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Biology: Topic 4, Genetic information, variation and relationships between…

- - - - The components of RNA nucleotides are ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil. Thymine, uracil and cytosine all have single ring structures and are classified as pyrimidines.
        
        Nucleotides joined together by phosphodiester bonds formed in condensation reactions.
        
        A DNA molecules is a double helix composed of two polynucleotides joined by hydrogen bonds between complementary bases where as RNA is a relatively short polynucleotide chain.
- - - - A gene is a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain.
        
        Not all the genome codes for proteins - Non-coding sections=introns - coding regions = exons.
  - - - Each amino acids is coded by one or more combination of triplets.
        
        There are 64 possible triplets meaning each amino acid is represented by at least one or more triplet.
  - - - Genes are separated by non-coding repeats of bases.
        
        Genetic code is degenerate meaning that more than one triplet codes for the same amino acid. This reduces the effect of mutations from mistakes in the base sequence.
        
        The genetic code contains start and stop codons.
    - - DNA molecules are found in the nucleus and are long and linear.
        
        Are associated with proteins called histones to form structures called chromosomes.
        
        Chromosomes are visible at the start of cell division and is the result of DNA being tightly coiled around the histones.
        
        Mitochondria and chloroplasts contain DNA.
    - - DNA is short and circular and not associated with proteins
  - - - Homologous pairs consist of two chromosomes that carry the same gene. They are not identical as they can carry different alleles.
        
        The 23rd chromosomes determines the sex of the individual.
        
        An allele is described as an alternative form of the same gene.
        
        Every individual inherits two allele of every gene from their parents.
- - - - Transfer RNA - small molecule made up of around 80 nucleotides. At one end is an anti-codon which is specific to amino acid at the other end.
  - - - Transcription occurs in the nucleus and involves DNA and mRNA.
        
        Translation involves mRNA, tRNA and ribosomes.
        
        Translation
        
        During translation amino acids join together to form a polypeptide chain:
        
        mRNA attaches to the ribosome and transfer RNA collects amino acids in the cytoplasm and carries them to ribosome.
        
        tRNA is a single stranded molecule with a binding site at one end thus it can only carry one type of amino acid, and a triple of bases at the other.
        
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        Transcription
        
        During transcription, a molecule of mRNA is made in the nucleus:
        
        Hydrogen bonds between complimentary bases break due to the action of an enzyme and the DNA uncoils separating the strands exposing the organic bases.
        
        One of the strands is used as a template to make the mRNA molecule, the the template is called the antisense strand
        
        Free Nucleotides line up by complimentary base pairing and adjacent nucleotides are joined by phosphodiester bonds, catalysed by the enzyme RNA polymerase. When a stop codon is reached this ceases.
        
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- - - - Non-disjunction - occurs when chromosomes fail to separate correctly in meiosis. As a result the gametes will have one more or one less chromosome.
  - - - Deletion - a deletion is when a nucleotide is lost from the sequence. This can have a significant impact because it leads to a frame shift.
- - - - Meiosis 1 - homologous chromosomes pair up whereby crossing over may occur. The cell then divides with each daughter cell contains one chromosome from each homologous pair
        
        Meiosis 2 - the chromatids of each chromosome are separated producing 4 haploid cells.
- - - - An environmental change occurs and as a result of that the selection pressure changes.
        
        Some individuals possess advantageous alleles which give them a selective advantage and allow them to survive and reproduce.
        
        The advantageous alleles are passed on to their offspring.
        
        Over time, the frequency of alleles in a population changes and this leads to evolution.
  - - - Directional selection - directional selection occurs when the environmental conditions change and the phenotypes best suited to the new conditions are more likely to survive. Overtime the mean population will move in the direction of these individuals.
        
        Stabilising Selection - those with successful characteristics are preserved and those of greater diversity are reduced. Selections doesn't occur due to changes in environment. If conditions stay the same the mean are favoured as their alleles have given them a survival advantage.
        
        Natural selection - species with best adaptations survive. Pass on advantageous genes to future generations.
        
        Niche - niche of a species is its role within environment.
  - - - Behavioural adaptations are changes in behaviour which improve the organisms chance of survival.
        
        Physiological adaptations are processes inside an organism's body that increase survival chance.
- - - - The generic name is the genus to which the organism belongs. If a species is closely related it will share the same name.
        
        The specific name is the species the organism belongs too.
        
        Writing these - the name must be underlined and the first letter of the generic name capitalised.
  - - - Recognise members of their own species.
        
        Synchronise mating.
        
        Form a pair bond.
        
        Become able to breed.
  - - - Organisms can be grouped into one of five kingdoms: animals, plants, fungi, prokaryotes and protocists
        
        Kingdom
        
        phylum
        
        class
        
        order
        
        Family
        
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        Molecular phylogeny - analysis of molecular differences in the different organisms to determine evolutionary relatedness. The data obtained has been accepted by scientists and this gave rise to new taxonomic groups - three domains: Bacteria, Archea and Eukaryota
  - - - Scientists then study the evidence in whats known as peer review
        
        Scientists start collecting evidence to either support or reject the suggestion.
- - - - Species diversity is the number of **different species in a community.
        
        Genetic diversity is a measure of genetic variation found in a specific species, the number of different alleles in a gene pool.
        
        Ecosystem diversity is the range of different habitats.
  - - - Techniques for maintaining biodiversity in agriculuture:
        
        Using hedgerows instead of fences.
        
        Growing different crops in the same area, known as intercropping.
        
        Reducing the use of herbicides and pesticides
        
        Preserving wetlands instead of draining for farm use.