Chapter 11: DNA and
Genes
11.2 – From DNA to Proteins…
RNA leads the way!
Genes and Proteins
O The sequences of nucleotides in DNA contain
information.
O This information is put into work by proteins.
O Structural or Chemical Reactions (Enzymes)
O Proteins are polymers of amino acids.
O The sequence of nucleotides in each gene
contains the information for assembling the string
of amino acids that make up a single protein.
RNA – Ribonucleic Acid
O RNA differs from DNA in 3 ways:
O RNA is single stranded
O RNA has ribose sugar
O RNA contains Uracil instead of Thymine
O What role does RNA play in the cell?
O Protein production/synthesis
O RNA is the worker
O DNA gives the instructions and RNA builds the proteins.
Types of RNA
O Messenger RNA (mRNA)
O Brings information from the DNA in the nucleus to the
cell’s cytoplasm.
O Ribosomal RNA (rRNA)
O Makes up the ribosome
O Clamps onto mRNA and uses its information to
assemble amino acids in the correct order.
O Transfer RNA (tRNA)
O “The Supplier”
O Transports amino acids to the ribosome to be
assembled into a protein.
The Genetic Code
O mRNA acts as a genetic messenger
O Bringing the complete information for building a
protein.
O A code is needed to convert mRNA into a protein.
O CODONS: A set of 3 Nitrogen bases in mRNA that
represent a specific amino acid.
O 64 Codons
O Some codons don’t code for a specific amino acid
but rather they supply instructions for assembling
the proteins (START and STOP).
O AUG = START and UAA, UAG, and UGA = STOP!
Genetic Code Continued
O The order of Nitrogen bases in mRNA will determine
the type and order of amino acids in a protein.
O Universal Code for ALL organisms.
O AUGC
O How do you name these amino acids…?
O THE CODON WHEEL
Transcription
O mRNA carries information from the DNA to the
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ribosomes for protein manufacturing.
In the nucleus, enzymes make an RNA copy of a
portion of a DNA strand by this process.
Forms a single-stranded RNA molecule rather than a
double-stranded DNA molecule.
Page 296, Figure 11.6 has a diagram and step-bystep information for this process.
http://www.dnalc.org/view/15510-TranscriptionDNA-codes-for-messenger-RNA-mRNA-3D-animationwith-basic-narration-.html
Translation
O How the language of mRNA is translated into the
language of proteins.
O Takes place at free ribosomes in the cytoplasm.
O tRNA molecules attach to only 1 type of amino acid.
O Correct translation depends on joining each mRNA
codon with the correct tRNA anticodon.
Process of Translation
O The starting end of mRNA strand attaches to a ribosome.
O tRNA approaches the ribosome.
O tRNAs anticodon pairs with the first mRNA codon and the
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two molecules temporarily join together.
Ribosome slides along the mRNA to the next codon.
A new tRNA molecule carrying an amino acid pairs with the
2nd mRNA codon.
When the 1st and 2nd amino acids are in place, an enzyme
joins them by forming a peptide bond.
As the process continues a chain of amino acids is formed
until the ribosome reaches a stop codon on the mRNA
strand.
Translation Continued
O http://www.youtube.com/watch?v=TfYf_rPW
UdY&feature=related
Time to Practice
DNA: TAC CCT ATG GAC CAT TAA AAC CCG GAG ATG
mRNA: _________________________________________
(Codon)
Amino Acid:
1) _____________ 2) ____________ 3) _____________
4) _____________ 5) ____________ 6) _____________
7) ______________ 8) ____________ 9) ______________
10) ______________
tRNA:
____________________________________________________
(Anti-Codon)
Connecting it all together
O http://www.youtube.com/watch?v=983lhh2
0rGY
NOVA: Cracking the Code of
Life
O http://www.pbs.org/wgbh/nova/body/cracki
ng-the-code-of-life.html
O We will watch this next week and take notes,
but if you want to watch it now you can.