3.1.2 Carbohydrates Flashcards
What are monosaccharides?
“Monosaccharides are the monomers from which larger carbohydrates are made.”
Name three common monosaccharides.
“Glucose galactose fructose.”
What type of reaction forms a glycosidic bond between two monosaccharides?
“A condensation reaction.”
What bond forms between two monosaccharides in a condensation reaction?
“A glycosidic bond.”
What is a disaccharide?
“A disaccharide is formed by the condensation of two monosaccharides.”
What monosaccharides form maltose?
“Maltose is formed by the condensation of two glucose molecules.”
What monosaccharides form sucrose?
“Sucrose is formed by the condensation of a glucose molecule and a fructose molecule.”
What monosaccharides form lactose?
“Lactose is formed by the condensation of a glucose molecule and a galactose molecule.”
How many isomers does glucose have?
“Glucose has two isomers α-glucose and β-glucose.”
What reaction forms polysaccharides?
Polysaccharides are formed by the condensation of many glucose units.
What monosaccharide forms glycogen and starch?
Glycogen and starch are formed by the condensation of α-glucose.
What monosaccharide forms cellulose?
Cellulose is formed by the condensation of β-glucose.
What is the function of glycogen in animals?
Glycogen acts as an energy storage molecule in animal cells.
How is glycogen adapted for its function?
Glycogen has a highly branched structure allowing rapid hydrolysis by enzymes for quick energy release.
What is the function of starch in plants?
Starch acts as an energy storage molecule in plant cells.
How is starch adapted for its function?
Starch is insoluble so does not affect water potential it is compact for storage and amylopectin has some branches for rapid energy release.
What are the two components of starch?
Amylose and amylopectin.
Describe the structure of amylose.
Amylose is a long unbranched chain of α-glucose forming a coiled helical structure held by hydrogen bonds making it compact.
Describe the structure of amylopectin.
Amylopectin is a long branched chain of α-glucose with 1,6 glycosidic bonds allowing enzymes to break down the molecule quickly for rapid glucose release.
How does the structure of amylose relate to its function?
Amylose is compact due to its helical structure allowing efficient storage of glucose.
How does the structure of amylopectin relate to its function?
Amylopectin is highly branched allowing rapid hydrolysis by enzymes to provide glucose quickly.
What is the function of cellulose in plant cells?
Cellulose provides structural support in plant cell walls.
How is cellulose adapted for its function?
Cellulose has straight unbranched chains of β-glucose linked by hydrogen bonds forming microfibrils for strength and rigidity.
What test is used to identify reducing sugars?
Benedict’s test.
Describe the Benedict’s test for reducing sugars.
Add Benedict’s reagent to the sample and heat in a water bath at 80°C a positive result is a brick-red precipitate.
How do you test for non-reducing sugars?
First hydrolyse the sample by heating with dilute hydrochloric acid then neutralise with sodium hydrogen carbonate then perform Benedict’s test.
What is a positive result for a non-reducing sugar test?
A brick-red precipitate after hydrolysis and Benedict’s test.
What test is used to identify starch?
Iodine/potassium iodide test.
Describe a positive test result for starch.
A blue-black colour change.
What technique can be used to separate a mixture of monosaccharides?
Chromatography with known standard solutions.
How can chromatography be used to identify monosaccharides?
Compare Rf values of unknown monosaccharides to known standards.
What technique can be used to determine glucose concentration in a solution?
Colorimetry using a calibration curve.
How is a calibration curve for glucose concentration produced?
Prepare a dilution series of glucose measure absorbance using a colorimeter and plot a graph of absorbance against concentration.
Glycogen - Glycogen Structure (3)
- Polysaccharide of α-glucose;
- (Joined by) glycosidic bonds;
- Branched structure
Glycogen - Glycogen compared with cellulose (4)
- Cellulose is made up of β-glucose (monomers) and glycogen is made up of α-glucose (monomers);
- Cellulose molecule has straight chain and glycogen is branched;
- Cellulose molecule has straight chain and glycogen is coiled;
- Glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has only 1,4- glycosidic bonds
Glycogen - Glycogen structure related to function (5)
- Insoluble (in water), so doesn’t affect water potential;
- Branched / coiled / (α-)helix, so makes molecule compact;
- Polymer of (α-)glucose so provides glucose for respiration;
- Branched / more ends for fast breakdown / enzyme action;
- Large (molecule), so can’t cross the cell membrane
Starch – Relate 3 properties to its function (6)
- Insoluble;
- Don’t affect water potential;
- Helical;
- Compact;
- Large molecule;
- Cannot leave cell
Test for reducing sugar
- Heat with Benedict’s reagent (1);
- colour change from blue to brick-red (1)
Test for a non reducing sugar
- Heat with Benedict’s reagent and no colour change (1);
- boil with acid (HCl) and then neutralise with (NaHCO3) (1);
- re- heat with Benedict’s reagent and colour change from blue to brick-red (1)
Test for starch
- Add iodine in potassium iodide solution (1);
- colour change from brown to blue-black (1)
