Classification and Diversity Unit 4 Flashcards
(88 cards)
1
Q
Describe prokaryotic DNA
A
DNA molecules are short, circular and not associated with proteins
2
Q
Describe the DNA inside mitochondria and chloroplast of Eukaryotic cells
A
contain DNA which, like the DNA of prokaryotes,
is short, circular and not associated with protein
3
Q
Describe eukaryotic DNA
A
DNA molecules are very long, linear and associated with proteins, called histones.
4
Q
What’s a gene
A
a sequence of bases on DNA which determines the amino acid sequence (primary structure) of a polypeptide. It does this by coding for a functional RNA
5
Q
Where are genes found and how can they exist
A
A gene occupies a fixed position, called a locus, on a particular DNA moleculeGenes can exist in different forms.
Different versions of genes are called alleles
The order of bases in each allele varies slightly, so they code for slightly different versions of the same
polypeptide
6
Q
Describe the genetic code.
A
A sequence of three DNA bases called a triplet, codes for a specific amino acid. A triplet is a codon
The code is universal for all living things - the same base triplets code for the same amino acids in all organisms
non-overlapping – each triplet is read separately
degenerate: some amino acids have more than one triplet code
7
Q
What does the nuclear DNA code for in eukaryotes
A
much of the nuclear DNA does not code for polypeptides: There are, for example, non-coding multiple repeats of base sequences between genes.
(within a gene only some sequences called exons which code for amino acid sequences. these exons are separated by one or more non coding sequences called introns within the gene.)
8
Q
What are exons and introns
A
Exons: sequences within a gene that code for amino acid sequences
Introns: Non-coding sequences
9
Q
Describe the structure of mRNA
A
-Single stranded
- Linear chain
- Longer chain/ has more nucleotides
- Corresponds to the genetic sequence of a gene
- Unpaired bases
10
Q
describe the structure of tRNA
A
- Single stranded folded into a clover shape
- Hydrogen bonds
- Anticodon
- Amino acid attachment site
- All similar lengths
11
Q
What’s a genome
A
The complete set of genes in a cell
12
Q
What’s a proteome
A
The full range of proteins that a cell is able to produce
13
Q
What does transcription do?
A
produces mRNA from DNA by copying the genetic code from DNA to mRNA
14
Q
Polypeptide synthesis:
A
1)The sequence of nucleotides on a gene on DNA acts as a template
2) A complimentary copy is transcribed onto mRNA in the nucleus
3)At the ribosomes the mRNA acts as a template that is translated into a chain of amino acids using complementary tRNA which carry specific amino acids which are linked together by in order peptide bonds by condensation reactions. This requires ATP.
15
Q
Where does transcription result in prokaryotes and eukaryotes.
A
In prokaryotes- transcription results directly in the production of mRNA from DNA
in eukaryotes- transcription results in the production of pre- mRNA; this is then spliced to form mRNA and Occurs in the nucleus in eukaryotes
16
Q
Describe the process of transcription
A
- H bonds between complementary base pairs of gene to be transcribed are broken. The DNA nucleotide bases are now exposed.
- One DNA strand acts as a template to make an mRNA copy.
- Free RNA nucleotides align by complementary base pairing on the template strand of DNA. Uracil base pairs with adenine (replaces adenine)
- RNA polymerase joins the adjacent nucleotides together with a phosphodiester bond,
- RNA Polymerase continues until it reaches a stop signal and then it detaches.
17
Q
Pre-mRNA & Splicing
A
In eukaryotic cells, mRNA produced during transcription contains both introns and exons. This is
termed pre-mRNA
* Non-coding regions (introns) need to be removed because they don’t contain any genetic information that can be translated into an amino acid sequence.
* The introns are “spliced” out of the mRNA sequence by an enzyme
* This produces a strand of mRNA that contains only exons – the coding regions. This is known as “mature mRNA”.
18
Q
What’s translation
A
formation of a polypeptide chain according to the original DNA code using amino acids
on tRNA and the mRNA code:
19
Q
Translation process
A
- mRNA attaches to a ribosome
- tRNA anticodons bind to complementary codons on mRNA
- tRNA brings a specific amino acid
- two tRNA can bind simultaneously
- Adjacent amino acids undergo a condensation reaction and form a peptide bond (using ATP)
- First tRNA detaches and the ribosome moves to the next codon.
- This continues, forming a polypeptide until a STOP codon is reached and the ribosome detaches.
20
Q
What are mutations
A
changes in the base sequence of chromosomes, resulting in a new allele. They can arise spontaneously during DNA replication
Mutations can be a substitution/deletion/insertion
21
Q
Substitution mutation
A
One base is replaced by a different base during dna replication. This changes one triplet so changes 1 mrna codon. so one amino acid in polypeptide changes (Only the codon with the mutation is affected.)
