Topic 4 Flashcards
Gene
a section of DNA that contains a code for making a polypeptide and functional RNA
Locus
the location of a particular gene on a chromosome
Allele
a different version of the same gene
Chromosome
Threadlike structure
composed of tightly coiled DNA wrapped around histones (if it is a eukaryotic cell)
Homologous chromosome
a pair of chromosomes - maternal and paternal
Have the same gene loci, however they can have alleles
therefore, they are the same size
Eukaryotic DNA
DNA is stored as chromosomes inside the nucleus
linear chromosomes
DNA is tightly coiled and wrapped around proteins called histones
Prokaryotic DNA
DNA molecules are shorter and circular
Circular chromosome
DNA is not wound around histones. Instead, it supercoils to fit in the cell
Codon
3 bases on mRNA that code for an amino acid
Start codon
3 bases at the start of an mRNA sequence which help to initiate translation
Stop codon
3 bases at the end of every mRNA or gene that doesn’t code for an amino acid
this causes ribosomes to detach
and therefore stops translation
Genetic code
an amino acid is coded for by 3 DNA bases which are described as the “triplet code”
What is meant by ‘the genetic code is degenerate?
each amino acid is coded for by more than one triplet of bases
What is the advantage of the genetic code being degenerate?
If a substitution mutation occurs, the new triplet of bases may still code for the same amino acid
Therefore the mutation will have no impact on the final protein produced
What is the advantage of the genetic code being universal?
genetic engineering is possible
a human gene can be inserted into another organism
e.g human gene for insulin inserted into bacteria to make insulin
Also the protein synthesis mechanism or machinery is universal
What is the advantage of the genetic code being non-overlapping?
if a point mutation(substitution)occurs, it will only affect one codon and therefore one amino acid
Triplet code
An amino acid is coded for by 3
Mutation
a change in the base sequence of DNA
can be a gene or chromosome mutation
Frequency can be increased by mutagenic agents
What is meant by ‘the genetic code is universal?
the same triplet of bases codes for the same amino acid in all organisms
What is meant by ‘the genetic code is non-overlapping?
Each base in a gene is only part of one triplet of bases that codes for one amino acid
Therefore each codon is read as a discrete unit
Or each base is only read once
Introns
Non-coding sequence of DNA
Exons
sequences of DNA that code for amino acids
What is splicing?
post-transcription modification
removing introns
Pre mRNA to mRNA
Genome
the complete set of genes in a cell
Proteome
The full range of proteins that a cell is able to produce
Anticodon
3 bases on the tRNA which are complementary to the codon on mRNA.
mRNA structure(5)
single-stranded
made up of codons
a copy of one gene
Uracil instead of thymine
Ribose sugar
tRNA structure
Single-stranded, folded to create a cloverleaf shape
Held in place by hydrogen bonds
Has an anticodon and amino acid binding site
mRNA function
A copy of a gene from DNA
Created in the nucleus, and it then leaves the nucleus
To carry the copy of the genetic code of one gene to a ribosome in the cytoplasm
tRNA function
A specific amino acid attaches at the binding site
Transfers this amino acid to the ribosome to create the primary sequence of polypeptide chain
Transcription and splicing
The first stage in protein synthesis
An enzyme acts on a specific region of DNA causing it to unwind and expose bases and one strand acts as template strand
Complementary RNA nucleotides attaches and RNA polymerase runs along these nucleotides and joins them to form pre mRNA
Once RNA polymerase reaches a specific sequence of bases - stop triplet code - detaches and forms pre mRNA molecule
The pre mRNA is spliced in the nucleus by spliceosome
where the introns are removed and mRNA only contains extrons
As pre mRNA too big to leaves nucleus
Therefore mRNA after splicing leaves through nuclear pore
In prokaryotes no splicing - directly mRNA produced
Translation and how it forms final protein
The second stage in protein synthesis
Occurs on ribosomes in the cytoplasm
The ribosome attaches to a specific code in the codon called the start codon and this initiates translation.
A tRNA molecule with complementary anticodon moves to the ribosome and attaches to the codon and this molecules also contains a specific amino acid.
One ribosome contains 2 tRNA molecule
Ribosome moves along codons and keeps bringing complementary tRNA with amino acids
The amino acids are joined by peptide bind using an enzyme and ATP which is hydrolysed to provide energy
When ribosome reaches a specific code which is the stop codon it detaches and primary sequence of amino acid formed.
So the triplet code on DNA decides the codon on mRNA which decides the anticodon and therefore the order in which the tRNA molecule line up
Therefore the sequence if amino acid - primary structure
Which is coiled or folded into secondary structure which folds further into tertiary structure.
Different polypeptides linked along with non protein group to form functional quaternary protein
Which enzymes are involved in transcription?
