Download 12-3 RNA and Protein Synthesis

Chapter 12
DNA & RNA
Section 12-3
RNA & Protein Synthesis
Types of RNA
RNA Used For Protein Synthesis
Three Types of RNA
Messenger RNA, mRNA
Ribosomal RNA, rRNA
Transfer RNA,
tRNA
Types of RNA
mRNA
Template to construct protein. It brings the
message from the DNA to the ribosome.
rRNA
Part of ribosome structure
tRNA
Transports amino acids from cytoplasm to the
ribosomes
Transcription
The process of copying part of the DNA
nucleotide sequence into a
complementary sequence of RNA
Transcription
Requires the enzyme RNA Polymerase
Step 1. RNA polymerase binds to
DNA and separates the DNA
strands.
Step 2. RNA Polymerase uses one
strand of DNA as a template to
polymerize nucleotides into RNA
RNA Editing
After Making mRNA Introns
Are Snipped Out
Exons Remain,
(active segments of
nucleotides)
The Genetic Code
Proteins are long chains of amino acids.
There are 20 different amino acids
The order of amino acids in the protein
determine its shape and function
The Genetic Code
There are 20 amino acids but only
4 bases in RNA
Adenine
Cytosine
Guanine
Uracil
A
C
G
U
The Genetic Code
The genetic code consists of
“words” three bases long
Each “word” is called a Codon:
three consecutive nucleotides that
specifies a single amino acid
The Genetic Code
For Example:
UCGCACGGU = RNA Sequence
UCG-CAC-GGU = Codons
UCG codes for Serine
CAC codes for Histidine
GGU codes for Glycine
Code Wheel
The Genetic Code
4 Bases
Codons Defined with 3 Bases
There Are 64 Possible
3-base codons
Since there are only 20 amino acids,
some amino acids are represented by
multiple codons
Translation
Translation is the process of of
decoding the mRNA into a
polypeptide chain
• Ribosomes
–Read mRNA and construct the
proteins
Translation Step 1
• mRNA leaves the Nucleus
Translation Step 2
• mRNA binds to the ribosome. tRNA attaches
• Anticodons on the tRNA line up with codons on
mRNA The other end of the tRNA is an amino acid
Translation Step 3
– Ribosome connects
the amino acids
together as they
come into the
ribosome
Translation
• Step 4
– A polypeptide
(Chain of Amino
Acids) is formed.
– Polypeptide chain
grows until the
mRNA STOP Codon
is reached
The Roles of RNA & DNA
DNA =
Master Plan
RNA =
Blueprints of the Master Plan
Proteins
• At the end of translation a protein
is formed.
• Proteins are enzymes that catalyze
and regulate chemical reactions
• Proteins can also be structural.