animals, like cows and termites whose diet is mainly cellulose, have mutualistic bacteria in their guts so that they can digest cellulose. Humans cannot digest cellulose, and it is referred to as fibre.
What is the basic general formula for any carbohydrate?
(CH2O)n
Name 3 properties of monosaccharides
*sweet polarcrystallisable
Give an example of a triose i.e. 3 C’s
Glyceraldehyde
Give an example of a pentose i.e 5 C’s
Ribose or deoxyribose
What is the test for a reducing sugar?
Benedicts solution and heat turning the solution brick red
What is the test for a non-reducing sugar?
*Don’t react with Benedicts solution. Negative. No colour change. So make sure there are no reducing sugars, then boil with HCl
What are carbohydrates important for (3) ?
StorageStructureRespiration
Why is starch well adapted to its function? (4)
compactinsolublehas no osmotic effecteasily hydrolysed
Describe how you would test a sample of food for the presence of starch.
- Add iodine/potassium iodide solution to the food sample;2. Blue/black/purple indicates starch is present;
The concentration of glucose in the blood rises after eating a meal containing carbohydrates.The rise is slower if the carbohydrate is starch rather than sucrose. Explain why.
- Starch digested to maltose/by amylase2. Maltose digested to glucose/by maltase3. Digestion of sucrose is a single step/only one enzyme/sucrase
Sucrose is a disaccharide formed by
condensation of glucose and fructose.
Lactose is a disaccharide formed by
condensation of glucose and galactose.
Glucose has two forms- chain and ring.There is also alpha glucose and beta glucose. What’s the difference?
The only difference with alpha and beta glucose are the positions of the OH group and the H on Carbon 1.(alpha has the OH above and the H below, beta has the H above and the OH below)
name 3 monosaccharides 3 disaccharides and 3 polysaccharides
Monosaccharides: fructose, glucose, galactose. Disaccharides: maltose, sucrose, lactose. Polysacchardies: starch, glycogen, cellulose
During a condensation reaction between two monosaccharides, what happens?
A molecule of water is released and a glycosidic bond forms between the two monosaccharides.
What are maltose sucrose and lactose hydrolysed into?
maltose (glucose and glucose), sucrose (glucose and fructose), lactose ( alpha glucose and galactose)
People who are lactose intolerant are not able to produce the enzyme lactase. Explain why these people get diarrhoea when they drink milk containing lactose.
Low / decreased water potential (in gut);Water enters gut / lumen / leaves cells by osmosis;
Describe how you could use the Biuret test to distinguish a solution of the enzyme, lactase from a solution of lactose
Add Biuret reagent to both solutionsLactase (an enzyme) will give purple / lilac / mauvebecause it is a proteinLactose ( a reducing sugar) will not give purple / lilac / mauve / will remain blue;
Name the monosaccharides of which the following disaccharides are composed. 1. Sucrosemonosaccharides ……………………………….. and ………………………………..
Glucose and fructose
- Lactose monosaccharides ……………………………….. and ………………………………..
Glucose and galactose
Describe how a student would show that reducing sugars were present in a solution.
- Add Benedict’s2. Heat3. Red/orange/yellow/green (shows reducing sugar present)
Sucrose is made of which 2monosaccharides ……………………………….. and ………………………………..
Glucose and fructose
Lactose is made of which 2 monosaccharides ……………………………….. and ………………………………..
Glucose and galactose
Name the type of reaction that joins monosaccharides together
Condensation
Describe how you would test a sample of food for the presence of starch.
- Add iodine/potassium iodide solution to the food sample2. Blue/black/purple indicates starch is present
The concentration of glucose in the blood rises after eating a meal containing carbohydrates.The rise is slower if the carbohydrate is starch rather than sucrose. Explain why.
Starch digested to maltose/by amylase2. Maltose digested to glucose/by maltase3. Digestion of sucrose is a single step/only one enzyme/sucrase
