4. genetics, biodiversity and classification P1 Flashcards
What are the three components of nucleotides?
a pentose sugar, a phosphate group and an organic base
describe the structure of DNA [5]
- A polymer of nucleotides
- Each nucleotide is formed from deoxyribose, a phosphate group and an organic nitrogenous base.
- Phosphodiester bonds between nucleotides
- Double helix
- Hydrogen bonds between adenine, thymine and cytosine, guanine
Describe the role of DNA
Carries genetic information and determines are inherited characteristics
describe the structure of RNA
made up of a ribose sugar, a phosphate group and one of four organic bases. single stranded.
Uracil replaces thymine
describe the role of RNA
Transfers genetic information from DNA to ribosomes for protein synthesis
How is DNA in eukaryotic cells different from prokaryotic cells?
eukaryotic: found in nucleus,
pro: not
eukaryotic is associated with proteins/histones, whereas prokaryotic isn’t.
eukaryotic is linear, and prokaryotic is circular.
eukaryotic contains introns, and prokaryotic doesn’t
eukaryotic had no plasmids, but prokaryotic does.
name the fixed position occupied by a gene on a DNA molecule
locus
describe how a gene is a code for the production of a polypeptide. Do not include information about transcription or translation in your answer [3]
- the base/ nucleotide sequence.
- in triplets
- determines the sequence of amino acids/ primary structure in polypeptide.
define the term exon
the base/ nucleotide sequence coding for a polypeptide/ sequence of amino acids.
what is the genetic code?
the order of bases on DNA. consists of codons (triplets of bases that code for a particular amino acid)
Describe how phosphodiester bond is formed between two nucleotides within a DNA molecule [2]
- condensation reaction
- between phosphate and deoxyribose
- catalysed by DNA polymerase
identify features of the genetic code
- non-overlapping - each triplet is only read once
- degenerate - more than one triplet codes for the same amino acid
- universal - same bases and sequences used by all species
what is a gene?
A sequence of bases on a DNA molecule that codes for a specific sequence of amino acids to make a polypeptide.
what is an allele
different versions of the same gene found at the same locus on a chromosome.
what are introns? and where are they found?
regions of DNA that don’t code for anything, between exons within genes
define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome [2]
- DNA that doesn’t code for protein/ polypeptide
- positioned between genes
what is the genome?
the complete set of genes contained in the cells of an organism
what is the proteome?
the full range of different proteins that DNA is able to code for
suggest advantages of using mRNA rather than DNA for translation
single stranded and linear - ribosome moves along strand and tRNA binds to exposed bases
contains no introns
shorter - breaks down quickly so no excess polypeptide forms
describe the structure of tRNA
a single strand of nucleotides that is folded over in a clover leaf shape.
On one end is an anti-codon and on the other is an amino acid binding site
what is produced by transcription?
mRNA
give 3 ways in which the DNA in a chloroplast is different from the DNA in a nucleus [3]
- in chloroplasts, DNA isn’t associated with proteins, but nuclear DNA is
- the DNA in chloroplasts is circular, rather than the linear nuclear DNA
- introns are absent in chloroplasts but present in nuclear DNA
- DNA is shorter in chloroplasts
not all mutations in the nucleotide of a gene cause a change in the structure of a polypeptide. give 2 reasons why [2]
triplets code for the same amino acid, which occurs in introns/ non-coding sequence
what is a homologous pair of chromosomes?
two chromosomes that carry the same genes
describe two differences between the structure of a tRNA molecule and the structure of an mRNA molecule [2]
tRNA is a ‘clover leaf shape’ and mRNA is linear
tRNA has an anticodon and mRNA has a codon
tRNA has amino acids binding site, mRNA doesn’t
describe and explain a difference in the structure of mRNA and pre- mRNA [2]
pre-mRNA has exons and introns, mRNA has only exons due to splicing
describe how mRNA is formed by transcription in eukaryotes [5]
- the hydrogen bonds between the DNA bases break (due to DNA helicase)
- one DNA strand acts as a template
- free RNA nucleotides align by complementary base paring
- RNA polymerase joins adjacent RNA nucleotides
- by forming phosphodiester bonds between adjacent nucleotides
- pre-mRNA is spliced to form mRNA/ introns are removed to form mRNA
describe how mRNA is produced from an exposed template strand of DNA. Don’t include DNA helicase or splicing in your answer [3]
Free RNA nucleotides form complementary base pairs
phosohodiester bonds form
by action of RNA polymerase
what is produced by translation?
