The chemistry of life (3)
28/05/2012 08:31:00
3.5.1 Compare the structure of RNA and DNA.
DNA and RNA both consist of nucleotides, which contain a sugar, a base and a
phosphate group. However there are a few differences. Firstly, DNA is composed of
a double strand forming a helix whereas RNA is only composed of one strand. Also
the sugar in DNA is deoxyribose whereas in RNA it is ribose. Finally, both DNA and
RNA have the bases adenine, guanine and cytosine. However DNA also contains
thymine, which is replaced by uracil in RNA.
3.5.2 Outline DNA transcription in terms of the formation of an RNA strand
complementary to the DNA strand by RNA polymerase.
DNA transcription is the formation of an RNA strand, which is complementary to the
DNA strand. The first stage of transcription is the splitting up of the DNA double
helix. Then, the free RNA nucleotides start to form an RNA strand by using one of
the DNA strands as a template. This is done through complementary base pairing,
however in the RNA chain, the base thymine is replaced by uracil. RNA polymerase
is the enzyme used in the formation of the RNA strand and the splitting up of the
double helix. The RNA strand then becomes longer and then separates from the
DNA template. The DNA strands then reform a double helix. The strand of RNA
formed is called messenger RNA.
3.5.3 Describe the genetic code in terms of codons composed of triplets of
bases.
A triplet of bases (3 bases) forms a codon. Each codon codes for a particular amino
acid. Amino acids in turn link to form proteins. Therefore DNA and RNA regulate
protein synthesis. The genetic code is the codons within DNA and RNA, composed
of triplets of bases that eventually lead to protein synthesis.
3.5.4 Explain the process of translation, leading to polypeptide formation.
Translation is the process through which proteins are synthesized. It uses
ribosomes, messenger RNA which is made up of codons and transfer RNA that has
a triplet of bases called the anticodon. The first stage of translation is the joining of
messenger RNA to the small subunit of the ribosome. The transfer RNA’s have a
specific amino acid attached to them that links to their anticodons. A transfer RNA
molecule will join to the ribosome however its anticodon must match the codon on
the messenger RNA. This is done through complementary base pairing. These two
form a hydrogen bond together. Another transfer RNA molecule then bonds. Two
transfer RNA molecules can bind at once. Then the two amino acids on the two
transfer RNA molecules form a peptide bond. The first transfer RNA then separates
from the ribosome and the second one takes it’s place. The ribosome moves along
the messenger RNA to the next codon so that another transfer RNA can bind. Again,
a peptide bond is formed between the amino acids and this process continues. This
forms a polypeptide chain and is the basis of protein synthesis.
3.5.5 Discuss the relationship between one gene and one polypeptide.
A polypeptide is formed by amino acids liking together through peptide bonds. There
are 20 different amino acids so wide ranges of polypeptides are possible. Genes
store the information required for making polypeptides. The information is stored in a
coded form by the use of triplets of bases that form codons. The sequence of bases
in a gene codes for the sequence of amino acids in a polypeptide. The information in
the genes is decoded during transcription and translation leading to protein
synthesis.
5/28/2012 8:31:00 AM
3.6.1 Define enzyme and active site.
Enzymes: Globular proteins which act as catalysts of chemical reactions. Active
site: Region on the surface of an enzyme to which substrates bind and which
catalyses a chemical reaction involving the substrates.
3.6.2 Explain enzyme–substrate specificity.
The active site of an enzyme is very specific to its substrates as it has a very precise
shape. This results in enzymes being able to catalyze only certain reactions as only
a small number of substrates fit in the active site. This is called enzyme-substrate
specificity. For a substrate to bind to the active site of an enzyme it must fit in the
active site and be chemically attracted to it. This makes the enzyme very specific to
it’s substrate. The enzyme-substrate complex can be compared to a lock and key,
where the enzyme is the lock and the substrate is the key.
3.6.3 Explain the effects of temperature, pH and substrate concentration on
enzyme activity.
Temperature as both positive and negative sides to enzyme activity. When the
temperature rises, the speed of reaction increases, bcause heat make shte particles
move faster, so there is more collision between the walls therefore the speed of
reaction increases, however when the temperatures rise too high, the enzymes may
denature and then they will not do the job anymore. The enzymre denature because
the high temperatures make the molecule vibrate and split up, so they stop
functioning.
Enzymes usually have an optimum pH level where the best work at, if the pH goes
beyond that, then the enzymes aren’t going to work at their best and most
efficient.
An increase in substrate concentration causes the rate of reactiong to increase
because the enzymes can work on more substrate. However if all active sites re
taken, the enzymes will not be enough, so as long as there are active sites, more
substrate will increase the rate of reaction.
5/28/2012 8:31:00 AM