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A-level Biology > Unit 3.4 - Genetic information, variation > Flashcards

Unit 3.4 - Genetic information, variation Flashcards

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1
Q

what is DNA in eukaryotic cells like?

A
  • it contains linear dna molecules that exist as chromosomes each made up of one long molecule of dna found in the nucleus. the dna molecules are wound around histone proteins which help to support the dna.
  • the dna and protein is then coiled up very tightly to make a chromosome
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2
Q

what is DNA like in prokaryotic cells?

A
  • they also carry dna as chromosomes, but the dna molecules are shorter and circular.
  • the dna isn’t wound around proteins, it condenses to fit in the cell by supercoiling
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3
Q

what is a gene?

A
  • its a sequence of dna bases codes for a polypeptide or functional rna. the sequence of amino acids in a polypeptide forms the primary structure of a protein.
  • different polypeptides have a different number and order of amino acids. its the order of bases in gene that determines the order of amino acids in a polypeptide
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4
Q

how is each amino acid coded?

A
  • coded for by a sequence of three bases in a gene called a triplet
  • to make a polypeptide, dna is copied into mRNA
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5
Q

what is the cell’s genome?

A
  • the complete set of genes in the cell

- a cells proteome is the full range of proteins that the cell is able to produce

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6
Q

what happens to genes in eukaryotic dna?

A
  • genes that do code for polypeptide contain sections that don’t code for amino acids, these sections of dna are called introns
  • all the bits of a gene that do code for an amino acid are called exons
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7
Q

wheb are introns removed?

A
  • during protein synthesis so they don’t affect the amino acid order
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8
Q

what are non coding repeats?

A
  • eukaryotic dna contains regions of multiple repeats of genes, they don’t code amino acids either so they’re called non coding repeats
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9
Q

what’s an allele?

A
  • a gene that can exist in more than one form, the order of bases in each allele is different, so they code for slightly different versions of the same polypeptide
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10
Q

what is mRNA?

A
  • its made during transcription. it carries the gentic code from the dna to the ribosomes, where its used to make a protein during transcription
  • mRNA is a single polynucleotide strand. in mRNA, groups of three adjacent bases are called codons
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11
Q

what is tRNA?

A
  • its involved in translation. it carries the amino acids that are used to make proteins to the ribosomes
  • its a single polynucleotide strand that’s folded into a clover shape, H bonds between specific base pairs hold the shape
  • every trna molecule has a specific sequence of three bases at one end called an anticodon, at the other end is an amino acid bonding site
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12
Q

what are the first 3 stages of transcription?

A

1 - RNA polymerase attaches to the DNA double helix at the beginning of a gene
2- the hydrogen bonds between the two DNA strands in the gene break, separating the strands and the DNA molecule uncoils at that point exposing some of the bases
3 - one of the strands is then used a template

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13
Q

what are stages 4&5 of transcription?

A

4 - RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand. the free bases are attached to the exposed bases. specific, complementary base pairing, means that mRNA strand ends up being a complementary copy of the DNA template strand (t swapped with U)
5 - once RNA nucleotides have paired up with their specific bases on dna strand, they’re joined together by RNA polymerase forming an mRNA molecule

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14
Q

what are the last four stages of transcription?

A

6 - the RNA polymerase moves along the dna, separating the strands and assembling the mRNA strand
7 - the H bonds between the uncoiled strands of dna re-form once the RNA polymerase has passed by and the strands coil back into a double helix
8 - when RNA polymerase reaches a particular sequence of dna called a stop signal, it stops making mRNA and detaches from the dna
9 - in eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm

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15
Q

what are the first two stages of translation?

A

1 - the mRNA attaches itself to a ribosome and transfer rna (tRNA) molecules carry amino acids to it. ATP provides the energy needed for the bond between the amino acid and the tRNA molecule to form
2 - a tRNA molecule (carrying amino acid), with an anticodon that’s complementary to the first codon on the mRNA, attaches itself to the mRNA by specific base pairing

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16
Q

what are stages 3,4 and 5 of translation?

A

3 - a second tRNA molecule attaches itself to the next codon
4 - the two amino acids attached to the tRNA molecules are joined by a peptide bond. the first tRNA molecule moves away, leaving the amino acid behind
5 - a third tRNA molecule binds to the next codon, its amino acid binds to the first two and the second tRNA molecule moves away

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17
Q

what are stages 6 and 7 of translation?

