Basics of Life: Molecules, Cells, Evolution, and Biological Classification

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Chapter 5

• Basics of Life Molecules, Cells, Evolution, and
  Biological Classification

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Key Concepts

• To understand living organisms, one must have a
  basic understanding of the variety of compounds
  from which organisms are built.
• Four groups of macromolecules are necessary for
  life carbohydrates, lipids, proteins, and
  nucleic acids.
• All living organisms are composed of cells.

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Key Concepts

• Cells can be either prokaryotic or eukaryotic.
• Cells produce new cells by the process of cell
  division.
• Evolution is the process by which the genetic
  composition of populations of organisms changes
  over time.
• Natural selection favors the survival and
  reproduction of those organisms that possess
  variations that are best suited to their
  environment.

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Key Concepts

• A species is a group of physically similar,
  potentially interbreeding organisms that share a
  gene pool, are reproductively isolated from other
  such groups, and are able to produce viable
  offspring.
• The binomial system of nomenclature uses two
  words, the genus and the species epithet, to
  identify an organism.

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Key Concepts

• Most biologists classify organisms into one of
  three domains, categories that reflect theories
  about evolutionary relationships.

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Building Blocks of Life

• Large molecules called macromolecules are some of
  the most important chemical compounds in
  organisms
• 4 major classes of macromolecules
• carbohydrates
• lipids
• proteins
• nucleic acids

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Carbohydrates

• Contain C, H and O, frequently in a 121 ratio
  CH2O
• Sugars
• monosaccharides are simple sugars, usually with 5
  or 6 C atoms
• ribose and deoxyribes are in nucleic acids
• glucose is the basic fuel molecule for cells
• disaccharides consist of 2 monosaccharides bonded
  together

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Carbohydrates

• types of disaccharides
• sucrose glucose fructose (table sugar)
• maltose glucose glucose
• lactose glucose galactose (milk sugar)
• Polysaccharides
• these carbohydrates are polymers, large molecules
  consisting of the same basic units linked together

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Carbohydrates

• storage forms of polysaccharides
• starches in plants, algae, and some
  microorganisms, made of units of glucose
• glycogen, animal starch is similar
• structural polysaccharides
• cellulose is found in cell walls of plants, algae
• chitin is in fungi cell walls and exoskeletons of
  some marine animals

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Lipids

• Composed primarily of C and H
• fatty acidslong hydrocarbon chains containing an
  acid group
• triglyceridessimple fats composed of 3 fatty
  acids attached to a glycerol molecule
• Functions within marine organisms
• store energy, cushion organs, buoyancy
• phospholipids are part of cell membranes
• steroids, which have complex ring structures, are
  chemical messengers
• waxes act as a covering or water barrier

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Proteins

• Proteins are polymers of amino acids
• 20 amino acids make up proteins
• polypeptideschains of amino acids, which are
  coiled and folded into complex, three-dimensional
  protein molecules
• Functions of proteins
• compose primary structural components of animals
  muscles and connective tissue
• enzymesbiological catalysts
• transport or store chemicals

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Nucleic Acids

• Nucleic acidspolymers of nucleotides
• nucleotide 5-carbon sugar nitrogen-containing
  base phosphate group

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Nucleic Acids

• DNA (deoxyribonucleic acid)
• large helix-shaped molecule
• sugar deoxyribose
• N-containing base adenine, guanine, cytosine or
  thymine
• DNA contains genes (genetic material)
• genes direct synthesis of proteins

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Nucleic Acids

• RNA (ribonucleic acid)
• usually a single-stranded molecule
• sugar ribose
• N-containing base adenine, guanine, cytosine or
  uracil
• functions in protein synthesis
• messenger RNA (mRNA)
• ribosomal RNA (rRNA)
• transfer RNA (tRNA)

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Cells

• Cells are basic units of living organisms
• All cells are capable of basic processes
• metabolism
• growth
• reproduction
• Surrounded by cell membrane
• Cytoplasm contains cytosol (fluid content of
  cell) and organelles

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Types of Cells

• Prokaryotic cells (e.g. bacteria, archaeans)
• lack a nucleus and membrane-bound organelles
• prokaryotes (prokaryotic organisms) are always
  unicellular
• Eukaryotic cells (e.g. plants, animals)
• have a well-defined nucleus and many
  membrane-bound organelles
• eukaryotes may be uni- or multicellular

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Organelles

• Nucleus and ribosomes
• nucleuslarge structure surrounded by a nuclear
  membrane which contains the cells DNA and acts
  as the control center
• chromosomes DNA protein
• ribosomes, which function in assembly of
  proteins, are assembled in an area of the nucleus
  called the nucleolus

