Exam exam!!

Good Luck for tomorrow's paper and make sure you read your bio notes I gave (:

-Pn Ziakiah Omar

CHAPTER 5 : CELL DIVISION

 Focus Practice 5.1 ( page 92 )

1.      Give two reason why mitotic cell division is important in living organism

·         Distributing an exact copy of each of their chromosomes to the new cells

·         For normal growth, development and maintenance

       

2.      Describe the process that takes place during the S phase.

·         Synthesis of DNA occurs during the S phase. The DNA in the nucleus undergoes replication. Each duplicated chromosome now consists of the two identical sister chromatids which contain identical copies of chromosome’s DNA molecule

3.      What is cytokinesis?

·         Cytokinesis is the division of the cytoplasm, occurs towards the end of telophase. 

4.      How does a normal cell change into a cancerous cell?

·         When a cell divides through mitosis repeatedly, without control and regulation, it produce cancerous cells.

Focus Practice 5.2 ( page 97 )

1. State two differences between meiosis I and meiosis II.

   

Meiosis 1	Meiosis 11
During prophase I, homologous chromosomes pair up and crossing over between non-sister chromatids occurs.	During prophase II, synapsis of homologous chromosomes and crossing over between non-sister chromatids does not take place
During metaphase I, homologous chromosomes align at the metaphase plate (equator) of the cell	During metaphase II, chromosomes align at the metaphase plate (equator) of the cell.
During anaphase I, homologous chromosomes separate and move to opposite poles. Sister chromtids are still attached together and move as a unit.	During anaphase II, sister chromatids separate, becoming daughter chromosomes that move to the opposite poles.
At the end of telophase I, two haploid daughter cells are formed. Each daughter cell has only one of each type of chromosomes; either the paternal or the maternal chromosome	At the end of telophase II, four haploid daughter cells are formed. Each daughter cell has the same number of chromosomes as the haploid cell produced in meiosis I, but each cell has only one of the sister chromatids.

2. How is mitosis different from meiosis?
• Mitosis which involves one nuclear division to produce two identical diploid daughter cells
• Meiosis which involves two nuclear divisions to produce four haploid daughter cells which are not identical

3. Explain how meiosis I reduces the number of chromosomes in the daughter cells?

During anaphase I, the spindle fibres pull the homologous chromosomes away from one another and move them to the opposite poles of the cell. This means each pole has only one member of the homologous chromosomes which is called haploid.

Focus Practice 5.3 ( page 97 )

1. Why is it important for both mitosis and meiosis to occur in a controlled manner?

·         To prevent cancer and tummour

2. What are the things that you can do to minimize the risk of getting cancer?

·         Balance diet

·         Regular exercise

·         No smoking and drink

·         Keep away from radioactive sources  

ASSESSMENT CHAPTER 5

SECTION A

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

SECTION B

1. Figure 1 ( refer to page 100 )

a)      Q, R,T,P, S

b)     Plant cell –because no cleavage furrow/no centriole.

c)       -During cytokinesis, there are cell plate in a plant cell but not in the     

         animal cell.  Cleavage furrow is formed in animal cell to split the animal cell into two daughter cells.

-Most of the plant cells do not have centrioles but animal cell has.

                  d)  T (metaphase)- the centromeres of all the chromosomes are lined up on the

                                                  metaphase  plate. The two sister chromatids are still

                                                 attached to one another at the centromere. Metaphase ends

                                                when the centromeres divide.

                        P ( anaphase)-two sister chromatids of each chromosome separate at the

                                               centromere. The sister are pulled apart to the opposite poles

                                               by the shortening of the spindle fibres that connect the

                                               chromosomes to the poles.

2. a ) anaphase

b ) P-spindle fibres

     Q-chromatid

c) 6

NOTES: Enzyme

The role of enzymes in organisms

Metabolisms are chemical reactions that occur within a living organism.

Enzymes regulate almost all the cellular reactions.

Enzymes are biological catalysts that speed up biochemical reactions in the cell.

The general characteristics of enzymes

1.    Enzymes are proteins which are synthesised by living organisms

2.    Enzymes alter or speed up the rates or chemical reactions but remain unchanged at the end of reactions.

3.    Enzymes have specific sites called active sites to bind to specific substrates.

4.    enzymes are highly specific; each enzyme can only catalyse one kind of substrate.

5.    Enzymes are needed in small quantities; because they are not used up but released at the end of  a reaction.

6.    Enzyme can catalyse specific reactions both in the forward and in the reverse directions. Most enzyme-catalysed reactions are reversible.

7.    Many enzymes require helper molecules, called cofactors, to function

(inorganic cofactor-ferum and copper; organic cofactor-vitamin B)

8.    Enzyme activities can be slowed down or completely stopped by inhibitors (heavy metals such as lead and mercury)

Naming of enzymes

1.                The name of enzyme is derived from the name of the substrate it catalyses.

2.                The name of most enzymes are derived by adding suffix –ase to the name of the substrates they hydrolyse.  For example:

Substrate	Enzyme
Lactose	Lactase
Sucrose	Sucrase
Lipid	lipase

3.                However, there are some enzymes that were named before a systematic way of naming enzymes was formulated.  For example, pepsin, trypsin and rennin.

Synthesis of enzymes

1.                Ribosomes are the sites of protein synthesis.  Since enzymes are proteins, ribosomes are also the sites of enzymes synthesis.

2.                The information for the synthesis of enzymes is carried by the DNA.  The different sequences of bases in the DNA are codes to make different proteins.  During the process, messenger RNA is formed to translate the codes into a sequence of amino acids.  These amino acids are bonded together to form specific enzymes according to DNA’s codes.

