2.1.3 Flashcards
What is a nucleotide made up of?
A pentose monosaccharide, a phosphate group, and a nitrogenous base
How are nucleotides linked together?
Condensation reactions between the phosphate group on the 5th carbon of the pentose sugar and the OH group on the third carbon of the pentose sugar.
What are the bonds between nucleotides called?
Phosphodiester bonds
Why is DNA replication semi-conservative?
Each new DNA molecule consists of one old strand of DNA and one new strand.
What happens in DNA replication?
The double helix unwinds and separate into two strands, so the hydrogen bonds holding the bases together are broken. Free nucleotides pair with the exposed complementary bases. Hydrogen bonds form. Then, the new nucleotides join to adjacent ones via phosphodiester bonds
Which enzyme is responsible for the unwinding and separating of the DNA strands?
DNA helicase
Which enzyme is responsible for the formation of phosphodiester bonds in the new strand?
DNA polymerase
In which direction does DNA polymerase move along the template strand?
From the 3’ end to the 5’ end, because DNA polymerase can only bind to the OH end
Which strand is the leading strand?
The strand that is unzipped from the 3’ end, as it can be continually replicated as the strands unzip. It undergoes continuous replication
What is discontinuous replication?
The DNA replication of the DNA strand that is unzipped from the 5’ end (lagging strand), because DNA polymerase has to wait until a section of the strand has been unzipped and then work back along the strand. This causes DNA to be produced in sections (Okazaki fragments) which need to be joined.
What are the features of DNA?
Degenerate code, non-overlapping, universal
What is a sense strand?
The sense strand is the strand of DNA that contains the code for the protein to be synthesised. It runs from 5’ to 3’
What is an antisense strand?
The antisense strand is a complimentary copy of the sense strand, and does not code for a protein
Which strand is used as the template during transcription?
The antisense strand, so that the complementary RNA strand formed carries the same base sequence as the sense strand
What happens in transcription?
Free RNA nucleotides will base pair with complementary bases on the antisense strand when the DNA unzips. RNA polymerase connects the nucleotides, forming one strand of mRNA.
