Topic 4 - Genetic information, variation and organism relationships Flashcards
what are the similarities between DNA in eukaryotic cells with DNA in prokaryotic cells
- nucleotide structure is identical: deoxyribose attached to phosphate and a base
- adjacent nucleotides joined by phosphodiester bonds, complementary bonds joined by hydrogen bonds
- DNA in mitochondria/chloroplasts have similar structure to DNA in prokaryotes: short, circular, not associated with proteins
what are the differences between DNA in eukarotiyc and prokaryotic cells
- eukaryotic DNA is longer
- eukaroytic DNA is linear, prokaryotic DNA is circular
- eukaroyitc DNA is associated with histone proteins, prokaryotice DNA isn’t
- eukaryotic DNA contain introns, prokaryotic DNA doesn’t
what is a chromosome
long linear DNA and is asssociated with histone proteins found in the nucleus of eukaryotic cells
what is a gene
a sequence of DNA (nucleotide) bases that code for:
- the amino acid sequence of a polypeptide
or
- a functional RNA e.g. ribosomal RNA or tRNA
what is a locus
the fixed position a gene occupies on a particular DNA molecule
describe the nature of the genetic code
triplet code, universal, non-overlapping, degenerate
what does triplet code mean
a sequence of 3 DNA bases, called a triplet, codes for a specific amino acid
what does universal mean
the same base triplets code for the same amino acids in all organisms
what does non-overlapping mean
each base is part of only one triplet so each triplet is read as a discrete unit
what does degenerate mean
an amino acid that can be coded for by more than one base triplet
where are non coding bases sequences found
- btwn genes e.g. non coding multiple repeats
- w/n genes - introns
fact
in eukaryotes, much of the nuclear DNA doesn’t code for polypeptides
what are introns
base sequence of a gene that doesn’t code for amino acids in eukaryotic cells
what are exons
base sequence of a gene coding for amino acid sequences
define genome
the complet set of genes in a cell incl. those in mitochondria and/or chloroplasts
define proteome
the full range of proteins that a cell can produce coded for by the cell’s DNA/genome
what are the two stages of protein synthesis
transcription and translation
describe transcription
production of mRNA from DNA in the nucleus
describe translation
production of polypeptides from the sequence of codons carried by mRNA at ribosomes
what is the similarity btwn tRNA and mRNA
both single polynucleotide strand
what are the differences btwn tRNA and mRNA
- tRNA is folded into a clover leaf shape whereas mRNA is linear/straight
- tRNA has hydrogen bonds btwn 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 binding site, mRNA doesn’t
describe how mRNA is formed by transcrription in eukaryotic cells
- hydrogen bonds btwn DNA bases break
- only one DNA strand acts as a template
- free RNA nucleotides align next to their complementary bases on the template strand. in RNA uracil is used instnead of thymine
- RNA polymerase joins adjacent RNA nucleotides
- this forms phosphodiester bonds via condensation reactions
- pre-mRNA is formed and this is spliced to remove introns forming mature mRNA
describe how production of mRNA in eukaryotic cell is different from the production of mRNA in a prokaryotic cell
- pre-mRNA is produced in eukaryotic cells whereas mRNA is produced directly in prokaryotic cells
- genes in prokaryotic cells don’t contain introns so no splicing in prokaryotic cells
describe how translation leads to the production of a polypeptide
- mRNA attaches to a ribosome and the ribosome moves to a start codon
- tRNA brings a specific amino acid
- tRNA anticodon binds to complementary mRNA codon
- ribosome moves along to the 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
- tRNA released after amino acid joined polypeptide
- ribosome moves along mRNA to form the polypeptide until a stop cocon is reached
describe the role of ATP in translation
hydrolysis of ATP to ADP + Pi releases energy so amino acids join to tRNAs and peptide bonds form btwn amino acids
describe the role of tRNA in translation
- attaches to transports a 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
describe the role of ribosomes in translation
- mRNA binds to ribosomes with space to 2 codons
- allows tRNA with anticodons to bind
- catalyses formation of peptide bond btwn amino acid, held by tRNA molecules
- moves along mRNA to the next codon e.g. translocation
describe how the base sequence of nucleic acids can be related to the amino acid sequence of polypeptides when provided with suitable data
- may be provided with a genetic code to identify which triplets/codons produce which amino acids
- tRNA anticodons are complementary to mRNA codons
- sequence of codons on mRNA are complementary to sequence of triplets on DNA template strand
- in RNA uracil replaces thymine
what is a gene mutation
a change in base sequence of DNA on chromosomes which can arise spontaneously during DNA replication (interphase)
what is mutagenic agent
a factor that increases rate of gene mutation e.g. ultraviolet light or alpha particles
explain how a mutation can lead to the production of a non-functional protein or enzyme
- changes in sequence of base triplets in DNA so changes seuqence of codons on mRNA
- changes sequence of amino acids in polypeptides
- changes position of hydrogen.ionic.disulphide bonds btwn amino acids
- changes protein tertiary structure of protein
- enzymes active site changes shape so substrate can’t bind, enzyme substrate complex can’t form
explain the possible effects of a substitution mutation
- base/nucleotide in DNA replaced by a different base/nucleotide
- this changes on triplet so changes one mRNA codon
