Summary
Summary of Nucleic Acids
- Course
- Biochemistry (MCB2021F)
- Institution
- University Of Cape Town (UCT)
Notes are the summary of the Nucleic Acids lecture series for MCB2021F
[Show more]
Seller
Follow
Content preview
Nucleic Acids:Information transfer in cells-
- Replication – DNA replication yields two DNA molecules that are identical to the
original one, ensuring transmission of genetic information to daughter cells with
exceptional fidelity
- Transcription – sequence of bases in DNA is recorded as a sequence of
complementary bases in a single-stranded mRNA molecule
- Translation – three-base codons on the mRNA corresponding to specific amino acids
direct the sequence of building a protein. Codons recognized by the tRNA carrying
the appropriate amino acids. Ribosomes are the ‘machinery’ for the protein
synthesis
Information transfer system is encapsulated in the dogma: DNA à RNA à Protein.
There are two basic kinds of nucleic acids:
1. Deoxyribonucleic acid (DNA) – repository of genetic information in cells
2. Ribonucleic acid (RNA) – serves in the expression of this information through
transcription and translation.
Nucleic acids are polymers of nucleotides, DNA has several hundred million nucleotides and
RNA has between 100 and 1000 nucleotides.
Structure of nucleotides:
nucleotides have a nitrogenous base, a 5-carbon sugar
(ribose) and a phosphate which makes up the principle
components of the structure.
Nitrogenous bases – Adenine, Thymine, Cytosine and Guanine and Uracil.
They are aromatic, hydrophobic nitrogenous
bases – two types: pyrimidine and purine
Pyrimidine bases – are a six membered ring,
that has 6 atoms and 2 nitrogen atoms.
Purine bases – are 2 rings (pyrimidine and
imidazole), that has 9 atoms and 4 nitrogen
atoms.
Common pyrimidine bases:
In their tautomeric form at pH include à Cytosine (pyrimidine), Uracil (pyrimidine),
Thymine (pyrimidine), Adenine (purine) and Guanine (purine).
,Properties of Pyrimidines and Purines
1. Acid/base dissociations – acid dissociation constant (pKa)
2. Keto-enol tautomerism
3. Strong absorbance of UV light
Acid-dissociation constant (Ka):
Acid-dissociation constant (Ka) is a quantitative measure of strength
of an acid in solution
Ka= equilibrium constant for a chemical reaction known as
dissociation in the context of acid-base reactions
In aqueous solutions, the equilibrium of acid dissociation can be
written as
HA + H2O ß à A- + H3O+
HA is a generic acid that dissociates into A- (conjugate base of acid)
and a hydrogen ion which combines with a water molecule to make a
hydronium ion
The dissociation constant is usually written
Ka = [A-][H3O+] / [HA][H2O]
Ka = [A-][H3O+] / [HA] water has a concentration of 1 so its negligible)
pKa = -log10Ka
The larger the value of pKa, the smaller the extent of dissociation at
any given pH.
Henderson-Hasselbalch equation:
The pH of a solution can be calculated, provided Ka and the concentration of the weak acid
(HA) and its conjugate base (A-) are known
When [HA] = [A-] then the pH = pKa
pH = pKa + log10 [A-]/ [HA]
pH and pKa:
The titration curves of several weak electrolytes: acetic acid,
imidazole and ammonium.
The shape of these curves is identical, only their position along
the pH scale is displaced, in accordance with their respective
affinities for H+ ion, as reflected in their differing pKa values
If the pH is higher than the pKa then the compound will be
deprotonated.
If the pH is lower than the pKa then the compound will be
protonated.
, The Keto/enol tautomerism of Uracil:
Keto and enol forms occur
pH = 7
based on changes in pH that are
relative to pKa (the affinity of
nitrogen bases for a hydrogen
ion).
The keto and enol are in
Keto Enol
equilibrium, at pH 7, keto
dominates (neutral pH of cell).
To lose protons and get to enol form, the pH of solution needs to be higher than pKa
pKa values specify whether the protons are associated with the ring nitrogen’s at neutral
pH, they determine whether these nitrogen’s serve as a H donor or acceptors during
hydrogen bonding between bases.
Keto/enol isomerism of Guanine:
UV absorption of nucleotide bases:
- Aromatic rings of the bases are made up of alternating single
and double bonds, these systems can absorb in the UV
spectrum
- Each of the bases absorb UV light at around 260nm
- Each of the four nucleotide bases has a slightly different
absorption spectrum and the spectrum of DNA is the
average of them
- Pure DNA solution appears transparent to the eye and
absorption doesn’t become measurable until 320 nm, ultra
violet region falls in the range of 190 – 380nm and visible
region falls between 380 – 750nm.
- Absorption peaks around 260 nm and then dips between
220-230 nm, the solution becomes essentially opaque in the far UV range
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through EFT, credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying this summary from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller calrosewitz. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy this summary for R200,00. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
68175 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy summaries for 15 years now