proteins
where does translation take place
in cytoplasm (on ribosomes)
describe how a polypeptide is formed by translation of mRNA [6]
- mRNA attaches to ribosomes (and moves to find the start codon)
- tRNA anticodons bind to complementary mRNA codons
- tRNA brings a specific amino acid
- amino acids join by peptide bonds (to form polypeptide)
- with the use of ATP
- tRNA is released after amino acid joined to polypeptide
- the ribosome move along the mRNA (to the next codon) to form the polypeptide
describe how one amino acid is added to a polypeptide that is being formed at a ribosome during transcription [3]
- tRNA brings specific amino acid to ribosome
- anticodon on tRNA binds to codon on mRNA
- amino acids join by condensation reaction (using ATP) and forming peptide bonds
describe the role of a ribosome in the production of a polypeptide [3]
- mRNA binds to ribosome
- allows tRNA with anticodon to bind
- catalyses formation of peptide bonds between amino acids
- moves along mRNA to next codon
the genetic code is described as degenerate. what is meant by this?
more than one codon codes for a single amino acid
give the 2 types of molecule from which a ribosome is made
RNA, protein
in eukaryotic cells, the base sequence of the mRNA might be different from the sequence of the pre- mRNA. explain why [2]
- introns in pre-mRNA
- removal of sections of pre-mRNA/ splicing
define the term mutagenic agent, and give examples
a factor that increases the rate of gene mutation, e.g. X-rays, UV light, gamma rays
what’s chromosome non-disjunction? [2]
- in meiosis
- when the chromosomes fail to separate (type of mutation)
genetic variation within a species is increased during meiosis by crossing over and independent segregation. apart from mutation, explain one other way genetic variation is increased [2]
random fertilisation - produces new allele combinations
give one reason why eggs produced by meiosis are genetically different
independent segregation or crossing over
the offspring produced from farmed trout are sterile. suggest and explain why [2]
homologous chromosomes don’t separate easily, so no meiosis
or
too many copies of chromosomes so no meiosis
define gene mutation
a change in the base sequence of DNA which results in the formation of new alleles
why might a gene mutation have no effect on an individual
- genetic code is degenerate so amino acid sequence may not change
- mutation may occur in intron so amino acid sequence may not change
what is substitution mutation?
when a nucleotide in the DNA sequence is replaced by another.
what is a deletion mutation?
when a nucleotide in the DNA sequence is lost - more likely to be harmful as whole amino acid sequence will be different
what is meiosis
a form of cell division that produces four genetically different haploid cells.
give differences between mitosis and meiosis
- one division in mitosis, 2 divisions in meiosis
- crossing over only in meiosis
- independent segregation only in meiosis
- 2 cells produced in mitosis, 4 produced in meiosis
- mitosis - diploid to diploid/ haploid to haploid, meiosis - diploid to haploid
- mitosis - genetically identical, meiosis - genetic variation
how might gene mutation result in a positive effect on an individual?
- may result in increased survival chances
- can result in change in polypeptide that positively changes the properties of the protein.
explain how the chromosome number is halved during meiosis [2]
- homologous chromosomes (pair)
- one of each pair goes to each daughter cell/ to opposite poles
describe the process of crossing over and explain how it increases genetic diversity [4]
- homologous pairs of chromosomes associate
- chiasmata form
- equal lengths of alleles are exchanged
- producing new combinations of alleles
explain why all the cells in a body will have the mutation [2]
- all cells derived from a single cell by mitosis
- mitosis produces genetically identical cells
what happens during meiosis 1
- homologous pairs of chromosomes associate forming chiasmata
- crossing over takes place (exchanging alleles between homologous chromosomes - resulting in new combinations of alleles)
- homologous chromosomes separate randomly (independent segregation- results in large number of possible combinations of alleles/chromosomes) each cell either contains maternal or paternal copy.
what happens during meiosis 2
- independent segregation of sister chromatids
- each cell divides again, producing 4 haploid cells
define population
all the organisms of a particular species that live in the same place
define genetic diversity
the total number of different alleles in a population
what advantage does a high genetic diversity provide?
ability to adapt to a change in environment - allows natural selection to occur
the enzyme encoded by the ADf allele catalyses the breakdown of alcohol faster than enzyme encoded by ADs allele. suggest why [3]
- different primary structure/ amino acid sequence
- different tertiary structure/ shape of active site
- enzyme-substrate complexes more likely with enzyme from ADf allele
alcohol is toxic to fruit flies. suggest and explain why the frequency of the ADf allele increased during the 45 generations [4]
- flies with ADf allele have selective advantage in presence of alcohol
- so are more likely to survive and reproduce
- and pass on ADf allele
- so allele frequency increases
describe how the student made a 1 in 10 dilution and the used this to make a 1 in 1000 dilution of the original liquid culture of bacteria
add one part bacteria culture to 9 parts sterile liquid to make 10^-1 dilution
mix well
add one part 10^-1 suspension to 99 parts sterile liquid to make 10^-3 dilution
OR
repeat using 9 parts fresh sterile liquid and one part of 10^-1 and 10^-2 dilutions to make 10^-3 dilution
explain how natural selection results in development of new characteristics
random mutations result in new alleles
some alleles provide an advantage, making an individual more likely to survive and reproduce
their offspring receive the new allele and frequency continues to increase over many generations
what is directional selection?
