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AS Biology - Unit 2 > Unit 3.2.2 - DNA > Flashcards

Unit 3.2.2 - DNA Flashcards

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1
Q

DNA acts as a?

A

Stable information-carrying molecule which contains your genetic information

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2
Q

Describe the structure of DNA?

A

Two polynucleotide strands twisted together to form a double helix, held together by hydrogen bonds

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3
Q

Why is one strand on DNA called a polynucleotide?

A

It consists off many nucleotides joined together in a long chain

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4
Q

What three things make up a nucleotide?

A

A phosphate group, a deoxyribose sugar and a base

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5
Q

What two things make up the backbone of the DNA?

A

The deoxyribose sugar and phosphate group make up the sugar-phosphate backbone

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6
Q

What is the a deoxyribose sugar?

A

A five carbon sugar

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7
Q

Name the four possible bases?

A

Adenine, Thymine, Cytosine and Guanine

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8
Q

What is meant by specific base pairing?

A

Bases can only join with a specific other bases

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9
Q

What are the two specific base pairings?

A

A-T

G-C

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10
Q

What forms between the bases to allow DNA to keep its structure?

A

Hydrogen bonds

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11
Q

How many hydrogen bonds form between Thymine and Adenine form?

A

2

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12
Q

How many hydrogen bonds form between Cytosine and Guanine?

A

3

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13
Q

Label the sections in the diagram of the DNA?

A

See flash card

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14
Q

Why is DNA stable and how does this relate to its function?

A

The nucleotides in a strand are held together by strong covalent bonds this means it can be easily be passed through generations relatively unchanged

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15
Q

How does the two DNA strands only being held together by weak hydrogen relative to its function?

A

It means the two strands can easily be separated during DNA replication and protein synthesis be DNA helicase

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16
Q

What property of DNA protects the bases from damage?

A

They are held within the cylindrical double helix

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17
Q

How does the specific base pairings relative to its function?

A

It is so one strand can act as a template and be copied easily

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18
Q

How does DNA being a large molecule relate to its function?

A

It can carry a large amount of information

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19
Q

What are genes?

A

Sections of DNA

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20
Q

What is a locus

A

The fixed position a gene occupies on a DNA strand

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21
Q

How do genes code for which protein is made?

A

Genes contain coded information as a specific sequence of bases, a triplet codes for one amino acid. And the sequence of amino acids determine which protein is made

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22
Q

What is a triplet?

A

Three bases

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23
Q

The code in DNA is said to be?

A

Degenerate

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24
Q

What is meant by DNA being degenerate?

A

More than one base triplet can code for the same amino acid

25
Q

What are introns?

A

Non coding sections of DNA

26
Q

What are exons?

A

Sections of DNA that code for amino acids

27
Q

What are multiple repeats?

A

Non coding sections of DNA where the same base sequence is repeated many times

28
Q

Are introns, exons or multiple repeats removed during protein synthesis?

A

Introns and multiple repeats

29
Q

Gives five points for why genes determine the nature and development of organisms?

A
  1. ) The DNA sequence in genes determine which amino acids they code for
  2. ) The amino acid sequence determines which protein or enzyme is formed
  3. ) Enzymes speed up most chemical reactions that occur in the body
  4. ) These reaction determine how we and develop
  5. ) And so genes help to determine our nature, development and phenotypes
30
Q

What causes the base sequence of a gene to change?

A

A mutation

31
Q

Does a mutation in the base sequence of DNA always have an effect?

A

No

32
Q

Give two reasons for why a mutation can have no effect?

A
  1. ) If the mutation occurs in an intron

2. ) DNA is degenerate

33
Q

Name the four types of mutations?

A

Substitution, Deletion, Duplication and Inversion

34
Q

What is a substitution mutation?

A

Where one base is replaced with another

35
Q

What is a deletion mutation?

A

When one base is loss, sifting the whole series to replace it

36
Q

What is a duplication mutation?

A

The repetition of a portion of the base sequence

37
Q

What is a inversion mutation?

A

The reversal of a portion of the base sequence

38
Q

Which mutation has the least effect and why?

A

A substitution mutation because it only changes one amino acid instead of all following amino acids

39
Q

Give a situation when a mutation is good?

A

When the new protein it codes for gives the organism some kind of advantage and so it is more likely to survive

40
Q

Give a situation when a mutation is bad?

A

If it occurs in an enzyme it can change the base sequence of DNA and so the sequence of amino acid changes, this means the primary structure of the enzymes is different and therefore the tertiary structure will also be altered. This can change the shape of the active site and so it is no longer complementary to the substrate and can’t form enzyme - substrate complexes and becomes non functional

41
Q

Do eukaryotic and prokaryotic cells store DNA in the same way?

A

No different

42
Q

How is DNA stored in eukaryotic cells?

A

DNA is linear and wound round proteins called histones, the DNA is then coiled up very tightly to make chromosomes

43
Q

How is the DNA stored in prokaryotic cells?

A

DNA is circular and forms circular chromosomes which are then coiled and condensed to fit into the cell by super coiling

44
Q

Is the DNA linear or circular in prokaryotic and eukaryotic cells?

A

Prokaryotic cells - circular

Eukaryotic cells - linear

45
Q

In eukaryotic cells why does the DNA have to wound up small?

A

So that it fits into the nucleus

46
Q

What does diploid number of chromosomes mean?

A

Two of each chromosome

47
Q

What type of number chromosomes do gametes have?

A

Haploid

48
Q

What does haploid number of chromosomes mean?

A

One copy of each chromosome - half the normal number

49
Q

Why is it important that gametes only have a haploid number of chromosomes?

A

So that when two fuse during fertilisation it creates a cell with the normal diploid number of chromosomes

50
Q

What is a diploid cell produced through fertilisation called?

A

A zygote

51
Q

What is meiosis and what does it produce?

A

A type of cell division that produces four genetically different gametes with a haploid number of chromosomes

52
Q

What are the 7 steps of meiosis?

A
  1. ) DNA unravels and replicates so that there are two copies of each chromosome - each called a chromatid
  2. ) DNA condenses and forms a double armed chromosome made from two sister chromosomes
  3. ) The chromosomes arrange themselves in homologous pairs
  4. ) Sections of DNA get swapped over
  5. ) Meiosis 1 - homologous pairs are separated
  6. ) Meiosis 2 - The sister chromatids are separated
  7. ) You end up with four gametes with a haploid number of chromosomes that are genetically different
53
Q

What three things produces genetic variation in gametees

A

Crossing over of chromatids, independent segregation and random fertilisation

54
Q

What happens during the crossing over of chromatids to produce genetically different gametes?

A

Sections of DNA are swapped over between homologous pairs of chromosomes producing a different combination of alleles

55
Q

What happens during the independent segregation to produce genetically different gametes?

A

The random arrangement of chromosomes on the equators during Meiosis 1 produces a different combination of alleles

56
Q

Why does random fertilisation produce genetically different gametes?

A

Any sperm cell can fertilise any egg and so the combination of alleles will be different

57
Q

Why don’t see you crossing over as often?

A

It is doesn’t happen very frequently

58
Q

What can you use to find the number of different combinations of chromosomes you could have?

A

2~n, where n is the number of pairs of chromosomes

AS Biology - Unit 2 (11 decks)

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