DNA and RNA Flashcards
what is a Pyrimidine
nitrogen containing single ring compound (6 membered) that occurs in nucleic acids.
How are nucleotides joined?
How are nucleotides joined?
DNA and RNA are what?
long nucleic chains forms of nucleotides (polynucleotides)
each strand of double helix is oreinated what?
in the opp direction
describe the opp ends of the double helix
5’ end contains a free polar phosphate group
3’ end contains a free polar hydroxyl group OH
where does the syntehsis of nucleic acid chain take place>
from 5’ to 3‘
how does the dna grow
The ‘bottom’ of the nucleic acid (3’ end)’s OH group is ‘attacked from below’ by the PO4 linked to 5’ end of a free nucleotide, which then adds onto the chain -‘extended bottom end’
is the backbone of the DNA HYDROPHILLIC
yes -sugar-phosphate backbone of DNA is polar
Hydrostatic Interactions in DNA
polar backbone of DNA likes water, while the non-polar bases don’t. This creates a stable structure where the hydrophobic bases are tucked away inside the DNA molecule, held together by the pressure created by their aversion to water.
a nucleic acid chain IS CALLED WHAT?
strand
Nucleic acid structure
length of a nucleic acid chain is measured by the number of bases it contains.
In double-stranded nucleic acids, the bases are paired between the two strands, and the length is often expressed in base pairs
Nucleic acid secondary structure:
DNA double helix
The two strands are “antiparallel“, i.e. one strand runs 5′ to 3′ while the other runs 3′ to 5′
hydrogen bonding in DNA double helix
the purine or pyrimidine base attached to each deoxyribose sugar points inward towards the axis of the helix.
Each base pairs up with its complementary base on the opposite strand through hydrogen bonding, forming base pairs, also known as nucleotide pairs.
RNA
tertiary structure is similar to DNA,
Single stranded but usually forms intra-molecular base pairs
Uracil instead of thymine
what are the 3 forms of RNA
MRNA-found in the nucleus and transfers genetic information to the ribosome for protein synthesis
RRNA- found in the cytoplasm and important structural component of ribosomes
TRNA- . transfers AA’s to ribosome
DNA replication?
-During nuclear division the two strands of the DNA double helix separate through the action of the enzyme DNA helicase
-Each DNA strand direct the synthesis of a complementary DNA strand through specific base pairing
-Resulting in two daughter DNA duplexes that are identical to the original parent molecule
why is dna described as semi conservative
only one strand of each resultant daughter molecule is newly synthesized.
DNA replication - requirements
Template strand of single-stranded DNA
‘Building blocks’ of DNA – nucleotides
how do we unwind the DNA
Helicase unwinds DNA double helix so that the single DNA strands are available to be templates for synthesizing new DNA strands
Describe DNA helicase
an ATP dependent catalytic enzyme
what happesn when the dna has been unwinded?
The two unwound DNA strands then each serve asa template for DNA polymerase to make complementary DNA strands
-using the four deoxynucleoside triphosphates
four deoxynucleoside triphosphates
(dATP, dCTP, dGTP, and dTTP).
Direction of replication
New nucleotides are only added to the 3’ end of a growing strand
The replication is in a 5’ to 3’ direction
Forming bifurcated Y-shaped structures known as replication forks
where is dna replication iniated?
ORIGINS OF REPLICATION
what is the leading strand
When DNA is being replicated, one of the two strands serves as a template for continuous synthesis.
the leading strand and dna polymerase
the DNA polymerase enzyme can move along this template strand in the 3’ to 5’ direction, adding nucleotides in the 5’ to 3’ direction. As a result, the new complementary strand is synthesized continuously in the same direction as the movement of the replication fork.
what is the lagging strand?
the one that doesnt act as a template
what happens to the lagging strand in dna replication?
replicated discontinuously.
This is because the DNA polymerase enzyme can only add nucleotides in the 5’ to 3’ direction. However, the lagging strand template is oriented in the 3’ to 5’ direction.
how does the dna not get repliocated discounitsly?
lagging strand is synthesized in short, separate fragments known as Okazaki fragments. These fragments are later joined together by an enzyme called DNA ligase to form a continuous complementary strand.
dna replication summarised easily?
during DNA replication, one strand is copied continuously from start to finish (leading strand), while the other strand is copied in short segments (Okazaki fragments) because of its opposite orientation
Joining of Okazaki fragments
Fragments are joined by the enzyme DNA ligase.
