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Genome, proteome, DNA in different organism types/ organelles
Prokaryotes, plasmids, chloroplasts, mitochondria have dna not associated with histones; plasmids/chloroplasts/mitochondria have necessary/ highly used genes
Eukaryotes have dna associated with histones
Genome - full set of genes in a cell
Proteome - full set of proteins coded by a genome
Chromosome structure
Chromosome → by two sister chromatids connected by a centromere → supercondensed/coiled chromatin → uncoiled chromatin → dna wrapped around a histone
Telomeres protect ends of the chromosome from damage.
Identical sister chromatids allow for genetically identical daughter cells
Features of genes
DNA is a sequence of bases which codes for a specific sequence of amino acids, which determines the structure of a protein.
Has:
Exons and introns,
Triplets which code for a specific amino acid
Code is degenerate, meaning multiple triplet combinations code for the same amino acid
Non-overlapping, code only read once
Genes are universal and occupy a fixed locus on every organisms dna strand
mRNA + tRNA
mRNA - long single strand, with base sequences determined by DNA, exposed unpaired bases (codons)
Chloroplast/ Mitochondria dna, not associated with proteins, circular dna, contains most important genes
tRNA - clover leaf produced by nucleotides, region of amino acid to bond to, anticodons (sequence of bases is able to base pair to mRNA)
Transcription
DNA helicase unwinds the dna strand
Free activated RNA nucleotides bond to complementary base pairs on antisense (exposed DNA template strand) via base pairing
RNA polymerase bonds RNA nucleotides together forming sugar-phosphate backbone, with phosphodiester bonds forming
order of triplets on dna determines order of amino acids, by determining order of codons
Eukaryotes have further steps:
introns and extrons are both transcribed forming pre-MRNA
Splicing to remove introns and produces mRNA with only exons
5a. alternative splicing will order the exons differently, proudcing mature mRNA
Translation
mRNA binds to ribosomes, ribosome moves to start codon
amino acids binds to tRNA, which binds to completely codon on mRNA at the ribosomes
peptide bond is formed between amino acids, ATP used. 2 tRNA can bind to site at a time
Stops binding and adding amino acids when a stop codon is reached.
Mutation
Change in the sequence of base pairs
Change in base pairs causes a different triplet, which hence changes the codon on an mRNA
Different codon results in a different amino acid in the polypeptide chain
So different hydrogen bonds form between the chain so secondary structure changes
Different hydrogen/ionic bonds, disulfide bridges forming (different interactions between the chain)
Causing altered tertiary structure and a denatured active site
Code is degenerate so not all changes effect protein
Mutation types
Deletion
Random deletion of base pair, changes all triplets past mutation
Insertion
Inserting of base pair into sequence, all triplets change past mutation
Substitution
Swapping of base pairs,
Silent - doesn’t change sequence of amino acids
Missense - Alters 1 amino acid
Nonsense - creates premature stop codon
Mutagenic agents - agent which increase chance of mutation
Genetic variation sources
Independent assortment: (meiosis)
Homologous pairs line up randomly, forming different chromosome combinations
Crossing over: (meiosis)
Alleles of non-sister chromatids are swapped, providing recombinant cells
Random fusion of zygotes during fertilisation (2n)
Alternative splicing (transcription)
Non-disjunction - chromosomes fail to separate (causing polydiploidy)
Variation
Differences in base sequences between individuals of a population
Genetic variation is passed across generations
Producing genetic diversity (number of different alleles in a gene pool)
producing different phenotypes
Natural selection
Certain phenotypes will be favoured as a result of selection pressures (due to environment), (natural selection occurs)
resulting in increased survival for best phenotypes, and allowing for reproduction and alleles to be passed to offspring, which changes allele frequency
Directional selection:
Extreme allele is favoured, so allele frequency shifts towards extreme allele end, as greater survival chance, so passes allele to offspring
Stabilising selection:
Extreme alleles favoured against, so allele frequency of extremes decreases, as lower survival chance, so cannot pass allele to offspring
Other factors effecting allele frequency
Founder effect: a portion of population creating a new population, Changes allele frequency in different direction due to chance
Bottle neck effect:
Large population has dramatic decrease due to disease etc, creating a reduced gene pool, and dramatic decrease in allele frequency as many are lost
Genetic drift:
Gradual change in allele frequency in small population due to chance (mutation)
Selection pressure, types of adaption
Organisms experience selection pressure due to environment and other factors, and have to adapt to enable a higher/ lower chance of survival
Anatomical - structural
Physiological - Biological processes change
Behavioural - change to behaviour
Species + recognition/ reproduction within species
two similar organisms which can reproduce to produce fertile offspring
To produce offspring courtship (as visual, chemical, audible stimuli) is needed
Required to identify a fertile mate, species member, synchronise mating
Classification
Phylogenetic classification required to class species based on evolutionary origin and relationships by using a hierarchy of groups with no overlap,
Binomial naming system (genus species, e.g. homo sapien)
3 domains:
Eukarya
Has nuclei, membrane bound organelles, reproduces via asexual/ sexual
Bacteria
No nuclei, have peptidoglycan cell wall, divide by binary fission
Archaea
No nuclei or peptidoglycan cell wall, transcribes rna like eukarya
Biodiveristy
Measure of variety and number of organisms in a habitat
required for an ecosystem to resist change, as higher biodiversity creates a more stable ecosystem
Species diversity - population of each species in a community
Genetic diversity - Variety of genes within gene pool of species
Ecosystem diversity - range of habitats
investigating biodiversity (ways to improve accuracy/representative), species richness, index of diversity, sdeviations+testing
Species richness - number of different species in a habitat
Index of diversity - calculation of all species and their abundance in an ecosystem
data collection needs to be representative so:
random sampling used to reduce bias
increasing sample size to make data more representative as the probability results are due to chance are reduced, and reducing the effect on anomalies
standard deviation used to show distribution of data around the mean
standard deviation shows whether overlap in data is significant between populations
Investigating species
DNA base sequence + mRNA base sequence + amino acid sequence comparisons
more similar = more closely related = recent speciation / very recent common ancestor
Immunology - comparison of proteins by binding to an antigen, more similar proteins bind to the same antigen