Protein Synthesis Flashcards
What is mRNA?
Messenger RNA.
It carries the coded message for protein building from DNA to the ribosomes.
What is tRNA?
Transfer RNA. It transports amino acids to the mRNA at the ribosomes.
How big is mRNA?
It varies in length, but is always much shorter than DNA. (1%)
How big is TRNA?
Very short, 70-90 bases only.
What is rRNA?
Ribosomal RNA. It binds the large and small subunits to form a functional ribosome.
How big is rRNA?
It varies in length, but is shorter than mRNA.
What is transcription?
The process of making mRNA from copying the information from a piece of DNA.
What are the steps in transcription?
Initiation, Elongation, Termination, and Post-transcriptional modifications.
What happens in initiation?
RNA polymerase binds to an AT rich section of DNA. It then unwinds it.
What happens in elongation?
RNA polymerase H bonds free-floating nucleotides to their complementary bases. DNA snaps back together behind RNA polymerase causing the created mRNA to hang free off the side by a few base pairs.
What happens in termination?
RNA polymerase encounters a terminator sequence at the end of the gene, causing RNA polymerase and a primary transcript to be released.
What happens in post-transcriptional modifications for prokaryotes?
5’ cap is added, 3’ poly-a-tail is added, mRNA transcript becomes ready for release from nucleus.
For eukaryotes, what else happens in post-transcriptional modifications?
Spliceosomes remove introns and ligate exons, forming mature mRNA transcript.
What is an intron?
A non-coding region.
What is an extron?
A coding region.
What is the purpose of a 5’ cap?
To protect the mRNA from cytoplasmic enzymes.
What is a poly-A-tail?
200 or more adenines.
What adds poly-A-tail to mRNA?
poly-A-polymerase.
How many enzymes are involved in transcription?
ONE
What kind of bonds are formed in transcription?
H bonds and covalent bonds.
What amount of the DNA is copied in transcription?
A small piece only
Which strands are copied in transcription?
Only the template strand.
How is the message on mRNA written?
In 3-letter triplets called CODONS.
How many possible codons are there?
4^3 (64)
Which are the two amino acids with a unique code?
UGG (trp) and AUG (met)
Which is the start code?
AUG
Why are UAA, UAG, and UGA stop codes>
BEcause there is no amino acid that is coded by these codons.
What happens at a stop code?
The protein breaks.
WHat adheres to the active ribosome?
The 5’ [CAP region]
In which direction will the ribosome move the mRNA through it?
5’ to 3’
What kind of structure does tRNA have?
A cross-like structure with an anticodon at its base. It also has an acceptor site at its 3’ end, that holds the amino acid.
What is an anticodon?
The compliment of the codon on the mRNA
WHat is the anticodon of AUG?
UAC
amino acid + 1 ATP + correct tRNA =
amino-acyl tRNA
How many ATP does it require to bond an amino acid to the correct tRNA?
1 ATP
How many possible tRNA are there for 20 amino acids?
61
How many enzymes does a cell need for the aa?
61
STEP 1 Protein synthesis:
mRNA, rRNA, tRNA, 40s, and 60s are drifting around the cytoplasm
STEP 2 Protein synthesis:
mRNA leaves nucleus and encounters 40s (attaches).
STEP 3 Protein synthesis:
rRNA attaches 60s to 40s (attached to mRNA). Using 1 ATP, tRNAs are activated by the attachment of an amino acid.
STEP 4 Protein synthesis:
tRNA with Met attached randomly enters Psite. It is held in place because its anti-codon matches the codon in the P-site.
Where are mRNA, rRNA, tRNA transcribed from?
DNA in the nucleus.
Where is the P-site?
on the ribosome
STEP 5 Protein synthesis:
tRNA for next amino acid moves into Asite.
STEP 6 Protein synthesis:
tRNA that first brought Met is now released, since Met has bonded to Pro.
mRNA is moved through ribosome until tRNA Met-Pro is in the P-site. Now the tRNA for the next code fits into the A-site.
STEP 7 Protein synthesis:
steps 5 and 6 are repeated until a stop code reaches the A-site.
The amino acids have now been bonded into a polypeptide chain (connected to the last tRNA in the P-site).
What level of protein structure is a polypeptide chain (step 7)?
Primary!
STEP 8 Protein synthesis:
There was no tRNA to match UAG (stop code). The polypeptide chain is released. RIBOSOME FALLS APART AND MRNA IS BROKEN DOWN.
