Biology25

Water (H2O)

Solvent for polar molecules and ions. Can lead away or take up heat (thermal conduction). Has high specific heat capacity. Provides buoyancy (floaty). Has low viscosity (not that sticky)

Adhesion

Water binding to a surface, especially polar materials

Cohesion

Water sticking to water

Dipole

A water molecule having one more positive end (H) and one more negative end (O)

Polar molecule

A water molecule with unequal sharing of electrons, resulting in partial charges

Covalent bonds

The bonds between oxygen and hydrogen atoms within a water molecule

Hydrogen bonds

The intermolecular bonds that form between water molecules

Hydrophilic

Waterloving substances

Hydrophobic

Waterhating substances

Water as a medium for life

Most molecules of life are dissolved in it, it can transport molecules, facilitates chemical reactions, and provides structure

Surface tension

A consequence of water cohesion, important for organisms like mosquitos in aquatic habitats

Hypothesis for origin of water on Earth

Water was unlikely to be present when Earth originally formed due to heat; one hypothesis is water was delivered by asteroids

Goldilocks zone

The distance from a star where temperatures allow liquid water—key for searching for extraterrestrial life

Retention of water on Earth

Distance from the sun prevents boiling, and Earth’s gravity holds oceans and atmospheric gases

Nucleic acids

One of the four major groups of organic compounds, including DNA, RNA, and ATP

DNA (Deoxyribonucleic Acid)

Genetic material of all living organisms

RNA (Ribonucleic Acid)

Polymer formed by nucleotide monomers

Nucleotide

Monomer of DNA/RNA composed of sugar, phosphate, and nitrogenous base

Polymer

Chain molecule formed when nucleotide monomers link by covalent bonds

Nitrogenous bases (DNA)

Adenine, Thymine, Cytosine, Guanine

Nitrogenous bases (RNA)

Adenine, Uracil, Cytosine, Guanine

Complementary base pairing

A with T (or U in RNA), C with G

DNA structure

Double helix of antiparallel strands linked by hydrogen bonds between complementary bases

DNA replication

DNA copying process before cell division, enabled by complementary base pairing

Genetic code

Universal code where triplets specify amino acids; evidence for universal common ancestor

Diversity of DNA base sequences

Differences in base sequences allow limitless information capacity

DNA vs. RNA differences

DNA is double-stranded, RNA single-stranded; DNA uses deoxyribose/T, RNA uses ribose/U

Purine to pyrimidine bonding

Maintains equal helix width and stability

Hershey-Chase experiment

Showed DNA, not protein, is genetic material

Conditions on early Earth

Low oxygen, high methane/CO2, hotter climate, no ozone layer allowing UV-driven reactions

Miller-Urey experiment

Simulated early Earth to test abiotic synthesis of organic molecules

Spontaneous formation of vesicles

Fatty acids can self-assemble into bilayer spheres

RNA as presumed first genetic material

RNA can store information and catalyze reactions

LUCA

Evidence includes universal code, universal ribosomes, and similar DNA/RNA-synthesizing enzymes

Hydrothermal vents

Hot, chemical-rich cracks hypothesized as origins of first cells

Cell

Smallest self-sustaining unit of life that can divide

Cell theory

All life is cellular; cells are the basic unit; cells arise from pre-existing cells

Structures common to all cells

Plasma membrane, cytoplasm, DNA

Prokaryotic cell structure

Plasma membrane, cytoplasm, nucleoid DNA, 70S ribosomes

Eukaryotic cell structures

Organelles including nucleus, ER, Golgi, mitochondria, lysosomes; some have walls and chloroplasts

Endosymbiosis theory

Eukaryotes formed by membrane infolding and engulfing aerobic bacteria (and possibly cyanobacteria)

