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A-Level Biology Paper 1 > Genetic information, variation and relationships between organisms > Flashcards

Genetic information, variation and relationships between organisms Flashcards

1
Q

What are the differences between prokaryotes and eukaryotes?

A

Prokaryotes are smaller
Prokaryotes have no Nucleus and instead have circular DNA rather than linear
prokaryotes have smaller ribosomes
Prokaryotes have marine walls however eukaryotes have chitin or Celulose

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2
Q

What are the features of DNA in prokaryotes?

A

Short, circular, not associated with proteins

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3
Q

What are the features of DNA in a eukaryote?

A

inside a nucleus, associated with proteins(histones), long and linear

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4
Q

What is an intron?

A

non-coding DNA within a gene

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5
Q

What are exons?

A

Coding regions of DNA

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6
Q

What type of DNA do prokaryotes not have?

A

introns

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7
Q

Why is the DNA of mitochondria and chloroplasts similar to that of prokaryotes?

A

Because it is short, circular and not associated with proteins

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8
Q

If a gene contains 240 bases, what is the maximum number of amino acids this gene code for?

A

80, (240➗3) this is because bases are read in triplets

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9
Q

Smallest to largest: gene, exon, base, nucleotide, chromosone, cell, nucleus

A

base, nucleotide, Exon, gene, chromosome, nucleus, cell

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10
Q

What is a gene?

A

A section of DNA that codes for a single specific protein

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11
Q

What is DNA?

A

The double-stranded polynucleotide from which genes are made

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12
Q

What is a chromosome?

A

Thread like structure made of DNA and associated proteins

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13
Q

What are histones?

A

proteins that associate with eukaryotic DNA to from chromosomes

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14
Q

Where are genes found?

A

On chromosomes

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15
Q

What are homologous chromosomes?

A

chromosomes that are the same size and have the same genes. (Although they may carry different alleles).

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16
Q

What is the fix position of a gene on a chromosome called?

A

the gene locus

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17
Q

What is an allele?

A

Any of two or more variants of a gene

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18
Q

What is a triplet?

A

The three bases each amino acid is coded for by

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19
Q

The genetic code is degenerate, what does this mean?

A

there are 64 triplets, but only 20 amino acids. Few amino acids have only a single triplet. There is more than one base triplet for each amino acid to be coded for by.

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20
Q

The genetic code is universal. What does this mean?

A

The same triplet codes for the same amino acid in all organisms

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21
Q

what is functional RNA?

A

any RNA (except mRNA) that perform special tasks during protein synthesis, e.g. tRNA. Some genes code for functional RNA, and not proteins.

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22
Q

What does mRNA do?

A

Copies messages from DNA for protein synthesis

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23
Q

what does mRNA move through to get to the ribosome after leaving the nucleus?

A

Cytoplasm

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24
Q

What are the two parts of protein synthesis?

A

Transcription and translation

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25
Q

What is unzipping in protein synthesis?

A

When RNA helicase unzips DNA by breaking the hydrogen bonds between bases, causing the two strands to separate and bases to be exposed, one strand becomes the template strand

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26
Q

During transcription, after the DNA is unzipped, what happens?

A

Free Nucleotides in the nucleus pair up with the exposed bases on the template strand (according to base pair ruling).

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27
Q

How is pre-mRNA formed?

A

RNA polymerase catalyses a condensation reaction, resulting in the formation of a complimentary pre-mRNA polynucleotide.

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28
Q

during transcription, when does RNA polymerase stop and detach from the DNA?

A

When a stop codon is reached.

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29
Q

What is splicing?

A

when introns are removed from pre-mRNA to form mRNA

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30
Q

Where does splicing occur?

A

In the nucleus

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31
Q

How does mRNA leave the nucleus?

A

Via a nuclear pore

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32
Q

What is translation?

A

The process, in which amino acids join together to make a polypeptide chain (protein) following the sequence of codons, carried by the mRNA.

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33
Q

what are the features of a tRNA molecule?

