Section 4 - Genetic information, variation, and relationships between organisms
8 DNA, genes, and protein synthesis
9 Genetic diversity
10 Biodiversity
DNA, genes, and chromosomes
DNA and protein synthesis
Genetic diversity and meiosis
Genetic diversity and adaptation
Species and taxonomy
Biodiversity within a community
Investigating diversity
Genes
Genetic code
Eukaryotic cells
Prokaryotic cells
Non-overlapping
Universal
Each triplet codes for the same amino acid in every organism
Degenerate
Multiple triplets code for one amino acid
Sequence of three bases e.g. GGA codes for a specific amino acid e.g. glycine
Found at a specific position on a DNA molecule
Locus
Base sequence of DNA
Codes for the amino acid sequence of a polypeptide, or a functional RNA
Ribosomal RNA and transfer RNA
Most of the DNA does not code for proteins
Large regions of repeats of bases between genes
Exon = coding sequence within a gene
Intron = non-coding sequence with a gene
DNA is long and linear
DNA and histones are tightly coiled to form chromosomes
Associated with proteins (histones)
DNA is short and circular
Not associated with proteins
Same type of DNA in prokaryotes as mitochondria and chloroplasts
Genome
RNA molecules
Protein synthesis
Complete set of genes in a cell
Proteome
Complete set of proteins the cell can produce
Transfer RNA (tRNA)
Messenger RNA (mRNA)
Small molecule, 80 nucleotides
Single stranded molecule
Clover leaf shape
Specific amino acid attached to tRNA
Anticodon at one end, bases complementary to mRNA codon
Has a ribose sugar and uracil instead of thymine
Long, single stranded molecule
Sequence of bases is complementary to sequence of DNA
Produced in nucleus, leaves via nuclear pores to go to ribosomes
Codon = sequence of 3 bases that codes for an amino acid, complementary to a triplet
Codons on mRNA determine amino acid sequence
Translation
Transcription
Synthesising the protein at the ribosome
Ribosome attaches to the starting mRNA codon
tRNA with complementary anticodon pairs with mRNA codon
Ribosome moves along mRNA, two tRNA molecules are held at once
Peptide bond forms between adjacent amino acids
Polypeptide chain forms
ATP and enzyme required
Pre-mRNA is spliced
Removal of introns
Pre-mRNA is only present in eukaryotes
mRNA leaves via a nuclear pore
Producing complementary mRNA from DNA
RNA polymerase
Gene mutations
Chromosome mutations
Meiosis
Changes in the number of chromosomes
Example - in Down's syndrome, there are three copies of chromosome 21 due to non-disjunction
Polyploidy - having more than one set of chromosomes
Can occur in plants
Chromosome mutations often arise during meiosis due to chromosome non-disjunction
A change in the base sequence of DNA
Can arise spontaneously during DNA replication in interphase
Can give rise to cancerous cells
Base deletion
May cause a frameshift
Completely different codons and amino acids, and so, a different protein is synthesised
Base substitution
May cause a change in one amino acid
New codon may code for same amino acid as original codon, so no change in protein
Degenerate nature of genetic code
Change to structure and folding of protein
Produces 4 daughter cells
Each cell has half the number of chromosomes of the parent cell (haploid)
Produces gametes (egg and sperm)
Meiosis I - 1st division
Homologous chromosomes pair up and separate into 2 daughter cells
Meiosis II - 2nd division
Chromatids separate
Independent segregation of homologous chromosomes
Crossin over of alleles
New genetic combinations, increased genetic variation
4 gametes with 23 chromosomes (for humans)
All genetically different from each other
Diversity
Natural selection
Types of selection
Gene pool
Genetic diversity = number of different alleles in a population
Genetic diversity contributes to natural selection
Greater diversity = more likely individuals in a population will survive an environmental change
Directional
Favours individual organisms that vary in one direction from the mean
Antibiotic resistance in bacteria
Changes characteristics of the population
Stabilising
Human birth weights
Preserves characteristics of a population
Favours individual organisms with the mean characteristics
Random mutations results in new alleles
Most of the time, these new mutations are harmful, but sometimes they can confer an advantage
The advantage means the organism is better adapted, so survives and reproduces
Adaptations may be behavioural, anatomical, or physiological
Better reproductive success
Results in species that are better adapted to their environment
Frequency of non-advantageous alleles decreases
Over many generations, the frequency of the beneficial allele increases
New allele is inherited by offspring
Better reproductive success
Enabling factor
Classification
Species
Taxonomy - classifying biological organism into groups
Phylogenetics - classifying organisms into groups based on evolutionary relationships
Advances in gene technology have allowed us to identify and clarify evolutionary relationships
Originally based on shared characteristics
Binomial naming
A hierarchy
Smaller groups within larger groups
No overlap
Each group is a taxon (plural taxa)
Domain, kingdom, phylum, class, order, family, genus, species
First name = generic name, the genus name
Second name = specific name, the species name
Example = homo sapiens
Two organisms are of the same species if they can breed together to
Similar to terms of appearance, biochemical processes and behaviour
Courtship behaviour is essential for successful mating
To ensure the other member is in a physiological state to breed
To synchronise mating
Forms a pair bond
Important for survival of offspring
Can identify a mate capable of breeding
Need to be fertile, mature, and receptive
Can recognise members of own species
Different behaviours for different species
Biodiversity
Index of diversity
Farming and conservation
The higher the biodiversity, the more stable the ecosystem is
Some individuals can survive environmental change
The variety of life in a habitat ranging from small ecosystems to the Earth itself
Ecosystem diversity = the range of habitats
Genetic diversity = variety of genes in a population of a species
Species diversity = range of different species and individual members of species in a community
Species richness is a way of measuring species diversity
Species richness is the number of different species in a community
D = (N(N - 1)) / (Ī£n(n - 1))
N = the total number of organisms of all species
n = the total number of organisms of each species
Index of diversity takes into account the number of individuals of a species, so is a better measure of diversity
Farming reduces biodiversity
Use of pesticides
Large space for one species only, other species compete for remaining resources
Techniques to improve biodiversity in agricultural ecosystems
Creating ponds
Using organic fertilisers
Using nitrogen-fixing crops
Planting trees and hedges
Proteins
Quantitative measurements of variation
Observable characteristics
DNA and mRNA base sequence
The amino acid sequence of a protein is determined by mRNA, which in turn is determined by DNA
Similar sequences of amino acids indicate more closely related species
Observable features can be changed by the environment, so not reflective of DNA differences
Most observable features are polygenic - coded for by more than one gene
As observable features are determined by DNA and proteins, it is useful way of seeing similarities and differences
Tend to vary continuously, so difficult to distinguish
Gene technology allows us to read the base sequence of DNA and mRNA
Cam compare how similar the base sequences are between species
More similar DNA = more closely related in evolutionry history
As mRNA sequences are complementary to DNA, we can also read the mRNA to ascertain how closely related species are
Inter- and intra- specific variation
Data collection
Normal distribution curves
Mean and standard deviation
Large standard deviation = large variation
Sampling
Random sampling reduces sampling bias
Large sample size to reduce chance
Statistical analysis to see if the results were the result of chance