Topic 4 Flashcards
1
Q
Describe the structure of DNA found in mitochondria and chloroplasts
3.4.1
A
circular, short and not associated with histone proteins
2
Q
Compare DNA in prokaryotes and eukaryotes
3.4.1
A
- prokaryotic cells have DNA molecules that are short, circular and not associated with histone proteins
- DNA molecules in eukaryotic cells long, linear, associated with histone proteins (molecules round up around histones to help support DNA). DNA molecules and histone proteins form chromosome in nucleus.
3
Q
What is the definition of a gene and what does it code for?
A
Gene= base sequence of DNA
Codes for:
* the amino acid sequence of a polypeptide (each amino acid coded for by triplet/codn in gene. To make polypeptide DNA is copied into mRNA (transcription)
* a functional RNA (ribosomal and tRNAs)
4
Q
What is a locus?
3.4.1
A
the fixed position a gene occupies on a particular DNA molecule
alleles coding for same characteristic found at same locus on each chromosome in a homologous pair
5
Q
What are introns?
A
sequences of gene that do not code for amino acids and are spliced in protein synthesis to not affect amino acid order. They separate exons within a gene
6
Q
What are exons?
A
sequences within a gene that code for amino acid sequences, separated by one or more introns
7
Q
Does all eukaryotic DNA code for polypeptides?
3.4.1
A
No
DNA contains non coding multiple repeats of base sequences between genes.
8
Q
What is a triplet?
3.4.1
A
a sequence of 3 bases that codes for a specific amino acid
9
Q
how is the genetic code degenerate, universal and non overlapping
A
degenerate- some amino acids coded for by more than one codon as more possible combinations of triplets than amino acids. not all triplets code for amino acids (stop signals at end of mRNA tell cell to stop producing a protein and start signals at stat of mRNA that tell cell when to start protein production)
universal- same specific base triplets code for same amino acids in all living things/organisms
non overlapping- each codon read in sequence seperate from codon before and after. codons do not share bases.
10
Q
what is the genome?
A
the complete set of genes in a cell
11
Q
What is the proteome?
A
the full range of proteins a cell is able to produce
12
Q
What is the structure and function of messenger RNA?
A
- mRNA is a copy of a gene from DNA
- created in nucleus and leaves to carry copy of genetic code of gene to ribosome in cytoplasm
- DNA too large to neave nucleus and would be at risk of being damaged by enzymes which would destroy genetic code permanently SO mRNA carries the genetic code to ribosome as is much shorter as only length of one gene and can leave nucleus
- short lived as only needed temporarily in protein synthesis
- single stranded and every 3 bases in sequence code for specific amino acid (codons)
13
Q
- What is the structure of transfer RNA?
- What is the function of transfer RNA?
A
- only found in cytoplasm, is single stranded and folded into a clover like shape held in place by hydrogen bonds between nucleotides. Have amino acid binding site at one end and anticodon at other end
- tRNA attaches to amino acid and transfers it to the ribosome to create a polypeptide chain in translation. Specific amino acids attach to specific tRNA molecules determined by anticodon on tRNA that is complementary to the codon on mRNA
14
Q
What occurs in transcription?
A
one gene on DNA is copied into mRNA
15
Q
What occurs in translation?
A
- mRNA joins with a ribosome and corresponding tRNA colecules brings specific amino acid that the codon on mRNA molecule codes for
- polypeptide chain created using mRNA base sequence and tRNA
16
Q
Describe the process of transcription as the first stage of protein synthesis
A
- Part of DNA helix unwinds as hydrogen bonds between base pairs break, catalysed by DNA helicase
- One of DNA strands acts as template strand
- free mRNA nucleotides in nucleus pair up, via hydrogen bonds, with exposed complementary DNA bases on template strand of DNA molecule
- RNA polymerase bonds together the RNA nucleotides by sugar phosphate groups to form a new RNA polymer chain. One entire gene copied
- mRNA molecule leaves nucleus via pore in nuclear envelope.
17
Q
Does transcription result in the direct production of mRNA from DNA?
