molecular genetics Flashcards
What did Gregor Mendell do?
traits are passed from parents to offspring
What did friedrich micsher do?
Discover “nuclein” (DNA) from looking at pus of wounded soldiers
Avery McCarty, McLoad
Nuclein is genetic material, not proteins as og thought
Erwin chargaf
Discovered nucleic bases and that A pairs with T and C pairs with G
Rosalind Franklin
Discovered theres 2 forms of DNA –> crystal structure
Figured out DNA is a helix first
James Walson and Francis Crick
Stole franklin’s work and published it
Double ringed nucleotides are:
purines, A and G
Single ringed nucleotides are:
Pyramidines, C and T
Structure of a nucleotide (DNA)
Built of deoxyribose sugar, nitrogenous base and phosphate group
- sugar has 5 C, 4 form the ring, the fifth sticks out
- base bonded to 1 prime, phosphate on 5 prime and hydroxyl on 3 prime (2 prime shows if its ribose or deoxy)
- 3 prime hydroxyl bonds nucleotides
Bases attaching
- complimentry bases are attached by hyrdogen bonds
- hydrogen bonds are strong so DNA is stable
- A and T use 2 hydrogen bonds
- G and C use 3 hydrogen bonds
The helix
- Right handed, turns clockwise every 10 nucleotides
- two strands run antiparallel one goes 5–> 3 other goes 3–> 5
What speeds up DNA replication
- DNA replicates semi conserverative meaning they’re half old half new
- Replication goes both way from the origin of replication
DNA replication initiation
- DNA is opened at the replication origin by a group of enzymes, its called a replication bubble
- DNA polymerase 3 enzymes insert in the space between strands. single stranded binding proteins stabilize single stranded DNA, prevent them from reforming their structure
- Helicases unwind the helix just ahead of replication fork by breaking hydrogen bonds and DNA gyrase relieves the tension produced by the unwinding
DNA replication elongation
- Needs an RNA primer to act as a starting point for adding nucleotides. the primer is made by primase
- DNA Polymerase 3 can only add to 3 prime hydroxyl group of a chain of nucleotides, hydroxyl is needed for condensation
- DNA replication can only happen 5 to 3
- So lagging strand uses okazaki fragments, which requires one primer and polymerase PER fragment
- RNA primers must be removed by DNA polymerase 1
- Gaps filled between okazaki fragments are filled by DNA ligase
DNA replication termination
- Daughter molecules re-wind
- because new nucleotides can only be added to 3 prime end at the end of replication a gap is left at 5 prime end
- eukaryotes have telomeres, highly repetitive DNA at the five prime end of a chromosome. Eventually they shrink, so telomerase adds telomeres back. Telomerase eventually fails, which is linked to aging.
DNA repair facts
- 3 billion nucleotides per cell
- DNA replication makes 1 mistake per 100 000 nucleotides
- 120 000 every time a cell divides
- proofreading fixes about 99% of those errors, leaving about 12 000 mistakes
Proofreading & mismatch repair
Proofreading happens during DNA replication, mismatch repair happens after.
They have the same process: 1. polymerase 1 and 3 recognize structural imperfections in improperly paired nucleotides
2. the enzyme exonuclease backtracts past mispaired nucleotide and excises it
3. exonuclease replaces nucleotides with the proper nucleotide
Initiation of DNA transcription
- Each gene of double stranded DNA has a coding and template strand (coding will look the same as mRNA, tempate is used by taking the inverse to make mRNA)
- start of a gene is indicated by a promotor sequence, where RNA polymerase can bind
- promotor sequence can be found in the TATA box
Elongation in DNA transcription
- RNA polymerase opens DNA one section at a time
- RNA polymerase works in the new strand, nucleotides added to 3 oh group
- No okazaki fragments
- Many RNA copies of the same gene can be made
Termination of DNA transcription
- RNA polymerase will continue along the DNA strand until a terminator sequence is encountered
- After this, RNA polymerase molecule separates from the DNA strand and RNA molecule dissociates
- becomes mRNA
Processing of DNA transcription
- only occurs in eukaryotes
- initial mRNA is called pre-mRNA
1. 5 prime cap made of a modified G nucleotide
2. Poly-A tail attaches to 3 prime end made of modified A
3. Splicing –> introns that dont code for anything are cut out by splicosome, exons that do code stay
Initation in translation
- mRNA reaches the cytoplasm
- rRNA binds fivve prime end of mRNA at a special ssequence
- Initiator tRNA with anticodon “UAC” binds ribosomal-mRNA complex (this anticodon matches start codon AUG
Composition of a tRNA
- three lobed shape
- anti codon complimentry to mRNA’s codon at the bottom
- amino acid at the top
- when an amino acid is bound to tRNA its called amino-acyl tRNA (aatRNA)
Elongation in translation
1.mRNA codon in A site forms a base pair with incoming aa-tRNA
2. peptide bond is formed joining new amino acid in A site to growing chain in P site
3. ribosome moves a distance of 3 nuclotidews along the rRNA molecule, called translocation (translocation brings the tRNA holding the chain into the P site, a new A site is exposed and the old tRNA from the P site moves to the E site
Termination in translation
- elongation continues until a stop codon is reached on the mRNA strand in the A site
- previous tRNA, carrying the polypeptide chain remains in the P site until a protein called a release factor binds to the A site. The release factor cuts off completed polypeptide from tRNA
- polupeptofe ois free to take its form
Causes of mutations
Spontaneous mutations: results of errors in DNA replication, occur without chemical change or radiation
Induced mutations: Result of chemical (structure similar to nucleoties usually, interact chemically with DNA like nitrites or cigarette smoke) or physical agent (messes with DNA structure like UV or an XRay)
SBLab squishing strawberries
- step one, increases surface area to increase reactions
SBLab salt solution
- step 2, stabilizes DNA, Na in salt neutralizes negatively charged DNA and allows it to precipitate
SBLab soap
- step 3
- pH precipitates lipids and proteins out of solution, breaks cell membranes
SBLab filter
- step 4
removes big chunks (unseperated cells)
SBLab add ethanol
- fifth step
- precipitated dna since its non soluable in ethanol
Why did DNA curl around glass stirring rod
- glass attracts neutral things
Whats translocation mutation
- swaps places with other part on dif chromosomes
