Biology

DNA

• Deoxyribonucleic acid

• Double-helix structure

• Nucleotide is made up of phosphate group, sugar molecule, nitrogen base

• Sugar + phosphate form outer structure

Nitrogen Bases

• Adenine

• Thymine

• Guanine

• Cytosine

• A+T = 2 Hydrogen bonds

• C+G = 3 Hydrogen bonds

Guide protein production

Genes

Responsible for inherited traits and influence characteristics such as eye colour and height

Chromosomes

• Tightly coiled structures

• DNA + protein found in nucleus of cells

• Contains thousands of genes linearly

• 46 chromosomes (23 pairs)

• Help organise DNA - fit inside nucleus and protect genetic information during cell division

Genetic Code

• Set of instructions within DNA that determines sequence of amino acids

• Uses combination of 3 DNA bases (codons) to specific amino acid to add during protein synthesis

• Proteins are built according to sequence of codons, and the type + order of amino acids determine protein’s shape/function

Codons

• Read in groups of 3 on mRNA strand

• Represents amino acids

• Start/stop in protein synthesis

Protein Synthesis

Process where cells generate proteins by translating genetic information encoded in DNA into amino acid sequences through transcription and translation.

Transcription

Gene’s DNA sequence is coped into mRNA

RNA polymerase reads strand and synthesises a complementary mRNA strand

Leaves nucleus and carries the genetic code to ribosome, where protein synthesis occurs

Translation

mRNA sequence is used to build protein

At ribosome, tRNA molcules bring amino acids that match the codons on the mRNA strand

Amino acids link together to form protein chain according to sequence in mRNA

Single Base Mutations (PC)

Protein Changes:

• One base in DNA sequence is altered

• DNA bases determine sequence of amino acids in protein

Single Base Mutations Types + Consequences

Types

• Silent

• Missense

• Nonsense

• Frameshift

Consequences:

• loss of function

• gain of function

• no effect

TANGO2 Disease

• Involved in regulating cellular energy metabolism

• Critical for energy production and maintaing homeostasis

Cell Division

• shsh

  Growth:

• Allows organisms to grow by increasing the number of cells

• Tissues and organs grow as cells divide and multiply

  Repair:

• Damaged tissues repaired

• Replacing old cells for new ells

• Eg. skin regeneration after a cut

Mitosis

1. Interphase

   Cell spends most life and obtains nutrients and replicates DNA in preperation for mitosis

2. Prophase

   Chromosomes condense and become visible. Nuclear membrane begins to break down, spindles form

3. Metaphase

   Chromosomes align along equator, spindles attach to centromeres of chromosomes

4. Anaphase

   Sister chromatids are pulled apart to opposite of the cell by spindles, each pole receives identical set of chromosomes.

5. Telophase

   Chromosomes decondense and nuclear membranes reform around each set of chromosomes.

6. Cytokinesis

   Cytoplasm divides, producing two genetically identical daughter cells

Dominant and Recessive Traits

Dominant: expressed when at least one dominant allele is present, capital letter.

Recessive: expressed only when both alleles are recessive, lowercase letter.

Genotype

Genetic makeup of an organism, representing alleles it possesses e.g. AA, Aa, aa

Phenotype

Observable physical/physiological traits of an organism, influenced by the genotype and environment e.g. having brown/blue eyes based on genotype

Pedigrees

• Square = male

• Circle = female

• Shaded = trait/disorder

• Half-Shaded = carrier of trait/disorder

• Square-Circle = mating

Heterozygous

2 different alleles for a gene. Shows dominant trait e.g. Aa

Homozygous

2 identical alleles for a gene e.g. AA, aa

Alleles

Different versions of a gene that determine specicif traits. Each person inherits two from each parent.

Evolution

The process in which an organism changes over time. Occurs in populations, not individuals

Genetic Traits

• Inherited from parents through genes

• Present in DNA from birth

• E.g. eye colour, blood type, hair texture

Acquired Traits

• Developed through lifetime due to environmental influence/experiences

• Not inherited or encoded in DNA and can’t be passed onto offpsring

• E.g. ability to ride a bike, scar, muscle strength from exercise

Mutation

Change in DNA sequence of a genome.

Variation is Essential to Evolution:

• Provided differences among individuals that natural selection can’t act upon

• Populations w/ more genetic variation are better equipped to adapt to changing environments, increasing chances of survival

• Development of new species (speciation) - prevent extinction

Mutation Types that Create Variation

• Point: single base is changed, inserted, or deleted e.g. A → G

• Insertion/Deletion: one or more bases added/removed, potentially altering frame of a gene (frameshift)

• Chromosomal: large scale changes in chromosome structure/number such as duplications and deletions.

