Carbohydrates Flashcards
What is a monosaccharide?
A small molecule which forms chemical bonds to produce a larger carbohydrate in a condensation reaction.
What is a disaccharide?
A carbohydrate that is produced by 2 monosaccharides forming a glycosidic bond in a condensation reaction.
What is a polysaccharide?
A carb that is produced when many glucose units form a glyosidic bond in a condensation reaction.
What is a monomer?
Smaller units that join together to form larger
molecules.
What are some examples of monomers?
Monosaccharides
Amino acids
Nucleotides
What is a polymer?
Molecules formed when many monomers join together.
What are some examples of polymers?
Polysaccharides
Protein
DNA / RNA
What is a condensation reaction?
When small molecules form a chemical bond to produce a larger molecule & water molecule is eliminated,
What is a hydrolysis reaction?
When a water molecule is used to break a chemical bond between 2 molecules.
Name the 3 hexose monosaccharides and where they are found.
Glucose (food)
Fructose (fruits)
Galactose (milk)
What is the general formula for monosaccharides?
C₆H₁₂O₆
What type of bond is formed when monosaccharides react?
A 1,4 or 1,6 glycosidic bond
Name 3 disaccharides and how they’re formed.
glucose + glucose –> maltose
glucose + fructose –> sucrose
glucose + galactose –> lactose
What formula do all disaccharides have?
C6H22O11
Draw the structure of α-glucose.
CH2OH at the 6th carbon
H element at both tops
OH ion at both bottoms
Draw the structure of β-glucose.
CH2OH at the 6th carbon
1x H element at one top and bottom
1x OH ion at one top and bottom
Describe the structure and function of starch
Polymer of α-glucose.
Energy source and storage found in plants.
Insoluble = doesn’t affect water potential (no osmosis)
Large = doesn’t diffuse out of cells.
Made from AMYLOSE and AMYLOPECTIN
Describe the features of amylose
Polymer of α-glucose.
Forms ONLY 1-4 glycosidic bonds.
Helix and unbranched structure.
Compact.
Why is it good for a molecule to be insoluble?
Won’t affect water potential of cells since it prevents osmosis to occur and water entering the cell which would swell and be damaged
Why is it good for a molecule to be large?
It cannot diffuse out of the cell
Why is it good to have a branched structure?
Many side branches means enzymes can act simultaneously at the ends of branches and ENERGY is released quickly.
Why is it good to have a compact structure?
Maximises the amount of energy it can store (as it fits a large amount in a small space)
Describe the features of amylopectin.
Polymer of α-glucose.
Forms BOTH 1,4 & 1,6 glycosidic bonds.
Helix and branched structure.
Compact.
Describe the structure and functions of glycogen.
Polymer of α-glucose.
Main energy source / storage in animals.
Forms BOTH 1,4 & 1,6 glycosidic bonds.
Branched structure.= many terminal ends for hydrolysis to glucose
Insoluble = doesn’t affect water potential
Large = doesn’t diffuse out of cells.
Compact = large energy release.
What are the main things to look for in the features of a carbohydrate?
1# What type of glucose it’s made from
2# Whether it has both 1,4 & 1,6 glycosidic bonds
3# Whether it’s branched
4# Insolubility
5# Compact
6# Large
7# Fibrils
8# Helix or straight structure
Describe the structure and function of cellulose.
Polymer of β-glucose.
Found in plant cell walls.
A structural unit = gives rigidity to plant cell walls (prevents bursting & holds stem up)
Hydrogen bonding between adjacent chains is found.
ONLY 1,4 glycosidic bonds
Straight-chain, unbranched structure
Alternate glucose molecules are rotated 180°
Forms microfibrils! = high tensile strength
How are microfibrils formed?
Hydrogen bonds crosslinks between parallel strands.
What is a reducing sugar?
Reducing sugars are able to donate electrons to other molecules (hence they reduce that molecule).
They act as reducing agents.
What kind of carbohydrates are reducing sugars?
ALL monosaccharides are reducing sugars.