A

6 - this process continues, producing a chain of linked amino acid ( a polypeptide chain) until there’s a stop signal on the mRNA
7 - the polypeptide chain moves away from the ribosome and translation is finished

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18
Q

what happens to the introns and exons in eukaryotes?

A
  • the introns and exons are both copied into mRNA during transcription, mRNA strands containing introns and exons are called pre-MRNA.
  • process called splicing occurs - introns are removed and the exons are joined together forming mRNA strands, this takes place in the nucleus
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19
Q

what happens introns in prokaryotes?

A
  • in prokaryotes, mRNA is produced directly from the dna without splicing taking place, as there are no introns in prokaryotic dna
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20
Q

How is the genetic code non overlapping?

A

The sequence of base triplets (codons) in mRNA which code for specific amino acids.
- In the code each base triplet is read in sequence, separate from the triplet before it and after it. Base triplets don’t share their bases, the code is non-overlapping

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21
Q

How is the genetic code degenerate?

A

It means there are more possible combinations of triplets than there are amino acids. This means that some amino acids are coded for by more than one base triplet

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22
Q

How is the generic code universal?

A
  • where the same specific base triplets code for the same amino acids in all living things
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23
Q

What are stop and start signals?

A
  • some triplets are used to tell the cell when to start and stop production of the protein - these are start and stop signals (codons). They’re found at the beginning and end of the mRNA
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24
Q

What happens when meiosis happens properly and not properly?

A

Properly - all four daughter cells will have 23 whole chromosomes one from each homologous pair
Not properly- the cells produced contain variations in the numbers of whole chromosomes or parts of it

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25
Q

What is chromosome mutation?

A

Its causes by errors during meiosis, they lead to inherited conditions because the errors are present in the gametes
Eg: one type of chromosome mutation is called non-disjunction its a failure of tje chromosomes to separate properly.

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26
Q

What is Down’s syndrome?

A
  • its caused by a person having an extra copy of chromosome 21. Non-disjunction means that chromosome 21 fails to separate properly during meiosis, so one cell gets an extra copy of 21 and another gets none
  • when the gamete with extra copy fuses to another gamete at fertilisation, the resulting zygote will have three copies of chromosome 21
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27
Q

What are the two types of mutations?

A

1) . Substitution - one base is substituted with another

2) . Deletion - one base is deleted

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28
Q

What does the degenerate nature of the genetic code mean?

A

It means that some amino acids are coded for by more than one dna triplet. So not all substitution mutations will result in a change to the amino acid sequence of the protein. Some substitutions will still code for the same amino acid

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29
Q

what does a deletion cause?

A
  • deletions will lead to changes in the amino acid sequence. the deletion of a base will cause a shift in all the base triplets after it
30
Q

what are mutagenic agents?

A
  • they are certain things that can cause an increase in the rate of mutations including UV radiation, some chemicals and some viruses are examples
31
Q

what is biodiversity, habitat and community?

A
  • biodiversity = the variety of living organisms in an area
  • habitat = the place where an organisms lives
  • community = all the populations of different species in a habitat
32
Q

what is local and global biodiversity?

A
  • local biodiversity = you could consider the variety of different species living in a small habitat that’s local
  • global biodiversity = you could also consider the variety of species on earth, it varies around the world but it is greatest at the equator and decreases towards the poles
33
Q

what is species richness?

A
  • a measure of the number of different species in a community. it can measure biodiversity too. the number of different species in a community isn’t the only thing that affects biodiversity. the population size of those species do too.
  • species that are in a community in very small numbers shouldn’t be treated the same as those with bigger populations
34
Q

what is the index of biodiversity?

A
  • another way of measuring biodiversity. the higher the number, the more diverse the area is. Using this formula. d=N(N-1) divided by the sum of n(n-1)
  • N is the total number of all species
  • n is the total number of organisms of one species
35
Q

what methods do farmers use that reduce biodiversity?

