Translation

Question 1

Translation

Answer 1

The process through which information encoded in messenger RNA (mRNA) directs the addition of amino acids during protein synthesis.

Question 2

Location

Answer 2

takes place in the cell cytoplasm where ribosomes enable the reading and translation of mRNA into a protein molecule consisting of amino acid residues.

Question 3

Key components of translation

Answer 3

• mRNA
• Amino acids (AAs)
• Transfer RNAs (tRNAs) • Ribosomes

Question 4

Structure of ribosomes

Answer 4

Structure: 2- to 4.5-megadalton (MDa) organelles made up of a small subunit (40S in eukaryotes) and a large subunit (60S in eukaryotes).
• The subunits are a complex of ~80 ribosomal proteins and ribosomal RNA (rRNA).
• The rRNAs are processed in the nucleolus and assembled there into ribosomal subunits with the ribosomal proteins.
• Around 10 million ribosomes are present in each eucaryotic cell

Question 5

Function of ribosomes

Answer 5

▪ Move along an mRNA strand, and together with tRNAs, initiation, elongation, and release factors, assemble the amino acid (AA) sequence indicated by the mRNA.
▪ Multiple ribosomes can translate a single mRNA molecule into polypeptides at the same time (aka “polysome”)

Question 6

How many amino acid-coding combinations the 4 nucleotides can form?

Answer 6

4 to the power of 3 so 64

Question 7

How many codons are there

Answer 7

64 codons
61 represent the 20 amino acids ans 3 represent stop signals

Question 8

Methionine

Answer 8

-Specified by the AUG also known as the start codon
-It establishes the reading frame in which a new codon begins every 3 nucleotides

Question 9

Reading frame

Answer 9

-no overlap in the genetic code during translation:read in 3’s
-termination codons (uaa,uag,uga) normally signal the end of polypeptide sequence

Question 10

Open reading frame

Answer 10

Nucleotide sequence located between the start and the stop codons

Question 11

tRNA

Answer 11

-heat stable and soluble small adaptor molecules(76-90 nucleotides)

-clover share structure with some hydrogen bonding
-2 important sites:amino acid binding site at the top specific to aa,anticodon at the bottom which bind to the specific codon on mRNA

-mature in the nucleus and are exported to the cytosol

Question 12

Function of t rna

Answer 12

bring AAs to the growing polypeptide chain at the ribosome and attach with the anticodon to the three base codon of the mRNA, thus defining the protein sequence.

Question 13

Stages of translation

Answer 13

▪ 1. Activation of amino acids before protein synthesis (aka “charging of tRNAs”)
▪ Core translation phases: 2. Initiation
3. Elongation 4. Termination

Question 14

Activation of the amino acids(charging of tRNAs).

Answer 14

• Takes place in the cytosol after the export of mature tRNAs from the nucleus
• Aminoacyl-tRNA synthases esterify (attach) in 2 steps a respective AA to its corresponding tRNA using ATP:
1. NH2-CH(R)-COOH + ATP → adenylated amino acid + PPi
2. adenylated amino acid + tRNA→aminoacyl-tRNA + AMP
AA + tRNA +ATP→aminoacyl-tRNA +AMP + PPi

Question 15

Activation of the amino acids 2

Answer 15

• In eukaryotes: 20 Aminoacyl tRNA synthetases, each specific for a respective AA and the anticodon of its tRNA(s)
• ATP is used to create a high energy bond between the AA and the respective tRNA
• The energy of this bond is used to link the AAs through peptide bonds in the later stages of translation

Question 16

Initiation of translation in eukaryotes

Answer 16

▪ The 2 ribosomal subunits assemble and attach to the 5’ of the mRNA strand.
Each ribosome has 4 bindings sites for RNA molecules – 1x for mRNA and 3 for tRNAs (E, P and A)
▪ The ribosome finds the beginning of the genetic message, the start (AUG) codon, which corresponds to AA methionine (Met)
▪ The specific tRNA that carries methionine recognizes this codon with its corresponding anti-codon and binds to it.

Question 17

Elongation

Answer 17

1. The ribosome shifts to the next codon on the mRNA.
2. The corresponding tRNA binds to this codon ➔ two tRNA molecules on the mRNA strand.
3. The AAs carried by these tRNA molecules are then bound together (peptide bond).
4. Using energy from GTP, the ribosome shifts again by 3 nucleotides (large subunit first, then small subunit), and the first tRNA, which is no longer connected to its corresponding amino acid, is released.

Question 18

Termination of translation(and ribosome recycling)

Answer 18

▪ The ribosome comes to a stop codon, which signals the end of the genetic message.
▪ As a result, the ribosome detaches from the mRNA, and with the help of releasing factors it releases the amino acid chain.

Question 19

What happens with peptides and proteins post translation

Answer 19

Folding
Post translational modifications

Question 20

What happens during or after the synthesis of the polypeptide chain

Answer 20

-it assumes its native conformation due to the formation of:

• Hydrogen bonds: the attractive interaction that occurs between a hydrogen atom bound in a molecule to an electronegative atom such as oxygen or nitrogen
• Van der Waals interactions: weak electrostatic forces that attract neutral molecules to one another
• Ionic interactions: result from electrostatic attractions between positively and negatively charged side chains of amino acids
• Hydrophobic effects

▪ Covalent bonds:
• Formation of disulfide cross-link bonds within the same protein (tertiary protein structure)
• Formation of disulfide cross-link bonds between distinct subunits (quaternary protein structure), e.g. antibodies

Question 21

Post translational modifications

Answer 21

1)amino terminal and carboxylate terminal modifications
2) Phosphorylation of Ser, Thr and Tyr residues by kinases using ATP Biological function: activation of proteins, signalling cascades, transport processes)
3) Glycosylation (attachment of carbohydrate side chains: N- glycosylation, O-glycosylation)
Biological function: affect the function/transportation/resilience to proteolysis of proteins – e.g. antibodies
4) Isoprenyl groups:
Biological function: help to anchor a protein in a membrane
5) Addition of prosthetic groups – e.g. heme in haemoglobin bound covalently to a histidine AA residue
6) Ubiquitination: attachment of the C-terminal glycine of ubiquitin, a 76 amino acid protein, to lysine AA resudue of the target protein
Biological function: directs the ubiquitinated protein for degradation

Question 22

Post-translational processing of proteins

Answer 22

▪ Proteolysis of proteins: proteins synthesised as inactive precursors, which produce active peptides after proteolytic cleavage:
Angiotensinogen (inactive)→Angiotensin 1 (active peptide)→ Angiotensin II (most active peptide)