protein synthesis Flashcards
state the two main stages of protein synthesis
- transcription
- translation
what is the anti-sense strand?
the strand used as the template strand in mRNA synthesis
what is the benefit of the genetic code being degenerate?
Minimizes the Impact of Mutations
what are the consequences of addition and deletion mutations?
frameshift mutation
define frameshift mutation
Shifts the reading frame of the mRNA, changing all downstream codons.
why can replacement mutation not be as serious as the others?
sometimes it only leads to silent mutation where the mutated codon still codes for the same amino acid as the original codon. This is due to degeneracy.
what are promoters?
A non-coding region of DNA
describe the role of enhancers
Increase transcription when bound by activator proteins.
describe the role of silencers
Decrease transcription when bound by repressor proteins.
What are introns?
non-coding regions in the DNA
describe the role of telomeres
Protect chromosome ends from degradation.
what are exons?
coding regions in DNA
What is an example of polypeptide modification?
Pre-proinsulin → insulin
* Signal peptide removed in RER
* C-peptide removed in Golgi
* Final insulin = A and B chains linked by disulfide bridges
what is proteasome and its function?
a protein complex that breaks down unneeded or damaged proteins to reuse them.
Stages of translation.
Stage 1: Initiation
Ribosome binds to mRNA at start codon (AUG)
tRNA brings first amino acid (methionine)
Stage 2: Elongation
tRNAs bring amino acids one by one
Ribosome forms peptide bonds between them
Stage 3: Termination
Ribosome reaches a stop codon (UAA, UAG, UGA)
Protein is released, ribosome disassembles
Stages of transcription.
Initiation – RNA polymerase binds to a promoter region and unzips DNA.
Elongation – RNA polymerase adds complementary RNA nucleotides.
Termination – RNA polymerase reaches a terminator sequence and releases the mRNA.
Explain how amino acid recycling works.
Proteasomes break down unneeded or damaged proteins into amino acids.
What is alternative splicing?
Different exons can be combined → different protein variants from one gene.
What is happens during post-transcriptional modification (eukaryotes)?
5′ cap and poly-A tail added – protection and stability.
Splicing: introns removed, exons joined. Done by spliceosomes.
What are the 3 different non-coding regions?
Introns
Telomeres
tRNA & rRNA genes
What are the types of point mutations?
Deletion, addition or replacement of a single nucleotide.
What is point mutation?
A change in a single base.
Define degeneration.
Many codons code for the same amino acid.
Role of rRNA.
Part of the ribosome that helps form peptide bonds.
Role of tRNA.
Brings amino acids to ribosomes.
Role of mRNA.
Carries the genetic code from DNA.
What proteins regulates the activation/repression of transcription?
Transcription factors.
What is the role of telomeres?
Protects chromosome ends.
