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Biology A-Level > Topic 4 - Genetic information, variation and organism relationships > Flashcards

Topic 4 - Genetic information, variation and organism relationships Flashcards

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1
Q

what are the similarities between DNA in eukaryotic cells with DNA in prokaryotic cells

A
  • nucleotide structure is identical: deoxyribose attached to phosphate and a base
  • adjacent nucleotides joined by phosphodiester bonds, complementary bonds joined by hydrogen bonds
  • DNA in mitochondria/chloroplasts have similar structure to DNA in prokaryotes: short, circular, not associated with proteins
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2
Q

what are the differences between DNA in eukarotiyc and prokaryotic cells

A
  • eukaryotic DNA is longer
  • eukaroytic DNA is linear, prokaryotic DNA is circular
  • eukaroyitc DNA is associated with histone proteins, prokaryotice DNA isn’t
  • eukaryotic DNA contain introns, prokaryotic DNA doesn’t
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3
Q

what is a chromosome

A

long linear DNA and is asssociated with histone proteins found in the nucleus of eukaryotic cells

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4
Q

what is a gene

A

a sequence of DNA (nucleotide) bases that code for:
- the amino acid sequence of a polypeptide
or
- a functional RNA e.g. ribosomal RNA or tRNA

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5
Q

what is a locus

A

the fixed position a gene occupies on a particular DNA molecule

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6
Q

describe the nature of the genetic code

A

triplet code, universal, non-overlapping, degenerate

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7
Q

what does triplet code mean

A

a sequence of 3 DNA bases, called a triplet, codes for a specific amino acid

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8
Q

what does universal mean

A

the same base triplets code for the same amino acids in all organisms

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9
Q

what does non-overlapping mean

A

each base is part of only one triplet so each triplet is read as a discrete unit

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10
Q

what does degenerate mean

A

an amino acid that can be coded for by more than one base triplet

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11
Q
A
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12
Q

where are non coding bases sequences found

A
  • btwn genes e.g. non coding multiple repeats
  • w/n genes - introns
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13
Q

fact

A

in eukaryotes, much of the nuclear DNA doesn’t code for polypeptides

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14
Q

what are introns

A

base sequence of a gene that doesn’t code for amino acids in eukaryotic cells

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15
Q

what are exons

A

base sequence of a gene coding for amino acid sequences

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16
Q

define genome

A

the complet set of genes in a cell incl. those in mitochondria and/or chloroplasts

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17
Q

define proteome

A

the full range of proteins that a cell can produce coded for by the cell’s DNA/genome

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18
Q

what are the two stages of protein synthesis

A

transcription and translation

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19
Q

describe transcription

A

production of mRNA from DNA in the nucleus

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20
Q

describe translation

A

production of polypeptides from the sequence of codons carried by mRNA at ribosomes

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21
Q

what is the similarity btwn tRNA and mRNA

A

both single polynucleotide strand

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22
Q

what are the differences btwn tRNA and mRNA

A
  • tRNA is folded into a clover leaf shape whereas mRNA is linear/straight
  • tRNA has hydrogen bonds btwn paired bases, mRNA doesn’t
  • tRNA is a shorter, fixed length whereas mRNA is a longer, variable length (more nucleotides)
  • tRNA has an anticodon, mRNA has codons
  • tRNA has an amino binding site, mRNA doesn’t
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23
Q

describe how mRNA is formed by transcrription in eukaryotic cells

A
  • hydrogen bonds btwn DNA bases break
  • only one DNA strand acts as a template
  • free RNA nucleotides align next to their complementary bases on the template strand. in RNA uracil is used instnead of thymine
  • RNA polymerase joins adjacent RNA nucleotides
  • this forms phosphodiester bonds via condensation reactions
  • pre-mRNA is formed and this is spliced to remove introns forming mature mRNA
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24
Q

describe how production of mRNA in eukaryotic cell is different from the production of mRNA in a prokaryotic cell

A
  • pre-mRNA is produced in eukaryotic cells whereas mRNA is produced directly in prokaryotic cells
  • genes in prokaryotic cells don’t contain introns so no splicing in prokaryotic cells
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25
Q

describe how translation leads to the production of a polypeptide

A
  • mRNA attaches to a ribosome and the ribosome moves to a start codon
  • tRNA brings a specific amino acid
  • tRNA anticodon binds to complementary mRNA codon
  • ribosome moves along to the next codon and another tRNA binds so 2 amino acids can be joined by a condensation reaction forming a peptide bond using energy from hydrolysis of ATP
  • tRNA released after amino acid joined polypeptide
  • ribosome moves along mRNA to form the polypeptide until a stop cocon is reached
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26
Q

describe the role of ATP in translation

A

hydrolysis of ATP to ADP + Pi releases energy so amino acids join to tRNAs and peptide bonds form btwn amino acids

