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A2 Biology - Unit 5 > Unit 3.5.6 - DNA > Flashcards

Unit 3.5.6 - DNA Flashcards

1
Q

Describe what DNA looks like.

A

Double helix formed from two polynucleotide strands coiled together.

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2
Q

What does one nucleotide look like?

A

A phosphate group, a deoxyrybose sugar and a base.

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3
Q

What type of sugar is a deoxyrybose sugar?

A

A pentose sugar.

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4
Q

What is the same for every nucleotide?

A

Sugar phosphate backbone.

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5
Q

What is different between each nucleotide?

A

The base.

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6
Q

What are the names of the four bases?

A

Adenine, Thymine, Cytosine and Guanine

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7
Q

What type of bonds are there between the two polynucleotide strands.

A

Hydrogen bonds between the bases.

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8
Q

What is meant by specific base pairing?

A

Each base can only join with one other particular base.

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9
Q

What are the two specific base pairs?

A

A-T C-G

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10
Q

What are genes?

A

Sections of DNA found on chromosomes.

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11
Q

What do genes code for?

A

Proteins

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12
Q

What in the gene determines what protein it codes for?

A

The order of the bases and so the order of the amino acids.

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13
Q

How many bases code for one amino acid?

A

Three

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14
Q

What are the three names that the three bases are called that code for amino acid?

A

Triplet, base triplet and codon

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15
Q

Where is DNA found in the cell?

A

In the nucleus.

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16
Q

What are the organelles that make proteins and where are they found?

A

Ribosomes - cytoplasm

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17
Q

Why is transcription carried out, why isn’t DNA used?

A

DNA is too large to move out of the nucleus.

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18
Q

What is transcription?

A

When mRNA is formed from DNA

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19
Q

What is translation?

A

When mRNA leaves the nucleus and joins with ribosomes where it can be used to synthesise proteins.

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20
Q

What is the nucleotides in RNA made up of?

A

A base, phosphate group and a ribose sugar.

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21
Q

Describe the structure of RNA?

A

Single strand polynucleotide.

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22
Q

What are the four bases in RNA?

A

Adenine, Uracil, Cytosine and Guanine

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23
Q

What are the specific base pairs in RNA?

A

A-U C-G

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24
Q

What are the two types of RNA that you have to know about?

A

mRNA and tRNA

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25
Q

What does mRNA stand for?

A

Messenger RNA

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26
Q

When is mRNA formed?

A

During transcription

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27
Q

What is the job of mRNA?

A

To carry genetic code from the DNA in the nucleus to the cytoplasm where it can be made to make proteins during translation.

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28
Q

What does tRNA stand for?

A

Transfer RNA

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29
Q

What does tRNA look like?

A

Single polynucleotide that is folded over into a clover shape, it has an anti codon at one end and an amino acid binding site at the other.

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30
Q

What holds tRNA in it’s clover shape?

A

Hydrogen bonds between the specific base pairs.

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31
Q

What is an anti codon?

A

Specific sequence of three bases at the end of one tRNA molecule.

32
Q

What is the job of tRNA

A

It carries amino acids that are used to make protein to the ribosomes during translation.

33
Q

How does the shape differ between DNA, mRNA and tRNA?

A

DNA - Double stranded helix
mRNA - Single strand
tRNA - Single strand held into a clover shape.

34
Q

How does the sugar group differ between DNA, mRNA and tRNA?

A

DNA - deoxyribose sugar
mRNA - Ribose sugar
tRNA - Ribose sugar

35
Q

How do the bases differ between DNA, mRNA and tRNA?

A

DNA - A-T C-G
mRNA - A-U C-G
tRNA - A-U C-G

36
Q

What other features differ between DNA, mRNA and tRNA?

A

DNA has codons
mRNA has codons
tRNA has an anti codon and an amino acid binding site.

37
Q

What is meant by the genetic code is said to be non overlapping?

A

Base triplets don’t share their bases.

38
Q

What is meant by the genetic code is degenerative?

A

There are more possible combinations of triplets than there are amino acids so some amino acids are coded for by more than one triplet.

39
Q

Why don’t all triplets code for amino acids?

A

Some act as start and stop signals.

40
Q

What is meant by the genetic code is universal?

A

The same specific base triplet codes for all the same amino acids in all living things.

41
Q

What is protein synthesis broken down into?

A

Transcription and translation.

42
Q

How many stages can transcription be broken down into?

A

Four

43
Q

What are the four stages during transcription?

A
  1. RNA polymerase attaches to the DNA.
  2. Complimentary RNA is formed.
  3. RNA polymerase moves down the DNA strand
  4. mRNA leaves the nucleus
44
Q

What are the three stages when RNA polymerase attaches to the DNA during transcription?

