The Study of Life Sciences

Condensation and Hydrolysis

2007-08-11T20:50:00.000-07:00

Condensation is a chemical reaction whereby 2 simple molecules are joined together to form a larger molecule with the removal of one molecule of water.

A reaction whereby a water molecule is added on to split up a complex molecule into its component units is known as hydrolysis or hydrolytic reaction.

hydro -> water ; lysis -> splitting

Condensation is the direct opposite of hydrolysis as condensation is the process of bonding molecules while hydrolysis is the process of splitting up the bond of molecules with the removal and addition of 1 water molecule respectively.

Enzymes

2007-08-11T19:29:00.000-07:00

- enzymes have 3D shapes.

- the part of the enzyme into which the substrate fits is called the active site.

- each active site is shaped specifically for the enzyme - substrate complex is formed. the substrate then undergoes a reaction.

- the product(s) formed are released from the active site while the enzye molecule is left unchanged and can catalyse the reaction.

- the enzyme is the lock while the substrate is the key.

- only a minute amount of enzymes are required to catalyse the reaction.

- enzyme reaction is specific.

- since the active site must fit the substrate perfectly, therefore only one enzyme can only catalyse one type of reaction.

- as the temperature increases, particles move faster, there is a higher chance of substrate and enzyme molecules bumping into each other, therefore the rate of reaction increases.

- enzymes work over a small range of temperatures.

- the rate of enzyme reaction increases as temperature increases - but only to a certain point.

- the temperature of which an enzyme works best is called the optimum temperature.

- beyond the optimum temperature, the rate of reaction catalysed by the enzyme decreases.

- very high temperatures alters the surface configuration of the enzyme molecule.

- when the active site changes shape, the enzyme can no longer bind with the substrate. the enzyme is then said to be denatured.

Effect of pH

- every enzyme functions best at its optimum pH.

- if the pH deviates too much from the optimum pH (either too acidic or alkaline), the presence of excess H+ or OH- ions can alter the surface configuration.

- when the active site changes shape, the enzyme cannot bind with the substrate.

Co-enzymes and Enzyme Inhibits

- co-enzymes are compounds that bind the enzyme molecule before the reaction. (example : Vitamin B complex)

- enzyme inhibitors are poisons that inhibit the enzyme from carrying out its function.

- one type of inhibitor binds with the active site and destroys the enzyme.

- another type of inhibitor compresses the enzyme molecule and changes the active site. (example : cyanide compounds)

Substrate Concentration

- under optimum conditions, as the substrate increases, the rate of reaction increases, therefore the substrate is the limiting factor.

- as the increasing substrates have no effect on the rate of reaction anymore, therefore other fators like the temperature or the amount of enzymes may be limiting factors.

Industrial Uses of enzymes

~ Biological Detergents
- they remove stains, especially coloured ones from animal or plant sources like blood and egg.

~ Food Industry
- Pectinase -> breaks down pectin which holds plant cells together, thus making it easier to squeeze out / extraction of fruit juice, and also makes the juice clear.
- Protease in baby food - partially digests proteins to polypeptides, thus helping the baby to digest and absorb the food faster.
- Isomerase - changes glucose to fructose, a much sweeter sugar.
- Amylase - converts starch into sugars (glucose).

~ Medical Industry
- Biosensors make use of enzymes to measure the blood glucose level. the gel used in the sensor contains oxidase. when the gel comes into contact with glucose, oxygen is used up in the reaction catalysed by the oxidase. the change in the oxygen level causes a current to flow which is detected by the sensor. the current is DF for DF amount of oxygen being used up, so the sensor measures the amount of glucose that is present.

~Enzymes and Germination of seeds
-the seed absorbs water and the seed swells.
- the testa becomes permeable to oxygen and carbon dioxide.
- when water enters the seed, the water will dissolve the inhibitory substances that prevents germination.
- the enzymes become active with the absorption of water.
- cotyledons produce enzymes to digest the stored food so that the growing embryo can use it.
- in endospermic seeds (example : maize grain), the enzymes flow into the endosperm to digest the food stored there.
- in non-endospermic seeds (example : sword bean seed), digestion of the stored food occurs within the cotyledons.
- in either case, the stored foods are digested and the end-product of digestion are transported to the growing points of the embryo, namely the plummule and radicle.

Enzymes that catalyse hydrolytic reactions are known as hydrolases.