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27
Q

describe the role of tRNA in translation

A
  • attaches to transports a specific amino acid, in relation to its anticodon
    tRNA anticodon
  • complementary base pairs to mRNA codon, forming hydrogen bonds
  • 2 tRNAs bring amino acids together so peptide bond can form
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28
Q

describe the role of ribosomes in translation

A
  • mRNA binds to ribosomes with space to 2 codons
  • allows tRNA with anticodons to bind
  • catalyses formation of peptide bond btwn amino acid, held by tRNA molecules
  • moves along mRNA to the next codon e.g. translocation
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29
Q

describe how the base sequence of nucleic acids can be related to the amino acid sequence of polypeptides when provided with suitable data

A
  • may be provided with a genetic code to identify which triplets/codons produce which amino acids
  • tRNA anticodons are complementary to mRNA codons
  • sequence of codons on mRNA are complementary to sequence of triplets on DNA template strand
  • in RNA uracil replaces thymine
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30
Q

what is a gene mutation

A

a change in base sequence of DNA on chromosomes which can arise spontaneously during DNA replication (interphase)

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31
Q

what is mutagenic agent

A

a factor that increases rate of gene mutation e.g. ultraviolet light or alpha particles

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32
Q

explain how a mutation can lead to the production of a non-functional protein or enzyme

A
  • changes in sequence of base triplets in DNA so changes seuqence of codons on mRNA
  • changes sequence of amino acids in polypeptides
  • changes position of hydrogen.ionic.disulphide bonds btwn amino acids
  • changes protein tertiary structure of protein
  • enzymes active site changes shape so substrate can’t bind, enzyme substrate complex can’t form
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33
Q

explain the possible effects of a substitution mutation

A
  • base/nucleotide in DNA replaced by a different base/nucleotide
  • this changes on triplet so changes one mRNA codon
  • so one amino acid in polypeptide changes, tertiary structure may change if position of hydrogen/ionic/disulphide bonds change
    OR
    amino acid doesn’t change due to degenerate nature of genetic code/mutation is in an intron
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34
Q

explain the positive effects of a deletion mutation (there’s 6)

A
  • one nucleotide/base removed from DNA sequence
  • changes sequence of DNA triplets from point of mutation (frameshift)
  • changes sequence of mRNA codons after point of mutation
  • changes sequence of amino acids in primary structure of polypeptide
  • changes position of hydrogen/ionic/disulphide bonds in tertiary structure of protein
  • changes tertiary structure/shape of protein
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35
Q

state the features of homologous chromosomes

A

same length, same genes but may have different alleles

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36
Q

describe the difference btwn diploid and haploid cells

A

diploid has 2 complete sets of chromosomes, represented as 2n

haploid has a single set of unpaired chromosomes represented as n

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37
Q

describe interphase in meiosis

A

DNA replicates, 2 copies of each chromosome [sister chromatids] joined by a centromere

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38
Q

describe meiosis I in meiosis

A

this is the first nuclear division which separates homologous chromosomes
- chromosomes arrange into homologous pairs
- crossing over btwn homologous chromosomes
- independent segregation of homologous chromosomes

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39
Q

describe meiosis II in meiosis

A

this is the 2nd nuclear division which separates chromatids

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40
Q

what is the outcome of meiosis

A

4 genetically varied daughter cells and they are usually haploid is there is a diploid parent cell

41
Q

explain why the number of chromosomes is halved during meiosis

A

homologous chromosomes are separated during meiosis I (first division)

42
Q

explain how crossing over creates genetic variation

A
  • homologous pairs of chromosomes associate/form a bivalent
  • chiasmata form (point of contact btwn non-sister chromatids - aka homologous pairs)
  • alleles (equal lengths) of non sister chromatids exchanged btwn chromosomes
  • creating new combinations of maternal and paternal alleles on chromosomes
43
Q

explain how independent segregation creates genetic variation

A

homologous pairs randomly align at equator so random which chromosome from each pair goes into each daughter cell. this creates different combinations of maternal or paternal chromosomes/alleles in daughter cells

44
Q

other than mutation and meiosis, explain how genetic variation w/n a species is increased

