Transcript 10.3 - Protein Synthesis / Translation

Chapter 10DNA, RNA and
Protein Synthesis
There are 2 Nucleic acids in a cell:
1.
•
2.
•
Deoxyribonucleic Acid
-DNARibonucleic Acid
-RNA-
10.1 – DNA Information
• DNA discovery:
1950s
• Mr. Watson and Mr.
Crick used X-rays of
DNA crystals to show
the structure of the
molecule
- X-rays were taken
by Rosalind Franklin
and Maurice Wilkins
• Model is called the Watson-Crick model
– Shape – 2 sided and twisted – DOUBLE
HELIX
DNA
DNA Structure
• DNA is a Polymer
• Monomers of DNA are ___________
Nucleotide has 3 parts:
1. Sugar – named deoxyribose - (pentose)
2. Phosphate group – phosphoric acid (phosphate
bonded to 4 oxygen atoms)
3. Nitrogenous base – contain Nitrogen and
carbon atoms
Structure of a Nucleotide
Nitrogen BASES
Nitrogen BASES: 2 sizes (p 198)
• Larger – structural formula shows double-ring
– Called PURINES
– Ex: Adenine (A) & Guanine (G)
• Smaller – structural formula shows single ring
-Called PYRIMIDINES
-Ex: Cytosine (C) & Thymine (T)
-Ex Uracil(U) in RNA, but NOT in DNA
• BASES will
chemically bond only
w/ certain other bases.
• Always makes pairs of
bases w/
A–T
C–G
• Bases bond w/ weak
Hydrogen bonds
DNA Base Pairs
DNA Replication
• The double-strands of
DNA make a
replication mechanism
intuitive!
• The DNA unwinds and
each strand re-pairs
with new matching
nucleic acids.
• Uses helicase and DNA
polymerase
How is information stored?
DNA is broken down into regions called genes
that are the key programs in determining how an
organism functions.
Promoter
Operon
Gene 1
Gene 2
Gene 3
How are genes used?
The promoter region signifies the beginning of a
group of genes, and the operon determines when
they are allowed to be used.
Using a gene involves two steps: transcription and
translation.
10.3 - Protein Synthesis
• Where: Ribosomes
• Why:
• What: Protein chem. review
– Building Blocks (monomers) = aa
• ______ different kinds
• ______ usual name ending
– Proteins are polymers =
_______________
• Includes 100’s of monomers bonded
together.
• Symbol: aa + aa + aa + aa + aa + …. =
Polypeptide chain
• Held together w/ ________bonds.
2 parts to Protein Synthesis
• 1. Transcription- copying of DNA code
into mRNA codons
• 2. Translation-The process of assembling
polypeptides using codons on mRNA.
Transcription Steps:
1. RNA polymerase moves to a specific area
on a DNA where the copying begins called
the promotor.
2. The DNA “unzips” at the promoter site.
The side of DNA that will be used to make
RNA is called the TEMPLATE.
3. mRNA forms chains of nucleotides
following the BASE PAIRING RULE.( The
“copying: procedure is like replication
except NO thymine is used, but INSTEAD
RNA uses URACIL. )
4. The copying continues until a site on the DNA
called the TERMINATION SIGNAL is
reached the procedure now STOPS.
5. The newly made mRNA now moves away from
the template and leaves the nucleus.
6. The “genetic code” or sequence of BASES on
the mRNA will determine which aa is used to
make the protein.
The Genetic Code
Proteins differ from each other by:
1. Size – use a different number of aa. The more aa
the larger the protein.
2. Chemistrya) Use dif. aa from each other (some proteins are
“incomplete”, usually from plants)
Ex: aa1 + aa20 + aa3 + aa4 ….
vs.
aa1 + aa20 + aa13 + aa4 ….
b) Put same aa in a dif. order or sequence.
Ex: aa1 + aa20 + aa3 + aa4 ….
vs.
aa20 + aa3 + aa1 + aa4 ….
aa = letter
protein = word
organism = dictionary
Proteins
As a protein is built, it
folds into a structure.
There are many levels
to protein this process.
Some proteins are just
structural, while others
(enzymes) will perform
functions
Basic translation steps
1. mRNA moves from nucleus to a
ribosome.
2. aa are transported to the ribosomes by
tRNA molecules.
a) The anticodon site on the tRNA is
complementary & pairs with the mRNA
codon.
b) Terminal end attaches to aa.
3. The aa on the tRNA matches the codon on
the mRNA to ensure correct sequencing of
aa assembled.
Protein Assembly:
1. Begins when ribosome attaches to the
start codon (AUG) on mRNA.
2. The start codon pairs with the anticodon
(UAC) on tRNA which carries the aa
methionine. (may be removed later)
3. The ribosome moves along the mRNA
pairing up the codons w/ anticodons on
tRNA
Protein Assembly con’t:
4. The pairing of [codon – anticodon] causes the specific
aa to create a covalent bond to the previous aa called a
__________ bond.
5. As the ribosome moves along the mRNA, a
polypeptide chain is created.
6. A stop codon is reached and the ribosome is released
from mRNA & polypeptide chain is complete.
•
•
Several ribosomes can translate from the same mRNA
simultaneously.
Polypeptide chain represents proteins primary
structure and will fold & associate with other
polypeptide chains.
Protein Synthesis Song
• Protein Synthesis Song-Waltz of the
Ribosomes
Ribosome translating DNA to a
protein
Web Sites to visit: Animation of
Translation
http://www.wiley.com/legacy/college/boyer/04700
03790/animations/translation/translation.htm
http://www.zerobio.com/translate.htm
http://www.pbs.org/wgbh/aso/tryit/dna/
(Click on DNA workshop activity)