Response to your questions

1. Why can the enzyme lower activation energy?

3 mechanisms by which enzymes accelerate reactions:

(a) By maintaining precise substrate orientation
Suppose you were to place a handful of nuts and bolts into a bag and shake the bag for 15 minutes. It is highly unlikely that any nut will be firmly attached to the bolt at the end of 15 mins. In contrast, if you were to pick up a bolt with one hand and a nut in the other, you could rapidly guide the bolt into the nut.
Similarly, when substrate(s) are complexed with an enzyme, they are brought very closely together in the proper orientation to facilitate the reaction. (Take note the enzyme is unchanged at the end of the reaction.)

(b) Changing substrate reactivity by altering its ionic structure
Enzymes are composed of amino acids with different types of R groups. A substrate molecule bound to the surface of the enzyme are influenced by the neighbouring R groups of the enzyme. R groups with a partial positive or negative charge are capable of chemically attacking the substrate to bring about a chemical change.

In turn, this is related to Codey's question on pH and enzymes.
We learnt that different enzymes work at various optimal pH, eg. salivary amylase works best at about pH 7, pepsin in the stomach at pH 2, and so on.
Extreme pH will denature the enzyme as the ionic interactions within the tertiary structure of the enzyme are upset by the extreme pH.

(c) Exerting physical stress on bonds in the substrate to be broken
The reason a particular enzyme will combine only with one kind of substrate is that the fit between the two is very precise. In fact, the fit is so precise, the combining of the enzyme and substrate results in a slight change in the shape of both. This precise fit that modifies both original molecules is called an induced fit. This "strained" fit acts to break old chemical bonds and form new ones, resulting in the formation of the product from the substrate. Once this change has occurred, the product is released from the enzyme, and the enzyme can combine with another molecule of substrate.

2. Is it possible for the enzymes to be inactive (but not denatured)?
Yes. At low temperatures.

Experimenting with Enzymes!

Explore the following website on enzymes! Check out the various animations to help you understand enzyme actions and how enzyme activity can be affected by temperature, pH, enzyme concentration and substrate concentration.

http://www3.moe.edu.sg/edsoftware/ir/files/bio-enzymes/

Online Biology Textbook

For those of you who think you wouldn't have anything to do this coming holiday, check out the link below!

http://www.estrellamountain.edu/faculty/farabee/biobk/biobooktoc.html

Happy holidays! Stay healthy!

Genetic Engineering - Animations

Get to know the steps involved in genetic engineering:

1. Basic info:
http://www.youtube.com/watch?v=AEINuCL-5wc

2. More advanced info:
http://www.youtube.com/watch?v=acKWdNj936o&feature=related

Test yourself!

Describe the steps involved in the production of human insulin using bacteria.

The Beauty of Diffusion & Osmosis

Couple of animated websites which might be useful for your learning... Enjoy!

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

http://www.phschool.com/science/biology_place/labbench/lab1/intro.html

Structure of a DNA molecule

Take note that the basic unit of a DNA molecule is a (deoxyribo)nucleotide.

Each nucleotide consists of :

1) A sugar-phosphate group -- deoxyribose)sugar + phosphate group

--> makes up the backbone of a the DNA molecule

2) A nitrogenous base (Adenine / Thymine / Guanine / Cytosine) which encodes for genetic information.

You should be able to identify these different components in a DNA molecule.

Organisation of DNA in cells