Cheat Sheet

Fall Biology

Table of contents

Terms and Concepts
Core Ideas
Meiosis and Mitosis
1. Meiosis vs Mitosis Table
2. Meiosis vs Mitosis Diagram
Important Experiments

Terms and Concepts

DNA Replication

Term	Definition
Chromosome theory of inheritance	Proposed that chromosomes contain genes.
Nitrogen 14	Normal nitrogen; used in the Meselson-Stahl experiment to distinguish parent strands from daughter strands.
Nitrogen 15	Heavy nitrogen with one more neutron; used in the Meselson-Stahl experiment to distinguish parent strands from daughter strands.
5’ to 3’ Direction	The direction in which DNA is synthesized.
Antiparallel strands	Strands of DNA that lie opposite each other.
Complementary base pairing	Base A matched with base T, base G matches with base C.
Density gradient centrifugation	Separates molecules based on their density. Lower-density molecules cluster in bands high in the centrifuge tube, higher-density molecules cluster in bands lower in the tube.
dNTP	DNA synthesis requires an input of energy, but potential energy of deoxyribonucleotide monomers is raiased by reactions tha add two phosphate groups, forming deoxyribonucleotide triphosphates (dNTPs). dNTP has high potential energy; forms phosphodiester bonds in DNA strand.
Discontinuous Replication	Proposed to explain how lagging strand was synthesized. Primase synthesizes new RNA primers for lagging strands as the moving replication fork opens single-stranded regions of DNA; DNA polymerase syntheses short DNA fragments from these primers. Fragments linked to form a continuous strand.
Lagging strand	The strand that runs opposite to the direction in which the replication fork is moving. This causes a lag.
Continuous strand	The strand that moves in the same direction as the replication fork.
Okazaki fragments	Short DNA fragments attached to RNA primers produced by the lag of the lagging strnad.
Origin of Replication	A sequence of bases that indicates the start of a replication bubble, in which two replication forks move in opposite directions to separate the DNA strand.
Replisome	Proteins and enzymes work in a macromolecular machine called the replisome. Replisome may contain up to three copies of DNA polymerase III.
RNA polymerase	A polymerase that can start synthesis from scratch. Primase is a RNA polymerase (enzymes that catalyze polymerization of ribonucleotides into RNA).
RNA primers	Because DNA polymerase cannot synthesize new nucleotides on its onw, but RNA polymerase (for example, primase) can. This is used to initiate building, and is later removed by DNA polymerase I.

