3.11 Messenger RNA carries instructions from DNA for building proteins

Processing of mRNA

-Before processing, it is referred to as pre-mRNA -Introns are removed by special proteins called spliceosomes, leaving only exon coding regions

Triplet

A sequence of three nucleotides found on a DNA strand.

ER signal sequence

A short amino acid sequence that marks a polypeptide for transport to the endoplasmic reticulum, where synthesis of the polypeptide chain is completed and the signal sequence removed.

Four nucleotides in DNA

Adenine, Thymine, Cytosine, Guanine

processing in the rough ER

An endoplasmic reticulum (ER) signal sequence in a newly forming protein causes the signal recognition particle (SRP) to direct the mRNA-ribosome complex to the rough ER

Role of RNA

Decoding mechanism for DNA. Decodes and carries message of DNA from nucleous to ribosomes in cytoplasm for manufacture. Uses Messenger RNA (mRNA), Ribosomal RNA (rRNA), Transfer RNA (tRNA). rRNA and tRNA act together to "translate" the message carried by mRNA

RNA and DNA differences

Differences: DNA is double stranded while RNA is single stranded DNA has T while RNA has U RNA is also found in the cytoplasm as well as the nucleus while DNA is not

aminoacyl-tRNA synthetase

During protein synthesis, an enzyme that attaches the correct amino acid to a tRNA molecule to form a "charged" aminoacyl-tRNA.

Transfer RNA

RNA in the cytoplasm that carries an amino acid to the ribosome and adds it to the growing protein chain

3:1

The ratio between DNA bases in the gene and amino acids in the polypeptide. Because each triplet stands for one amino acid.

Sequence of events in translation

Three phases that require ATP, protein factors, and enzymes Initiation Elongation Termination

Intron

a segment of a DNA or RNA molecule that does not code for proteins and interrupts the sequence of genes.

Exons

coding regions, the parts of a gene that are expressed

Translation

decoding of a mRNA message into a polypeptide chain

Messenger RNA (mRNA)

form of RNA that carries genetic information from the nucleus to the cytoplasm, where it serves as a template for protein synthesis

Anticodon

group of three bases on a tRNA molecule that are complementary to an mRNA codon and they bind together.

polypeptide synthesis

involves two major steps; transcription and translation

Gene

sequence of DNA that codes for a protein and thus determines a trait

Transcription

synthesis of an RNA molecule from a DNA template

genetic code

the rules that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid

Codon

three-base sequence on an mRNA molecule that provides the genetic info used in protein synthesis; codes for a given amino acid. Since there are four kinds of nucleotides there are (4^3) or 64 possible types of codon. Three of those 64 are stop signs to stop polypeptide synthesis. The other 61 are for amino acids.

Role of tRNA

to act as transporters bringing amino acids to the site of protein synthesis.

Ribosomal RNA

type of RNA that combines with proteins to form ribosomes