A

it has an amino acid binding site
It is clover leaf shaped
It has an anti codon

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34
Q

When does translation start?

A

when a ribosome binds to mRNA at the start codon

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35
Q

How does tRNA attach to mRNA?

A

by it’s complimentary anti codon

36
Q

what is needed for amino acids to bind to tRNA?

A

ATP

37
Q

What happens in translation after the first tRNA molecule attaches to mRNA?

A

A second tRNA with a complimentary anti codon attaches itself to the next codon on the mRNA chain.

38
Q

What bond is formed between two amino acids during translation?

A

A peptide bond formed from a condensation reaction

39
Q

For a peptide bond to be formed between amino acids during translation, what is needed?

A

ATP

40
Q

what happens after the first two amino acid in translation form a peptide bond?

A

The ribosome moves along the mRNA by one codon on the first tRNA is released into the cytoplasm (free to collect another amino acid)

41
Q

What happens after a third tRNA molecule binds to mRNA during translation?

A

The process of translation continues until I stop codon is reached. Then the mRNA and ribosomes separate turn. The protein is released.

42
Q

How is a polypeptide given a secondary structure?

A

when phosphate, hydrogen, and ionic bonds been created, folding the polypeptide into either an alpha helix, or beta pleated sheet.

43
Q

How is a polypeptide chain given a tertiary structure?

A

When the secondary structure is twisted and folded into a specific 3-D shape.

44
Q

What is the quaternary structure of a polypeptide?

A

when different polypeptides along with non protein groups join the protein.

45
Q

What kind of offspring does sexual reproduction create?

A

Genetically, distinct offspring

46
Q

What are sex cells called?

A

Gametes

47
Q

What does haploid mean?

A

Having half the normal number of chromosomes, sex cells have these before they fuse.

48
Q

What does diploid mean?

A

The normal, full number of chromosomes

49
Q

What are the differences between haploid and diploid?

A

Diploid is 2n and haploid is n.
Diploid cells have two copies of every chromosome, cells only have one copy of every chromosome in haploid cells.

50
Q

What is the female and male gametes of humans and where are they produced?

A

The female gamete is the egg, and it is produced in the ovary. The male gamete is sperm, and it is produced in the testes.

51
Q

What is the female and male gametes in plants and where are they produced?

A

is the female gamete in plants is egg and it is produced in ovaries. The male gamete in plants is pollen and it’s produced in the anther.

52
Q

why is meiosis is needed?

A

So that diploid number is restored when gametes fuse.
To introduce genetic variation.
So that chromosome number is maintained each generation.

53
Q

What happens during interphase, before meiosis?

A

DNA condenses into chromosomes. Each chromosome exists as genetically identical criminal chromatids attached at the centromere.

54
Q

What happens during meiosis one?

A

chromosomes line up in homologous pairs at the equator of the cell. Spindle fibres attach to the centromeres. The homologous pairs of separated as the cell divides.

55
Q

What happens during meiosis two?

A

Chromosomes in each cell lineup at the equator of the cell.

The chromosomes separate into their individual chromatids by spindle fibres as the cell divides.

56
Q

What is the result of meiosis?

A

four genetically varied daughter cells with a haploid number.

57
Q

What are the differences between mitosis and meiosis?

A

Meiosis reduces the chromosome number. Mitosis maintains the same chromosome number is the parent cell.

Meiosis produces genetically different daughter cells, but meiosis produces genetically identical ones.

There are four offspring cells in meiosis and two in mitosis.

Crossing over occurs in meiosis, but not in mitosis.

58
Q

in what ways does meiosis lead to variation?

A

independent assortment
Crossing over
Random fertilisation

59
Q

What does independent assortment mean?

A

In meiosis one, homologous pairs of chromosomes lineup opposite each other at the equator.

It is random which side of the equator, each homolog lies, and therefore which door to sell it goes into.

60
Q

how do you work out how many combinations of chromosomes there could be in a daughter cell?

