vii rna and protein synthesis. genes, segment of dna, are coded dna instructions that control the...
TRANSCRIPT
Genes, segment of DNA, are coded DNA instructions that control the production of proteins.
Genetic messages can be decoded and used in protein synthesis by copying part of the nucleotide sequence from DNA into mRNA.
mRNA contains coded information for making proteins.
The Structure of RNA
There are three main differences between RNA and DNA:
• The sugar in RNA is ribose instead of deoxyribose.
• RNA is generally single-stranded.
• RNA contains uracil in place of thymine.
Types of RNA
Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins.
During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome.
Amino acid
Transfer RNA
Protein Synthesis
DNADNAmoleculemolecule
DNA strandDNA strand(template)(template)
33
TRANSCRIPTIONTRANSCRIPTION
CodonCodon
mRNAmRNA
TRANSLATIONTRANSLATION
ProteinProtein
Amino acidAmino acid
3355
55
TranscriptionDNA is copied in the form of RNA
This first process is called transcription.
The process begins at a section of DNA called a promoter.
RNA EditingSome DNA within a gene is not needed to produce a
protein. These areas are called introns.
The DNA sequences that code for proteins are called exons.
The introns are cut out of RNA molecules.
The exons are the spliced together to form mRNA.
Exon IntronDNA
Pre-mRNA
mRNA
Cap Tail
The Genetic Code
The genetic code is the “language” of mRNA instructions.
The code is written using four “letters” (the bases: A, U, C, and G).
Nucleus
mRNA
Translation
Translation is the decoding of an mRNA message into a polypeptide chain (protein) on ribosomes.
During translation, the cell uses information from messenger RNA to produce proteins.
LysinetRNAPhenylalanine
Methionine
Ribosome
mRNAStart codon
The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA and the anticodons of tRNA match the mRNA codons.
DNA
mRNA
Protein
CodonCodon Codon
Codon Codon Codon
mRNA
Alanine Arginine Leucine
Amino acids within a polypeptide
Single strand of DNA