Topic 4 - Genetic information, variation & relationships between organisms Flashcards
(69 cards)
1
Q
Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells
A
- Similarities
-> nucleotide structure is identical - deoxyribose attached to phosphate and a base
-> adjacent nucleotides joined by phosphodiester bonds, complementary bases are joint by hydrogen bonds
-> DNA in mitochondria/chloroplasts similar to DNA in prokaryotes - short, circular and aren’t associated with proteins - Differences
-> eukaryotic DNA is longer
-> eukaryotic DNA is linear, prokaryotic DNA is circular
-> eukaryotic DNA is associated to histone proteins, prokaryotic DNA is not
-> eukaryotic DNA contain introns, prokaryotic DNA does not
2
Q
What is a chromosome
A
- Long linear DNA and its associated histone proteins
- In the nucleus of a eukaryotic cell
2
Q
What is a gene
A
- Sequence of DNA (nucleotide) bases that codes for
- Amino acid sequence of a polypeptide OR a functional RNA
3
Q
What is a locus
A
Fixed position a gene occupies on a particular DNA molecule
4
Q
Describe the nature of the genetic code
A
- Triplet code -> sequence of 3 DNA bases, called a triplet, codes for a specific amino acid
- Universal -> 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 -> amino acid can be coded for by more than one base triplet
5
Q
What are non coding base sequences - where are they found
A
- DNA that does not code for amino acid sequences/polypeptides
- Found between genes (non coding multiple repeats) and within genes (introns)
- In eukaryotes much of nuclear DNA doesn’t code for polypeptides
6
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
7
Q
Define genome and proteome
A
- Genome -> complete set of genes in a cell (including those in mitochondria and/or chloroplasts)
- Proteome -> full range of proteins that a cell can produce (coded for by cell’s DNA/genome)
8
Q
Describe two stages of protein synthesis
A
- Transcription -> production of messenger RNA from DNA in the nucleus
- Translation -> production of polypeptides from the sequence of codons carried by mRNA or ribosomes
9
Q
Compare structure of tRNA and mRNA
A
- Similarities
Both single polynucleotide strand - Differences
tRNA is folded into clover leaf shape, whereas mRNA is linear/straight
tRNA has hydrogen bonds between base pairs, mRNA does not
tRNA is a shorter fixed length, mRNA is a longer variable length (more nucleotides)
tRNA has an anticodon, mRNA has codons
tRNA has an amino acid binding site, mRNA does not
10
Q
Describe how mRNA is formed by transcription in eukaryotic cells
A
1 - hydrogen bonds between DNA bases break
2 - only one DNA strand acts as a template
3 - free RNA nucleotides align next to complementary bases on template strand (for RNA, uracil is used in place of thymine, pairing with adenine in DNA)
4 - RNA polymerase joins adjacent RNA nucleotides
5 - forms phosphodiester bonds by condensation reactions
6 - pre-mRNA formed and is spliced to remove introns, forming mature mRNA
11
Q
How is production of mRNA in eukaryotes different to production of mRNA in prokaryotes
A
- pre-mRNA is produced in eukaryotic cells, whereas mRNA is produced directly in prokaryotic cells
- Because genes in prokaryotic cells don’t contain introns so no splicing in prokaryotic cells
12
Q
Describe how translation leads to production of a polypeptide
A
1 - mRNA attaches to ribosome and ribosome moves to a start codon
2 - tRNA brings a specific amino acid
3 - tRNA anticodon binds to complementary mRNA codon
4 - ribosome moves along to next codon, another tRNA binds so 2 amino acids can be joined by condensation reaction - forming peptide bond - uses energy from ATP hydrolysis
5 - tRNA released after amino acid joined polypeptide
6 - ribosome moves along mRNA to form polypeptide until a stop codon is reached
12
Q
Describe role of ATP in translation
A
- Hydrolysis of ATP to ADP + Pi releases energy
- So amino acids join to tRNAs and peptide bonds form between amino acids
13
Q
Describe role of tRNA in translation
A
- Attaches to/transports 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
14
Q
Describe role of ribosomes in translation
A
- mRNA binds to ribosome, with space for 2 codons
- Allows tRNA with anticodons to bind
- Catalyses formation of peptide bond between amino acids (held by tRNA molecules)
- Moves along (mRNA to next codon)/ translocation
15
Q
Describe how base sequences of nucleic acids can be related to amino acid sequence of polypeptides when provided with suitable data
A
