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Biology AS > Genetic Information and Variation 3.4 > Flashcards

Genetic Information and Variation 3.4 Flashcards

1
Q

When are chromosomes visible?

A

When they are dividing.

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2
Q

What is DNA combined with in eukaryotes?

A

Histones.

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3
Q

What is a nucleosome?

A

The DNA-Histone complex.

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4
Q

What is the centromere on a chromosome?

A

The point where two chromatid are joined together to form a chromosome.

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5
Q

What is the difference between DNA in a eukaryote to a prokaryote?

A

In prokayotes it is shorter and circular rather than linear, it is also not wound around histones in prokaryotes.

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6
Q

What does the DNA in chloroplast and mitochondria code for?

A

Enzymes and proteins which are needed for respiration and photosynthesis.

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7
Q

What is the structure like for the DNA in chloroplast and mitochondria?

A

It is short and circular and not wound around histones.

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8
Q

What is the endosymbiotic theory?

A

The theory that states that mitochondria and chlorplasts were once prokaryotic and they made their way into eukaryotic cells forming a symbiotic relationship.

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9
Q

Why is mitochondrial DNA only inherited from the mother?

A

This is because mitochondria is only present in the eggs and not the sperm.

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10
Q

What are the two mechanisms involved in meiosis?

A

Independent segregation and the crossing over betwee homologus chromosomes.

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11
Q

What does meiosis produce?

A

Four genetically non-identical daughter haploid cells.

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12
Q

What happens during independent segregation?

A

The homologus pairs of chromosomes line up opposite each other on th equator, this is random as to which side they end up on and they are seperated in order to have one of each pair in each daughter cell which creates a large amount of possible variation changes.

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13
Q

What happens during the crossing over of homologus pairs of chromosomes?

A

They line up randomly opposite each other at the eqautor, he sister chromatids can twist over others and cause tension which leaves pieces to break off and reattach on a different chromatid which result in new combinations.

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14
Q

When do independent segregation and the crossing over between homologus chromosomes happen?

A

During Meiosis I.

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15
Q

What is meiosis?

A

A type of cell division whih is used to produce gametes for sexual reproduction.

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16
Q

Why does meiosis happen?

A

To ensure that genetic information is halved so that there is the correct number of chromosomes at fertilisation.

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17
Q

Where does meiosis occur in plants?

A

In the anthers and ovules

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18
Q

What is the point where chromatids join as they cross over each other?

A

The Chiasma.

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19
Q

What are introns?

A

Non-coding sections of a gene.

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20
Q

What are exons?

A

Coding sections of a gene.

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21
Q

What bonds form between the nucelotides in RNA?

A

Phosphodiester bonds.

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22
Q

What is messenger RNA?

A

A copy of a gene, made in protein synthesis during a
process called transcription.

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23
Q

What is longer DNA or mRNA?

A

DNA becomes mRNA is only as long as a gene.

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24
Q

What type of sugar does mRNA have?

A

A ribose sugar.

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25
Q

What is transfer RNA?

A

It is a single polynucleotide
strand. Folded into a clover shape. Hydrogen bonds between specific base pairs hold the tRNA molecule in shape.
Every tRNA molecule has a
specific sequence of 3 bases at
one end = anticodon and a
specific amino acid binding site.

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26
Q

What is the genetic code?

A

It Is the sequence of codons (base triplets) in mRNA which code for specific amino acids.

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27
Q

What type of code is the genetic code?

A

A triplet code.

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28
Q

How many bases code for one amino acid?

A

Three.

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29
Q

What is one triplet called?

A

A codon.

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30
Q

Is the genetic code overlapping or non-overlapping?

A

Non-overlapping.

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31
Q

What is meant by the genetic code being non-overlapping?

A

Each base is part of only one triplet.

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32
Q

The genetic code is universal, true or false.

A

True.

33
Q

What is meant by the genetic code being universal?

A

The same sequence of bases codes for the same amino acids in all organisms.

34
Q

What is meant by the triplet code being degenerate?

A

Each amino acid is coded for by more than one triplet.

35
Q

What is the first step of transcription?

A

At the start codon- RNA polymerase attaches to DNA

In eukaryotes a DNA helicase is attached to the RNA polymerase and breaks the hydrogen bonds the two polynucleotide strands.

In prokaryotes the RNA polymerase separates the DNA strands.

36
Q

What is the second step of transcription?

A

RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand (only ONE DNA strand acts as a template) The free bases are attracted to the exposed bases.

Complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA (except thymine – uracil instead)

Once RNA nucleotides paired with their base on the DNA strand, RNA polymerase joins adjacent nucleotides together with a phosphodiester bond forming an mRNA strand.

Makes 5’ end of mRNA first moving down RNA

37
Q

What is the third step of transcription?

A

RNA polymerase moves along the DNA assembling the mRNA strand. Once passed the hydrogen bonds form again between the DNA strands

38
Q

What is the fourth step of transcription?

A

When a stop signal is reached RNA polymerase stops making mRNA and detaches from the DNA

In eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm.

39
Q

What has to happen to mRNA before it can be used to make proteins?

