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Module 102: Molecular cell biology > Translation > Flashcards

Flashcards in Translation Deck (26)
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1

Initiation translation

- 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

2

Addition of amino acids during translation

- 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

3

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

In close proximity.

4

The coding of mRNA

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

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

5

Codon that initiates translation

AUG,

codes for Met (Methionine)

6

Codons that terminate translation

UAG, UAA, UGA

7

Aminoacylation of tRNA

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

8

Polyribosome

Group of ribosomes which translates a protein from the same mRNA

Allows mass production of proteins at a very quick rate.

9

Ribosome

- 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.

10

Elongation factors (EF)

- Protein complexes in translation that promotes elongation of proteins during translation.

- EF-G and EF-T

11

Use of antibiotics on the ribosome

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

12

Tetracycline

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

13

Streptomycin

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

14

Chloramphenicol

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

15

Rifamycin

Antibiotic that blocks RNA polymerase.

Inhibits translation.

16

Cycloheximide

Antibiotic that blocks the translocation of the ribosome during translation

17

Frameshift mutation

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.

18

What type of mutation occurs in Sickle-cell disease?

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

19

What type of mutation occurs in Beta-Thalassemia?

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

This shortens the protein.

20

What type of mutation occurs in congenital deafness?

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.

21

microRNA

- 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.

22

Regulation of gene expression by microRNA

- 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.

23

Chronic lymphocytic leukemia.

- 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

24

miRNA-200 family

Group of miRNA that promotes metastasis:

Important in the spread of cancer

25

miRNA-31

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

26

miRNA as biomarkers

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.