Degree: Molecular & Cellular Biochemistry (Masters) - Oxford, Oriel College University
|Biology||A Level||£20 /hr|
|Chemistry||A Level||£20 /hr|
|Extended Project Qualification||A Level||£20 /hr|
|Maths||A Level||£20 /hr|
|-Personal Statements-||Mentoring||£20 /hr|
|Physics (AS-LEVEL)||A-Level||A (AS-LEVEL)|
|Extended Project Qualification||A-Level||A*|
A key point to remember here is that a^x could mean the base (a) is not “e”-that special number which has a gradient function, dy/dx (the differential), EQUAL to the function itself, y=e^x. When "a" is any real number, you must treat it differently to functions with the base "e".
For the function y=a^x, the rule is simply dy/dx=a^x*lna
(^ means “to the power of”. * means “multiply”)
The proof for this requires an understanding of implicit differentiation (differentiating both x and y terms within an implicit relation).
Start with the function
ln (natural log) both sides of the equation
(the implicit part means you differentiate with respect to y but multiply by dy/dx after...)
1/y*dy/dx=lna (<----"xlna" differentiates to simply lna because a is just a constant and so lna is also just a constant)
Multiply across by y
N.B. differentiating a^(f(x)) where f(x) is a function of x requires use of the chain rule too (first set the function f(x) to another letter, say u, so you have a^u. Differentiate a^u with the above rule. Differentiate u=f(x) separately, then use chain rule).
The easiest way to visualise this is to imagine a line of four dinner ladies serving you different parts of a school meal e.g. the first peas, the second mash potatoes, the third chicken and the fourth gravy. To move to the next station you must have the preceding station’s food on your plate (e.g. you must have mash to be served chicken).You're walking down the line of dinner ladies, you have your peas and mash, but then the lady serving chicken is reallyyyyy slow-she is slowing the entire process down! However fast you collect your peas and mash, it is impossible to reduce the time it takes to reach the gravy dinner lady because it’s the chicken collection that is the slowest stage, relative to the other workers. Similarly, in a multi-stage reaction, the stages usually follow on one from the other, the finishing materials of one stage acting as the starting materials of the next. Therefore, the RATE OF THE SLOWEST STEP WILL GOVERN THE RATE OF THE ENTIRE REACTION. This is the rate determining step.
N.B. any step that occurs AFTER the rate-determining step will not affect rate. Also, by studying the order of a reaction from the rate equation, you are able to learn more about the rate-determining step (what is involved, what isn’t).see more
Firstly, there are chemical differences between the two nucleic acids. DNA has the following structural properties:
-double stranded and anti-parallel polymer held together by (relatively) weak hydrogen bonds
-strong deoxyribose sugar backbone
-consists of the four nucleobases adenine, cytosine, guanine and thymine
-many C-H bonds that improve stability
-helical ('B' form)
On the other hand, RNA (mRNA, tRNA, rRNA, snRNA etc.) has a different structure:
-single stranded polymer that is more flexible
-ribose sugar backbone
-consists of the four nucleobases adenine, guanine, cytosine and URACIL (replacing thymine)
-C-OH groups make it less stable
-helical (but 'a' form)
The structure of the two polymers determines their functions. For example, the double stranded DNA is important for the replication of genetic information and conserving it for generations to come so the process can be repeated again and again (similar to photocopying a recipe book and then storing the photocopies in a safe for future use). This is known as semi-conservative replication. Each strand (after "unzipping" the DNA by breaking the hydrogen bonds) is used as a template to synthesise a new complementary strand. The strong backbone of deoxyribose sugar protects the base sequence, preventing random mutations changing the precious genetic code of a cell. This is reinforced by strong hydrocarbon bonds which increase its stability.
In comparison, RNA is single stranded meaning it can fold in on itself and form intrastrand complementary bonds (as we see in tRNA) and hence perform catalytic functions similar to the way a tertiary protein would. This catalytic ability plays an integral role in processes such as translation, where RNA is responsible for piecing together amino acids into a polypeptide chain (this occurs at the ribosome which is made of rRNA). Similarly, siRNA molecules in the cytoplasm utilise their catalytic ability to "chop" mRNA transcribed from a gene into tiny pieces. This prevents translation taking place and hence a protein is not manufactured, silencing the gene originally transcribed. Therefore, RNA has the ability to control gene expression. Finally, in contrast to DNA, the lack of stability means that RNA serves only as an intermediate rather than a "store" of genetic information.
In conclusion, structure and function go hand in hand. The differences in structure between DNA and RNA determines the differences in their biochemical functions in the cell.see more