Cell Division

2007-08-11T19:20:00.000-07:00

- DNA (ATGC) replicates so each chromosome becomes 2 chromatids held together.

- replication is to make an exact copy.

- chromatids split and move in opposite directions to form 2 identical daughter cells.

- mitosis brings about growth, reparation of tissue, occurs in any part of the body, and can be done by any cells (except sex cells).

- meiosis occurs only in sex cells.

- homologous chromosomes come together and then split in opposite directions to form 2 daughter cells.

- the 2 chromosomes in each chromosome of daughter cells split to form 2 cells, so a total of 4 new and non-identical cells are formed.

Diploid - double sets of chromosomes
Haploid - single set of chromosomes

Cell Organelles

2007-08-10T02:37:00.000-07:00

VACUOLES - NUCLEUS - MITOCHONDRIA - CHLOROPLASTS - GOLGI BODIES - ENDOPLASMIC RETICULUM (ER)

-vacuoles in animal cell might contain air, liquid or food particleds found in the cytoplasm. these vacuoles are small and numerous. it is large and occupies a large part of a plant cell. thevacuole usually reduces the cytoplasm to a thin lining. in every plant cell, there is usually a central vacuole filled with cell sap.

- cell sap is a liquid containing dissolved substances such as sugar and salt. the cell sap keeps the cell firm by taking in water (either by active transport or osmosis). if the cell sap loses its water, the cell will wilt.

- the nucleus controls all the chemical reactions which takes place in the cell, hence it is known as the "control centre". chromosomes are found in the nucleus.

- chromosomes are thread-like substances that store chemical instructions to build the cell, control its functions and determine its structure. chromosomes are passed down from 1 generation to another. they are responsible for inherited characteristics in the next generation.

When metabolism takes place, there is energy.

- mitochondria stores information. ther more active the cell, the more mitochondria there is.

- chloroplasts are disc-like structures containing a green substance called chlorophyll. the chlorophyll absorbs energy from the sun and makes food.

- the Golgi body is a series of tubes with double membranes. the chemical the cell produces will be passed through the Golgi body and at the end, it will be "pinched off" to form a vesicle. vesicles that contain enzymes are called lysosomes.

- endoplasmic reticulum (ER) -> smooth ER has no ribosomes, while the rough ER has ribosomes.

Most cells have special functions. They do not usually exist without a reason.

Cells = tissues = organs
BUT
Cells not = organs
LOL.

Cell theory

2007-07-24T18:39:00.000-07:00

Cell Theory
- all organisms are made at least one cell.
- the CELL is the basic unit of life.
- all cells come from pre-existing cells.
- cells carry genetic information in the form of DNA or RNA.
- these genetic information are passed down from parent cell to daugther cell.

Prokaryotic Cells
- these are cells with no nucleus.
- they have no membrane-bound organelles.
- they have cell walls. (different from plant cell walls.)
- example : red blood cells are single-celled organelles.

Eukaryotic Cells
- these are cells with a nucleus.
- there are membrance-bound organelles present.
- example : protists, fungi, plants and animals.
- only plant and fungi cell walls are different from others. (chitinous and cellulose cell walls respectively.)

Living things with just one cell are known as unicellular organisms. Most things are multicellular, that is, they are made up of more than 1 cell.

*

Pit-like structures in plant cells have 2 different names. If a pit contains enzymes, it is celled a lysosome. If it does not have enzymes, it is called a vacuole.

- cytoplasm is a jelly-like substance that contains many tiny structures. chemical reactions take place in the cytoplasm where new substances are made with energy.
- vacuoles allow support, metabolism, storage, and waste disposal. (plants only.)

Plants store their excess glucose as starch; animals store their excess glucose as glycogen in the liver and muscles.

- the cell membrane is a partially permeable layer which controls the movements of substances in and out of the cell. as it is partially permeable, it only allows certain substances to pass through, but not others as their molecular structure may be too big to pass through the cell membrane.
- the plasma membrane has 2 layer of phospholipid molecules. there are no bonds between these molecules, with protein molecules interspersed in between. phospholipid molecules are made up of fatty acid tails and polar heads. the fatty acid tails are hydrophobic (anti-water), while the polar heads are hydrophilic (pro-water). the plasma membrane gies protection, information, nutrients, and helps in waste disposal. it is made of fat, protein and phosphorus molecules.
- the cell wall is made up of a thick layer of cellulose. it supports a plant cell, gives it a regular shape, and holds it together with other plant cells.