DNA Flashcards

Question

The phosphate end is called the...

Answer 1

...5’ end.

Answer 2

...3’ end

Answer 3

The information contained in the sequence of bases is “read” starting at the 5’ end.

Answer 4

...a helical structure

Answer 5

An x shape.

Answer 6

... calculate the dimensions of DNA

Answer 7

...x ray diffraction images.

Answer 8

- The notches illustrate the distance between the different bases. - Each notch is a nucleotide/base.

Answer 9

Triple helix model states that the phosphates form the helical core, with the bases pointing outwards, which is impossible under normal conditions.

Answer 10

Linus Pauling

Answer 11

Triple helix model

Answer 12

Paulings model

Answer 13

C and G base pairs have 3 hydrogen bonds between them. Slightly stronger and more stable bonds.

Answer 14

A and T base pairs have only 2 hydrogen bonds between them.

Answer 15

DNA exists naturally with two strands that are aligned so that the bases are on the inside and the sugar-phosphate backbone is on the outside

Answer 16

The bases form pairs using hydrogen bonds to stabilise them.

Answer 17

The two strands run anti-parallel.

Answer 18

Hydrophobic base core

Answer 19

...Hydrophilic phosphate

Answer 20

...same length,

Answer 21

- DNA from any cell of all organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine.

Answer 22

a donor atom with Hydrogen covalently attached and a acceptor atom which attracts the hydrogen.

Answer 23

- O and N can have lone e- pairs that partake in H-bonding - the dipole to be from the lone pair (δ- charge) interacts with the dipole on H (δ+ charge), which forms due to the electronegative nature of O and N

Answer 24

- DNA has a helical structure. - But what is the biological reason for this? - The bases are hydrophobic – so they are repelled by water. - Within cells the DNA molecule is surrounded by water - The bases therefore try to avoid water. - if it had a ladder structure – there would be gaps where water would associate between bases - Twists allow for the removal of these spaces and brings the hydrophobic surfaces of bases close together - Bases are perpendicular to the sugar-phosphate backbone. - Resulting in bases stacking on each other.

Answer 25

Stacking contributes to stability:- * Hydrophobic effect * Base pairs attract one another through van der Waals forces.

Answer 26

Although van der Waals forces are small the overall net effect of all the atoms involved in van der Waals contacts is substantial.

Answer 27

...major and minor grooves in the dna structure.

Answer 28

- the sugar molecules attached to the glycosidic bonds are not directly opposite to each other - this results in the exposure of more of the surface of the bases at the major groove – these bases are then available for interacting with other molecules.

Answer 29

...Right-handed and the form of most DNA under physiological conditions

Answer 30

Right handed and Double-stranded RNA and some RNA-DNA hybrids

Answer 31

...Left-handed and occurs in certain GC-rich areas. - Affects which proteins can bind. e.g. some viral proteins interact with Z-form DNA

Answer 32

- In order for any cell to reproduce it first has to copy its genetic material. - DNA polymerase catalyses addition of nucleotides to a DNA strand by a condensation reaction creating the ester bond - Strands grow at the 3’ end and require a template strand - Complementary nucleotides form base pairs with bases in the template strand and are then attached to the growing chain.– (A with T and C with G)

Answer 33

- replication forks can be seen in electron micrographs of chromosomes replicating - in eukaryotes there are multiple replication forks occurring at many places on the chromosome - in prokaryotes there tends to be one origin of replication only

Answer 34

DNA is polymerised by a complex of proteins at the replication fork: 1 - DNA polymerase (catalyses the addition of bases to the 3’ end) 2 - Topoisomerase (unwinds the helix to prevent torsion) 3 - Helicase (melts the double stranded molecule) 4 - DNA primase (makes short RNA primers [gives a free 3’ end]) 5 - Single stranded binding proteins (prevents premature annealing) 6 - DNA ligase (joins Okazaki fragments on the lagging strand)

Answer 35

In order to interact with proteins such as those involved in DNA replication, the bases in the major groove form intermolecular interactions with amino acids on the surface of proteins - these can be through Van der Waals forces or H bonding.

Answer 36

1) DNA strands run anti-parallel to one another 2) The enzyme Helicase unwinds the DNA double helix by melting the molecule. 3) DNA polymerase attaches to a ‘leading’ strand 4) DNA polymerase synthesises a new DNA strand in the 5’ to 3’ direction 5) Another DNA polymerase molecule attaches to the ‘lagging’ strand 6) DNA is synthesised in the 5’ to 3’ direction 7) Helicase continues to unwind the DNA double helix 8) Continuous synthesis proceeds on the ‘leading’ strand 9) DNA polymerase detaches from the ‘lagging’ strand, and rejoins further down 10) Synthesis of DNA continues on the ‘lagging strand’ 11) DNA polymerase is unable to join up the fragments on the lagging strand 12) This is done by the enzyme Ligase which joins Okazaki fragments on the lagging strand.

DNA Flashcards

(61 cards)