A

A number of combinations= 2^n

E.g. if there are two pairs of chromosomes, there are 2^2 = 4 combinations.

61
Q

how many combinations are there of arranging chromosomes in a human cell?

A

over 8 million, (2^23)
This means each human is capable, through independent assortment alone, of producing over 8 million genetically different gametes.

62
Q

What is crossing over?

A

Homologues associate and exchange sections of that inner chromatids (different alleles) with each other. This results in new combinations of alleles on recombinant Chromatids.

63
Q

What is the name of the crossing over part of the chromosomes?

A

A chiasmata, and a bivalent is formed.

64
Q

What does random fertilisation mean?

A

fertilisation is random, any sperm can fertilise any egg.

This produces zygotes with new combinations of alleles from both parents.

This increases genetic diversity.

65
Q

What is the exam technique for identifying meiosis in an unfamiliar life cycle?

A

identify the change from diploid to haploid cells, and that’s where meiosis takes place.

66
Q

What is a mutation?

A

Any change to the base sequence of an organisms DNA

67
Q

What is the effect of a mutation on a protein? (chronological order)

A

Change in DNA sequence
Change in mRNA sequence
Change in codon sequence
Change in amino acid sequence
Change in H bonds and ionic bonds, leading to change in tertiary protein structure
Change in protein function

68
Q

what will happen if there is a mutation in the base sequence of a protein that is an enzyme?

A

The active site will no longer be complimentary to the substrate, so it won’t catalyse a reaction.

69
Q

what are the types of gene mutation?

A

substitution, (addition) or deletion.

70
Q

What is a substitution gene mutation?

A

this occurs when one base is removed and replaced by a different base.

71
Q

Why is a substitution gene mutation not always a problem?

A

Because only one triple is affected, and therefore only one amino acid is affected. Due to degeneracy this does not always result in a change in amino acid sequence. If it is changed, there is still a chance it will not affect the tertiary structure of protein.

72
Q

What is a silent mutation?

A

this occurs when the substitution of a base results in a triplet that still codes for the same amino acid. This is possible due to degeneracy and has no effect on the production of the final polypeptide.

73
Q

what is a mis-sense mutation?

A

this occurs when substitution of a base results in a triplet that codes for a different amino acid. This may affect the function of the protein depending on where it is.

74
Q

What is a nonsense mutation?

A

This occurs when substitution of a base leads to a premature stop codon. This would lead to the premature end to synthesis of a polypeptide.

The protein would almost certainly not be able to function normally.

75
Q

What is the deletion gene mutation?

A

When one or more base is lost from the normal DNA sequence so codons can no longer be read properly. This results in a frameshift. This usually means the amino acid sequence of the new code will be entirely different so the tertiary structure of a protein almost certainly will be affected.

76
Q

what does deletion result in?

A

Frameshift

77
Q

what are chromosomal mutations?

A

Alterations that affect whole chromosomes rather than just individual nucleotides.

78
Q

how do chromosomal mutations occur?

A

From errors in cell division

79
Q

What is chromosome disjunction?

A

Chromosomes being pulled apart by spindle fibres.

80
Q

what is non-disjunction?

A

failure of chromosomes to separate properly

81
Q

what are the two kinds of non-disjunction?

A

Polyploidy and aneuploidy

82
Q

What is polyploidy?

A

when all chromosomes have three or more sets in an organism rather than 2n.

83
Q

how is polyploidy caused?

A

All chromosomes failing to separate equally in meiosis one or two.

84
Q

How does aneuploidy occur?

A

when individual chromosomes fail to separate, during mitosis, one or two.

85
Q

What is aneuploidy?

A

When a gamete has an extra/one less chromosome. If fertilisation occurs with a gamete that has a normal number of chromosomes, the resultant zygote will have more of you are chromosomes, the normal in all body cells.

86
Q

What is monosomy?

A

Cells only have one copy of a chromosome

87
Q

what is trisomy?

A

Cells have three copies of a chromosome.

A-Level Biology Paper 1 (8 decks)

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