Nucleic Acids

Question 1

Why do we crush the strawberries when purifying DNA?

Answer 1

To damage the cell wall, so we can access the components of the cell within

Question 2

Why do we mix the sample with detergent?

Answer 2

To break the phospholipid bilayer in the cell membrane

Question 4

Why do we add protease enzyme when purifying DNA?

Answer 4

To break down the histone proteins that are associated with DNA

Question 5

Why do we add ethanol to the mixture when purifying DNA?

Answer 5

Ethanol is what actually causes the DNA to precipitate out of the solution

Question 6

Why should the ethanol be cold?

Why should it be added AFTER the protease enzyme is added?

Answer 6

• so it doesn’t damage the DNA molecules

- so it doesn’t slow down the enzymes action

Question 8

Why do we add salt when purifying DNA?

Answer 8

Salt acidifies the sugar phosphate backbone and breaks the hydrogen bonds holding the structure together

Question 9

What are nucleotides?

Answer 9

the monomers of DNA

Question 10

what are the four nucleotides?

Answer 10

adenine, thymine, cytosine, guanine

Question 11

what base is different in RNA?

Answer 11

URACIL instead of thymine

Question 12

differences between purines and pyrimidines?

Answer 12

purines bigger, double carbon ring structure.

pyrimidines smaller, single carbon ring structure.

Question 13

name the purine bases

Answer 13

adenine and guanine

Question 14

name the pyrimidine bases

Answer 14

cytosine and thymine

Question 15

name the complementary bases and how many bonds and which bonds they make

Answer 15

adenine and thymine- 2 hydrogen bonds

cytosine and guanine- 3 hydrogen bonds

Question 16

why is DNA described as anti parallel?

Answer 16

the strands run in opposite directions to each other

Question 17

which is the 3 prime end (3’)

Answer 17

one that ends with a hydroxyl group

Question 18

which one is the 5 prime end (5’)

Answer 18

one that ends with a phosphate group

Question 19

how many strands in a DNA molecule?

Answer 19

2

Question 20

the distance between the strands is always ___________ because there is an ____________ of complementary bases.

Answer 20

equidistant, equal number

Question 21

differences between RNA and DNA

Answer 21

• 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.

Question 22

similarity between RNA and DNA

Answer 22

RNA uracil still forms 2 hydrogen bonds with adenine.

Question 23

how are DNA polynucleotides formed? and where?

Answer 23

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.

Question 24

what does DNA nucleotide consist of?

Answer 24

• pentose sugar deoxyribose
• phosphate group PO4-2
• nitrogenous base (A,T,C,G)

Question 25

what happens to RNA after protein synthesis?

Answer 25

they are degraded in the cytoplasm and the phosphodiester bonds are hydrolysed, and nucleotides are released and recycled.

Question 26

what is DNA replication?

Answer 26

the process where one DNA molecule is replicated to produce two identical DNA molecules

Question 27

role of DNA helicase in DNA replication

Answer 27

DNA helicase= hydrolysed the hydrogen bonds between the bases causing the DNA strands to separate

Question 28

role of DNA polymerase in DNA replication

Answer 28

DNA polymerase= joins the sugar phosphate backbone by creating phosphodiester bonds between the new nucleotides in the middle

Question 29

role of DNA ligase in DNA replication

Answer 29

DNA ligase= joins the okazaki fragments?.?.??????

Question 30

describe continuous and discontinuous DNA replication

Answer 30

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

Question 31

what is the leading and lagging strand?

Answer 31

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.

Question 32

what are okasaki fragments?

Answer 32

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.

Question 33

what is meant by DNA replication being semi-conservative?

Answer 33

• one strand from original DNA and one strand is newly formed
• one of the strands acts as a template for the replication

Question 34

what is the triplet code?

Answer 34

the three bases which are a codon

Question 35

what is a codon?

Answer 35

three bases which code for one amino acid

Question 36

why is the genetic code universal?

Answer 36

all organisms use this code although the sequence of bases will be different

Question 37

what are stop and start codons? what do they do? how are they useful?

Answer 37

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

Question 38

why is the genetic code non-overlapping?

Answer 38

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

Question 39

what is the genetic code degenerate?

Answer 39

more than one codon codes for one amino acid, 64 codons and only 20 amino acids.