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A-level Chemistry > PL - DNA and RNA > Flashcards

PL - DNA and RNA Flashcards

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1
Q

What is DNA a polymer of?

A

Nucleotides.

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2
Q

What does DNA stand for?

A

Deoxyribonucleic acid.

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3
Q

What does DNA contain?

A

All the genetic information of an organism.

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4
Q

What is DNA made up from?

A

Lots of monomers called nucleotides.

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5
Q

What are the monomers of DNA?

A

Nucleotides.

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6
Q

What are nucleotides made from?

A

A phosphate group, a pentose sugar and a base.

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7
Q

What is a pentose sugar?

A

A five-carbon sugar.

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8
Q

What pentose sugar is found in DNA?

A

Deoxyribose.

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9
Q

How many bases in DNA are there?

A

4

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10
Q

What are the four bases in DNA?

A

Adenine (A), cytosine (C), guanine (G) and thymine (T).

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11
Q

What do nucleotides join together to form?

A

A polynucleotide chain - DNA.

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12
Q

Where does the bond form between each pair of nucleotides?

A

The phosphate group of one nucleotide and the sugar of another.

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13
Q

What do the phosphate bonds forming between the phosphate and the sugar make?

A

A phosphate-sugar backbone.

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14
Q

What holds the information in DNA?

A

The order of the bases.

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15
Q

What is RNA?

A

A polymer of nucleotides, with a series of bases attached to a phosphate-sugar backbone.

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16
Q

What pentose sugar is in RNA?

A

Ribose.

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17
Q

How are the bases different in DNA and RNA?

A

RNA has the base uracil instead of thymine.

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18
Q

What is different about DNA and RNA?

A

DNA contain the pentose sugar deoxyribose whereas RNA contains ribose (the only difference here is that ribose contains an OH group instead of just a H).

RNA has the base uracil instead of thymine.

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19
Q

Through what reaction/process do nucleotides link together?

A

Condensation polymerisation.

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20
Q

Explain how the sugar-phosphate backbone is formed by condensation polymerisation in DNA

A

1) When a phosphate and sugar react, a molecule of water is lost anda a phosphate-ester link is formed.
2) There are still -OH groups in the phosphate-ester, so further ester links can be formed. So a polymer forms made up of an alternating phosphate-sugar chain.
3) The phosphate groups always attach to the -CH2OH group and the -OH group on the adjacent carbon.
4) The reaction to make the phosphate-sugar backbone of RNA is exactly the same, expect the sugar is ribose, not deoxyribose.

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21
Q

By what reaction do DNA and RNA bases join to the sugar?

A

Via a condensation reaction.

22
Q

How do DNA and RNA bases join to the sugar?

A

All of the bases have an -NH group somewhere in their structure. It’s the N atom of the -NH groups that bonds to the sugar, eliminating an -OH group from the sugar and a H from the -NH group to form water.

23
Q

Where is the water formed from when joining bases and sugars?

A

From an -OH group from the sugar and a H from the -NH group.

24
Q

Which -OH group is always replaced by the base in the condensation reaction between a base and a sugar?

A

Always replaces the -OH group on the carbon adjacent to the -O- atom in the ring.

25
Q

What shape does DNA form?

A

A double helix.

26
Q

DNA is made up of 2…

A

…polynucleotide strands.

27
Q

How does DNA form a double helix?

A

1) DNA is made up of 2 polynucleotide strands.
2) The two strands spiral together to form a double helix structure, which is held together by hydrogen bonds between the bases.
3) Each base can only join with one particular partner - this is called specific or complementary base pairing.
4) Adenine always pairs with thymine (A-T) and guanine always pairs with cytosine (G-C).
5) The two strands of DNA are complementary - this means that they match up. So, whenever there’s an adenine base on one strand, there will be a thymine base on the other, and whenever there’s a guanine base on one strand, there will be a cytosine on the other and vice versa.

28
Q

What is the DNA double helix held together by?

A

Hydrogen bonds.

29
Q

What is specific/complementary base pairing?

A

Each base can only join with one particular partner.

