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AQA-A level Biology-revision cards > Topic 1 - Year 1 - Biological Molecules - DNA and RNA > Flashcards

Topic 1 - Year 1 - Biological Molecules - DNA and RNA Flashcards

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1
Q

What are DNA and RNA ?

A

DNA and RNA are nucleic acids that are found in all living cells and carry information.

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2
Q

What does DNA stand for?

A

Deoxyribonucleic acid

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3
Q

What does RNA stand for?

A

Ribonucleic acid

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4
Q

What is DNA used for?

A

DNA is used to store all your genetic inormation

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5
Q

What is RNA used for?

A

RNA is used to transfer genetic information from the DNA to the ribosomes , it does this so that proteins can be made.

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6
Q

What is the monomer of DNA and RNA ?

A

Nucleotides are the monomer that builds polymers DNA and RNA

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7
Q

Describe the structure of a nucleotide:

A

A nucleotide has 3 diffrent components

  1. A pentose sugar , in DNA this is deoxyribose sugar and in RNA it is ribose sugar
  2. A phosphate group
  3. A nitrogenous base
    (adenine , thymine , cytosine , guanine , uracil)
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8
Q

What type of reaction joins nucleotides to make polynucleotide chains?

A

Condensation Reactions

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9
Q

What type of bond is formed between two nucleotides

A

A phosphodiester bond , forms between the pentose sugar and the phosphate group.

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10
Q

When phosphodiester bonds form , what is created?

A

A sugar phosphate backbone is created as phosphodiester bonds form between the pentose sugar and the phosphate group.

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11
Q

Name 5 nitrogenous bases

A 
Adenine 
Thymine 
Cytosine 
Guanine 
Uracil
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12
Q

In DNA what would a nitrogenous base labelled A be?

A

Adenine

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13
Q

In DNA what would a nitrogenous base labelled T be?

A

Thymine

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14
Q

In DNA what would a nitrogenous base labelled C be?

A

Cytosine

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15
Q

In DNA what would a nitrogenous base labelled G be?

A

Guanine

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16
Q

In RNA what would a nitrogenous base labelled U be?

A

Uracil

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17
Q

Cytosine makes 3 hydrogen bonds to which other nitrogenous base?

A

Guanine

18
Q

Adenine makes 2 hydrogen bonds to which other nitrogenous base?

A

Thymine

19
Q

Cytosine and Guanine make how many hydrogen bonds?

A

3

20
Q

Adenine and Thymine make how many hydrogen bonds?

A

2

21
Q

What type of structure does DNA have and how does this make it fit for purpose?

A

DNA has a double helix structure , two strands wind around each other to form a spiral , these strands are polynucleotides. DNA molecules are very long and coiled up very tightly so a lot of genetic information can fit into a small space in the cell nucleus.

22
Q

Are both polynucleotide chains oriented the same way in a molecule of DNA?

A

No the two polynucleotide chains in a double helix of DNA run antiparallel to each other , there is one forward strand which runs 5’ to 3’ and a reverse strand which runs 3’ to 5’

23
Q

The pairing of Thymine + Adenine and Guanine + Cytosine is referred to as?

A

Complimentary Base Pairing

24
Q

Which nitrogenous bases are found in DNA?

A

Adenine
Thymine
Cytosine
Guanine

25
Q

Which nitrogenous bases are found in RNA?

A

Adenine
Uracil
Cytosine
Guanine

26
Q

What replaces Thymine as a base in RNA?

A

Uracil

27
Q

Which pentose sugar is found in DNA?

A

Deoxyribose sugar

28
Q

Which pentose sugar is found in RNA?

A

Ribose sugar

29
Q

What are the main differences between DNA and RNA?

A

1 . Their pentose sugars are different DNA=deoxyribose sugar RNA= robose sugar

  1. Thymine , a base found in DNA is not found in RNA , in its place is uracil.
  2. DNA is a double helix where as RNA is a single polynucleotide strand
  3. RNA polynucleotide strands are much shorter than DNA polynucleotide strands.
30
Q

When does DNA replicate its self?

A

DNA replicates itself before cell division so that each new cell has the full amount of DNA.

31
Q

By which method does DNA replicate?

A

DNA replicates by the semi-conservative replication

32
Q

Why is the model known as the semi conservative model?

A

The model is known as the semi conservative model as in each piece of DNA replicated there is a strand of the parental DNA and a strand of new DNA.

33
Q

How is DNA replicated?

A

DNA is replicates as firstly the enzyme DNA Helicase breaks the hydrogen bonds between nitrogenous bases , separating the two polynucleotide strands appart , this causes the helix to unwind and form two single strands.

Each original single strand acts as a template for a new strand.

Complimentary base pairing means that free floating DNA nucleotides are extracted to their complimentary exposed bases that lie on the original strand.

Condensation reactions (catalysed by DNA polymerase) join the new nucleotides together forming phosphodiester bonds.

Hydrogen bonds form between the bases on the original strand and new strand .

Each new DNA molecule contains one strand from the original DNA molecule and one new strand of DNA.

34
Q

what does the enzyme DNA Helicase do?

A

DNA helicase is an enzyme that breaks hydrogen bonds between nitrogenous bases in a double helix of DNA so that it will unzip and expose its bases.

35
Q

What does the enzyme DNA polymerase do?

A

DNA polymerase is an enzyme that catalyses the condensation reactions between nucleotides in the new strands of DNA.

36
Q

Isotopes of which element were used to prove semi-conservative replication? and which isotopes if this element were used?

A

Nitrogen

N^14 and N^15

37
Q

Explain how Meselson’s and Stahl’s experiment acted as evidence for semi conservative replication

A

In the experiment bacteria was grown in dishes containing nitrogen 14 (light nitrogen) and nitrogen 15 (heavy nitrogen). As the two samples of bacteria grew they took up nitrogen from the dishes to help make new nucleotides for new DNA so the nitrogen gradually became part of the bacterias DNA.

A sample of each of the bacteria was taken and spun in a centrifuge . The DNA from the bacteria grown in the heavy nitrogen (15^N) settled lower in the tube than the DNA from the bacteria grown in light nitrogen (14^N)

Next the DNA grown in the heavy nitrogen were transferred to a dish containing light nitrogen. The bacteria were left in this light nitrogen for enough time to allow the DNA to replicate once.

Another DNA sample was taken and spun in the centrifuge.

If the conservative model was correct then there would have been two layers of DNA one off heavy at the bottom made of purely original material and then a layer of light at the top made of purely new material. If the conservative model was correct and there was now one strand of original and one strand of new material in each helix of DNA then theoretically it should have settled in around the middle of the tube between where the 14^N had settled and the 15^N had settled.

The result was that it settled in the middle proving the semi-conservative model.

38
Q

What is a purine?

A

A purine is a nitrogenous base it consist of two rings.

39
Q

Which two of the nitrogenous bases in DNA are purines?

A

Adenine

Guanine

40
Q

What is a pyrimidine ?

A

A pyrimidine is a nitrogenous base that consists of a singe ring

41
Q

Which two nitrogenous bases are pyrimidines?

A

Thymine

Cytosine

AQA-A level Biology-revision cards (21 decks)

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