Mutations Contribute to Variation

• Creates new alleles e.g. produce new coat colour in animals

• Increases genetic diversity - providing raw material for evolution

Sources of Mutations

• Spontaneous: errors during DNA replication/repair

• Environmental: radiation, chemicals, or viruses (mutagens) can induce

• Reproduction: errors during meiosis cause in gametes

Natural Selection

The process by which individuals with traits better suited to their environment are more likely to survive, reproduce and pass those traits to offspring.

Leads to gradual adaptation of populations with more advantageous traits becoming more common and less favourable traits are eliminated.

Selection Pressures

Definition: environmental factors that influence which traits are advantageous or disadvantageous for survival and reproduction.

Positive Selection Pressures

Traits that improve survival/reproduction increase in frequency over time e.g. camouflage

Negative Selection Pressures

Traits that reduce individual’s fitness are less likely to be passed on and decrease in frequency e.g. bright coloured pray in predator-rich environments.

Changes in Population Characteristics

Populations evolve as selection pressures fewer certain traits, leading to shifts in allele frequences. E.g. antibiotic resistance in bacteria under pressure of antibiotic use

Adaptation to Environment

Organisms with advantageous traits are better adapted to specific challenges. E.g. drought-tolerant plants thrive in arid regions.

Diversity Reduction/Maintenance

Strong selection pressures reduce genetic diversity by favouring specific traits. In contrast, varying pressures may maintain or even increase diversity

Role of Natural Selection in Evolution of Species

• Favouring advantageous traits (traits become more common as passed down through generations)

• Driving adaptations (better suited to environment)

• Shaping genetic diversity (eliminates disadvantageous traits, reducing frequency)

• Responding to environmental challenges (evolve in response to new selection pressures such as predators, climate, food availability)

• Leading to Speciation (new species)

• Ensuring evolutionary progress (continually acts on variation)

3 Elements Needed for Evolution Through Natural Selection

1. Variation

2. Inheritance

3. Fitness

Traits More Common Over Time in Population

Natural Selection:

• Elimination of disadvantageous traits

• Survival advantages

• Inheritance

• Reproduction success

How Species Evolve Adaptations Through Natural Selection

• Variation in traits

• Selection pressures

• Survival and reproductive advantage

• Increased frequency pf beneficial traits

Strucrural Adaptations

Physical features/characteristics of an organism that help it survive in environment e.g. camouflage, sharp claws and teeth, body shape

Physiological Adaptations

Internal, biochemical processes that help an organism survive in environment e.g. temperature regulation, venom production, hibernation.

Behavioural Adaptations

The actions of an organism that help it survive or reproduce e.g. migration, noctural, mating calls

Human Impact Nitrogen Cycle Fertiliser

1. • Large amount of synthetic nitrogen fertilisers used on soils to promote plant growth

   • Excess can leach into waterways - eutrophication (water bodies overly enriched leaving to algal blooms and oxygen depletion)

   • Ecosystem: disrupts aquatic ecosystems as less oxygen for organisms - dead zones

   • Agriculture: fertiliser overuse leads to soil degradation, nutrient imbalanced, and increased reliance on fertilisers

Human Impact Nitrogen Cycle Combustion

• Burning of fossil fuels release nitrogen oxides into atmosphere - nitric acid

• Ecosystems: acid rain lowers pH of soil and water, affecting plant growth and aquatic life which kills species, reducing biodiversity

• Agriculture: acid rain can damage crops and reduce soil fertility - lower productivity for Ag

Human Impact Nitrogen Cycle Deforestation

• Reduces amount of nitrogen fixing vegetation - maintaining balance of nitrogen in soils

• Ecosystem: disrupts nitrogen cycling - nutrient loss in soil and altered plant communities

• Agriculture: soil fertility decline - reduced crop yield - additional fertiliser used

Human Impact Carbon Cycle Combustion

• Carbon stored in fuels is released as CO2 into atmosphere - GG concentration

• CC: GGE → CO2 traps heat in atmosphere → global warming

Human Impact Carbon Cycle Deforestation

• Trees/plants absorb CO2 from atmosphere during photosynthesis - acting as carbon sinks

• Forests cleared means carbon stored is released back in atmosphere

• Diminishes Earth's capacity to regulate carbon levels

• CC: adds to build up of CO2 - exacerbating GGE - mitigate emissions

Solutions/Mitigation for Carbon Cycle

1. Carbon Sequestration

   • Reforestation/Afforestation

   • Soil Carbon Sequestration

   • Carbon Capture + Storage

2. Renewable Energy

   • Renewable Energy Sources (wind, solar, hydro, geothermal)

   • Nuclear Energy

3. Education + Public Awareness

   • Promoting sustainable lifestyle choices (footprint, plant-based diet, green products)