biochemistry of nucleic acids Flashcards
nucleoside:
base and 5 carbon sugar
nucleotide:
nucleoside and phosphate group
purines:
adenine and guanine
pyrimidines:
cytosine, thymine, uracil
Phosphodiester bonds:
form between 3’ OH group and 5’ triphosphate, link nucleotides
describe the DNA structure
- Anti-parallel double helix
- One strand 5’ to 3’, other strand 3’ to 5’
- Sugar-phosphate backbone
- Base pairs in the inside, held together with H bonds
describe the process of DNA replication
- DNA primer required
- Helix unwound by helicase
- Replication fork with leading and lagging strand
- Leading synthesized in 5’→ 3’ direction - catalyzed by DNA polymerase
- Lagging is synthesized in Okazaki fragments which are then joined by DNA ligase
what are the origins of replication
- In eukaryotes, replication starts simultaneously at several points in the genome
- Speeds up replication
- Bidirectional
rRNA:
combines with proteins to form ribosomes
tRNA:
carries amino acids to be incorporated into protein
mRNA:
carries genetic information for protein synthesis
describe RNA polymerase
- Multi-subunit complexes which make RNA
- Eukaryotes have 3 types: Pol I, Pol II, Pol III
- Pol II synthesizes all mRN
Premature → mature mRNA
- Splice out introns (exons = coding, intron = non-coding)
- Add poly-adenosine tail
- Add 5’ cap
translation Initiation-
formation of initiation complex, energy provided by GTP
translation Elongation-
anticodons of tRNA form base pairs with codons on mRNA, aminoacyl-tRNA synthetases catalyse the covalent attachment of amino acids to their corresponding tRNA molecules
translation Peptide bond formation and translocation-
peptidyl transferase catalyzes peptide bond formation between amino acids in P and A sites, EF-2 moves ribosome along mRNA
translation Termination-
A site encounters stop codon, termination protein binds to the codon and the ribosome dissociates, leads to a change in peptidyl transferase activity which results in the release of the protein from the last tRNA to which it was attached
Post-translational modifications
- Glycosylation
- Disulphide bods (ER)
- Folding/assembly of multi-subunit proteins (ER)
- Specific proteolytic cleavage (ER, Golgi, secretory vesicles)
Features of the genetic code
- Degenerate
- Unambiguous
- Near universal
Point mutations:
change in single base in DNA
Nonsense mutation:creates new termination codon
creates new termination codon
Missense mutation:
results in change of amino acid sequence
Silent mutation:
no change of amino acid sequence
Frameshift mutation:
addition or deletion of 1 or 2 bases which changes the reading frame of translation
describe the leading strand
- always has a free 3’ end
Other strand has to be replicated in short segments
transcription 1
TATA box at (-25) - TATA box binding protein introduces a kink into DNA to determine the start and direction of transcription and provides landing platforms for further transcription factors and RNA pol
transcription 2
- TFIID - first general transcription factor to bind to the promotor, binds to TATA box through TBP
- General transcription factor required for all Pol II transcribed genes
transcription 3
RNA poly II binds specific promotor (0)
transcription 4
Transcription belongs at nucleotide +1
transcription 5
DNA chain separation - unwinding of DNA, catalyzed by helicase
transcription Initiation-
selection of first nucleotide of growing RNA
- Requires additional general transcription factors
transcription elongation
addition of further nucleotides to RNA chain in the 5’→ 3’ direction
transcription termination
release of finished mRNA
