protein synthesis Flashcards
state the two main stages of protein synthesis
- transcription
- translation
State the three stages of transcription/translation
- initiation
- elongation
- termination
describe what happens in the initation stage of transcription
RNA polymerase binds to the DNA at the start of a gene. It then separates the two strands of the DNA by breaking the hydrogen bonds, exposing the bases.
describe what happens in the elongation stage of transcription
RNA polymerase builds a molecule of mRNA on one of the strands of DNA (antisense)
describe what happens in the termination stage of transcription
a terminator sequence in the DNA is reached and the mRNA is released
what is the anti-sense strand?
the strand used as the template strand in mRNA synthesis
describe what happens in the initiation stage of translation
The ribosome binds to the mRNA at the start codon (AUG), which codes for the amino acid methionine.
Transfer RNA (tRNA) carrying methionine binds to the start codon through its anticodon.
describe what happens in the elongation stage of translation
The ribosome reads the mRNA codon by codon (groups of three nucleotides).
Each codon specifies a particular amino acid, which is brought to the ribosome by a corresponding tRNA.
The ribosome links the amino acids together, forming a polypeptide chain.
describe what happens in the termination stage of translation
When the ribosome encounters a stop codon (UAA, UAG, or UGA), translation stops.
The newly synthesized protein is released from the ribosome.
what is the role of mRNA?
Carries the genetic code from DNA.
what is the role of tRNA?
Brings the correct amino acids to the ribosome.
define degeneracy
most amino acids are encoded by more than one codon
what is the benefit of the genetic code being degenerate?
Minimizes the Impact of Mutations
define point shift mutation
a genetic mutation where a single nucleotide in the DNA sequence is altered.
what are the 3 types of point mutation?
- deletion
- addition
- replacement
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.
describe the role of promoters in transcription
Initiate transcription of genes by allowing transcription factors to bind to it and therefore RNA polymerase to bind and start building.
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.
describe what happens in Post-Transcriptional Modification of mRNA
- 5’ cap and a poly-A tail is added to mRNA to protect it from degredation
- splicing: Introns are removed and exons are joined together
what are exons?
coding regions in DNA
define alternative splicing
when exons are combined in various ways, creating different mRNA versions from the same gene.
explain how pre-proinsulin is modified into proinsulin
- Pre-proinsulin is made in ribosomes attached to the rough endoplasmic reticulum (ER).
- The signal peptide (which directs it to the ER) is removed.
- This removal converts pre-proinsulin into proinsulin, leaving the A chain, B chain, and C-peptide connected.
what is proteasome and its function?
a protein complex that breaks down unneeded or damaged proteins to reuse them.