30
Q

What are the complementary base pairs in DNA and RNA?

A

Adenine always pairs with thymine/uracil (A-T/A-U) and guanine always pairs with cytosine (G-C).

31
Q

What does it mean that the two polynucleotide strands in DNA are complementary?

A

It means that they match up. So, whenever there’s an adenine base on one strand, there will be a thymine base on the other, and whenever there’s a guanine base on one strand, there will be a cytosine on the other and vice versa.

32
Q

What causes the bases to form specific pairs?

A

Hydrogen bonds.

33
Q

Why does base pairing happen?

A

It happens because of the arrangement of atoms in the base molecules that are capable of forming hydrogen bonds.

A hydrogen bond forms between a hydrogen in a polar bond (H attached to anything highly electronegative like N) and a lone pair of electrons on a nearby O, N ot F atom. To bond, the two atoms have to be the right distance apart.

34
Q

Where do hydrogen bonds form in the double helix/base pairs?

A

A hydrogen bond forms between a hydrogen in a polar bond (H attached to anything highly electronegative like N) and a lone pair of electrons on a nearby O, N ot F atom. To bond, the two atoms have to be the right distance apart.

35
Q

What does there have to be for a hydrogen bond to form between the two atoms?

A

They need to be the right distance apart.

36
Q

Why do A and T join up?

A

Because they have the right atoms in the right places to each form 2 hydrogen bonds.

37
Q

Why to C and G join up?

A

Because they have the right atoms in the right places to each form 3 hydrogen bonds.

38
Q

How many hydrogen bonds do A and T form?

A

2

39
Q

How many hydrogen bonds do C and G form?

A

3

40
Q

Why are A and T and then C and G the only possible base pair combinations?

A

Because other base pairings would put the partially charged atoms too close together (they’d repel each other), or too far apart. In others, the bonding atoms just wouldn’t line up properly.

41
Q

Why does the DNA double helix have to twist?

A

So that the bases are in the right alignment and at the right distance apart for the complementary base pairs to form.

42
Q

How many strands are there in RNA?

A

1 but occasionally the bases in separate strands pair up and form hydrogen bonds with each other. When this happens, G always pairs with C, and A always pairs with U (RNA doesn’t have any T bases).

43
Q

Explain the process of base pairing as a result of hydrogen bonding

A

1) A and T have the right atoms - in the right places - to each form 2 hydrogen bonds. This allows them to pair up. G and C can each form 3 hydrogen bonds, so they pair up as well.
2) These are the only possible base pair combinations. Other base pairings would put the partially charged atoms too close together (they’d repel each other), or too far apart. In others, the bonding atoms just wouldn’t line up properly.
3) The DNA double helix has to twist so that the bases are in the right alignment and at the right distance apart for the complementary base pairs to form.

44
Q

Through what process does DNA copy itself?

A

Self-replication (semi-conservative replication).

45
Q

What is cell division essential for?

A

Growth and reproduction.

46
Q

What has to happen before cells divide?

A

They have to be able to copy their genetic information.

47
Q

How does DNA copy itself?

Explain the process

A

1) The hydrogen bonds break and the DNA double helix starts to split into two single strands - a bit like a zip.
2) Bases on free-floating nucleotides in the cytoplasm (the part of the cell outside of the nucleus) now pair up with the complementary bases on the nucleotides in the DNA. Complementary base pairing makes sure the correct nucleotide joins in the correct place.
3) An enzyme called DNA polymerase joins the new nucleotides together to form a polynucleotide chain.
4) This happens on each of the strands to make an exact copy of what was on the other strand. The result is two molecules of DNA, identical to the original molecule of DNA.

48
Q

What enzyme joins the new nucleotides together during its replication?

A

DNA polymerase.

49
Q

What does DNA polymerase do?

A

It is an enzyme that joins the new nucleotides together during its replication.

50
Q

What is DNA polymerase?

A

It joins the new nucleotides together during its replication.

51
Q

After the DNA has replicated itself, what do each of the new DNA molecules contain?

A

One parent strand/original strand and one new strand.

A-level Chemistry (51 decks)

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