[FMS] MCG - translation (gene products and protein synthesis)

Question 1

what does it mean if code is degenerate

Answer 1

64 codons for 20 amino acids.

Question 2

what codon signals the start of translation

Answer 2

AUG

Question 3

who worked out how to synthesise RNA with specific sequences

Answer 3

Har Gobind Khorana

Question 4

what does tRNA do

Answer 4

Transfer RNA (tRNA) is the adaptor molecule that links an mRNA codon with a specific amino acid.

Question 5

how many nucleotides is a tRNA molecule made up of?

Answer 5

75-90

Question 6

whats the structure of a tRNA molecule

Answer 6

Clover leaf structure​.

Question 7

what sequence does a tRNA molecule have at the 3’ end

Answer 7

CCA-OH

Question 8

where is anticodon found on tRNA

Answer 8

central loop

Question 9

there are 61 amino acids but less than 61 trna molecules, what process allows this to happen?

Answer 9

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.

Question 10

a ‘charged’ tRNA has an amino acids attached at the … end via an … linkage

Answer 10

attached at 3’ end via ester linkage

Question 11

Energy for addition of amino acid to tRNA comes from what

Answer 11

hydrolysis of ATP.

Question 12

prokaryote ribosomes have a …S complex

Answer 12

70s complex

Question 13

what is the 70s complex of a prokaryote made up of?

Answer 13

Large subunit (50S)
23S rRNA + 5S rRNA
+ 34 proteins

Small subunit (30S)
16S rRNA +21 proteins

Question 14

what are the 3 tRNA sites on a ribosome

Answer 14

E P A

Question 15

tRNAs are charged with the correct amino acids by …

Answer 15

by specific aminoacyl-tRNA-synthetases.

Question 16

3 steps of translation?

Answer 16

initiation

elongation

termination

Question 17

what happens in initiation in translation

Answer 17

1. Initiation factors (IFs) IF1 and IF3 bind the 30S subunit.
2. This complex binds mRNA.
3. fMet-tRNAfMet in complex with IF2-GTP enters the P site.
4. 16srRNA binds to Shine-Dalgarno sequence
5. The large 50S subunit binds.
6. Accompanied by hydrolysis of GTP.
7. GDP + Pi, and IFs (1,2,3) released.

Question 18

why do 16S rRNA binds to Shine-Dalgarno sequence in the mRNA ?.

Answer 18

to line up fMet-tRNA with AUG start codon

Question 19

what happens in elongation in prokaryotic translation

Answer 19

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.

Question 20

what happens in the termination stage of prokaryotic translation

Answer 20

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

Question 21

where does transcription of prokaryotes take place?

Answer 21

cytoplasm

Question 22

where does transcription of eukaryotes take place?

Answer 22

nucleus

Question 23

what is the initator tRNA in prokaryotes

Answer 23

Initiator tRNA is fmet-tRNA

Question 24

what is the initator tRNA in eukaryotes

Answer 24

Initiator tRNA is met-tRNAmet.

Question 25

is the rna Polycistronic or monocistronic in prokaryotes?

Answer 25

Polycistronic mRNA that encodes more than one protein.

Question 26

is the rna Polycistronic or monocistronic in eukaryotes?

Answer 26

That mRNA is monocistronic - encodes for one protein only.

Question 27

in which one, eukaryotes and prokaryotes, are polyribosomes free?

Answer 27

polyribosomes free in both

Question 28

Which of these is not a type of RNA? a) messenger RNA b) polymerase RNA c) ribosomal RNA d) transfer RNA

Answer 28

B

Question 29

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.

Answer 29

d

Question 30

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.

Answer 30

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.

Question 31

) 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.

Answer 31

D

Question 32

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.

Answer 32

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.

Question 33

How can we find out which bases encode which amino acid?

Answer 33

1) Make synthetic mRNA 2) Find out which amino acids are incorporated into protein in a cell-free system

Question 34

what amino acid do all proteins start with?

Answer 34

Met

Question 35

Answer 35

So the anticodon we are looking for is: 5’ ?AG 3’ → tRNA in panel C.

Question 36

Answer 36

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)

Question 37

which part of the shine delgaro sequence in mRNA does the ribosome bind to?

Answer 37

Shine-Dalgarno sequence is in the **5’ UTR of the mRNA**

Question 38

where does translation of prokaryotes take place vs eukaryotes

Answer 38

in both of them, translation occurs in cytoplasm

Question 39

which part interacts with ribosome in prokaryote vs eukaryote

Answer 39

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.