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Biology and Psychology > Genetic Information and Variation > Flashcards

Genetic Information and Variation Flashcards

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1
Q

Give 2 similarities between DNA in eukaryotic cells and DNA in prokaryotic cells

A
  • Nucleotide structure is identical - deoxyribose attached to phosphate and a base
  • Adjacent nucleotides joined by phosphodiester bonds and complementary bases joined by hydrogen bonds
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2
Q

Give 4 differences between DNA in eukaryotic cells and DNA in prokaryotic cells

A
  • Eukaryotic DNA is longer
  • Eukaryotic DNA is linear, prokaryotic DNA is circular
  • Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not
  • Eukaryotic DNA contain introns, prokaryotic DNA does not
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3
Q

What is a chromosome?

A

Long, linear DNA and its associated histone proteins, found in the nucleus of eukaryotic cell

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4
Q

What is a gene?

A

A sequence of DNA bases that codes for a 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

Fixed position a gene occupies on a particular DNA molecule.

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6
Q

What are the 3 features of the genetic code and explain what they mean.

A
  • Universal: The same base triplets code for the same amino acids in all organisms
  • Non-overlapping: Each base is part of only one triplet so each triplet is read as a discrete unit
  • Degenerate: An amino acid can be coded for by more than one base triplet
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7
Q

Why is the genetic code described as a triplet code?

A

Because each amino acid is coded for by 3 DNA bases

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8
Q

What are introns and exons?

A

Exon: Base sequence of a gene coding for amino acid sequences (in a polypeptide)
Intron: Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells

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9
Q

What is the genome?

A

The complete set of genes in a cell

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10
Q

What is the proteome?

A

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

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11
Q

Briefly describe the two stages of protein synthesis

A
  • Transcription: Production of messenger RNA from DNA, happens in the nucleus
  • Translation: Production of polypeptides from the sequence of codons carried by mRNA, happens at ribosomes
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12
Q

Give the differences between the structure of tRNA and mRNA

A
  • tRNA is folded into a ‘clover leaf shape’, whereas
    mRNA is linear / straight
  • tRNA has hydrogen bonds between 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 acid binding site, mRNA doesn’t
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13
Q

Describe how mRNA is formed by transcription in eukaryotic cells

A
  1. Hydrogen bonds between DNA bases break, catalysed by DNA Helicase
  2. One DNA strand acts as a template
  3. Free RNA nucleotides align next to their complementary bases on the template strand. In RNA, uracil is used in place of thymine (pairing with adenine in DNA)
  4. RNA polymerase joins adjacent RNA nucleotides
  5. This forms phosphodiester bonds via condensation reactions
  6. Pre-mRNA is formed and this is spliced to remove introns, forming mRNA
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14
Q

Describe how translation leads to the production of a polypeptide

A
  1. mRNA attaches to a ribosome and the ribosome moves to a start codon (AUG)
  2. tRNA brings a specific amino acid
  3. tRNA anticodon binds to complementary mRNA codon
  4. Ribosome moves along to 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
  5. tRNA released after amino acid joined polypeptide
  6. Ribosome moves along mRNA to form the polypeptide, until a stop codon is reached
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15
Q

Describe the role of ATP, tRNA and ribosomes in translation

A
  • ATP: Hydrolysis of ATP to ADP + Pi releases energy, so amino acids join to tRNAs and peptide bonds form between amino acids
  • tRNA: Attaches to and transports specific amino acids 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.
  • Ribosomes: mRNA binds to ribosome, with space for 2 codons. Allows tRNA with anticodons to bind and catalyses formation of peptide bond between amino acids. It then moves along to the next codon
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16
Q

What is a gene mutation?

A

A change in the base sequence of DNA, can occur spontaneously during DNA replication in interphase

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17
Q

What is a mutagenic agent?

A

A factor that increases rate of gene mutation, e.g. ultraviolet (UV) light or alpha particles.

