Biology: Characteristics of Life and Hierarchy

Five Fundamental Characteristics of Living Organisms

• All living organisms are composed of cells
• Reproduction is a goal for all organisms
• Processing information from genes is important
• Acquiring and using energy (ATP) is essential
• All life forms are a product of evolution

Hierarchy of Life

• Atom → Molecule → Macromolecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere

Definitions

• Atom: Smallest identifiable unit of matter
• Molecule: Two or more atoms held together by covalent bonds
• Macromolecule: Large, complex molecules essential for life, made of smaller molecular subunits called monomers
• Organelle: Specialized structures within eukaryotic cells, performing distinct functions
• Cell: Membrane-bound unit, fundamental structural and functional unit of life
• Tissue: Group of cells functioning as a unit, specialized and working together for a specific function
• Organ: A structure composed of multiple tissues, working together to perform specific functions
• Organ System: Groups of organs that work together for one or more functions
• Organism: An individual living thing
• Population: A group of organisms of the same species in a given area
• Community: All the populations of different species in an area
• Ecosystem: Both the biotic and abiotic components of an environment, including the interactions between organisms and their surroundings
• Biosphere: The collection of all ecosystems on Earth

Organ Systems

• Endocrine: Hormone production (thyroid, pituitary, and adrenal)
• Lymphatic/Immune: Maintaining fluid balance and defending against infection (white blood cells, thymus, and bone marrow)
• Respiratory: Absorbing oxygen and releasing carbon dioxide (nose, lungs, and bronchi)
• Reproductive: To reproduce (uterus, ovaries, fallopian tubes)
• Cardiovascular: Transporting nutrients, oxygen, wastes, hormones, etc. (heart and blood vessels)
• Digestive: Breaking down and absorbing nutrients (mouth, pharynx, esophagus, stomach, intestines, liver, and gallbladder)
• Urinary: Eliminating waste (kidneys and bladder)
• Skeletal: Providing support, movement, and protection; blood formation (bones, cartilage, ligaments)
• Muscular: Enabling movement and stability (muscles)
• Nervous: Rapid internal communication, coordination, and motor control (brain, spinal cord, and nerves)

DNA/RNA Structure

• DNA, deoxyribonucleic acid, is a molecule that contains the genetic code unique to each individual, responsible for creating all proteins; hereditary
• The information coded in DNA is passed from parent to child
• DNA is a double helix
• RNA, ribonucleic acid, present in the majority of living organisms and viruses, made up of nucleotides
• Nucleotides consist of ribose sugar, phosphate groups, and nitrogenous bases: adenine, guanine, uracil, and cytosine.
• RNA is a single helix

DNA Replication

• Before cell division, cells duplicate DNA to provide a complete set to each daughter cell
• DNA replicates using the principle of complementary base pairing
• Enzymes, such as DNA helicase and polymerase, are involved in the process
• DNA polymerase fixes errors in new base pairs

Transcription

• Process where a cell creates RNA copy (mRNA) of a DNA segment
• This mRNA carries genetic information to the cytoplasm for protein creation
• RNA polymerase builds mRNA corresponding to a DNA template
• RNA polymerase opens up DNA, then rewinds the DNA
• Pre-mRNA is generated by transcription, and it contains both introns (non-coding regions) and exons (coding regions).
• Removing introns and joining exons via alternative splicing produces mature mRNA
• One gene can code for multiple proteins

Translation

• Process where ribosomes use mRNA to synthesize proteins
• Ribosomes translate the nucleotide sequence of mRNA into the amino acid sequence of proteins
• Involves tRNA bringing specific amino acids to the ribosome according to mRNA codons
• A codon is a three-nucleotide sequence that specifies an amino acid.
• Anticodons on tRNA match with specific codons on mRNA
• Ribosomes assemble amino acids into a polypeptide chain, which folds into a functional protein

Other Biological Processes

• Transcription: DNA → RNA
• Translation: RNA → Protein
• Active transport: Movement of molecules against the concentration gradient, requiring energy
• Passive transport: Movement of molecules with the concentration gradient, without energy

Chemical Components of Organisms

• Atom: the most fundamental building block of matter
• Isotopes: Atoms of the same element, but with different numbers of neutrons.
• Ions: Charged atoms or molecules.
• Molecules: Two or more atoms held together by chemical bonds.
• Compounds: A substance formed when two or more different types of atoms combine chemically.
• Electronegativity: The tendency of an atom to attract electrons in a chemical bond.
• Chemical Bonds: A force that holds two or more atoms together

Cell Structure

• Plasma Membrane: The outermost membrane, made of phospholipids, with hydrophilic heads and hydrophobic tails. It regulates substance transport.
• Chromosomes: Structures containing the cell's DNA.
• Cytoplasm: The jelly-like substance inside the plasma membrane.
• Nucleus: The organelle that contains the cell's DNA in eukaryotes.

Cellular Processes

• Mitosis: Division of somatic cells, producing two genetically identical daughter cells.
• Meiosis: Cell division specific to reproduction, producing four haploid daughter cells with half the genetic material of the parent cell.
• Endocytosis/Exocytosis: Processes facilitating movement of large molecules into/out of cells.

Prokaryotic & Eukaryotic Cells

• Both have Cell membranes and cytoplasm and ribosomes
• Eukaryotic cells have a nucleus while prokaryotic cells do not
• Prokaryotic cells tend to be simpler and smaller, while eukaryotic cells tend to be more complex, and larger.
• Eukaryotic cells have organelles; prokaryotic cells do not
• Eukaryotic cells have more DNA than prokaryotic cells
• Eukaryotic cells are larger, more complex, have a nucleus, and internal membranes
• Prokaryotic cells lack a nucleus