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Organelles

• Organelles involved in synthesis, processing, and
  storage
• endoplasmic reticulum (ER)series of membranes
  winding through cytoplasm
• rough ER has ribosomes attached to its surface,
  and functions in modification of proteins during
  synthesis
• smooth ER (no ribosomes) functions in synthesis
  of lipids and carbohydrates, and detoxification
  of harmful substances

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Organelles

• Golgi apparatusorganelle which functions in the
  modification of proteins and places plasma
  membranes around them
• lysosomesmembrane-bound sacs produced by the
  Golgi apparatus which contain enzymes that
  function in digestion
• vacuolesstructures surrounded by a plasma
  membrane that may contain food, wastes, or water

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Organelles

• Organelles involved in energy conversion
  (reproduce themselves)
• chloroplastsorganelles found in photosynthetic
  organisms that function in converting radiant
  energy of light into chemical energy
• mitochondriaorganelles which transfer chemical
  energy in food to molecules of adenosine
  triphosphate (ATP)
• ATP supplies energy for metabolism

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Organelles

• Organelles of movement
• flagellalong, hair-like organelles (usually 1, 2
  or 3 per cell) used to propel the cell through
  the watery environment
• ciliashort, hair-like organelles which are quite
  numerous, sometimes covering the cell surface
  used by single cells to move through the water,
  and to move materials along the cells surface in
  multicellular organisms

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Energy Transfer in Cells
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Energy Transfer in Cells

• Photosynthesis
• low-energy molecules (CO2 and H2O) combine to
  form high-energy food molecules (carbohydrates)
• in prokarytes, occurs in areas of thecell where
  the membrane has folded in to form a surface for
  needed participants
• chloroplasts
• two membranes
• thylakoids, arranged in stacks (grana)
• stromafluid containing enzymes necessary for
  carbon fixation

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Energy Transfer in Cells

• Cellular respiration
• releases energy from food molecules
• most occurs within mitochondria
• two membranes, with inner membrane folded many
  times to form mitochondrial cristae
• food molecules are broken down to create some ATP
  and release CO2 as a waste product

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Cellular Reproduction

• Cell division in prokaryotes
• have a single, circular chromosome
• binary fissionchromosome is duplicated, and cell
  splits into 2 daughter cells

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Cellular Reproduction

• Cell division in eukaryotes
• mitosis(occurs after duplication of all
  chromosomes) nuclear membrane disappears,
  chromosomes separate, and new membranes form to
  make 2 copies
• after mitosis, the cell divides (cytokinesis)

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Levels of Organization

• Cells within a multicellular organism that serve
  1 particular function are grouped into tissues
• Tissues combine into structures called organs
• Groups of organs make up organ systems

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Evolution and Natural Selection

• Evolutionthe process by which populations of
  organisms change over time
• Evolutionary biology investigates
• how and when organisms evolved
• what role the environment plays in determining
  the characteristics of organisms that can live in
  a given area

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Darwin and the Theory for Evolution

• Voyage of discovery
• Darwin traveled on the HMS Beagle for 5 years,
  beginning in 1831
• Darwin read books by geologist Charles Lyell, and
  was influenced by his conclusions
• since geological change is slow and continuous,
  the earth is very old
• slow and subtle changes become substantial when
  they continue for centuries/millenia

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Darwin and the Theory for Evolution

• Formulating a theory for evolution
• Darwin was inspired by Thomas Malthuss essay
  about factors that control the human population
• Darwin developed his hypothesis evolution by
  natural selection to explain why populations
  generally do not exhibit unchecked growth and how
  they change over time
• published in On the Origin of Species by Means of
  Natural Selection

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Darwin and the Theory for Evolution

• Theory of evolution by natural selection
• artificial selection is practiced by farmers to
  obtain desirable traits in plants/animals
• natural selection favors survival and
  reproduction of those organisms best suited to
  their environment
• selective forcesphysical and biological
  characteristics of the environment that favor
  survival of one species over another
• e.g. temperature, salinity, predation, etc.

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Darwin and the Theory for Evolution

• 4 basic premises of Darwins theory
• All organisms produce more offspring than can
  possibly survive to reproduce.
• There is a great deal of variation in traits
  among individuals in natural populations. Many of
  these variations can be inherited.
• The amount of resources necessary for survival is
  limited. Therefore organisms must compete with
  each other for these resources.

