DNA replication

Question 1

What is DNA?

Answer 1

DNA is a polymer

Question 2

What does it mean by “dna is a polymer”

Answer 2

meaning it consists of repeated subunits – molecules – in this case nucleotides

Question 3

What bonds connect nucleotides together?

Answer 3

phosphodiester bonds.

Question 4

How is the DNA polymer chain formed?

Answer 4

the DNA polymer chain is formed by the sugar part of one nucleotide being covalently bonded to the phosphate group of the next nucleotide (phosphodiester bond) – and so on…

Question 5

How are dna strands held together?

Answer 5

DNA strands are held together by hydrogen bonds between the nucleotides.

These bonds are formed between the sugar and phosphate molecules of adjacent nucleotides, creating a double helix structure.

Question 6

What does DNA consist of?

Answer 6

Polymerised dNTPs

Question 7

What are the bases of DNA?

Answer 7

The bases are nitogen-containing ring compounds, either pyrimidines or purines.

Question 8

What bases are pyrimidines?

Answer 8

uracil, cytosine, thymine

Question 9

What bases are purines?

Answer 9

Adenine, guanine

Question 10

How many rings does a pyrimidine have?

Answer 10

1 ring

Question 11

How many rings does a purine have?

Answer 11

2 rings

Question 12

How are nucleotides added to a growing chain of DNA?

Answer 12

nucleotides are added on to a growing chain of DNA by the release of pyrophosphate (PPi) after the addition of a nucleotide – the remaining phosphate group then forms a phosphodiester bond.

so adjacent nucleotides on a DNA strand are joined by covalent bonds on the sugar phosphate backbone

Question 13

Adjacent nucleotides on a DNA strand are joined by…

Answer 13

covalent bonds on the sugar phosphate backbone

Question 14

What does a nucleotide consist of?

Answer 14

Base [nitrogenous]
Phosphate group
Sugar

Question 15

Nucleotides are the subunits of…

Answer 15

nucleic acids.

Question 16

What are the subunits of nucleic acids?

Answer 16

nucleotides.

Question 17

DNA is a polymer of nucleotides consisting of…

Answer 17

…adenine (A), cytosine (C), guanine (G) and thymine (T)

Question 18

How many strands in a DNA molecule?

Answer 18

DNA molecules are double-stranded

Question 19

How do the two strands in a DNA molecule pair together?

Answer 19

the two strands ‘pair’ together with complementary sequences forming the pairs

Question 20

What are the two types of groove in DNA molecule?

Answer 20

Minor groove
Major groove

Question 21

What bonds hold the bases together?

Answer 21

Hydrogen bonds

eg: hydrogen bond between G and C

Question 22

What direction does DNA run in?

Answer 22

5 prime to 3 prime

On left, 5 down to 3
On right 5 up to 3.

Question 23

In double stranded DNA, how do bases pair together?

Answer 23

in double stranded DNA A always pairs with T and C always pairs with G.

the two strands are paired because of hydrogen bonds (H bonds)

Question 24

How many hydrogen bonds between A and T?

Answer 24

2 H bonds

Question 25

In a molecule of water...

Answer 25

...an oxygen (O) atom shares electrons with 2 hydrogen (H) atoms

Question 26

Do oxygen or hydrogen atoms pull electrons toward their nucleus more strongly?

Answer 26

oxygen atoms pull electrons towards their nucleus more strongly than hydrogen atoms - more electronegative

Question 27

Oxygen atoms are more [...] than hydrogen atoms.

Answer 27

Oxygen atoms are more electronegative the hydrogen atoms.

Question 28

Due to oxygen atoms pulling electrons towards their nucleus more strongly than hydrogen atoms (being more electronegative the hydrogen), what has happened to the charge of the overall water molecule?

Answer 28

because of this the water molecule has a charge difference across the molecule

Question 29

Why is there a charge difference across water molecules?

Answer 29

Oxygen atoms more electronegative than hydrogen atoms.

Question 30

because the atoms within water molecules have a net charge difference...

Answer 30

...adjacent molecules attract one another and hydrogen bonds form between the H atom of one molecule and the O atom of an adjacent molecule - intermolecular forces

Question 31

you can think of the bonding in DNA as ...

Answer 31

...analogous to the simple case in water

Question 32

define adjacent

Answer 32

next to or near to something. eg: a neighbour.

Question 33

Where are covalent bonds located in relation to bases?

Answer 33

Covalent bonds are located between adjacent bases within a single strand in the dna molecule. Hydrogen bonds are between bases which connect the TWO strands together within dna molecule.

Question 34

What happens to electrons in covalent bonds?

Answer 34

electrons shared.

Question 35

What are the strength level of covalent bonds?

Answer 35

strong bonds.

Question 36

What are the strength level of hydrogen bonds?

Answer 36

weak bonds

Question 37

unwinding of the double helix makes...

Answer 37

...two single strands

Question 38

polymerisation depends upon...

Answer 38

...the presence of a template strand.

Question 39

What does unwinding of the dna double helix and polymerisation require?

Answer 39

requires dNTPs, a polymerase, Mg2+ and a free 3’ OH end

Question 40

For any cell to reproduce it first must?

Answer 40

copy its genetic material.

Question 41

What does the genetic material of a cell contain?

Answer 41

the genetic material contains the blueprint for making all the proteins a cell needs - without it the daughter cells cannot function

Question 42

How does dna replicate?

Answer 42

DNA replicates by copying itself – each strand of the double helix contains the information to make a duplicate strand – because DNA molecules pair by complementary base pairing. this is called semi-conservative replication

Question 43

Describe DNA polymerisation:

Answer 43

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