Translation

Question 1

Initiation translation

Answer 1

• Starts at the 5’ end of mRNA, which is bound to the small sub-unit of the ribosome.
• Initiator tRNA attached to amino acid Met (methionine) searches along mRNA for starting codon- AUG
• When tRNA binds to AUG, initiation factors unbind form the sub-unit and the large subunit binds to the smaller one.
• An aminoacyl tRNA then binds to the A site in the ribosome before a peptide bond is formed between them

Question 2

Addition of amino acids during translation

Answer 2

• The tRNA in the E site is ejected.
• A peptide bond is formed between the amino acids in the P and A site, using peptidase transferase.
• tRNA at the P site releases its amino acid.
• The large subunit translocates forward.
• The amino acids previously in the P and A site are changed to the E and P site.
• The small subunit translocates

Question 3

Where are the 3’ and 5’ end of mRNA located during translation?

Answer 3

In close proximity.

Question 4

The coding of mRNA

Answer 4

Read in codons: 3 nucleotides code for an amino acid.

There can be 3 reading frames in the genetic sequence, rare in humans.

Question 5

Codon that initiates translation

Answer 5

AUG,

codes for Met (Methionine)

Question 6

Codons that terminate translation

Answer 6

UAG, UAA, UGA

Question 7

Aminoacylation of tRNA

Answer 7

The addition of an amino acid to tRNA using aminoacyl tRNA Synthase

ATP is used to form a high-energy bond between the amino acid and tRNA

Question 8

Polyribosome

Answer 8

Group of ribosomes which translates a protein from the same mRNA

Allows mass production of proteins at a very quick rate.

Question 9

Ribosome

Answer 9

• Organelle involved in the translation of mRNA to produce proteins.
• Contains: small and large sub-unit.
• Composed of RNA and accessory proteins.
• Large subunit: EPA sites for binding of tRNA.

Question 10

Elongation factors (EF)

Answer 10

• Protein complexes in translation that promotes elongation of proteins during translation.
• EF-G and EF-T

Question 11

Use of antibiotics on the ribosome

Answer 11

• Antibiotics are made to bind on the ribosomes of some bacteria to prevent certain protein production.

Question 12

Tetracycline

Answer 12

Antibiotic that blocks aminoacyl tRNA from binding to the A site of the ribosome in bacteria.

Question 13

Streptomycin

Answer 13

Antibiotic that prevents the transition from initiation to chain elongating ribosome.

Question 14

Chloramphenicol

Answer 14

Antibiotic that blocks peptidase transferase reaction on ribosome:
the formation of peptide bonds between adjacent amino acids.

Question 15

Rifamycin

Answer 15

Antibiotic that blocks RNA polymerase.

Inhibits translation.

Question 16

Cycloheximide

Answer 16

Antibiotic that blocks the translocation of the ribosome during translation

Question 17

Frameshift mutation

Answer 17

Occurs when there is an insertion or deletion change in nucleotide sequence in non-multiples of 3.

Causes the whole amino acid sequence to change which codes for a different protein or a stop codon, which shortens the protein.

Question 18

What type of mutation occurs in Sickle-cell disease?

Answer 18

Missense mutation:
Substitution of Adenine to Thymine changes amino acid glutamic acid to valine.

This aggregates the protein and causes sickly rbc.

Occurs in the HBB gene

Question 19

What type of mutation occurs in Beta-Thalassemia?

Answer 19

Non-sense:
Mutation in GIn39X protein where a stop codon is formed prematurely in the start of the second exon.

This shortens the protein.

Question 20

What type of mutation occurs in congenital deafness?

Answer 20

Frameshift mutation:
In 26(GJb2) gene.
Guanine is inserted which changes the sequence of amino acids.

Causes STOP codon to be produced which shortens the protein.

Question 21

microRNA

Answer 21

• Very small non-coding 21-23 nucleotides in length, processed from longer precursor RNAs found in all cells.
• Bind to the 3’ untranslated region of mRNA
• Causes degradation and repression of mRNA transcripts.

Question 22

Regulation of gene expression by microRNA

Answer 22

• miRNA is process and transported into the cytoplasm after being formed in the nucleus.
• miRNA binds to RISC proteins to form RISC.
• The RISC-miRNA complex searches for a specific complementary sequence in the mRNA.
• If there is an extensive match: mRNA is rapidly degrade and the RISC protein is released.
• If the match is not extensive: Translation is reduced.
  mRNA is sequestered (isolated) and then degraded.

Question 23

Chronic lymphocytic leukemia.

Answer 23

• Type of cancer caused by the loss of miRNA expression in B lymphocytes.
• 13q-14.3 deletion causes an overexpression of BLC2 (proteins that repress apoptosis) and reduces apoptosis.
• This reduces the repression of cancerous growth

Question 24

miRNA-200 family

Answer 24

Group of miRNA that promotes metastasis:

Important in the spread of cancer

Question 25

miRNA-31

Answer 25

Group of miRNA that prevents the spread of cancer by inhibiting metastasis.

Question 26

miRNA as biomarkers

Answer 26

Overexpression of certain miRNA from certain tissues can indicate the presence of a cancer.

miR-21 in glioblastomas
miR-55 in many B-cell malignancies

In body fluids:

miRNA is found in blood, cerebrospinal fluid and urine.
Very useful in diagnosing hematological diseases.