A
  1. woodland clearance - done to increase the area of farmland. it reduces the no of trees and destroys habitats so species could lose their shelter and food source. they then die or are forced to migrate
  2. hedgerow removal - done to increase the area of farmland by turning lots of small fields into larger fields
  3. pesticides - chemicals that kill pests that feed on crops. this reduces diversity by directly killing the pests. any species that feed on pests will lose their food source also
  4. herbicides - chemicals that kill weeds. this reduces plant biodiversity and could reduce the number of organisms that feed on weeds
  5. monoculture - when farmers have field containing only one type of plant, this reduces biodiversity and will support fewer organisms
36
Q

how do conversationalists protect biodiversity?

A
  1. giving legal protection to endangered species
  2. creating protected areas eg SSSIs which restrict further development, including agricultural development
  3. environmental stewardship scheme which encourages farmers to conserve biodiversity eg by replacing hedgerows
37
Q

what is taxonomy?

A
  • the science of classification. it involves naming organisms and organising them into groups. there are eight levels to classifying organisms, they are called taxa.
  • each group is called a taxon. the groups are arranged in a hierarchy, with the largest groups at the top and the smallest groups at the bottom
38
Q

how are organisms sorted in taxonomy?

A
  • they are first sorted into three large groups called domains - Eukarya, Bacteria and Archaea. related organisms in a domain are sorted into smaller groups called kingdoms.
  • ## more closely related organisms from that kingdom are sorted in a phylum and so on down the eight levels
39
Q

what is the trend in taxonomy?

A
  • as you move down the hierarchy, there are more groups at each level but fewer organisms, the organisms in each group also become closely related. - organisms can only belong to one group at each level, there is no overlap
40
Q

what does the hierarchy end in?

A
  • species, which are a group of similar organisms able to reproduce to give fertile offspring
41
Q

what is the binomial system?

A
  • the nomenclature used for classification is the binomial system - all organisms are given one internationally accepted scientific name in latin that has two parts
  • the first part is the genus name and has a capital letter, the second par is the species name. it is used to avoid confusion by using common names
42
Q

what is courtship behaviour?

A
  • its carried out by organisms to attract a male of the right species. it is species specific - only members of the same species will do and responds to that behaviour.
  • this allows members of the same species to recognise each other, preventing interbreeding and making reproduction more successful
43
Q

what can courtship behaviour be used for?

A
  • to classify organisms as the more closely related species are, the more similar their courtship behaviour
44
Q

what is genetic diversity?

A
  • the number of different alleles of genes in a species or a population. it is increased within a population by:
    1. mutations in the dna - forming new alleles
    2. or GENE flow where different are alleles introduced into a population when individuals from another population migrate into them and reproduce
45
Q

what is a genetic bottleneck?

A
  • an event that causes a big reduction in a population eg when a large number of organisms within a population die before reproducing. this reduces the number of different alleles in the gene pool and so reduces genetic diversity.
46
Q

what is the founder effect?

A
  • it describes what happens when just few organisms from a population start a new colon ans there are only a small number of different alleles in the initial gene pool
  • the effect can occur as a result of migration leading to geographical separation or if a new colony is separated from the original population
47
Q

describe the problem ssociated with the frequency in the founder effect?

A
  • the frequency of each allele in the new colony might be very different to the frequency of those alleles in the original population.
    eg an allele that was rare in the original population might be more common in the new colony which can lead to a higher incidence of genetic disease
48
Q

what is natural selection?

A
  • when an allele that codes for a characteristic that increases the chances of an organism surviving, its frequency within the population can increase
49
Q

how does natural selection work?

A

1 - not all individuals are as likely to reproduce as each other. there’s a differential reproductive success in a population - a allele that increases an organisms chance of survival are more likely to survive and pass on genes
2- this means that a greater proportion of the next generation will inherit the beneficial genes
3 - they are then more likely to survive, reproduce and pass on their genes
4 - so the frequency of the beneficial allele increases from generation to generation
5- over generations this leads to evolution as the advantageous alleles become common in the population

50
Q

whats evolution?

A
  • the gradual change in species over time, adaption and selection are key factors in evolution. it has lead to the huge diversity of living organisms
51
Q

what are behavioural adaptions?

A
  • ways an organism acts that increases that chance of survival and reproduction eg some animals play dead if they’re being threatened by a predator to escape attack
52
Q

what are physiological adaptions?

A
  • processes inside an organisms body that increases its chance of survival. eg brown bears hibernate over winter, this lowers their metabolic rate which conserves energy, so they don’t need to look for food in the months when its scarce
53
Q

what are anatomical adaptions?