A

The introns need to be removed in order to leave just exons, called splicing. It only happens in eukaryoes.

40
Q

Why does splicing only happen in eukaryotes?

A

Prokaryotes do not have any introns.

41
Q

Where does transcription occur in the cell?

A

In the nucleus.

42
Q

Name the enzymes involved in transcription and explain what they do.

A

DNA helicase – unwinds DNA section and exposes nucleotides
RNA polymerase – adds complementary RNA nucleotides to form pre-mRNA

43
Q

What happens when the RNA polymerase attaches to the DNA at the start codon?

A

The hydrogen bonds between the DNA strands break, separating the strands and the DNA molecule unwinds

44
Q

What happens when RNA polymerase reaches a stop codon?

A

It stops making mRNA and detaches from the DNA.

45
Q

What is pre-mRNA?

A

mRNA that contains introns and exons – before it has been spliced.

46
Q

What happens during mRNA splicing?

A

Introns removed and exons joined, and possibly rearranged, to form mRNA

47
Q

Why does pre-mRNA need to be spliced?

A

To remove introns (non-coding sections).

48
Q

Even though DNA codes for proteins directly, why is mRNA needed to be made for making proteins?

A

Because DNA is too large to move out of the nucleus, so a section is copied onto mRNA.

49
Q

Where does translation happen?

A

In the ribosomes in the cytoplasm.

50
Q

What happens in translation?

A

The mRNA attaches to the ribosome and tRNA molecules carry specific amino acids to it.
tRNA + amino acid with an anticodon that is complementary to the first codon on mRNA attaches to the mRNA by base paining.
A second tRNA + amino acid attaches to the next codon in the same way.
The two amino acids are then joined by a peptide bond by the ribosome (ATP provides energy), and the first tRNA molecule moves away leaving the amino acid
A third tRNA molecule then binds to the next codon on the mRNA, and the ribosome moves along the mRNA so the bext amino acid can bind
This continues until there is a stop signal

51
Q

Define proteome

A

All the proteins that can be expressed from the genome of an organism.

52
Q

What is a ribosome made of?

A

Proteins, rRNA (NO MEMBRANE!).

53
Q

What is a protein made of?

A

A polymer of amino acids

54
Q

What is a codon?

A

Triplet of bases that codes for an amino acid.

55
Q

What does it mean by ‘non overlapping’?

A

Each codon is read in sequence, separate from the codon before and after it. Codons do not share bases.

56
Q

Explain the term ‘degenerate’?

A

There are more possible combinations of codons than there are amino acids. Some amino acids are coded for by more than one codon

57
Q

What is the product of translation?

A

A polypeptide chain.

58
Q

Where does translation take place?

A

In the ribosomes in cytoplasm or RER

59
Q

What is tRNA?

A

Found in cytoplasm, has an amino binding site at one end and an anticodon on the other end, carries amino acids that are used to make proteins to the ribosomes

60
Q

Describe the structure of tRNA

A

tRNA is folded, has hydrogen bonds holding the structure together, is a fixed size, has an anticodon, has an amino acid binding site.

61
Q

What is an anti-codon?

A

Triplet of bases on tRNA which is complementary to binding site on mRNA.

62
Q

Which part of tRNA binds to the mRNA?

A

The anticodon binding site/loop

63
Q

What are the stop and start codons for?

A

Triplets that tell the cell when to start and stop production of the protein. Found at the beginning and end of the gene

64
Q

What is a mutation?

A

Change to the base sequence of DNA.

65
Q

How can a gene mutation result in a protein not being synthesised properly?

A

Mutation changes sequence of bases so that it no longer codes for the same protein sequence.

66
Q

What is a mutation?

A

A Mutation is an change to the quantity or structure of
DNA in an organism.

67
Q

When can mutations be inherited?

A

Only mutations in the formation of gametes can be inherited.

68
Q

What are the two types of point mutations?

A

Substitution of bases or addition/deletion of bases.

69
Q

What happens in the subsitution of bases mutation?

A

A nucleotide is replaced by
another, with a different base.

70
Q

What are the three types of subsitution point mutations?

A

Silent, nonsense and misense.

71
Q

What is a nonsense substiution mutation?

A

Stop codon is formed.

72
Q

What is a misense substiution mutation?

A

A different amino acid is coded for.

73
Q

What is a silent substiution mutation?

A

The subsituted base still codes for the same amino acid.

74
Q

What happens in an addition/subsitution of bases mutation?

A

A nucleotide is gained or
lost from the normal DNA
sequence.

75
Q

What does an addition/subsitution of bases mutation cause?

A

A frame shift.

76
Q

What is a mutagenic agent?

A

An external agent which increases the basic mutation rate.

77
Q

What causes mutations?

A

They can arise spontaneously in DNA replication, at around the rate of mutation rates in eukaryotes are roughly 0.1–100 per genome per generation. Or throught the addition of a mutagenic agent.

78
Q

What is chromosome non-disjunction?

A

Where one gamete may not get the correct numer of chromosome copies and the other gets them all/too many.

79
Q
A

Biology AS (12 decks)

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