A
  1. RNA polymerase attaches to the double helix at the beginning of the gene.
  2. The hydrogen bonds between the two DNA strands break separating the DNA strands causing them to uncoil.
  3. One of the strands is used as a template to make a mRNA copy.
45
Q

What are the three stages when complimentary mRNA is formed during transcription?

A
  1. RNA polymerase lines up free nucleotides alongside the template strand.
  2. Specific base pairing means the mRNA strand ends up being complimentary to the DNA template.
  3. Once the RNA nucleotides have paired up with their specific bases bonds form between the sugar and phosphate groups to form a mRNA molecule.
46
Q

What are the three stages when RNA polymerase moves down the DNA strand during transcription?

A
  1. The RNA polymerase moves along the DNA separating the strands and assembling the mRNA strands.
  2. The hydrogen bonds between the uncoiled strands of DNA reform once the RNA polymerase has passed by.
  3. The strands then recoil back into the double helix.
47
Q

What are the two stages when mRNA leaves the nucleus during transcription?

A
  1. When RNA polymerase reaches a stop signal it stops making mRNA and detaches from the DNA.
  2. The mRNA moves out of the nucleus through a nucleur pore and attach to a ribosome in the cytoplasm so translation can happen.
48
Q

Why is mRNA in eukaryotic cells edited?

A

Because the DNA contain strands that don’t code for amino acids.

49
Q

What are introns?

A

Non coding sections of DNA

50
Q

What are exons?

A

DNA that codes for amino acids

51
Q

Are both introns and exons copies during transcription?

A

Yes

52
Q

What is the difference between mRNA and pre mRNA?

A

Pre mRNA contains introns.

53
Q

How are introns removed from pre mRNA?

A

Splicing

54
Q

Where does splicing take place?

A

The nucleus

55
Q

Where does translation take place?

A

At the ribosome.

56
Q

What are the five steps in translation?

A
  1. mRNA attaches itself to a ribosome and tRNA molecules carries amino acids to the ribosome.
  2. a tRNA with an anti codon complimentary to the first codon on the mRNA attaches itself to the mRNA by specific base pairing.
  3. a second tRNA molecule attaches itself to the next codon in the same way.
  4. Two amino acids attached to the other side of the tRNA are joined by peptide bonds and the first tRNA molecule moves away.
  5. This process is repeated until there is a stop signal on the mRNA.
57
Q

What is a mutation?

A

A change to the base sequence of DNA

58
Q

What two things can mutations be caused by?

A

Errors during DNA replication or mutagenic agents.

59
Q

What are the three types of mutations?

A

Substitution, deletion and addition

60
Q

Why do not all mutuations affect the order of amino acids

A

DNA is degenerative so a base might be substituted for another base but both triplets code for the same amino acid.

61
Q

What two types of mutation will always change the sequence of amino acids and why?

A

Deletion and addition, they cause a change in the number of bases present and cause a shift in all the base triplets.

62
Q

What is a mutagenic agent?

A

Something that increases the rate of mutation.

63
Q

What are the three ways mutagenic agents can increase the rate of mutation?

A

Act as a base, altering bases or changing the structure of DNA (errors during replication)

64
Q

What two things can mutations be?

A

Hereditary or acquired.

65
Q

When do hereditary mutations occur?

A

Present in the gamete before fertilisation so the foetus will have the mutation.

66
Q

When do acquired mutations occur?

A

In the individual cells after fertilisation

67
Q

What two things can hereditary mutations cause?

A

Genetic disorders or cancer

68
Q

What are the two types of genes that control cell division?

A

Tumour suppressor gene and proto-onco genes.

69
Q

What happens if a mutation occurs in a gene that controls cell division?

A

Causes uncontrollable cell division resulting in a tumour.

70
Q

What is a tumour?

A

Mass of abnormal cells

71
Q

When does a tumour become cancer?

A

When it invades and destroys surrounding tissues.

72
Q

What happens when tumour suppressor genes function normally?

A

Slow cell division by producing proteins that stop cells dividing or cause them to self destruct.

73
Q

What happens if a mutation occur in a tumour suppressor gene?

A

The gene will be inactivated, the protein it codes for will no longer be produced so the cells divide uncontrollably resulting in a tumour.

74
Q

What do proto-onco genes do when functioning normally?

A

Stimulate cell division by producing proteins that make cells divide.

75
Q

What happens if a mutation occurs in a proto-onco gene?

A

The gene will become overactive stimulating the cell to divide uncontrollably resulting in a tumour.

76
Q

What is a mutated proto-onco gene called?

A

An onco gene.

A2 Biology - Unit 5 (8 decks)

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