A
Only in Prokaryotic cells, not in eukaryotic cells
18
Q
Describe the process of splicing in eukaryotic cells
A
- in eukaryotes, transcription results in production of pre-mRNA
- introns in pre-mRNA molecule are removed by protein called a spicesome and exons joined together to produce mRNA molecule for translation
19
Q
Where does Translation take place?
A
ribosomes in cytoplasm
20
Q
Describe the process of Translation as the second stage of protein synthesis
A
- mRNA attaches to ribosome in cytoplasm. Ribosome attaches at start codon of mRNA
- tRNA molecule with complementary anticodon to start codon aligns opposite mRNA, held in place by ribosome
- ribosome moves along mRNA molecule to enable another complementary tRNA to attach t next codon on mRNA
- amino acids joined by peptide bond in a condensation reaction, catalysed by an enzyme and requires ATP. First tRNA molecule moves away leaving amino acid, third tRNA molecule binds to next codon on mRNA and amino acid binds to other 2 and second tRNA leaves.
- continues until ribosome reaches stop codon at end of mRNA molecule and ribosome detaches and translation ends.
- polypeptide chain complete and enters golgi body for folding and modification.
21
Q
What are gene mutations?
A
a change to the base sequence of chromosomes.
- arise spontaneously during DNA replication
- include base deletion and base substitution
22
Q
What is base substitution and what effects does it have on the amino acid sequence?
A
- one base substituted with another
- genetic code is degenerate (some amino acids coded for by more than one codon) so not all sustitution mutations cause amino acid sequence to change
23
Q
What is base deletion and what effect does it have on the amino acid sequence?
A
- one base is deleted
- causes change to amino acid sequence as it changes number of bases, causing a shift in all base triplets after it.
24
Q
What do mutagenic agents do? Provide examples
A
- Mutations occur spontaneously, but mutatgenic agents increase chance of them occurring.
- ionising radiation (x rays, gamma)
- ultraviolet radiation (UV)
- some chemicals and viruses
25
What does meiosis produce?
- involved 2 nuclear divisions and produces 4 haploid daughter cells that are genetically different from each other, from a single diploid parent cell
26
How is variation introduced in meiosis?
1. independent segregation of homologous chromosomes
2. crossing over between homologous chromosomes
- both occur in meiosis I
27
Describe independent segretation that occurs in meiosis I
* in meiosis I, homologous chromosome pairs line up opposite each other at equator of cell (completely random which side of equator paternal and maternal chromosomes from each pair lie
* pairs are separated so one of each homologous pair ends up in daughter cell
* creates many possible combinations of chromosomes in daughter cells produced
28
Describe Crossing Over which occurs in meiosis I
* homologous chromosomes pairs line up at opposite sides of equator and parts of chromatids can become twisted around each other
* this puts tension of chromatids causing pairs of of chromatids to break
* broken parts of chromatid reccombine with the other chromatid
* results in new combinations of alleles in gametes
29
identify the differences between meiosis and mitosis
* meiosis has 2 nuclear divisions
* mitosis has one nuclear division
* meiosis produces 4 genetically different haploid daughter cells (introduces genetic variation)
* mitosis produces 2 genetically identical diploid daughter cells
30
How do mutations occur during meiosis?
