Chapter (4) Chemical Composition Of Cells

Question 1

What does living organisms consist of?

Answer 1

⭐️💛* Living organisms consist of organic compounds that contain 6 elements of life: CHONPS
( they contain carbon atoms covalently bonded to CHONPS)

⭐️💛* All living things are made up of four classes of large biological molecules : Carbohydrates, lipids , proteins , and nucleic acids

Question 2

Three of four classes of life’s organic molecules are :

Answer 2

Polymers

Question 3

Are lipids polymers ?? 🫒

Answer 3

→ the forth class, lipids, are not polymers nor macromolecules.🤍🍰

→ fats & oils are not polymers but contain glycerol and fatty acids. They are repeated units but they are not the same monomers, also not big enough, so they aren’t considered as polymers.🤍🍰

Question 4

Starch is a polymer of:

Answer 4

Glucose.

Question 5

Proteins are polymers of:

Answer 5

Amino acids

Question 6

What are reagents??

Answer 6

Reagents are chemicals that will be used to test for the presence of certain molecules.

Question 7

Principle of reagents:

Answer 7

If a color change is observed, the test is positive, indicating that a particular molecule is present. If color change is not observed, the test is negative and the molecule is not present.

Question 8

What is the definition of organic compounds?

Answer 8

Compounds that contain carbon atoms, covalently bonded to oxygen, nitrogen, hydrogen, sulfur, or phosphorus

Question 9

What are the large organic molecules or macromolecules or polymers?

Answer 9

They are molecules consisting of small molecules (monomers), joined in acid sequence 

Question 10

What are the monomers of starch or glycogen or cellulose?

Answer 10

Glucose

Question 11

What are the monomers of nucleic acids?

Answer 11

Nucleotides

Question 12

Monomer of carbohydrates

Answer 12

monosaccharides

Question 13

The carbohydrate can be monomers or polymers

Answer 13

A) Monosaccharides: consist of simple sugars (the simplest carbohydrate) for example: glucose ,galactose , fructose

B) disaccharide: or double sugars, consisting of two monosaccharides, joined by a covalent bond . For example.: sucrose, lactose ,maltose .

C) polysaccharides : are composed of many sugar building blocks, and they are considered as a macromolecules, for example, starch , cellulose , glycogen.

Question 14

Depending on the location of the carbonyl group, monosaccharide, classified as:

Answer 14

1) Aldose : aldehyde sugar
2) ketose : ketone sugar

Question 15

General information about lipids:

Answer 15

= they are generally not big enough to be considered macromolecules.

= lipids share an important trait.They are hydrophobic.

= they consist mostly of hydrocarbons, which form non-polar covalent bonds.

= there are three types of lipids that are most biologically important : Fats, phospholipids , and steroids.

Question 16

What are fats phospholipid consist of?

Answer 16

1- Fats (triacylglycerol or triglyceride) constructed of one glycerol and three fatty acids.

2- phospholipids are one glycerol and two fatty acid and one phosphate group.

3- steroids are four fused rings.

Question 17

General information about protein

Answer 17

**. Proteins are constructed from the same set of 20 amino acids.
**. The bond between amino acids is called bide bond.
**. Polypeptides Range in length from a few amino acid to 1000 or more.
**. Each specific polypeptide has a linear sequence amino acids.

Question 18

What are vitamins :

Answer 18

Vitamin are complex chemical compounds of high molecular weight that are essential to normal growth a health maintenance.

For example:
🍋 vitamin C [ascorbic acid ] 🍋

Question 19

Negative tests:

Answer 19

If the color change is not observed, the test is negative and the molecule is not present.

Question 20

Positive test:

Answer 20

If a color change is observed, the test is positive, indicating that a particular molecule is present.

Question 21

Control sample:

Answer 21

A distilled water sample that will go through all the steps of the experiment and give a negative test result.

Question 22

Is there a test for all types of carbohydrates??

Answer 22

Carbohydrates comprise a wide variety of monomers and polymers, and no single test can be used as a marker for all of them.

Question 23

Benedict test is used for :

Answer 23

• It’s a blue chemical reagent which is made up of a complex mixture of chemicals including copper (ii) sulfate.
• it’s used to test the presence of glucose (reducing sugar)
• when a reaction occurs between reducing sugar & a Benedict reagent it produces red ppt.

Question 24

Write the chemical reaction of Benedict reagent & reducing sugars

Answer 24

Guycose+ CuSO4 → gluconic acid+ Cu2O ( red ppt)

Question 25

How can the Benedict test show the amount of reducing sugar present in the solution ??

Answer 25

The test shows the amount of reducing sugars present in the solution through the color change :-
🍎 if the color is blue, that means no reaction- there is no reducing sugars due to the not changing in the color.
🍎 A reaction with a small amount of reducing sugar present in the solution will turn the color to green as an indicator of traces of reducing sugar.
🍎 when it’s moderate, the color is orange red ppt.
🍎 when the color is brick red precipitate. There is large amount of reducing sugars.

Question 26

What does it mean when the color of the solution of Benedict turns from blue to green / yellow??

Answer 26

• There is traces of reducing sugar.

Question 27

What does it mean when therefor of Benedict turns to Orange!!!

Answer 27

Moderate amount of reducing sugars.

Question 28

What does it mean when the color of the Benedict solution turns to brick-red ppt??

Answer 28

It indicates large amount of reducing sugars.

Question 29

What would we do to convert non reducing sugars (sucrose) to a reducing sugars???

Answer 29

Breakdown sucrose into glucose and fructose monomers (reducing sugars) by acid hydrolysis (hcl)

—————
Note :
The steps are :
* Add HCl on sucrose and boil it to speed up the hydrolysis of the sucrose into its monomers.

• Then after boiling for 5 min , we are now sure that the sucrose is converted into its monomers.
• Now , to perform the Benedict test, it’s better to get rid of the acidic environment by adding NaOH to neutralize the HCl.
• Now add Benedict solution.

Question 30

What is the lugols test ?

Answer 30

The test is used to distinguish certain polysaccharides such as starch,
glycogen, cellulose from other Mono-, di-, and polysacchrides.

The original color of lugols test is yellow

The negative test is brown / yellow color , and the test positive is blue / purple color

Question 31

How does starch interact with lugols test ?

Answer 31

*Starch is a polymer of glucose

• the chains are coiled up in a
  particular way so it can interact with iodine molecules in Lugol’s solution
• give a distinctive blue- black colour.

Question 32

Do other polymers interact with lugols test as the starch do?

Answer 32

**Other polymers even those of glucose, lack the precise coiled structure of starch and do not give the blue colour. (( so they don’t give the same result of starch , but not the negative result also))

** violet-brown to red-brown colour is given by cellulose.

** A red colour is given by glycogen.

Question 33

When potato juice give a positive result that means: -

Answer 33

I it contains starch // cellulose but it is impossible to have glycogen

Question 34

Define Emulicification

Answer 34

The mechanical breakdown and dispersal of large globules into smaller droplets.

Question 35

What is the emulsifier and how can it perform mechanical breakdown of the fat ?

Answer 35

🍓 An emulsifier contains molecules with polar and nonpolar ends.
🍓When the nonpolar ends are attached to the nonpolar fat, the polar ends are exposed.
🍓 Since the polar ends are soluble in water, the fat is dispersed.

Question 36

Why is sucrose considered non reducing sugar?

Answer 36

It cannot convert to an open chain form of an aldehyde group.