Explain how the H1N1 virus evolved, the global response, and the dangers of influenza viruses over the past 100 years.
H1N1 evolved from influenza crossed with an Asian swine flu virus, WHO declared it a pandemic and it was treated effectively. Influenza causes high numbers of deaths, particularly in very young, old, or sick people.
Explain what was and was not known about DNA by the early 1950s.
1950s
- Known: DNA is a chemical in cells, it can store genetic information, and it is passed down generation to generation.
Describe and compare the chemical compositions of DNA and RNA.
Both DNA and RNA are nucleotides and both contain the nitrogenous bases cytosine, adenine, guanine
- DNA: sugar is deoxyribose, includes thymine, double helix
- RNA: includes uracil, single helix
Describe the key features of the overall shape of a DNA molecule. Explain how Watson and Crick determined the structure of DNA.
DNA is a double helix with complementary paired nitrogenous bases (adenine with thymine and cytosine with guanine).
Watson and Crick determined the structure of DNA by using x-ray crystallography data.
Describe the process of DNA replication
- DNA replicates from certain locations within the DNA strand by separating and using the existing strands as templates via DNA polymerases
Define transcription and translation. Explain why the hypothesis “one gene–one enzyme” is not correct.
- transcription, the transfer of genetic information from DNA into an RNA molecule and
- translation, the transfer of information from RNA into a protein.
Explain how the language of DNA directs the production of polypeptides.
Genetic information is transcribed from DNA to RNA, and then translated into polypeptides, which are folded into proteins.
Explain how codons are used to construct polypeptides.
A codon is a triplet of bases. There are 64 triplets. 61 of them code for amino acids, 3 code for stops (to end the polypeptide).
Describe the steps of transcription and the processing of RNA before it leaves the nucleus. (1/4)
“Start Transcribing”
- The “start transcribing” signal is a nucleotide sequence called a promoter, which is
- located in the DNA at the beginning of the gene and
- a specific place where RNA polymerase attaches.
Describe the steps of transcription and the processing of RNA before it leaves the nucleus. (2/4)
“Initiation”
- The first phase of transcription is initiation, in which
- RNA polymerase attaches to the promoter and
- RNA synthesis begins.
Describe the steps of transcription and the processing of RNA before it leaves the nucleus. (3/4)
“Elongation”
- During the second phase of transcription, called elongation,
- the RNA grows longer and
- the RNA strand peels away from its DNA template.
Describe the steps of transcription and the processing of RNA before it leaves the nucleus. (4/4)
“Termination”
- During the third phase of transcription, called termination,
–RNA polymerase reaches a special sequence of bases in the DNA template called a terminator, signaling the end of the gene,
–polymerase detaches from the RNA and the gene, and
–the DNA strands rejoin.
mRNA
mRNA is messenger RNA
- molecule is translated into a protein
tRNA
tRNA is transfer RNA
- acts as a molecular interpreter,
- carries amino acids,
- and matches amino acids with codons in mRNA using anticodons, a special triplet of bases that is complementary to a codon triplet on mRNA.
rRNA
rRNA is ribosomal RNA
- together with proteins forms ribosomes
- ribosomes coordinate the functions of tRNA and mRNA
Describe in detail the process of translation
phase 1/3
“Initiation”
•Initiation brings together
–mRNA,
–the first amino acid with its attached tRNA, and
–two subunits of the ribosome.
•The mRNA molecule has a cap and tail that help the mRNA bind to the ribosome.
Describe in detail the process of translation
phase 2/3
“elongation”
•Elongation occurs in three steps.
–Step 1: Codon recognition. The anticodon of an incoming tRNA pairs with the mRNA codon at the A site of the ribosome.
–Step 2: Peptide bond formation.
–The polypeptide leaves the tRNA in the P site and attaches to the amino acid on the tRNA in the A site.
–The ribosome catalyzes the bond formation between the two amino acids.
–Step 3: Translocation.
–The P site tRNA leaves the ribosome.
–The tRNA carrying the polypeptide moves from the A to the P site.
Describe in detail the process of translation
phase 3/3
“termination”
•Elongation continues until
–a stop codon reaches the ribosome’s A site,
–the completed polypeptide is freed, and
–the ribosome splits back into its subunits.
insertion mutation
Addition of an additional nucleotide into the gene
deletion mutation
subtracting a necessary nucleotide from the gene
substitution mutation
the replacement of one base by another
Explain how mutations can be harmful or beneficial to an organism.
Mutations make natural selection possible. Often, mutations lead to disastrous results and cause damage to the organism. Occasionally, however, they can lead the organism to be better suited to survive.
Compare the lytic and lysogenic cycles of bacteriophages.
Lytic
- many copies of the phage are produced within the bacterial cell, and
- then the bacterium lyses (breaks open).
- Lysogenic
- the phage DNA inserts into the bacterial chromosome and
- the bacterium reproduces normally, copying the phage at each cell division.
Compare DNA and RNA viruses
Plants are only affected by RNA viruses. These viruses have no cure, and are best avoided by producing plants that resist them.
Animals may encounter RNA or DNA based viruses, and they are a common cause of disease amongst animals.
