Characteristics of Life: Organisation and Cells

Characteristics of Life

• Living organisms are composed of cells
• Living organisms undergo reproduction
• Living organisms experience growth & development
• Living things obtain & use energy. The process of doing so is called metabolism
• Living organisms respond to their environment
• Homeostasis is a characteristic of living organisms
• DNA is the universal genetic code in living organisms
• Evolution and adaptation are characteristics of living organisms

Levels of Organization:

• Atoms form molecules
• Molecules make up cells
• Cells are organized into tissues
• Tissues compose organs
• Organs work together in organ systems
• Organ systems make up an organism
• Organisms form populations
• Populations exist within communities
• Communities interact within ecosystems
• Ecosystems comprise the biosphere

Cellularity

• A cell is the basic unit of life
• Cells come from preexisting cells
• Unicellular organisms consist of a single cell
• Multicellular organisms consist of many cells
• Multicellular organisms show diversity and specialization of function. The human body has over 85 types of cells

Complex Tissues

• As multicellular organisms, animals develop specialized cells that group into tissues performing specialized functions
• Tissues consist of similar cells sharing a common embryonic origin
• The four main types of animal tissues are nervous, muscle, connective, and epithelial
• Nervous tissue contains neurons that transmit nerve impulses
• Muscle tissue contracts to cause body movement
• Connective tissues include specialized types, like blood for transport and bone for structural support

Reproduction

• Asexual reproduction involves a single parent copying its DNA
• During asexual reproduction the parent cell then divides or buds
• Asexual reproduction produces genetically identical offspring
• Asexual reproduction can result in rapid reproduction of identical organisms
• Sexual reproduction involves two parents
• Sexual reproduction results in the union of two different parent cells to produce the first cells of a new organism
• Sexual reproduction leads to offspring that are genetically unique, which promotes genetic diversity and speciation

Growth and development

• Single-celled organisms like bacteria primarily grow through a simple increase in size
• Multicellular organisms undergo extensive development from a single fertilized egg
• Multicellular development involves numerous cell divisions, leading to a multitude of cells in mature organisms
• Differentiation is the process where cells change shape and structure to perform different functions

Use of Energy/Metabolism

• All living things obtain energy from their environment to support growth, development, reproduction, and excretion, which occur at different rates
• Metabolism involves the combination of chemical reactions, Anabolism which synthesizes compounds and expends energy and Catabolism which breaks down compounds into simple components and releases energy
• Metabolism consists of total activity in chemical reactions that build and break down materials for life processes

Response to Stimuli

• Organisms detect and respond to stimuli, or signals, from the internal or external environment.
• Internal stimuli include blood glucose levels triggering feelings of hunger
• External stimuli include light, touch, sound, heat, and smell.

Homeostasis

• Homeostasis refers to autonomic, self-controlled processes
• Organisms use homeostasis to respond to stimuli to maintain suitable internal conditions for sustaining life.
• An example is a response of the body to bleeding or heat stress

DNA: The Universal Genetic Code

• All life uses a universal genetic code based on DNA
• DNA determines the inherited traits of all organisms
• DNA refers to a nucleic acid which has a three-dimensional shape called a double helix
• The shape of DNA enables duplication and 'reading' or expression of genes it encodes

Evolution and Adaptation

• Evolution is the ability of a group of organisms to change over time
• Evolution is valuable for survival in constantly changing environments
• Adaptation is a trait enhancing an organism's ability to compete and reproduce in its environment

The Cell

• The cell is the lowest level of organization capable of performing all activities required for life
• Cells enclose cell membranes
• Cells use DNA as their genetic information
• Eukaryotic cells have membrane-enclosed organelles
• The nucleus is usually the largest membrane bound organelle in a cell
• Prokaryotic cells are simpler and usually smaller
• Prokaryotic cells do not have a nucleus or other membrane-enclosed organelles

Cell Theory

• Cells receive their name from Englishman Robert Hooke in 1665
• The cell serves as the fundamental unit of structure and function in organisms
• Organisms consist of one or more cells
• All cells originate from pre-existing cells

Types of Cells: Prokaryotic

• Prokaryotic cells are the first and most primitive types of cells
• Prokaryotic cells lack a nucleus and other membrane-bound organelles like mitochondria
• Bacteria are the ONLY prokaryotes

Types of Cells: Eukaryotic

• Eukaryotic cells are found in most organisms, including all plant and animal cells,
• Eukaryotic cells contain genetic material is contained in a nucleus
• Eukaryotic cell have membrane-bound organelles

Plasma Membrane Function

• The plasma membrane serves as physical barrier
• The plasma membrane protects the cell components
• The plasma membrane allows separate activities inside and outside
• The plasma membrane provides structural support to the cell
• Plasma membranes exhibit selective permeability
• Selectively Permeable membranes only allow certain molecules to pass
• Endocytosis is the ingestion of relatively larger molecules via channels
• Exocytosis is the release of materials
• The plasma membrane facilitates cell signaling. Proteins on the cell can "mark" it for identification
• The plasma membrane contains receptors enabling cells to carry out tasks when molecules like hormones bind to those receptors

Passive Transport: Diffusion

• Diffusion occurs when molecules and ions move freely in gases and liquids
• Diffusion results in each type of particle spreading out evenly within available space
• Diffusion is the net movement of molecules from a region of its higher concentration to a region of its lower concentration without energy use

Passive Transport: Facilitated diffusion

• Facilitated diffusion enables movement of specific molecules
• Transport occurs down a concentration gradient with help from special channel or carrier proteins.
• Facilitated diffusion does not require energy
• Ions or electrically charged molecules cannot diffuse through the phospholipid bilayer
• Large molecules cannot move through the phospholipid bilayer freely
• Channel proteins enable transport of these special ions and molecules

