Biology Midterm 1 Review
Unit 1: Intro to the Cell
Cell Theory: A brief History
Robert Hooke (1635-1703)- invented first microscope and viewed slices of cork (“cellula” which
means little rooms)
Antoni Van Leeuwenhoek (1632-1723)- worked with glass and made huge improvements in the
quality of lenses. Nearly 300x magnification became possible. He was the first to observe single-
celled organisms (animalcule), protists from pond water, sperm, bacteria from his own mouth,
blood cells, banded pattern in muscle cells. Father of microbiology.
Progress of the microscope stalled for a century or so because of limited resolving power and
the emphasis on description rather than explanation.
In the 1830’s the compound microscope was developed with improved magnification and
resolution. It allowed visualization of objects less than one micrometer.
Beginnings of Cell Theory
Robert Brown (1833)- botanist that noticed every plant cell contained a round structure
Matthias Schleiden (1838)- another botanist that discovered all plant tissues are composed of
cells. He discovered that embryonic plants always arose from a single cell.
Theodor Schwann (1839)- was a zoologist that had similar observations in animal cells. He
recognized the structural similarities between plant and animal cells. Formulated Cell Theory.
All organisms consist of one or more cells.
All cells come from pre-existing cells.
The cell is the basic unit of structure for all organisms.
Facts and the Scientific Method
Fact: something we know or believe to be true.
Fact (scientific)- An attempt to state our best current understanding based on observations and
experiments. Valid only until revised or replaced by a better understanding, based on more
careful observations or more discriminating experiments.
What is the Scientific method?
Use inductive reasoning to develop tentative explanation (hypothesis)
Make predictions based on your hypothesis. Make further observations or design and carry out controlled experiments to test your
Interpret your results to see if they support your hypothesis.
What is a theory?
A hypothesis that has been tested under many different conditions and by many different
investigators using a variety of different approaches.
By the time an explanation is regarded as theory it is widely accepted by most sciences as truth.
The “solid ground” of science- ie cell theory, evolution, germ theory
What is more solid than a theory?
If a theory is thoroughly tested and confirmed over many years by such large numbers of
investigators and there is no doubt of its validity, it may become law (ie gravity, gas law)
Strands of Cell biology
Biochemistry, cytology (light microscopy-bright field, phase contrast, Fluorescence microscopy,
electron microscopy- scanning and transmission), and genetics. Scanning allows us to see birds
eye view, transmission allows us to see cross sectional view of structures inside the cell.
Basic properties of cells
Cells are highly complex and organized. (composed of macromolecules, atoms, molecules,
organelles, plasma membrane)
Cells follow the central dogma (DNA synthesis-DNA to RNA to proteins)
Cells are capable of reproducing themselves but must first replicate genetic material
Cells acquire and use energy (glycolysis, krebs cycle) and carry out a variety of chemical
reactions (cellular metabolism)
Cells have many processes that are highly conservative at the molecular level: membrane
structure, genetic code, ATP synthesis, actin filament, etc.
Cells engage in many mechanical activities (transports of materials within cell, assembly &
disassembly of structures, movement of cell)
Cells respond to environmental signals: move away or towards stimuli and respond to
hormones, growth factor, etc.
Cells are capable of self regulation (homeostasis) which is most evident when control systems
break down. Cells can fix defects in DNA replication, DNA repair, and cell cycle control.
Prokaryotes vs. Eukaryotes
Prokaryotes have no membrane bound nucleus. They have “naked” DNA that are single, circular
strands. Prokaryotes have a cell wall and plasma membrane.
Eukaryotes have a membrane bound nucleus. Prokaryotes are the most diverse cell group (ie spherical, rod-shaped, and spiral cells)
Prokaryotes have two domains: eubacteria (all have cell walls except mycoplasma-smallest and
most complex cyanobacteria) and archaebacteria (all have cell walls, extremophiles)
Eukaryotes have four groups: 1) Protists- are a very diverse group. They are mostly single celled,
some are colonies. Protists include algae, slime mold, protozoa, water molds. 2) Fungi- are single
celled (yeast) and multicellular (mushrooms). They have cell walls and are heterotrophs. 3)
Plants- are multicellular autotrophs and have cell walls. 4) Animals- are multicellular
Organelles of Eukaryotes
Cytoplasm: everything between plasma membrane and nuclear membrane. Includes all
membrane bound organelles except the nucleus.
