CfE Higher Biology - Unit 1

Key Area 1 - DNA Structure
1. Genetic info is stored in the base sequence of DNA
2. Genotype is determined by the sequence of bases
3. Nucleotide - deoxyribose sugar, phosphate, base
5. Sugar phosphate backbone - phosphate joins carbon 5 on sugar and carbon 3 on other sugar
6. Hydrogen bond between bases
7. Double helix, antiparallel
8. Prokaryotes - circular chomosomal DNA & plasmids, no membrane bound nucleus
9. Eukaryotes - linear chromosomes in nuclei, tightly packaged with associated proteins
10. Mitochondria and chloroplasts have circular chromosomes
Key Area 2 - DNA Replication
1. Required so that each daughter cell has an identical copy of DNA
  1. Important to help give growing cells exact copies
2. Requires the DNA (template), free DNA nucleotides, ATP, enzymes & primers
  1. Enzymes: DNA polymerase - adds complementary nucleotides and Ligase - joins fragments together
  2. Primer - allows DNA polymerase to bind
    1. Primers form at the 3' end
3. 1. DNA unwinds, hydrogen bonds break
4. 2. DNA polymerase adds nucleotides to the 3' end
5. 3. On the leading strand (beginning with 3'), a primer binds to the DNA
6. 4. DNA polymerase adds nucleotides to the 3' end
7. PCR (Polymerase Chain Reaction) - replicate DNA quick in a lab
  1. 1. Heated (approx 90 degrees) to break the hydrogen bonds, seperate strands
  2. 2. Cooled (approx 60 degrees) to allow the primer to anneal to its target sequence
  3. 3. Heated (approx 72 degrees) so heat-tolerant DNA polymerase can add nucleotides to the primers at 3' end. Then it repeats.
  4. Used for forensics and the study of evolution
8. 5. Fragments of DNA are joined together by ligase.
Key Area 3 - Control of Gene Expression
1. Phenotype is determined by the proteins produced as a result of gene expression
2. Gene expression is controlled by the regulation of transcription and translation
3. Gene expression is influenced by intra- and extra-cellular factors
4. Amino acids - peptide bonds, folded, hydrogen bonds
5. RNA: one strand, uracil replaces thymine, ribose sugar
  1. mRNA - carry copy of DNA to ribosome tRNA - transports AA to ribosome to be translated
6. Transcription
  1. In nucleus
  2. RNA polymerase unwinds DNA
  3. RNA nucleotides form a primary transcript
  4. Introns - non-coding Exons - coding
  5. Introns are removed by RNA splicing
7. Translation
  1. Mature mRNA goes to cytoplasm to find a ribosome
  2. tRNA carries an amino acid
    1. tRNA has an AA attachment site, anticodon
  3. Anticodons on tRNA pair with codons on the mRNA
  4. Peptide bonds form between amino acids, polypeptide chain
8. Post-translational modification: cutting and combining polypeptide chains, adding phosphate or carbohydrate groups
Key Area 5 - The Structure of the Genome
1. Genome of an organism is the complete set of genetic info encoded in its DNA that can be inherited by offspring
2. Genes - DNA sequences that code for protein
3. A genome is made up of genes and other DNA sequences that don't code for proteins
4. Most of the genome consists of non-coding regions
  1. Regulation of transcription by turning genes on or off
  2. Transcribed but not translated (e.g. rRNA, tRNA)
  3. No known function
Key Area 7 - Evolution
1. Changes to organisms over time mainly caused by natural selection
2. Vertical inheritance - from parent to offspring (asexual and sexual)
3. Horizontal inheritance - prokaryotes, rapid evolutionary change
  1. Prokaryotes and viruses transfer genes horizontally into the genomes of eukaryotes
4. Natural selection - non-random increasein frequency of DNA sequences that increases survival
5. Sexual selection - natural selection of characteristics that increase reproductive success
6. Selection pressure
  1. Stabilising - favours the middle characteristics in a range of variation
  2. Directional - favours an extreme characteristic away from the middle
  3. Disruptive - favours two extreme characteristics at the expense of the middle
7. Genetic drift - random increase or decrease to DNA sequences
  1. Happens in small populations by chance events , neutral mutation, colonisation, founder effect
    1. Founder effect - groups become isolated from the main group
8. Speciation - generation of a new biological speciesby evolution due to isolaion, mutation and selection
  1. Allopatric - geographical barriers (mountains, oceans)
  2. Sympatric - ecological and behavioural barriers
  3. Hybrid zones form in regions where frequent interbreeding between two species occur
Key Area 8 - Genomic Sequencing
1. To compare sequence data, computer and statistical analyses (bioinformatics) are required
2. Phylogenetics - study evolutionary relatedness among groups of organisms
3. Sequence divergence - used to estimate time since lineages diverged
4. 3 domains of life: bacteria, archea, eukaryotes
5. Analysis of a persons genome could lead to personalised medicine (pharmacogenetics)
  1. Difficulties in relating individual genome data to treatments and in the complex nature of many diseases
6. Comparing genes from different species reveals that many genesare highly conserved across different organisms
Key Area 4 - Cellular Differentiation
1. Cellular differentiation - cell develops more specialised function
2. Meristems are regions of unspecialised cells in plants
  1. Can divide and differentiate into specialised cells
  2. Apical: root tip and shoot tip Lateral: between phloem and xylem
3. Stem cells are unspecialised somatic cells than divide (self-renew) and differentiate into specialised cells
  1. Embryonic stem cells can differentiate into all cell types (pluripotent)
  2. Adult stem cells have a narrower differentiation potential, genes are switched off (multipotent)
    1. Needed for growth, repair and renewal of tissues
4. Ethical issues regarding stem cells
  1. What's more important: Our duty to prevent disease or respect the value of human life?
  2. Should we allow healthy people to use stem cells to change body characteristics?
  3. Stem cells might be bought and sold illegally and treatment could cost money
Key Area 6 - Mutations
1. Mutation are random, rare changes to DNA sequences (ROLF)
2. Single gene mutations - alter DNA nucleotide sequence (DIGS)
  1. Substitution - A nucleotide is removed and replaced by another. Minor impact (missense). Major impact if production or loss of a stop codon (nonsense)
  2. Insertion - Add a nucleotide. Deletion - removal of a nucleotide. Frame-shift mutations, all amino acids are affected
  3. Splice-site - introns are left in the mature mRNA leading to an altered protein
3. Regulatory sequence mutations can alter gene expression
4. Mutations are important in evolution
5. Chromosome mutations: affect number and structure of a chromosome (DICTD)
  1. Duplication - extra copies of genes on a chromosome. Can be detrimental or important to evolution
  2. Deletion - detached genes are lost completely (cri du chat syndrome)
  3. Translocation - detached genes join onto another chromosome (1 type of Down syndrome)
  4. Inversion - Chromosome breaks in 2 places and rotates 180. Results in infertility as gametes can't be formed
6. Polyploidy - possession of extra sets of chromosomes due to errors during the seperation of chromosomes during cell division
  1. Banana, potato, strawberry

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	Created by Claire Purves over 8 years ago