Unit 1: Nucleic Acids Flashcards
what is a nucleic acid made up of?
nucleotides
what are the differences between DNA and RNA
DNA - double stranded, deoxyribose sugar, bases A,T,C,G
RNA - single stranded, ribose sugar, bases A,U,C,G
Why are hydrogen bonds important in base pairing?
A hydrogen bond is weak, this means that its relatively easy for these bonds to be formed and broken. This is very important if information is to be copied from a sequence of bases as in during DNA replication
what is a nucleotide made up of?
nitrogen containing ring (base)
five carbon sugar (pentose)
phosphate
what is attached to C1 in a nucleotide?
base
what is attached to C2 in a nucleotide?
Hydrogen or Hydroxyl group
what is attached to C3 in a nucleotide?
hydroxyl group
what is attached to C5 in a nucleotide?
phosphate
what are the two main types of bases called?
purines and pyrimidines
what is a purine?
base that has a double ring structure - adenine and guanine
what is a pyrimidine?
base that has a single ring structure - cytosine and thymine/uracil
what is the trick to remember Purine and Pyrimidine?
Pure Agony
what bond holds complementary base pairs together?
weak hydrogen bonds
For the hydrogen bond to be stable, what must each base be?
the base pair must consist of one purine and one pyrimidine
how are nucleotides joined together?
by condensation reaction between phosphate of one nucleotide and the hydroxyl group on the sugar of the next nucleotide. link by 5’ to 3’
what is the bond between nucleotides called?
phosphodiester bond
are the double strands in DNA, parallel or antiparallel?
antiparallel
what is polymerase?
an enzyme capable of adding nucleotides to a DNA strand during replication or an RNA strand during transcription
what is ligase?
an enzyme that catalyses the formation of phosphodiester bonds to join nucleotides together.
what is the purpose of copying DNA?
for DNA replication during the S phase of the cell cycle
for transcription of DNA and RNA during protein synthesis
what is the difference between replication and transcription?
new strand of nucleic acid can only happen in 5’ to 3’ direction because of the polymerase enzyme, so can only add on 3’
RNA - one strand
DNA - double strand so 5’ to 3’ and 3’ to 5’ need to be replicated
what are the requirements for DNA replication?
DNA template
enzymes
four types of nucleotide
ATP
DNA polymerase and RNA polymerase can only build in a what direction?
5’ to 3’
What are the steps in DNA replication?
- Enzymes open up a replication fork in the DNA double helix
- the leading strand is synthesised complete in the 5’ to 3’ direction
- replication starts with a short RNA primer, this is replaced with DNA later
- DNA polymerase adds a new nucleotide to the 3’ end of the primer and so starts to build the new DNA chain
- DNA polymerase matches free DNA nucleotides to their complementary bases on the template strand of DNA and then catalyses the formation of the phosphodiester bond between the end of the growing strand and the nucleotides
- The phosphodiester bond is formed when the OH of the 5’ phosphate and the OH of the 3’ deoxyribose are involved in a condensation reaction
- The other strand is called a lagging strand and is made in short 5’ to 3’ fragments (okazaki fragments)
- as on the leading strand, the RNA primers are made first and DNA polymerase adds nucleotides to the 3’ end.
- After the RNA primer has been replaced with DNA, DNA ligase links to 5’ to 3’ fragments of the lagging strand together and catalyses the formation of phosphodiester bonds between the nucleotides at the end of the fragments.