A
  • random fertilisation/fusion of gametes
  • creating new allele combinations/new maternal and paternal chromosome combinations
45
Q

explain the different outcomes of mitosis and meiosis

A
  • mitosis produces 2 daughter cells whereas meiosis produces 4 daughter cells (1 division vs 2)
  • mitosis maintains the chromosome number (diploid to diploid or haploid to haploid) but meiosis halves the number of chromosomes cuz homologous chromosomes separate in meiosis and not mitosis
  • mitosis produces generically identical daughter cells whereas mitosis produces genetically varied daughter cells
46
Q

explain the importance of mitosis

A

two divisions creates haploid gametes so diploid number is restored at fertilisation - chromosome number is maintained btwn generations.
independent segregation and crossing over creates genetic variation

47
Q

where does mitosis occur in a life cycle

A

occurs btwn stages where chromosome number is maintained

48
Q

where does meiosis occur in a life cycle

A

occurs btwn stages where chromosome number is halved

49
Q

describe how mutations in the number of chromosomes arise

A
  • spontaneously by chromosome non-disjunction during meiosis
  • homologous chromosomes (meiosis I) or sister chromatids (meiosis II) fail to separate during meiosis
  • so some gametes have an extra copy (n=1) of a particular chromosome and others have none (n-1)
50
Q

suggest how number of possible combinations of chromosomes in daughter cells following meiosis can be calculated

A

2^n where n = number of pars of homologous chromosomes (half the diploid number)

51
Q

suggest how number of possible combinations of chromosomes in daughter cells following random fertilisation of two gametes can be calculated

A

(2^n)^2 where n = number of pairs of homologous chromosomes (half the diploid number)

52
Q

what is genetic diversity

A

number of different alleles of genes in a population

53
Q

what are alleles

A

variations of a particular gene with the same locus that has different base sequence

54
Q

how do alleles arise

A

via mutation

55
Q

what is a population

A

a group of interbreeding individuals of the same species

56
Q

explain the importance of genetic diversity

A
  • enables natural selection to occur
  • as in certain environments, a new allele of a gene might benefit its possessor
  • by resulting in a change in the polypeptide coded for that positively changes its properties
  • giving a possesser a selective advantages this means increased chances of survival and reproductive success
57
Q

what is evolution

A

change in allele frequency over many generations in a population occurring through the process of natural selection

58
Q

name 2 factors which are major factors in evolution and contribute to the diversity of living organisms

A

adaptation and selection

59
Q

state and explain the 5 principles of natural selection in the evolution of populations

A

mutation - random gene mutation can result in [named] new alleles of a gene
advantage - in certain [named] environments the new allele might benefit its possessor [explain why] -> organism has a selective advantage
reproductive success - possessors are more likely to survive and have increased reproductive success
inheritance - advantageous allele is inherited by members of the next generation (offspring)
allele frequency - over many generations, [named] allele increases in frequency in the population

60
Q

what does natural selection result in

A

species that are better adapted to their environment

61
Q

state 3 types of adaptations

A

anatomical, behavioural, physiological

62
Q

describe anatomical adaptation

A

structural/physical features which increase chance of survivial

63
Q

describe physiological adaptation

A

processes/chemical reactions that increase chance of survival

64
Q

describe behavioural adaptation

A

ways in which an organaism acts that increases chance of survival

65
Q

what is directional selection

A
66
Q

give an example of directional selection

A

antibiotic resistance in bacteria. those with an extreme variation of a trait has selective advantage. usually change in environment

67
Q

what is the effect of directional selection on population over many generations

A

increased frequency of organisms with alleles for extreme trait. normal distribution curve shifts towards extreme trait

68
Q

what is stabilising selection

A
69
Q

give an example of stabilising selection

A

human birth weight - those with average/modal variation of a trait has selective advantage. no change in environment, usually stable

70
Q

what is the effect of stabilising selection on population over many generations

A

increased frequency of organisms with alleles for average trait. normal distribution curve is similar/less variation around the mean (graph curve squeezes in gets taller n thinner, like maxwell boltzham distribution curve when temp cold)

71
Q

what is a speicies

A

a group of organisms that can interbreed to produce fertile offspring

72
Q

suggest why 2 different species are unable to produce fertile offspring

A
  • different species have different chromosome numbers -> offspring may have odd chromosome number
  • homologous pairs cannot form = meiosis cannot occur to produce gametes
73
Q

explain why courtship behaviour is a necessary precursor to successful mating (5 reasons)

A
  • allows recognition of members of same species so fertile offspring is produced
  • allows recognition/attraction of opposite sex
  • stimulates/synchronises mating/production/release of gametes
  • indicates sexual mating/fertility
  • establishes a pair bond to raise young
74
Q

describe a phylogenetic classification system

A

species attempted to be arranged into groups called taxa, based on their evolutionary origins (common ancestors) and relationships
uses a hierarchy where:
- similar groups are placed w/n larger groups
- no overlaps btwn groups

