Biochemistry: From DNA to Protein Flashcards
genome
all the DNA in each cell
nucleoside
base and sugar
nucleotide
nucleoside and phosphate
where do phosphodiester bonds occur
between the free 3’ OH and 5’ triphosphate of two nucleotides
how do nucelotide analogues work as drugs
have a higher affinity for viral DNA than human and stop elongation as they lack a 3’ OH
role of DNA helicase
unwinds DNA strand
what synthesised RNA primers
primase
describe the leading strand
DNA replicated 5’ to 3’ in one continuous strand
describe the lagging strand
DNA replicated 5’ to 3’ in short okazaki fragments which are later bound together
describe DNA polymerases role in proof reading
exonuclease activity - remove incorrect nucleotides
what are stem loops
regions of intra-molecular base pairing in DNA
what are the 3 classes of RNA
- mRNA
- tRNA
- rRNA
what types of RNA are stable
tRNA and rRNA
describe mRNA
carries genetic information for protein synthesis
describe tRNA
carries amino acid to be incorporated into protein
describe rRNA
bnds with proteins to form ribosomes - site of protein synthesis
what is the 2D shape of tRNA
clover leaf
anti-codon
triplet of bases that are complementary to a codon on the strand being replicated
what are the 3 eukaryote RNA polymerases
Pol I, Pol II, Pol III
what RNA polymerase synthesises all mRNA
Pol II
give a brief overview of transcription
- TATA box at -25 makes a kink in the DNA determining transcription start point and direction
- general transcription factors are needed for initiation
- transcription bubble moves along the DNA being unwound infrontof the polymerase and rewound behind it
- new RNA strand creates a stem loop and a sequence of U bases to terminate transcription, mRNA is cleaved and DNA polymerase dissociates
how is transcription regulated
by transcription factors binding to enhancers
what are the 2 domains of transcription factors
- DNA binding region
- transcription activated region
describe how steroid receptors regulate transcription
- steroid is activated and translocates to the nucleus where it binds to SREs on DNA and regulates transcription either -ve or +ve
describe how glucocorticoid receptors regulate transcription
- bound to albumin/transporter protein in blood and enter the cell via diffusion once free
- binds to inactive steroid receptor in the cytoplasm and translocates to nucleus
- binds to SRE
what is at the ends of mRNA
- 3’ - poly(A) tail
- 5’ - G cap
give a brief overview of translation
- initiation factors initiate (using GTP)
- small ribosomal subunit binds to the 5’ end of mRNA and looks for a start codon
- once found the initiator tRNA pairs at the P site and the large ribosomal subunit joins
- elongation factors bring the next tRNA which binds at the A site, GTP hydrolysed, EF released
- peptide bonds form between the P and A site - peptide in A
- the free tRNA moves to the E site and exits (reused later)
- the peptide is now in P and the A site is free for the next tRNA
- once a stop codon is reached there is no tRNA pairinf and a release factor bonds in its place
- GTP hydrolysed, protein cleaved and tRNA, mRNA and rRNA dissociate
how is the genetic code degenerate
many amino acids have more than 1 codon
how is the genetic code unambiguous
codons code for 1 amino acid or a stop
function of amino-acyl tRNA synthases
binds amino acid to its corresponding tRNA (needs ATP)
what catalyses peptide bond formation
peptidyl transferase
what 3 things can happen after protein synthesis
- modification
- targeting
- degradation
modification
addition of chemical groups to proetin
targeting
protein moved to final cellular destination
degradation
unwanted/damaged proteins removed
‘free’ ribosomes
- are located where
- make proteins for where
- proteins are moved when
- in cytosol
- cytosol, nucleus, mitochondria
- post-translationally
‘bound’ ribosomes
- are located where
- make proteins for where
- proteins are moved when
- bound in rough ER
- ER, golgi, secretions, plasma membrane
- co-translationally
types of post-translational modifications
- glycolysation - addition of carbs in ER/golgi
- formation of disulphide bridges
- folding and assembly of multisubunits in ER
- cleavage in ER, golgi or vesicles
what is I-cell disease
inherited recessive disorder of protein targeting
- lysosomes are sorted right in the golgi and are secreted but unable to digest stuff
what is a consequence of I-cell disease
early death
