Nucleic Acids Flashcards
Why do we crush the strawberries when purifying DNA?
To damage the cell wall, so we can access the components of the cell within
Why do we mix the sample with detergent?
To break the phospholipid bilayer in the cell membrane
Why do we add protease enzyme when purifying DNA?
To break down the histone proteins that are associated with DNA
Why do we add ethanol to the mixture when purifying DNA?
Ethanol is what actually causes the DNA to precipitate out of the solution
Why should the ethanol be cold?
Why should it be added AFTER the protease enzyme is added?
- so it doesn’t damage the DNA molecules
- so it doesn’t slow down the enzymes action
Why do we add salt when purifying DNA?
Salt acidifies the sugar phosphate backbone and breaks the hydrogen bonds holding the structure together
What are nucleotides?
the monomers of DNA
what are the four nucleotides?
adenine, thymine, cytosine, guanine
what base is different in RNA?
URACIL instead of thymine
differences between purines and pyrimidines?
purines bigger, double carbon ring structure.
pyrimidines smaller, single carbon ring structure.
name the purine bases
adenine and guanine
name the pyrimidine bases
cytosine and thymine
name the complementary bases and how many bonds and which bonds they make
adenine and thymine- 2 hydrogen bonds
cytosine and guanine- 3 hydrogen bonds
why is DNA described as anti parallel?
the strands run in opposite directions to each other
which is the 3 prime end (3’)
one that ends with a hydroxyl group
which one is the 5 prime end (5’)
one that ends with a phosphate group
how many strands in a DNA molecule?
2
the distance between the strands is always ___________ because there is an ____________ of complementary bases.
equidistant, equal number
differences between RNA and DNA
- RNA has 1 strand , DNA has 2
- DNA has A,T,C,G and RNA has A,U,C,G
- RNA is much smaller
- RNA has ribose as pentose sugar, DNA has deoxyribose.
similarity between RNA and DNA
RNA uracil still forms 2 hydrogen bonds with adenine.
how are DNA polynucleotides formed? and where?
condensation reaction to form phosphodiester bonds between the hydroxyl group on the 3 carbon on one nucleotide and phosphate group on carbon 5 on the next nucleotide.
what does DNA nucleotide consist of?
- pentose sugar deoxyribose
- phosphate group PO4-2
- nitrogenous base (A,T,C,G)
what happens to RNA after protein synthesis?
they are degraded in the cytoplasm and the phosphodiester bonds are hydrolysed, and nucleotides are released and recycled.
what is DNA replication?
the process where one DNA molecule is replicated to produce two identical DNA molecules
role of DNA helicase in DNA replication
DNA helicase= hydrolysed the hydrogen bonds between the bases causing the DNA strands to separate
role of DNA polymerase in DNA replication
DNA polymerase= joins the sugar phosphate backbone by creating phosphodiester bonds between the new nucleotides in the middle
role of DNA ligase in DNA replication
DNA ligase= joins the okazaki fragments?.?.??????
describe continuous and discontinuous DNA replication
when DNA polymerase travels only in the 3’ to 5’ direction and joins the nucleotides ini the leading strands then travels back and joins the nucleotides on the lagging strand in okazaki fragments
what is the leading and lagging strand?
When replication begins, the two parent DNA strands are separated. One of these is called the leading strand, and it is replicated continuously in the 3’ to 5’ direction. The other strand is the lagging strand, and it is replicated discontinuously in short sections called okazaki fragments.
what are okasaki fragments?
Okazaki fragments are short sequences of DNA nucleotides which are synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication.
what is meant by DNA replication being semi-conservative?
- one strand from original DNA and one strand is newly formed
- one of the strands acts as a template for the replication
what is the triplet code?
the three bases which are a codon
what is a codon?
three bases which code for one amino acid
why is the genetic code universal?
all organisms use this code although the sequence of bases will be different
what are stop and start codons? what do they do? how are they useful?
these are codons that are either at the start or end of a sequence and the start codon ensures that the DNA is read in ‘frame’ e.g. it is read from base 1 and not 2/3.
the 3 stop codons signal the end of the sequence
why is the genetic code non-overlapping?
one base does not form more than one codon, so having a start codon means that one base won’t be part of more than one codon
what is the genetic code degenerate?
more than one codon codes for one amino acid, 64 codons and only 20 amino acids.
