Nucleotides & DNA Structure
- made up of a pentose sugar, nitrogenous base, a phosphate group, and 5-carbon sugar
- Purines: A & G Prymidines: C & T & U
- the nitrogenous bases are attached to the 1st carbon of sugar
- 3 h-bonds between C & G, 2 h-bonds between A & T
- the DNA backbone alternates between a 5-carbon sugar attached to a phosphate group
- 5 prime end has a phosphate attached to the 5th carbon
- 3 prime end has a hydroxyl attached to the 3rd carbon
Semi-conservative model
if you start with one strand of DNA< when everything’s done you’;; have 1 old strand and 1 new strand (olds never meet again and new never meet)
DNA Replication
- begins at the origin of replication, which forms a bubble
- the leading strand is 5’ to 3’, the lagging strand is 3’ to 5’
- the helicase unzips the 2 strands
- the DNA polymerase puts down nucleotides that match up with the old strand
- it can only add to the 3’ end (where the fork is) of the leading strand
- for the lagging strand, the RNA primes puts down a primer for the DNA to attach to
- the DNA polymerase puts down nucleotides on top of the primer away from the replication fork
- the Okasaki fragments are the DNA fragments of the lagging strand
- the primers between the Okasaki fragments are removed by the DNA ligase
DNA vs RNA
DNA RNA
- deoxyribose -ribose
- double-helix -single strand
- thymine -uracil
- in the nucleus -in the cytoplasm
Transcription
- the RNA polymerase unzips the double helix and lays down the RNA
- the mRNA is 5’ to 3’
1) Initiation
- the RNA polymerase binds to DNA at the promoter
- it unravels the strand by breaking the h-bonds
- it follows DNA in 3’ to 5’ as RNA is made from 5’ to 3’
2) Elongation
- making the mRNA
- to get to the end you find the terminator
3) Termination
- the RNA polymerase stops and detaches
- the double helix rebinds and the h-bonds get back together
Translation
-the mRNA leaves the nucleus and goes to the cytoplasm to be translated into a protein
- the mRNA codes are read 3 bases at a time to form a triplet codon, which codes for 1 amino acid
- the Genetic Code is the table of 20 coded amino acids in living organisms
- the mRNA leaves the nucleus and goes to the cytoplasm
- a ribosome (with a large and small subunit) attaches to the mRNA strand
- the start codon AUG arrived in the P site, and the tRNA binds to it and codes MET
- then the tRNA brings an amino acid to the A site
- the polypeptide sequence in the P site is transferred to the A site, a peptide bond is formed
Exons & Introns and pre-mRNA
- exons: coding region in pre-mRNA
- introns: non-coding, clipped out region of pre-mRNA
- pre-mRNA is 5’ cap and 3’ tail
- the cap & tail seal in the nucleotides
Mutations
- base substitution: when a nucleotide isn’t paired correctly when the DNA or RNA strand is being formed
- insertion: an extra nucleotide is inserted into the reading frame
- deletion: a nucleotide is deleted from the reading frame
- spontaneous mutations: occur during DNA replication or recombination
- mutagens: caused by chemical or physical agents such as x-rays and UV
DNA Scientists
- Watson & Crick
- Martha Wilkins
- Rosalind Franklin
Antibiotics
They fight bacterial infection by inactivating prokaryotic ribosomes and leaving eukaryotic ribosomes unaffected
3 steps of translation
1) Codon recognition
- anticodon pairs with mRNA in the A site
2) Peptide bond formation
- the polypeptide separates from tRNA and attaches to the amino acid by a peptide bond
- the ribosome catalyzes bind formation, so the chain is multiple amino acids
3) Translocation
- the P sIte mRNA leaves the ribosome, the ribosome translocates A to P
Gene regulation
Turning a gene on and off by turning the transcription on and off
Operators, enhances, silencers
- “switches” that determine whether the RNA polymerase can attach to the promoter and start transcribing the gene
- DNA sequences that regulate the game from far away
- repressor proteins that bind to DNA sequences and function analogously to inhibit the start of transcriptio
Eukaryotic vs prokaryotic regulatory proteins
- each eukaryotic has it’s own promoter, other control sequences, and activator
- proteins are more important in eukaryotes
Transduction and conjugation
- the transfer of bacterial genes by a phage
- the union of cells and the DNA transfer between them
Plasmids
- DNA molecules separated from the bacterial chromosome that bring on conjugation
- R Plasmids carry genes that can affect cell survival
Restriction Enzymes & Complementary DNA
- protect bacterial cells from intruding DNA from outside organisms
- DNA made from reverse transcriptase: transcription, RNA splicing (removing introns), mRNA isolation, RNA breakdown, 2nd DNA strand synthesis