- you may be provided with genetic code to identify which triplets/codons produce which amino acids
- tRNA anticodons are complementary to mRNA codons
- sequence of codons on mRNA are complementar to triplet sequence on DNA template strand
- in RNA uracil replaces thymine
16
Q
What is a gene mutation
A
- Change in base sequence of DNA on chromosome
- Can arise spontaneously during DNA replication (interphase)
17
Q
What is a mutagenic agent
A
Factor that increases rate of gene mutation, eg - ultraviolet light, alpha particles
18
Q
Explain how a mutation can lead to production of a non functional protein or enzyme
A
- Changes sequence of base triplets in DNA (in gene) so changes sequence of codons on mRNA
- Changes sequence of amino acids in polypeptide
- Changes position of hydrogen/ionic/disulphide bonds between amino acids
- Changes protein tertiary structure (shape) of protein
- Enzymes - active site changes shape so substrate can’t bind, enzyme substrate complex cant form
19
Q
Explain possible effects of substitution mutation
A
- DNA base/nucleotide replaced by different base/nucleotide
- Changes one triplet so changes one mRNA codon
- One amino acid in polypeptide changes
- Tertiary structure may change if position of hydrogen/ionic/disulphide bonds change
- OR amino acid does not change - due to degenerate nature of genetic code (triplet could code for same amino acid) OR if mutation is in an intron so removed in splicing
20
Q
Explain possible effects of deletion mutation
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
21
Q
Describe features of homologous chromosomes
A
Same length, same genes at same loci, but may have different alleles
22
Q
Describe difference between 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
23
Describe how a cell divides by meiosis
- In interphase, DNA replicates -> 2 copies of each chromosome are joined by centromere
1 - Meiosis 1 -> separates homologous chromosomes
- chromosomes arrange into homologous pairs
- crossing over between homologous chromosomes
- independent segregation of homologous chromosomes
2 - Meiosis 2 - separates chromatids
Outcome = 4 genetically varied daughter cells - normally haploid if diploid parent cell
24
Diagram showing chromosome content during meiosis
25
Explain why number of chromosomes is halved during meiosis
homologous chromosomes are separated during meiosis 1
26
Explain how crossing over creates genetic variation
- Homologous pairs of chromosomes associate/form a bivalent
- Chiasmata form (point of contact between non sister chromatids)
alleles / equal lengths of chromatids exchanged between chromosomes
- Creating new combinations of maternal and paternal alleles on chromosomes
27
Explain how independent segregation creates genetic variation
- Homologous pairs randomly align at equator - random which chromosome from each pair goes into each daughter cell
- Creating different combinations of maternal and paternal chromosomes/alleles in daughter cells
27
Other than mutation and meiosis, explain how genetic variation in a species is increased
- Random fertilization/fusion of gametes
- Creates new allele combinations/new maternal and paternal chromosome combinations
28
Explain different outcomes of mitosis and meiosis
1 - mitosis produces 2 daughter cells whereas meiosis produces 4 daughter cells - one division in mitosis but 2 division in meiosis
2 - mitosis maintains chromosome number (diploid -> diploid) whereas meiosis halves number of chromosomes (diploid -> haploid) - as homologous chromosomes separate in meiosis not mitosis
3 - mitosis produces genetically identical daughter cells whereas meiosis produces genetically varied daughter cells - as crossing over and independent segregation occurs in meiosis not mitosis
29
Explain importance of meiosis
- 2 divisions creates haploid gametes (halves number of chromosomes)
- Diploid number is restored at fertilization -> chromosome number is maintained between generations
- Independent segregation and crossing over leads to genetic variation
30
How can you recognise where meiosis & mitosis occur in life cycles
Mitosis occurs between stages where chromosome number is maintained (diploid -> diploid or haploid ->haploid)
31
Describe how mutations in the number of chromosomes arise
- 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)
- be able to draw what it could look like in meiosis 1 and 2
32
How can the number of possible combinations of chromosomes in daughter cells following meiosis can be calculated
