molecular biology 2.7 dna replication, transcription and translation
TRANSCRIPT
Molecular Biology2.7 DNA Replication, transcription and translation
DNA to Protein Synthesis The function of most genes is to specify
the sequence of amino acids in a particular polypeptide.
Two processes are needed to produce a polypeptide using the base sequence of a gene. Transcription Translation
Transcription Transcription is the synthesis
of mRNA copied from the DNA base sequences by RNA polymerase.
The enzyme RNA polymerase binds to a site on the DNA at the start of a gene
The RNA polymerase separates the double strand of DNA and pairs up RNA nucleotides with complementary bases.
Transcription The RNA polymerase
forms covalent bonds between the nucleotides
Transcription stops at the end of the gene. The completed mRNA is released.
Transcription The completed mRNA has
a base sequence that is complementary to the template DNA strand. Note: Uracil replaces
Thymine
Complete the transcription portion of the practice sheet
Translation Translation is synthesis
of polypeptides on ribosomes
Ribosomes are complex structures that consist of a small and large sub-unit with binding sites for each of the molecules used in translation.
Translation The amino acid
sequence of polypeptides is determined by mRNA according to the genetic code
Translation Codons of three bases
on mRNA correspond to one amino acid in a polypeptide
“Genetic Code” = The translation “dictionary” that enables the cellular machinery to convert the base sequence on mRNA into the amino acid sequence
Translation There are 20 amino
acids and only 4 nucleotide bases.
Living organisms use a triplet code with 3 bases coding for an animo acid.
The sequence of 3 bases on the mRNA = CODON
Examine the list of codons
Translation There are 3 “stop”
codons that code for the end of translation.
Different codons can code for the same amino acid. The code is
“degenerate”
Translation Translation depends on
complementary base pairing between codons on mRNA and anticodons on tRNA
The amino acids are carried on tRNA
The tRNA has a 3 base ANTICODON complementary to the mRNA codon
Complete the translation portion of the worksheet