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biology > module 4; genetic info, variation & relationships between organisms > Flashcards

module 4; genetic info, variation & relationships between organisms Flashcards

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1
Q

state the similarities between eukaryotic & prokaryotic DNA

A

made of DNA nucleotides containing deoxyribose, a phosphate group & nitrogenous base
nucleotides are joined together by phosphodiester bonds to make a polymer chain

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2
Q

state the differences between eukaryotic & prokaryotic DNA

A

eukaryotic DNA:
longer
linear
associated with histones

prokaryotic DNA:
shorter
circular
not associated with histones

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3
Q

state the similarities between mitochondria & chloroplast of eukaryotic cells & prokaryotic DNA

A

they are both short, circular & not associated with histones

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4
Q

define the term gene

A

a gene is a base sequence that codes for the amino acid sequence of a polypeptide & a functional RNA

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5
Q

what is a locus?

A

a locus is the particular position in which the gene occupies on the chromosome

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6
Q

what is the triplet code?

A

a sequence of 3 DNA bases, code for a specific amino acid

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7
Q

state the features of the genetic code

A
  1. degenerate
  2. universal
  3. non-overlapping
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8
Q

how many amino acids is the genetic code able to code for & why?

A

20 amino acids as there are 4 DNA bases (GCTA), & so 3 bases are needed to make enough combinations to code at least 20 amino acids

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9
Q

explain the proof in which the genetic code requires 3 bases to code for 20 amino acids

A

if 1 base is coded for 1 amino acid, it would allow for 4 aminos to be coded for - insufficient to code for 20 amino acids

if 2 bases code for 1 amino acid, it would allow for 16 aminos to be coded for (4x4 combinations) - also insufficient

if 3 bases code for 1 amino acid, it would allow for 64 aminos to be coded for (4x4x4 combinations) - more than needed to code for 20 aminos

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10
Q

explain the meaning of a degenerate genetic code

A

it’s where there are more combinations of amino acids to code for 20 aminos - it results in 1 amino being coded for by more than 1 triplet of bases (e.g. tyrosine is coded for by ATA & ATG)

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11
Q

how can we work out combinations of bases?

A

by using the genetic code wheel

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12
Q

what is an advantage of using the genetic code wheel?

A

it’s an advantage as if a point mutation occurs, even though the triplet bases will be different, it may still code for the same amino & so have no effect

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13
Q

what does universal mean in terms of coding for amino acids?

A

means the same triplet of bases codes for the same amino acid in all organisms

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14
Q

what does non-overlapping mean in terms of coding for amino acids?

A

means that each base in a gene is only part of 1 triplet of bases that codes for 1 amino acid - therefore, each codon, or triplet of bases, is read as a discrete unit

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15
Q

why is it an advantage that the genetic code doesn’t overlap?

A

it’s an advantage as if a point mutation occurs, it will only affect 1 codon, therefore 1 amino

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16
Q

define the term intron

A

introns are sections of DNA that do not code for polypeptides & are found in eukaryotic not prokaryotic DNA

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17
Q

define the term exon

A

exons are the sequences of DNA that code for amino acids

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18
Q

define the term codon

A

3 bases on mRNA that code for a specific amino acid

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19
Q

define the term start codon

A

3 bases at the start of every gene that initiate translation

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20
Q

define the term stop codon

A

3 bases at the end of every gene that causes ribosomes to detach & therefore stop translation

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21
Q

state the differences between a genome & proteome

A

the genome is an organism’s complete set of genes in a cell, whereas the proteome is a full range of proteins that a cell can produce

the genome should never change whereas the proteome of the cell is constantly changing depending on which proteins are currently needed

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22
Q

what is messenger RNA?

A

AKA - mRNA:
they are short, single stranded molecules found in the cytoplasm & nucleus

in mRNA, groups of 3 adjacent bases are called codons

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23
Q

how is mRNA made?

A

made during transcription - it’s copied from DNA & is therefore complementary to the DNA sequence

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24
Q

what is transfer RNA?

A

AKA tRNA:
in the cytoplasm, amino acids become attached to tRNA molecules - each tRNA is specific for 1 amino

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25
Q

what is an anticodon in terms of tRNA?

A

each tRNA molecule has a sequence of 3 bases called an anticodon - they are complementary to codons on the mRNA molecule

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26
Q

what is tRNA’s role in translation?

A

it carries the amino acids that are used to make proteins to the ribosomes

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27
Q

describe the structure & bonding of tRNA

A

it’s a single polynucleotide strand that is folded into a clover shape
H bonds between base pairs hold the shape

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28
Q

where are proteins created?

A

they are created on ribosomes

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29
Q

state & explain the stages of the production of proteins from the DNA code

A
  1. transcription:
    where one gene on the DNA is copied into mRNA
  2. translation:
    where the mRNA joins with a ribosome & corresponding tRNA molecules bring the specific amino acid the codons code for
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30
Q

what is transcription?

A

this is where one gene on the DNA is copied on to the mRNA

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31
Q

why is mRNA able to carry the genetic code?