* can arise spontaneously during chromosome non disjunction
* occurs when chromosomes/chromatids do not separate equally in anaphase
* resulting gamete does not have correct number of chromosomes
* can occur in 2 forms: changes in whole sets of chromosomes (Polyploidy) or changes in number of individual chromosomes (aneuploidy)
31
Explain how random fertilisation of haploid gametes further increases genetic variation within a species
* there are 2(n) possible chromosome combinations in gametes (2(23) in humans- 23 is the number of chromosome pairs)
* it's random which egg and sperm will fuse in fertilisation, so variation is increased
* there is actually (2(n))(2) possible combinations of chromosomes when random fertilisation considered
* this is before crossing over considered
32
Describe the process of meiosis
1. Before meiosis, DNA replicates in interphase so there are 2 copies of each chromosome
2. DNA condenses
3. Meiosis I- chromosomes arrange themselves into homologous pairs and separate which halves the chromosome number
4. pairs of sister chromatids separate as centromere divides
5. this produces 4 haploid daughter cells that are genetically different from each other and the diploid parent cell
33
Polyploidy is a form of chromosome non disjunction that occurs in meiosis. Describe how it occurs
* polyploidy occurs when there are changes to whole sets of chromosomes so organisms have 3 or more sets of chromosomes
* mainly occurs in plants
* in humans, this would be fatal as zygote would not successfully develop into a foetus
1. each chromosome homologous pair doubled due to DNA replication in interphase
2. polyploidy non disjunction in meiosis I means ALL chromosomes fail to separate equally
3. this means when chromatids separate in meiosis II, 2 of the gametes end up being diploid with 2 copies of every chromsome and the other 2 have no chromosomes at all
4. when diploid gamete fuses with haploid gamete, the cell produced is a triploid (3 copies of every chromosome). This zygote would not survive
5. If polyploidy occurs in meiosis II, all chromatids fail to separate equally so results in gamete without chromosomes and diploid gametes
34
Describe how aneuploidy non disjunction occurs
* changes in the number of individual chromosomes
* individual (just 1) homologous chromosome pairs fail to separate during meiosis, usually resulting in gamete having one more/less chromosome
* on fertilisation with gamete with normal number of chromosomes, zygote will have more/less chromosomes than normal in all their body cells e.g. Downs syndrome (3 copies of chromosome 21)
1. each homologous pair of chromosomes doubled due to DNA replication in interphase
2. non disjunction in meisosis 1 means 1 chromosome does not separate equally
3. meiosis 2 happens normally so chromatids separate equally
4. 2 gametes have one extra chromosome (n+1) and 2 gametes have one less (n-1)
5. when (n+1) gamete fertilises with (n) gamete, diploid zygote has one extra chromosome
6. when (n-1) gamete fertilises with (n) gamete, diploid zygote has one less chromosome
7. if aneuploidy occurs in meiosis 2, then normal division occurs in meiosis 1, but in meiosis 2, chromosome non disjunction means one chromatid fails to separate equally so 2 haploid gametes made (n), one gamete has an extra chromosome (n+1) and one has one less (n-1).
35
Define genetic diversity
number of different alleles of genes in a species or population
- genetic diversity is a factor that enables natural selection to occur (can only occur if there is genetic diversity)
36
What is natural selection?
The process that leads to evolution in populations
- evolution= the change in allele frequency over many generations in a population
- natura; selection results in species becoming better adapted to their environment
- adaptions may be anatomical, physiological or behavioural
37
describe the process of natural selection
1. new alleles for a gene are created by random mutations
2. if new alleles increase chances of individual to survive in that environment then they are more likely to survive and reproduce
3. reproduction means advantageous allele passed to next generation
4. as a result, over many generations, the new allele increases in frequency in the population
38
why is genetic diversity important?
populations with low genetic diversity may not adapt to environmental changes
39
how is genetic diversity increased?
1. mutations in DNA forming new alleles- may be advantageous or problematic
2. different alleles being introduced into a population when individuals from another population migrate and reproduce (gene flow)
40
what is directional selection? Provide an example
* one of the extreme traits has the selective advantage
* occurs when there is a change in the environment
* the modal trait changes
* e.g. antibiotic resistance in bacteria: original environment has no antibiotics and so bacteria can thrive as being resistant to antibiotics not advantageous. Change in environment caused by human starting taking antibiotics, any individuals with mutated allele that makes them resistant to antibiotics now have selected advantage so can survive, reproduce and pass on advantageous allele. Over many generations, the advantageous allele increases in frequency, so frequency of extreme trait increases.
41
what is stabilising selection? Provide an example
* occurs when there is no change in environment
* the modal trait has the selective advantage
* the modal trait remains the same
* standard deviation decreases as individuals with the extreme trait decrease
* medium sized babies more likely to survive and reproduce than very large or small babies (small babies may have underdeveloped organs and large babies may have complications when being born increasing chance of health risks to mother and baby). Over many generations, medium birth weight most common as allele frequency has increased over time.