Cytosol: the fluid component of cytoplasm.
Endomembrane system: involved in cells transport- nuclear envelope, endoplasmic reticulum,
golgi apparatus, lysosomes, vacuoles.
Nucleus- stores genetic info
Mitochondria- generate energy to power the cell
Chloroplasts- capture energy from sunlight, convert to carbohydrate (only in plants)
Cytoskeleton: regulates cell shape, movement of materials and organelles within cell,
movement of the cell itself
Transcription (making of mRNA) occurs in nucleus while translation occurs in cytoplasm via
nuclear pore. The mRNA runs through the ribosome and connects amino acids in a sequence
creating a polypeptide chain.
Flow of traffic within endomembrane system: rough ER-synthesis of proteins for export,
insertion into membranes, and lysosomes. Golgi apparatus- collection, packaging and
Lysosomes: cell stomachs- contain enzymes that digest old organelles and material brought in
Mitochondria and chloroplasts contain DNA that encodes some of their own proteins. They have
unusual double layered membranes.
Endosymbiont theory: Eukaryotes engulfed mitochondria (which were aerobic prokaryotic cells) and
some engulfed chloroplasts (which were photosynthetic cyanobacterium). Advantage to host- aerobic
respiration, photosynthesis. Advantage to bacteria- protected environment and a supply of carbon
compounds from host cell’s prey.
Evidence supporting Endosymbiont theory:
Mitochondria and chloroplasts:
Are similar sizes to bacteria, reproduce by fission like bacteria
Have double membranes Have their own ribosomes
Have their own genomes (like prokaryotic genomes)
Organisms used in research
E. Coli- DNA replication, gene transcription and translation
Brewers yeast- cell cycle
Arabidopsis thaliana- all flowering plants closely related
Worm- first animal genome to be sequenced
Mouse- genetics well understood and similar to humans
Unit 2a-Intro to Cellular Chemistry
Chemistry dictates biology- living organisms are complex chemical systems built from inanimate
matter. The chemistry that sustains life must obey the same physical principles as non-living
Cells are made of C, H, N, and O (99%). These elements are combined mostly in macromolecules
that make up cell but are also present in simple forms such as water and carbon dioxide.
Parts of an atom
Nucleus- dense core made of protons and neutrons
Electrons- continually orbit around nucleus
Atomic number=number of protons
Mass number= number of protons +number of neutrons
And isotope of an element has same number of protons but diff number of neutrons
#of protons= #of electrons in a neutral element
Electrons travel around nuclei in orbitals. Orbitals are grouped into layers or shells, based on
how far the electron travels from the nucleus
Electron, Shells, and Valence electrons: innermost shells fill first. Once the first shell is filled (2),
the next shell fills in pairs (8), etc. Outermost valence electrons influence an atoms reactivity.
Unpaired valence electrons determine the number of bonds an atom can make (valence #)
Unpaired valence electrons and reactivity: completely filled valence electrons are non-reactive
(inert gases). Closest to being full are most reactive (Cl, F, O). Elements abundant in living
organisms have at least one unpaired valence electron.
How can atoms achieve full valence shells?- By sharing electrons (covalent bond), or transferring
electrons (ionic bond)-> negatively charged-anion (gained e-), positively charged- cation (lost e-).
Covalent bonds are strongest and the kinds of bonds present in living organisms most of the
Molecule- a group of atoms held together by energy in a stable association.
Compound- molecule composed of two or more different types of atoms.
Polar covalent bonds- electrons are shared unequally b/c one element is more electronegative
than the other. Water is polar, a good solvent, able to form H-bonds. Humans are 70% water.
H-bonding: electrical attraction between electronegative atoms and partial positive charge of H.
Hydrophilic means has an affinity for water, hydrophobic means has no affinity for water. Polar
compounds are hydrophilic.
Dissociation: dissolving into ions in water. Water is not completely stable and dissociates into
H3O+ and OH-.
Short bonds =stronger, longer bonds= weaker. Bond length determined by atom’s properties,
and when repulsive and attractive forces are equal.
Pka: When ph=Pka, species is 50% ionized. When ph>pka, equilibrium lies to the right (ionized
form dominates). When ph