DNA helicase
RNA polymerase
DNA helicase
catalyses the breaking of hydrogen bonds between the two strands of DNA
RNA polymerase
joins adjacent RNA nucleotides together
forming a phosphodiester bond
pre-mRNA
mRNA in eukaryotes that still contains the introns after transcription
Inside nucleus
How is pre-mRNA modified?
the introns are removed by a protein called a spliceosome
this leaves just the exons
What is ATP used for in translation?
forming the peptide bond between amino acids
Haploid
one copy of each chromosome in a cell
Diploid
two copies of each chromosome in a cell
Meiosis
Meiosis contains two divisions - 1 and 2
Meiosis 1 - homologous chromosome separated and here independent segregation and crossing over occurs
Meiosis 2 - individual chromosomes are separated by pulling apart sister chromatids.
Produces 4 haploid, genetically different daughter cells
Independent segregation
-homologous pairs of chromosomes randomly line up opposite each other at the equator of the cell forming BIVALENT
-when they separate it creates a large number of possible combinations of chromosomes in the daughter cells produced - measured by 2^n where n=no.of pairs of homologous chromosome
Crossing over
-homologous pairs of chromosomes line up opposite each other at the equator in meiosis 1
-parts of the chromatids twist, which creates tension and strains the bonds causing it to break and recombine with chromatids of homologous partner
-Usually equivalent portions exchanged
-results in new combinations of alleles in the gametes
-The overlap of chromatids is called chiasmata
Introduces genetic variation
This is rare so doesn’t occur often
Gametes
sex cells (sperm and egg)
Haploid
Form diploid cells by random fertilisation
How does meiosis introduce variation?
crossing over
independent segregation in meiosis 1
After meiosis the gametes fuse by random fertilisation which introduces variation too.
No.of possible chromosome combinations in each daughter cell after independent segregation is 2^n
No.of possible chromosome combinations in offspring after random fertilisation- (2^n)^2
Types of gene mutations
deletion and addition - frameshift
substitution
What is a frameshift?
-the removal or addition of one base changes all of the subsequent codons
-all the bases shift back or forward one position
Chromosome mutation
-change in the number of chromosomes
-occurs during meiosis
Deletion mutation
-a gene mutation
-a base is removed from a sequence
-causes a frameshift
Substitution mutation
a gene mutation
a base is swapped for a different one
Non-disjunction
the chromosomes or chromatids do not split equally during anaphase in meiosis causing aneuploidy
Eg Down syndrome with additional 21 chromosome
Polyploidy
-changes in whole sets of chromosomes
-e.g. when organisms have three or more sets of chromosomes eg triploid or tetraploid instead of haploid and diploid
-mainly occurs in plants
Aneuploidy
a change in the number of individual chromosomes
e.g 3 copies of chromosome 21 causes Down syndrome
Arises due to non disjunction
Down’s syndrome
caused by a chromosome mutation
an example of aneuploidy
3 copies of chromosome 21
Genetic diversity
-the number of different alleles in a population
Natural selection
Natural selection - survival of fittest causes evolution of population.
Within any population of species there is a gene pool with a wide variety of alleles
Random mutation creates new allele which in most cases harmful but in some cases beneficial and give it an advantage over other individuals when conditions change
More likely to survive competition with others and therefore use resources to grow and live longer. While the ones without the alleles dies
These one with advantageous allele more likely to reproduce and pass on advantageous allele
Overtime this allele common in population leads to evolution in population
Gene pool
all the genes and alleles in a population at a particular time
Allele frequency
the proportion of organisms within the population carrying a particular allele
Evolution
-the change in allele frequency
-over many generations in a population
Selection pressure
-factors that affect the survival of an organism eg competition for resources and mates
-the driving force of natural selection which causes evolution
Types of selection
stabilising
directional
Directional selection
-one of the extreme traits has a selective advantage
-occurs when there is a change in the environment
-the modal trait changes which is the most common trait
Stabilising selection
-the middle (median) trait has a selective advantage and continues to be the most
frequent in the population - modal trait
-represented by a normal distribution graph
-range decreases as the extreme traits are lost over time
An example of directional selection
Antibiotic resistance
An example of stabilising selection
human birth weight
Definition of a species
a group of similar organisms that can breed to make fertile offspring
Binomial system
-a universal naming system
-individuals are named after their genus and species
-e.g. Homo sapiens
Courtship behaviour
-different sequences of behaviours that animals demonstrate to attract a mate
-each species demonstrates its own unique behaviour
-Courtship maximises successful mating by - recognising members of same species, identifying a mate capable of breeding, form a pair bond for raising off spring and synchronise mating.
Importance of courtship
-Helps to synchronise mating behaviour so that the animals are more likely to mate when the female is releasing eggs
-Increases the likelihood of successful mating
-Enables individuals to recognise members of the same species and opposite sex
Enables forming pair bond
What is meant by a hierarchy?
