Wednesday, January 21, 2009

Chapter 17: Translation and Mutations

Sorry this is so late...

The Synthesis of Protein Translation

Translation is the synthesis of a polypeptide, under the direction of a ribosome.

tRNA is a type of RNA that functions in transferring particular amino acids from a pool of amino acids in the cell’s cytoplasm to a ribosome. The ribosome takes an amino acid and incorporates it into a growing polypeptide.

Each type of tRNA is specific for a particular amino acid; at one end it loosely binds the amino acid, and at the other end it has a nucleotide triplet called an anticodon, which allows it to pair specifically with a complementary codon on the mRNA.

The mRNA is read codon by codon, and one amino acid is added to the chain for each codon read.

In translation, wobble refers to the fact that the third nucleotide of a tRNA can form hydrogen bonds with more than one kind of base in the third position of a codon.


Mutations are alterations in the genetic material of the cell; point mutations are alterations of just one base pair of a gene.

Types of point mutations include:

Base- Pair Substitutions

  • missense mutations: the altered codon still codes for an amino acid that makes sense, although not necessarily the right sense
  • nonsense mutations: changes a codon for an amino acid to a stop codon; the resulting polypeptide will be shorter and probably nonfunctional
Base-Pair Insertions or Deletions
  • Frameshift Mutation: occurs whenever the number of nucleotides inserted or deleted is not a multiple of three
Here's a real basic overview, big picture type of video on translation. Keep in mind that they omitted the E site.

Here's an overview of protein synthesis:
  1. TRANSCRIPTION: RNA is transcribed from a DNA template.
  2. RNA PROCESSING: In eukaryotes, the RNA transcript (pre-mRNA) is spliced and modified to produce mRNA, which moves from the nucleus to the cytoplasm
  3. FORMATION OF INITIATION COMPLEX: After leaving the nucleus, mRNA attaches to the ribosome.
  4. AMINO ACID ACTIVATION: Each amino acid attaches to its proper tRNA with the help of a specific enzyme (aminoacyl-tRNA synthetase) and ATP.
  5. TRANSLATION: A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosomoe one codon at a time. (When completed, the polypeptide is released from the ribosome--its a protein in primary structure!)

Multiple Choice:

1. How many ribosomal subunits are there?
a. 1
b. 2
c. 3
d. 4
2. What is added to the mRNA before it leaves the nucleus?
a. Promoter and Terminator
b. 5' cap and 3' Poly-A tail
c. Initiation Complex and End Sequence
d. Codon and Anticodon
3. In which direction does the mRNA get built?
a. 3' to 5'
b. 5' to 3'
4. What does the growing polypeptide chain become after translation?
a. a nucleic acid
b. lipid
c. carbohydrate
d. protein

Answers: b, b, b, d

Good night and good luck...
Remember, tomorrow: Ch 17 Essay, and Ch 18 Vocab Check. The take home packet isn't due til Jan 30th, the day after the talent show. And since I know you're all coming to that, you will be getting it done before that night! :D

Jen M.

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