SOME disaccharides are reducing sugars.
Which functional group do reducing sugars have?
O - C - OH
What is a non-reducing sugar?
A non-reducing sugar cannot donate electrons to other molecules - they are not reducing agents.
Describe the Benedict’s test for reducing sugars.
1~ Add an equal volume of Benedict’s reagent to food sample.
2~ Heat mixture in water bath at 100°C for 5mins.
Positive result: colour change from blue to green, orange, brick red precipitate forms
Why is there a range of colours produced during the Benedict’s test?
The colour of the solution depends on the glucose concentration.
Green (0.1 concentration / M)
Orange (0.25 concentration / M)
Red (0.5 concentration / M)
Describe the Benedict’s test for non-reducing sugars.
Negative result: Benedict’s reagent remains blue.
1~ Add 1cm³ of dilute HCl and boil in water bath for 5mins.
2~ Neutralise mixture with sodium hydrogen carbonate solution.
3~ Proceed with Benedict’s test.
If positive: contains non-reducing sugars.
Why do we put a dilute acid (HCl) in the food sample?
It hydrolyses the non-reducing sugars disaccharides (e.g. sucrose) into monosaccharides by breaking the bonds between molecules.
Monosaccharides are reducing sugars and can be detected.
Why do we neutralise the food sample with sodium hydrogen carbonate?
Benedict’s reagent requires an alkaline environment to work properly.
Describe the test for starch.
1~ Place food sample on spotting tile
2~ Add few drops of iodine solution
Positive result: colour change from orange to blue-black.
How can colorimetry be used to give qualitative results for the presence of sugars and starch?
1~ Make solutions with known concentrations.
(Record absorbance or (% transmission values)
2~ Plot calibration curve: absorbance / % transmission (y-axis), concentration (x-axis).
3~ Record absorbance / % transmission values of unknown samples.
Use calibration curve to read off concentration.
Describe the lipid (emulsion test)
1~ Place food sample in test tube.
Add 3cm³ of ethanol.
2~ Shake lidded tube thoroughly to dissolve any lipid in sample.
3~ Add 3cm³ of water and shake gently.
Positive test: solution turns cloudy (white emulsion forms)
Which 2 substances are branched molecules?
Amylopectin
Glycogen
Which 2 substances are unbranched molecules?
Amylose
Cellulose
A carbohydrate can be…
Monosaccharides
Disaccharides
Polysaccharides
What are carbohydrates?
A molecule consisting of…
carbon
hydrogen
oxygen atoms
What type of bond is formed when monosaccharides react?
1,4 and/or 1,6 glycosidic bonds.
How do you prepare a food test?
1~ Grind the food sample with a pestle and mortar while adding distilled water to help dissolve.
2~ Filter the food sample and collect the food sample solution.
3~ Place liquid into a test tube.
What is the name given to sugars with 6 carbon atoms? Give examples.
Hexose sugars
Glucose
Galactose
What is the name given to sugars with 5 carbon atoms? Give examples.
Pentose sugars
Fructose
Ribose
What is one key feature of monosaccharides?
They are hydrophilic and soluble in water due to the many OH (hydroxyl) groups.
What is an isomer?
Molecules with the same molecular formulas, but different arrangements of atoms / structure.
What’s the difference between amylopectin and glycogen?
Glycogen is very similar to amylopectin BUT has lots more side branches coming off it + shorter chains
What’s the difference between amylopectin and glycogen?
Glycogen is very similar to amylopectin BUT has lots more side branches coming off it + shorter chains
How do you test for the presence of protein? (Biuret test)
Biuret test confirms presence of peptide bonds,
1~ Add equal volume of NaOH to sample at room temp.
2~ Add drops of dilute copper (II) sulfate solution.
Swirl to mix.
Positive result: colour change - blue to purple.
Negative result: solution remains blue.
Steps 1 & 2 make Biuret reagent.
What type of data does a Benedict’s solution test produce? What does it mean?
Semi-quantitative data =
gives an approximate idea of levels - range of values.