Transcription and Translation

Term	Definition
mutation	The altering of genes of chromosomes in some sort of way.
codon	A group of three nucleotide bases that specifies an amino acid.
fitness	In the context of transcription and translation, the ability for a gene expression to positively impact the phenotype such that the genotype gets passed down to another generation.
frameshift	Mutations that shift the reading frame. These are usually point addition or deletions that affect the position of every base after it.
gene expression	The process by which gene information is used to produce a gene product.
genetic code	The mapping of each codon to an amino acid.
messenger RNA (mRNA)	The form of RNA used to carry information from the DNA in the nucleus to the ribosome in the cytoplasm to produce proteins.
mutants	Genes whose sequence or chromosomes that have been altered in some sort of way.
reading frame	The sequence of codons, the sequence broken down into groups of three beginning at the start codon and ending at the end codon.
RNA polymerase	A polymerase that can synthesize RNA without a primer, unlike DNA polymerase.
start codon	A codon that indicates when protein synthesis should begin. This is `AUG`.
stop codon	Indicate when protein synthesis should stop. There are three: `UAA`, `UAG`, and `UGA`.
transcription	The transferring of genetic information from DNA to forms of RNA.
translation	The transferring of information from RNA to proteins.
translocation	A chromosomal error in which a broken piece of a chromosome is attached to a different chromosomes.
triplet code	A three-base code (forming codons).
3’ poly(A) tail	Enzyme cuts the 3’ end of the pre-MRNA after the poly(A) signal, and specialized RNA polymerase adds 100 to 250 adenine nucleotides, forming this. It is not encoded by the DNA template strand, yet required for ribosomes to start translation and to protect the end of mRNA from attack by enzymes.
5’ cap	An added cap consisting of odified guanine nucleotide linked to transcript in an unusual way when the 5’ end of pre-mRNA emerges. Enables ribosomes to bind to the mRNA and protects the 5’ end of the mRNA from enzymes that degrade RNA (ribonucleases).
aminoacyl tRNA	THe amino acid attached to the transfer RNA.
aminoacyl/A site	The first site an aminoacyl tRNA diffuses to in ribosomal protein synthesis. If its anticodon matches the codon in mRNA, it stays in the ribosome.
anticodon	The codon attached to tRNA that is the base-pair complement of a codon in the mRNA. For example, the anticodon of `AAA` is `UUU`.
AUG codon	The one start codon.
coding strand	The strand opposite to the one used during transcription to build the complementary pre-mRNA strand (template strand). The transcripted pre-mRNA is synthesized in the same direction as the coding strand.
downstream	The RNA polymerase moves in this direction when moving along the DNA.
elongation	Occurs after RNA polymerase leaves the promoter region as it synthesizes RNA, during which the enzyme reads the DNA template on the 3’ end at a rate of 50 nucleotides per second.
exit/E site	The last of three sites through which tRNA passes through, in which the uncharged tRNA is ejected from the ribosome after dropping off its amino acid.
exons	Regions that are transcribed and represented in final RNA (expressed in mature DNA).
introns	Regions of a gene that are transcribed but not represented in the final RNA.
peptidyl/P site	The second of three sites through which tRNA passes through, in which the amino acid attached to a tRNA forms a peptide bond with the existing polypeptide.
phosphorylation	The introduction of phosphate groups after a protein has been synthesized, which drastically increases the activity of the protein.
polyribosomes	Formed in bacteria when ribosomes attach to mRNA and begin synthesizing proteins before transcription was complete. Polyribosomes increase the number of copies of a protein that can be made from single mRNA.
pre-mRNA	Eukaryotic genes initially copied from nonfunctional RNAs. Same as ‘primary RNA transcript’.
primary RNA transcript	Eukaryotic genes initially copied from nonfunctional RNAs. Same as ‘pre-mRNA’.
promoters	Sites where transcription should begin.
protein folding	Impacts how the protein functions. Folding is often facilitated by molecular chaperones.
ribosomal RNA	Combined with proteins, these make up ribosomes. rRNA is found in ribosomes and constitutes most of the active site of ribosomes, which are considered ribozymes.
ribosome	A component of the cell outside of the nucleus that is responsible for reading mRNA and synthesizing an appropriate protein.
RNA processing	Is used to convert primary transcripts (pre-mRNA) into mature and functional RNA.
RNA splicing	Is the removal and rejoining of introns from a transcription. Done with snRNPs (small nuclear ribonucleoproteins).
spliceosomes	An aggregate macromolecular machine consisting of snRNPs (small nuclear ribonucleoproteins).
template strand	The strand used during transcription to build the complementary pre-mRNA strand.
termination	The termination of a process is when it ends.
transfer RNA (tRNA)	tRNA is the ‘intermediate’ step between mRNA and amino acids. Each tRNA has an amino acid has on the 3’ end of the molecule a site for amino acid attachment and on the opposite side an anticodon to attach to the mRNA.
upstream	DNA is upstream of the point of reference. The RNA polymerase moves in the opposite direction of this when moving along the DNA.
wobble hypothesis	Most amino acids are specified by more than one codon. Codons for the same amino acid often have the same nucleotides for the first and second positions but different nucleotides in the third position. Certain bases bind to bases that do not match Watson-Crick base pairing, producing flexibility (‘wobble’) in base pairing. This allows tRNA to read more than one codon. Wobble pairing does not account fo redundancy.