42
What are physiological adaptations
## Footnote
adaptations are features that help organisms to survive in their environment
processes in an organism's body that increase chance of survival
- bacteria producing antibiotics that kill other species of bacteria reducing competition so more likely to survive
43
What are behavioural adaptations?
ways an organism acts to increase chance of survival
- scorpions dance before mating which ensures they attract a mate of same species so increases chance of successful mating
44
what are anatomical adaptations?
structural features of an organism's body that increase chance of survival
- whales have thick layer of fat to keep them warm in the sea which increases chance of survival in places where their food is found
45
What is a species?
a group of similar organisms that can breed to make fertile offspring
- species must reproduce and pass on advantageous alleles for the survival of their species
46
why is courtship behaviour needed?
* essential for successful mating and for species recognition
* behaviours carried out by organisms to attract a mate of right species
47
What are courtship rituals?
a sequence of actions which is unique to each species. This is how animals identify members of their own species to reproduce with.
- mostly performed by males
- can include sequence of dance moves, sounds, release of pheromones, display of colourful feathers or fighting
- females observe courtship ritual and decide if they want to mate with male
48
Why is courtship important?
1. to ensure successful reproduction
- enables them to recognise own species and opposite sex as ritual unique to each species
- synchronises mating behaviour-indicates sexually mature and in season (releasing egg) for sucessful reproduction
2. to ensure survival of offspring
- form a pair bond between male and female during ritual
- choose a strong and healthy mate (courtship ritual indicates this)
49
What do courtship rituals show when they are studied?
* the more similar a courtship ritual is between different species, the most closely related a species are
* courtship rituals are genetically determined, so the more similar a species sequence is, the more similar their DNA base sequence is
50
how are immunological comparisons carried out to clarify the evolutionary relationships between organisms?
* similar proteins will also bind to the same antibodies
* e.g. if antibodies to a human version of a protein added to isolated samples from other species then any protein like the human version also recognised by antibodies
51
how is genome sequencing carried out to clarify the evolutionary relationships between organisms?
* advances in genome sequencing means the entire base sequence of an organim's DNA can be determined.
* comparisons can be made of one organism's base sequence to another
* shows how closely related they are
52
how does comparing amino acid sequences allow the clarification of evolutionary relationships between organisms?
* related organisms have similar DNA sequences
* so have similar amino acid sequences in proteins as coded for by base sequence in DNA
53
54
What is the binomial system?
* naming system to classify organisms.
* avoids confusion during scientific communication
* all organisms given one internationally accepted scientific latin name with 2 parts
* first name is GENUS second name is SPECIES
* same genus shows close relationship
* advantages: universal so avoids confusion during scientific communication and shows the relationship between organisms using genus
55
why do different species look similar?
1. live in similar environments
2. have similar selection pressures
3. similar alleles will have the selective advantage
4. produces similar/same proteins and therefore have similar characteristics
56
What is a hierarchy?
* smaller groups are arranged within larger groups
* no overlap between groups
* each group called a taxon (pl. taxa)
57
State the order of taxa in the classification system
1. Domain
2. Kingdom
3. Phylum
4. Class
5. Order
6. Family
7. Genus
8. Species
58
What is the purpose of organising organisms into a classification system?
* understand relationships between organisms and keep track of changes (e.g. evolution, impact of climate change etc)
* The system used is universal (uses binomial system) for scientific communication of all organisms around the world
* system is based on putting organisms into groups (taxonomy)
59
What is a phylogenic classification system?
* arranges species into groups according to their evolutionary origins and relationships
* phylogeny shows which organisms are related and how close the relationship is
* phylogenic trees how all organisms have evolved from shared common ancestors (relatives).
