Download Protein Synthesis Notes

III. How a protein is made: Protein Synthesis
A. Why are proteins made and what does this have to do with
genetics?
1. DNA holds the information to make proteins
2. A “gene” is a segment of DNA that codes for 1 protein
B. DNA holds the recipes for making proteins. It uses RNA
(the “chefs”) to send these recipes to the ribosomes
(“kitchen”) so they can be made.
1. The basic unit of a protein is an amino acid
a. we use 20 amino acids to make all of our proteins
2. A chain of amino acids together is a protein
3. Types of proteins include: hormones, enzymes,
structural proteins
C. RNA = ribonucleic acid
1. Similar structure to DNA with a few differences
DNA
RNA
Basic unit
nucleotide
nucleotide
4 nitrogen bases
A,T,C,G
A,U,C,G (u=uracil)
Sugar
deoxyribose
ribose
Structure
double stranded
single stranded
D. There are 3 types of RNA each having a different role in
making a protein
1. mRNA : messenger RNA
a. reads the information from the DNA and carriers the
message to the ribosomes (this process is called
“transcription”
DNA: A T T G C C G A T
mRNA: U A A C G G C U A
Codon
Codon
Codon
2. tRNA: Transfer RNA
a. made in the nucleus and reused in the cytoplasm
b. reads mRNA and brings the correct amino acid to
make a chain of amino acids (protein). This process is
called “translation”
c. The code is being translated into the language of
amino acids.
d. structure looks like an upside down t.
Anticodon that corresponds with
the mRNA codon
Amino Acid
3. rRNA : Ribosomal RNA
a. located in the ribosome
b. plays role in helping the
amino acids join together
during translation
c. scientists are using this
sequence to classify
organisms.
E. The process of making a protein
1. Transcription: Making mRNA from DNA
2. Translation: Translating the mRNA code into a chain of
amino acids using tRNA to make a protein
1. Transcription: making mRNA from DNA
a. enzyme “RNA polymerase” unzips DNA and
attaches corresponding RNA nucleotides
DNA: A T T C G C G A T
mRNA: U A A G C G C U A
b. When RNA polymerase reaches the sequence of
DNA bases that tells it to “stop” the RNA strand is
released and DNA zips back up
c. mRNA strand carries the
message out of the nucleus
into the cytoplasm to the
ribosome
2. Translation: Translating the mRNA codons into a chain
of amino acids to make a protein
a. 2 subunits of a ribosome bind to mRNA
b. the 1st tRNA binds to the mRNA (the anticodon
corresponds with the codon)
c. the 2nd tRNA binds to the mRNA
d. the amino acid from the 1st tRNA binds to the amino
acid from the 2nd tRNA.
e. the ribosome moves down the mRNA and the 1st
tRNA is released (leaving a vacancy for the next
tRNA)
f. The process continues until the “STOP” signal codon is
reached and the protein is released.