Cellular Respiration

Term	Definition
Glycolysis	Means “breaking up glycose” (glycol = glycose, ysis = break up). Breaks up the glucose from a 6-carbon molecule (e.g. `C-C-C-C-C-C`) into two (`C-C-C` and `C-C-C`). Is the first process in cellular respiration. Releases 4 ATP and requires 2 ATP (net releases 2 ATP). Is an anaerobic process (does not need oxygen).
Glucose	A sugar (`glucose = gluc (sweet) + ose (sugar)`) in which carbohydrates are decomposed into. This is converted via cellular respiration into ATP.
ATP	Abbreviated for adenosine triphosphate, ATP is a fundamental unit of energy in cells. Its energy is stored in chemical bonds between a phosphate group; this is released when one phosphate detaches and ATP becomes ADP (adenosine diphosphate).
Pyruvate	The two 3-carbon molecules that result when glycolysis breaks down the 6-carbon glucose. Pyruvate is later converted into acetyl-CoA in acetyl-coenzyme A synthesis.
Citric Acid	Another name for the Krebs cycle.
Krebs Cycle	Each molecule of acetyl-CoA is metabolized; energy is released via electrons, which are used in the electron transport chain. Produces an additional 2 ATP and is an aerobic process (needs oxygen).
Acetyl CoA	The molecule pyruvate is converted to in acetyl-coenzyme A synthesis. This is later used in the Krebs cycle.
Electron transport chain	A series of proteins that electrons are moved through; hydrogens and electrons are removed from `NADH` and `FADH2` electron carriers for ATP synthesis.
`NAD+`/`NADH`	An electron carrier; oxidized form is `NAD+` (is not carrying electrons) and reduced form is `NADH` (is carrying electrons). Will transition between these two states throughout cellular respiration.
`FAD`/`FADH2`	An electron carrier; oxidized form is `FAD` (is not carrying electrons) and reduced form is `FADH2` (is carrying electrons). Will transition between these two states throughout cellular respiration.
Respirometer	A respirometer is composed of a vial and a volume of air. It measures the rate of consumption of oxyugen of a living organism.

Meiosis

Term	Definition
asexual reproduction	Reproduction in which the offspring’s genetic data is the exact same as their parent’s genetic information.
autosomes	Chromosomes that are not sex chromosomes (like `X` and `Y` 23rd chromosomes in humans).
centromere	The region of a chromosome to which the microtubules of the spindle attach, via the kinetochore, during cell division.
crossing over	During prophase I, non-sister chromatids of homologous chromosomes exchange parts of their DNA at the same spots. This promotes genetic variation.
daughter cell	The cell produced by a parent cell.
diploid cell	A cell with two versions of each chromosome. These are our somatic (body) cells.
haploid cell	A cell with only one version of each chromosome. These are our sex cells (sperm and egg).
ploidy	The number of chromosome sets. Diploid cells have a ploidy of 2, haploid cells have a ploidy of 1. This is the coefficient of n when describing chromosome count.
genetic recombination	The creation of new combinations of alleles.
homologous chromosomes	Chromosomes that are the same size and shape, and contain the same genes at the same location.
independent assortment	A phenomenon in which homologous chromosomes line up in meiosis I irrespective of what other chromosomes are. This allows for different combinations of alleles.
unreplicated chromosome	A chromosome that has not yet been replicated.
replicated chromosome	A chromosome that has been replicated, meaning that it consists of two chromatids, each the size of an unreplicated chromosome.
homologous pair	A pair of chromosomes that are homologous. (see homologous chromosomes)
maternal and paternal chromosomes	Chromosomes that come from the mother and the father, respectively.
meiosis	The process by which four haploid daughter cells are generated from one diploid parent cell.
non-sister chromatids	Chromatids in a chromosome from different homologs.
reduction division	Meiosis I is a reduction division operation in that the number of chromoomes goes from 2n to n. Meiosis II is not so because the number of chromosomes goes from n to n, although the absolute quantity of DNA decreases.
sex chromosomes	The chromosomes that determine the offspring’s ex.
sperm	The male sex cell.
zygote	The cell fromed by the union of the sperm and egg.
egg	The female sex cell.
gamete	A haploid sex cell.
sexual reproduction	Reproduction that requires the union of two gametes.