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18
Q

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

A
  1. Changes sequence of base triplets in DNA (in a gene) so changes sequence of codons on mRNA
  2. So changes sequence of amino acids in the polypeptide
  3. So changes position of hydrogen / ionic / disulphide bonds (between amino acids)
  4. So changes protein tertiary structure (shape) of protein
  5. Enzymes - active site changes shape so substrate can’t bind, enzyme-substrate complex can’t form
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19
Q

Explain the possible effects of a substitution mutation

A
  1. DNA base is replaced by a different base
  2. This changes one triplet so changes one mRNA codon.
  3. So one amino acid in the polypeptide chain changes. Tertiary structure may change if position of hydrogen/ionic/disulphide bonds change.
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20
Q

Explain the possible effects of an addition or deletion mutation

A
  1. One nucleotide / base removed or added from DNA sequence
  2. Changes sequence of DNA triplets from point of mutation (frameshift)
  3. Changes sequence of mRNA codons after point of mutation
  4. Changes sequence of amino acids in primary structure of polypeptide
  5. Changes position of hydrogen / ionic / disulphide bonds in tertiary
    structure of protein
  6. Changes tertiary structure / shape of protein
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21
Q

Describe the difference between diploid and haploid cells

A

Diploid cells have 2 complete sets of chromosomes, and Haploid cells have a single set of unpaired chromosomes

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22
Q

Describe how a cell divides by meiosis

A
  1. Meiosis I separates homologous chromosomes
    * Chromosomes arrange into homologous pairs
    * Crossing over between homologous chromosomes
    * Independent segregation of homologous chromosomes
  2. Meiosis II separates sister chromatids, resulting in 4 genetically varied haploid daughter cells
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23
Q

Explain why the number of chromosomes is halved during meiosis

A

Homologous chromosomes are separated during meiosis I

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24
Q

Explain how crossing over creates genetic variation

A

Alleles are exchanged between chromosomes, creating new combinations of maternal and paternal alleles on chromosomes

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25
Q

Explain how independent segregation creates genetic variation

A

Homologous pairs randomly align at equator, so it is random which chromosome from each pair
goes into each daughter cell, creating different combinations of maternal & paternal chromosomes in daughter cells

26
Q

Other than mutation and meiosis, explain how genetic variation within a species is increased

A

Random fertilisation / fusion of gametes, creating new allele combinations

27
Q

Explain the different outcomes of mitosis and meiosis

A
  • Mitosis produces 2 daughter cells, whereas meiosis produces 4 daughter cells, as there is 1 division in mitosis but 2 divisions in meiosis
  • Mitosis maintains the chromosome number (results in diploid cells) whereas meiosis halves the chromosome number (results in haploid cells). As homologous chromosomes separate in meiosis but not mitosis
  • Mitosis produces genetically identical daughter cells, whereas meiosis produces genetically varied daughter cells, because crossing over and independent segregation happen in meiosis but not mitosis
28
Q

Explain the importance of meiosis

A

The 2 divisions creates haploid gametes, so that the diploid number is restored at fertilisation and the chromosome number is maintained between generations. Also, independent segregation and crossing over creates genetic variation.

29
Q

How can you recognise where meiosis and mitosis occur in a life cycle?

A

Mitosis occurs between stages where chromosome number is maintained, and Meiosis occurs between stages where chromosome number halves

30
Q

Describe how mutations in the number of chromosomes arise

A

Occurs 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 of a particular chromosome and others have none

31
Q

What is genetic diversity?

A

Number of different alleles of genes in a population

32
Q

What are alleles and how do they arise?

A

Variations of a particular gene, they arise by mutation

33
Q

What is a population?

A

A group of interbreeding individuals of the same species.

34
Q

Explain the importance of genetic diversity

A

Enables natural selection to occur, as in certain environments, a new allele of a gene might be beneficial. Having advantageous genes increases chances of survival and reproductive success.

35
Q

What is evolution?

A

Change in allele frequency over many generations in a population. It occurs through the process of natural selection

36
Q

Explain the principles of natural selection in the evolution of populations

A

MARIA
* Mutation: Random gene mutations can result in new alleles of a gene
* Advantage: In certain environments, the new allele might benefit its possessor, so the 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, the advantageous allele increases in frequency in the population

37
Q

Describe 3 types of adaptations

A
  • Anatomical - structural / physical features that increase chance of survival
  • Physiological - processes / chemical reactions that increase chance of survival
  • Behavioural - ways in which an organism acts that increase chance of survival
38
Q

What is directional selection?

A

Organisms with an extreme variation of a trait has a selective advantage over the other extreme. This results in an increased frequency of organisms with alleles for the extreme trait. An example is antibiotic resistance in bacteria.

39
Q

What is stabilising selection?

A

Organisms with an average variation of a trait has a selective advantage. This results in an increased frequency of organisms with alleles for the average trait. An example is human birth weight.

40
Q

What is disruptive selection?

