Biochem DNA --> Protein Flashcards
What is a nucleoside?
A nucleotide base and a sugar (ribose in RNA, deoxyribose in DNA)
eg. adenosine, cytidine, guanosine, thymidine and uridine
What is a neucleotide?
A nucleotide base, a sugar and a phosphate group
What are purines?
Neucleotide bases A and G. Double ring bases
What are pyrimidines?
Nucleotide bases T + C + U. Single ring bases
What are the DNA building blocks?
dATP, dCTP, dGTP and dTTP
deoxyadenosine triphosphate
What are the RNA building blocks?
ATP, CTP, GTP and UTP
adensine triphosphate
What is polymerisation of DNA building blocks?
When a phosphodiester bond is formed between a free 3’OH group and a 5’triphosphate. Consumes 2 high energy bonds as the pyrophosphate ion bonds are hydrolysed.
Nucleic acids have direction. Which end are nucleotides added too and which direction is the sequence read?
New nucleotides are added to free 3’ ends
Sequence is read 5’-3’
AZT (ZDV) is an antireteroviral drug. How does it work?
Analogue of thymidine and is incorporated into viral DNA but it has no 3’ OH group meaning their is no chain elongation.
Works as a viral reverse transcriptase and has a high affinity for ZDV than human DNA polymerases
The DNA double helix is antiparalel. What does this mean?
2 nuceotide strands- one 5’-3’ and one 3’-5’.
How many hydrogen bonds between AT and CG?
AT = 2 CG = 3
When is DNA replicated?
Before cell division
How is DNA replicated?
Semi conservative replication
Which enzyme unzips DNA and also prevents rewinding?
DNA helicase
Which enzyme catalyses the addition of nucleotide to a single strand of DNA in replication?
DNA polymerase
Can DNA polymerase begin a new single strand of DNA?
What is needed to initiate replication?
No- it can only add to existing strands.
RNA primer is needed to start DNA replication
How many origins of replication in eukaryotes and prokaryotes?
Eukaryotes = many Prokaryotes = one
Why is having many origins of replication beneficial for eukaryotes?
Ensures replication can be finished in a reasonable length of time.
Replication starts simultaneously at several points on the genome and is bidirectional forming a DNA bubble with 4 sites for DNA polymerase
DNA replication is discontinuous. What is meant by this?
Neucleotides can only be added to a 3’ end.
Generates a leading strand- always has a free 3’ end and a lagging strand which is replicated in short segments
How is the lagging strand replicated in DNA replication?
OKAZAKI fragments. RNA primers are needed and the gaps between okazaki fragments are joined by DNA ligases
What synthesises RNA primers?
DNA primase
What joins the gaps between okazaki fragments?
DNA ligase
How frequently does a mutation in DNA replication occur and how is this reduced?
10^4-10^5 base pairs
DNA polymerase has 3’–>5’ endonuclease activity and removes incorrect nucleotides by back tracking
Reduces error rate to 10^9-10^10 base pairs.
Other repair systems = nucleotide incision repair
What are the 3 main classes of RNA?
1) Ribosomal RNA (rRNA) 80%
2) Transfer RNA (tRNA) 15%
3) Messenger RNA (mRNA) 5%