12-3: RNA AND PROTEIN
SYNTHESIS
Biology 2
Introduction
• DNA double helix structure
explains how DNA can be
copied, but not how genes
work
• GENES: sequence of DNA that
codes for a protein and thus
determines a trait
• DNA must copy messages onto
RNA
• RNA contains “codes” for
making proteins
Structure of
RNA
Ribose Sugar
• RNA is made of building blocks
called nucleotides
• NUCLEOTIDES: monomer of
nucleic acids made up of a 5carbon sugar, a phosphate
group, and a nitrogenous base
• Can have 4 different types of
base:
– Adenine
– Guanine
– Uracil (replaces Thymine)
– Cytosine
Components
and
Structure of
DNA
• Backbone of RNA is sugar and
phosphate groups
– FORM THE OUTSIDE
• Bases DO NOT bond together
to connect inside
Differences Between RNA
and DNA
1. DNA uses deoxyribose
– RNA uses ribose sugar in
nucleotides
2. DNA is double stranded
– RNA is single stranded
3. DNA uses Thymine
– RNA uses Uracil
Types of
RNA
• 3 types of RNA:
• mRNA: carries messages to
ribosomes
• tRNA: transfers amino acids to
the ribosomes
• rRNA: make up different parts
of the ribosome
Transcription
• TRANSCRIPTION: process in
which part of the nucleotide
sequence of DNA is copied into
a complementary sequence in
RNA
• DNA creates a temporary copy
of messages on mRNA, its
carried to ribosomes and tRNA
carries amino acids for building
the proteins
Transcription
• During transcription enzyme
attaches to PROMOTER
sequence (like a green light)
• Enzyme will read all bases on a
DNA strand to make mRNA
message
• Enzyme will stop at
TERMINATOR sequence (like a
red light)
The Genetic • Proteins are made by joining
Code
amino acids into long chains
– 20 different amino acids possible
• Properties of proteins are
determined by sequence
(order) of amino acids
• The message mRNA carries is
called the Genetic Code
The Genetic • Each set of 3 bases on mRNA is
Code
known as a codon
– CODON: three-nucleotide sequence
on messenger RNA that codes for a
single amino acid
• Each codon has instructions for
specific amino acid
– Can have more than 1 codon for
each amino acid
Translation
• Sequence (order) of bases in
mRNA are instructions for
which amino acids should be
joined in a specific order
• Creating the chain of amino
acids is called translation
– TRANSLATION: decoding of a
mRNA message into a polypeptide
chain
• This is reading the mRNA message
to figure out the order of amino
acids
Translation
• Enzyme will read all bases on a
DNA strand to make mRNA
message
– mRNA message is sent to
ribosomes
• Ribosomes “read” the message
• tRNA carries the amino acids
anti-codon matching the
mRNA codon message to the
ribosome
• Ribosome “glues” amino acids
together to form protein chains
Protein Synthesis – Translation Process
http://www.youtube.com/watch?v=B6O6uRb1D38
Bill Nye – Genes and Chromosomes
http://www.youtube.com/watch?v=HqoQoJMG0Lc