protein synthesis

Protein Synthesis

The process by which cells produce proteins using the genetic information carried by genes (DNA).

Transcription

The process of copying the sequence of nucleotides of the transcribed DNA strand of a gene to produce m-RNA.

Where does transcription take place?

Transcription occurs in the nucleus.

Product of Transcription

The product of transcription is m-RNA.

Steps of Transcription

1. Unwind the double helix 2. Unzip the double strand by RNA polymerase 3. Addition of complementary bases with T replaced by U to form m-RNA 4. m-RNA leaves the nucleus and DNA rewinds.

Difference between DNA and RNA: Location

DNA is located in the nucleus; RNA is located in the nucleus and cytoplasm.

Difference between DNA and RNA: Sugar

DNA contains deoxyribose; RNA contains ribose.

Difference between DNA and RNA: Number of Strands

DNA has 2 strands; RNA has 1 strand.

Difference between DNA and RNA: Nitrogenous Bases

DNA uses A, T, C, G; RNA uses A, U, C, G.

Difference between DNA and RNA: Size

DNA is longer; RNA is shorter.

Difference between DNA and RNA: Presence

DNA is permanent; RNA is temporary.

Hypothesis on m-RNA synthesis

m-RNA is synthesized in the nucleus and is exported toward the cytoplasm.

Product of Translation

The product of translation is a peptide chain.

Tools needed for translation

1. m-RNA 2. t-RNA (transfer RNA) 3. Ribosome.

Initiation of Translation

The small ribosomal subunit binds to m-RNA at the start codon, and the initiator t-RNA binds to the start codon carrying methionine.

Elongation in Translation

New t-RNA arrives at the A-site, a peptide bond forms between amino acids, and the ribosome moves to accommodate the next t-RNA.

Termination of Translation

Translation stops when the ribosome reaches a stop codon, and the peptide chain is released.

Properties of Genetic Code: Universal

A codon codes for the same amino acid in all living things.

Properties of Genetic Code: Redundant

More than one codon can code for the same amino acid.