- so one amino acid in polypeptide changes, tertiary structure may change if position of hydrogen/ionic/disulphide bonds change
OR
amino acid doesn’t change due to degenerate nature of genetic code/mutation is in an intron
explain the positive effects of a deletion mutation (there’s 6)
- 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
state the features of homologous chromosomes
same length, same genes but may have different alleles
describe the difference btwn diploid and haploid cells
diploid has 2 complete sets of chromosomes, represented as 2n
haploid has a single set of unpaired chromosomes represented as n
describe interphase in meiosis
DNA replicates, 2 copies of each chromosome [sister chromatids] joined by a centromere
describe meiosis I in meiosis
this is the first nuclear division which separates homologous chromosomes
- chromosomes arrange into homologous pairs
- crossing over btwn homologous chromosomes
- independent segregation of homologous chromosomes
describe meiosis II in meiosis
this is the 2nd nuclear division which separates chromatids
what is the outcome of meiosis
4 genetically varied daughter cells and they are usually haploid is there is a diploid parent cell
explain why the number of chromosomes is halved during meiosis
homologous chromosomes are separated during meiosis I (first division)
explain how crossing over creates genetic variation
- homologous pairs of chromosomes associate/form a bivalent
- chiasmata form (point of contact btwn non-sister chromatids - aka homologous pairs)
- alleles (equal lengths) of non sister chromatids exchanged btwn chromosomes
- creating new combinations of maternal and paternal alleles on chromosomes
explain how independent segregation creates genetic variation
homologous pairs randomly align at equator so random which chromosome from each pair goes into each daughter cell. this creates different combinations of maternal or paternal chromosomes/alleles in daughter cells
other than mutation and meiosis, explain how genetic variation w/n a species is increased
- random fertilisation/fusion of gametes
- creating new allele combinations/new maternal and paternal chromosome combinations
explain the different outcomes of mitosis and meiosis
- mitosis produces 2 daughter cells whereas meiosis produces 4 daughter cells (1 division vs 2)
- mitosis maintains the chromosome number (diploid to diploid or haploid to haploid) but meiosis halves the number of chromosomes cuz homologous chromosomes separate in meiosis and not mitosis
- mitosis produces generically identical daughter cells whereas mitosis produces genetically varied daughter cells
explain the importance of mitosis
two divisions creates haploid gametes so diploid number is restored at fertilisation - chromosome number is maintained btwn generations.
independent segregation and crossing over creates genetic variation
where does mitosis occur in a life cycle
occurs btwn stages where chromosome number is maintained
where does meiosis occur in a life cycle
occurs btwn stages where chromosome number is halved
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)
suggest how number of possible combinations of chromosomes in daughter cells following meiosis can be calculated
2^n where n = number of pars of homologous chromosomes (half the diploid number)
suggest how number of possible combinations of chromosomes in daughter cells following random fertilisation of two gametes can be calculated
(2^n)^2 where n = number of pairs of homologous chromosomes (half the diploid number)
what is genetic diversity
number of different alleles of genes in a population
what are alleles
variations of a particular gene with the same locus that has different base sequence
how do alleles arise
via mutation
what is a population
a group of interbreeding individuals of the same species
explain the importance of genetic diversity
- enables natural selection to occur
- as in certain environments, a new allele of a gene might benefit its possessor
- by resulting in a change in the polypeptide coded for that positively changes its properties
- giving a possesser a selective advantages this means increased chances of survival and reproductive success
what is evolution
change in allele frequency over many generations in a population occurring through the process of natural selection
name 2 factors which are major factors in evolution and contribute to the diversity of living organisms
adaptation and selection
state and explain the 5 principles of natural selection in the evolution of populations
mutation - random gene mutation can result in [named] new alleles of a gene
advantage - in certain [named] environments the new allele might benefit its possessor [explain why] -> 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, [named] allele increases in frequency in the population
what does natural selection result in
species that are better adapted to their environment
state 3 types of adaptations
anatomical, behavioural, physiological
describe anatomical adaptation
structural/physical features which increase chance of survivial
describe physiological adaptation
processes/chemical reactions that increase chance of survival
describe behavioural adaptation
ways in which an organaism acts that increases chance of survival
what is directional selection
give an example of directional selection
antibiotic resistance in bacteria. those with an extreme variation of a trait has selective advantage. usually change in environment
what is the effect of directional selection on population over many generations
increased frequency of organisms with alleles for extreme trait. normal distribution curve shifts towards extreme trait
what is stabilising selection
give an example of stabilising selection
human birth weight - those with average/modal variation of a trait has selective advantage. no change in environment, usually stable
