Week 1 – Defining Life

Aspects of life

Four key characteristics of living organisms

• Complexity (precise spatial organisation, cellular structure, discrete organs/components that perform specific functions) • Ability to respond to environmental stimuli • Ability to reproduce, as all life dies • Capacity to evolve (species change over time in response to environmental pressure in advantage to a particular trait)

More complex characteristics

• Metabolism (conversion of energy into a form a cell can use) • Homeostasis (ability to maintain a stable internal environment in the face of a changing external environment) • Regulated growth and development

The minimum unit of life is the cell

• Stores and transfers genetic information (DNA) • Enclosed in a membrane for spatial definition (but selectively permeable) • Undergoes metabolism • Reproduces through replication

The scientific method

Observation

• Observation in the form of a statement that leads to a question • Hypothesis (logical, testable proposed explanation for the behaviour observed; requires proof) • Predictions (based on hypothesis; testable) • New observations • If results not consistent with hypothesis it is disproven, then rejected or revised • If results are consistent, doesn't mean hypothesis is correct but simply supported • Further observations • Conclusion etc

Experiment

• Tests 2 or more groups • Controlled conditions (so the results are purely reflective of the desired variables' interaction) • Unwanted variables are not necessarily eliminated through environmental regulation but instead are cancelled out by using control groups • Assesses the effect of an independent variable on a dependent variable Week 10 – Development & Reproduction

Reproduction

Asexual

Production of genetically identical cells (clones)

• Binary fission • Eg Bacteria, archaea • Genetic variation via horizontal gene transfer • Budding • Eg Yeast, fungi, some animals • Unequal division between mother and daughter cell/organism • Result of mitosis thus genetically identical offspring • Prpogation via fragmentation • Eg Corals, molds, algae, worms, sea stars • Organisms splits, each part forms new individual • Parthenogenesis/"virgin birth" • Eg some insects, crustaceans, fish, reptiles • Single maternal parents • Females produce eggs not fertilised by males but divide by mitosis and develop into individuals • In some cases haploid egg becomes haploid adult, other cases DNA doubles during development so adult is diploid, other cases diploid egg becomes diploid adult.

Sexual

Most organisms reproduce sexually/exchange genetic material, suggesting advantages over asexuality.

Characterised by formation and fusion of gametes.

Meiotic cell division

• Products: gametes, 1n chromosomes • Spermatozoa/sperm & LARGER ova/egg • Fungi etc produce two types of gametes of similar size • Genetic var: recombination + random segregation of chromosomes into gametes (lining up along metaphase plate)

Fertilisation

• Fusion of 2 different gametes • Prodct: zygote, 2n chromosomes • Zygote mitotically divices and develops into an embryo, the early stage of multicellular development. • Genetic var: 2 unique gametes fuse, creating a new genetic combination and a unique individual Week 11b - Cellular Respiration

Cellular respiration

Harvesting energy from carbohydrates and other fuel molecules.

The process of cellular respiration converts the chemical potential energy stored in organic molecules to chemical potential energy that is useful to cells (the chemical potential energy stored in ATP's bonds), producing CO2 as a by-product.

A major set of catabolic reactions. Fuel molecules such as glucose (carbohydrates), fatty acids (lipids), and proteins and catabolised into smaller units.

Energy in cellular respiration: Glucose is oxidized through a series of chemical reactions, releasing energy in the form of ATP and reduced electron carriers.

In eukaryotes, glycolysis takes place in the cytoplasm, and pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation all take place in mitochondria. The electron transport chain is made up of proteins and small molecules associated with the inner mitochondrial membrane. In some bacteria, these reactions take place in the cytoplasm, and the electron transport chain is located in the plasma membrane.

Aerobic respiration

• Energy is released/-ve∆G as the bonds of CO2 & H2O contain less potential energy than the fuel molecules. • Max free energy released is -686kcal/mol of glucose. • This equation skips many intermediate steps. Not all glucose's energy can be released at once (or it would be lost as heat), so it is broken down gradually in a series of reactions. • On average: 32 ATP from 1 glucose molecule. • Energy to form one mole of ATP from ADP and Pi is at least 7.3 kcal. Thus, cellular respiration harnesses at least 32 × 7.3 = 233.6 kcal of energy in ATP for every mole of glucose that is broken down in the presence of oxygen. • Relatively efficient: 34% of the total energy released by aerobic respiration is harnessed in the form of ATP (233.6/686 = 34%).

ATP generation

1. Substrate-level phosphorylation a. A phosphorylated organic molecule directly transfers a phosphate group (Pi) to ADP b. 2 energetically-coupled reactions: hydrolysis of this organic molecule & addition of Pi to ADP. Pi (produced by PEP hydrolysis) + ADP -> ATP + H2O. PEP hydrolysis drives ATP synthesis. c. Both carried out by a single hormone. The organic molecule is the enzyme substrate, hence the process name. d. Responsible for producing 12% of ATP from glucose. 2. Oxidative phosphorylation a. Chemical energy from organic molecules transferred to e- carriers. Week 12 – Lifespan & Death

Lifespan

Telomeres

• Chromosomes: 2 strands, one "sen strand", one "anti-sen strand" • DNA polymerase replicates chromosomes, and stops doing so when there is no DNA left, so without telomeres not all of the DNA would be replicated, and chromosomes would get shorter over generations. • Caps on either end stabilise chromosome, providing extra space for the DNA to hold on to, so entire chromosome is replicated.

Telomere attrition theory

• Over generations telomeres shorten, eventually reaching a critical point () that compromises chromosome's integrity, and the chromosome is marked for cell death via a p53 mechanism. • Telomerase exists to lengthen telomeres, preventing chromosomal instability • This enzyme not produced in all cells however, so in most cells the telomeres do shorten leading to death • Functional telomerase is in often turned on in cancerous cells

Stress-induced premature (SIPS) theory

• Over time we accumulate from food, environment… • These hit a critical point where our cells are no longer viable, and body can no longer support them

Antagonistic pleitropy theory

• Certain mutations have different effects at different stages of life • Eg resulting in excess testosterone = increased reproductive fitness and more prone to reproduce, peak in early 20s • Negative consequence: higher risk of prostate cancer, succumbing to premature death • Because already reproduced before cancer, no selective pressure to avoid this premature death

Mutation accumulation theory

• Similar to SIPS • The critical point may occur after reproduction • Creates selection shadow in which there is no selective pressure to maintain life as genetic code already passed on; no to repair mutations

Lifespans

• Length differs between organisms