Translation – Interactive Worksheet

Student Information

Name:

ID / Number:

Class/Group:

Collapsible Review Notes

1. Introduction & Central Dogma

Translation is the process of synthesizing proteins from an mRNA template, after transcription of DNA to RNA.
In prokaryotes translation occurs in the cytoplasm; in eukaryotes it mainly occurs on ribosomes attached to the rough endoplasmic reticulum or free in the cytoplasm.
The central dogma describes the flow of genetic information: DNA → RNA → Protein.
Proteins determine the phenotype of an organism and are made of one or more polypeptide chains.

2. Types of RNA in Protein Synthesis

mRNA (messenger RNA): carries the genetic code from DNA to the ribosome; its codons specify the amino acid sequence.
rRNA (ribosomal RNA): together with ribosomal proteins, forms the ribosome. Prokaryotic ribosomes are 70S (30S + 50S); eukaryotic ribosomes are 80S (40S + 60S).
tRNA (transfer RNA): has an anticodon that base-pairs with an mRNA codon and carries its specific amino acid.
Aminoacyl-tRNA synthetases (about 20, one per amino acid) “charge” tRNAs by attaching the correct amino acid using ATP.

3. Genetic Code

The genetic code is read in triplets of bases (codons). There are 64 codons in total.
61 codons specify amino acids; 3 are stop codons (UAA, UAG, UGA).
AUG is the usual start codon and also codes for methionine (Met); in prokaryotes the initiator tRNA carries N-formylmethionine (fMet).
The code is degenerate (several codons can specify the same amino acid) and nearly universal across organisms.

4. Ribosome Structure & L1 Stalk

Ribosomes have two subunits (large and small) and three main tRNA-binding sites:
- A site (aminoacyl): incoming charged tRNA.
- P site (peptidyl): tRNA holding the growing polypeptide.
- E site (exit): deacylated tRNA leaves the ribosome.
The L1 stalk is a flexible region of the large subunit that interacts with deacylated tRNA in the E site and helps move tRNA during translocation.

5. Initiation of Translation

Prokaryotes:
- The small 30S subunit binds the Shine–Dalgarno (ribosome-binding) sequence on mRNA.
- Initiation factors, GTP, and the initiator tRNA (fMet-tRNA_fMet) form the initiation complex.
Eukaryotes:
- eIF4E (cap-binding) and eIF4G recruit the capped mRNA; eIF4A and eIF3 assist.
- The 40S subunit scans from the 5′ cap to find the AUG start codon; then the 60S subunit joins to form the complete 80S ribosome.

6. Elongation

In prokaryotes and eukaryotes:
- A charged tRNA enters the A site and base-pairs with the codon.
- Peptidyl transferase (in the large subunit rRNA) forms a peptide bond between the amino acids in the P and A sites.
- The ribosome shifts three nucleotides (one codon) along the mRNA; tRNAs move from A → P → E sites.
Eukaryotic elongation factors:
- eEF1A-GTP delivers aminoacyl-tRNA to the A site.
- eEF2 promotes ribosome translocation along the mRNA.
Many ribosomes can translate the same mRNA simultaneously, forming a polyribosome (polysome).

7. Termination & Regulation

When a stop codon enters the A site:
- Prokaryotes: RF1 and RF2 recognize stop codons; RF3 helps trigger release of the polypeptide.
- Eukaryotes: the eRF1–eRF3-GTP complex recognizes stop codons and promotes polypeptide release.
After release, ribosomal subunits, mRNA and tRNA dissociate.
Translation can be regulated, for example:
- Phosphorylation of eIF2 can inhibit initiation.
- Heme availability, interferon, and iron-response elements (IREs) can modulate translation of specific mRNAs.

Section A – Multiple Choice Questions (20)

Select the best answer for each question.

1. In prokaryotes, where does translation occur?

A. Nucleus B. Cytoplasm C. Mitochondria D. Lysosome

2. Which organelle hosts ribosomes that carry out translation for many secreted proteins in eukaryotic cells?

A. Smooth endoplasmic reticulum B. Rough endoplasmic reticulum C. Golgi apparatus D. Lysosome

3. The usual start codon in both prokaryotic and eukaryotic mRNAs is:

A. UAA B. AUG C. GUG D. UAG

4. In prokaryotes, the initiator tRNA carries which amino acid?

A. Methionine (Met) B. Valine (Val) C. N-formylmethionine (fMet) D. Tryptophan (Trp)

5. How many codons exist in the standard genetic code?

A. 3 B. 20 C. 61 D. 64

6. Which type of RNA carries the genetic code from DNA to the ribosome?

A. tRNA B. rRNA C. mRNA D. miRNA

7. Which ribosomal site holds the tRNA carrying the growing polypeptide chain?

A. A site B. P site C. E site D. Q site

8. Aminoacyl-tRNA synthetase is an enzyme that:

A. Synthesizes mRNA from DNA B. Joins amino acids by peptide bonds in the ribosome C. Attaches amino acids to their specific tRNAs D. Unwinds the DNA helix