A

as mRNA is much shorter than DNA, it’s able to carry the genetic code to the ribosome in the cytoplasm to enable the protein to be made

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32
Q

describe the process of transcription

A
  1. the DNA helix unwinds to expose the bases to act as a template
  2. only one chain of the DNA acts as a template
  3. like with DNA replication, this unwinding & unzipping is catalysed by DNA helicase
  4. DNA helicase breaks the H bonds between bases
  5. free mRNA nucleotides in the nucleus align opposite exposed complementary DNA bases
  6. the enzyme RNA polymerase joins together the RNA nucleotides to create a new RNA polymer chain - one entire gene is copied

once copied, the mRNA of modified & then leaves the nucleus through the nuclear envelope pores

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33
Q

what is pre-mRNA & when is it formed in eukaryotes?

A

in eukaryotes, after transcription, pre-mRNA is made & it’s the mRNA that still contains the introns - the introns are spliced out by a protein called splicesome which leaves just the exons (the coding regions)

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34
Q

what does transcription create in prokaryotes?

A

it directly creates mRNA as prokaryotes don’t contain introns in their DNA

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35
Q

what is translation?

A

it’s the stage in which the polypeptide chain is created using both the mRNA base sequence & the tRNA

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36
Q

describe the process of translation

A
  1. once the modified mRNA has left the nucleus it’s attached to a ribosome in the cytoplasm
  2. the ribosome attaches at the start codon
  3. the tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA, held
  4. the ribosome will move along 1 codon on the mRNA molecule to enable another complementary tRNA to attach to the next codon on the mRNA
  5. the 2 aminos that the tRNA has delivered are joined by a peptide bond - an enzyme catalyses this & requires ATP
  6. this continues until the ribosome reaches the stop codon at the end of the mRNA molecule - the stop codon doesn’t code for an amino & so the ribosome detaches & the translation ends

the polypeptide chain is now created & will enter the golgi body for folding & modification

37
Q

define the term gene mutation

A

it’s a change in the base sequence of the DNA

38
Q

when do gene mutations occur?

A

they randomly occur during DNA replication

39
Q

what factors increase the likelihood of gene mutations occuring?

A

mutagenic agents can interfere with DNA replication such as; high energy radiation (UV light), ionisation radiation (gamma rays & x-rays) & chemicals (carcinogens)

40
Q

how do gene mutations affect bases?

A

a gene mutation could result in a base being deleted or substituted for a different one

41
Q

state the impact of a base substitution mutation

A

it may not have an impact because the new codon may still code for the same amino - this is because the genetic code is degenerate

42
Q

state the impact of a base deletion mutation

A

base deletions result in a frameshift - removal of 1 base changes all of the subsequent codons, which is more harmful as multiple aminos being incorrectly coded for

43
Q

define the term chromosome mutation

A

mutations in the no.of chromosomes can arise spontaneously by chromosome non-disjunction during meiosis

44
Q

define the term non-disjunction

A

non-disjunction is when the chromosomes or chromatids don’t split equally during anaphase

45
Q

state the effects of chromosome non-disjunction

A

causes changes in the number or structure of whole chromosomes

46
Q

state the forms in which chromosome non-disjunction during meiosis

A
  1. changes in whole sets of chromosomes (polyploidy)
  2. changes in the number of individual chromosomes (aneuploidy)
47
Q

define the term polyploidy

A

it’s a process that changes in whole sets pf chromosomes occur when organisms have 3 or more sets of chromosomes rather than the usual 2 - mainly occurs in plants

48
Q

describe the process of polyploidy

A
  1. there are 3 homologous chromosomes - each homologous pair is doubled due to DNA replication in interphase
  2. there is non-disjunction in meiosis I - all chromosomes fail to separate equally
  3. normal division in meiosis II - chromatids separate equally
  4. in meiosis II - no chromosomes in the 2 gametes (they won’t function)
  5. also in meiosis II - normal division so the chromatids will separate equally to the opposite poles in anaphase
  6. the resulting gametes have 2 copies of every chromosome so instead of a haploid gamete there is a diploid gamete
49
Q

what occurs when a haploid gamete fuses with a diploid gamete?

A

a triploid gamete - 2 chromosomes from a diploid gamete & 1 chromosome from a haploid gamete

50
Q

define the term aneuploidy

A

changes the number of individual chromosomes

51
Q

state the cause of aneuploidy

A

causes when individual homologous pairs of chromosomes fail to separate during meiosis - this is non-disjunction & usually results in a gamete having 1 more or fewer chromosome

52
Q

explain how down syndrome occurs

A

on fertilisation with a gamete that has the normal number of chromosomes, the resultant zygote will have more or fewer chromosomes than normal in all their body cells - down’s syndrome is 3 copies of chromosome 21

53
Q

what is meiosis?

A

it involves 2 nuclear divisions & creates 4 haploid daughter cells from a single diploid parent cell

54
Q

what does meiosis produce?