22
Q
Deletion mutation
A
One base is removed from dna sequence during DNA replication. This changes sequence of dna triplets from point of mutation.
(This results in a frame shift – all the codons after the mutation are affected.o)
23
Q
Insertion mutation
A
An extra base is added during DNA replication. This results in a frame shift – all The codons after the mutation are affected.
24
Q
Why might a Mutations not cause a change in a proteins structure.
A
- A mutation may result in a codon which codes for the same amino acid (degenerate code); the amino acid sequence remains the same; the ionic/hydrogen/disulphide bonds between R groups remain unchanged; the tertiary structure does not change.
- The mutation may be in an intron
- The mutation may be in a recessive allele
- The mutation may code for an amino acid with the
same properties as the original one and so the protein structure remains unchanged
25
What could change in a codon result in a protein?
result in a change in a proteins structure and function because:
• The amino acid sequence changes
• The hydrogen/ionic/disulphide bonds between R groups changes
• The tertiary structure changes
If the change is in the active site of an enzyme, then the active site is no longer complementary to the
substrate and the enzyme cannot form enzyme-substrate complexes – the enzyme is nonfunctional.
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What do mutagenic agents do
can increase the rate of gene mutation eg. UV radiation, some chemicals
27
When are chromosome mutations most likely to occur
Chromosome mutation by non-disjunction during meiosis can arise spontaneously and affect the number
of chromosomes:
Chromosome mutations are most likely to occur in meiosis. This is when the chromosomes are not prope;y
separated and are not shared equally between the daughter cells in metaphase and anaphase.
This results in daughter cells have different numbers of chromosomes.
This known as non-dysjunction
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What do histones do and why
The DNA is very long, so must be wound up to fit into the nucleus. Histones help support the DNA.
Together histones and DNA are coiled tightly to form compact chromosomes
29
Why would a base substitution not cause a change in the sequence of encoded amino acids?
Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids. This means that more than one codon codes for the same amino acid.
30
Describe the features of a homologous pair of chromosomes
Carry the same genes, have same length but may have different alleles.
31
Difference between diploid and haploid
Diploid- (2n) with 2 copies of each chromosome. Most organisms.
Haploid - (n) with only half the number of chromosomes present. Gametes. When they fuse in sexual reproduction the diploid numbers restored,
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What happens in meiosis one and what does it do,
Seperates homologous pair of chromosomes. Crossing over homologous chromosomes, independent segregation of homologous chromosomes
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What happens in meiosis 2 and the outcome
similar to mitosis with the separation of sister chromatids
Four haploid cells are produced.
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How does meiosis lead to variation and genetic diversity by crossing over?
Produces unique gametes that are genetically different
Crossing over occurs in **prophase I** with the formation of chiasmata
(Chromatids become twisted which puts tension on them, causing them to break, broken parts recombines on the other chromosome pair)
1. Homologous pairs of chromosomes associate and form a bivalent;
2. Chiasmata forms;
3. Equal lengths of alleles are exchanged;
4. Producing new combinations of alleles;i
35
Explain how independent segregation creates genetic variation.
1. In Metaphase 1, homologous pairs of chromosomes randomly line up at equator
2. When they are separated, one of each pair ends up in a daughter cell
3. This process is when maternal and paternal chromosomes are reshuffled in any combination, leading to different combinations of the maternal and paternal chromosomes in daughter cells
(It's random which chromosome from each pair goes into each daughter cell.)
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Other sources of variation:
Random Fertilisation of gametes produces new allele combinations
mutations may occur
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Comparison of the cells produced in mitosis and meiosis:
Mitosis- same number of chromosomes
Genetically identical, 2 cells, 2n-->2n or n---n
Meiosis- half the number of chromosomes
Genetically different as crossing over and independent segregation happens in meiosis but not mitosis,
Four cells
2n--->n as homologous chromosomes seperate
38
What're gene mutations
Changes in the base sequence of chromosomes, resulting in new alleles. They can arise spontaneously during DNA replication.
