2 - Nucleotides Nucleic Acids Flashcards
What are the building blocks of nucleic acids
Nucleotides / nucleosides p
Carboxyl group
C=O with a -OH attached to the C
Which of the following is NOT a component of a nucleotide? A. A purine or pyrimidine base B. A carboxyl group C. A pentose sugar D. A phosphate group
B
Types of bases
Purines: (6 membered ring)
- Adenine
- Guanine
Pyrimidines: (6 + 5 membered rings)
- cytosine
- thymine
- urical
Properties of bases
- hydrophobic sides where VDW interactions occur bw them
- non polar
- lots of electron delolization
- tautomers (movement of atoms…not electrons=resonance)
- very planar and rigid = very little bond rotation
Why do bases absorb light
- Average in nucleic acid (GATC) = peak at 260nm Electrons are excitable and absorb UV light.
- each base is chemically diff = diff peaks.
- G,T,A, and C all have an average in a nucleus acid peak at around 260 nm ~ maximum.
G = 2 peaks (220 - 300nm)
A = 1 peak (260nm)
T = 1 peak ( 260nm)
C = 1 peak after a huge dip (260nm)
• Average in nucleic acid (GATC) = peak at 260nm
What Elise absorbs light?
Free bases, nucleotides, and nucleic acids = 1.9
Relation bw absorbances and concetration.
Linear, hence the ratio = abs/conc
If A260 nm 1.000 is a concentration of 50 g/mL DNA, what is the concentration of a sample with A260 nm = 0.200? A. 0.1 g/mL B. 0.2 g/mL C. 2 g/mL D. 10 g/mL E. 20 g/mL
D
You purify DNA from cells. The measured A260:A280 ratio in your sample is 1.4
What might this mean?
A. Your sample contains protein.
B. Your sample contains RNA.
C. Your sample contains free nucleotides.
D. It’s time to go home.
A
Ratio of 1.9 is
Ideal
&
The standard for bases, nucleotides and coeliac acids, anything lower than that means its contaminated with proteins that have a lower ratio.
DNA ands RNA ratio?
It’s identical = 1.9
They absorb light the same
SS DNA and DS DNA difference in absorbing light
Single stranded has a higher ratio then double stranded DNA
Both have higher then protiens (1.4)
If the abs. Ratio increases OVER 1.9, then?
Then it could be due to a single stranded DNA or nucleotide available
Bonds bases form
H-bonds between their hydrophilic side groups (like amine or carboxyl)
How many H bonds possible?
Count the:
- # of side groups
- # of atoms on the base that can H-bond
- # of H bonds possible max theoretical
O = 2 h bond acceptors N = 1 donor H = 1 donor
Pentose
Ribose sugar = m5 membered with one O in the ring.
- base attaches to C1 = N-beta-glycosyl bond
- phosphate attaches at C5 = phosphoester bond
- 2 forms = deoxyribose and ribose
Difference bw ribose and deoxyribose?
Deoxyribose:
- had H and H on C2’
- DNA
- beta conformation
Ribose:
- H and OH on C2
- RNA
- beta conformation
What are the 2 conformations of ribose
Beta and alpha
Beta: where base is Up conformation = always in nucleotides and nucleic acids
Alpha: down conformation = not in either of them
Base attaches to C1 through…
Prymidine = N1 (CTU)
Purine = N9 (AG)
Phosphate is connected to C5 through a
phosphoester bond (covalent) (POC or COP)
Within tetra and tri phosphates what other bond exists?
A phosphoanhydride bond (POP) (covalent)
Nucleotisde is diff form nucleotide in that it has
- no phosphate
- all H atoms by O at C5
A triphosphate has how mnay of what bonds?
1 phosphoester and 2 phosphoanhydride
Naming nucleosides of DNA and RNA
Deoxadosine 5’ ____phosphate (d_MP)
Adenosine 5’ ___phispnhate
A thymine attached to a ribose is called a
Ribothymidine
When a base is attached to a ribose only
It’s ribobase(idine)
Whihc base is rarely in RNA
Thymidine
Primary strcure for nucleic acids
Sequences of nucleotides joined by phosphodiester bonds
(COPOC)
- Monomers joined by covalent bonds
Phosphodiester bond
COPOC
Primary structure of RNA and DNA
DNA: ATCG
RNA: AUCG