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Darwin and the Theory for Evolution

• Those organisms that inherit traits that make
  them better adapted to their environment are more
  successful in the competition for resources. They
  are more likely to survive and produce more
  offspring. The offspring inherit their parents
  traits, and they continue to reproduce,
  increasing the number of individuals in a
  population with the adaptations necessary for
  survival.
• an organism evolves traits that are beneficial,
  as well as traits that are neither harmful nor
  beneficial

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Genes and Natural Selection

• Modern evolutionary theory
• the modern synthetic theory of evolution is
  essentially Darwins 1858 idea refined by modern
  genetics
• genes
• produce traits when genetic information is
  translated into proteins by protein synthesis
• can exist in different forms called alleles
• the offspring receives 1 allele for a trait from
  each parent, producing many possible combinations
  of alleles in the offspring

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Genes and Natural Selection

• Role of reproduction
• in asexual reproduction, offspring are clones of
  the single parent, and variation may only result
  from mutation

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Genes and Natural Selection

• Role of reproduction
• chromosomes from 2 parents are combined in sexual
  reproduction
• gametes (sex cells) unite during fertilization
• gametes have a haploid number (N) of chromosomes
  instead of a diploid number (2N)
• the haploid number of chromosomes from 2 gametes
  combine to form the diploid number

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Genes and Natural Selection

• meiosis (reduction division) is the process
  through which gametes are formed
• chromosomes are duplicated once, and the cell
  divides twice
• results in cells with ½ the number of chromosomes
  in the parent cell
• during the initial phase, chromosomes connect and
  allow crossing over and recombination
• meiosis increases variety by shuffling the gene
  pool

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Genes and Natural Selection

• Population genetics
• organisms must adapt to changing environmental
  conditions to survive
• ability to adapt is limited by the gene pool
• fitness (biological success) is measured by the
  number of an organisms own genes that are
  present in the next generation

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New Species Evolve from Existing Species

• Typological definition of species
• typological definitions are based on morphology,
  the structure and appearance of the organism
• a species as defined this way will have a
  definable set of characteristics different from
  those of other species
• weaknesses of typological definition
• males may look different than females (sexual
  dimorphism) and juveniles than adults
• there may be great variations in appearance
  within a single population (e.g. color)

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New Species Evolve from Existing Species

• Modern species definition
• a species is one or more populations of
  potentially interbreeding organisms that are
  reproductively isolated from other such groups
• reproductive isolationmembers of a different
  species are not in the same place at the same
  time or are physically incapable of breeding, so
  genes from different species are not mixed

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New Species Evolve from Existing Species

• isolating mechanisms that prevent fertilization
• habitat isolationsimilar species of organisms
  live apart and never encounter each other
• anatomical isolationincompatible copulatory
  organs prevent similar species from reproducing
  with one another
• behavioral isolationexhibiting of special
  behaviors during the breeding season, so that
  only members of the same species recognize the
  behavior as courtship

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New Species Evolve from Existing Species

• temporal isolationthe time members of one
  species are ready to reproduce does not coincide
  with the time members of a related species
  reproduce
• biochemical isolationbiochemical or genetic
  differences between the gametes of 2 species
  prevent successful copulation from resulting in
  offspring

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New Species Evolve from Existing Species

• isolating mechanisms that prevent successful
  reproduction following fertilization
• incompatible genes or biochemical differences can
  prevent a fertilized egg from developing
• the hybrid offspring may survive but be infertile
  or poorly equipped to compete (so that it dies
  without reproducing)

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New Species Evolve from Existing Species

• Process of speciation
• allopatric speciation2 or more populations of
  the same species become geographically isolated
• gene flow between the 2 populations stops
• natural selection operates of each segment of the
  original population independently

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Linnaeus and Biological Classification

• Binomial system of naming
• binomial nomenclaturesystem of naming that uses
  2 words, the genus and species epithet
• introduced by Swedish botanist Karl von Linné
  (Carolus Linnaeus) in 1750
• e.g. Chaetodon longirostris (long-nose
  butterflyfish) and Chaetodon ocellata (spotfin
  butterflyfish) are both in the same genus

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Linnaeus and Biological Classification

• Taxonomic categories
• Early schemes of classification
• all living things were classified into 1 of 2
  kingdoms, Animalia and Plantae, until 1960s
• Modern classification
• major categories domain, kingdom, phylum, class,
  order, family, genus, and species
• domains Archaea, Eubacteria, Eukarya
• kingdoms Eukarya contains 3 kingdoms, Fungi,
  Plantae and Animalia
• protistseukaryotic organisms that do not fit the
  definition of animal, plant or fungus

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Archaebacteria live in extreme conditions
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Sand-dwelling marine fungus (Corollospora)
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