what is the effect of stabilising selection on population over many generations
increased frequency of organisms with alleles for average trait. normal distribution curve is similar/less variation around the mean (graph curve squeezes in gets taller n thinner, like maxwell boltzham distribution curve when temp cold)
what is a speicies
a group of organisms that can interbreed to produce fertile offspring
suggest why 2 different species are unable to produce fertile offspring
- different species have different chromosome numbers -> offspring may have odd chromosome number
- homologous pairs cannot form = meiosis cannot occur to produce gametes
explain why courtship behaviour is a necessary precursor to successful mating (5 reasons)
- allows recognition of members of same species so fertile offspring is produced
- allows recognition/attraction of opposite sex
- stimulates/synchronises mating/production/release of gametes
- indicates sexual mating/fertility
- establishes a pair bond to raise young
describe a phylogenetic classification system
species attempted to be arranged into groups called taxa, based on their evolutionary origins (common ancestors) and relationships
uses a hierarchy where:
- similar groups are placed w/n larger groups
- no overlaps btwn groups
name the taxa in the hierarchy of classification
domain
kingdom
phylum
class
order
family
genus
species
how is each species universally identified
binomial naming - genus and species
suggest an advantage of binomial naming
universal so no confusion as many organisms have more than one common name
how do you interpret phylogenetic trees
- branch point = common ancestor
- branch = evolutionary path
- if two species have a more recent common ancestor, they are more closely related
what two advances have helped clarify evolutionary relationships btwn organisms
genome sequencing, immunology
explain how advances in genome sequencing has helped to clarify evolutionary relationships btwn organisms
- allows comparison of DNA base sequences
- more differences in DNA base sequences = more distantly related/earlier common ancestor
- mutations build up over time
explain how advances in immunology has helped to clarify evolutionary relationships btwn organisms
- allows comparison of protein tertiary structure
- higher amount of protein from one species binds to antibody against same protein from another species = more closely related/more recent common ancestor
- indicates similar amino acid sequence and tertiary structure = less time for mutations to build up
what is biodiversity
variety of living organisms - species, genetic and ecosystem diversity
what is a community
all populations of different species that live in an area
what is species richness
a measure of the number of different species in a community
what does an index of diversity do
describes the relationship btwn
- number of species in a community = species richness
- number of individuals in each species = population size
suggest why index 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
what is the formula for index diversity
d = [N(n-1)]/ sum of n(n-1)
where N = total number of organisms of all species
n = total number of organisms of each species
describe how index of diversity values can be interpreted
high = many species present and species evenly represented
low = habitat dominated by one/few species
state 4 farming techniques which reduces biodiversity
- removal of woodland and hedgerows
- monoculture
- use of herbicides to kill weeds
- use of pesticides to kill pests
how does:
- removal of woodland and hedgerows
- monoculture
- herbicides
reduce biodiversity
reduces variety of plants = fewer habitats so less variety of food sources
how does pesticides reduce biodiversity
predator population of pest decreases
explain the balance btwn conservation and farming
conservation required to increase biodiversity but when implemented on farms, yields and profit will reduce for farmers as it reduces land area for crop growth, increasing competition and pest population
to offset loss, financial incentives/grants are offered
give 4 examples of how biodiversity can be increased in area of agriculture
- reintroduction of field margins and hedgerows
- reduce use of pesticides
- growing different crops in the same area (intercropping)
- using crop rotation of nitrogen fixing crops instead of feertilisers
state four ways genetic diversity w/n or btwn species can be measured
- 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
explain how comparing DNA, mRNA and amino acid sequences can indicate relationships btwn organisms w/n a species and btwn species
- more difference in sequences = more distantly related/earlier common ancestor
- as mutations build up over time. more mutations = more changes in amino acid sequences
explain the 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 gene
gene technologies allowed this to be replaced by direct investigation of DNA sequences
explain the key considerations in quantitative investigations of variation w/n a species
- collect data from random samples to remove bias
- large sample size to get a representative of whole population
- ethical sampling, must not harm organism/allow release unchanged
- calculate a mean value of collected data and standard deviation of that mean
- interpret mean values and their standard deviations
- use [named] statistical test to analyse if there is a significant difference btwn populations
what does standard deviation show
spread of values about the mean, the higher the standard deviation, the higher the variation
if standard deviations overlap, causing 2 sets of data to be shared, any difference btwn the 2 may be due to chance/not significant