Core Ideas

Chemistry, Origin of Life, Nucleic Acids

Chemical Foundation of Life Terms and Concepts

Term	Definition
Atom	the smallest identifiable unit of matter.
Element	a substance that consists entirely of a single type of atom.
Isotope	forms of an element with different numbers of neutrons.
Atomic Number	characteristic number of protons in an atom.
Mass Number	sum of protons and neutrons in an atom.
Covalent Bond	when two atoms share electrons, and the connected atoms form a molecule. Make the atoms more stable, often complete shells.
Compound	atoms of different elements are bonded together.
Electronegativity	when atoms of different elements bond, they may pull electrons towards their nuclei with different strengths.
Nonpolar Covalent Bond	a bond that involves equally shared electrons.
Polar Covalent Bond	a bond that involves assymetrically shared electrons.
Ionic Bond	electrons in ionic bonds are completely transferred from one atom to another.
Solvent	an agent for dissolving, or getting substances into solution.

Two Theories

Theory	Process
Prebiotic Soup Model	Simple molecules like `N2`, `NH3`, and `CO` were present in the atmosphere of ancient earth. Energy in sunlight drove reactions among simple molecules to produce molecules like `formaldehyde` and `hydrogen cyanide`. Stimulated by heat, the products formed more complex molecules like `ribose`, `glycine`, and `acetaldehyde`.
Surface Metabolism Model	Simple molecules like `N2`, `NH3`, and `CO` were present in early oceans and hydrothermal events. Vent minerals catalyzed spontaneous reactions among high-energy molecules to produce, for instance, `acetic acid`. Concentration and heat formed more complex molecules like ribose.

RNA vs DNA Levels of Structure

Level of Structure	DNA	RNA
Primary	Sequence of deoxyribonucleotides: bases are A, T, G, C	Sequence of ribonucleotides: bases are A, U, G, C
Secondary	Two antiparallel strands twist into a double helix, stabilized by hydrogen bonding, hydrophobic bonding, hydrophobic interactions, and van der Waals interactions	Single strand folds back on itself to form a double-helical ‘stem’ and an unpaired ‘loop’.
Tertiary	Double helical DNA forms compact structures by wrapping around histone proteins or twisting into supercoils.	Secondary structures fold to form a wide variety of distinctive three-dimensional shape.

3 DNA Replication Hypotheses

Hypothesis	Description
Semiconservative replication	If parental strands of DNA separate, each could be used as a synthesis of a new daughter strand. Each daughter DNA molecule consists of one old strand and one new strand. Conserves only one of the strands.
Conservative replication	If bases of strands turned out from the helix, they could serve as a template for an entirely new double helix all at once.
Dispersive replication	Parental double helix was fragmented into small pieces before replication, and each piece was replicated either with conservative or semiconservative mechanisms. Fragments would be joined into two molecules that contained a mixture of parental and daughter strands.

Proteins

Protein Levels of Structure

Level of Structure	Description	Stabilized by
Primary	Each protein has a unique primary structure, determined by the number and sequence of amino acids, making up the polypeptide chain. 20 amino acids are used to build proteins. Various amino acids could be linked in almost any sequence.	Peptide bonds
Secondary	Parts of the polypeptide chain are folded or coiled. For example, forms alpha helix - chain twists forms a helix or beta pleated sheats - chain folds back on itself, or two regions lie parallel. Results from hydrogen bonding between atoms of the polypeptide backbone.	Hydrogen bonding between groups along the peptide-bonded backbone
Tertiary	Superimposed on primary and secondary structure: irregular loops and folds that give the protein its 3d shape. Results from interactions along R groups - hydrophilic or polar `R`-groups may hydrogen bond with each other or turn outwards and bond with surrounding water and hydrophobic or nonpolar `R` groups cluster on the inside of the protein, away from water.	Bonds and other interactions between R-groups or between R-groups and a peptide-bonded backbone; sulfur-containing strong covalent bonds
Quaternary	Some proteins are made up multiple polypeptide chains. Results from combination of two or more polypeptide	Same interactions that stabilize tertiary structure.

