CHAPTER 4 : CHEMICAL COMPOSITION OF THE CELL

Activity 4.1 (page 59 textbook)

Discussion

1. Carbon, hydrogen, oxygen and nitrogen
2. carbohydrates proteins, nucleic acids and lipids (organic compounds); water (inorganic compounds)
3.  

Compounds	Elements
Carbohydrates	C, H, O
Proteins	C, H, O, N (S and P)
Lipids	C, H, O
Nucleic acids	C, H, O, P, N
Water	H, O

Activity 4.3 (pg64)

 

2.

a	Monosaccharides	Disaccharides	Polysaccharides
	Glucose, fructose, galactose	Sucrose, maltose, lactose	Starch, glycogen, cellulose
b	Formation: through hydrolysis of disaccharides or polysaccharides Word equation:	Formation: through condensation of two monosaccharides Word equation:	Formation: through condensation of hundreds monosaccharides
c	Breakdown: simplest sugar-cannot be broken down	Breakdown: can be broken down into their constituent monosaccharides by hydrolysis Word equation:	Breakdown: can be broken down into smaller molecules through hydrolysis by adding diluted acid or through enzymatic reaction Word equation:

Focus Practice 4.2 (page 64)

1. Carbon, hydrogen and oxygen. 
2. (i) Maltose --------> Glucose + Glucose      } Hydrolysis

    (ii) Sucrose --------> Glucose + Fructose    } Hydrolysis

    (iii) Lactose ------> Glucose + Galactose  } Hydrolysis

3. Hundreds of monosaccharides can combine through condensation to form a long chain of polysaccharides 

4. Fructose is better than sucrose because fructose does not increase the concentration of glucose in blood but sucrose will be       hydrolysed (broken down)    into glucose and fructose  and this will increase the    concentration of glucose      in blood-can cause diabetes .

Differences between fructose and sucrose

Fructose	Sucrose
i.   Monosaccharides	i.   Disaccharides
ii.  Reducing sugar.      ( Reducing agent)	ii.  Non-reducing      (Non-reducing agent)
iii. Does not increase the      concentration of glucose in      blood.	iii. Sucrose can be        hydrolysed (broken down)      and will increase the      concentration of glucose      in blood-can cause diabetes

Activity 4.4 (page 67)

1. The various structures of proteins :

i.                    Primary structure (lysosome)

-          the linear sequence of amino acids in a polypeptide chain

           

ii.                  Secondary structure

-          the coiling (keratin in hair-alpha helix) and folding(fibroin in silk -beta-pleated sheet) of polypeptide chain by hydrogen bonds.

iii.                Tertiary structure (enzymes, hormones)

-          The helix chain or the beta-pleated sheets are folded into  three dimensional shape of a polypeptide chain.

iv.                Quarternary structure (haemoglobin, collagen).

-          the combination of two or more tertiary polypeptides that make up a protein.

Focus Practice 4.3 (page 67)

1. The elements found in proteins are carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus.
2. Dipeptides are broken down through a series of hydrolysis reactions to form amino acids.
3. The quarternary structure of protein is formed by the combination of two or more tertiary structure of polypeptide chains to form one large and complex protein molecule.

     (you may refer to Figure 4.7 (d) : page 66)

Activity 4.5 (page 69)

Saturated Fats	Differences	Unsaturated Fats
No / Do not have any double bond.	The presence of double bonds between carbon atoms in fatty acids	Yes / Have at least one double bond
Cannot form any chemical bonds with other atoms / Cannot react with additional hydrogen atom.	Ability to react with an additional hydrogen atom	Can form another chemical bonds / Can react with additional hydrogen atom.
Solid	Condition at room temperature	Liquid
Increase the cholesterol level	Cholesterol level	Decrease the cholesterol level
Butter, margarine, cheese	Examples	(Vegetables oil) Corn oil, olive oil, peanut oil.

Focus Practice 4.4 (page 69)

1. Fats and oils are being formed from the combination of one molecule of glycerol and three molecules of fatty acids.
2. “Unsaturated fats” means unsaturated fatty acids.
3. It is better to cook with unsaturated fats compared to saturated fats because :

Unsaturated fats	Saturated fats
Decrease the level of cholesterol      in the blood.	Increase the level of cholesterol in      the blood.
Do not increase the risk of heart      disease.	Increase the risk of heart disease.

           

            Differences between unsaturated fats and saturated fats

Unsaturated fats	Saturated fats
Contain at least one double bond      between the Carbon atoms.	Do not have any double bond      between the Carbon atoms.
Have a low melting point.	Have a high melting point.
Decrease the level of cholesterol      in the blood.	Increase the level of cholesterol in      the blood.
Do not increase the risk of heart      disease.	Increase the risk of heart disease.

Focus Practice 4.5 (page 76)

1. An enzyme is the biological catalyst that regulate almost all the cellular reactions (activities).
2. Characteristics of enzymes :

i.                    Alter / speed up the rates of chemical reactions.

ii.                  Remain unchanged at the end of the reactions.

iii.                They are not destroyed by the reaction they catalyse.

iv.                Their actions are specific.

v.                  Just need in small quantity.

vi.                Most enzyme-catalysed are reversible.

