Translation and Mutations

Question 1

Translation

Location?

Answer 1

the RNA directed synthesis of a polypeptide

Occurs at ribosomes

Question 2

tRNA (transfer RNA)

Structure? Function?

Answer 2

Transfer RNA is the translator molecule for mRNA. It transfers an amino acid from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome. It has an amino acid on one end and an anticodon on the other.

Question 3

Anticodon

Answer 3

Part of the tRNA molecule. The anticodon base-pairs with a complementary codon on the mRNA

Question 4

Aminoacyl-tRNA synthetase

How many different ones are there? What are the steps?

Answer 4

The enzyme that binds amino acids to their respective tRNAs.
1. Amino acid and tRNA enter active site
2. Using ATP, synthetase catalyzes covalent bonding between amino acid and its tRNA
3. Aminoacyl tRNA released (charged)

There are 20 different synthetases one for each amino acid

Question 5

Wobble

Answer 5

The wobble is the flexible pairing at the third base of the codon, allowing some tRNAs to bind to more than one codon.

If U is at the third base, it can pair with A or G

Question 6

Ribosomes

Structure? What are subunits made of?

Answer 6

Ribosomes are the sites for protein synthesis. They are made of a small and a large subunit, which are both made of proteins and ribsomal RNA (rRNA).

Question 7

What is the structure of the large subunit of the ribosome?

Answer 7

The large subunit is composed of 3 “sites.”
* The A site is where each successive tRNA binds to
* The P site is where the initiator tRNA binds and is where amino acids are covalently bonded
* The E site is where the tRNA exits

Question 8

What happens in the three steps of Translation?

What is the translation initiation complex made of?

Answer 8

1. Initiation: GTP is used to attach the large ribosomal subunit to the small subunit, mRNA strand, and initiator tRNA to create the Translation initiation complex.
2. Elongation: Each addition of amino acid involves elongation factors and occurs in three steps: codon recognition, peptide bond formation, and translocation
3. Termination: When a stop codon is read, a release factor goes into the A site, which promotes hydrolysis freeing the polypeptide. Complex disassembles.

The translation initiation complex is composed of the large subunit, the small subunit, the initiator tRNA, and the mRNA strand.

Question 9

Polyribosomes

Answer 9

Polyribosomes allow a single mRNA to be translated by multiple ribosomes simultaneously. They enable a cell to make many copies of a poplypeptide very quickly.

Question 10

What are mutations?

Answer 10

Mutations are changes in the genetic material of a cell or virus

Question 11

Point mutations

Answer 11

Chemical changes in just one base pair of a gene. Can lead to an abnormal protein.

Question 12

What is the cause of sickle-cell anemia?

Answer 12

Sickle cell anemia is the result of a point mutation. The Glu amino acid is replaced with Val.

Question 13

Nucleotide-pair substitution

Answer 13

This kind of substitution replaces one nucleotide and its partner with another pair of nucleotides

Question 14

Silent mutations

Answer 14

Silent mutations have no effect on the amino acid because of redundancy in the genetic code

Question 15

Missense mutations

Answer 15

This kind of mutation changes the amino acid that is coded for producing a different amino acid.

Question 16

Nonsense mutations

Answer 16

This kind of mutation artificially produces a stop codon and nearly always leads to a nonfunctional protein.

Question 17

What are the two frameshift mutations and what makes them more harmful than other types of mutations?

Answer 17

Insertions and deletions are the two types of frameshift mutations and they are the additions or losses of nucleotide pairs in a gene. They both can lead to extensive missense even if only one nucleotide is added or removed to the beginning of an mRNA strand.

Question 18

What are the steps of translation elongation?

Answer 18

1. Codon Recognition
2. Peptide Bond Formation
3. Translocation: the ribosome moves one codon over

Question 19

How are some proteins targeted to the ER?

Answer 19

1. A signal peptide binds to a ribosome destined to end up in the ER
2. SRP binds to signal peptide, halting protein synthesis
3. SRP binds to receptor protein at a pore in the ER
4. SRP detaches and polypeptide synthesis resumes
5. Signal Peptide is removed
6. Completed polypeptide folds and is released into ER lumen