A
  • structural features of an organisms body that increase the chance of survival eg whales have a thick layer of blubber which keeps them warm in the sea
54
Q

what is a homologous pair?

A

its always two chromosomes that carry the same genes but not necessarily the same alleles of the genes.

55
Q

what do changes in the base sequence of a gene do?

A

it produces a new allele of that gene and results in a different sequence of amino acids being coded for. this different amino acid sequence will lead to the production of a different polypeptide and so a different protein. this protein may not function properly

56
Q

describe RNA?

A
  • the pentose sugar ribose
  • one of the organic bases A, C, G and U
  • a phosphate group
57
Q

what is species diversity?

A

refers to the number of different species and the number of individuals of each species within any one community

58
Q

what is ecosystem diversity?

A

refers to the range of different habitats from a small local habitat to the whole of the earth

59
Q

what happens when a change occurs in whole sets of chromosomes?

A

it occurs when organisms have three or more sets of chromosomes rather than the usual two. this condition is called polyploidy and occurs mostly in plants

60
Q

what is mitosis and meiosis?

A
  • mitosis produces two daughter cells with the same number of chromosomes as the parent cell and as each other
  • meiosis usually produces four daughter cells, each with half the number of chromosomes as the parent cell
61
Q

what do every diploid cell of organism have?

A

it has two complete sets of chromosomes, one set provided by each parent. during meiosis, homologous pairs of chromosomes separate, so that only one chromosome from each pair enters a daughter cell. this is HAPLOID number of chromosomes

62
Q

what does meiosis involve?

A
  • first division meiosis 1: homologous chromosomes pair up and their chromatids wrap around each other. equivalent portions of these chromatids may be exchanged in crossing over.
  • second division meiosis 2: the chromatids move apart. at the end of meiosis 2, four cells have usually been formed. in humans, each of these cells contain 23 chromosomes
63
Q

how does meiosis bring about genetic variation?

A

1- independent segregation of homologous pairs

2- new combinations of maternal and paternal alleles by crossing over

64
Q

describe independent segregation of homologous chromosomes?

A
  1. during meiosis 1, each chromosome lines up alongside its homologous partner, there will be 23 homologous pairs of chromosomes
  2. when these pairs arrange themselves in this line they do so at random, one of each pair will pass to each daughter cell
  3. the combination of chromosomes of maternal and paternal origin that go into the daughter cell at meiosis 1 is chance -> INDEPENDENT SEGREGATION
65
Q

what does each gamete have?

A

it has its own make-up and their random fusion therefore produces variety in offspring

66
Q

what happens after each chromosome lines up alongside its homologous partner?

A
  1. the chromatids of each pair become twisted around one another
  2. during the twisting process tensions are created and portions of the chromatids break
  3. these broken portions might then rejoin with the chromatids of its homologous partner
  4. usually its the equivalent portions of homologous chromosomes that are exchanged
  5. in this way new genetic combinations of maternal and paternal alleles are produced
67
Q

how does crossing over increase genetic variety?

A

if there is no recombination by crossing over only two different types of cell are produced. however if recombination does occur, four different cell types are produced which increases variety

68
Q

what is the equation that can be used to calculate the number of chromosomes in an organism to determine the possible combinations of chromosomes for each daughter cell?

A

2n = where n is the number of homologous chromosomes

69
Q

how does courtship behaviour help mating?

A
  1. recognise members of their own species
  2. identify a mate that is capable of breeding
  3. form a bond pair
  4. synchronise mating so that it takes place where there is maximum probability a egg and sperm will meet
  5. become able to breed by bringing member of the opposite sex into state that allows them to breed
70
Q

what is phylogenetic classification?

A
  1. based upon evolutionary relationships between organisms and ancestors
  2. classifies species into groups using shared features
  3. arranges the groups into a hierarchy in which these groups are contained within larger groups no overlaps
71
Q

how do we determine the evolutionary relationships between organisms?

A
  1. comparison of observable characteristics, based on the fact that their determined by certain genes. (has limitations as large number of features coded for by more than one gene, some features influenced by environment)
  2. comparison of DNA base sequences,
  3. comparison of base sequence of mRNA
  4. comparison of amino acid sequences in proteins

A-level Biology (8 decks)

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