Can be substitution, elimination and addition
39
Describe and explain other processes than mutations which result in increases in genetic variation within a species
1. Independent segregation of homologous chromosomes
2. Crossing over between homologous chromosomes
3. Random fertilisation of gametes;
4. (Produces) new combinations of alleles
40
Explain why all cells of the body would have a Mutation if a chromosome mutation occurred
All cells derive from a single cell
Mitosis produces genetically identical cells
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Whats genetic diversity
the total number of different alleles of genes that exist in a population
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what are alleles and how do they arise
variations of a particular gene, arise by mutation
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whats a population
a group of organisms that can breed with eachother to produce
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Hows having a greater genetic diversity beneficial
More alleles in a population / species is beneficial as it gives the species a greater chance to survive a changing environment
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things which can affect the genetic diversity of a population
Population size – smaller populations generally have a lower genetic diversity and larger
populations a larger one
2. 3. 4. 5. 6. 7. Inbreeding – reduces genetic diversity
Migration – increases genetic diversity
Mutations – increases genetic diversity
Genetic Bottlenecks – reduces genetic diversity
Founder effect – reduces genetic diversity
Natural selection – increases the frequency of beneficial alleles
46
Whats evolution
A change in the allele frequency in a population; whereby an advantageous allele increase
Leads to a population becoming better adapted to survive in their environment.
Can be broken down into:
• Mutation
• Advantage and survival
• Reproduction
• Change in allele frequency
47
Explain Directional selection
Eg antibiotic resistance in bacteria
Organisms with an extreme variation of a trait have a selective advantage. so more likely to survive and reproduce. some bacteria have alleles that give them resistance to an antibiotic: Change in evironment. normal population killed bythe antibiotic. resistant bacteria survive and reproduce without competition passing on the allele for antibiotic resistance to their offspring. results in increased frequency of organisms with alleles for extreme traits. normal distribution curve shifts towards extreme trait.
48
principles of natural selection in the evolution of population
mutation
1. natural selection starts, when a random gene mutates resulting in new alleles of a gene giving the possessor an advantage. increasing the organisms chance of survival. some can be harmful alleles
2. Advantage and survival
in a certain environment the new allele may benefit its possesor as the organism has a selective advantage
3. Reproduction
Organisms which have the advantageous allele are more likely to reproduce.
The offspring are likely to inherit this advantageous allele making the next generation better adapted to their environment.
4. Change in allele frequency
advantageous allele is inherited by members of the next generation and over many generations allele increases in frequency in the population
The offspring with the advantageous allele are better adapted to their environment so they are
more likely to survive and reproduce passing on the allele to the next generation.
This continues over time over multiple generations causing the frequency of the allele to increase
49
describe the 3 types of adaptations
Anatomical adaptations: Structural features. Eg whales have a thick layer of blubber to keep warm in
the cold sea
• Physiological adaptations: Processes within the organism. Eg. Hibernation over winter reducing the
metabolic rate to conserve energy when food is scarce
• Behavioural adaptations: The way an organism acts. Eg possums playing dead near to predators
50
whatre selection pressures
environmental factors that effect the chance of survival of an organism van have different effects on the allele frequencies of a population through natural selection
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directional selection
Individuals with alleles for an extreme type are more likely to
survive and reproduce
• Some bacteria have alleles that give them resistance to an
antibiotic
• The normal population of bacteria are killed by the antibiotic
• Resistant bacteria survive and reproduce without competition
passing on the allele for antibiotic resistance to their offspring
• After some time, most of the population will have the
antibiotic resistance allele
52
stabilising selection
Stabilising selection as shown by human birth weight:
• Individuals with alleles for the middle of the range are more
likely to survive and reproduce
• Small babies find it hard to maintain their body temperature
so less likely to survive
• Large babies less likely to survive also
• So conditions most favourable for medium sized babies
• The weight of human babies shifts towards the middle of the range
53
Explain Stabilising selection
Eg human birth rate
Organisms with an average variation of a trait have a selective advantage so mote likely to survive and reproduce - extremes are selected against. small babies find it hard to maintain their body temp so less liekly to survive - big die so conditions favourable for medium sized babies Population is usually stable, Increased frequency of organisms with alleles for average trait. normal distribution curve similar- less variation around the mean
54
Explain examples of aseptic techniques that could be used
Wash hands with soap to kill microbes
Sterilise pipette growth medium to prevent contamination
Flame neck of bottle of bacteria to kill microbes
Bunsen burner close as upward current of air draws air-borne microbes away to prevent contamination
Lift lid of petri dish slightly to prevent entry of microbes
55
Describe a method to investigate the effect of antimicrobial substances on microbial growth
1.Prepare area using aseptic techniques so wash hands with soap to kill microbes
2.Use a sterile pipette to transfer bacteria from broth to agar plate using aseptic techniques
3. Use a sterile spreader to evenly spread bacteria over agar plate
4. Use sterile forceps to place same size discs that have been soaked in different concentrations of antimicrobials for same length of time, onto agar plate (at equal distances)
5. Lightly tape lid onto plate (not fully sealed), invert and incubate at 25°C for 48 hours Measure diameter of inhibition zone around each disc and calculate area using pie r2
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Why is it important to maintain a pure culture of bacteria?