Types of Transport: Phagocytosis

• Phagocytosis is dubbed as "cellular eating"
• Phagocytosis is carried out via lysosomes

Types of Transport: Pinocytosis

• Pinocytosis is identified as "cellular drinking"

Types of Transport: Receptor-mediated

• Receptor-mediated endocytosis is triggered by a ligand signal

Exocytosis Process

• Exocytosis uses a secretory vesicle to remove food and waste from cells

Cell Membranes: Construction and function

• Membrane proteins mediate a variety of cell functions

Osmosis

• Osmosis involves the movement of water
• The direction of osmosis is determined by comparing total solute concentrations
• Hypertonic solutions have more solute and less water
• Hypotonic solutions have less solute and more water
• Isotonic solutions have equal amounts of solute and water

Erythrocyte Equilibrium

• No osmotic pressure occurs when cells occur in an isotonic solution, so water does not cross the membrane
• In hypotonic solutions, there is increased osmotic pressure in cytoplasm, leading to water entering the cell causing it to swell
• In hypertonic solutions, there is decreased osmotic pressure in cytoplasm, leading to water leaving the cell causing it to shrinking

Cell Lysis

• Cell lysis involves the use of hypotonic solutions
• In cell lysis, normal sodium (Na+) equilibrium processes are interrupted, causing cells to burst
• Lysis can be used to researchers’ advantage when isolating cells

Mitochondria Structure and Function

• Mitochondria is are organelles also referred to as the "Powerhouse of the cell"
• Mitochondria are double-membrane bound organelles, rod-shaped and found in most eukaryotic organisms inside the cytoplasm
• Mitochondria play a role in breaking down nutrients and generating energy-rich molecules
• Many biochemical reactions involved in cellular respiration occur within mitochondria
• Mitochondria ranges from 0.5 to 1.0 micrometers in diameter
• Mitochondria consist of an outer membrane, an inner membrane, and a gel-like materials called the matrix.
• The outer and inner membranes consist of proteins and phospholipid layers separated by the intermembrane space
• The outer membrane possesses many special proteins called porins
• The inner membrane of mitochondria is rather complex.
• The inner membrane posses numerous folds known as cristae, which form a layered structure, helping increase the surface area inside the organelle.
• Cristae and the proteins of the inner membrane help in ATP production
• The inner mitochondrial membrane is strictly permeable to oxygen and ATP molecules
• Various chemical reactions occur within the inner membrane of mitochondria.
• The Mitochondrial Matrix is a viscous fluid that contains a mixture of enzymes and proteins
• Within the Mitochondrial Matrix there are ribosomes, inorganic ions, mitochondrial DNA, nucleotide cofactors, and organic molecules
• Enzymes in the matrix play an important role in ATP synthesis

Mitochondria Function

• Mitochondria produces main ATP for cellular energy
• Mitochondria regulates metabolism of the cell
• Mitochondria promotes growth of new cells and cell multiplication
• Mitochondria helps in detoxifying ammonia in the liver cells
• Mitochondria has a role in apoptosis, or cell death
• Mitochondria helps maintain concentration of calcium ions in the compartments of the cell
• Mitochondria is involved in cellular activities such as cellular differentiation and cell signalling
• Mitochondria controls the cell cycle

Mitochondrial DNA (mtDNA)

• Most DNA is kept in the nucleus, mitochondria has its own DNA, known at Mitochondrial DNA (mtDNA)
• Mitochondrial DNA (mtDNA) resembles bacterial DNA
• Mitochondrial DNA (mtDNA) encodes instructions for proteins (a number of proteinsTrusted Source) that support equipment across 37 genes
• The human genome in cell nuclei contains around 3.3 billion base pairs
• Mitochondrial DNA (mtDNA) contains less than 17,000 Trusted Source
• Children receive half their DNA from their father and half from their mother, whereas mtDNA is inherited from their mother
• Mitochondrial DNA (mtDNA) useful for tracing genetic lines

Energy Production

• ATP powers metabolic processes and is often a unit of currency
• Most ATP is produced in mitochondria through glycolysis and Krebs cycle
• Energy production occurs on the folds or cristae of the inner membrane
• Mitochondria converts energy from in food to an energy form usable by the cell (oxidative phosphorylation)
• Krebs cycle produces NADH, which are used by enzymes to produce ATP

Mitochondria in Cell Death

• Cell death (apoptosis) is an essential part of life.
• Old or broken cells are cleared away and destroyed.
• Mitochondria help to determine which cells need to be destroyed.
• Mitochondria releases cytochrome C, which activates caspase, an enzyme involved in cell death
• Because some diseases involve a breakdown in normal apoptosis, mitochondria may play a role in diseases such as cancer
• Calcium is critical for regulating mitochondria and calcium, the cell regulates it tightly.
• Mitochondria quickly absorbs calcium ions
• Calcium is needed for neurotransmitter release by a nerve cell, and hormones from endocrine cells, muscle function and blood clotting.

Symptoms of mitochondrial diseases:

• Poor growth
• Muscle weakness, muscle pain, low muscle tone, exercise intolerance
• Vision and/or hearing problems
• Learning disabilities, delays in development.
• Heart, liver or kidney diseases.
• Swallowing difficulties, diarrhea or constipation, unexplained vomiting.
• Increased risk of infection.
• Neurological problems.
• Movement disorders.
• Thyroid problems.
• Respiratory (breathing) problems.