Protein Synthesis

7.3 p. 146-153

WHAT IS RNA

– What is RNA?

• RNA has the same primary structure as DNA .

• It consists of a sugar-phosphate backbone, with nucleotides attaches to the 1' carbon of the sugar.

• RNA = disposable copy of DNA

The differences between DNA and RNA are that:

• RNA has a hydroxyl group on the 2' carbon of the sugar

• Instead of using the nucleotide thymine, RNA uses uracil:

• Single stranded

Types of RNA

• mRNA - messenger RNA – is a copy of a gene having a sequence

complementary to one strand of the DNA and identical to the other strand.

– = a busboy to carry the info stored in the DNA in the nucleus to the cytoplasm where the ribosomes can make it into protein.

Types of RNA

• tRNA - transfer RNA – is a small RNA that has a very specific

structure such that it can bind an amino acid at one end, and mRNA at the other end.

– It acts as an adapter to carry the amino acid elements of a protein to the appropriate place as coded for by the mRNA.

Types of RNA

• rRNA - ribosomal RNA – is one of the structural components of the

ribosome. It has sequence complementarily to regions of the mRNA so that the ribosome knows where to bind to an mRNA it needs to make protein from.

PROTIEN SYNTHESIS OVERVIEW

TRANSCRIPTION

• RNA polymerase must be able to recognize the beginning of a gene so that it knows where to start synthesizing an mRNA. = promoter sequence = a particular DNA sequence that appears at the beginning of genes.

TRANSCRIPTION CON’T

• The RNA polymerase then stretches open the double helix at that point in the DNA and begins synthesis of an RNA strand complementary to one of the strands of DNA.

• We call the strand from which it copies the antisense or template strand, and the other strand, to which it is identical, the sense or coding strand.

TRANSCRIPTION SUMMARY– The steps in transcription are:

• DNA unzips and RNA polymerase enzyme binds to one strand of DNA

• RNA polymerase makes an elongating chain of RNA nucleotides, each complementary to the DNA nucleotide it is hydrogen bonded to

• The completed mRNA molecule is released from RNA polymerase - DNA complex and can begin translation. In eukaryotic cells this means first moving from the nucleus into the cytoplasm. In prokaryotic cells (bacteria), ribosomes can bind and begin translation before polymerase has completed of the new mRNA strand.

TRANSLATION– The steps in translation are:

• the ribosome binds to mRNA at a specific area

• the ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence

• each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain

• the ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA

• the polypeptide forms into its native shape and starts acting as a functional protein in the cell