Protein Functions and Types

Type	Functions
Structural Proteins	Anchors cell parts; serves as tracks along which cell parts can move. Binds cells together to form muscles, ligaments, etc.
Signal Proteins	Hormonal proteins that coordinate an organism’s activity by acting as a signal between cells.
Transport Proteins	Carry molecules from place to place.
Sensory Proteins	Detect environmental signals like light.
Enzyme Proteins	A protein that changes the rate of a chemical reaction without itself being changed into a different molecule in the process.
Storage Proteins	Stockpile materials used to make other proteins. Store nutrient and energy-rich molecules for later use.
Contractile (Motor) Proteins	Move parts of a cell.
Gene Regulatory Proteins	Bind to DNA in particular locations and control whether certain genes will be read.
Defensive Proteins	Defensive proteins help organisms fight infection, heal damaged tissue, and evade predators.

Proteins Required for Synthesis in Bacteria

Purpose	Name	Function
Opening the helix	Helicase	Catalyzes the separation of DNA strands to open the double helix. Breaks hydrogen bonds.
Opening the helix	Single-strand DNA-binding Proteins (SSBPs)	Stabilizes single-stranded DNA.
Opening the helix	Topoisomerase	Breaks and rejoins the DNA double helix by breaking phosphodiester bonds to relieve twisting forces caused by the opening of the helix.
Leading-strand synthesis	Primase	Catalyzes the synthesis of the RNA primer.
Leading-strand synthesis	DNA Polymerase III	Extends the leading strand.
Leading-strand synthesis	Sliding clamp	Holds DNA in place during strand extention.
Lagging-strand synthesis	Primase	Catalyzes the synthesis of the RNA primer on the Okazaki fragment.
Lagging-strand synthesis	DNA Polymerase III	Extends an Okazaki fragment.
Lagging-strand synthesis	Sliding clamp	Holds DNA polymerase in place during strand extention.
Lagging-strand synthesis	DNA Polymerase I	Removes the RNA primer and replaces it with DNA.
Lagging-strand synthesis	DNA ligase	Catalyzes the jooining of Okazaki fragments into a continuous strand.

Translation, Transcription, and the Genetic Code

Complete Genetic Code Table

Complete Genetic Code

Properties of the Genetic Code

Property	Description
Redundant	All amino acids (except for 2) are coded for by more than one codon. Codons specifying the same amino acid are synonymous codons.
Unambiguous	A given codon never codes for more than one amino acid.
Non-overlapping	Once the ribosome locks onto the first codon, the reading frame is established and the ribosome adds one codon one after another.
Universal	With a few exceptions, codons specify the same amino acids in all organisms.
Conservative	Several codons specify the same amino acid, but the first two bases are usually identical.

If a change in DNA sequence leads to a change in the third position, it is less likely to alter the amino acid in the protein.
Genetic code minimizes the phenotypic affects of small alterations.
- Genetic code not assembled randomly; honed by natural selection and is remarkably efficient.

Types of Point Mutations

Types of point mutations

The 3 Categories of Mutations

Beneficial. Some mutations increase the fitness of an organism.
Neutral. If the mutation has not effect on fitness, it is neutral. e.g. silent mutations.
Deleterious. Most individuals are well-adapted to their current habitat and mutations are random changes in genotype; most mutations lower fitness.

Process of Initiating Transcription in Bacteria

Initiation begins. Sigma binds to the promoter region of the DNA, characterized by the -35 box and the -10 box.
Initiation continues. RNA polymerase opens up the DNA helix and transcription begins. NTPs are used to create the complement of the template strand.
Initiation completes. Sigma is released from the core enzyme and RNA synthesis continues. The RNA polymerase moves downstream along the DNA.