-smaller groups arranged within larger groups
-there is also no overlap between groups
Phylogenetics
the study of species’ evolutionary origins and relationships
Arranges groups into hierarchy- smaller groups inside larger ones and no overlap
These are partly based on homologous characteristics
Common ancestor
the species from which another species evolved
Taxon
the term for each group in classification
What are the taxa in the Linnaeus classification system?
domain
kingdom
phylum
class
order
family
genus
species
Species diversity
the number of different species and the number of individuals within each species in a community
Species richness
the number of different species in a particular area at the same time
Index of diversity
-a measure of species diversity
-a calculation to measure the relationship between the number of species in a
community and the number of individuals in each species
Community
all the species in a particular
area at a particular time
Environment
the abiotic (non-living) factors in an area
Habitat
The range of physical, biological and environmental factors in which a species can live
Which farming techniques reduce biodiversity?(7)
destruction of hedgerows
selective breeding
monocultures
over-grazing
filling in ponds and draining wetlands
Lack of intercropping
Use of pesticides and inorganic fertilisers
Biodiversity
-a measure of the range of habitats - ecosystem diversity
-from a small local habitat to the entire Earth
-a measure of species diversity
-a measure of genetic diversity
How is standard deviation more useful than a mean?
-it gives you the spread of data (variance) around the mean
-overlaps in standard deviation indicate no significant difference in the means and difference is due to chance
If error bars of standard deviation is small it’s more reliable as it shows the data collected is more precise and consistent. And therefore there would be significant difference between means
How do you make sure your sampling is representative of the population?
-take a large sample (at least 30)
-randomly sample to avoid bias eg using random number generator for coordinates
How can you measure genetic diversity?
-by comparing the base sequence of DNA, mRNA and the amino acid sequence of the
proteins
More similarities - more closely related
Genetic diversity
the measure of how many different alleles there are for each gene
Formula for Index of Diversity
D = N(N-1)/Sum of (n(n-1))
N= total no.of organisms of all the species
n=the population size of one species
D=Simpsons index of diversity
Compare the DNA in chloroplast/mitochondria to prokaryotic DNA
-the DNA is similar to prokaryotic DNA, in that it is:
-short
-circular
-not histone bound
How does transcription differ between prokaryotes and eukaryotes
-Transcription in prokaryotic organisms results in mRNA that requires no modification
-because prokaryotic DNA does not contain any introns
-eukaryotic transcription results in pre-mRNA that needs introns removed
What is the role
of ribosomes in
translation?
-it holds two tRNA molecules
-to enable peptide bonds to form between the amino acids
What is the role of tRNA in translation?
-it carries a specific amino acid
-anticodons align opposite complementary codons on the mRNA
Gene mutations
-a change in the base sequence of DNA
-substitution or deletion
When in the cell cycle do gene mutations occur?
-interphase (s phase)
-this is when DNA is replicated
Standard deviation
It’s the distance from the mean to the point where the curve change from convex to concave - point of inflection
Within 1 sd- 68% of data
Within 2 sd or exactly 1.96sd is 98% data
Normal distribution curve
Bell shapes curve
Shows continuous variation eg height
Also shows stabilising selection
Method for random sampling
Make a grid by extending two tape measures at right angle to each other
Then use random number generator to give coordinates of intersection
Measure data from this to reduce bias
Minimise chance by using a large sample size and analyse data using stats test to find if differences are due to chance
Why is comparison of observable characteristics not good to measure genetic diversity
As most of these characteristics are polygenic - coded for by more than one gene and as a result it’s more continuous than discrete
And environment has an effect on it so these limitations makes it not so reliable.
So using sequence of DNA, mRNA and amino acid sequence is used
Farming techniques to increase biodiversity and also not decrease crop yield?(5)
Use crop rotation using N2 fixing crops - leguminous
Plant hedgerows and maintain them at the most beneficial height
Intercropping instead of herbicides to control weeds
Organic fertilisers instead of inorganic
Reduce use of pesticides
What are the 2 types of biological classification
Aritificial classification - divides organisms based on analogous characteristics which are those that have same function but not same evolutionary origin eg wings of butterfly and birds
Phylogenetic classification- divides organisms depending on evolutionary origin and relationships
Arranges groups into hierarchy- small groups inside larger ones and no overlap between groups
Partly based on homologous characteristics
What are the 3 domains? 3 characteristics of each
Bacteria - single celled prokaryotes, cell wall made of murein, naked DNA - circular not wound around histones, 70s ribosome, no membrane bound organelles
Archaea - single celled prokaryotes, protein synthesis and genes more similar to eukaryotes, membrane contains fatty acid attached to glycerol by ether linkages, more complex form of RNA polymerase than bacteria
Eukarya- eukaryotes, not all contain but if they do then it’s cell wall of cellulose or chitin, membrane bound organelles, ribosomes are larger 80s, membrane with fatty acid attached to glycerol by ester linkages
Natural selection results in species becoming more adapted to the environment they live in? What are these adaptations
-Anatomical - eg shorter ears in artic foxes
-Physiological -oxidising fat instead of carbohydrates in kangaroo
-Behavioural - different migration time or breeding time or courtship behaviour