A

Organisms with either extreme
variation of a trait has a selective advantage. This results in an increased frequency of organisms with alleles for both extremes of the trait. An example is bird beak size

41
Q

What is a species?

A

A group of organisms that can (interbreed to) produce fertile offspring

42
Q

Suggest why 2 different species are unable to produce fertile offspring

A

Different species have different chromosome numbers, so homologous pairs cannot form and meiosis cannot occur to produce gametes for reproduction

43
Q

Explain why courtship behaviour is a necessary precursor to successful
mating

A

It allows recognition of member of the same species, so that fertile offspring is produced

44
Q

What is a phylogenetic classification system?

A

Species are arranged into groups, called taxons, based on their evolutionary origins (common ancestors) and relationships. They use a hierarchy in which smaller groups are placed within larger groups and there is no overlap between groups

45
Q

Name the taxons in the hierarchy of classification

A

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

46
Q

How is each species universally identified and what is an advantage of this?

A

Each species is given a Latin name using the binomial naming system. The name consists of their genus and species. An advantage of this is that it avoids confusion as scientists using different languages can have one universal name for the species

47
Q

How can phylogenetic trees be interpreted?

A

Each branch point represents a common ancestor and each branch represents an evolutionary path. Species with a more recent common ancestor are more closely related

48
Q

Describe an advancement that has helped to clarify evolutionary
relationships between organisms

A

Advances in genome sequencing has allowed comparison of DNA base sequences. The more differences in DNA base sequences there are, the more distantly related the organisms are and the earlier their common ancestor is because mutations build up over time

49
Q

What is biodiversity?

A

A measure of the variety of living organisms

50
Q

What is a community

A

All populations of different species that live in an area.

51
Q

What is species richness?

A

A measure of the number of different species in a community

52
Q

What does an index of diversity do?

A

Describes the relationship between: The number of species in a community (species richness) and the number of individuals in each species (population size)

53
Q

Why is index of diversity more useful than species richness?

A

Index of diversity also takes into account number of individuals in each species, so takes into account that some species may be present in small or large numbers

54
Q

How do you calculate index of diversity?

A
  1. Calculate the total number of organisms (N)
  2. Multiply N by (N - 1)
  3. For each species, multiply the number of organisms (n) by (n - 1)
  4. Add up all the values of n(n - 1) to get Σn(n - 1)
  5. Divide N(N - 1) by Σn(n - 1)
55
Q

Describe how index of diversity values can be interpreted

A
  • High - There are many species present and each species is evenly represented
  • Low - The community is dominated by one or a few species
56
Q

Explain how some farming techniques reduce biodiversity

A
  • Deforestation and removal of hedgerows, monoculture (growing one type of crop) and use of herbicides reduces the variety of plants, so there are less habitats and less variety in food sources.
  • Use of pesticides means that the predator population of the pest will also decrease as they have less food
57
Q

Explain the balance between conservation and farming

A

Conservation is required to increase biodiversity, but when implemented, yield can be reduced, decreasing profit and income for farmers. To offset loss, financial incentives and grants are offered.

58
Q

Give examples of how biodiversity can be increased in areas of agriculture

A
  • Reintroduction of hedgerows
  • Reduce use of pesticides
59
Q

How can genetic diversity within or between species 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
60
Q

Explain how comparing DNA, mRNA and amino acid sequences can indicate relationships between organisms within a species and between species

A

The more differences in the sequence, the more distantly related the organisms are and the earlier their common ancestor is, as mutations build up over time. The more mutations there are, the more changes there are in the amino acid sequence

61
Q

Explain the key considerations in quantitative investigations of variation within a species

A
  • Collect data from random samples (use a random number generator) → removes bias
  • Use large sample size to ensure sample is representative of whole population
  • Ethical sampling → must not harm organisms
  • Calculate a mean value of collected data and standard deviation of that mean
  • Interpret mean values and their standard deviations. If standard deviations overlap, the difference is not statistically significant
  • Use statistical tests → analyse whether there is a significant difference between populations
62
Q

Describe how production of messenger RNA (mRNA) in a eukaryotic cell is
different from the production of mRNA in a prokaryotic cell

A

In Eukaryotic Cells, the pre-mRNA undergoes splicing to remove introns, whereas in Prokaryotic Cells the mRNA is produced directly, so no splicing occurs because prokaryotic DNA contains no introns

Biology and Psychology (10 decks)

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