Process of Ending Transcription in Bacteria

Hairpin forms. RNA polymerase transcribes a transcription-termination signal, which codes for RNA that forms a hairpin.
Termination. The RNA hairpin leads to the RNA separating from RNA polymerase, terminating transcription.

Processed mRNA Strand Diagram

Process of Protein Synthesis in Ribosomes

Aminoacyl tRNA diffuses into the A site. If its anticodon matches a codon in mRNA, it stays in the ribosome.
A peptide bond forms between the amino acid held by the aminoacyl tRNA in the A site and the growing polypeptide in the P site.
The ribosome moves relative to the mRNA by one codon. All three tRNAs are shifted one position within the ribosome.
- tRNA in E site exits.
- tRNA in P site moves to the E site.
- tRNA in A site switches to P site.
- A site is empty and ready to accept another aminoacyl tRNA.

Process of Initiating Translation in Bacteria

mRNA binds to a small subunit. A sequence in mRNA called the ribosome binding site binds to a complementary seuqnece in an RNA molecule, which is part of the small subunit of the ribosome. This is helped by initiation factors.
Initiator aminoacyl tRNA binds to the start codon. This usually carries f-Met.
The large subuit of the ribosome binds, completing the ribosome assembly; translation can begin.

Process of Elongation Phase of Translation

Incoming aminoacyl tRNA moves into the A site. Its anticodon base pairs with the mRNA codon.
Peptide bond formation. The amino acid attached to the tRNA in the P site is transferred by formation of a peptide bond to the amino acid of the tRNA in the A site.
Translocation. The ribosome moves one codon down the mRNA with the help of elongation factors. THe tRNA attached to the polypeptide moves into the P site. The A site is empty.
Incoming aminoacyl tRNA. A new charged tRNA moves into the A site, where its anticodon base-pairs with an mRNA codon.
Peptide-bond formation. The polypeptide chain attached to the tRNA in the P site is transferred by peptide bond formation to the aminoacyl tRNA in the A site.
Translocation. THe ribosome moves one codon down the mRNA. The tRNA attached to the polypeptide chain moves into the P site. Uncharged tRNA from P site moves to the E site, where tRNA is ejected. The A site becomes empty again.

Process of Terminating Translation

Release factor binds to stop codon. When the translocating ribosome reaches a stop codon, a protein release factor fills up the A site and breaks the bond linking tRNA to the polypeptide chain.
Polypeptide and uncharged tRNA are released.
Ribosome subunits separate. They are ready to attach tot he start codon of another message.

Complete Process of the Central Dogma

Through transcription, DNA stored in the nucleus of the cell is used via RNA polymerase to create pre-mRNA.
Through RNA processing, the primary transcript (pre-mRNA), through which introns are removed and caps & tails are added to produce mature mRNA.
Outside of the nucleus in the cytoplasm, the mature mRNA is translated to produce a polypeptide.
Post-translational modifications, including folding, glycosylation, and phosphorylation are made to make the polypeptides formed by translation functional.

Central Dogma in Bacteria vs Eukaryotes

Process	Aspect	Bacteria	Eukaryotes
Transcription	RNA polymerase	One	Three, each produces a different class of RNA.
Transcription	Promoter structure	Contains a -35 box and a -10 box	Variable and larger, often includes a TATA box about -30 from the transcription start site.
Transcription	Proteins that associate with promoter	Sigma and variants	General transcription factors
RNA processing		Rare	Extensive, several steps occur before RNA is exported to the cytoplasm.
Translation	Initiation and termination	Less complex	More complex
Translation	Elongation	Similar to eukaryotes	Similar to bacteria