Intracellular enzymes and extracellular enzymes

1.    Enzymes are synthesised by specific cells.

2.    Enzymes which are produced and retained in the cell for the use of the cell itself are called intracellular enzymes.  These  enzymes are found in the cytoplasm, nucleus, mitochondria and chloroplasts.  For example, the enzymes oxireductase catalyses biological oxidation and reduction in mitochondria.

3.    Enzymes which are produced in the cell but secreted from the cell to function externally are called extracellular enzymes.  For example, digestive enzymes produced by the pancreas are not used by the cell in the pancreas but are transported to the duodenum, which is the actual site of the enzymatic reaction.

Production of extracellular enzymes

1.    Many enzymes produced by specialised cells are secreted outside the cell.  For example, pancreatic cells secrete pancreatic amylase outside the cells to be transported to the target organ  (duodenum).

The production of extracellular enzymes

a.     The nucleus contains DNA which carries the information for the synthesis of enzymes.

b.    Protein that are synthesised at the ribosomes are transported through the space within the rough endoplasmic reticulum (rough ER).

c.     Proteins depart from the rough ER wrapped in vesiscles that bud off from the membranes of the rough ER.

d.    These transport  vesicles then fuse with the membrane of the Golgi apparatus and empty their  contents into the membranous space.

e.     The proteins are further modified during their transport in the Golgi apparatus, for example, carbohydrates are added to protein to make glycoproteins.

f.      Secretory vesicles containing these modified proteins bud off from the Golgi apparatus and travel to the plasma membrane.

g.     These vesicles will then fuse with the plasma membrane before releasing the protein outside the cell as enzymes.

Mechanism of enzyme action

1.      Each enzyme molecule has a region with a very precise shape called the active site.

2.      The substrate molecule fits into the active site of the enzyme like a key into a lock.

3.      Various types of bonds including hydrogen bonds and ionic bonds hold the substrate(s) in the active site to form an enzyme-substrate complex.

4.      The enzyme then changes the substrate(s) either by splitting it apart (as in hydrolysis) or linking them together (as in condensation).

5.      Once formed, the products no longer fit into the active site and escape into the surrounding medium, leaving the active site free to receive other substrate molecule.

Enzyme + substrateàenzyme-substrate complexàenzymes + products

6.      The explanation of enzyme action is known as the ‘lock and key’ hypothesis, where the substrate is like a key whose shape is complementary to the enzyme or lock.

7.      The ‘lock and key’ hypothesis is able to explain:

a.      why enzymes are specific, and

b.     why any change in the shape of enzyme alters its effectiveness.

Factors affecting enzyme activity

(i) Temperature

1.      At low temperature, the enzyme-catalysed reaction progresses slowly.

2.      An increase in temperature leads to an increase in the rate of reaction because the kinetic energy of the enzyme and substrate molecules produces more collisions, and therefore more enzyme-substrate complexes are formed.

3.      For every increase in temperature of 10° C, the rate of reaction is doubled.

4.      The rate of reaction increase up to a maximum at the optimum temperature.

5.      The optimum temperature of human enzymes is about 37° C.

6.      Above the optimum temperature, the rate of reaction falls quickly because the bonds maintaining the structure of the enzymes start to break and the active site loses its shape.

7.      The enzyme-substrate complexes can no longer be formed and the enzyme is denatured.

8.      Most enzyme-catalysed reactions stop at about 60° C.

(ii) pH

1.      Most enzymes are effective in a narrow pH range only.

2.      The optimum pH is the particular pH at which the rate of reaction is fastest(maximum).

3.      A change in pH can alter the charges on the active sites of the enzymes and the substrate surfaces.  This can reduce the ability of both molecules to bind each other.

4.      Unlike the effects of temperature on enzymes, the effects of pH on enzymes are normally reversible.  When the pH in the environment reverts to the optimum level for the enzymes, the ionic charges on the active sites are restored.  Thus, the enzyme resume their normal function.

5.      Pepsin function most effectively in an acidic medium at pH of about 2.  Pepsin is found in the stomach where the conditions are acidic.

6.      Trypsin functions most effectively in an alkaline medium at about pH 8.5.  It is found in the duodenum where conditions are alkaline.

 (iii) Substrate concentration

1.      Initially, an increase in substrate concentration increases the chance of enzyme-substrate collisions and, therefore,the rate of reaction increases.

2.      Eventually, all the active sites are filled at any one time and the rate remains constant.  The enzyme molecules are said to be saturated and the reaction has reached its maximum rate.

3.      The concentration of enzyme become a limiting factor.  At this stage,the only way to increase the rate of reaction by increasing the concentration of enzyme.

(iv) Enzyme concentration

1.      As the concentration of enzyme increases, there is more chance of enzyme-substrate collisions.  The rate of reaction increases linearly as long as no other factors  are limiting( there is abundant supply of substrate; pH, temperature and pressure are constant).  Thus, the rate of reaction is directly proportional to the concentration of the enzyme present until a maximum rate is achieved.  After the maximum rate, the concentration of substrate becomes a limiting factor.

2.      Figure 4.15 (pg 75 textbook) shows a linear graph is obtained when we plot a graph of the rate of reaction against enzyme concentration.  When the enzyme concentration is doubled, the rate of reaction will also doubled, provided that substrate concentrations are in excess .(As more active sites are available, more substrate can be converted to products-Figure 4.16pg 75 textbook). 

 

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.