Molecular Genetics Flashcards
(30 cards)
Hershey chase experiment
Solidified the concept of DNA being hereditary material
T2 pages grown in medium containing radioactive phosphorus (only found in DNA) and results were that the infected bacteria when centrifuged, had the p32. Sulfur was not
Griffiths experiment
Trying to develop a strain for bacteria
Two kinds, R (rough w/ no polysaccharide coat) and S (smooth and with)
After mixing R strain with heat killed S strain, he noticed the mice died
Conclusion: transformation is defined as a change in genotype and phenotype due to assimilation of external DNA
Chargaff’s rule
Amount of adenine=amount of thymine
DNA copying direction
New nucleotides are added to the 3’ carbon of the sugar
Enzymes in DNA replication
Helicase: unwind/separate DNA
Single strand binding proteins: holds strands apart
Primase: starts copying process by adding an RNA primer
DNA Polymerase: adds DNA nucleotides beginning at primer
Polymerase II: removes primers and replaces with DNA
Ligase: joins strands together
Function of DNA
DNA codes for genes which are expressed in an organisms genotype and phenotype
Follows three steps:
- Transcription
- RNA processing
- Translation
Redundant code
A protein can be coded for by multiple three-sequence DNA strands with only a change in the last letter
DNA transcription
Occurs in nucleus
RNA polymerase has two duties:
- unwind DNA
- make RNA copy of DNA
To make the copy, polymerase begins imitation and attached to the promoter on the template strand, then begins elongation and adds RNA nucleotides, and finally termination so mRNA can detach
RNA processing
Occurs throughout many steps:
- first, a modified guanosine triphosphate attaches to the 5 prime end to make a 5’ cap, which tells ribosome to attach here to begin translation
- on the other end, a poly a tail is added to keep mRNA from getting hydrolyzed
- introns or “intervening sequences” are removed from the coding segment by spliceosomes, which are made of “snurps”
Order of segments on RNA strand
5' cap Leader Start codon Coding segment (exons) Stop codon Trailer (has termination signal) Poly a tail
Protein synthesis
At initiation, a small ribosomal subunit binds to the mRNA at the start codon, AUG. A tRNA molecule with methionine and the anticodon, AUC, also binds to the mRNA at the same place
A large ribosomal subunit attaches to the mRNA at its “p” site which is in the center. So far, an initiation complex had formed
Next phase is elongation, which begins when tRNA molecules from the cell approach the complex and match up with the correct codons located at “a” sites to the right. Up top, peptide bonds are formed between amino acids in a growing chain that leaves from the “e” site.
Termination begins when any of the three stop codons (UAA, UAG, UGA) enters the p site, after which a release factor binds to the a site causing everything to collapse
Point mutations
A change in one or a few base pairs in a gene
Can be divided into Base pair substitutions or base pair insertions/deletions
Base pair substitutions
The replacement of one nucleotide and its partner with another pair
Silent mutations: no effect
Missense mutation: a single amino acid is changed in the resulting protein
Nonsense mutation: change creates a stop codon; protein is nonfunctional
Base pair insertions/deletions
Also called frameshift mutations because a single addition/deletion can cause a complete shift in the reading frame
Can be disastrous by creating amino acids to make a protein that’s really not useful, or harmless (if it adds three)
Viral structure
Protective coat:
- Capsid (made of protein)
- Envelope that cloaks capsid and is made from membrane of host cell
Viral genome
Double stranded/single stranded are both possible
DNA/RNA are both possible
Viral reproduction
For example: (lytic cycle)
T4 phage uses tail fibers to stick to receptor sites on E. coli cell
Phage injects DNA through hole
Cells DNA is hydrolyzed
Phage DNA directs production of phage proteins and DNA
To leave the phage directs production of lysozyme which splits open the cell
In the lysogenic cycle, phage integrates into the bacterial chromosome, and remains dormant for generations until prophage separates and undergoes lytic cycle
Retroviruses
Viruses such as HIV that can make DNA from RNA using reverse transcriptase
Prion
A protein particle that is the cause of brain diseases
Scrapie agent that leads to disease could be a malformed protein
All about bacteria
Chromosome: double stranded circular DNA, located in membrane less “nucleoid”
Plasmids are smaller and more numerous
Asexual reproduction is with binary fission and starts at origin of replication
Bacterial DNA exchange
Transformation (taking up of naked, foreign DNA from surroundings)
Transduction (phage viruses carry genes from one bacterial cell to another)
Conjugation (direct transfer between two cells temporarily joined)
The operon
A mechanism that represses expression of genes needed for a pathway when the end product is too high
Tryptophan operon: e. Coli synthesizes tryptophan in five steps, each step is controlled by an enzyme that is coded by a different gene, all of which lie on the same DNA strand and are controlled by a promoter. The operator is a segment after the promoter, and proteins attach here to act as repressors so the operon is turned off. For the repressor to exist in active form, tryptophan needs to allosterically activate it
The allolactose operon functions the opposite way, with a regulatory gene that produces proteins in their active form, and the end product must inhibit them so the operator is free and the operon can resume production
Transposon
A piece of DNA that can move from one location to another in a cells genome
Two types:
Insertion sequences have the DNA for the transposition, as well as inverted repeats on either side
Composite transposons include more genes than transposase
DNA packaging
Histones are proteins that provide first level of packaging
Nucleosomes are the combo of histones and DNA