* uses a hierarchy in which smaller groups placed within larger groups with no overlap between groups
* each group called a taxon (plural taxa)
60
Define Biodiversity
the variety of living organisms in an area
61
Define Habitat
the place where an organism lives
62
Define Community
all the populations of different species in a habitat
63
What is local biodiversity?
the variety of different species living in a small habitat locally e.g. pond
64
What is Global Biodiversity?
variety of species on earth
- biodiversity greatest at equator, decreases towards poles
65
66
What is Species Richness?
* the measure of the number of different species in a community (biodiversity)
* worked out by taking random samples of a community and counting number of different species
67
Why is Biodiversity important?
* low biodiversity may not be a concern e.g. expected in artic or deserts
* a decrease in biodiversity that was once high is a cause for concern. Often caused by human activity
68
How is Biodiversity measured?
* Index of Diversity: the measure of species diversity. It measures the relationship between the number of species in a community (species richness) and the number of indivuals in each species (abundance)
* the higher the number, the more diverse the area is
* biodiversity index=1 (no biodiversity as all individuals are same species)
69
What is the difference between species richness and index of diversity?
Index of diversity measures the relationship between the number of species in a community (species richness) and the number of indivuals in each species (abundance), where as species richness only considers the number of species in a community.
70
How is index of diversity calculated?
d=N(N-1)/En(n-1)
- N=total number of organisms of all species
- n=total number of organisms of one species
- E=sum of (i.e. added together)
71
How do farming techniques reduce biodiversity?
| farming techniques carried out to maximise amount of food produced
1. woodland clearance increases area of farmland but reduces trees and number of tree species, destroys habitats so some species lose shelter/food so species die or are forced to migrate
2. hedgrow removal turns small fields into larger fewer ones
3. herbicides kill unwanted plants reducing plant diversity and number of organisms that food on weeds
4. pesticides kill organisms that feed on crops, so any species that feed on them also lose food source so may die
5. monoculture means fields are grown with only one type of plant reducing biodiversity and supports fewer organisms in terms of their habitats/food source
72
What is Genetic Diversity?
the number of different alleles in a population
73
How is genetic diversity within or between species made by comparing the frequency of measurable or observable characteristics?
* measure the frequency of measurable or observable characteristics in a population
* e.g. the number of different eye colours in a population and the number of people with each eye colour
* replaced with new gene technologies (inferring DNA differences from measurable or obserable characteristics has been replaced with direct investigation of DNA sequences.
74
How is genetic diversity within or between species made by comparing the base sequence of DNA?
* different alleles from the same gene have slightly different DNA base sequences
* comparing the DNA base sequences of same gene in different organisms in a population allows scientists to find out how many alleles of that gene are in that population.
75
How can genetic diversity within or between species be made by comparing the base sequence of mRNA?
* different alleles produce slightly different mRNA base sequences
* these can be compared
76
How can genetic diversity within or between species be made by comparing the amino acid sequence of the proteins encoded by DNA and mRNA?
* compare them
77
Why are gene technologies used to make genetic diversity within or between species isntead of comparing the frequency of measurable or observable characteristics?
* give a more accurate estimate of genetic diversity within a population/species
* allows genetic diversity of different species to be compared more easily
78
Define Variation
the differences that exist between species and within species
79
What are the causes of variation?
1. environment (climate, food, lifestyle etc)
2. genetic factors (different species have different genes and organisms of same species have same genes but different alleles)
3. mostly caused by combo of genetic and environmental factors
80
How can quantitative investigations of variation within a species be made?
* collecting data from random samples
* sample data will be used to draw conclusions about the whole population so it needs to accurately represent whole population and that any patterns are tested to ensure they are not due to chance
* eliminates biased samples
81
Give examples of quantitative investigations of variation within a species
1. collecting data from random samples
2. calculating a mean value of collected data and the standard deviation (SD) of that mean- ensures any variation observed in a random sample is not just due to chance
- mean used to tell if there is variation between samples.
- mean=total of all values in data/number of values in data
- SD measures the spread of values about the mean.
- shows how much values in a single sample vary
- greater SD=greater variation
3. interpreting mean values and their standard deviations
