Download RNA and Protein Synthesis

RNA and Protein Synthesis
12.3
p.336-341
RNA
RNA = ribonucleic acid
 RNA has many jobs, but its main job is
protein synthesis.

Structure
RNA
 Ribose sugar
 Single-stranded
 Uracil replaces
thymine to pair with
adenine
DNA
 Deoxyribose sugar
 Double-stranded
 Thymine pairs with
adenine
3 Types of RNA
1.Messenger RNA (mRNA)—carries
information from the nucleus to the
ribosome. A 3 base sequence is called a
codon. It codes for the 20 amino acids.
2. Ribosomal RNA (rRNA)—contained in the
ribosome where proteins are made. It
reads the mRNA and sends a chemical
message to the tRNA to bring the
anticodon.
3.Transfer RNA (tRNA)—transfers each
amino acid and anticodon to the
appropriate place on the mRNA strand.
Transcription=part of the nucleotide
sequence of DNA is copied into a
complementary sequence of RNA.
1. The enzyme RNA polymerase binds to
and unzips the DNA. It uses 1 strand as a
template.
2. A single strand of mRNA is made. (U)
replaces (T).
3. mRNA breaks off from the DNA, leaves
the nucleus and goes to the ribosome.
4. DNA zips back together.
Codons
These codons are used to form the
polypeptide (protein) in the right order.
 AUG serves as a “start” codon. (or methionine)
 There are 3 “stop” codons that signal the end
of the polypeptide.
 There are 64 possible three-base codons for
mRNA (4x4x4=64)

Genetic
code
Molecular Genetics
Translation=the decoding of an mRNA
into a polypeptide chain (protein)
1.
2.
3.
4.
5.
6.
mRNA brings the codons to the ribosome.
Start codon, AUG, is always first.
tRNA brings an amino acid on one end and an
anticodon on the other end.
Anticodon pairs with the complementary
codon.
This continues until a stop codon is reached.
Amino acid chain (protein) is released.
Recap

Transcription happens in the nucleus


DNA to mRNA
Translation happens in the cytoplasm (ribosome)

mRNA to polypeptide (protein)
mRNA has the codons
 tRNA has the anticodons and the amino acids


Jokes are next!