Cell differentiation

Cells specialize by expressing specific genes, while keeping same DNA

Multicellularity

Leads to longer life spans, larger bodies, greater complexity

Virus common features

Genetic material, capsid, few/no enzymes, no cytoplasm, fixed small size

Viral origin

Multiple origins suggested by structural/genetic diversity

Rapid viral evolution

Due to high mutation rate, especially in RNA viruses

Species

Organisms that can interbreed to produce fertile viable offspring

Variation

Differences between individuals within a species

Binomial system

Two-part naming: Genus and species

7 Taxa of living organisms

Kingdom, Phylum, Class, Order, Family, Genus, Species

Genome

Complete set of DNA instructions in an organism

Genome diversity within species

SNPs and other differences despite mostly shared genomes

Karyotyping

Pairing and ordering chromosomes

Karyogram

Display of chromosomes arranged in homologous pairs by size

Chromosome 2 fusion hypothesis

Human chromosome 2 likely formed by fusion of two ancestral ape chromosomes

Evolution

Change in heritable traits of a population

Evidence for evolution (Molecular)

DNA/RNA and protein sequence comparisons

Evidence for evolution (Selective breeding)

Domesticated animal/plant changes from human selection

Homologous structures

Structures with shared ancestry but different functions

Analogous structures

Similar functions evolved independently (convergent evolution)

Speciation

One species splitting into two or more via reproductive isolation

Allopatric speciation

Geographical separation leading to new species

Sympatric speciation

New species arising without geographical separation via reproductive/behavioral barriers

Adaptive radiation

Rapid evolution into diverse species filling ecological niches

Hybridization/Sterility

Different species produce sterile hybrids like mules

Abrupt speciation in plants

Hybridization or polyploidy rapidly creates new species

Biodiversity

Variety of life at ecosystem, species, and genetic levels

Anthropogenic species extinction

Human-caused extinction

Causes of current biodiversity crisis

Population growth, hunting, exploitation, urbanization, deforestation, pollution, invasive species

Conservation approaches

In situ conservation and ex situ conservation

EDGE of Existence Programme

Conserves species that are Evolutionarily Distinct and Globally Endangered

Macromolecule production

Condensation (anabolism) links monomers into polymers

Digestion of macromolecules

Hydrolysis (catabolism) breaks polymers into monomers

Carbon atom

Forms four covalent bonds enabling diverse stable biomolecules

Glucose function

Used in respiration, builds polysaccharides, transported in blood, produced by photosynthesis

Carbohydrate functions

Energy, storage, structure, recognition, nucleotide components

Cellulose

Structural polysaccharide formed from beta-glucose

Glycoprotein

Protein with attached carbohydrate aiding cell-cell recognition

Lipid properties

Hydrophobic and mostly insoluble in water

Triglyceride

Glycerol plus three fatty acids

Phospholipid

Glycerol, two fatty acids, and a phosphate group

Triglycerides in adipose tissue

Energy storage and insulation in mammals

Saturated fatty acids

Only single bonds; higher melting point

Unsaturated fatty acids

One or more double bonds; lower melting point; increase membrane fluidity

Phospholipid bilayer formation

Spontaneous due to hydrophobic tails inward, hydrophilic heads outward

Steroid membrane passage

Non-polar steroids cross membrane directly

Protein monomer

Amino acid

Polypeptide

Chain of amino acids linked by peptide bonds

Amino acid structure

Amine group, carboxyl group, variable R-group on central carbon

Essential amino acids

Nine amino acids required from diet

R-group diversity

R-group chemistry underlies immense protein diversity

Primary structure

Specific amino acid order

Secondary structure

Alpha helix and beta sheet stabilized by backbone hydrogen bonds

Tertiary structure

3D shape from R-group interactions

Polar/Non-polar R-groups effect

Hydrophobic groups hide internally; hydrophilic groups face outward

Quaternary structure

Multiple polypeptides assembling into one functional protein

Globular proteins

Folded proteins for transport, hormones, enzymes

Fibrous proteins

Long parallel chains for structure/support

Protein denaturation

Extreme pH or heat disrupts 3D structure

Plasma membrane function

Selectively permeable boundary controlling traffic