Bacteria may outcompete bacteria being investigated
Or could be harmful to humans
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Why hold lid with 2 pieces of tape instead of sealing it completely?
Allows oxygen in preventing growth of anaerobic bacteria
Which are more likely to beharmful to humans
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Why use a paper disc with water / no antimicrobial agent?
Act as a control
• Ensuring antimicrobial prevented growth, not paper disc
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Why incubate upside down?
Condensation drips onto lid rather than surface of agar
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What if inhibition zones are irregular?
Repeat readings in different positions, calculate a mean
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Why not use higher antimicrobial conc.?
Mole enciere killed so clear zones may overlap
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Why incubate at 25°C or less?
below human body temperature to prevent growth of pathogens
63
Whats a species
A group of organisms that can (interbreed to) produce fertile offspring
64
Suggest why 2 different species are unable to produce fertile offspring
• Different species have different chromosome numbers - offspring may have odd chromosome number
• So homologous pairs cannot form → meiosis cannot occur to produce gametes
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How is each species universally identified?
A binomial consisting of the name of its genus and species, eg. Homo sapiens
66
Suggest an advantage of binomial naming
Universal so no confusion as many organisms have more than one common name
67
Describe a phylogenetic classification system
• Species (attempted to be) arranged into groups, called taxa, (each group is a taxon) based on their evolutionary origins (common ancestors) and relationships
• Uses a hierarchy:
Smaller groups are placed within larger groups
No overlap between groups
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What does the phylogenetic classification system attempt to do
to arrange species into groups based on their evolutionary origins and relationships
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Name the taxa in the hierarchy of classification
Domain (largest / broadest) - kingdom → phylum → class → order → family - genus → species (smallest)
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Describe two advances that have helped to clarify evolutionary relationships between organisms
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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 (change in DNA base sequences) build up over time
2. Advances in immunology → (similar proteins in organisms will bind the same antibodies) 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
• As indicates a similar amino acid sequence and tertiary structure
• So less time for mutations to build up
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Problems with using observable features in classification
some organisms will look alike due to convergent evolution
2 organisms evolve similar features but not closely related
they live in similar environments & exposed to similar selection pressures. similar alleles provide similar selective advantages
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How can phylogenetic trees be interpreted?
Branch point = common ancestor
Branch = evolutionary path
• If two species have a more recent common ancestor, they are more closely related
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Name the taxa in the hierarchy of classification
Domain (largest / broadest) - kingdom → phylum → class → order → family - genus → species (smallest)
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Explain why courtship behaviour is a necessary precursor to successful mating
Allows recognition of members of same species → so fertile offspring produced
Allows recognition of opposite sex
Synchronises mating and stimulates release of gametes
Indicates sexual maturity and fertility
increases the survival of offspring by the formation of pair bonds- 2 parenfs looking after the offspring increases its survival
Establishes a pair bond to raise young
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What's index diversity
Describes the relationship between
the number of species in a community and the number of individuals in each species
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Whats Biodiversity
Its the variety of living organisms in an area
Can relate to a range of habitats, from a small local habitat to the earth
Measure of the species richness and the abundance
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What's habitat
habitat is the place where an organism lives.
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Whats a community
A community is all the populations of different species in a habitat
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Whats Species richness
A measure of the number of different species in a community
It can be calculated by taking random samples of a community and counting the number of different species
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Suggest why index of diversity is more useful than species richness
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
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What's the formula for index diversity
• N = total number of organisms of all species
• n = total number of organisms of each species
• The higher the number d, the more diverse an area is
N(N-1)
d= -----------
{n(n-1)
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Describe how index of diversity values can be interpreted
High - many species present and species evenly represented
Low - habitat dominant by a few species
84
What's agriculture
the cultivation of soil to grow crops
85
Explain how some farming techniques reduce biodiversity
1.Removal of woodland&hedgerows
2. Monoculture
3. Use of herbicides to kill weed ALL- reduces variety of plants. - so fewer habitats and niches - and less variety of food sources
Use of pesticides - predator population of pest decreases
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Explain the balance between conservation and farming
Conservation required to increase biodiversity
But when implemented on farms, yields can be reduced, reducing profit for farmers (eg by reducing land area for crop growth, increasing competition, increasing pest population.
To offset loss, financial grants are offered
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Give examples of how biodiversity can be increased in areas of agriculture
Reintroduction of field margins and hedgerows where farmers can only grow one type of crop.
Reduce use of pesticides
Growing different crops in the same area.
Using crop rotation of nitrogen fixing crops instead of fertilisers
