[FMS] MCG - translation (gene products and protein synthesis) Flashcards
what does it mean if code is degenerate
64 codons for 20 amino acids.
what codon signals the start of translation
AUG
who worked out how to synthesise RNA with specific sequences
Har Gobind Khorana
what does tRNA do
Transfer RNA (tRNA) is the adaptor molecule that links an mRNA codon with a specific amino acid.
how many nucleotides is a tRNA molecule made up of?
75-90
whats the structure of a tRNA molecule
Clover leaf structure.
what sequence does a tRNA molecule have at the 3’ end
CCA-OH
where is anticodon found on tRNA
central loop
there are 61 amino acids but less than 61 trna molecules, what process allows this to happen?
wobble pairing:
^ Often first 2 letters in codon are the same,third base can vary.
Third position less critical and can follow non-Watson-Crick base pairing between mRNAand tRNA.
Allows a single tRNA species to recognize more than one codon.
a ‘charged’ tRNA has an amino acids attached at the … end via an … linkage
attached at 3’ end via ester linkage
Energy for addition of amino acid to tRNA comes from what
hydrolysis of ATP.
prokaryote ribosomes have a …S complex
70s complex
what is the 70s complex of a prokaryote made up of?
Large subunit (50S)
23S rRNA + 5S rRNA
+ 34 proteins
Small subunit (30S)
16S rRNA +21 proteins
what are the 3 tRNA sites on a ribosome
E P A
tRNAs are charged with the correct amino acids by …
by specific aminoacyl-tRNA-synthetases.
3 steps of translation?
initiation
elongation
termination
what happens in initiation in translation
- Initiation factors (IFs) IF1 and IF3 bind the 30S subunit.
- This complex binds mRNA.
- fMet-tRNAfMet in complex with IF2-GTP enters the P site.
- 16srRNA binds to Shine-Dalgarno sequence
- The large 50S subunit binds.
- Accompanied by hydrolysis of GTP.
- GDP + Pi, and IFs (1,2,3) released.
why do 16S rRNA binds to Shine-Dalgarno sequence in the mRNA ?.
to line up fMet-tRNA with AUG start codon
what happens in elongation in prokaryotic translation
Next aminoacyl tRNA binds to elongation factor EF-Tu GTP, and enters A site in the ribosome.
If the anticodon of the incoming tRNA is complementary to the codon, then hydrolysis of GTP takes place, and EF-Tu GDP + Pi are released.
The protein is synthesized by ‘lifting’ the incomplete polypeptide, and placing the incoming (‘new’) amino acid underneath. (PEPTIDYL TRANSFERASE STEP)
Translocation of the ribosome occurs with hydrolysis of the GTP bound to EF-G. The A site is now free again.
The discharged tRNA is released from the E site.
what happens in the termination stage of prokaryotic translation
Stop codon (UAA, UAG or UGA) on mRNA presented in the A site.
Release factor (RF1 or RF2) mimics shape of a tRNA.
Release factor enters A site with H2O molecule.
Peptide is hydrolysed from the final tRNA using H2O molecule.
Ribosome disassembles. This requires a ribosomal recycling factor and IF3
where does transcription of prokaryotes take place?
cytoplasm
where does transcription of eukaryotes take place?
nucleus
what is the initator tRNA in prokaryotes
Initiator tRNA is fmet-tRNA
what is the initator tRNA in eukaryotes
Initiator tRNA is met-tRNAmet.
is the rna Polycistronic or monocistronic in prokaryotes?
Polycistronic mRNA that encodes more than one protein.
is the rna Polycistronic or monocistronic in eukaryotes?
That mRNA is monocistronic - encodes for one protein only.
in which one, eukaryotes and prokaryotes, are polyribosomes free?
polyribosomes free in both
Which of these is not a type of RNA?
a) messenger RNA
b) polymerase RNA
c) ribosomal RNA
d) transfer RNA
B
How does RNA differ from DNA?
a) RNA is single-stranded, contains U instead of A and ribose instead of deoxyribose.
b) RNA is double-stranded, contains U instead of A and deoxyribose instead of ribose.
c) RNA is joined 5’ to 2’, contains U instead of T and ribose instead of deoxyribose.
d) RNA is single-stranded, contains U instead of T and ribose instead of deoxyribose.
d
Which statement incorrectly describes mRNA?
a) It is transcribed from DNA.
b) It does not contain 5’ and 3’ UTRs.
c) It is used as a template for protein synthesis.
d) In eukaryotes, it is a messenger from the nucleus to the cytoplasm.
B
Explanation:
a) This statement is true. mRNA is transcribed from DNA during the process of transcription.
b) This statement is incorrect. mRNA typically contains both 5’ and 3’ untranslated regions (UTRs), which are important for various regulatory functions, such as mRNA stability, localization, and translational efficiency.
c) This statement is true. mRNA serves as a template for protein synthesis during translation.
d) This statement is true. In eukaryotes, mRNA is synthesized in the nucleus and then transported to the cytoplasm, where protein synthesis occurs.
) Which statement incorrectly describes rRNA?
a) It is a structural component of the ribosome.
b) It is an enzymatic component of the ribosome (participates in the reaction which joins amino acids).
c) It is transcribed in the nucleolus.
d) It is used as a template for protein synthesis.
D
Which statement incorrectly describes tRNA?
a) It is transcribed by RNA Pol III in eukaryotes.
b) It delivers amino acids to the ribosome.
c) It is a structural component of the ribosome.
d) It is single stranded, but internal base-pairing gives it secondary structure.
C
Explanation:
a) This statement is true. tRNA is transcribed by RNA polymerase III (Pol III) in eukaryotes.
b) This statement is true. tRNA molecules deliver amino acids to the ribosome during protein synthesis.
c) This statement is incorrect. While tRNA is involved in protein synthesis and interacts with the ribosome, it is not a structural component of the ribosome. The ribosome is primarily composed of proteins and ribosomal RNA (rRNA).
d) This statement is true. tRNA molecules are single-stranded RNA molecules, but they fold into a characteristic cloverleaf secondary structure due to internal base-pairing interactions.
How can we find out which bases encode which amino acid?
1) Make synthetic mRNA
2) Find out which amino acids are incorporated into protein in a cell-free system
what amino acid do all proteins start with?
Met
So the anticodon we are looking for is: 5’ ?AG 3’
→ tRNA in panel C.
So the codons we are looking for are: 5’ UG? 3’
→ 5’ UGU 3’
5’ UGC 3’
remember they’re trying to trick you because the diagram they’ve shown is flipped, so make sure you draw it out right in order for it to make sense which is the nucleotide at the 3rd position that can change (pic included)
which part of the shine delgaro sequence in mRNA does the ribosome bind to?
Shine-Dalgarno sequence is in the 5’ UTR of the mRNA
where does translation of prokaryotes take place vs eukaryotes
in both of them, translation occurs in cytoplasm
which part interacts with ribosome in prokaryote vs eukaryote
PROKARYOTE:
Ribosome positioned at the start codon by interaction of the 16S rRNA with the Shine-Dalgarno sequence.
EUKARYOTE
5’ cap interacts with the ribosome – not clear how the start codon is found.
