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A Level Biology > Nucleic Acid > Flashcards

Nucleic Acid Flashcards

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1
Q

What is the structure of a nucleotide?

A
  • A phosphate group
  • A Penrose sugar
  • A nitrogenous base (1 of 5)
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2
Q

Which 4 nitrogenous bases does DNA contain

A

Adenine
Thymine
Guanine
Cytosine

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3
Q

Which 4 nitrogenous bases does RNA contain?

A
  • Adenine
    -Uracil
    -cytosine
    -Guanine
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4
Q

How many polynucleotide chains does DNA have?

A

2 antiparallel polynucleotide chains

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5
Q

How many polynucleotide chains does RNA have?

A

1 polynucleotide chain

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6
Q

What protein is associated with DNA

A
  • Histones
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7
Q

What is the function of DNA?

A
  • codes for proteins (amino acid sequences)
  • DNA replication for cell division
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8
Q

What is the function of RNA

A

Transfers the genetic information from DNA to ribosomes

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9
Q

What are Pyrimidines?

A

They have a single ring structure
- cytosine
- thymine
- Uracile

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10
Q

What is a purine?

A

A double ring structure
- adenine
- guanine

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11
Q

What bond forms between neighbouring nucleotides?

A

A phosphodiester bond is formed between the pentode sugar and phosphate group.

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12
Q

What forms when many nucleotides are joined together (through phosphodiester bonds)

A
  • a sugar phosphate back bone
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13
Q

What type of bond forms between complimentary base pairs?

A

Hydrogen bonds(H2)

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14
Q

How many hydrogen bonds form between Adenine and thymine (Uracil for RNA)?

A

2 hydrogen bonds

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15
Q

How many hydrogen bonds form between guanine and cytosine?

A

3 hydrogen bonds
-More stable

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16
Q

What function does DNA being a long and large molecule give it?

A

So it can store lots of genetic information

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17
Q

What function does DNA being a coiled helix give it?

A

So it is compact

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18
Q

What function does DNA having a sugar phosphate back bone give it?

A

The bases in the double helix are protected

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19
Q

Why does DNA have bases arranged in specific sequences?

A

So it can code for a sequence of amino acids

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20
Q

Why is DNA double stranded?

A

So it can be separated and unwound to act as a template for accurate replication using complimentary base pairing

21
Q

DNA has weak hydrogen bonds between the bases on each strand- how does this make it better for its function?

A

So the DNA helicase can easily be separated when it replicates

22
Q

Which two enzymes are involved in DNA replication

A

DNA helicase
DNA polymerase

23
Q

Describe the process of DNA replication

A
  • the enzyme DNA helicase causes the DNA double helix to unwind and separate into two strands by breaking the hydrogen bonds between the complimentary base pairs exposing the bases.
  • Both strands then act as a template for DNA replication.
  • free activated nucleotides (in the nucleoplasm) are attracted and hydrogen bond to complimentary bases on the exposed template strands by complimentary base pairing
  • The newly added nucleotides are the joined by DNA polymerase in a condensation reaction to for phosphodiester bonds between adjacent nucleotides.
  • This results in two identical DNA molecules being produced each of which contain one original DNA strand and one newly synthesised strand. (Semi-conservative)
24
Q

What does DNA helicase do?

A

Unwinds and separates the double helix by breaking the hydrogen bonds.

25
Q

How is DNA replicated

A

Semi-conservative

26
Q

Describe what is meant by semi-conservative replication

A

The two identical DNA molecules produced contain one original DNA and one newly synthesised DNA strand

27
Q

What happens when the hydrogen bonds between the complimentary base pairs are broken?

A

The base pairs on the strand are exposed to act as a template

28
Q

What molecules are attracted and hydrogen bonded to their complimentary bases?

A

Free nucleotides

29
Q

How do free activated DNA nucleotides bond to the template strands?

A

They hydrogen bond to their complimentary base pairs

30
Q

Which enzyme joins the newly added nucleotides together?

A

DNA polymerase

31
Q

What type of bond forms between adjacent nucleotides?

A

Phosphodiester bond

32
Q

How is chromatin formed?

A

DNA is wound around histone protein

33
Q

What is Chromatin?

A

A more spread out form of DNA (which forms fibres)

34
Q

What is a chromosome?

A

Most condensed form of DNA (formed form chromatin)

35
Q

What are the two main stages of cell division?

A

Nuclear division (mitosis/meiosis) - nucleus divides
Cytokinesis - whole cell (cytoplasm) divided into two daughter cells

36
Q

What must happen before a nucleus can divide?

A

DNA replication

37
Q

What’s a replication fork?

A

When DNA helicase and DNA polymerase are working simultaneously so the bases aren’t exposed for too long

38
Q

Why does DNA polymerase only add nucleotides in a 5’ to a 3’ direction?

A

DNA polymerase has a complimentary active site to the 3’end

39
Q

What were the 3 proposed DNA replication models?

A

-conservation
-dispersive
- semi-conservative

40
Q

What does the conservative model suggest about DNA replication?

A

One completely newly synthesised molecule is made and the original molecule is conserved

41
Q

What does the dispersive model suggest about DNA replication

A

Fragments of DNA molecules are copied and dispersed in the structure

42
Q

Which two scientists tried to validate Watson and Cricks model of semi-conservative replication?

A

Meselson and Stahl

43
Q

What 3 facts did Meselson and Stahl base their work on?

A

All DNA contains nitrogen
Nitrogen has an isotope
When bacteria grows in a medium they will absorb any nitrogen from the growth medium and incorporate it into any new DNA formed

44
Q

What are the stages of Meselson and Stahl’s experiment?

A
  1. Bacteria are grown for several generations in a growth medium containing heavy nitrogen (N15)
  2. DNA is then extracted and spun in a centrifuge solution of caesium chloride.This forms a band near the bottom of the test tube.
  3. The bacteria from the end of stage 1 is transferred and grown for one generation in a growth medium containing light nitrogen (N14)
  4. The DNA is extracted and spun in a centrifuge and a intermediate band is formed. (Due to one heavy and one light strand per DNA molecule)
  5. The bacteria from the end of stage 2nis grown for a second generation in the light nitrogen before the DNA is extracted and spun in a centre (a light and intermediate band forms)
45
Q

When spun in a centrifuge, what happens to DNA

A

Based on density/mass DNA will settle in the test tube
-heaviest/most dense towards the bottom
- lightest/least dense towards the top

46
Q

At the end of the 5 stage of the (DNA) experiment, why do we have one light and one intermediate strand?

A

Two DNA molecules are made from completely newly synthesised light nitrogen
2 DNA molecules have one light and one heavy strand

47
Q

How can we disprove the conservative model?

A

After the 1st generation in the light nitrogen, we would have seen one denser band and one less dense band but an intermediate strand was observed

48
Q

How can we disprove the dispersive model for DNA replication.

A

After the second generation in the light nitrogen, the band in the test tube would still be intermediate because there are still heavy DNA fragments in the molecule (although more light molecules have been joined)

A Level Biology (13 decks)

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