3. Enzyme-catalysed reactions are specific as they have their own specific sites called active sites, to bind to specific substrates. Hence, the shape of the substrate must fit the enzyme precisely if a reaction is to take place. So that, each enzyme can only catalyse (react on) one kind of substrate.

4. The effects of temperature and pH on the rate of reactions which are catalysed by enzymes.

Temperature

i.                    At low temperature, the rate of enzyme reaction is low (substrate molecules move slow).

ii.                  As the temperature increases, the collision between substrate molecules and enzyme molecules occur more frequently and the rate of enzyme reaction also increases until the optimum temperature 37°C (which is also our body temperature).

iii.                At high temperature (above 40°C), enzymes (proteins) become denatured rapidly due to changes in shape of the enzymes molecules.

iv.                At 60°C, all enzymes are denatured and the reactions stop.

pH

i.                    Each enzymes functions actively at its optimum pH.

ii.                  If not, they will be inactive.

iii.                For example, an enzyme that functions at pH 7 will be inactive when its reaction medium becomes too acidic or too alkaline.

iv.                A change in the pHvalue can alter the charges on the activesites of an enzyme and the surface of a substrate. This can reduce the ability ofboth molecules to bind with each other.

 

Focus Practice 4.6

1.

Chemical substances	Main function	Consequence of deficiency
Carbohydrate	Major storage of energy	Lack of energy
Protein	For growth	Impaired mental and physical growth
Lipids	Important source of energy	No energy
Enzyme	Biological catalyst	Biochemical reaction will be too slow to sustain life

Chapter 4 Assessment

1	C	2	C
3	D	4	C
5	A	6	C
7	D	8	D
9	C	10	D

Section

1.(a)  Hydrolysis is a chemical reaction that involves the breaking up of large molecules by adding water to them.

(b)        one molecule glycerol and three molecules fatty acids

(c )       cholesterol and sex hormones(testosterone, oestrogen, progesterone)

(d)       

Unsaturated fats	Saturated fats
Contain at least one double bond      between the Carbon atoms.	Do not have any double bond      between the Carbon atoms.
Have a low melting point.	Have a high melting point.
Decrease the level of cholesterol      in the blood.	Increase the level of cholesterol in      the blood.
Do not increase the risk of heart      disease.	Increase the risk of heart disease.

(e)                Saturated fats in diet increases the risk of heart diseases.

2. (a)        Both are polysaccharides/ storage of carbohydrates

      (b) starch-main carbohydrate reserve in plants

                 Glycogen- main carbohydrate reserve in animals and yeast

(c)        through hydrolysis by adding diluted acid or through enzymatic reaction.

(d)        i.  glucose and fructose

            ii. glucose and galactose

(e)        heat the sample of food and Benedict’s solution in a water bath, if the solution      turns brick-red precipitate, the food sample contains reducing sugar.

3.(a)     RNA, DNA

(b)        P: phosphate group, Q: pentose sugar ,S: nitrogenous base

(c )       refer text book pg 60

     4.a)  A: tertiary structure, B:  quarternary structure

(b)   through condensation/combination of two or more tertiary polypeptide(A)

(c)    haemoglobin/collagen

(d)       

Essential amino acids	Non-essential amino acids
Cannot be synthesized by the body Can only be obtained from the diet	Can be synthesized by the body
There are altogether nine essential amino acids	There are eleven essential amino acids
Are called first class protein-because contain all the essential a.acids needed by the body	Are called second class protein because they do not contain all the essential a. acids needed by the body
Animal protein	plant protein

                       

Section C

1.       Enzymes are biological catalyst that direct or guide almost all cellular reactions.  Without enzymes, biological reactions will take too long to complete.

2.

Type of industry/ application	Enzymes used	Uses
Food processing industry meat products	Protease	Tenderises meat Housewives use papaya juice (papain enzyme) to tenderise meat (text book pg 77)
2.  fish products	Protease	Removes the  skin of fish
3. dairy products	Lipase	Ripening of cheese
	Lactase	Hydrolyses lactose to glucose and galactose in the making of ice-cream
	Rennin	Solidifies milk protein (manufacture cheese)
4. seaweed products	Cellulase	Breaks down cellulose(cell wall) and frees the agar/extract the agar from seaweed.
Alcoholic drinks(beer,wine)	Zymase	Converts sugar into ethanol
Leather products	Trypsin	Removal of hair from animals hides
Biological washing powder or detergents	Protease, lipase and amylase	Dissolve protein, fat and starch stains in clothes

C (i)           The enzyme has an active site which can bind to a specific substrate molecule.  The enzyme remain unchanged at the end of reactions.  They are not destroyed by the reactions they catalyse. The enzyme is not affected by the reaction.

(ii)              In the lock and key hypothesis, the substrate molecule represents the key and the enzyme molecule represent the lock.

 Enzymatic reaction is highly specific in that a specific substrate can only bind to a particular enzyme in the same way a certain key only fits a particular lock.

The substrate molecule bind to the active site  to form an enzyme-substrate complex.

The enzyme catalyses the substrate to form products, which then leaves the active site.

The enzyme molecule is now free to bind to more substrate molecules.   Enzymatic reaction is highly specific in that a specific substrate can only bind to a particular enzyme in the same way a certainkey only fits a particular lock.