Biological molecules: Carbohydrates Flashcards

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1
Q

What are biological molecules?

A

Substances where a C-H bond is present

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2
Q

What is a monomer?

A

The individual molecules that make up polymers

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3
Q

Why is carbon dioxide an inorganic molecule?

A

It doesn’t have the C-H bond

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4
Q

What chemical elements are polymers usually based on?

A

Carbon, hydrogen, oxygen and nitrogen

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5
Q

What is a monosaccharide?

A

The basic monomer unit of carbohydrates

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6
Q

What is a disaccharide?

A

2 monosaccharide units joined together to form a glycosidic bond in a condensation reaction

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7
Q

What is a polysaccharide?

A

A long chain of monosaccharides

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8
Q

Give the four monomers you need to know and their corresponding polymer

A

Amino acids - proteins
Nucleotides - nucleic acids (DNA, RNA)
glycerol and fatty acids - triglyceride fats
Monosaccharides - polysaccharides (these are under carbohydrates which refers to both monomer and polymer)

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9
Q

What is the general formula of a monosaccharide?

A

(CH ₂O)n where n can be any number from 3 to 7

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10
Q

Give three examples of monosaccharides

A

Glucose, fructose and galactose

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11
Q

What kind of sugar is glucose?

A

A hexose sugar because it had 6 carbons

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12
Q

What are the two isomers of glucose and draw them.

A

Alpha glucose and beta glucose ( drawing in camera roll)

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13
Q

What is a reducing sugar?

A

A sugar that can donate electrons to (or reduce) another chemical (in this case that chemical is benedicts solution)

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14
Q

What is reduction?

A

A chemical reaction involving the gain of electrons or hydrogen

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15
Q

What is the test for reducing sugars and how do you carry it out?

A

Benedict’s test:

  1. Add 2cm of the food sample to be tested in a test tube and it should be in liquid for, by grinding it up in water
  2. Add an equal volume of benedict’s reagent
  3. Heat the mixture in a gently boiling water bath for 5 minutes. If reducing sugar is present, solution turns orange-brown
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16
Q

Why is benedict’s test semi quantitative?

A

Because there are differences in the colour in the result

17
Q

What are the three disaccharides you need to know and what monosaccharides form them?

A
Maltose = glucose + glucose
Sucrose = glucose + fructose
Lactose = glucose + galactose
18
Q

Why is it when monomers become polymers they go through a condensation reaction?

A

Because for each monomer that bonds, a molecule of water is released

19
Q

What kind of reaction happens when a disaccharide breaks down into a monosaccharide?

A

A hydrolysis reaction because water is added to the disaccharide because water is added to the disaccharide breaking the glycosidic bond and releasing the constituent monosaccharide

20
Q

What are all monosaccharides?

A

Reducing sugars

21
Q

What must you do if you want to detect a non reducing sugar? Give the steps to the process

A

By hydrolysing it into its monosaccharide components via hydrolysis:

  1. If not already make the substance liquid form by grinding it with water
  2. Add 2cm of the food sample being tested to 2cm of benedicts solution in a test tube and filter
  3. Place the test tube in a gently boiling water bath for 5 mins (if no colour change is present and solution stays blue then there is no reducing sugar present)
  4. Add another 2cm of the food sample to 2cm of dilute hydrochloric acid in a test tube and place the test tube in a gently boiling water bath for 5 minutes. The dilute hcl will hydrolyse any disaccharide present into its constituent monosaccharides
  5. Slowly add some sodium hydrogen carbonate solution to the test tube to neutralise the hcl as benedicts solution doesn’t work in acid and check its alkaline with pH paper
  6. Retest the solution with 2cm of benedicts solution and leave in a gently boiling water bath for 5 minutes
  7. If non reducing sugar was present in the original sample, the benedicts reagent will now turn orange brown due to the reducing sugars that were reduced by the hydrolysis of the non reducing sugar
22
Q

Give an example of a disaccharide that is a reducing sugar and one that’s not

A

Maltose is a reducing sugar and sucrose is not

23
Q

Why are polysaccharides insoluble? What does this make them suitable for?

A

Because they are very large molecules, making them suitable for storage

24
Q

Give an example of a polysaccharide in plants that isn’t used for storage and why its useful

A

The polysaccharide cellulose is useful as it gives structural support to the plant cell

25
Q

Where is the polysaccharide starch found?

A

In many parts of plants in the form of small granules or grains for example starch grains in chloroplasts

26
Q

How is the polysaccharide starch formed?

A

By the joining of between 200- 100000 alpha glucose molecules by glycosidic bonds in a series of condensation reactions

27
Q

What are the steps to carrying out the test for starch?

A
  1. Place 2cm of the sample being tested into a test tube
  2. Add 2 drops of potassium iodide solution and shake or stir
  3. The presence of starch is indicated when the iodine solution goes from yellow to blue-black
28
Q

Why does benedicts reagent turn red when heated with a reducing sugar?

A

Benedicts reagent turns red when heated with a reducing sugar because it has formed in insoluble layer of copper (I) oxide where electrons have been donated from the reducing sugar to the copper