DNA structure and function Flashcards
Properties of DNA
- Carries the information required to build proteins
- Can be replicated so that an exact copy is passed to the next generation
Proteins vs DNA differences
PROTEINS
- The arrangement of was changes the structure of the protein
- The function of protein is dependent on its structure
DNA
- The arrangement of nucleotides does NOT change the structure of the molecule
- The information encoded by DNA is independent of its structure
basic features of DNA
- DNA is a polymer of 4 different nucleotides (A, C, G, T)
- The order of the nucleotides determines the information encoded by DNA
- 2 complementary strands running in opposite directions
- Complimentary nature allows replication
- sugar-phosphate backbone
The sugar phosphate backbone of DNA
- Sugar in DNA is a pentose (5-C) called ribose
- Ribose can either be liner or a ring structure
- in nucleic acids, ribose occurs in it’s ring form
- The ring has 4Cs and includes one oxygen molecule
- The 5th carbon is not not part of the ring, it sticks out of the molecule.
- Each molecule is numbered from 1’ to 5’
draw ribose and deoxyribose
…..
what is phosphate ?
A molecule consisting of one atom of phosphorus and 4 atoms of oxygen
what can phosphate form bonds with ?
It can form ester bonds with the OH groups on the 5’and 3’ carbons of ribose or deoxyribose producing a diester bond. Resulting in altering sugar and phosphate subunits.
Directionality of DNA
- 5’ end has a phosphate group bound to 5’ carbon
- The 3’ end has an OH on the 3 ‘ carbon and does not have a phosphate group attached
what is a diester bond ?
ester groups are connected through a shared oxygen atom.
Properties of Pyrimidine bases (C,T,U)
- They have an aromatic ring structure
- Pyrimidine is composed of more that one atom (carbon+nitrogen atoms = heterocyclic
- Pyrimidines are known as diazenes
- ENE = 6 MEMEBER RING
- DIAZ= 2 CARBONS REPLCED BY NITROGEN
Pyramidine bases found in DNA or RNA
- They all share a common 4 carbon + 2 nitrogen ring structure
- Uracil has the simplest structure
how to make thymine and cytosine from uracil ?
- Addition of methyl group to make thymine
- Addition of an amine group to make cytosine
What kind of ring do purines have ?
They contain a pyrimidine ring but bound to a second kind of ring structure called : IMIDAZOLE.
Thus, purines have a DOUBLE RING STRUCTURE consisting of a pyrimidine bound to an imidazole
what is an IMIDAZOLE ?
A diazole: a 5 member ring containing 2 nitrogens
PURINES found in DNA and RNA
- they share a common double ring structure
- both rings have an additional amine group, their location differs in adenine and guanine
what is the same of the bond linking a base and a sugar ? and what does it mean ?
N - glycosidic bond, which means a nitrogen atom of the base is bound to the sugar
what is a nucleoside ?
a base bound to a sugar
what is a nucleotide ?
- building blocks of DNA
- a nucleoside phospahte
each nucleotide consists of 3 elements:
- A nitrogenous base
- (A,T,C,G)
- Deoxyribose
- Phosphate
What is DNA synthesised from ?
Deoxy nucleoside triphosphate (dNTPs)
what is triphosphate (e.g. dNTPs) ?
- stores a lot of energy
- hydrolysis of its bond provides energy for DNA synthesis.
Given that purines and pyrimidines have very different sizes, how is this possible?
one purine and one pyrimidine always bind together
e.g. A-T base pair is exactly equal to the size of a G-C base pair
how many H-bonds between A and T ?
2H bonds
how many H-bonds between G and C ?
3H bonds (help together more strongly)
how much nm are adjacent bases separated by ?
0.34nm
How many bases per helix turn ?
10 bases
how many nm does helix replicate ?
3.4nm
what is the diameter of the helix ?
2nm
what are the 2 grooves on the surface of the helix ?
Major and Minor
which groove do DNA binding proteins bind to and why ?
the major groove because there is more space
are bases hydrophobic or hydrophilic ?
hydrophobic
What is melting ?
When Anna strands separate for replication or transcription.
To do this H bonds must be broken
DNA melting temperature ??
92 - 95C
How do strands spontaneously re-associate ?
by lowering the temperature
which one is less stable between DNA and RNA?
RNA is less stable than DNA