75
Q

name the taxa in the hierarchy of classification

A

domain
kingdom
phylum
class
order
family
genus
species

76
Q

how is each species universally identified

A

binomial naming - genus and species

77
Q

suggest an advantage of binomial naming

A

universal so no confusion as many organisms have more than one common name

78
Q

how do you interpret phylogenetic trees

A
  • branch point = common ancestor
  • branch = evolutionary path
  • if two species have a more recent common ancestor, they are more closely related
79
Q

what two advances have helped clarify evolutionary relationships btwn organisms

A

genome sequencing, immunology

80
Q

explain how advances in genome sequencing has helped to clarify evolutionary relationships btwn organisms

A
  • allows comparison of DNA base sequences
  • more differences in DNA base sequences = more distantly related/earlier common ancestor
  • mutations build up over time
81
Q

explain how advances in immunology has helped to clarify evolutionary relationships btwn organisms

A
  • allows comparison of protein tertiary structure
  • higher amount of protein from one species binds to antibody against same protein from another species = more closely related/more recent common ancestor
  • indicates similar amino acid sequence and tertiary structure = less time for mutations to build up
82
Q

what is biodiversity

A

variety of living organisms - species, genetic and ecosystem diversity

83
Q

what is a community

A

all populations of different species that live in an area

84
Q

what is species richness

A

a measure of the number of different species in a community

85
Q

what does an index of diversity do

A

describes the relationship btwn
- number of species in a community = species richness
- number of individuals in each species = population size

86
Q

suggest why index diversity is more useful than species richness

A

also takes into account number of individuals in each species so takes into account that some species may be present in small or high numbers

87
Q

what is the formula for index diversity

A

d = [N(n-1)]/ sum of n(n-1)

where N = total number of organisms of all species
n = total number of organisms of each species

88
Q

describe how index of diversity values can be interpreted

A

high = many species present and species evenly represented
low = habitat dominated by one/few species

89
Q

state 4 farming techniques which reduces biodiversity

A
  • removal of woodland and hedgerows
  • monoculture
  • use of herbicides to kill weeds
  • use of pesticides to kill pests
90
Q

how does:
- removal of woodland and hedgerows
- monoculture
- herbicides

reduce biodiversity

A

reduces variety of plants = fewer habitats so less variety of food sources

91
Q

how does pesticides reduce biodiversity

A

predator population of pest decreases

92
Q

explain the balance btwn conservation and farming

A

conservation required to increase biodiversity but when implemented on farms, yields and profit will reduce for farmers as it reduces land area for crop growth, increasing competition and pest population
to offset loss, financial incentives/grants are offered

93
Q

give 4 examples of how biodiversity can be increased in area of agriculture

A
  • reintroduction of field margins and hedgerows
  • reduce use of pesticides
  • growing different crops in the same area (intercropping)
  • using crop rotation of nitrogen fixing crops instead of feertilisers
94
Q

state four ways genetic diversity w/n or btwn species can be measured

A
  • comparing frequency of measurable or observable characteristics
  • comparing base sequence of DNA
  • comparing base sequence of mRNA
  • comparing amino acid sequence of a specific protein encoded by DNA and mRNA
95
Q

explain how comparing DNA, mRNA and amino acid sequences can indicate relationships btwn organisms w/n a species and btwn species

A
  • more difference in sequences = more distantly related/earlier common ancestor
  • as mutations build up over time. more mutations = more changes in amino acid sequences
96
Q

explain the change in methods of investigating genetic diversity over time

A

early estimates made by inferring DNA differences from measurable or observable characteristics
- many coded for by more than one gene = difficult to distinguish one from another
- many influenced by environment = differences due to environment not gene
gene technologies allowed this to be replaced by direct investigation of DNA sequences

97
Q

explain the key considerations in quantitative investigations of variation w/n a species

A
  • collect data from random samples to remove bias
  • large sample size to get a representative of whole population
  • ethical sampling, must not harm organism/allow release unchanged
  • calculate a mean value of collected data and standard deviation of that mean
  • interpret mean values and their standard deviations
  • use [named] statistical test to analyse if there is a significant difference btwn populations
98
Q

what does standard deviation show

A

spread of values about the mean, the higher the standard deviation, the higher the variation
if standard deviations overlap, causing 2 sets of data to be shared, any difference btwn the 2 may be due to chance/not significant

Biology A-Level (11 decks)

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