3.1.2 Carbohydrates Flashcards
Monosaccharides
- Monomers from which larger carbohydrates are made
- Soluble
Examples of monosaccharides
- Glucose
- Galactose
- Fructose
What does a condensation reaction between 2 monosaccharides form?
Glycosidic bond
Disaccharides
2 monosaccharides joined together
Examples of disaccharides
- Maltose
- Sucrose
- Lactose
Maltose
glucose + glucose
Sucrose
glucose + fructose
Lactose
glucose + galactose
Isomers of glucose
- Alpha glucose
- Beta glucose
Formula of glucose
C6H12O6
Polysaccharides
- Many monosaccharides joined together
- Large (so insoluble)
General formula of monosaccharides
(CH2O)n
n = any number between 3 and 7
Types of sugars
- Reducing sugars
- Non-reducing sugars
Reducing Sugars
- A sugar that can reduce another chemical (the chemical gains electrons)
- All monosaccharides and some disaccharides
Test for reducing sugars
- Benedicts test
- If food sample is not in liquid form, grind up in water. Filter
- In test tube, add liquid sample + benedicts reagant
- Heat in boiling water bath
- If reducing sugar is present: colour change; blue -> brick red
Semi-quantitive use of benedicts reagent
From low to high:
Blue
Green
Yellow
Orange
Orange-brown
Non-Reducing sugars
Some disaccharides
Test for non-reducing sugars
- Start with test for reducing sugars. If no colour change, then a reducing sugar is not present.
- In another test tube, add a fresh liquid sample + dilute HCl.
- Heat in boiling water bath
- Retest this solution with the reducing sugars test
- If non-reducing sugar was present in original sample, it will turn brick-red
Why is the reducing sugar test carried out first in the non-reducing test
To make sure no reducing-sugars are present, which would hinder the end result
Why was dilute HCl added to the second sample in the non-reducing sugar test
Dilute HCl will hydrolyse the disaccharide into its monosaccharides
Test for starch
- Add iodine to food sample
- If starch is present, colour change: orange -> blue/black
Examples of polysaccharides
- Starch
- Glycogen
- Cellulose
Where is starch found
Plant cells
What is starch made of
Alpha glucose
Characteristics of starch
- Branched or unbranched
- Unbranched is wound in tight coil to make molecule compact
Role of starch
Important component of food + majot energy source in diets
Where is glycogen found
Animal + bacteria cells
What is glycogen made of
Alpha glucose
Role of glycogen
major carbohydrate storage of animals. very little quantity as fat makes up most of the energy store
Comparison of starch and glycogen structure
Glycogen has same structure as starch but shorter chains and more branches
Adaptations of starch and glycogen for energy storage
- Insoluble - doesn’t affect osmosis
- Large + insoluble - doesn’t diffuse out of cells
- Compact - lots can be stored
- Lots of branches - high S.A. for enzyme activity so glucose is released quickly
What happens when starch and glycogen is hydrolysed to form glucose
It is readily used in respiration
Adaptation of glycogen for energy storage compared to starch
More branches than starch so higher enzyme activity (as animals have high respiration rate)
Where is cellulose found
Plant cell walls
What is cellulose made of
beta glucose
Structure of cellulose
Straight, unbranched chains which are parallel to eachother (hydrogen bonds form cross-linkages between adjacent chains)
- The hydrogen bonds are individually weak but collectively strong (good for cell walls)
- The cellulose chains are grouped to form microfibrilis -> fibres = more strength
Adaptations of cellulose
- Hydrogen bonds for strength + rigidity of cell wall
- Microfibrilis for strength
