Topic 7 Flashcards
What are the purines?
Guanine & Adenine -> they contain 2 rings in their structure
What are the pyrimidines?
T & C -> they contain 1 ring in their structure
What are the enzymes involved in DNA replication?
- DNA gyrase
- DNA helicase
- DNA polymerase (III)
- DNA polymerase (I)
- DNA ligase
- DNA primase
- SSB proteins(not an enzyme but important)
The regions of DNA that do not code for any proteins are what?
- introns
- telomeres
- genes for tRNA’s
What are tandem repeats?
sequences of non-coding DNA, normally the length of 2-5 base pairs, that are repeated numerous times in a head-tail manner
Lagging strand
the strand of DNA that is replicated discontinuity in small fragments in the 5’3’ direction away from the replication fork
Leading strand
the strand of DNA that is being replicated continuously in the 5’3’ direction by continuous polymerisation at the 3’ growing tip
Enhancers
sequences that increase the rate of transcription (when a protein is bound to it)
Silencers
sequences that inhibit transcription (when a protein is bound to it)
Promoter
a promoter is a short DNA sequence situated just before a gene, which acts as a binding point for the RNA polymerase enzyme
Operator
a region of DNA that can regulate transcription, typically inhibiting the transcription gene
Methylation
the addition of methyl groups to DNA
what is the effect of methylation?
DNA is more tightly bound to the histone which makes the DNA less accessible to transcription factors -> can inhibit transcription
Acetylation
addition of acetyl groups to histones
what is the effect of acetylation?
causes the DNA to bind less tightly to the histones
Events that occur to form mature mRNA
- capping
- polyadenylation
- splicing
Capping
- involves the addition of a methyl group to the 5’-end of the transcribed RNA
- the methylated cap provides protection against degradation by exonucleases
- allows the transcript to be recognised by the cells transitional machinery
Polyadenylation
- describes the addition of a ling chain of adenine nucleotides to the 3’-end of the transcript
- the poly-A tail improves the stability of the RNA transcript and facilitates its export from the nucleus
Splicing
- can happen in different ways to the same gene
- introns are removed & the non-coding exons are fused together to form a continuous sequence
Alternative splicing
- the removal of extrons
- The selective removal of specific exons will result in the formation of different polypeptides from a single gene sequence
translation occurs in 3 distinct stages:
- initiation
- elongation
- termination
Initiation
involves the assembly of the components that carry out the process
What happens in initiation/
- small ribosomal unit binds to the 5’-end of the mRNA & moves along until it reaches the start start codon (AUG)
- next, the appropriate tRNA molecule binds to the codon via its anticodon (according to complementary base pairing)
- finally, the large ribosomal subunit aligns itself to the tRNA molecule at the P site & forms a complex w the small subunit
What happens in Elongation
- a second tRNA molecule pairs w the next codon in the ribosomal A site
- the amino acid in the P site is covalently attached via a peptide bond (condensation reaction) to the amino acid in the A site
- the tRNA in the P site is not deacylated (no amino acid), while the tRNA in site A carries the peptide chain
- the ribosome moves along the the mRNA strand by 1 codon position (in a 5’→3’ direction)
- the deacylated tRNA moves into the E site & is then released, while the tRNA carrying the peptide chain moves to the P site
- another tRNA molecule is attached to the next codon in the now occupied A site, & the process is then repeated
