UGEB2361 L1 Biochemical and evolutionary foundations of life

  1. What is life?
    Life is living organisms which:
    ●Highly organized and complex
    ●Are composed of one or more cells
    ●Contain a blueprint of their characteristics
    ●Acquire and use energy
    ●Carry out and control numerous reactions
    ●Maintain constant internal environment
    ●Produce offspring
    ●Respond to environmental changes
    ●May evolve
  2. The idea of evolution preceded Darwin
    ①Middle Ages: “Ladder of life”
    ●Complex organisms at highest rungs; Simple organisms at lower rungs
    ●From highest to lowest: God, Angels, Men, Women, Children, Other organisms
    ②1800’s: Fossils were studied scientifically by a French scientist Georges Cuvier
    ●The line separating rock layers seemed sudden
    ●Natural catastrophes, like floods, periodically wiped out existing species, which were then replaced with new ones
    ③1830: Geological changes take place slowly found by English geologist Charles Lyell
    ●Transitions between rock layers may have taken much longer to occur than it appears because of erosion and other forces
    ●Organisms living in the periods of transition have simply vanished
    ④1809: Theory of the inheritance of acquired characteristics found by Jean-Baptiste Lamarck
    ●Organisms could acquire new characteristics and pass to their offspring
Giraffes’ necks are lengthened for reaching leaves
Lamarck believed that giraffes stretched their necks to reach food. Their offspring and later generations inherited the resulting long necks.

3. How did Darwin account for species? (1859)
Mechanism: Natural Selection (Only some organisms survive)
Individuals with favorable variations are more likely to survive and reproduce
Evolution: accumulation of inheritable variation over many generations

4. Examples of adaptations (characteristics that enhance survival)
Adaption 1. Morphological-anatomical 形態解剖學

Jackrabbits (北美洲長耳大野兔): long ears for dissipating heat in hot desert
Arctic hares (北極野兔) have usually short ears to conserve body heat

Adaption 2. Biochemical-physiological: modifications in the production and use of chemicals by organsims
●For protection, some organisms produce chemicals that they can tolerate but are poisonous to other organims

The poisonous mushroom Amanita phalloides (毒鵝膏) can produce α-amanitin

Adaption 3. Behavioral Adaptations: Modifications in animal interactions with others and environment
●Social wasps (黃蜂) are much more tolerant of others than their near relatives, the solitary wasps

5. Mendelian Genetic 孟德爾定律 (how are traits inherited?)
●Gregor Mendel studied plant breeding in a monastery 修道院 in the Czech Republic (1866)
●He loved to read especially about natural sciences and was aware of Darwin’s findings
●He studied the inheritance of traits in pea (豌豆) plants
●He studied traits that occur in distinct forms and used mathematical analysis in his studies

Anther: the part of a flower containing pollen
Stigma: the top of the central female part of a flower, where pollen is received

Allele: a gene that is found in one of two or more different forms in the same position in a chromosome, and so produces a particular characteristic that can be different for different people, such as eye colour.

Law of Segregation: A parent contributes only one of its alleles for a trait to each offspring. The particular allele donated to the offspring is random.

Law of Independent Assortment: Alleles of one gene are passed to offspring independently of the alleles of other genes

This independent assortment of genes occurs during meiosis (減數分裂,發生在生殖器官的細胞分裂過程,一個細胞分為四個配子,每個均擁有不同的混合染色體,其染色體數目是原細胞的一半) in eukaryotes (真核生物). Meiosis is a type of cell division that reduces the number of chromosomes in a parent cell by half to produce four reproductive cells called gametes. In humans, diploid cells contain 46 chromosomes, with 23 chromosomes inherited from the mother and a second similar set of 23 chromosomes inherited from the father. Pairs of similar chromosomes are called homologous chromosomes. During meiosis, the pairs of homologous chromosome are divided in half to form haploid cells, and this separation, or assortment, of homologous chromosomes is random. This means that all of the maternal chromosomes will not be separated into one cell, while the all paternal chromosomes are separated into another. Instead, after meiosis occurs, each haploid cell contains a mixture of genes from the organism’s mother and father.

6. Why aren’t members of the same species identical?
→ Sources of genetic variation: Law of Independent Assortment & Mutation in DNA sequence

7. Building blocks of DNA

Nitrogenous base 含氮鹼基
Phosphate group 磷酸基團
Deoxyribose sugar 脫氧糖
Nucleotides 核甘酸

8. DNA double helix

●Watson and Crick: determined DNA structure — a double helix

9. How does DNA copy itself?
●DNA replication: precedes cell division
●Process: DNA strands separate; New complementary base pairs are added forming a new strand
●Complementarity in DNA allows for replication with near-perfect fidelity

10. Natural selection favors some mutation
●Despite the near-perfect fidelity of genetic replication, infrequent unrepaired mistakes in the DNA replication process occur
●Lead to changes in the nucleotide sequence of DNA and produce a genetic mutation and changing the instructions of cellular components
●Mutations occur more or less randomly
●Mutations that give organisms an advanatge in a given environment are more likely to be propagated (繁殖).

Mutation Example 1
Gene duplication and mutation: one path to generate new enzymatic activities

Glucose 葡萄糖
Galactose 半乳糖

Mutation Example 2
Antibiotic resistance: bacteria are able to survive after exposure to antibiotics.

Mutation Example 3
Viral mutation of SARS-CoV-2: Researchers have been tracking changes to the spike of the virus.

●Researchers in the US and UK have identified hundreds of mutations to the virus which causes the disease Covid-19.
●Preliminary research from the US has suggested one particular mutation — D614G — is becoming dominant and could make the disease more infectious.

Spike D614G substitution increases SARS-CoV-2 replication increasing virion infectivity.