DNA history,relication, transcription and translation Flashcards
Why do scientist though proteins were more likey DNA material
Proteins were made of 20 amino acids and give different codes
Griffith’s Transformation experiment, 4 step, what it told us
s.pneumonia strains smooth cells (s) with a slime layer coating and rough cells (r) without coating
experiment:
take s cells, inject to mouse, muse dies from pneumonia
take r cell, inject t mouse, sick mouse lives
take heat killed s cells, inject to mouse, sick mouse lives
take dead s cell ad living r cells, inject to mouse, mouse dies and find living smooth cells
tells us about horizontal gene transfer, dead s cells were transformed.
hershy and chase
Radioactive sulfur (give radioactive protein) and phosphorus (give radioactive DNA)
when phages infected, DNA lit up.
esult: genetic material was fund to be radioactive. Confirmed DNA is the genetic material passed, not proteins.
Avery McacLeod and McCarty 3 steps and result
Heat killed strep cells with only RNAm DNA, and Proteins
added enzymes to digest one of each of those 3 and insert it into R cells
only transformation when DNA was in the R cell.
told us: transformation requires DNA
Watson and Crick- what were the 3 main competing models? what was their model and how did it fit with Chargoff’s rule?
Semi-conservative - strands separate, each being a template for new strand synthesis. One template one new strand.
dispersive: two template strands, each mixed with new DNA.
conservative. After replication, two template strands come together and two new Dna strands come together. Each is it’s own.
Watson and crick suggested the semi-conservative. the structure of DNA- has a double helix, with phosphate backbone, and nitrogenous bases facing inside (CR)
Bases are equal in amount to each other
How did Meselson and Stahl (1958) identify the correct model? And which one was it?
- Bacteria grown in heavy nitrogen and bacteria grown in lighter nitrogen
- Cells grown in heavier media, transferred to light media and allowed one generation to produce. A second generation was later produced.
- Generally, 3 results could occur: conservative, dispersive, or semi-conservative.
- Able to tell which is which by looking at combinations of bands
- 1 band in the first replication, two bands in second generation (semi-conservative)
Topoisomerase
Reduces supercoils when being unwind
Helicase
Separates two stands by breaking apart hydrogen bond
SSBP’s
Stabilizes isolated strands. Protect two strands from cleavage and prevents them from snapping back together.
DNA poly 1
removes primer and replaces it wih DNA material
Primase
Adds RNA primers-needed to bigin DNA replication
DNA ligase
spaces in between Okazaki fragments. seals nick after primer is replaced with DNA
DNA POLY 3 . Lagging strand vs leading strand
Will attach to where RNA primer is and adds nucleotides in the 5’ to 3’ directions
Leading strand: RNA polymerase runs in the 5 to 3 direction even though the template runs from 3 to 5. goes along the template. Only needs one primer to continuously add
Lagging strand: will still attach at 5 to 3 direction in the opposite side. Will need more primase for DNA poly III to add nucleotides. Not continuous
Where does energy come from to power DNA synthesis
ATP
What does DNA poly 3 use to power
ATp, GTP, dNTP
How does the current model, the Trombone Model, work for a complete Replication Fork?
Trombone models: lagging strand forms a loop so that the lagging and leading stand replication proteins are in contact of one another
Helicase and DNA poly 3 are in contact
More efficient
Be able to briefly describe how scientists deciphered the genetic code
synthetic mRNA with multiple units of uracil to instruct amino acids to add phenylalanine. Poly U sequence served as a messenger for protein synthesis. Demonstrated that mRNA transcribes genetic information from DNA
Key point of gentic code
aminoa cids are encoded by three nucleotides (codon)
most amino acids have more than one codon
variability comes from third position of the “wobble”
- allows for silent mutations and genetic engineering
is universal
Three codes that dont have assigned amino acid and which one is unambiguous
UAA, UAG , UGA
AUG always codes for Methionine, and UUU for Phenylalanine
Transcription is
gene specific
RNA Polymerase vs DNA polymerase
○ RNA Pol does not require a primer (sort of like Primase in that way – but then it just keeps going)
○ RNA POL utilizes UTP rather than TTP, and NTP’s in general instead of dNTP’s
○ There is Topoisomerase both ahead and behind the RNA POL to relieve or build back in supercoiling.
○ No need for Helicase or SSBP’s
○ Synthesis is still 5’ -> 3’
○ Termination of Transcription in Eukaryotes follows transcription of the AAUAAA sequence known as the Polyadenylation signal.
role of 5’-Cap and 3’-Poly-A tai
- 5 prime cap: modified guanine added to first nucleotide in transcript. Protects transcript from being broken down and help ribosomes attach to mRNA. the pass that allows mRNA out of nuclues
- Poly A tail: Sequence called polyadenylation signal shows up , nuclear proteins chops the rna. Another enzyme adds adnine nucleotided to the cut end and from ploy a tail. Tail makes transcript more stable and help it exported to cytosol
- Both protect mRNA and guide to cytoplasm
5’-Cap and 3’-Poly-A tail are formed,
Poly A
1. RNA poly synthesizing new strand.
2. Codes polyadenylation signal (termination signal)
3. Nuclear proteins bind to RNAP and cut later on in sequence.
4. enzymes add poly a tail
What are the roles of snRNP’s and snRNA’s in the process
Spliceosomes had small nuclear RNA and binds to proteins to form a complex. This complex snRNP identify and remove introns
- snRNA are specific for each protein