2^n -> n=number of pairs of homologous chromosomes (half the diploid number)
33
How can the number of possible combinations of chromosomes following random fertilisation of two gametes can be calculated
(2^n)^2 -> n=number of pairs of homologous chromosomes (half the diploid number)
34
What is genetic diversity
Number of different alleles of genes in a population
35
What are alleles - how do they arise
- Variations of a certain gene (same locus) -> different DNA base sequence
- Arise by mutations
36
What is a population
- Group of organisms of the same species in a certain space at a certain time
- Can interbreed to produce fertile offspring
37
Importance of genetic diversity
- Enables natural selection
In certain environments, a new allele of a gene might benefit its possessor
- By resulting in a change in the polypeptide (protein) coded for that, positively changes its properties
- Gives possessor a selective advantage (increased chance of survival and reproductive success)
38
What is evolution
- Change in allele frequency (how common allele is) over many generations in a population
- Occurs through natural selection
39
Explain principles of natural selection in evolution of populations
1 -> Mutation - random gene mutations can lead to new alleles of a gene
2 -> Advantage - in certain environments, this new allele can benefit the possessor, so organism has selective advantage
3 -> Reproduction - possessors of the allele are more likely to survive, have increased reproductive success
4 -> Inheritance - advantageous allele gets inherited by members of the next generation/offspring
5 -> Allele frequency - over many generations, allele increases in frequency within the population
40
3 types of adaptations
- Natural selection leads to species being better adapted to their environment
- Anatomical - structural and physical features increasing chances of survival
- Physiological - processes/chemical reactions increasing chances of survival
- Behavioural - ways in which an organism acts increasing chances of survival
41
Directional selection
- Directional selection eg - antibiotic resistance in bacteria
-> organisms with an extreme variation of a trait have selective advantage eg - bacteria with high level of resistance to a particular antibiotic
-> often a change in environment eg - antibiotic is introduced
-> increased frequency of organisms with the alleles for extreme trait - normal distribution curve shifts towards the extreme trait
42
Stabilising selection
- Stabilising selection eg - human birth weight
-> organisms with an average/modal variation of a trait eg - babies with average weight
-> often usually stable environment
-> increased frequency of organisms with alleles for average trait - normal distribution curve similar - less variation around the mean
43
What is a species
Group of organisms that can interbreed to produce fertile offspring
44
Why are 2 different species unable to produce fertile offspring
- Different species have different number of chromosomes - so offspring may have an odd chromosome number
- Homologous pairs can’t form - meiosis can’t occur to produce gametes
45
Why is courtship behaviour a necessary precursor to successful mating
- Allows recognition of members of the same species -> fertile offspring produced
- Allows recognition and attraction of opposite sex
- Stimulates/synchronises mating/production/release of gametes
- Indicates sexual maturity/fertility
- Establishes pair bond to raise the young
46
Describe phylogenetic classification system
- Species arranged into groups called taxa - based on evolutionary origins and relationships
- Uses a hierarchy - smaller groups placed within larger groups - no overlap between groups
47
Name the taxa in hierarchy of classification
1 -> Domain
2 -> Kingdom
3 -> Phylum
4 -> Class
5 -> Order
6 -> Family
7 -> Genus
8 -> Species
48
How are phylogenetic trees interpreted
- Branch point = common ancestor
- Branch = evolutionary path
- If 2 species have a more recent common ancestor, they are more closely related
48
Advantage of binomial naming
Universal -> no confusion as many organisms have more than one common name
48
How are species universally identified
Binomial consisting name of the genus and species
49
Describe two advances that have helped to clarify evolutionary relationships between organisms
1 - Advances in genome sequencing → allowing comparison of DNA base sequences
-> more differences in DNA base sequences -> more distantly related / earlier common ancestor - as mutations build up over time