occurs when environmental conditions change. individuals with phenotypes suited to the new conditions will survive and pass on their genes. over time the mean of the population will move towards these characteristics
give an example of directional selection
antibiotic resistance - bacteria with a mutation allowing them to survive in the presence of antibiotics will reproduce. therefore frequency of this allele will increase and the population will shift to have greater antibiotic resistance.
what is stabilising selection?
occurs when environmental conditions stay the same. individuals closest to the mean are favoured, and any new characteristics are selected against. results in low diversity.
give an example of stabilising selection
human birth weights: babies that weigh around 3kg are more likely to survive than those at lower or higher weights.
what are the three types of adaptation? give examples of each
anatomical (changes to body structure) e.g. oily fur
physiological (changes to bodily processes) e.g. venom production
behavioural (changes to actions) e.g. hibernation
suggest and explain one reason why bacteria resistant to tetracycline are more common that bacteria resistant to streptomycin in these farm animals [2]
- tetracycline is used more often/ in higher doses
- so resistant bacteria are more likely to survive and reproduce and pass on allele for tetracycline resistance
in recent years, these farm animals haven’t been given tetracycline, but the percentage of bacteria resistant to it has remained constant. suggest one reason why
bacteria pass on resistance gene when they reproduce
OR
environment doesn’t change, so stabilising selection occurs
define species
a group of organisms that are able to produce fertile offspring
what are the advantages of courtship behaviour?
individuals can recognise sexually mature members of their own species of the opposite sex, synchronise mating, form a pair bond, and successfully breed
define classification
the process of arranging organisms into groups
an organism is identified by referring to the species name and the genus name. what term is used to describe this method of naming organisms
binomial
name the eight groups in the classification hierarchy, from largest to smallest
domain, kingdom, phylum, class, order, family, genus, species
what is phylogenetic classification
the process of arranging organisms into groups based on their evolutionary origins and relationships
how can we clarify evolutionary relationships between organisms
analyse their molecular differences
advances in immunology/ genome
sequencing provides clear pictures of how related two species are.
explain hierarchical classification
smaller groups within larger groups with no overlap between groups
each group is called a taxon
what is biodiversity?
the variety of living organisms.
what is meant by species richness?
a measure of the number of different species in a community
what is the difference between species richness and index of diversity?
species richness measured only number of different species and doesn’t measure the number of individuals in each species. (index of diversity does)
explain why it is more useful to calculate index of diversity than to record species richness [2]
- index of diversity also measures number of each species
- so useful because there may be many of some species and few of other species
what data would the students need to collect to calculate their index of diversity in each habitat? [1]
number of species and number of individuals in each species
give 2 ways the students would have ensured their index of diversity was representative of each habitat [2]
- random samples
- large number of samples
what impact does farming have on species diversity
farmland is typically used for only one species and use of pesticides (decreases species diversity as farmers select for certain characteristics, which reduces number of different alleles in the population
how can biodiversity be increased in areas of agriculture?
- use hedgerows instead of fences
- grow different crops in the same area or rotate crops around after a season.
- limit use of pesticides
give four ways we can compare genetic diversity between organisms
frequency of observable characteristics
base sequence of DNA
base sequence of mRNA
amino acid sequence
what is meant by gene technology?
sampling DNA or mRNA in order to read and compare the base sequence of organisms
or amino acid sequence can be studied
why do scientists prefer to use gene technology instead of observation?
simply inferring DNA differences by observing an organisms characteristics isn’t reliable; the characteristics could be coded for by more than one gene, or could be influenced by the environment.
how can a random sample be achieved?
create a grid, and randomly generate coordinates where a quadrat will be placed. repeat until sample size is reached
suggest how the scientist measured the rate of water flow in the river [1]
time to fill container of known volume
or
movement of floating object over known distance and given time.
outline a method the ecologists could have used to determine the plant species richness at one site [3]
- a method of selecting sampling sites at random (e.g. create a grid, and randomly generate coordinates where a quadrat will be placed. repeat until sample size is reached)
- use of quadrat
- count number of different plant species in each quadrat
the index of diversity ot the insects was higher in the hedge than in the barley field. explain why [3]
- more plant species
- more food sources
- more habitats
the scientists decided to collect animals from the soil samples for 40 minutes. suggest how the scientists decided 40 minutes was an appropriate time [2]
repeat soil sorting for different times and record numbers of species collected
find optimum time
describe how you would investigate the effect of an invasion by a non-native species of plant over many years on the abundance of a native species of plant in a community [3]
- set up a grid system with coordinates
- place large number of quadrats at coordinates selected at random
- count number of native plant in quadrats
- repeat at same time each year for many years
the genetic diversity of species is measured by comparing differences in the base sequence of DNA/ mRNA. give 2 other ways genetic diversity between species is measured
- comparing measurable/ observable features/ characteristics
- comparing amino acid sequences