9. Which of the following is a stop codon?

A. AUG B. UGG C. UAA D. AAA

10. The three-base sequence on tRNA that pairs with an mRNA codon is called a:

A. Intron B. Anticodon C. Exon D. Promoter

11. In eukaryotes, the small ribosomal subunit is:

A. 30S B. 40S C. 50S D. 60S

12. Which statement about the genetic code is TRUE?

A. Each codon can specify more than one amino acid. B. The code is nearly universal across almost all organisms. C. Only prokaryotes use the code. D. Codons consist of two nucleotides.

13. Which RNA forms the structural and catalytic core of the ribosome?

A. mRNA B. rRNA C. tRNA D. miRNA

14. The Shine–Dalgarno sequence in bacteria is important for:

A. Transcription termination B. Ribosome binding to mRNA C. DNA replication initiation D. RNA splicing

15. During elongation, which enzyme catalyzes peptide bond formation?

A. RNA polymerase B. DNA ligase C. Peptidyl transferase D. Primase

16. Which elongation factor delivers aminoacyl-tRNA to the A site in eukaryotes?

A. EF-Tu B. eEF1A C. eRF1 D. eIF4E

17. Which statement about translation in prokaryotes is TRUE?

A. Transcription and translation are separated in different compartments. B. Translation occurs in the nucleus. C. Transcription and translation can occur simultaneously. D. mRNA must be exported to the cytoplasm through nuclear pores.

18. The L1 stalk of the large ribosomal subunit mainly helps to:

A. Recognize the start codon. B. Move deacylated tRNA through the E site. C. Bind the Shine–Dalgarno sequence. D. Cap the 5′ end of mRNA.

19. In eukaryotes, which factor recognizes all three stop codons?

A. RF1 B. RF2 C. eRF1 D. eEF2

20. Proteins that assist newly synthesized polypeptides in folding correctly are called:

A. Helicases B. Chaperonins C. Ligases D. Topoisomerases

Section B – Fill in the Blanks (10)

Type the correct term in each blank. Spelling matters, but answers are not case-sensitive.

1. The process of synthesizing proteins from an mRNA template is called .

2. According to the central dogma, genetic information flows from DNA to to protein.

3. The three-nucleotide unit on mRNA that specifies an amino acid is called a .

4. The three-nucleotide unit on tRNA that base-pairs with the codon is called an .

5. In most cells there are about different aminoacyl-tRNA synthetases, one for each standard amino acid.

6. The ribosomal site holds the tRNA carrying the next amino acid to be added.

7. The ribosomal site holds the tRNA carrying the growing polypeptide chain.

8. In bacteria, the ribosome-binding site on mRNA is called the sequence.

9. The usual start codon that also codes for methionine is .

10. In prokaryotes, both transcription and translation occur in the .

Section C – Short Answer Questions (10)

These questions are not auto-graded. Answer in complete sentences; your teacher will review them.

1. Explain the role of mRNA in translation.

2. Describe the structure and function of tRNA and how it ensures the correct amino acid is added during translation.

3. Compare ribosomes in prokaryotic and eukaryotic cells in terms of size and location.

4. The genetic code is often described as both degenerate and nearly universal. Explain what each of these terms means.

5. Outline the key steps in the initiation of translation in prokaryotes.

6. Summarize how translation initiation occurs in eukaryotes, highlighting the role of the 5′ cap and initiation factors.

7. Describe what happens during one full cycle of elongation, including the roles of the A, P and E sites.

8. Explain how translation is terminated in either prokaryotes or eukaryotes. Include the role of release factors.

9. What is the L1 stalk, and how does it contribute to the movement of tRNA during translation?

10. Give one example of how translation can be regulated in eukaryotic cells and explain why this regulation is biologically important.

MCQ Score: 0/20
Fill in the Blanks Score: 0/10
Total Auto-graded Score: 0/30