A

meiosis produces daughter cells. that are genetically different from each other

55
Q

state the mechanisms involved in meiosis that introduce variation

A
  1. independent segregation of homologous chromosomes
  2. crossing over between homologous chromosomes
56
Q

when do the mechanisms that introduce variation occur?

A

in the 1st round of division in meiosis (meiosis I)

57
Q

describe the process of independent segregation

A
  1. homologous pairs of chromosomes line up opposite each other at the equator of the cell
  2. it’s random which side of the equator the paternal & maternal chromosomes from each homologous pair lie
  3. these pairs are separated, so one of each homologous pair ends up in the daughter cell
  4. this creates a large no.of possible combinations of chromosomes in the daughter cells produced - can be calculated with 2n
58
Q

describe the process of crossing over

A
  1. when homologous pairs line up opposite each other at the equator in meiosis I, parts of chromatids can become twisted around each other
  2. this puts tension on the chromatids - causes parts of the chromatids to break
  3. the broken parts of the chromatid recombine with another chromatid
  4. results in new combinations of alleles
59
Q

state the differences between meiosis & mitosis

A

meiosis:
2 nuclear divisions
results in a haploid cell (one set of chromosomes)
introduces genetic variation

whereas mitosis:
one nuclear division
results in diploid cells (two sets of chromosomes)
creates genetically identical cells

60
Q

how can meiosis be identified in a life cycle?

A

meiosis involves a diploid (2n) parent cell dividing to become a haploid (n) cell

61
Q

define the term genetic diversity

A

genetic diversity is the no.of different alleles of genes in a population

62
Q

what does genetic diversity enable?

A

natural selection

63
Q

define the term natural selection

A

it’s the process that leads to evolution in populations

64
Q

what causes evolution?

A

the changes in allele frequency over many generations in a population

65
Q

how does natural selection affect a species?

A

results in species becoming better adapted to their environment - the adaptation may be anatomical, physiological or behavioural

66
Q

describe the process of natural selection

A
  1. random mutations create new alleles for a gene
  2. if the new alleles increase the chances of the individual to survive, then they are more likely to survive & reproduce
  3. this reproduction passes on the advantageous allele to the next generation
  4. results in: over many generations, the new allele increases in frequency in the population
67
Q

state the types of selection

A
  1. directional selection
  2. stabilising selection
68
Q

what is directional selection?

A

it’s when the advantageous allele codes for an extreme trait

69
Q

when does directional selection occur?

A

occurs when there is a change in the environment - the modal trait changes

70
Q

what is stabilising selection?

A

it’s when whenever the middling trait remains the selective advantage

71
Q

when does stabilising selection occur?

A

occurs when there is no change in the environment - the modal trait remains the same

72
Q

define the term species

A

a species is when two organisms belong to the same species if they can produce fertile offspring

73
Q

how does species ensure their survival?

A

they reproduce to pass on their advantageous alleles - so courtship behaviour is essential for successful mating & species recognition

74
Q

what is courtship behaviour?

A

a sequence of actions which is unique to each species - it’s how animals identify members of their species to reproduce with

75
Q

state the importance of courtship

A

to ensure successful reproduction & survival of their offspring - enables them to recognise their species & opposite sex, synchronises mating behaviour

76
Q

what can courtship sequences tell us about species?

A

can tell us how closely related different species are - if the courtship sequence is similar between different species they are more closely related

the more similar a species sequence is = the more similar its DNA sequence is

77
Q

define the term phylogenetic classification

A

it arranges species into groups according to their evolutionary origins & relationships - tells us how closely related species are

78
Q

what is a hierarchy?

A

smaller groups arranged within larger groups - no overlaps between groups

79
Q

give an example of a hierarchy

A

domain - kingdom - phylum - class - order - family - genus - species

80
Q

what is the binomial system?

A

it’s a universal way of identifying organisms using the binomial (2 names) - 1st name is genus & 2nd name is species

81
Q

define the term species diversity

A

the no.of different species & individuals within each species in a community

82
Q

define the term species richness

A

the no.of different species in a community

83
Q

define the term genetic diversity

A

the variety of genes amongst all the individuals in a population of one species

84
Q

define the term ecosystem diversity

A

the range of different habitats

85
Q

give examples of farming techniques that reduce biodiversity

A
  1. destruction of hedgerows
  2. selective breeding
  3. monocultures
  4. over-grazing
  5. filling in ponds & draining wetlands
86
Q

define the term index of diversity

A

it describes the relationship between the no.of species in a community (species richness) & the no.of individuals in each species (population)

87
Q

how is the index of diversity calculated?

A

D = N(N - 1) / ∑n(n - 1)

N: the total no.of organisms of all species
n: total no.of organisms of a particular species
D: simpson’s diversity index

88
Q

what do we compare to investigate biodiversity?

A
  1. the frequency of observable characteristics
  2. the base sequence of DNA
  3. the base sequence of mRNA
  4. the amino acid sequence of proteins

biology (6 decks)

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