Cellular Respiration

Process Input Output Table and Chemical Equation

Process	Starting Material	Net Energy Output
Glycolysis	1 Glucose	2 `NADH`, 2 ATP
Acetyl-CoA Synthesis and the Krebs Cycle	2 Pyruvate	8 `NADH`, 2 `FADH2`, 2 ATP
Electron-Transport Chain	10 `NADH`, 2 `FADH2`	32 ATP

Chemical Equation:

C6 H12 O6 + 6O2 ➡️ 6CO2 + 6H2O + Energy (36-38 ATP)

Cellular Respiration Diagram

Meiosis and Mitosis

Meiosis vs Mitosis Table

Meiosis vs Mitosis Diagram

Important Experiments

Miller-Urey Experiment

Aspect	Description
Question	Can simple molecules and kinetic energy lead to chemical evolution?
Hypothesis	Chemical evolution of organic molecules will occur in environments simulating early Earth conditions.
Null Hypothesis	Chemical evolution will not occur in early Earth simulations.
Prediction of Hypothesis	If kinetic energy is added to a mix of simple molecules, complex organic compounds will be produced.
Prediction of Null Hypothesis	No complex organic compounds will be produced.
Results	Samples from solution contained formaldehyde, hydrogen cyanide, and several complex compounds with C=C bonds, like amino acids (e.g. glycine).
Conclusion	Chemical evolution occurs readily if simple molecules with high free energy are exposed to a source of kinetic energy.
Significance	Paved the idea for foundation for ideas of chemical evolution and sparked further experiments.

Griffith Experiment

Aspect	Description
Question	Can bacteria transfer genetic information through transformation?
Hypothesis	Bacteria can transfer genetic information through tranformation.
Null Hypothesis	Bacteria do not transfer genetic information through tranformation.
Experimental Setup	Take four types of strains: rough strain (virulent), smooth strain (virulent), heat-killed smooth strain, and mix of rough strain and heat-killed smooth strain. Inject strains into mice and see if they live or die.
Prediction of Hypothesis	If bacteria can transfer genetic information through transformation, the mix of rough strain and heat-killed smooth strain will kill the mouse.
Prediction of Null Hypothesis	If bacteria do not transfer genetic information through tranformation, the mix of rough strain and heat-killed smooth strain will kill the mouse.
Results	Mice did not die from the rough strain, did die from the smooth strain, did not die from the heat-killed smooth strain, and did die from the mix of rough strain and heat-killed smooth strain.
Conclusion	There is a ‘transformation principle’ that is allowing the smooth strain, even if it has been killed, to transfer its genetic information to the rough strain to make it become a smooth strain, thus killing the mouse.
Significance	Provided basis for the Avery-MacLeod-McCarty experiment.

Avery-MacLeod-McCarty Experiment

Aspect	Description
Question	What is causing the mix of rough strain and heat-killed smooth strain to kill the mouse in the Griffith Experiment?
Hypothesis	The DNA in the heat-killed smooth strain is transfering genetic information and ‘corrupting’ the rough strain to kill the mouse.
Null Hypothesis	Some other aspect of the heat-killed smooth strain (i.e. proteins) is killing the mouse.
Experimental Setup	Perform chemical actions to isolate parts of the mix of rough strain and heat-killed smooth strain. Mix each part with the rough strain, inject it into the mouse, and see if it lives or dies. Analyze the part that causes the mouse to die.
Prediction of Hypothesis	If DNA in the heat-killed smooth strain is transfering genetic information, the part that kills the mouse will be DNA.
Prediction of Null Hypothesis	Some other aspect of the heat-killed smooth strain is killing the mouse, the part that kills the mouse will not be DNA.
Results	When analyzing the ratios of nitrogen in the part that killed the mouse, it was confirmed that the part was DNA, not proteins.
Conclusion	DNA is responsible for the transfer of genetic information.
Significance	Was part of a growing field of research that proposed DNA, not proteins, held genetic information.

