Unit 4 Study Guide DNA
Griffith: was trying to learn how bacteria make people sick. He wanted to learn how
certain types of bacteria cause pneumonia.
During his experiment he mixed heat killed pneumonia causing bacteria with a strain of
harmless bacteria and discovered that some factor is transferred between the two types to
cause pneumonia.
Oswald Avery and others: wanted to discover what was the transforming factor in
Griffith’s experiment. Used a series of enzymes that destroyed carbohydrates, proteins,
lipids (fats), RNA, and DNA. When DNA was destroyed by enzymes, transformation did
not occur. Therefore DNA is the transforming factor.
Alfred Hershey and Martha Chase: wanted to discover if Protein or DNA was the
transforming factor in Bacteriophage Viruses. They radioactively labeled Phosphorus (P32) and Sulfur (S-35) and found Phosphorus within the Bacteria. Since Phosphorus is a
component of DNA and not protein, DNA was labeled as the transforming factor.
Bacteriophage – virus that destroys bacteria
Rosalind Franklin: worked with Maurice Wilkins - used x-ray diffraction photography
to provide an “X” shaped image. This led to two clues about DNA. DNA molecules are
twisted (helical), and their large groups of molecules are spaced at regular intervals
Erwin Chargaff: discovered that within a segment of DNA, the amount of Adenine is
always equal to the amount of Thymine and the amount of Cytosine is always equal to
the amount of Guanine. He did not know that Adenine always paired with Thymine and
that Cytosine always paired with Guanine.
James Watson and Francis Crick: used the work of Erwin Chargaff, Maurice Wilkins,
and Rosalin Franklin to build a 3-D model of DNA. The model was universally accepted
immediately since it explained how DNA replicated.
DNA – Deoxyribonucleic acid
o DNA is a double stranded twisted molecule; double helix, twisted ladder
o The sides of each strand or ladder are composed of alternating sugar
(deoxyribose) and phosphate. The “rungs” or “steps” of the ladder are composed
of nitrogenous bases; adenine paired with Thymine and Guanine paired with
Cytosine.
o DNA is a polymer which is composed of many monomers called Nucleotides
o Nucleotides are composed of three parts: sugar, phosphate, and nitrogenous base
o DNA Sugar: Deoxyribose
o DNA N-Bases – A, T, C, G (A pairs with T; C with G)
o DNA is double stranded and referred to as a double helix or twisted ladder
RNA – Ribonucleic Acid
o RNA is a single stranded molecule
o RNA is a polymer which is composed of many monomers called Nucleotides
o Nucleotides are composed of three parts: sugar, phosphate, and base
o DNA Sugar: Ribose
o DNA N-Bases – A, U, C, G (A pairs with U; C with G)
o There are three types of RNA: mRNA, tRNA, and rRNA
o mRNA is messenger RNA; carries DNA message from DNA to Ribosomes
o tRNA is transfer RNA; transfers Amino Acids to Ribosomes
o rRNA is ribosomal RNA; composes Ribosomes
o Ribosomes are the site of protein synthesis; site of Translation
DNA Replication – the process of copying DNA; occurs in the nucleus
Transcription – the process of using DNA nucleotides to create the correct order of
mRNA nucleotides; occurs in the nucleus. mRNA then leaves the nucleus to go to the
ribosomes
for
translation
Translation – the process of using mRNA to create the correct order of Amino Acids in
proteins. Also known as protein synthesis. Occurs on a ribosome
Codon – a group of 3 mRNA nucleotides that code for a specific amino acid
Anticodon – a group of 3 tRNA nucleotides that are opposite of a codon
There are 64 codons that code for 20 different amino acids.
Hundreds to thousands of amino acids may link together to form a protein. This means
there are literally millions of possible proteins that can be created from just 20 amino
acids.
Amino acids are held together by peptide bonds. Proteins are also called polypeptides
(poly = many, amino acids = peptides)
Levels of Classification:
Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
Genus and Species are used in binomial nomenclature to create a scientific name for an
organism
Eukaryote – organism that has a “true nucleus.” Includes members of the following
Kingdoms: plants, animals, fungi, and protists
Prokaryote – organism that does not have a nucleus. Includes two Kingdoms of
bacteria: Archaebacteria and Eubacteria. Archae = ancient. Archaebacteria are believed
to be the first organisms to live on earth
Autotroph – (Producers) – organisms that create their own food. For example, plants
are photosynthetic and make their own food from the sunlight
Heterotroph – (Consumers) – organisms that must eat other things to get their energy
Organisms are classified based on their similarities in appearance, DNA, RNA, and
proteins.
Evolution – the gradual change in species of organisms over time
Gene – a segment of DNA on a chromosome that codes for a specific protein
Gene Mutation –
Mutation – change in DNA
Mutagen – something that causes DNA to mutate
Point Mutation – change in one DNA nucleotide within a sequence
Frameshift Mutation – a change in DNA that changes the codon reading frame
Substitution – the replacement of a single nucleotide by a different nucleotide
Insertion – adding a nucleotide within a sequence
Deletion – removing a nucleotide from a sequence