CfE Higher Biology - Unit 1

CfE Higher Biology - Unit 1

1. Key Area 1 - DNA Structure

   • Genetic info is stored in the base sequence of DNA
   • Genotype is determined by the sequence of bases
   • Nucleotide - deoxyribose sugar, phosphate, base
   • Sugar phosphate backbone - phosphate joins carbon 5 on sugar and carbon 3 on other sugar
   • Hydrogen bond between bases
   • Double helix, antiparallel
   • Prokaryotes - circular chomosomal DNA & plasmids, no membrane bound nucleus
   • Eukaryotes - linear chromosomes in nuclei, tightly packaged with associated proteins
   • Mitochondria and chloroplasts have circular chromosomes

2. Key Area 2 - DNA Replication

   • Required so that each daughter cell has an identical copy of DNA
     • Important to help give growing cells exact copies
   • Requires the DNA (template), free DNA nucleotides, ATP, enzymes & primers
     • Enzymes: DNA polymerase - adds complementary nucleotides and Ligase - joins fragments together
     • Primer - allows DNA polymerase to bind
       • Primers form at the 3' end
   • 1. DNA unwinds, hydrogen bonds break
   • 2. DNA polymerase adds nucleotides to the 3' end
   • 3. On the leading strand (beginning with 3'), a primer binds to the DNA
   • 4. DNA polymerase adds nucleotides to the 3' end
   • PCR (Polymerase Chain Reaction) - replicate DNA quick in a lab
     • 1. Heated (approx 90 degrees) to break the hydrogen bonds, seperate strands
     • 2. Cooled (approx 60 degrees) to allow the primer to anneal to its target sequence
     • 3. Heated (approx 72 degrees) so heat-tolerant DNA polymerase can add nucleotides to the primers at 3' end. Then it repeats.
     • Used for forensics and the study of evolution
   • 5. Fragments of DNA are joined together by ligase.

3. Key Area 3 - Control of Gene Expression

   • Phenotype is determined by the proteins produced as a result of gene expression
   • Gene expression is controlled by the regulation of transcription and translation
   • Gene expression is influenced by intra- and extra-cellular factors
   • Amino acids - peptide bonds, folded, hydrogen bonds
   • RNA: one strand, uracil replaces thymine, ribose sugar
     • mRNA - carry copy of DNA to ribosome tRNA - transports AA to ribosome to be translated
   • Transcription
     • In nucleus
     • RNA polymerase unwinds DNA
     • RNA nucleotides form a primary transcript
     • Introns - non-coding Exons - coding
     • Introns are removed by RNA splicing
   • Translation
     • Mature mRNA goes to cytoplasm to find a ribosome
     • tRNA carries an amino acid
       • tRNA has an AA attachment site, anticodon
     • Anticodons on tRNA pair with codons on the mRNA
     • Peptide bonds form between amino acids, polypeptide chain
   • Post-translational modification: cutting and combining polypeptide chains, adding phosphate or carbohydrate groups

4. Key Area 5 - The Structure of the Genome

   • Genome of an organism is the complete set of genetic info encoded in its DNA that can be inherited by offspring
   • Genes - DNA sequences that code for protein
   • A genome is made up of genes and other DNA sequences that don't code for proteins
   • Most of the genome consists of non-coding regions
     • Regulation of transcription by turning genes on or off
     • Transcribed but not translated (e.g. rRNA, tRNA)
     • No known function

5. Key Area 7 - Evolution

   • Changes to organisms over time mainly caused by natural selection
   • Vertical inheritance - from parent to offspring (asexual and sexual)
   • Horizontal inheritance - prokaryotes, rapid evolutionary change
     • Prokaryotes and viruses transfer genes horizontally into the genomes of eukaryotes
   • Natural selection - non-random increasein frequency of DNA sequences that increases survival
   • Sexual selection - natural selection of characteristics that increase reproductive success
   • Selection pressure
     • Stabilising - favours the middle characteristics in a range of variation
     • Directional - favours an extreme characteristic away from the middle
     • Disruptive - favours two extreme characteristics at the expense of the middle
   • Genetic drift - random increase or decrease to DNA sequences
     • Happens in small populations by chance events , neutral mutation, colonisation, founder effect
       • Founder effect - groups become isolated from the main group
   • Speciation - generation of a new biological speciesby evolution due to isolaion, mutation and selection
     • Allopatric - geographical barriers (mountains, oceans)
     • Sympatric - ecological and behavioural barriers
     • Hybrid zones form in regions where frequent interbreeding between two species occur

6. Key Area 8 - Genomic Sequencing

   • To compare sequence data, computer and statistical analyses (bioinformatics) are required
   • Phylogenetics - study evolutionary relatedness among groups of organisms
   • Sequence divergence - used to estimate time since lineages diverged
   • 3 domains of life: bacteria, archea, eukaryotes
   • Analysis of a persons genome could lead to personalised medicine (pharmacogenetics)
     • Difficulties in relating individual genome data to treatments and in the complex nature of many diseases
   • Comparing genes from different species reveals that many genesare highly conserved across different organisms

7. Key Area 4 - Cellular Differentiation

   • Cellular differentiation - cell develops more specialised function
   • Meristems are regions of unspecialised cells in plants
     • Can divide and differentiate into specialised cells
     • Apical: root tip and shoot tip Lateral: between phloem and xylem
   • Stem cells are unspecialised somatic cells than divide (self-renew) and differentiate into specialised cells
     • Embryonic stem cells can differentiate into all cell types (pluripotent)
     • Adult stem cells have a narrower differentiation potential, genes are switched off (multipotent)
       • Needed for growth, repair and renewal of tissues
   • Ethical issues regarding stem cells
     • What's more important: Our duty to prevent disease or respect the value of human life?
     • Should we allow healthy people to use stem cells to change body characteristics?
     • Stem cells might be bought and sold illegally and treatment could cost money

8. Key Area 6 - Mutations

   • Mutation are random, rare changes to DNA sequences (ROLF)
   • Single gene mutations - alter DNA nucleotide sequence (DIGS)
     • Substitution - A nucleotide is removed and replaced by another. Minor impact (missense). Major impact if production or loss of a stop codon (nonsense)
     • Insertion - Add a nucleotide. Deletion - removal of a nucleotide. Frame-shift mutations, all amino acids are affected
     • Splice-site - introns are left in the mature mRNA leading to an altered protein
   • Regulatory sequence mutations can alter gene expression
   • Mutations are important in evolution
   • Chromosome mutations: affect number and structure of a chromosome (DICTD)
     • Duplication - extra copies of genes on a chromosome. Can be detrimental or important to evolution
     • Deletion - detached genes are lost completely (cri du chat syndrome)
     • Translocation - detached genes join onto another chromosome (1 type of Down syndrome)
     • Inversion - Chromosome breaks in 2 places and rotates 180. Results in infertility as gametes can't be formed
   • Polyploidy - possession of extra sets of chromosomes due to errors during the seperation of chromosomes during cell division
     • Banana, potato, strawberry

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