Herschey-Chase Experiment

Aspect	Description
Question	Do viral genes consist of DNA or protein?
DNA Hypothesis	T2 virus genes consist of DNA.
Protein Hypothesis	T2 virus genes consist of protein.
Experimental Setup	Label viruses (grow one set of TS w/ radioactive DNA and radioactive protein). Infect bacteria. Agitate cultures. Centrifuge solutions and force cells into pellet. Record location of radioactive labels.
Prediction of DNA Hypothesis	Radioactive DNA will be located within the pellet of the centrifuge.
Prediction of Protein Hypothesis	Radioactive protein will be located within the pellet of the centrifuge.
Results	Radioactive DNA is in pellet. Radioactive protein is in solution.
Conclusion	T2 virus genes consist of DNA.
Significance	Proved that heritable information takes the form of DNA, not proteins.

Meselson-Stahl Experiment

Aspect	Description
Question	Is replication semiconservative, conservative, or dispersive?
Hypothesis 1	Replication is conservative.
Hypothesis 2	Replication is semiconservative.
Hypothesis 3	Replication is dispersive.
Experimental Setup	Grow E. coli cells in medium with `15_N` (heavy nitrogen, see DNA Replication Terms and Concepts). Transfer cells to medium with `14_N` (regular nitrogen). Let the cells divide twice (total 3 generations). Centrifuge the three samples separately. Compare locations of DNA bands.
Prediction 1	After two generations: 1/2 low-density DNA, 1/2 intermediate-density DNA.
Prediction 2	1/4 high-density DNA, 3/4 low-density DNA.
Prediction 3	All intermediate-density DNA.
Results	After 2 generations, 1/2 low-density DNA and 1/2 intermediate-density DNA.
Conclusion	Replication is semiconservative.
Significance	Proved that, in accordance with Watson and Crick’s suspicions, that DNA replicated by splitting down the middle and using each half as a template. Thus, each DNA is half-old and half-new.

Srb-Horowitz Experiment

Aspect	Description
Question	What do genes do?
Hypothesis	Each gene contains information needed to make one enzyme.
Null Hypothesis	Genes do not have a one-to-one correspondence with enzymes.
Experimental Strategy	Produce mutants unable to synthesize arginine, then test different steps in the mtabolic pathway for synthesizing arginine.
Experimental Setup	Isolate Neurospora crassa that cannot synthesize arginine in four environments: no supplement, supplemented with only ornithine, supplemented only with citrulline, supplemented only with arginine
Prediction of Hypothesis	There will be 3 distinct types of mutants corresponding to defects in enzyme 1, 2, and 3 in the pathway for synthesizing arginine. Each mutant will be able to grow on different combinations.
Prediction of Null Hypothesis	There will not be a simple correspondence between a particular mutation and a particular enzyme.
Results	Three types of mutants arg1, arg2, arg3. They are able to grow in the metabolic pathway from orthinine, citrulline, and arginine, respectively. arg1 cells lack enzyme 1 from precursor to orthinine, arg2 cells lack enzyme 2 from orthinine to citrulline, etc.
Conclusion	The one-gene, one-enzyme hypothesis is supported.

Zamecnik et al Experiment

Aspect	Description
Question	What happens to amino acids attached to tRNAs?
Hypothesis	Aminoacyl tRNAs transfer amino acids to growing polypeptides.
Null Hypothesis	Aminoacyl tRNAs do not transfer amino acids to growing polypeptides.
Experimental Setup	Attach radioactive leucine molecules to tRNAs. Attach aminoacyl tRNAs to an in vitro system that allows protein synthesis. Follow the path of radioactive amino acids.
Prediction of Hypothesis	Radioactive amino acids will be found in the polypeptides.
Prediction of Null Hypothesis	Radioactive amino acids will not be found in the polypeptides.
Results	Radioactive signal of tRNA and polypeptides are inversely proportional to each other. When there is low radioactive signal in tRNA, there is high radioactive signal in the polypeptides, and vice versa.
Conclusion	Aminoacyl tRNAs transfer amino acids to growing polypeptides.