2. Advances in immunology → allowing comparison of protein tertiary structure (eg.
albumin)
-> Higher amount of protein from one species binds to antibody against the same protein from another species → more closely related / more recent common ancestor - as indicates similar amino acid sequence and tertiary structure - less time for mutations to build up
50
What is biodiversity
Variety of living organisms -> can relate to range of habitats, from small local habitats to the entire Earth
51
What is a community
All populations of different species that live in an area
52
What is species richness
Measure of the number of different species in a community
53
What does an index of diversity do
- Describes relationship between
1 - number of species in a community (species richness)
2 - number of individuals in each species (population size)
54
Why is an index of diversity more useful than species richness
- Takes into account number of individuals in each species
- So takes into account that some species can be present in either small or large numbers
55
Formula and method for index of diversity
d = N(N-1) / En(n-1)
- N = total number of organisms of all species
- n = total number of organisms of each species
1 - calculate N
2 - multiple N by (N-1)
3 - for each species multiply number of organisms (n) by (n-1)
4 - add up all values of n(n-1)
5 - divide N(N-1) by En(n-1)
56
How can index of diversity values be interpreted
- High value -> many species present (high species richness) - species evenly represented
- Low value -> habitat is dominated by one/few species
57
How can some farming techniques reduce biodiversity
- Removal of woodland and hedgerows
- Monoculture (growing one type of crop)
- Use of herbicides to kill weeds
-> all 3 - reduces variety of plant species - fewer habitats and niches - less variety of food sources
- Use of pesticides to kill pests - predator population of pests decreases
58
Explain balance between conservation and farming
- Conservation is necessary to increase biodiversity
- When implemented on farms - yields reduce, reducing profit/income for farmers (eg- reduces land area for crop growth, increases competition, increases number of pests)
- To offset these losses, financial incentives or grants are offered
59
Examples of how biodiversity can be increased in areas of agriculture
- Reintroduction of field margins and hedgerows (farmers would only grow one type of crop)
- Reduce pesticide usage
- Grow different crops in the same area - intercropping
- Use crop rotation of nitrogen fixing crops rather than fertlisers
60
How can genetic diversity within/between species be measured
- Compare frequency of measurable/observable characteristics
- Compare base sequence of DNA and mRNA
- Compare amino acid sequence of a specific protein encoded by DNA and mRNA
61
How does comparing DNA, mRNA, and amino acid sequences indicate relationships between organisms within and between species
- More differences in sequences -> more distantly related/earlier common ancestor
- Mutations build up over time
- So more mutations cause more changes in amino acid sequences
62
Explain change in methods of investigating genetic diversity over time
- 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 genes
- Gene technologies allowed this to be replaced by direct investigation of DNA sequences
63
Explain how data should be collected when investigating variation within a species quantitatively
- Collect data from random samples → to remove bias
-> Use a grid / divide area into squares
-> Use a random number generator to obtain random coordinates
- Use same method of measurement each time
- Use a large sample size / measure a large number of organisms → so representative of population
- Calculate a running mean and sample until number becomes (fairly) constant
- (Where applicable) ensure sampling is ethical → must not harm organism / must allow release unchanged
64
Explain how data should be processed and analysed when investigating variation within a species quantitatively
- Calculate a mean value of collected data and standard deviation (S.D) of that mean
-> Mean = sum of values in data set / number of values in data set
- S.D shows spread of values about the mean → higher S.D = higher variation
- If standard deviations overlap, causing values of two sets of data to be shared, any difference between the two may be due to chance / not significant
- Use [named] statistical test
-> To analyse whether there is a significant difference between populations
